UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

   OFFICE OF

                                                                        
                                    PREVENTION, PESTICIDES AND 

            TOXIC SUBSTANCES

September 30, 2007

MEMORANDUM

SUBJECT:		Revised Preliminary Ecological Hazard and Environmental Risk
Assessment Science Chapter for the Busan 77 Reregistration Eligibility
Decision (RED) Document

	DP Barcode:  none		Reregistration Case No.:  3034

FROM:		Genevieve Angle, Biologist

Risk Assessment and Science Support Branch (RASSB)

Antimicrobials Division (7510P)

TO:			Mark Hartman, Branch Chief

Diane Isbell, Team Leader

Regulatory Management Branch II

Antimicrobials Division (7510P)

Talia Lindheimer, Risk Assessor

THRU:		Nader Elkassabany, Team Leader, Team Two

Risk Assessment and Science Support Branch (RASSB)

Antimicrobials Division (7510P)

Norman Cook, Branch Chief

Risk Assessment and Science Support Branch (RASSB)

Antimicrobials Division (7510P)

Chemical Name	PC Code	CAS#		Common Names

Poly(oxyethylene	069183	31512-74-0	Busan 77

(dimethylminino)ethylene(dimethyliminio)ethylenedichloride)

  

Attached is the Ecological Hazards and Environmental Risk Assessment
Science Chapter for the Busan 77 RED Document.

ECOLOGICAL HAZARD AND ENVIRONMENTAL 

RISK ASSESSMENT CHAPTER

Busan 77

PC Code: 069183

CASE No.: 3034

07/27/07

Genevieve Angle - Biologist

Antimicrobials Division

Office of Pesticide Programs

U.S. Environmental Protection Agency

1200 Pennsylvania Avenue, NW

Washington, DC 20460

Table of Contents

												    Page

Executive Summary
………………………………………………………………
……………… 1

I.  Ecological Toxicity Data . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2  

A.  Toxicity to Terrestrial Animals . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . .2 

1.  Birds, Acute  . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 2

2.  Birds, Subacute. . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . 3 

3.  Mammals, Acute and Chronic . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . .4  

B.  Toxicity to Aquatic Animals . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . .4 

1.  Freshwater Fish, Acute . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .4  

2.  Freshwater Invertebrates, Acute . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .5  

3.  Estuarine and Marine Organisms, Acute . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . .6

4.  Aquatic Organisms, Chronic . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .8 

Toxicity to Plants . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . ..8

II.  Risk Assessment and Risk Characterization . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .. . . ..11

A.  Environmental Fate Assessment Summary . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . .. . . . ..12 

B.  Environmental Exposure and Risk Assessment… . ..
…………………………. . . . . ..12

C.  Endangered Species Considerations . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . .  . .  . . . . ..19

III.  Confirmatory Data Required. . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . .. . . . . . . . . ..20   

IV.  Label Hazard Statements for Terrestrial and Aquatic Organisms. . .
. . . . . . . .  . . . . . . . . .. 20

V.  References . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .  . . . . . . . . . . 22

LIST OF TABLES

																			  Page

Table 1 – Acute Oral Toxicity of Busan 77 to Birds. …. . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . .3 

				

Table 2 – Subacute Oral Toxicity of Busan 77 to Birds. . . . . . ….
. . . . . . . . . . . . . . . . . . . . . . 4

Table 3 – Acute Toxicity of Busan 77 to Freshwater Fish. . . . . . . .
. . . . …. . . . . . . . . . . . . . . 5

Table 4 – Acute Toxicity of Busan 77 to Freshwater Invertebrates. . .
. . . …. . . . . . . . . . . . . . 6 

Table 5 – Acute Toxicity of Busan 77 to Estuarine and Marine
Organisms……………………6

Table 6 – Chronic Toxicity of Busan 77 to Freshwater Organisms. . . .
…. . . . . . . . . . . . . . . .. 8

Tables 7-9 – Toxicity of Busan 77 to Terrestrial
Plants……………………………...…………9

Table 10 – Toxicity of Busan 77 to Aquatic Plants. . . . . . . .. . .
. …. . . . . . . . . . . . . .  . . . . . ...10

Table 11 - Busan 77 Dosage Information for Once-through Cooling Water
Systems…………13

Table 12 - Concentrations of Concern Selected for the Environmental
Exposure 

Assessment of Busan
77……………………………………………………………
…………..14

Table 13 - Effluent Discharge and Stream Flow Data for Modeled
Facilities…………………16

Table 14 - Number and Percent of Days with Downstream Busan 77 

Concentrations Exceeding
COCs…………………………………………………………
…....17

Table 15 - Percent of Facilities with Downstream Busan 77 Concentrations


Exceeding COCs on at Least One
Day………………………………………………………....18


Ecological Hazard and Environment Risk Assessment

For Busan 77

Executive Summary:

	Busan 77 is currently registered by the EPA as a bacteriostat,
fungicide, algaecide, microbicide/microbiostat and molluscicide for
swimming pools, aquatic areas, materials preservation, industrial
process and water systems and residential and public access premises. 
Its swimming pool uses include pools, spas, whirlpools and hot tubs. 
Its aquatic areas uses include ornamental ponds and aquariums.  Its
materials preservation uses include metal working fluid and fire water
protection systems.  Its industrial process and water system uses
include cooling towers (both once-through and recirculating), petroleum
secondary recovery systems, paper mill process water and air water
washer systems.  The residential and public access premises uses include
water bed mattresses. 

