ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, DC 20460

			OFFICE OF  PREVENTION, PESTICIDES,  AND TOXIC SUBSTANCES

 

DP Barcode:	D347645

Chemicals:	Tributyltin oxide, Tributyltin benzoate, Tributyltin maleate

PC Codes:	083001, 086106, 083118

Case No.:	2620



January 18, 2008

Memorandum:

Subject:	Ecological Hazards and Risk Assessment for Tributlytin
Compounds

To:	Jill Bloom, Review Manager

	Special Review and Reregistration Division 

From: 	William Erickson, Ph.D., Biologist

Risk Assessment and Science Support Branch (RASSB)

Antimicrobials Division (AD)

Thru:	Norm Cook, Branch Chief

RASSB/AD

Attached is the ecological assessment for the TBT compounds.  A hazards
assessment was conducted for all currently registered uses.  Due to
potential exposure of aquatic organisms from runoff of TBT due to
wood-preservative applications, a risk assessment also was conducted for
TBT applications to houses, fences, decks, and utility poles.  TBT
hazards, risks from wood preservative uses, data requirements, and
required label statements are summarized below.

Hazard and Risk Conclusions:

        •	TBT is very highly toxic to aquatic organisms; a
precautionary label statement (specified below) is required for all
products

        •	the acute-risk LOC is equaled or exceeded only for listed
(e.g., endangered and threatened) freshwater and estuarine/marine
invertebrates exposed in the water column 

        •	the chronic risk LOC (based on adverse affects to
reproduction and growth) is not exceeded for either listed or non-listed
aquatic animals exposed in the water column

        •	sublethal affects (e.g., imposex, shell deformities,
behavioral abnormalities) to aquatic organisms exposed to TBT at parts
per trillion in the water column is reported in the literature; although
most information is from TBT released from antifoulant paints used on
boat hulls (use has been canceled), expected environmental
concentrations from wood preservative uses may pose similar concerns in
some situations

        •	TBT bioconcentrates in the soft tissues of exposed
organisms, which may have implications for exposure of predatory and
scavenging species of fish, birds, mammals, and reptiles that feed on
exposed fish or invertebrates

        •	risk to aquatic plants cannot be assessed until required
guideline studies are submitted; limited non-guideline data indicate
that TBT is highly phytotoxic to some algae and diatoms 

        •	TBT accumulates and persists in sediments, but toxicity data
are not available to assess acute and chronic risks to aquatic organisms

Label requirements:  

	All products:

	All product labels must have the following ENVIRONMENTAL HAZARDS
statement:  

"This pesticide is toxic to fish and aquatic invertebrates. Do not
contaminate water when disposing of equipment washwaters.  Do not
discharge effluent containing this product into lakes, streams, ponds,
estuaries, oceans, or other waters unless in accordance with the
requirements of a National Pollutant Discharge Elimination System
(NPDES) permit and the permitting authorities are notified in writing
prior to discharge.  Do not discharge effluent containing this product
to sewer systems without previously notifying the local sewage treatment
plant authority.  For guidance contact your State Water Board or
Regional Office of the EPA."

Products with wood preservative uses:

If honeybee studies 850.3030 and 171-4 are waived, the following label
statement is required:  

“Treated wood shall not be used in the construction of beehives.”

Products also must have a statement prohibiting use of TBT-treated wood
in the aquatic environment.

Data requirements:

	•  Whole sediment: acute freshwater invertebrates (850.1735)

	•  Whole sediment: acute marine invertebrates (850.1740)

	•  Whole sediment: chronic invertebrates (no guideline no.)

	•  Freshwater diatom (850.5400); TGAI or EP

	•  Marine diatom (850.5400); TGAI or EP

	•  Blue-green cyanobacteria (850.5400); TGAI or EP

	•  Freshwater green alga (850.5400); TGAI or EP

	•  Freshwater floating macrophyte duckweed (850.4400); TGAI or EP

	•  Freshwater rooted macrophyte rice seedling emergence (850.4225);
EP

	•  Freshwater rooted macrophyte rice vegetative vigor (850.4250); EP

	•  Honey/beeswax residues and acute toxicity of treated wood residues
to bees 

(see Confirmatory Data Required section of assessment for more
information; study can be waived by label statement specified in Label
Hazard Statements)

RASSB notes that a label statement prohibiting use of TBT-treated wood
in the aquatic environment will reduce potential exposure of aquatic
organisms.  However, TBT leachate is still expected to reach water
bodies (water column and sediments) due to environmental transport from
wood-preservative application sites.  Therefore, the data specified
above are needed to assess risks to animals and plants in the aquatic
environment.



Table of Contents

Ecological Hazards Assessment . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

         Toxicity to Terrestrial Animals  . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

         Toxicity to Aquatic Organisms . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7

Ecological Risk Assessment and Characterization . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 14

         Environmental Fate Summary . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

         Aquatic Exposure Assessment . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

         Aquatic Risk Assessment . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

         Aquatic Risk Characterization . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

         Terrestrial Risk Assessment . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

         Endangered Species Considerations . . . . . . . . . . . . . . .
. . . . . . . . . . .  . . . . . . . . . . . . . . . . . 22

Confirmatory Data Required. . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  24

Required Label Statements . . . . . . . . . .  . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  25

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .  . . . . . . . . . . . . . .
 26

Attachments:

         A:  OPP Ecotoxicity Profile for Tributyltin Compounds .  . . .
. . . . . . . . . . . . . . . . . . . . . . .  29

         B:  EECs for Tributyltin Oxide (TBTO) Leached from Wood into
Soil and Water . . . . . . . 35

Ecological Hazard and Environment Risk Assessment

Tributlytin-containing Compounds (TBT)

Three tributlytin-containing compounds are currently registered. 
Tributyltin oxide (33 products) is registered as a bacteriostat,
microbicide/microbistat, fungicide, algaecide, antifoulant, slimacide,
virucide, disinfectant, sanitizer, miticide, and insecticide.  End-use
products are ready-to-use soluble concentrates used primarily in or on
wood, material preservatives, and in industrial processes and water
systems.  Additional uses include agriculture, animal kennels,
veterinary facilities, sewage systems, and paint manufacturing systems. 
Tributyltin benzoate (two ready-to-use soluble concentrates) is used as
a bacteriostat, disinfectant, sanitizer, and fungicide in materials
preservatives.  Tributyltin maleate (one product) is a bacteriostat and
fungicide used to protect polyolefin drip irrigation tubing and piping
for sewage effluent, recycled water and grey-water.   

TBT poses potential problems in the aquatic environment, because it is
extremely toxic to aquatic organisms, is linked to imposex (i.e.,
masculinization of females) and immuno-supression in snails and
bivalves, has very high bioconcentration and bioaccumulation factors,
and it persists in sediments (EPA 2003).  Environmental exposure levels
from wood preservative applications may be hazardous to organisms
exposed to leachate and runoff into surface waters.  Therefore, an
ecological risk assessment is conducted for the wood preservative uses. 
Expected aquatic environmental concentrations (EECs) are modeled for
several wood-treatment uses, and risk quotients (RQs) are calculated by
comparing EECs to the most sensitive hazards endpoints for each
taxonomic group as identified in the hazards assessment.  Risk
presumptions are based on comparing the RQs to the Agency's Levels of
Concern (LOCs) for acute and chronic risks to the various taxa for which
data are available.  Information from previous EPA assessments,
including the Ambient Aquatic Life Water Quality Criteria for
Tributyltin (TBT) – Final (EPA 2003), also is used to help
characterize aquatic risks.  

A hazards assessment is conducted for all registered uses of TBT.  An
ecological risk assessment is not currently required for uses other than
wood-preservative applications, because release and exposure levels are
expected to be low when those products are applied according to label
directions and use precautions.  The hazards assessment is used to meet
current labeling requirements for precautionary statements and to
determine hazard endpoints for ecological organisms potentially exposed
in the event of a spill or other unintended environmental releases.

Ecological Hazards Assessment

The toxicity endpoints used in OPP's assessments are obtained from
guideline toxicity studies conducted for wildlife, aquatic organisms,
and plants (40 CFR §158.2060).  Guideline studies are required to
provide acute and reproductive/chronic measures of effect for one or
more test species in several taxonomic groups.  Some studies are only
required on a case-by-case basis, depending on factors such as use
patterns and environmental fate characteristics.  The available toxicity
endpoints and data requirements for TBT compounds are summarized below
and presented in more detail in the Ecotoxicity Profile (Attachment A). 
Additional toxicity data were obtained from the OPP TBT chemical files
(e.g., USEPA Animal Biology Laboratory 1976 Reports of Analysis), data
presented in the OPP/EFED Pesticide Ecotoxicity Database, and data
compiled in the Ambient Aquatic Life Water Quality Criteria for
Tributyltin (TBT) – Final (EPA 2003).

	Toxicity to Terrestrial Animals

	

		Birds, Acute and Dietary

The Agency requires one acute-oral study to establish the toxicity of
TBT compounds (technical grade active ingredient, TGAI) to birds for all
registered uses.  The preferred test species is either the mallard (Anas
platyrhynchos) or the northern bobwhite (Colinus virginianus).  Avian
dietary toxicity studies (northern bobwhite and mallard) are only
conditionally required for antimicrobial pesticides, depending on the
avian acute-oral toxicity, pertinent environmental fate characteristics,
and a potential for exposure.  Three available acute-oral and dietary
studies indicate that technical-grade TBT is moderately toxic to birds
if ingested (Table 1).  Based on these data, an avian precautionary
statement is not required on TBT-compound product labels.  The
guidelines for avian acute-oral toxicity (OPPTS 850.2100) and avian
dietary toxicity OPPTS 850.2200) are satisfied.  

Table 1.  Acute-oral and Dietary Toxicity of TBT Compounds to Birds

Test

Species	Test

Type	Test material

(% ai)	Toxicity

Endpoint	Toxicity Category	Study

Status	MRID No.

Mallard	acute 

oral	TBTO

(tech.)	LD50 >167a 

(mg ai/kg bw)	moderately toxic	supplemental	130548

	dietary	TBTO

(95)	LC50 = 840

(ppm)	moderately toxic	core	165211

Northern bobwhite	dietary	TBTO

(95)	LC50 = 545

(ppm)	moderately toxic	core	136468

a test doses were too low (< 167 mg ai/kg bw) to establish an LD50 but
do indicate that TBTO is no more than moderately toxic to birds on an
acute-oral basis

		

Mammals, Acute 

The available mammalian acute toxicity data from several studies
indicate that TBT compounds are moderately toxic to small mammals on an
acute-oral basis (laboratory rat LD50s ranging from 123 to 193 mg ai/kg
bw).  Refer to the human toxicology chapter for more details on
mammalian toxicity studies submitted for the human-health assessment.

Nontarget Insects - Honeybees

No guideline data are available for TBT.  For wood preservative uses, a
study addressing honey/beeswax residues and acute toxicity of treated
wood residues to bees is required (see Confirmatory Data Required
section); or, in lieu of this study, product labels with wood
preservative use can include a statement prohibiting use of  TBT-treated
wood for beehive construction (see Label Statements section).  

	Toxicity to Aquatic Organisms

		Freshwater Fish, Acute

Two acute toxicity studies with the TGAI are required to establish the
toxicity of TBT compounds to freshwater fish.  The preferred test
species are the rainbow trout (Oncorhynchus mykiss), a coldwater fish,
and the bluegill (Lepomis macrochirus), a sunfish.  Six tests are
available for technical-grade TBTO, including two conducted at the
former EPA Animal Biology Laboratory and another using the channel
catfish (Ictalurus punctatus) as the test species.  Additional LC50 data
are reported in EPA (2003), including toxicity values for rainbow trout,
lake trout (Salvelinus naymaycush), fathead minnow (Pimephales
promelas), bluegill, and channel catfish.  The data characterize
technical-grade TBT as being very highly toxic to freshwater fish (Table
2).  Therefore, a precautionary statement is required on product labels.
 The guideline for freshwater-fish acute toxicity (OPPTS 850.1075) is
satisfied.

