	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	

.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. 

The anaerobic half-life for TBTO was used for a 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.

File:  MyFiles\2007 reports\TBTO\ Estimated Environmental Concentrations
for Tributyltin Oxide (TBTO) Leached from Wood into Soil and Water.

	   CC: RASSB Chemical File

			     Siroos Mostaghimi, RASSB

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