	An ecological risk assessment is not typically conducted for the types
of uses registered for Busan 77 except for the once-through cooling
water use.  A risk assessment for once-through cooling water uses using
maximum application rates and the toxicity values for various organisms
from section I below has been conducted in this document.  All other
uses are considered indoor and have minimal to no environmental exposure
potential following use.  

	The results of the assessment of once-though cooling water uses
indicate that there may be risk to freshwater fish, freshwater
invertebrates and estuarine/marine invertebrates from the use of Busan
77.

Data Gaps:  

1)  850.1300: Aquatic invertebrate life-cycle study (using TGAI and most
sensitive species -                        freshwater or
estuarine/marine)

2)  850.1400: Fish early-life stage study (using TGAI and most sensitive
species - freshwater     or estuarine/marine)

3)  850.4225: Seedling emergence study - dose response using rice (Oryza
sativa)

4)  850.4400: Freshwater floating macrophyte duckweed study

5)  850.5400: Aquatic plant growth (algal toxicity) – 2 studies
outstanding (marine diatom -                         Skeletonema
costatum and green algae - Selenastrum capricornutum); Tier II          
                (using TGAI or TEP)

6)  850.1735: Whole sediment, acute invertebrates (freshwater) (using
TGAI)

7)  850.1740: Whole sediment, acute invertebrates (estuarine/marine)
(using TGAI)

	8)  Depending on the results of the whole sediment, acute invertebrate
studies, the following data may be required: Whole sediment - chronic
invertebrates (freshwater and/or estuarine/marine) (using TGAI or TEP)

Label Hazard Statements/Use Recommendations:

Busan 77 labels must state:  

“This pesticide is toxic to fish, aquatic invertebrates and clams.”

"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."

I.	Ecological Toxicity Data

	The toxicity endpoints presented below are based on the results of
ecotoxicity studies submitted to EPA to meet the Agency’s data
requirements for the uses of Busan 77.

	A.	Toxicity to Terrestrial Animals

(1)	Birds, Acute 

	In order to establish the toxicity of Busan 77 to avian species, the
Agency requires an acute oral toxicity study using the technical grade
active ingredient (TGAI).  The preferred-test species is either mallard
duck (a waterfowl) or bobwhite quail (an upland game bird).  The results
of two acute oral toxicity studies, submitted for Busan 77, are provided
in the following table (Table 1).



Table 1.  Acute Oral Toxicity of Busan 77 to Birds

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint

(mg/kg a.i.)	

Toxicity Category	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Mallard duck

(Anas platyrhynchos)	Busan 77 61.7%	LD50 = 497

NOAEL = 51

	Moderately toxic	Yes (core)

- 14-day test duration

- 36 weeks of age	416548-01

Bobwhite quail

(Colinus virginianus)	Busan 77 

% purity unknown	LD50 = 690

NOAEL = <172

(based on the assumption of 60% a.i.)	Slightly toxic	No (supplemental)

- 21-day test duration

- young adult

- study conducted before adoption of GLP principles	ID 0522-010-20



	These two acceptable acute oral toxicity studies indicate that Busan 77
is moderately toxic to slightly toxic to birds on an acute oral basis.
The guideline requirement OPPTS 850.2100/(71-1) is satisfied by the
mallard duck study.

(2)	Birds, Subacute

	A subacute dietary study using the TGAI may be required on a
case-by-case basis depending on the results of lower-tier ecological
studies and pertinent environmental fate characteristics in order to
establish the toxicity of a chemical to avian species.  This testing was
required for Busan 77.  The preferred-test species is either the mallard
duck or bobwhite quail.  The results of two subacute dietary toxicity
studies, submitted for Busan 77, are provided in the following table
(Table 2).



Table 2.  Subacute Oral Toxicity of Busan 77 to Birds

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint

(ppm a.i.)	

Toxicity Category	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Mallard duck

(Anas platyrhynchos)	Busan 77 60.3%	LC50 (diet) = >12,000

NOAEC = 3,000	Relatively nontoxic	No (supplemental)

-	8-day test duration

-	10 days of age

- study conducted before adoption of GLP principles	414115-01

Bobwhite quail

(Colinus virginianus)	Busan 77 

61.6%	LC50 (diet) = >3,462

NOAEC = 3,462	Slightly toxic	Yes (core)

- 8-day test duration

- 11 days of age 	001593-07



	The results of these two acceptable studies indicate that Busan 77 is
slightly toxic to relatively nontoxic to avian species through subacute
dietary exposure. The bobwhite quail study fulfills guideline
requirement OPPTS 850.2100/ (71-2a – Bobwhite quail/71-2b – Mallard
duck). 

 (3)	Mammals, Acute and Chronic Toxicity

Wild mammal testing is not required by the Agency.  In most cases, rat
toxicity values obtained from studies conducted to support data
requirements for human health risk assessments substitute for wild
mammal testing.  Refer to the human toxicology chapter of this RED for
mammalian toxicity data.

B.	Toxicity to Aquatic Animals

	The Agency requested that aquatic toxicity studies be conducted with
Busan 77 since, under typical use conditions, it may be introduced into
the aquatic environment.

(1)	Freshwater Fish, Acute

	In order to establish the acute toxicity of Busan 77 to freshwater
fish, the Agency requires freshwater fish toxicity studies using the
TGAI.  The preferred test species are rainbow trout (a coldwater fish)
and bluegill sunfish (a warmwater fish).  The results of 3 freshwater
fish acute studies submitted for Busan are presented in Table 3.