Table 2.  Acute Toxicity of TBT Compounds to Freshwater Fish

Test

Species	Test material

(% ai)	

96-h LC50

(µg ai/L)	

Toxicity

Category	

Study

Status	

MRID

No.

Rainbow trout	TBTO

(95)	5.6	very highly toxic	core	EPAa

	TBTO

(97.5)	7.4	very highly toxic	core	41518501

	TBTO

(96-97.5)	5.4-7.1

(4 tests)	very highly toxic	n/a	EPA 2003

Lake trout	TBTO

(97)	12.7	very highly toxic	n/a	EPA 2003

Fathead minnow	TBTO

(96)	2.6	very highly toxic	n/a	EPA 2003

Bluegill	TBTO

(97.5)	8.7	very highly toxic	core	41518301

	TBTO

(95)	7.6	very highly toxic	core	136471

	TBTO

(95)	13.2	very highly toxic	core	EPAa

	TBTO

(95-97.5)	7.2-8.3

(2 tests)	very highly toxic	n/a	EPA 2003

Channel catfish	TBTO

(95)	12	very highly toxic	core	136470

	TBTO

(95-96)	5.5-11.4

(2 tests)	very highly toxic	n/a	EPA 2003

a Report of Analysis, USEPA Animal Biology Laboratory, 1976

		Freshwater Invertebrates, Acute

A study with the TGAI is required to establish the acute toxicity of TBT
to freshwater invertebrates.  The preferred test species is the water
flea, Daphnia magna.  Results from two guideline studies categorize
technical-grade TBT0 as being very highly acutely toxic to the water
flea (Table 3).  Therefore, a precautionary statement is required on
product labels.  A study testing dibutylyin dichloride categorizes this
degradates as moderately toxic.  The guideline requirement (OPPTS
850.1010) is satisfied. Additional data from EPA (2003) and presented in
Table 3 further characterize the acute toxicity to other freshwater
invertebrates.  Test species include 3 species of hydra (Hydra
littoralis, H. oligactis, Chlorohydra viridissmia), an annelid
(Lumbriculus variegates), a clam (Elliptio complanatus), an amphipod
(Gammarus pseudolimnaeus), and mosquito larva (Culex sp.).

Table 3.  Acute Toxicity of TBT Compounds to Freshwater Invertebrates

Test

Species	Test material

(% ai)	

48-h EC50

(µg ai/L)	

Toxicity 

Category	

Study 

Status	

MRID 

No.

Water flea	TBTO

(95)	1.67	very highly toxic	supplemental	136468a

	TBTO

(97.5)	11.5	very highly toxic	core	41518401

	degradatea 

(89.6)	1400	moderately toxic	supplemental	41572201

	TBTO

(95-97.5)	1.58-11.2

(3 tests)	very highly toxic	n/a	EPA 2003

Hydra	TBTO

(97.5)	1.1-1.8

(4 tests)	very highly toxic	n/a	EPA 2003

Annelid	TBTO

(96)	5.4	very highly toxic	n/a	EPA 2003

Clam	TBTO

(95)	24,600	moderately toxic	n/a	EPA 2003

Amphipod	TBTO

(96)	3.7	very highly toxic	n/a	EPA 2003

Mosquito

larva	TBTO

(96)	10.2	very highly toxic	n/a	EPA 2003

a EPA/OPP/EFED Pesticide Ecotoxicity Database

b dibutyltin dichloride

		Estuarine and Marine Fish and Invertebrates, Acute

Acute toxicity of the TGAI with estuarine/marine fish and invertebrates
is required when the end-use product is intended for direct application
to the marine/estuarine environment or the active ingredient is expected
to reach this environment in significant concentrations because of its
expected use and environmental mobility.  The preferred fish test
species is sheepshead minnow (Cyprinodon variegatus).  Two guideline
fish toxicity studies are available (Table 4), one that tested a
formulation (Polyace S-1000, 29.2% ai) and another in which the
Mummichog (Fundulus heteroclitus) was the test species.  The results of
these studies indicate that TBT compounds are very highly toxic to
estuarine/marine fish.  The guideline for estuarine/marine-fish acute
toxicity (OPPTS 850.1075) is satisfied.  Additional data in EPA (2003)
also indicate that TBT is very highly toxic to the sheepshead minnow,
mummichog, and to Chinook salmon (Oncorhyncus tshawytscha).

Table 4.  Acute Toxicity of TBT Compounds to Estuarine/Marine Fish  

Test

Species	Test material

(% ai)	

96-h LC50

(µg ai/L)	

Toxicity 

Category	

Study 

Status	

MRID 

No.

Sheepshead

minnow	 TBTO

(29.2)	16.1	very highly toxic	core	41041402

	TBTO

(not reported)	2.3-16.5

(4 tests)	very highly toxic	n/a	EPA 2003

Mummichog	TBTO

(95)	24	very highly toxic	core	136470

	TBTO

(95)	23.3	very highly toxic	n/a	EPA 2003

Chinook salmon	TBTO

(not reported)	1.46	very highly toxic	n/a	EPA 2003



Preferred estuarine/marine invertebrate test species are the mysid
shrimp (Mysidopsis bahia) and the Eastern oyster (Crassostrea
virginica).  For TBT compounds, toxicity tests also are available for
the Pacific oyster (Crassostrea gigas), bay mussel (Mytilus edulis),
fiddler crab (Uca pugilator), pink shrimp (Penaeus duorarum), and grass
shrimp (Palaemonetes pugio).  Findings indicate that TBT compounds,
including a formulation (Polyace S-1000, 29.2% ai) tested with oysters
and shrimp, are very highly toxic to a variety of estuarine/marine
invertebrates (Table 5).  This toxicity is corroborated by data
presented in EPA (2003) for the grass shrimp, American lobster (Homarus
americanus), shore crabs (Carcinus maenas, Hemigrapsus nudus), mud crab
(Rhithropanopeus harrisii), and amphioxus (Branchiostoma caribaeum). 
The guidelines for estuarine/marine-invertebrate acute toxicity are
satisfied.  

Table 5.  Acute Toxicity of TBT Compounds to Estuarine/Marine
Invertebrates  

Test

Species	% ai

tested	

EC50 or LC50

(µg ai/L)	

Toxicity Category	

Study Status	

MRID No.

Pacific oyster	TBTO

(97.5)	48-h EC50 = 0.28

(embryo-larval)	very highly toxic	core	41403801

Eastern oyster

	TBTO

 (97.5)	96-h EC50 = 0.126

(shell deposition)	very highly toxic	supplemental	41460701

	TBTO

(95)	48-h EC50 = 0.9

(embryo-larval)	very highly toxic	acceptable	114085

	TBTO

(29.2)	48-h EC50 = 0.67

(embryo-larval)	very highly toxic	core	41041401

Bay mussel	TBTO

(97.4)	72-h EC50 = 0.8

(embryo-larval)	very highly toxic	core	41403802

Fiddler crab	95	96-h EC50 = 7300	moderately toxic	core	114084

Mysid shrimp	TBTO

 (29.2)	96-h LC50 = 3.9	very highly toxic	supplemental	41041403

Pink shrimp	TBTO

(95)	96-h LC50 = 11	very highly toxic	core	114083

Grass shrimp	TBTO

(97)	96-h LC50 = 19	very highly toxic	core	40228401a

	TBTO

(nr)b	20-31.4

(2 tests)	very highly toxic	n/a	EPA 2003

American lobster	TBTO

(nr)	1.74	very highly toxic	n/a	EPA 2003

Shore crab	TBTO

(nr)	9.73	very highly toxic	n/a	EPA 2003

Shore crab	TBTO

(nr)	83.28	very highly toxic	n/a	EPA 2003

Mud crab	TBTO

(nr)	34.9	very highly toxic	n/a	EPA 2003

Amphioxus	TBTO

(nr)	<10	very highly toxic	n/a	EPA 2003

a EPA/OPP/EFED Pesticide Ecotoxicity Database

b % ai not reported in EPA (2003)

Aquatic Organisms, Chronic

No guideline studies are available to assess chronic risks of
TBT-containing compounds to freshwater fish and invertebrates.  However,
EPA’s (2003) Ambient Aquatic Life Water Quality Criteria for
Tributyltin (TBT) – Final presents chronic toxicity values for a
32-day early life-stage study with the fathead minnow (Pimephales
promelas) and for two 21-day life-cycle studies with Daphnia magna. NOEC
values for adverse reproductive affects ranged from 0.1 to 0.19 µg ai/L
across the three studies (Table 6).

Table 6.  Chronic Toxicity of TBT Compounds to Freshwater Fish and
Invertebrates

Test

Species	% ai

tested	NOEC/LOEC

(µg ai/L)	Endpoints

affected	Study Status	MRID No.

Fish

Fathead minnow	TBTO

(96)	0.15 / 0.45	growth

(length and weight)	n/a	EPA 2003

Invertebrates

Water flea	TBTO

(96)	0.1 / 0.2	no. young per adult per day	n/a	EPA 2003

	TBTO

(100)	0.19 / 0.34	no. young per adult per day; adult survival	n/a	EPA
2003



t a TBT concentration of 0.19 μg/L, the number of juvenile mysids
released per female was reduced 50% from that of the control treatment;
no difference occurred at 0.09 μg/L.  The number of females releasing
viable juveniles was reduced at 0.19 and 0.33 μg/L, survival and weight
of females were reduced at >0.38 μg/L, and all mysids died at 0.48
μg/L.    

Table 7.  Chronic Toxicity of TBT Compounds to Estuarine/Marine Fish and
Invertebrates

Test

Species	% ai

tested	NOEC/LOEC

(µg ai/L)	Endpoints

affected	Study Status	MRID No.

Fish

Sheepshead minnow	TBTO

(97.5)	0.42 / 0.66	parental survival,

juvenile growth	core	41813901

	TBTO

(95)	0.24 / 0.56	parental survival	supplemental 	154629 

Invertebrates

Saltwater mysid, Acanthomysis sculpta	nr

(antifouling paint leachate)	0.09 / 0.19	no. juveniles released per
female	n/a	EPA 2003



		Sediment Toxicity, Acute and Chronic

Acute and chronic sediment toxicity data are required for TBT wood
preservative uses because of expected movement of active ingredient into
the aquatic environment and its expected deposition and persistence in
sediments as indicated by pertinent environmental fate data (Kd >10 for
acute and >50 for chronic, log Kow >3, Koc >1,000, soil aerobic
half-life = 127 days  in sediment).  No guideline studies are available.

		Aquatic Plants

Aquatic plant growth testing (850.5400) with the TGAI or TEP is required
for all pesticides having wood preservative uses.  No guideline studies
have been submitted for TBT.  The EPA (2003) Ambient Aquatic Life Water
Quality Criteria for Tributyltin (TBT) – Final provides some
information indicating that phytotoxicity of TBTO to aquatic plants
might be of concern.  Based on population growth, 72-h EC50s ranged from
approximately 0.3 to <1.5 μg/L for the dinoflagellate, Gymnodinium
splendens, the microalga, Pavlova lutheri, and the macroalga, Fucus
vesiculosus.  In a study with a freshwater green alga (Scenedesmus
obliquus), growth was reduced 87.6% at a concentration of 1 µg TBTO/L,
and an EC50 = 5.0 µg TBTO/L (based on chlorophyll production) was
reported in another study with the same species.  An EC50 = 1.19 µg
TBTO/L was determined in a study testing a saltwater diatom (Nitzschia
sp.).  In another study with a saltwater diatom (Skeletonema costatum),
an EC50 = 0.062 µg TBTO/L was based on dry cell weight.  A study with
TBT provided an EC50 of 0.68 µg/L (reduced growth) with mixed saltwater
algae (Dunaliella salina and D. viridis).