 Table 3.  Acute Toxicity of Busan 77 to Freshwater Fish 

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint

(mg a.i./L)	

Toxicity Category	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Rainbow Trout (Oncorhynchus mykiss)	Busan 77 

61.9%	LC50 = 0.047

NOAEC = 0.037	Very highly toxic	Yes (core)

-	96-hr test duration

-	static test system	413520-01

Bluegill sunfish (Lepomis macrochirus)	Busan 77 

61.9%	LC50 = 0.21 

NOAEC = 0.13	Highly toxic	Yes (core)

-  96-hr test duration

-  static test system	413520-02

Rainbow Trout (Oncorhynchus mykiss)	Busan 77 

60%	LC50 = 0.26

NOAEC = 0.11	Highly toxic	No (supplemental)

-	96-hr test duration

-	static test system

- study lacks important information

- study conducted before adoption of GLP principles	001072-07



	Freshwater acute toxicity tests indicate that Busan 77 is very highly
toxic to highly toxic to fish on an acute basis.  These studies fulfill
guideline requirement OPPTS 850.1075 (72-1a&b).  Because acute toxicity
to fish is <1.0 mg/L, the environmental hazard section of Busan 77
labels must state: “This pesticide is toxic to fish.”

	(2)	Freshwater Invertebrates, Acute

	The Agency requires a freshwater aquatic invertebrate study using the
TGAI to establish the acute toxicity to freshwater invertebrates.  The
preferred test species is Daphnia magna.  The results of one study
submitted for Busan 77 is provided in the following table (Table 4).



	Table 4.  Acute Toxicity of Busan 77 to Freshwater Invertebrates

 

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint

(mg a.i./L)	

Toxicity Category	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Waterflea (Daphnia magna)	Busan 77

61.9%	EC50 = 0.280 

NOAEC = 0.130	Highly toxic	Yes (core)

-	48-hr test duration

-	static test system	413520-03



	The results of this study indicate that Busan 77 is highly toxic to
freshwater invertebrates on an acute basis.  This study fulfills
guideline requirement OPPTS 850.1010 (72.2a).  Because the acute aquatic
invertebrate toxicity value is < 1.0 mg/L, the environmental hazard
section of Busan 77 labels must state:  “This pesticide is toxic to
aquatic invertebrates.”

(3)	Estuarine and Marine Organisms, Acute

	Acute toxicity testing with estuarine and marine organisms using the
TGAI is required when the end-use product is intended for direct
application to the marine/estuarine environment or effluent containing
the active ingredient is expected to reach this environment.  The
preferred fish test species is the sheepshead minnow.  The preferred
invertebrate test species are mysid shrimp and eastern oysters.  This
testing is required for Busan 77 based on the chemical’s potential to
reach estuarine and marine environments.  The results of three toxicity
studies submitted for Busan 77 are presented in Table 5.



Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint

(mg a.i./L)	

Toxicity Category	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Sheepshead minnow (Cyprinodon varigates)	Busan 77

60.0%	LC50  > 360

NOAEC = 360	Relatively nontoxic	Yes (core)

-	96-hr test duration 

- static test system	401392-02

Mysid shrimp (Mysidopsis bahia)	Busan 77

60.0%	LC50  = 7.8

NOAEC <7.8	Moderately toxic	Yes (core)

-	96-hr test duration 

- static test system	401392-03

Quahog clam (Mercenaria mercenaria)	Busan 77

60.0%	EC50 = 0.21

NOAEC = 0.14	Highly toxic	Yes (core)

-	48-hr test duration 

-	static test system

- embryo/larval stage	403342-01

Table 5.  Acute Toxicity of Busan 77 to Estuarine and Marine Organism
The results of these three acceptable studies indicate that Busan 77 is
highly toxic to moderately toxic to estuarine/marine invertebrates on an
acute basis and relatively nontoxic to estuarine/marine fish on an acute
basis.  The Quahog clam study (403342-01) fulfills the guideline
requirement OPPTS 850.1055/(72-3b) for an acute estuarine/marine mollusk
study. Study MRID 401392-03 for mysid shrimp fulfills the guideline
requirement OPPTS 850.1035/(72-3c) for an estuarine/marine shrimp study.
 Study MRID 401392-02 for the sheepshead minnow fulfills the guideline
requirement OPPTS 850.1075/(72-3a) for an acute estuarine/marine fish
study.  Because the estuarine/marine acute toxicity values are < 1.0
mg/L in the clam study, the environmental hazard section of Busan 77
labels must state:  “This pesticide is toxic to clams.”

(4)	Aquatic Organisms, Chronic

	Chronic toxicity testing (fish early life stage and aquatic
invertebrate life cycle) is required for pesticides when certain
conditions of use and environmental fate apply.  The preferred
freshwater fish test species is the fathead minnow.  The preferred
freshwater invertebrate is Daphnia magna.  This testing is required for
the Busan 77 once-through cooling water uses.  The results of one
toxicity study submitted for Busan 77 is presented in Table 6.

Table 6.  Chronic Toxicity of Busan 77 to Freshwater Organisms

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint

(mg a.i./L)	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Waterflea 

(Daphnia magna)	Busan 77

60.3%	LOEC = 0.020

NOAEC = 0.012

	No (supplemental)

-  21-day test             duration 

-  static renewal test     system

-  organisms not distributed or fed properly

-  excess mortality	424796-01

	

No fathead minnow study has been submitted. The study on the waterflea
does not fulfill the guideline requirement for a chronic aquatic
invertebrate study.  Neither guideline requirement OPPTS 850.1300 nor
guideline requirement OPPTS 850.1400 is fulfilled.

Toxicity to Plants

	Non-target plant phytotoxicity testing is required for pesticides when
certain conditions of use and environmental fate apply.  This testing is
required for the once-through cooling water uses of Busan 77.  Testing
has been conducted with Busan 77 on several aquatic and terrestrial
plant species.  Testing is normally conducted with one species of
aquatic vascular plant (Lemna gibba) and four species of algae:  (1)
freshwater green alga, Selenastrum capricornutum, (2) marine diatom,
Skeletonema costatum, (3) freshwater diatom, Navicula pelliculosa, and
(4) bluegreen cyanobacteria, Anabaena flos-aquae.  The rooted aquatic
macrophyte rice (Oryza sativa) is also tested in seedling emergence and
vegetative vigor tests.

	One study that evaluates the toxicity of Busan 77 to several species of
terrestrial plants (seedling emergence-tier I and vegetative vigor-tier
I and tier II) and five studies that evaluate the toxicity of Busan 77
to freshwater aquatic plants have been submitted. Results of the
terrestrial plant study are presented in Tables 7-9 and results of the
aquatic plant studies are presented in Table 10.  Although the tier I
study in Tables 7 and 8 has been previously designated as fulfilling the
guideline requirement, since the study does not include the rice species
(Oryza sativa), a seedling emergence study with this species (OPPTS
850.4225) will still need to be submitted.

Table 7.  Seedling Emergence (Tier I) Toxicity of Busan 77 to
Terrestrial Plants*

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint

(ppm a.i.)*	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Monocot

  Oat (Avena sativa)	Busan 77 60.3%	EC25 = >73

NOAEC = 73	Yes (core)

-	14-day test duration

-	most sensitive parameter: shoot length (14% reduction)	420381-01

Dicot

  Lettuce (Lactuca sativa)	Busan 77 

60.3%	EC25 = >73

NOAEC = 73	Yes (core)

- 14-day test duration

- most sensitive   parameter: shoot length (17% reduction)	420381-01

*Data are listed for most sensitive species and most sensitive
parameter.  Species tested were cabbage, carrot, cucumber, lettuce,
soybean, tomato, corn, oats, onion and ryegrass.

Table 8.  Vegetative Vigor (Tier I) Toxicity of Busan 77 to Terrestrial
Plants*

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint**

(ppm a.i.)	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Monocot

  Corn (Zea mays)	Busan 77 60.3%	EC25 = >74

NOAEC = 74	Yes (core)

-	14-day test duration

-	most sensitive parameter: shoot weight (39% reduction)	420381-01

Dicot

  Cucumber (Cucumis sativus)	Busan 77 

60.3%	EC25 = >74

NOAEC = 74	Yes (core)

- 14-day test duration

- most sensitive   parameter: root weight (31% reduction)	420381-01

*Data are listed for most sensitive species and most sensitive
parameter.  Species tested were cabbage, carrot, cucumber, lettuce,
soybean, tomato, corn, oats, onion and ryegrass.

**EC25 value for corn based on shoot length and root weight.  EC25 for
cucumber based on shoot length and shoot weight.

Table 9.  Vegetative Vigor (Tier II) Toxicity of Busan 77 to Terrestrial
Plants*

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint*

(ppm a.i.)	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Monocot

  Ryegrass (Lolium perenne)	Busan 77 60.3%	EC25 = >74

NOAEC = 74	No (supplemental)

-	14-day test duration

-	most sensitive parameter: root weight (0% reduction)	420381-01

Dicot

  Tomato (Lycopersicon esculentum)	Busan 77 

60.3%	EC25 = >74

NOAEC = 74	No (supplemental)

- 14-day test duration

- most sensitive   parameter: shoot weight (15% reduction)	420381-01

*Data are listed for most sensitive species and most sensitive
parameter.

Table 10.  Toxicity of Busan 77 to Aquatic Plants

Species	

Chemical,

% Active Ingredient

(a.i.)

Tested	

Endpoint 

(mg a.i./L)	

Satisfies Guidelines/

Comments	

Reference

(MRID No.)

Marine diatom (Skeletonema costatum)	Busan 77

60.3%	EC50 = 0.090

NOEC < 0.024	No (supplemental)

-  120-hour test duration

-  static test system	420133-02

Freshwater diatom (Navicula pelliculosa)	Busan 77

60.3%	EC50 = 0.083

NOEC = 0.044	Yes (core)

-  96-hour test duration

-  static test system	420133-03

Bluegreen cyanobacteria (Anabaena flos-aquae)	Busan 77

60.3%	EC50 = 0.11

NOEC = 0.05	Yes (core)

-  120-hour test duration

-  static test system	420133-04

Green alga (Selenastrum capricornutum)	Busan 77

60.3%	EC50 = 0.0088

NOEC < 0.001	No (supplemental)

-  120-hour test duration

-  static test system	420133-05

Duckweed (Lemna gibba)	Busan 77

60.3%	EC50 > 0.65

NOEC = 0.043	No (supplemental)

-	14-day test duration

-	static renewal test system

-  maximum concentration tested produced only 30% growth inhibition
420133-01



	The guideline requirement for an algal toxicity test (850.5400, 123-2)
is partially fulfilled.  Two additional algal toxicity tests under
850.5400 are outstanding because they do not meet guideline
requirements: a test with the freshwater green alga, Selenastrum
capricornutum, and a test with the marine diatom, Skeletonema costatum. 
The other non-target aquatic plant toxicity requirement, floating
freshwater aquatic macrophyte duckweed (Lemna gibba) – guideline
850.4400 - is not satisfied because the submitted study does not meet
the guideline requirements.  A study on the rooted freshwater macrophyte
rice (Oryza sativa) – 850.4225 (seedling emergence test) -- has not
been submitted.