		Other Information on Sublethal Effects to Aquatic Organisms

Numerous studies have been conducted and published in the open
literature on adverse sublethal affects of TBT to aquatic animals.  Much
of this information is discussed in previous EPA reports.  An OPP
Environmental Fate and Effects Division environmental risk
characterization for TBT (Rexrode and Spatz 2001) provides the following
information:

"Recent data on TBT toxic effects have been reported on organs and
tissues in a variety of different species.  Histopathological studies
conducted by Wester et al. (1990) on medaka (Oryzias latipes, the
Japanese rice patty fish) found a no-observed-effect concentration for
TBTO at 0.32 ug/L.  Schwaiger et al. (1992), showed that sublethal TBT
concentrations (0.6 - 6.0 ug/L) can cause severe histopathological
changes in the spleen, liver, gills and pseudobranch of rainbow trout
(Oncorhynchus mykiss).  Studies on the bioconcentration of TBT by fish
embryos and larvae (Phoxinus phoxinus) by Kent (1991) showed an
extremely slow catabolism of the compound during these critical life
stages resulting in a strong potential for bioconcentration.  Working
with adult oysters (C. gigas), Chagot et al. (1990) found that at
experimental levels of 2.0 - 64.8 ppt the digestive gland is the primary
target organ.  He concluded that safe levels of TBT in mariculture
waters should be lower than 2 ppt.

Additional information on sublethal affects of TBT is provided in the
EPA (2003) Ambient Aquatic Life Water Quality Criteria for Tributyltin
(TBT) – Final:

“TBT is an endocrine-disrupting chemical (Matthiessen and Gibbs 1998).
The chemical causes masculinization of certain female gastropods. It is
likely the best studied example of endocrine disrupting effect. The
metabolic mechanism is thought to be due to elevating testosterone
titers in the animals and over-riding the effects of estrogen. There are
several theories of how TBT accomplishes the buildup of testosterone.
Evidence suggests that competitive inhibition of cytochrome
P450-dependent aromatase is probably occurring in TBT exposed gastropods
(Matthiessen and Gibbs 1998).  TBT may also interfere with sulfur
conjugation of testosterone and its phase I metabolites and their
excretion resulting in a build-up of pharmacologically active androgens
in some animal tissues (Ronis and Mason 1996).

In summary, in both field and laboratory studies, concentrations of TBT
in water of about

0.0015 μg/L or less and in tissues of about 0.2 μg/g dry wt. or less
do not appear to cause imposex in N. lapillus. Imposex begins to occur
at about 0.003 μg TBT/L, and some reproductive failure at
concentrations greater than 0.005 μg/L, with complete sterility
occurring after chronic exposure of sensitive early life-stages at 0.009
μg/L (for less sensitive stages, imposex does not occur until about
0.02 μg/L in some studies and greater than 0.2 μg/L in others).

Seinen et al. (1981) reported a 20% reduction in growth of rainbow trout
after 110 days exposure to 0.18 μg/L.  de Vries et al. (1991) measured
a similar response in rainbow trout growth in another 110 day exposure. 
They demonstrated decreased survival and growth at 0.200 μg/L but not
at 0.040 μg/L. Triebskorn et al. (1994) found reduced growth and
behavior changes in the fish at 21 days when exposed to 0.5 μg/L.”

Ecological Risk Assessment and Characterization

Risk assessment and characterization integrates exposure and toxicity
information to evaluate the potential for adverse ecological effects. 
Risk quotients (RQs) are determined for each taxa or ecological group by
comparing exposure estimates (Estimated Environmental Concentrations,
EECs) to the available acute and chronic ecotoxicity values, where:  

RQ = Exposure estimate (EEC) / Toxicity value

RQs are compared to OPP's levels of concern (LOCs).  Exceedance of an
LOC indicates a potential for acute or chronic adverse effects on
nontarget organisms and identifies a need for regulatory action to
mitigate risk.  LOCs currently address the following risk presumptions: 

acute: 	regulatory action may be warranted to reduce or preclude 

acute exposure

acute, listed species:	additional regulatory action may be warranted to
protect 

listed (i.e., endangered or threatened) species

chronic:	regulatory action may be needed to reduce or preclude 

chronic exposure 



The LOCs for the various risk presumptions are listed below for
terrestrial and aquatic animals and plants: 

	Aquatic 

Animals	Terrestrial Animals   	

Plants

Acute:	0.5	0.5	1

Acute, listed species:	0.05	0.1	1

Chronic:	1	1	n/a



The following toxicity endpoints are used as inputs to the RQ method for
expressing risk: 

Aquatic Animals

Acute:	Lowest tested EC50 or LC50 for freshwater fish and invertebrates
and estuarine/marine fish and invertebrates 

Chronic:	Lowest NOEC for freshwater fish and invertebrates and
estuarine/marine fish and invertebrates (early life-stage or full
life-cycle tests)



Terrestrial Animals

Avian acute: 

	Lowest LD50 (single oral dose) and LC50 (subacute dietary)

Avian chronic:	Lowest NOEC (21-week avian reproduction test)

Mammalian acute:	Lowest LD50 from single oral dose test.

Mammalian

chronic:	Lowest NOEC for two-generation reproduction test

Plants

Terrestrial:	Lowest EC25 values from both seedling emergence and
vegetative vigor for both monocots and dicots

Terrestrial

listed:	Lowest EC05 or NOEC for both seedling emergence and vegetative
vigor for both monocots and dicots

Aquatic vascular

and algae:	Lowest EC50 

Aquatic vascular

listed:	NOEC or EC05



When available, toxicity measures or other appropriate information from
non-guideline studies or from the open literature also may be used to
characterize risk.  

OPP generally uses computer simulation models to estimate exposure of
aquatic organisms to an active ingredient.  These models estimate EECs
in surface waters using product-label information (e.g., treatment site,
application rate, application method,) and available environmental-fate
data to determine how fast the pesticide breaks down and its expected
movement in the environment.  The models used in the risk assessment for
TBT compound wood preservative uses are described in more detail in the
Aquatic Exposure Assessment section.

For aquatic organisms, the following EECs are used to calculate the RQ
for each taxa:

Fish

Acute:	Instantaneous 

Chronic:	60-day average

Invertebrates

Acute: 	Instantaneous

Chronic:	21-day average

Plants

Acute: 	Instantaneous

Chronic:	Not applicable 



Environmental Fate Summary 

TBT is essentially stable to hydrolysis and photolysis in freshwater and
saltwater.  Biodegradation is the major breakdown pathway in both water
and sediments.  Half-lives are in the range of several days to weeks in
water and from several days to more than a year in sediments.  The
octanol/water partition coefficient is very high, and TBT has a high
tendency to bioconcentrate.  Refer to the environmental fate science
chapter for presentation and discussion of the available environmental
fate information for TBT.  

Aquatic Exposure Assessment

EECs resulting from leaching of TBT from treated wood into soil and
surface waters were calculated for six uses, including transmission
poles, fence posts, fences, deck posts, decks, and houses.  Use
scenarios were evaluated using an estimate of the maximum cumulative
aqueous release of TBT from treated wood over a 14-day period.  The
methodology for this analysis is based on an environmental risk
assessment previously prepared by the Rohm and Haas (2006) for
4,5-dichloro-2-n-octyl-3(2H)-isothiazolone (DCOIT).  In this
methodology, leaching of TBT from treated wood surfaces is modeled to
estimate soil loadings and concentrations.  Soil concentrations and
other input data are then used with EPA’s Express model EXAMS-PRZM
Exposure Simulation Shell (version 1.03.02) to estimate concentrations
in surface water.  The EECs are presented in Table 8.  See Attachment B
for information on the calculations used to derive these EECs and the
associated uncertainties and limitations of the methodology.

Table 8.  10th-percentile Estimated Environmental Concentrations of TBTO
in Dissolved Surface Water from Runoff as a Consequence of Leaching from
Treated Wood

Use	EEC (µg ai/L)

	instantaneous	21-day avg.	60-day avg.

House	0.057	0.024	0.011

Fence	0.040	0.017	0.007

Deck Post	0.025	0.010	0.005

Fence Post	0.015	0.006	0.003

Deck	0.011	0.004	0.002

Transmission Pole	0.003	0.001	0.001



Aquatic Risk Assessment

The full complement of acute and chronic toxicity data exposure in the
water column were presented in Tables 2 through 7.  The toxicity
endpoints used in the risk assessment are based on the most sensitive
species tested (Table 9).  Sediment toxicity data are not available.

Table 9.  Endpoint Selection for Ecological Risk Assessment

Taxa	Exposure	Species	Toxcitya

(ppb)

Freshwater fish	Acute	Fathead minnow	2.6

Freshwater invertebrate	Acute	Hydra	1.1

Estuarine/marine fish	Acute	Chinook salmon	1.46

Estuarine/marine invertebrate	Acute	Eastern oyster	0.126

Freshwater fish	Chronic	Fathead minnow	0.15

Freshwater invertebrate	Chronic	Water flea	0.1

Estuarine/marine fish	Chronic	Sheepshead minnow	0.24

Estuarine/marine invertebrate	Chronic	Mysid	0.09

a LC50 or EC50 for acute; NOEC for chronic

	Freshwater Fish and Invertebrates, Acute

The acute risk presumptions for freshwater fish and invertebrates
potentially exposed to TBT from wood treatments are presented in Table
10.   The LOC is equaled or exceeded only for listed (i.e., endangered
and threatened) invertebrates for TBT use on houses.  The LOC is not
exceeded for non-listed species for any wood-treatment use.  

Table 10.  Acute Risk Quotients and Risk Presumptions for Freshwater
Fish and Invertebrates Exposed in the Water Column 

Use	EEC

(µg ai/L)	Toxicity

(µg ai/L)	RQa	acute LOCs

exceededb

Fish

House	0.057	2.6	0.02	none

Fence	0.040	2.6	0.01	none

Deck Post	0.025	2.6	<0.01	none

Fence Post	0.015	2.6	<0.01	none

Deck 	0.011	2.6	<0.01	none

Transmission pole	0.003	2.6	<0.01	none

Invertebrates

House	0.057	1.1	0.05	listed species

Fence	0.040	1.1	0.04	none

Deck Post	0.025	1.1	0.02	none

Fence Post	0.015	1.1	0.01	none

Deck 	0.011	1.1	0.01	none

Transmission pole	0.003	1.1	<0.01	none

a acute RQ = instantaneous EEC/LC50 or EC50

b acute LOC = 0.5 (non-listed species) and 0.05 (listed species)

	Estuarine/marine Fish and Invertebrates, Acute

The acute risk presumptions for estuarine/marine fish and invertebrates
potentially exposed to TBT from wood treatments are presented in Table
11.   The LOC is exceeded for listed (i.e., endangered and threatened)
invertebrates for TBT use on houses fences and decks.  The LOC is not
exceeded for non-listed species for any wood-treatment use.  

Table 11.  Acute Risk Quotients and Risk Presumptions for
Estuarine/Marine Fish and Invertebrates Exposed in the Water Column 

Use	EEC

(µg ai/L)	Toxicity

(µg ai/L)	RQa	acute LOCs

exceededb

Fish

House	0.057	1.46	0.04	none

Fence	0.040	1.46	0.03	none

Deck Post	0.025	1.46	0.02	none

Fence Post	0.015	1.46	0.01	none

Deck 	0.011	1.46	<0.01	none

Transmission pole	0.003	1.46	<0.01	none

Invertebrates

House	0.057	0.126	0.45	listed species

Fence	0.040	0.126	0.32	listed species

Deck Post	0.025	0.126	0.20	listed species

Fence Post	0.015	0.126	0.12	listed species

Deck 	0.011	0.126	0.09	listed species

Transmission pole	0.003	0.126	0.02	none

a acute RQ = instantaneous EEC/LC50 or EC50

b acute LOC = 0.5 (non-listed species) and 0.05 (listed species)

	Aquatic Organisms, Chronic

The chronic risk presumptions for freshwater and estuarine/marine fish
and invertebrates potentially exposed to TBT from wood treatments are
presented in Tables 12 and 13.  The chronic LOC is not exceeded for
either listed (i.e., endangered and threatened) or non-listed fish and
invertebrates for any TBT wood-treatment use.  

Table 12.  Chronic Risk Quotients and Risk Presumptions for Freshwater
Fish and Invertebrates Exposed in the Water Column 

Use	EEC

(µg ai/L)	NOEC

(µg ai/L)	RQa	chronic LOC

exceededb

Fish

House	0.011	0.15	<0.1	no

Fence	0.007	0.15	<0.1	no

Deck Post	0.005	0.15	<0.1	no

Fence Post	0.003	0.15	<0.1	no

Deck 	0.002	0.15	<0.1	no

Transmission pole	0.001	0.15	<0.1	no

Invertebrates

House	0.024	0.1	0.2	no

Fence	0.017	0.1	0.2	no

Deck Post	0.010	0.1	0.1	no

Fence Post	0.006	0.1	<0.1	no

Deck 	0.004	0.1	<0.1	no

Transmission pole	0.001	0.1	<0.1	no

a chronic RQ = 60-day avg. EEC/NOEC and 21-day-avg. EEC/NOEC for
invertebrates

b chronic LOC >1

Table 13.  Chronic Risk Quotients and Risk Presumptions for
Estuarine/Marine Fish and Invertebrates Exposed in the Water Column 

Use	EEC

(µg ai/L)	NOEC

(µg ai/L)	RQa	chronic LOC

exceededb

Fish

House	0.011	0.24	<0.1	no

Fence	0.007	0.24	<0.1	no

Deck Post	0.005	0.24	<0.1	no

Fence Post	0.003	0.24	<0.1	no

Deck 	0.002	0.24	<0.1	no

Transmission pole	0.001	0.24	<0.1	no

Invertebrates

House	0.024	0.09	0.3	no

Fence	0.017	0.09	0.2	no

Deck Post	0.010	0.09	0.1	no

Fence Post	0.006	0.09	<0.1	no

Deck 	0.004	0.09	<0.1	no

Transmission pole	0.001	0.09	<0.1	no

a chronic RQ = 60-day avg. EEC/NOEC for fish and 21-day-avg. EEC/NOEC
for invertebrates

b chronic LOC >1

Aquatic Risk Characterization

Based on exceedance of the Agency’s acute LOC, acute risk to listed
aquatic invertebrates is presumed from exposure to TBT as a result of
wood-preservative uses.  This presumption of risk necessitates a more
comprehensive risk assessment for listed species, but that is not
included in the current assessment (see Endangered Species
Considerations section).

Although the Agency's chronic LOC is not exceeded for either fish or
aquatic invertebrates, evidence exists that chronic exposure may be a
concern for some organisms.  EPA's Office of Water considers TBT to be a
concern in the aquatic environment due in part to its persistence and
its link to imposex and immuno-supression in snails and bivalves. 
Through its authority under the Clean Water Act, the Agency has
developed ambient water quality criteria for TBT (EPA 2003).  The
criteria are established based on lines of evidence such as traditional
endpoints of adverse effects on survival, growth, and reproduction as
demonstrated in numerous laboratory studies; the endocrine disrupting
capability of TBT as observed in the production of imposex in field
studies; that TBT bioaccumulates in commercially and recreationally
important freshwater and saltwater species; and that an important
commercial organism already known to be vulnerable to a prevalent
pathogen was made even more vulnerable by prior exposure to TBT.  EPA's
water quality criteria for TBT are as follows:  

Freshwater organisms:

acute (1-hr avg.):  	0.46 μg/L

chronic (4-day avg.):  	0.072 μg/L

Saltwater organisms:

acute (1-hr avg.):  	0.42 μg/L

chronic (4-day avg.):  	0.0074 μg/L 



EPA does not regulate based on these criteria, but they do provide some
indications of TBT concentrations that may be detrimental to aquatic
organisms.  From Table 8 it can be seen that the modeled 21-day-average
EECs for houses (0.024 μg/L), fences (0.017 μg/L), and deck posts
(0.01 μg/L), and even the 60-day-average for houses (0.011 μg/L),
exceed the chronic 4-day-average ambient water quality criteria
established for saltwater organisms.  This potential will need to be
examined in more detail when RASSB conducts a more in-depth risk
assessment to address and mitigate risks to listed species.

Risk to aquatic plants cannot be assessed until required guideline
toxicity tests are available.  RASSB notes that aquatic plant EC50
values as low as 0.062 ppb in the open literature indicate that aquatic
plants may be at risk from the EECs modeled for wood preservative use of
TBT. 

TBT also is expected to accrue in aquatic sediments, with half-lives
from several days to months or more (EPA 2003); thus, sediments may be a
long-term source of exposure of aquatic organisms in some situations. 
However, such risk cannot be assessed until required acute and chronic
sediment-toxicity tests are available.  There is some evidence that
sediment concentrations in the 100-1000 ng/g range have caused severe
effects in clams and polychaetes.  Meador (2000) cites Fent and Hunn
(1995) in noting that clams have disappeared in areas where sediment TBT
values exceeded 800 ng/g dry wt.  Meador and Rice (2001) documented
moderate to severe reductions in growth for the polychaete Armandia
brevis at sediment concentrations ranging from 100-1000 ng/g dry wt.. 
As noted by Rexrode and Spatz (2001), a sediment concentration of 120
ng/g would provide an interstitial water concentration of about 10 ng/L
(0.01 µg/L), which exceeds the chronic ambient water quality standard
for saltwater organisms (see below).

The available evidence also suggests a strong potential for
bioconcentration and bioaccumulation of TBT in some aquatic organisms. 
Bioconcentration factors of 1810 (fillet), 2120 (head), and 4580
(viscera) reported in the sheepshead minnow and 700-1100 (fillet),
1050-1800 (viscera), and 21-2210 (whole body) in two studies with the
bluegill sunfish (MRIDs 41668901 and 41811501).   Bioconcentration
factors for three species of bivalve molluscs range from 192 for soft
parts of the European flat oyster to 60,000 for soft parts of the
juvenile blue mussel, Mytilus edulis. (EPA 2003).  As noted by Rexrode
and Spatz (2001), TBT has been found in tissues of marine mammals
(various species of dolphins, and stellar sea lions) and other
organisms.  

Terrestrial Risk Assessment

TBT is moderately toxic to birds and mammals, and acute risk is possible
if TBT-contaminated food is eaten.  Because TBT bioaccumulates in
tissues of organisms, food sources such as earthworms could expose birds
and mammals.  Currently, RASSB has no data to assess risks to birds and
mammals that eat contaminated food.  Uncertainty could be reduced if
bioaccumulation data for the earthworm were available.

Guideline toxicity data are not available to assess risk to honey bees. 
TBTO is reported to be toxic to honey bees (Apis mellifera) housed in
hives made from TBTO-treated wood (WHO 1999).  However, if product
labels prohibit use of treated wood in bee hives (see Required Label
Statements section), minimal exposure and risk would be presumed.

Endangered Species Considerations

Section 7 of the Endangered Species Act (ESA), 16 U.S.C. Section
1536(a)(2), requires that federal agencies consult with the National
Marine Fisheries Service (NMFS) for marine and andronomus listed
species, or with the United States Fish and Wildlife Services (FWS) for
listed wildlife and freshwater organisms, if proposing an "action" that
may affect listed species or their designated habitat.  Each federal
agency is required under the Act to insure that any action they
authorize, fund, or carry out is not likely to jeopardize the continued
existence of a listed species or result in the destruction or adverse
modification of designated critical habitat.  To jeopardize the
continued existence of a listed species is to "to engage in an action
that reasonably would be expected, directly or indirectly, to reduce
appreciably the likelihood of both the survival and recovery of a listed
species in the wild by reducing the reproduction, numbers, or
distribution of the species." 50 C.F.R. §402.02.

To comply with subsection (a)(2) of the ESA, EPA’s Office of Pesticide
Programs has established procedures to evaluate whether a proposed
registration action may directly or indirectly appreciably reduce the
likelihood of both the survival and recovery of a listed species in the
wild by reducing the reproduction, numbers, or distribution of any
listed species (U.S. EPA 2004).  If any of the Listed Species LOC
Criteria are exceeded for either direct or indirect effects in the
Agency’s screening-level risk assessment, the Agency identifies any
listed or candidate species that may occur spatially and temporally in
the footprint of the proposed use.  Further biological assessment is
undertaken to refine the risk.  The extent to which any species may be
at risk determines the need to develop a more comprehensive consultation
package as required by the ESA.

For TBT uses other than wood preservatives, the Agency assumes there
will be minimal environmental exposure, and only a minimal toxicity data
set is required (Overview of the Ecological Risk Assessment Process in
the Office of Pesticide Programs U.S. Environmental Protection Agency -
Endangered and Threatened Species Effects Determinations, 1/23/04,
Appendix A, Section IIB, p 81).  Uses in these categories do not undergo
a full screening-level risk assessment and are considered to fall under
a no effect determination.  

The assessment for wood treatment uses indicates that there is a
potential for TBT exposure of listed freshwater and estuarine/marine
organisms, and possibly terrestrial birds and mammals, and a more
refined assessment is warranted for direct, indirect, and habitat
effects.  The refined assessment will involve clear delineation of the
action area associated with proposed use of TBT and best available
information on the temporal and spatial co-location of listed species
with respect to the action area.  This analysis has not been conducted
for this assessment.  An endangered species effect determination will
not be made at this time.  The label statement required for wood
preservative products is expected to provide some mitigation until a
full endangered species assessment is conducted.

Confirmatory Data Required To Support Wood Treatment Uses:

        •	Whole sediment: acute freshwater invertebrates (850.1735)

        •	Whole sediment: acute marine invertebrates (850.1740)

        •	Whole sediment: chronic invertebrates (no guideline no.)

        •	Freshwater diatom (850.5400); TGAI or EP

        •	Marine diatom (850.5400); TGAI or EP

        •	Blue-green cyanobacteria (850.5400); TGAI or EP

        •	Freshwater green alga (850.5400); TGAI or EP

        •	Freshwater floating macrophyte duckweed (850.4400); TGAI or
EP

        •	Freshwater rooted macrophyte rice seedling emergence
(850.4225); EP

        •	Freshwater rooted macrophyte rice vegetative vigor
(850.4250); EP

        •	A study addressing honey/beeswax residues and acute toxicity
of treated wood residues to bees is required if bee hives might be
constructed of treated wood or if any product is intended for
application to a bee hive.  The study is a combination of Guidelines
171-4 and 850.3030 (see information regarding residue data requirements
for uses in beehives in the residue chemistry section of 40 CFR part
158).  The toxicity portion of this study is conducted in lieu of a
honeybee contact LD50 test. The number of bees tested and the
methodology for collection/ introduction of bees into hives, feeding,
and observations for toxicity and mortality must be consistent with
those described in OPPTS Guideline 850.3030, “Honey Bee Toxicity of
Residues on Foliage”.  However, this study will be waived if product
labels with wood preservative use are amended to prohibit the use of
treated wood for beehive construction (see section IV Label Hazard
Statements). 

RASSB notes that a label statement prohibiting use of TBT-treated wood
in the aquatic environment will reduce potential exposure of aquatic
organisms.  However, TBT leachate is still expected to reach water
bodies (water column and sediments) due to environmental transport from
wood-preservative application sites.  Therefore, the data specified
above are needed to assess risks to animals and plants in the aquatic
environment.

Required Label Statements

	All products:

	All product labels must have the following ENVIRONMENTAL HAZARDS
statement:  

"This pesticide is toxic to fish and aquatic invertebrates. Do not
contaminate water when disposing of equipment washwaters.  Do not
discharge effluent containing this product into lakes, streams, ponds,
estuaries, oceans, or other waters unless in accordance with the
requirements of a National Pollutant Discharge Elimination System
(NPDES) permit and the permitting authorities are notified in writing
prior to discharge.  Do not discharge effluent containing this product
to sewer systems without previously notifying the local sewage treatment
plant authority.  For guidance contact your State Water Board or
Regional Office of the EPA."