II.	Risk Assessment and Characterization

	An ecological risk assessment is not typically conducted for the types
of uses registered for Busan 77 except for the once-through cooling
water use.  A risk assessment for once-through cooling water uses using
maximum application rates and the toxicity values for various organisms
from section I below has been conducted in this document.  All other
uses are considered indoor and have minimal to no environmental exposure
potential following use.  

	 A.        Environmental Fate Assessment Summary 

	Busan 77  is a pale yellow liquid that has been demonstrated to be both
hydrolytically and photolytically stable.  When aqueous solutions of
Busan 77 were tested for hydrolysis at pHs 5, 7 and 9, no degradation
was observed at any tested pH over a 30-day period at 25( C in the dark.
 Busan 77 also showed no appreciable degradation at any of the pH levels
tested over a 30-day period in a photolysis study.  Studies have also
shown that Busan 77 rapidly becomes sediment-bound in both aerobic and
anaerobic aquatic systems.  (See the Environmental Fate Chapter of this
document for further details.)

  

B.	Environmental Exposure and Risk Assessment

	This section presents an environmental exposure and risk assessment for
releases of
Poly[oxyethylene)(dimethylimino)ethylene(dimethylimino)ethylenedichlorid
e] (Busan 77) used for control of mollusks in once-through cooling water
systems.  The Probabilistic Distribution Model (version 4) was used to
estimate the number and percentage of days per year that Busan 77
concentrations exceed ecotoxicity concentrations of concern (COCs).  If
the number of days a COC is exceeded is greater than the number of days
used to determine the endpoint in toxicity testing, risk is assumed. 
Analyses were performed for Busan 77 treatment scenarios derived from
product label information.  The approach used for this assessment is
based on the methodology developed in support of the environmental
exposure assessment for bromonitrostyrene.

1. 	Methodology

	Components of the methodology described in this section include the
probabilistic distribution model (PDM), Busan 77 application rates,
environmental exposure concentrations of concern (COCs), model
facilities and flow data, and modeling scenarios.

1.1 	PDM Model

PDM is a screening-level exposure assessment tool developed by EPA to
model chemical releases from point sources to flowing surface waters. 
For this analysis, the PDM component within EPA’s Exposure and Fate
Assessment Screening Tool Version 2.0 (E-FAST2) was used.   

PDM uses detailed U.S. Geological Survey (USGS) stream flow data and
facility-specific data from National Pollutant Discharge Elimination
System (NPDES) permits to model chemical releases from actual
facilities.  For a modeling period of a given number of days, PDM
calculates the probability distribution of the chemical concentration in
the receiving stream, and then estimates the number of days during which
the in-stream chemical concentration is expected to exceed a COC.  PDM
counts a day as having an exceedence of a COC if the COC is exceeded for
any part of a 24-hour day.  As a screening-level model, PDM outputs do
not include the duration, location, or aerial extent of exceedences.

Inputs to PDM include facility NPDES number, pretreatment release (i.e.,
loading rate), post-treatment release, number of release days, and COCs.
 Input values and assumptions used for this analysis are discussed
below.  

1.2 	Busan 77 Application Rates

Product labels were reviewed to identify application rates for the
analysis.  Application instructions were identified specifically for
mollusk control in once-through industrial cooling water systems. 
Treatment instructions from the product labels are summarized in Table
11.  Control of mollusks may be achieved by either an intermittent or a
continuous application.  A single application scenario based on the
highest dosage provided on the product labels was developed.  The
application scenario consisted of continuous treatment using the highest
product dosage.  For all products listed in Table 11, the maximum
application rate of active ingredient (a.i.) is 12 ppm.

The number of release days assumed for this analysis was 250.  This
approach assumes that Busan 77 is not applied on weekends and holidays. 


Table 11

Busan 77 Dosage Information for Once-through Cooling Water Systems

Product	Percent Active Ingredient	Label Directions	Application Rate for
Analysis

Busan 77

Bioguard Algae All 60

	60 percent

	Add product at dosage rates of 2 to 20 ppm.  Additions should be made
continuously or intermittently to the intake water.  Continuous addition
is required for noticeably fouled systems.  Intermittent feeding is used
to maintain control.	Continuous application at 12 ppm a.i. (i.e., 20 ppm
product * 60%)



Bio/Tec 112	20 percent

	Add Bio/Tec 112 at dosage rates of 6 to 60 ppm.  Additions should be
made continuously or intermittently to the intake water.  Continuous
addition is required for noticeably fouled systems.  Intermittent
feeding is used to maintain control.	Continuous application at 12 ppm
a.i. (i.e., 60 ppm product * 20%)





1.3 	COCs

COCs for this analysis were identified from ecological effects
information for Busan 77 provided to EPA by registrants (see Section I).
 At least one COC was chosen for each of the following study types:
acute toxicity to freshwater fish, acute toxicity to freshwater
invertebrates, life-cycle (chronic) toxicity to freshwater
invertebrates, and acute toxicity to estuarine and marine organisms. 
The chosen COCs are shown in Table 12 along with species, endpoint type,
study type and references.  Note that the studies for life-cycle
toxicity to freshwater invertebrates and toxicity to freshwater fish did
not meet guideline requirements. (Another study on freshwater fish did
meet guideline requirements with a NOEC of 37 µg/L.  So the risk to
freshwater fish can be most closely estimated using the COC of 12 µg/L
for the Daphnia life-cycle test NOT the COC for freshwater fish that is
listed in the Table 12.)