Products with wood preservative uses:

If honeybee studies 850.3030 and 171-4 are waived, the following label
statement is required:  

“Treated wood shall not be used in the construction of beehives.”

Products also must have a statement prohibiting use of TBT-treated wood
in the aquatic environment.

References

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Geneva. 201 pp.

Matthiessen, P. and P.E. Gibbs. 1998. Critical appraisal of the evidence
for tributyltin-mediated endocrine disruption in mollusks. Environ.
Toxicol. Chem. 17:37-43.

Meador, J.P.  2000.  An analysis in support of a sediment quality
threshold for tributyltin to protect prey species for juvenile salmonids
listed by the Endangered Species Act.  Northwest Fisheries Science
Center, National Oceanic and Atmospheric Adminsitration, Seattle, WA. 
20 pp.

Rexrode, M. and D. Spatz.  2001.  EFED Response to Request for Update on
Tributyltin (TBT) Environmental Risk Characterization.  5/11/2001.  

Ronis, M.J.J. and A.Z. Mason. 1996. The metabolism of testosterone by
the periwinkle (Littorina littorea) in vitro and in vivo: Effects of
tributyl tin. Mar. Envir. Res. 42(1-4):161-166.

Schwaiger et al. (1992) A prolonged toxicity study on the effects of
sublethal concentrations of bis(tri-n-butyltin)oxide (TBTO):
histopathological and histochemical findings in rainbow trout
(Oncorhynchus mykiss). Aquatic Toxicology 23:31-48

Seinen, W., T. Helder, H. Vernij, A. Penninks and P. Leeuwangh. 1981.
Short term toxicity of tri-nbutyltin chloride in rainbow trout (Salmo
gairdneri - Richardson) yolk sac fry. Sci. Total Environ. 19:155-166.

Strand, J.; Antrim, L.; Fortman, T.; et al. (1990) Bis(tributyltin)
Oxide--Acute Effects on Bay Mussel (Mytilus sp.) Embryos: Lab Project
Number: 12716. Unpublished study prepared by Battelle Marine Sciences
Laboratory. 76 p.  MRID 41403802

Strand, J.; Antrim, L.; Fortman, T.; et al. (1990) Bis(tributyltin)
Oxide--Acute Effects on Pacific Oyster (Crassostrea gigas) Embryos: Lab
Project Number: 12716. Unpublished study prepared by Battelle Marine
Sciences Laboratory. 63 p.  MRID 41403801

Thompson, K.; Cohle, P. (1990) Acute 96-hour Flow-through Toxicity of
Bis(tri-n-butyltin)Oxide to Bluegill (Lepomis macrochirus): Lab Project
Number: 38307. Unpublished study prepared by Analy- tical Bio-Chemistry
Laboratories, Inc. 279 p.  MRID 41518301

Triebskorn, R., H. Kohler, J. Flemming, T. Braunbeck, R. Negele and H.
Rahmann. 1994. Evaluation of bis(tri-n-butyltin)oxide (TBTO)
neurotoxicity in rainbow trout (Oncorhynchus mykiss). I. Behaviour,
weight increase, and tin content. Aguat. Toxicol. 30:189-197.

Walker, W. (1989) Acute and Life-Cycle Toxicity of Bis(tributyltin)
Oxide and Dibutyltin Dichloride to the Sheepshead Minnow (Cyprinodon
variegatus) in a Flow-through System: Final Report: Lab Project Number:
CONTRACT No. ES-7339 Subtask 2B. Unpublished study prepared by Gulf
Coast Research Lab. 174 p.  MRID 41813901

Wester et al. (1990) The toxicity of bis(tri-n-butyltin)oxide (TBTO) in
small fish species Oryzias latipes (medaka) and Poecilia reticulata
(guppy). Aquat. Toxicol. 16:53–72.

WHO.  1999.  Tribultyltin Oxide.  Concise International Chemical
Assessment Document 14, World Health Organization, Geneva. 

Attachment A:  OPP Ecotoxicity Profile for Tributyltin-Compound
Guideline Studies

Guideline No./

Study Type	

Chemical Name	

MRID No./

Reference Information/

Study Classification

	

Dosing and Animal Information	

Results

Aquatic Fauna

850.1010

Aquatic invertebrate acute toxicity test, freshwater daphnids

	TBTO	MRID 41518401

Burgess, D.; Hicks, S.; Lochhaas, C. (1990) Acute Toxicity of Bis-
(Tributyltin)Oxide to

Daphnia magna: Lab Project Number: 38308. Unpublished study prepared by
Analytical

Bio-Chemistry Labora- tories, Inc. 255 p.

Core 	Purity: 97.5% a.i.

Test substance TBTO were exposed to first instar Daphnia magna (< 24
hours old). Ten/each of the two replicates/concentration. 

Test concentrations were 0.86, 1.4, 2.3, 4.1, 7.2 µg/l.	Very highly
toxic to Daphnia magna.

48 – hour EC50 = 11.5 µg/l.

NOEC= 3.5 µg/l.



850.1055

Bivalve acute toxicity test 	TBTO	MRID 136470

Buccafusco, R. (1976) Acute Toxicity of Tri-n-butyltin Oxide to Channel
Catfish (Ictalurus punctatus), the Fresh Water Clam (Elliptio
complanatus), the Common Mummichog (Fundulus hetero- clitus) and the
American Oyster (Crassostria virginica). (Un- published study received
Jan 17, 1977 under 5204-1; prepared by E G & G Bionomics, submitted by M
& T Chemicals, Inc., Rahway, NJ; CDL:227596-A)

Supplemental	Purity: 95% a.i.

Test species:

Eastern oyster Crassostria virginica	LC50 > 560 < 1000 ppm.

Observation:

 concentrations ≥ 100 ppm, the solution was cloudy in proportion to
the concentration presumably due to insolubility of TBTO. Oysters
displayed a reduced response to external stimuli and remained open after
expiration.

	TBTO	MRID 114084

Heitmuller, T. (1977) Toxicity of Tri-n-butyltin Oxide (TBTO) to Fiddler
Crabs (Uca

pugilator). (Unpublished study received Nov 14, 1977 under 5204-1;
prepared by EG & G,

Bionomics, submitted by M & T Chemicals, Inc., Rahway, NJ; CDL:232248-B)

Core 	Purity: 95% a.i.

Ten fiddler crabs (Uca Pugilator) were tested at each of the six
concentrations.

Test concentrations were 1,8, 3.2, 5.6 10 ppm.. 	96 – hour EC50 = 7.3
ppm (95% C.I. 6.4 – 8.3 ppm).



	TBTO	MRID 114083

Heitmuller, T. (1977) Toxicity of Tri-n-butyltin Oxide (TBTO) to Pink
Shrimp (Penaeus

duorarum). (Unpublished study received Nov 14, 1977 under 5204-1;
prepared by EG & G,

Bionomics, submitted by M & T Chemicals, Inc., Rahway, NJ; CDL:232248-A)

Core 	Purity: 95% a.i.

Test substance were exposed to  pink shrimp (Penaeus

duorarum) and observed for 96 hours.

Test concentrations were 1.0, 1.8, 3.2, 5.6, 10, 18 and 32 ppb.	96 –
hour LC50 = 15 ppb (6 – 38 ppb).

850.1055

Bivalve acute toxicity test 	TBTO	MRID 41403802

Strand, J.; Antrim, L.; Fortman, T.; et al. (1990) Bis(tributyltin)
Oxide--Acute Effects on Bay Mussel (Mytilus sp.) Embryos: Lab Project
Number: 12716. Unpublished study

prepared by Battelle Marine Sciences Laboratory. 76 p.

Core	Purity: 97.4% a.i.

Test substance TBTO were exposed to 6 bay mussel (Mytilus sp.) (one per
concentration) for 72 hours.

Test concentrations were 401, 572, 818, 1168, 1669 and 2389 ng/l.	TBTO
is highly toxic to bay mussles. embryos

72 – hour EC50 = 805 ng/l;

72 – hour LC50 = 952 ng/l.

NOEC (mortality) = 515 ng/l.

NOEC (development) = 454 ng/l.

850.1055

Bivalve acute toxicity test 	TBTO	MRID 41403801

Strand, J.; Antrim, L.; Fortman, T.; et al. (1990) Bis(tributyltin)
Oxide--Acute Effects on

Pacific Oyster (Crassostrea gigas) Embryos: Lab Project Number: 12716.
Unpublished

study prepared by Battelle Marine Sciences Laboratory. 63 p.

Core	Purity: 97.4% a.i.

Test substance TBTO were exposed to 16 Pacific oyster (Crassostrea
gigas) for 48 hours.

Test concentrations were 172, 287, 478, 798, 1327, 2212 ng/l.	TBT is
highly toxic to pacific oysters embryos.

48 – hour EC50 = 277 ng/l.

48 – hour LC50 = 319 ng/l.

NOEC = 229 ng/l.

850.1055

Bivalve acute toxicity test	TBTO	MRID 114085

Hollister, T. (1977) Toxicity of Tri-n-butyltin Oxide (TBTO) to Embryos
of Eastern

Oysters (Crassostrea virginica). (Unpub- lished study received Nov 14,
1977 under 5204-1;

prepared by EG & G, Bionomics, submitted by M & T Chemicals, Inc.,
Rahway, NJ;

CDL:232248-C)

Core 	Purity: 95% a.i.

Test substance TBTO were exposed to Eastern oysters (Crassostrea
Virginica).

Test concentrations were 0.1, 0.3, 0.6, 3.2, 5.6 ppb.

	48 – hour EC50 = 0.9 ppb (95% C.I. 0.4 – 1.9) ppb.



850. 1075

Fish acute toxicity test

	TBTO	MRID 41518301

Thompson, K.; Cohle, P. (1990) Acute 96-hour Flow-through Toxicity of
Bis(tri-nbutyltin)

Oxide to Bluegill (Lepomis macrochirus): Lab Project Number: 38307.

Unpublished study prepared by Analy- tical Bio-Chemistry Laboratories,
Inc. 279 p.

Core 	Purity: 97.5% a.i.

Test substance TBTO were exposed to 10 blue gill fishes (Lepomis
macrochirus). 

Test concentrations were 1.5, 3.0, 6.0, 12, and 24 µg/l and observed
for 96 hours.	Highly toxic. 

96 – hour LC50 = 8.7 µg/l.

NOEC = 5.8 µg/l. 

850. 1075

Fish acute toxicity test

	TBTO	MRID 136470

Buccafusco, R. (1976) Acute Toxicity of Tri-n-butyltin Oxide to Channel
Catfish (Ictalurus punctatus), the Fresh Water Clam (Elliptio
complanatus), the Common Mummichog (Fundulus hetero- clitus) and the
American Oyster (Crassostria virginica). (Un- published study received
Jan 17, 1977 under 5204-1; prepared by E G & G Bionomics, submitted by M
& T Chemicals, Inc., Rahway, NJ; CDL:227596-A)

Core 	Purity: 95% a.i.

Test species Channel Catfish (Ictalurus punctatus)

	96 – hour LC50 = 12 (7.3 – 20) ppb.

Observation:

0% mortality at 7.5 ppb and 100% mortality at 18 ppb. AT 7.5 ppb
treatment levl, fish displayed partial or complete loss of equilibrium.



850. 1075

Fish acute toxicity test

	TBTO	MRID 136470

Buccafusco, R. (1976) Acute Toxicity of Tri-n-butyltin Oxide to Channel
Catfish (Ictalurus punctatus), the Fresh Water Clam (Elliptio
complanatus), the Common Mummichog (Fundulus hetero- clitus) and the
American Oyster (Crassostria virginica). (Un- published study received
Jan 17, 1977 under 5204-1; prepared by E G & G Bionomics, submitted by M
& T Chemicals, Inc., Rahway, NJ; CDL:227596-A)

Core	Purity : 95% a.i.

Test species Common Mummichog (Fundulus hetero- clitus)	96 – hour LC50
 = 24 (18 -33) ppb.

Observation:

Zero (0)% mortality at 18 ppb, 100% mortality at 32 ppb.

850. 1075

Fish acute toxicity test

	TBTO	MRID 136471

Buccafusco, R. (1976) Acute Toxicity of Tri-n-butyltin Oxide to Bluegill
(Lepomis

macrochirus). (Unpublished study received Jan 17, 1977 under 5204-1;
prepared by E G &

G Bionomics, submitted by M & T Chemicals, Inc., Rahway, NJ;
CDL:227596-B)

Core 	Purity: 95% a.i.

	96 – hour LC50 = 7.6 (5.6 – 10) ppb.

Observation:

In concentrations ≥ 18 ppb (at 24 hours of exposure) the fish
completely lost equilibrium. No discernable effects at 4.2 ppb. Range
between 0 and 100% mortality ≤ 4.4 ppb.

850. 1075

Fish acute toxicity test

	TBTO	MRID 41518501

Cohle, P. (1990) Acute 96-hour Flow-through Toxicity of Bis(tri-n-
butyltin)Oxide to

Rainbow Trout (Oncorhynchus mykiss): Lab Pro- ject Number: 38306.
Unpublished study

prepared by Analytical Bio-Chemistry Laboratories, Inc. 277 p.

Core	Purity: 97.5% a.i.

Test substance TBTO were exposed to 10 rainbow trout (Oncorhynchus
mykiss).

Test concentrations were 1.5, 3.0, 6.0, 12, and 24 µg/l and observed
for 96 hours.	Very highly toxic

96 - hour LC50 = 7.4 µg/l.

NOEC = 2.5 µg/l.

850.1500

Fish life cycle toxicity	TBTO	MRID 41813901

Walker, W. (1989) Acute and Life-Cycle Toxicity of Bis(tributyltin)
Oxide and Dibutyltin

Dichloride to the Sheepshead Minnow (Cyprinodon variegatus) in a
Flow-through System:

Final Report: Lab Project Number: CONTRACT No. ES-7339 Subtask 2B.
Unpublished

study prepared by Gulf Coast Research Lab. 174 p.

Core	Purity: 97.5% a.i.

Test substance TBTO were exposed to  25 embryos (< 24 hours old)
sheepshead minnow (Cyprinodon varigatus) for 180 days of flow-through
life cycle toxicity test.

Test concentrations were 0.6, 1.2, 2.4, 4.9, and 9.8 µg/l.	Based on the
occurrence  of sublethal  effects and a significant effect on parental
minnow survival at concentrations ≥ 0.66 TBT+/l, the maximum
acceptable toxicant concentration was > 0.42 and < 0.66 µg/l TBT+/l
(geometric mean MATC = 0.53 TBT+ µg/l.

Terrestrial Wildlife

850.2100

Avian acute oral toxicity test

	TBTO	MRID 130548

Anon. (1979) LD50 for bis (tributyltin) oxide in mallard ducks. Final
Report prepared by Environmental Consultants, Inc. for M&T Chemicals,
Rahway, NJ

(Acc. 241152)

Supplemental

	Purity:  tech.

Test birds (>16 wks old) given oral dose of  0, 81.2, 97.4, 116, 139, or
167 mg/kg and onserved for 22 days.	LD50 >167 mg/kg

mortality:

control – none

81.2 – 27%

97.4 – 45%

116 – 36%

139 – 27%

167 – 36%

850.2200

Avian dietary toxicity test

	TBTO

	MRID 136468

Fletcher, D. (1976) Report to M & T Chemical Company: 8-Day Dietary LC50
Study with Tributyltin Oxide in Bobwhite Quail: IBT No. 8580-09264.
(Unpublished study received Sep 27, 1976 under 5204-1; prepared by
Industrial Bio-Test Laboratories, Inc., submitted by M & T Chemicals,
Inc., Rahway, NJ; CDL:226129-B)

Core	Purity: 95% a.i.

Test species bobwhite quail administered the test substance TBTO and
observed for 8 days.	LC50 = 545 (395 – 752) ppm.



850.2200

Avian dietary toxicity test

	TBTO	MRID 165211

Fletcher, D. (1976) 8-Day Dietary LC50 Study with Tributyltin Oxide in
Mallard Ducklings:

IBT No. 8580-09262. Unpublished study prepared by Industrial Bio-Test
Laboratories, Inc.

18 p.

Core	Purity: 95% a.i.

Test species Mallard ducklings administered the test substance TBTO and
observed for 8 days.	LC50 = 840 (542 – 1302) ppm.

Observation:

Anorexia and general weakness was noted in all treated birds.



Attachment B:  Estimated Environmental Concentrations for Tributyltin
Oxide (TBTO) Leached from Wood into Soil and Water

	UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

	WASHINGTON, D.C.  20460

	

						12/18/2007

	MEMORANDUM

	SUBJECT:	Estimated Environmental Concentrations for Tributyltin Oxide
(TBTO) Leached from Wood into Soil and Water

		From:		Siroos Mostaghimi, Ph.D., Senior Scientist

		Risk Assessment and Science Support Branch (RASSB)

		Antimicrobials Division (7510P)

			To:	Norm Cook, Chief

		Risk Assessment and Science Support Branch (RASSB)

					Antimicrobials Division (7510P) 	 

Chemical NO: 083001

CAS Registry Number: 56-35-9

Attached please find the result of modeling for leaching of TBTO from
wood into soil and water. 

Introduction

This report presents estimates of environmental concentrations of
bis(tri-n-butyltin) oxide (TBTO) in soil, surface water, and sediment
pore water resulting from the use of TBTO as a wood preservative.  TBTO
is registered for use as a bacteriostat, micorbicide/microbistat,
fungicide, algaecide, antifoulant, slimacide, virucide, disinfectant,
sanitizer, miticide and insecticide.  TBTO is also registered for use on
agricultural farm buildings and equipment, commercial and industrial
water cooling systems, medical buildings and equipment, textiles,
adhesives, caulks, and plastics.

The methodology for this analysis is consistent the methodology used
previously for the wood preservative AMICAL   This methodology was based
on an environmental risk assessment previously prepared by the Rohm and
Haas Company (2006) for 4,5-dichloro-2-n-octyl-3(2H)-isothiazolone
(DCOIT), as well as a lumber leaching methodology developed by Krahn and
Strub (1990) .  In this methodology, leaching of TBTO from treated wood
surfaces is modeled to estimate soil loadings and concentrations.  The
estimated soil concentrations and other input data are used with EPA’s
PE5 PRZM-EXAMS Model Shell (version 5.0) to estimate concentrations in
surface water and sediment pore water.  

Section 1 of this memorandum presents the estimation of environmental
concentrations of TBTO in soil.  Estimates of dissolved surface water
and sediment pore water concentrations of TBTO are presented in Section
2.  Section 3 identifies key assumptions, limitations, and uncertainties
of this analysis.  Section 4 identifies referenced literature.

1. 	Estimation of TBTO Concentrations in Soil

	This section describes the estimation of environmental concentrations
of TBTO in soil.  Soil concentrations of TBTO were estimated for six
wood preservative use scenarios developed by Rohm and Haas (2006):
transmission pole, fence post, fence, deck post, deck, and house.  Data,
assumptions, and calculations for these use scenarios are presented in
Section 1.2.  Section 1.1 describes the approach used with all use
scenarios to estimate TBTO leaching from treated wood surfaces.  Section
1.3 describes how soil concentrations estimated for each use scenario
were used to estimate soil compartment loading rates for use with the
PE5 model.

 

Cumulative Quantity of TBTO Leached Out of Wood

Leaching of TBTO from treated wood surfaces was estimated based on
chemical properties and a treated lumber leaching methodology developed
by Krahn and Strub (1990).  

Krahn and Strub (1990) conducted a field experiment to measure rainfall
leaching of an antisapstain chemical from treated wood.  Stacks of
treated lumber (2 feet x 4 feet x 16 feet) were placed outdoors above
leachate collection trays, and leachate was collected following a
five-hour rainfall event.  The volume of leachate collected, the
concentration of the leachate, and the surface area of lumber exposed to
rainfall were then be used to calculate the mass of antisapstain
chemical released per square meter of wood surface during the five-hour
rain cycle.  Kahn and Strub (1990) then used this experiment to devise a
general protocol for estimating antisapstain leaching and surface runoff
from a lumber yard containing 16 lumber stacks of various ages.  

Versar (2005) applied the Krahn and Strub (1990) protocol to estimate
runoff of the antisapstain chemical ADBAC from a hypothetical lumber
yard.  First, Versar (2005) developed Equation 1 to estimate leaching
from a lumber stack and single five-hour leaching cycle.

Equation 1

 

Where:

Ci	=	Concentration of leachate produced during a five-hour leaching
cycle i (ppm or 

		mg/L)

Mo            =        Mass of chemical applied to leachable portion of
wood at time t = 0 (131,467.61 mg from spreadsheet attached with this
memorandum)

ti	=	Time at which leaching cycle i ends (each leaching cycle is 5
hours) (i + 5 hrs) 

Vleachate	=	Volume of leachate per stack of lumber (119 L calculated
from Krahn and 

		Strub, 1990) 

SAtop	=	Surface area of the top of a stack of lumber (5.95 m2 calculated
from 

		Krahn and Strub, 1990)

SAtotal	=	Total surface area of the exposed to rain (i.e., all surfaces
except bottom; 13.4 

		m2 calculated from Krahn and Strub, 1990)

I	=	Rainfall Intensity (0.003 m/hr from Versar, 2005)

KOC	=	Organic carbon partition coefficient (5080 mL/g from EPA, 2007) 

Z	=	Surface thickness of leachable wood (0.01 m from EPA, 2004)

	Parameter values and sources for this Equation 1 are shown with the
parameter definitions.  In this equation, the chemical-specific leaching
behavior is predicted using the organic carbon partition coefficient
(Koc).  For more explanation of how this Equation 1 was derived, refer
to ICF (2007b) and Versar (2005). 

Rohm and Hass (2006) estimated soil environmental concentrations using
cumulative leaching data obtained from an aqueous leaching study in
which a block of treated wood was immersed for 14 days.  To make the
TBTO analysis consistent with the Rohm and Hass (2006) methodology, the
rainfall leaching equation (i.e., Equation 1) to calculate cumulative
leaching of TBTO after 67 five-hour rain cycles totaling 13.9 days
(i.e., approximately equivalent to the 14-day immersion study).  The
cumulative quantity of TBTO leached per m2 of treated wood over the 13.9
day time period was calculated to be 85.8 mg/m2.  All calculations are
provided in an Excel spreadsheet submitted with this memorandum.

  

TBTO Use Scenarios

Six TBTO use scenarios defined by Rohm and Haas (2006) were used to
estimate post-application environmental concentrations in soil.  The use
scenarios included application of TBTO to from transmission poles, fence
posts, fencing, deck posts, decking, and wood clad houses into soil. 
Spreadsheets containing calculations for each scenario are provided with
this memorandum.

Transmission Poles

The environmental concentration in soil following application of TBTO to
a transmission pole was estimated by first calculating the quantity of
TBTO leached into the volume of the soil surrounding a transmission
pole, as shown in Equation 2.  This value (Qpole) is the product of the
sum of the treated wood surface areas above and below ground and the
cumulative quantity of TBTO leached per 1 m2 of treated wood over a 14
day period. 