Table 12

Concentrations of Concern Selected for the Environmental Exposure
Assessment of Busan 77

COC	Test Species	Endpoint Type	Study Type	Reference (MRID)

12 µg/La	Waterflea (Daphnia magna)	NOEC	Life-cycle toxicity to
freshwater invertebrates	

42479601

130 µg/L	Waterflea (Daphnia magna)	NOEC	Acute toxicity to freshwater
invertebrates	

41352003

140 µg/L	Quahog clam (Mercenaria mercenaria)	NOEC	Acute toxicity to
estuarine and marine organisms	

40334201

260 µg/La	Rainbow trout (Oncorhynchus mykiss)	LC50	Acute toxicity to
freshwater fish	

00107207

7,800 µg/L	Mysid shrimp (Mysidopsis bahia)	NOEC	Acute toxicity to
estuarine and marine organisms	

40139203

360,000 µg/L	Sheepshead minnow (Cyprinodon varigates)	NOEC	Acute
toxicity to estuarine and marine organisms	

40139202



a COC is based on a study that does not fulfill the guideline
requirements.

1.4 	Modeled Facilities and Flow Data

	The modeled facilities consist of Busan 77 releases for 30 steam
electric power plants (SIC 4911) that were identified by EPA during
development of the exposure assessment methodology for Alkyl Dimethyl
Benzyl Ammonium Chloride (ADBAC).  Although this sample of facilities
was chosen to include a range of receiving stream flow rates and
includes facilities located throughout the U.S., it is not necessarily
statistically representative of all facilities with once-through cooling
water systems.   

Table 13 lists the stream flow data and modeled effluent discharge rates
for the 30 facilities used in the analysis.  The mean and 7Q10 flows of
receiving stream reaches are available in the PDM model and were used
for the analysis.  Facility-specific effluent discharge rates also are
available in PDM.  For the analysis, the modeled effluent discharge
rates were based on either facility-specific effluent discharges or the
7Q10 flows of the receiving streams.  Specifically, the modeled effluent
discharge rate for each facility was the lower of these two values.  The
7Q10 flow rate represents the rate that could be maintained continuously
by an electric steam generating plant to ensure a steady supply of
cooling water.  

2. 	Results

PDM was run once for each facility.  The number of days exceeding each
COC was copied electronically from the PDM output files into a Microsoft
® Excel workbook where averages and standard deviations were
calculated.  In addition, the percent of days per year above the COCs
was calculated.  Because the number of release days per year was 250,
the highest possible percent of days per year above COCs was 68 percent.
 The percent of days during the release period above COCs (maximum 100
percent) was also calculated.  Standard deviations were calculated for
all averages.

The results are presented in Table 14.  The table shows the average
numbers of days when downstream concentrations of Busan 77 are predicted
to exceed each of the COCs.  The average numbers of days were calculated
from the modeling results for the 30 individual facilities.  Because the
numbers of days with exceedences varied among the facilities, standard
deviations are presented with each of the averages.  Table 14 also
presents the averages and standard deviations of the percentage of days
per year as well as the percentage of the 250 release days with
exceedences of the COCs.  

For a one year period that includes continuous releases during 250 days,
the lowest COC (12 µg/L) was exceeded on 57 percent of the days (or 83
percent of the 250 release days).  The highest COC (360 mg/L) was
exceeded on less than one percent of the days on average.  Table 15
shows the percentage of facilities that had exceedences at least once
(i.e., on at least one day) for each COC.  For example, the highest COC
(360 mg/L) was exceeded only at three (10 percent) of the 30 facilities.
 All other COCs were exceeded at least once in at least 57 percent of
the facilities.  The lowest COC was exceeded at least once at 29 (97
percent) of the 30 facilities. 

If the number of days an COC is exceeded is greater than the number of
days used to determine the endpoint in toxicity testing, risk is
assumed.  This assumes that the number of days exceeded are consecutive,
a conservative but not impossible assumption.  Based on this assumption,
Table 14 shows there will be risk at the average number of days exceeded
to freshwater fish, freshwater invertebrates (both acute and chronic),
and estuarine/marine invertebrates.

Table 13

Effluent Discharge and Stream Flow Data for Modeled Facilities

Facility NPDES Number	Mean Stream Flow (MGD)	7Q10 Stream Flow (MGD)
Modeled Effluent Discharge (MGD)a

FL0025526	401.26	263.63	117.20

GA0004341	1047.42	221.25	0.14

IA0000108	521.26	16.19	0.46

IA0033235	47.81	1.94	0.03

IL0002186	960.51	308.89	308.89

IL0036919	635.87	635.88	635.879

IL0048321	88.85	25.64	12.259

IN0032948	146.03	36.18	0.019

IN0038806	170.59	35.54	0.089

IN0041246	279.79	115.66	23.78

KS0079057	277.85	18.74	18.74

LA0003042	101.33	11.77	0.68

LA0036145	0.78	0.06	0.06

MA0004367	417.42	91.11	5.62

MI0038172	21.322	6.46	6.46

MN0000906	462.212	7.64	0.98

NC0005088	975.75	214.63	43.67

NH0001431	296.59	73.02	7.99

NM0000108	520.519	1.56	1.15

OH0010421	486.089	15.80	9.21

OK0002682	95.91	1.23	1.23

PA0002054	473.50	30.37	30.37

PA0002062	103.30	13.73	13.73

PA0008443	88.90	7.64	7.64

SC0001104	964.98	13.27	0.97

TX0001163	86.58	10.34	10.34

TX0054500	5.88	1.55	1.55

UT0000116	126.00	82.71	0.16

WA0003280	704.31	213.23	34.20

WV0005525	33.60	5.94	5.94



a If the effluent discharge value from PDM was less then the receiving
stream 7Q10, the 7Q10 was used as the modeled effluent discharge.

Table 14

Number and Percent of Days with Downstream 

Busan 77 Concentrations Exceeding COCs

COC

(µg/L)	Number of Days With Exceedences	Percent of Days with Exceedences
per Year	Percent of Release Days with Exceedences

	Average Days COC Exceeded	Standard Deviation	Average Days COC Exceeded
Standard Deviation	Average Days COC Exceeded	Standard Deviation

12 µg/La	207	72	57%	20%	83%	29%

130 µg/L	152	94	42%	26%	61%	37%

140 µg/L	149	94	41%	26%	60%	37%

260 µg/La	129	92	35%	25%	51%	37%

7,800 µg/L	12	18	3%	5%	5%	7%

360,000 µg/L	1	5	<1%	2%	<1%	2%

a COC is based on a study that does not fulfill the guideline
requirements.

Table 15

Percent of Facilities with Downstream Busan 77

Concentrations Exceeding COCs on at Least One Day (n = 30)

COC

(µg/L)	Percent of Facilities with at Least One Day with an Exceedence 

12 µg/La	97%

130 µg/L	87%

140 µg/L	87%

260 µg/La	87%

7,800 µg/L	57%

360,000 µg/L	10%

                                  a COC is based on a study that does
not fulfill the guideline requirements.

3. 	Uncertainties and Limitations

	This analysis is a screening level evaluation of the potential for
discharges from once-through cooling water systems to exceed Busan 77
ecotoxicity COCs in receiving streams.  The methodology involves the
following potential limitations:

Because exceedences predicted by the PDM do not necessarily occur on
consecutive days, the analysis may overestimate the actual potential for
ecological toxicity impacts.  

Downstream concentrations of Busan 77 are considered to exceed a COC on
any given day if the COC is exceeded for any portion of the day.  PDM
does not identify the duration of the exceedences, so results may
overestimate the actual potential for Busan 77 releases to result in
ecological risks.

The estimated numbers of days with downstream concentrations of Busan 77
above COCs are averages calculated from the results for individual
facilities.  Facility level results varied considerably, as shown by the
standard deviations presented with the averages.  Thus, this analysis
may under or overestimate the potential for exceedences at specific
facilities.

The analysis used an assumed release period of 250 days.  This
assumption is likely to overestimate the number of release days for
Busan 77 treatment, especially for initial control.  Thus, the results
of the analysis may overestimate the number of days with downstream
Busan 77 concentrations above COCs.  

The scenario used for this analysis was based on the maximum application
rate (i.e., 12 ppm a.i.) identified on product labels.  It may be
possible to control target organisms with application rates below the
maximum.  In addition, continuous dosing was assumed throughout the
release period.  This assumption may overestimate the daily treatment
duration that would be required for effective mollusk control.

For this analysis, effluent discharge rates were assumed to equal the
lower of either the facility-specific effluent flow rates or the 7Q10
flows of the receiving streams.  This approach may over or underestimate
average actual effluent discharges.    

The analysis used flow and discharge data for a sample of 30 steam
electric generating facilities.  This sample is not necessarily
statistically representative of the national population of facilities
with once-through cooling water systems where Busan 77 may be used.

Two of the COCs evaluated were based on ecotoxicity endpoints from
studies that did not fulfill the applicable guideline requirements.

      Endangered Species Considerations

Section 7 of the Endangered Species Act, 16 U.S.C. Section 1536(a)(2),
requires all federal agencies to consult with the National Marine
Fisheries Service (NMFS) for marine and anadromous listed species, or
the United States Fish and Wildlife Services (FWS) for listed wildlife
and freshwater organisms, if they are 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 means "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 facilitate compliance with the requirements of the Endangered Species
Act subsection (a)(2) the Environmental Protection Agency, Office of
Pesticide Programs has established procedures to evaluate whether a
proposed registration action may directly or indirectly 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 any listed species (U.S. EPA 2004).  After the
Agency’s screening-level risk assessment is performed, if any of the
Agency’s Listed Species LOC Criteria are exceeded for either direct or
indirect effects, a determination is made to identify if any listed or
candidate species may co-occur in the area of the proposed pesticide
use.  If determined that listed or candidate species may be present in
the proposed use areas, further biological assessment is undertaken. 
The extent to which listed species may be at risk then determines the
need for the development of a more comprehensive consultation package as
required by the Endangered Species Act.

For certain use categories, 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, pg.81).  Chemicals in these categories therefore do not undergo a
full screening-level risk assessment.