Equation 2:

 Qpole = (AreaAG+AreaBG)*QLT

Where:

Qpole	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding 

a transmission pole (6.09E-04 kg)

AreaAG	= 	Wood surface area above ground (5.5 m2 from Rohm and Haas,
2006)

AreaBG	= 	Wood surface area below ground (1.6 m2 from Rohm and Haas,
2006)

QLT	= 	Cumulative quantity of TBTO leached out of 1 m2 of treated wood
over a 

14 day period (8.58E-05 kg/m2 from Section 1.1)

Next, the concentration of TBTO in the soil surrounding the transmission
pole was calculated by dividing the estimated quantity of TBTO leached
into the soil surrounding the transmission pole (Qpole) by the product
of the volume of wet soil and the bulk density of wet soil:

Equation 3:

 Csoilpole = (Qpole*CONVkgmg)/(Vsoil*RHOsoil)

Where: 

Csoilpole	= 	Estimated concentration of TBTO in soil surrounding a
transmission pole (1.49 mg/kg)

Qpole	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding a

		transmission pole (6.09E-04 kg from Equation 2)

CONVkgmg	= 	Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

Vsoil	= 	Wet soil volume (0.24 m3 from Rohm and Haas, 2006)

RHOsoil	= 	Bulk density of wet soil (1,700 kgww/m3 from Rohm and Haas,
2006)

Fence Posts

Environmental concentrations of TBTO in soil from treated fence posts
were estimated by first calculating the quantity of the TBTO leached
into the volume of the soil surrounding a fence post, as shown in
Equation 4.  QFencePost is the product of the sum of the wood surface
area above and below ground and the cumulative quantity of TBTO leached
per m2 of treated wood over a 14 day period.

Equation 4:

 QFencePost = (AreaAG+AreaBG)*QLT

Where:

QFencePost	= 	Estimated quantity of TBTO leached into the volume of soil


		surrounding a fence post (6.86E-05 kg)

AreaAG	= 	Wood surface area above ground (0.6 m2 from Rohm and Haas,
2006)

AreaBG	= 	Wood surface area below ground (0.2 m2 from Rohm and Haas,
2006)

QLT	= 	Cumulative quantity of TBTO leached from 1 m2 of treated wood 

		over a 14 day period (8.58E-05 kg/m2 from Section 1.1)

Using Equation 5, the concentration of TBTO in the soil surrounding the
fence post was then calculated by dividing the estimated quantity of
TBTO leached into the soil surrounding the fence post (QFencePost) by
the product of the volume of wet soil and the bulk density of wet soil: 

Equation 5:

 CsoilFencePost = (QFencePost*CONVkgmg)/(Vsoil*RHOsoil)

Where:

CsoilFencePost	= 	Estimated concentration of TBTO in soil surrounding a
fence post (0.82 mg/kg)

QFencePost	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding 

			a fence post (6.86E-05 kg from Equation 4)

CONVkgmg		= 	Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

Vsoil	= 	Wet soil volume (0.049 m3 from Rohm and Haas, 2006)

RHOsoil	= 	Bulk density of wet soil (1,700 kgww/m3 from Rohm and Haas,
2006)

Fence

The environmental concentration of TBTO in soil following application to
a fence was estimated by first calculating the quantity of the TBTO
leached into the volume of the soil surrounding a one meter length of
fence.  As shown in Equation 6, this value (QFence) is the product of
the surface area of wood per meter of fence and the cumulative quantity
of TBTO leached per m2 of treated wood over a 14 day period. 

Equation 6:

 

QFence = AreaFence*QLT

Where:

QFence	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding 

		a one meter length of fence (1.72E-04 kg)

AreaFence	= 	Wood surface area per meter of fence (2 m2 from Rohm and
Haas, 2006)

QLT	= 	Cumulative quantity of TBTO leached per m2 of treated wood over a


		14 day period (8.58E-05 kg/m2 from Section 1.1)

Using Equation 7, the concentration of TBTO in the soil surrounding the
fence was calculated by dividing the estimated quantity of TBTO leached
into the soil surrounding the fence (QFence) by the product of the
volume of wet soil and the bulk density of wet soil: 

Equation 7: 

CsoilFence= (QFence*CONVkgmg)/(Vsoil*RHOsoil)

Where:

CsoilFence	= 	Estimated concentration of TBTO in soil surrounding a 1 m
length 

		of fence (10.09 mg/kg)

QFence	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding 

		the fence (1.72E-04 kg from Equation 6)

CONVkgmg	= 	Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

Vsoil	= 	Wet soil volume (0.01 m3 from Rohm and Haas, 2006)

RHOsoil	= 	Bulk density of wet soil (1,700 kgww/m3 from Rohm and Haas,
2006)

Deck Post

The concentration of TBTO in soil surrounding a treated deck posts was
estimated by first calculating the quantity of the TBTO leached into the
volume of the soil surrounding a deck post.  As shown in Equation 8,
this value (QDeckPost) is the product of the sum of the surface area of
treated wood above and below ground and the cumulative quantity of TBTO
leached per m2 of treated wood over a 14 day period. 

Equation 8:

 QDeckPost = (AreaAG+AreaBG)*QLT

Where:

QDeckPost	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding 

a deck post (1.03E-04 kg)

AreaAG	= 	Wood surface area above ground (0.9 m2 from Rohm and Haas,
2006)

AreaBG	= 	Wood surface area below ground (0.3 m2 from Rohm and Haas,
2006)

QLT	= 	Cumulative quantity of TBTO leached out of 1 m2 of treated wood 

over a 14 day period (8.58E-05 kg/m2 from Section 1.1)

Then, Equation 9 was used to calculate the concentration of TBTO in the
soil surrounding the deck post.  In Equation 9 the estimated quantity of
TBTO leached into the soil surrounding the deck posts (QDeckPost) is
divided by the product of the volume of wet soil and the bulk density of
wet soil: 

Equation 9:

 

CSoilDeckPost = (QDeckPost*CONVkgmg)/(Vsoil*RHOsoil)

Where:

CsoilDeckPost	= 	Estimated concentration of TBTO in soil surrounding a
deck post (0.98 mg/kg)

QDeckPost	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding a 

		deck post (1.03E-04 kg from Equation 8)

CONVkgmg	= 	Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

Vsoil	= 	Wet soil volume (0.062 m3 from Rohm and Haas, 2006)

RHOsoil	= 	Bulk density of wet soil (1,700 kgww/m3 from Rohm and Haas,
2006)

Deck

The environmental concentration of TBTO in soil associated with a
treated deck was estimated by first calculating the quantity of the TBTO
leached into the volume of the soil surrounding a deck.  As shown in
Equation 10, QDeck is the product of the wood surface area above the
soil and the cumulative quantity of TBTO leached from 1 m2 of treated
wood over a 14 day period. 

Equation 10: 

QDeck = AreaDeck*QLT

Where:

QDeck	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding 

		the deck (2.06E-03 kg)

AreaDeck	= 	Wood surface area above soil (24 m2 from Rohm and Haas,
2006)

QLT	= 	Cumulative quantity of TBTO leached per m2 of treated wood over 

		a 14 day period (8.58E-05 kg/m2 from Section 1.1)

The concentration of TBTO in the soil surrounding the deck was then
calculated with Equation 11, in which the estimated quantity of TBTO
leached into the soil surrounding the deck (QDeck) is divided by the
product of the volume of wet soil and the bulk density of wet soil: 

Equation 11: 

CsoilDeck= (QDeck*CONVkgmg)/(Vsoil*RHOsoil)

Where:

CsoilDeck	= 	Estimated concentration of TBTO in soil surrounding the
deck (0.50 mg/kg)

QDeck	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding the deck				(2.06E-03 kg from Equation 10)

CONVkgmg	= 	Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

Vsoil	= 	Wet soil volume (2.4 m3 from Rohm and Haas, 2006)

RHOsoil	= 	Bulk density of wet soil (1,700 kgww/m3 from Rohm and Haas,
2006)

House

The environmental concentrations of TBTO in soil surrounding a treated,
wood-clad house was estimated by first calculating the quantity of the
TBTO leached into the volume of the soil surrounding a house.  This
quantity, which is estimated with Equation 12, is the product of the
treated wood surface area above the soil and the cumulative quantity of
TBTO leached per m2 of treated wood over a 14 day period. 

Equation 12:

QHouse = AreaHouse*QLT

Where:

QHouse	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding 

		a house (1.07E-02 kg)

AreaHouse	= 	Wood surface area above soil (125 m2 from Rohm and Haas,
2006)

QLT	= 	Cumulative quantity of TBTO leached per m2 of treated wood over 

		a 14 day period (8.58E-05 kg/m2 from Section 1.1)

Then, the concentration of TBTO in the soil surrounding the house was
calculated (see Equation 13) by dividing the estimated quantity of TBTO
leached into the soil surrounding the house (QHouse) by the product of
the volume of wet soil and the bulk density of wet soil: 

Equation 13: 

CsoilHouse = (QHouse*CONVkgmg)/(Vsoil*RHOsoil)

Where:

CsoilHouse	= 	Estimated concentration of TBTO in soil surrounding the
house (12.6 mg/kg)

QHouse	= 	Estimated quantity of TBTO leached into the volume of soil
surrounding 

		the house (1.07E-02 kg from Equation 12)

CONVkgmg	= 	Conversion factor from kilograms to milligrams (1.00E+6
mg/kg)

Vsoil	= 	Wet soil volume (0.5 m3 from Rohm and Haas, 2006)

RHOsoil	= 	Bulk density of wet soil (1700 kgww/m3 from Rohm and Haas,
2006)

Soil concentrations calculated for the six use scenarios are summarized
in Table 1.

Table 1.  Summary of Estimated Environmental Concentrations of TBTO in
Soil for Six Use Scenarios 

TBTO Use scenario	

TBTO Mass (ai) Leached into Soil Associated with Treated Wood Surface
(kg)1,2

	TBTO Concentration (ai) in Soil (mg/kg wet weight)1,3



Transmission Pole	

6.1E-04	

1.5



Fence Post	

6.9E-05  	

0.82



Fence	

1.7E-04	

10.



Deck Post	

1.0E-04	

0.98



Deck	

2.1E-03	

0.50



House	

1.1E-02	

13



1  All values are rounded to two significant digits.

2 TBTO mass leached into soil associated with treated wood surfaces is
calculated with 

Equations 2, 4, 6, 8, 10, and 12.

3 TBTO mass leached into soil associated with treated wood surfaces is
calculated with 

Equations 3, 5, 7, 9, 11, and 13.



2.	Dissolved Surface Water and Sediment Pore Water Concentration
Modeling

EPA’s PE5 PRZM-EXAMS Model Shell (PE5) was used to simulate transport
of TBTO from soil to a surface water body.  In this modeled scenario,
the water body is assumed to be a farm pond adjacent to a fruit orchard
where the contaminated soil is located. Soil compartment loading rates
based on the soil concentration estimates in Table 1 were entered into
PE5 to estimate concentrations of TBTO in dissolved surface water and
sediment pore water.  PE5 was run for each of the six TBTO use scenarios
identified in Section 1.2 (e.g., deck, fence post).

The PE5 model requires hectare-scale estimates of TBTO released in soil
(kg TBTO per ha) as an input value.  The hectare-scale loading rates are
estimates of the amount of TBTO released in the soil compartment in a
one-hectare area.  For all use scenarios, it was assumed that five
treated wood units (e.g., transmission poles, houses) are present per
hectare.  Therefore, the hectare-scale loadings were calculating by
multiplying the TBTO mass leached into soil per treated wood unit (i.e.,
the middle column in Table 1) by five units per hectare.  This approach
is consistent with the methodology developed by Rohm and Haas (2006). 
Table 2 shows the resulting TBTO loadings per hectare.

  Additional inputs for the PE5 runs include various chemical-specific
properties and assumptions.  Table 3 lists the inputs to the PE5 runs,
including input values, units, and information sources.  Assumed values
were chosen according to suggestions from Dr. Ronald Parker at EPA’s
Office of Pesticide Programs (Parker, 2007).

The PE5 model calculates multiple-year chemical concentrations in the
water and benthic sediments, which are then reported, for each year, the
single-day peak concentration, the maximum 24-hour, 96-hour, 21-day,
60-day, and 90-day mean concentrations, and the mean annual
concentration (EPA, 2006a).  Model outputs display the upper 10
percentiles of the single-year results (e.g., the upper tenth percentile
of the mean annual concentrations).

The results of the Express model runs for TBTO are presented in Tables 4
and 5.  Table 4 reports dissolved surface water concentrations in µg/L
and Table 5 reports sediment pore water concentrations in µg/L. 

Table 2.  Calculation of TBTO Loading Rates in Soil per Hectare 

Soil Loading	

TBTO Use Scenario

	Transmission Pole	Fence Post	Fence	Deck Post	Deck	House

TBTO Mass Leached into Soil Associated One Unit of Treated Wood Surface
(kg)1	6.1E-04	6.9E-05  	1.7E-04	1.0E-04	2.1E-03	1.1E-02

TBTO Mass Loading per Hectare (kg/ha)1,2	3.1E-03	3.4E-04	8.6E-04	5.2E-04
1.0E-02	5.4E-02



1 All values are rounded to two significant digits.

2 Mass loadings per hectare equal the TBTO mass leached into soil per
unit (e.g., transmission pole) times five units per hectare.





Table 3. PE5 Inputs

Parameter	Value	Units	

Source

OPP/EFED Scenario: CA Fruit Orchard	CA Fruit

EPA Assumption1

Meteorological File: PE5 default	w93193.dvf

EPA, 2006a

EXAMS Environment: Standard Pond	pond298.exv

EPA, 2006a

Field Size	EPA Pond

EPA, 2006a

Runoff Flow	None

Parker, 2007

Molecular weight	596	g/mole	EPA, 2007

Henry's Law Constant	6.80E-05	atm m3/mol	EPA, 2007

Vapor pressure	7.50E-06	mm Hg	EPA, 2007

Solubility	8.96E-02	mg/L	EPA, 2007

Soil Partition Coefficient (Koc)	5080	mL/g	EPA, 2007

Chemical Application Method (CAM): Incorporated Uniform with Depth	4

EPA Assumption2

Incorporation Depth	2.54	cm	EPA Assumption3

Soil Compartment Loading Rate/ Application Rate	See Table 2	kg/ha
Calculated

Application Efficiency	1

Parker, 2007

Spray Drift	0

Parker, 2007

Number of applications	1

Parker, 2007

IPSCND: Method of post-harvest foliar pesticide disposition	1

Parker, 2007

Hydrolysis half life (pH 7)	245	days	Maguire, Tkacz 1988; EPA 2007

Aquatic photolysis half life	90	days	Maguire et al, 1983; EPA 2007

Water half life	505	days	EPA, 2007

Benthic half life	1095	days	Fent, Hunn 1995

Soil half life	127	days	EPA, 2007



1 California fruit orchard scenario from the orchard scenarios available
in PE5.

2 Chemical application method 4, the default incorporation CAM, which
assumes uniform incorporation with a depth specified by the user.

3 A depth of 1 inch (~2.54 cm).



Table 4. 10th Percentile Estimated Environmental Concentrations of TBTO
in Dissolved Surface Water from Runoff as a Consequence of Leaching from
Treated Wood

Use scenario	Instantaneous1

(µg/L)	96-Hour1

(µg/L)  	21-Day1 

(µg/L) 	60-Day 1 

(µg/L) 	90-Day1

(µg/L)  	

Annual1

(µg/L)  





Transmission Pole	

3.3E-03	

2.6E-03	

1.4E-03	

6.6E-04	

5.4E-04	

2.6E-04



Fence Post	

1.5E-02	

1.2E-02	

6.3E-03	

2.7E-03	

1.9E-03	

1.1E-03



Fence	

4.0E-02	

3.2E-02	

1.7E-02	

7.4E-03	

5.2E-03	

3.0E-03



Deck Post	

2.5E-02	

2.0E-02	

1.0E-02	

4.5E-03	

3.2E-03	

1.8E-03



Deck	

1.1E-02	

8.5E-03	

4.4E-03	

2.1E-03	

1.7E-03	

8.5E-04



House	

5.7E-02	

4.6E-02	

2.4E-02	

1.1E-02	

9.4E-03	

4.6E-03

       

1 All values are rounded to two significant digits.

Table 5. 10th Percentile Estimated Environmental Concentrations of TBTO
in Sediment Pore Water from Runoff as a Consequence of Leaching from
Treated Wood

Use scenario	Instantaneous1

(µg/L)	96-Hour1

(µg/L) 	21-Day1

(µg/L) 	60-Day1

(µg/L)	90-Day1 

(µg/L) 	

Annual1

(µg/L) 





Transmission Pole	4.4E-04	4.4E-04	4.4E-04	4.2E-04	4.0E-04	2.5E-04



Fence Post	1.8E-03	1.8E-03	1.7E-03	1.6E-03	1.6E-03	1.0E-03



Fence	4.9E-03	4.9E-03	4.7E-03	4.5E-03	4.3E-03	2.8E-03



Deck Post	2.9E-03	2.9E-03	2.8E-03	2.7E-03	2.6E-03	1.6E-03



Deck	1.4E-03	1.4E-03	1.4E-03	1.4E-03	1.3E-03	8.0E-04



House	7.7E-03	7.7E-03	7.6E-03	7.3E-03	7.0E-03	4.3E-03

     

	1 All values are rounded to two significant digits.

3.	Assumptions/Limitations

Because wood leaching studies are not available for TBTO, the cumulative
release of TBTO from treated wood was derived using a method developed
by Krahn and Strub (1990) which estimates leaching from wood treated
with antisapstain chemicals.  This methodology simulates leaching of
TBTO from treated wood exposed to rainfall.

An input to the Krahn and Strub (1990) methodology ICF used to calculate
cumulative release of TBTO from treated wood is the mass of the active
ingredient applied to the leachable portion of the wood.  This value was
calculated using information from the label for a specific TBTO product,
Flexguard Waterbase Preservative (Registration No. 9339-14).  The mass
calculation requires the percent active ingredient of the product as it
is applied (2.76%), the maximum number of applications of the product
(2), and the minimum application rate of the product.  The label
specifies an application rate of “275 ft2/gal or less.”  275 ft2/gal
was used as the application rate.  However, higher application rates
(i.e., fewer square feet covered per gallon) would be expected to result
in higher environmental concentrations in soil, surface water, and
sediment pore water

Estimation of the mass of TBTO applied per square foot of treated lumber
required an assumption about the density the antisapstain product.  EPA
assumption about the density of antifoulant paint, 10 lb/gal (EPA,
2006b) was used.

The estimate of cumulative release of TBTO assumed that all of the
active ingredient was absorbed into the wood when the product was
applied.

This methodology does not address a number of physical and environmental
variables (e.g., chemical formulation, wood surface texture, ambient
temperature, soil type, soil moisture, and soil pH) that may affect the
release of TBTO from treated wood and subsequent movement in
environmental media.  In addition, the methodology does not address
chemical or biological degradation. 

This analysis uses assumptions about the surface areas of wood treated
for six TBTO use scenarios, as well as assumptions about the number of
treated surfaces per hectare.  These assumptions, which were obtained
from Rohm and Haas (2006) may over- or under-estimate the potential for
TBTO releases to soil associated with the six scenarios.  

The methodology includes an assumption that soil, surface water, and
sediment pore water concentrations are affected by only one of the six
TBTO use scenarios at a time.

The PE5 model estimates concentrations in sediment pore water. 
Concentrations of TBTO adsorbed to sediment are not calculated.

EPA (2007) reported that TBTO is essentially stable to hydrolysis at pH
5, 7 and 9 but specific half-lives were not reported.  Maguire and Tkacz
(1985) reported that tributyltin is susceptible to biodegradation in
water with half-lives between 6 days and 35 weeks (245 days).  245 days
was chosen as it represents the most conservative estimate (i.e., the
longest period of time that TBTO will persist in water).

EPA (2007) reported that it TBTO is essentially stable to photolysis at
pH 5, 7, and 9 but specific half-lives were not reported.  Maguire et
al. (1983) reported that photodegradation in water will be at least a
few months; therefore a value of 90 days was used. 

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water half-life as it was the only specific aquatic metabolism reported
by EPA (2007).

EPA (2007) did not report a benthic half-life for TBTO.  Fent and Hunn
(1995) reported that half-lives in anaerobic sediment are in the range
of 2-3 years (730-1095 days).  1095 days was chosen as it represents the
most conservative estimate (i.e., the longest period of time that TBTO
will persist in benthic soil).

4.	References

Carbone, J. and Jacobson, A. 2006. Environmental risk assessment of
DCOIT for wood preservative applications. Report # 06R-1006. Rohm and
Haas Company. 9 February 2006.

EPA, 2007.  “TBT Oxide Fate Profile,” Power Point Presentation by
Jim Breithaupt, US Environmental Protection Agency.  Document provided
by Siroos Mostaghimi, U.S. Environmental Protection Agency, 16 November
2007.

EPA, 2006a.  “PE5 User’s Manual for PRZM EXAMS Modeling Shell,
Version 5.0.”   Environmental Fate and Effects Division. Office of
Pesticide Programs, U.S. Environmental Protection Agency. November 15
2006.

EPA, 2006b.  “Draft, Antimicrobials Division’s (AD) Standard
Operating Procedures (SOPs) for Residential and Occupational Exposure
Assessments.”  Prepared by: Cassi Walls,Talia Milano, and Timothy
Leighton, Antimicrobials Division, U.S. Environmental Protection Agency,
November 2006.

Fent, K and Hunn, J, 1995. Organotins in freshwater harbors and rivers:
Temporal distribution, annual trends and fate. Environmental Toxicology
and Chemistry. Vol. 14. No. 7: 1123-1132.

EPA, 2007.  Revised Estimated Environmental Concentrations for AMICAL
Leached from Wood into Soil and Water using PE5 PRZM-EXAMS Model Shell. 
Memorandum from Siroos Mostaghimi to Norm Cook, U.S. Environmental
Protection Agency,, November 28, 2007

Krahn, P. and Strub R. 1990. Standard leaching test for antisapstain
chemicals: Regional Program Report 90-10. Environment Canada.
Conservation and Protection, Pacific and Yukon Region North Vancouver,
BC. 1990.

Maguire, RJ, Carey JH, Hale, EJ, 1983. Degradation of the tri-n-butylin
species in water. Journal of Agricultural and Food Chemistry. 31:
1060-5.

Maguire, RJ, Tkacz, RJ, 1985. Degradation of the tri-n-butylin species
in water and sediment from Toronto Harbor. Journal of Agricultural and
Food Chemistry. Vol. 33: 947-53.

Parker, Ronald. 2007. Office of Pesticide Programs. U.S. Environmental
Protection Agency. Personal communication with ICF. November.

Rohm and Haas, 2006.  Environmental Risk Assessment of DCOIT for Wood
Preservative Applications.  Prepared by John P Carbone and Andrew H.
Jacobson, Rohm and Haas Company, Spring House, PA.  Company Report
06R-1006.  February 9, 2006.

Williams, M. and Bradley, A., 1996. Aqueous Availability of TBTO 48:
Final Report: Lab Project Number: 42782: ABC 42782.  Unpublished study
prepared by ABC Laboratories Europe, Ltd. 78 p.  MRID 43997001.

Versar, 2005. "ADBAC Antisapstain Modeling (TAF 1-4-10, CM-43),"
memorandum to Najim Shamim, U.S. EPA, from Ron Lee and Jignasha Patel,
Versar, Inc., December 5, 2005.

 Overview of the Ecological Risk Assessment Process in the Office of
Pesticide Programs, U.S. Environmental Protection Agency: Endangered and
Threatened Species Effects Determinations.  Office of Prevention,
Pesticides and Toxic Substances Office of Pesticide Programs,
Washington, D.C., January 23, 2004. 

 the profile includes only guideline studies submitted by registrants
and does not include studies from other EPA documents or from the open
literature

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