	For the once-through cooling water uses of Busan 77 this preliminary
analysis indicates that there is a potential for Busan 77 use to overlap
with listed species and that a more refined assessment is warranted, to
include direct, indirect and habitat effects.  The more refined
assessment should involve clear delineation of the action area
associated with proposed once-through use of Busan 77 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.  

Confirmatory Data Required:

1)  850.1300: Aquatic invertebrate life-cycle study (using TGAI and most
sensitive species -                        freshwater or
estuarine/marine)

2)  850.1400: Fish early-life stage study (using TGAI and most sensitive
species - freshwater     or estuarine/marine)

3)  850.4225: Seedling emergence study - dose response using rice (Oryza
sativa)

4)  850.4400: Freshwater floating macrophyte duckweed study

5)  850.5400: Aquatic plant growth (algal toxicity) – 2 studies
outstanding (marine diatom -                         Skeletonema
costatum and green algae - Selenastrum capricornutum); Tier II          
                (using TGAI or TEP)

6)  850.1735: Whole sediment, acute invertebrates (freshwater) (using
TGAI)

7)  850.1740: Whole sediment, acute invertebrates (estuarine/marine)
(using TGAI)

	8)  Depending on the results of the whole sediment, acute invertebrate
studies, the following data may be required: Whole sediment - chronic
invertebrates (freshwater and/or estuarine/marine) (using TGAI or TEP)

IV.	 Label Hazard Statements for Terrestrial and Aquatic Organisms:

Busan 77 labels must state:  

“This pesticide is toxic to fish, aquatic invertebrates and clams.”

"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."

V.  REFERENCES

00107207	Knott, W.B. 1970.  Busan 77 (WSCP) - Evaluation of Acute LC50
for Rainbow Trout.  Study performed by Woodward Research Corporation for
Buckman Laboratories, Inc., Memphis, TN.

00159307	Beaver, J.B.  1985.  Busan 77 - A Dietary LC50 Study with the
Bobwhite.  Project No. 210-104. Study performed by Wildlife
International, Ltd. for Buckman Laboratories, Inc., Memphis, TN.

052201020	WARF Institute, Inc.  1971.  Report on Acute Oral LD50 in
Bobwhite Quail.  Prepared for Buckman Laboratories, Inc., Memphis, TN.

40139202	Surprenant, D.C. 1987a.  Acute Toxicity of Busan 77 to
Sheepshead Minnow (Cyprinodon varigatus).  Report No. BW-87-2-2294. 
Study performed by Springborn Bionomics, Inc. for Buckman Laboratories,
Inc., Memphis, TN.

40139203	Surprenant, D.C. 1987b.  Acute Toxicity of Busan 77 to Mysid
Shrimp (Mysidopsis bahia).  Report No. BW-87-3-2346.  Study performed by
Springborn Bionomics, Inc. for Buckman Laboratories, Inc., Memphis, TN.

40334201	Surprenant, D.C. 1987c.  Acute Toxicity of Busan 77 to
Embryos-Larvae of the Quahog Clam (Mercenaria mercenaria).  Report No.
BW-87-8-2459.  Study performed by Springborn Bionomics, Inc. for Buckman
Laboratories, Inc., Memphis, TN.

41352001	LeLievre, M.K. et al. 1990c.  (Busan 77) - Acute Toxicity to
Rainbow Trout (Oncorhynchus mykiss) Under Static Conditions.  Report No.
89-12-3182.  Study performed by Springborn Laboratories, Inc. for
Buckman Laboratories, Inc., Memphis, TN.

41352002	LeLievre, M.K. et al. 1990a. (Busan 77) - Acute Toxicity to
Bluegill (Lepomis macrochirus) Under Static Conditions.  Report No.
89-12-3176.  Study performed by Springborn Laboratories, Inc. for
Buckman Laboratories, Inc., Memphis, TN.

41352003	LeLievre, M.K. et al.  1990b.  (Busan 77) - Acute Toxicity to
Daphnids (Daphnia magna) Under Static Conditions.  Report No.
89-11-3181.  Study performed by Springborn Laboratories, Inc. for
Buckman Laboratories, Inc., Memphis, TN.

41411501	Bodden, R.M.  1974.  Busan 77 - Acute Avian Dietary Toxicity
Study in Mallard Ducks.  Report No. 4043621.  Study performed by the
WARF Institute, Inc. for Buckman Laboratories, Inc., Memphis, TN.

41654801	Campbell, S. et al.  1990.  Busan 77: An Acute Oral Toxicity
Study with the Mallard. Project No. 210-114A.  Study performed by
Wildlife International, Ltd. for Buckman Laboratories, Inc., Memphis,
TN.

42013301	Hoberg, J.R.  1991a.  Busan 77 - Toxicity to the Duckweed Lemna
gibba G3.  Report No. 91-5-3749.  Study performed by Springborn
Laboratories, Inc. for Buckman Laboratories, Inc., Memphis, TN. 

42013302	Hoberg, J.R.  1991b.  Busan 77 - Toxicity to the Marine Diatom
Skeletonema costatum. Report No. 91-9-3864.  Study performed by
Springborn Laboratories, Inc. for Buckman Laboratories, Inc., Memphis,
TN.

42013303	Hoberg, J.R. 1991c.  Busan 77 - Toxicity to the Freshwater
Diatom Navicula pelliculosa.  Report No. 91-4-3728.  Study performed by
Springborn Laboratories, Inc. for Buckman Laboratories, Inc., Memphis,
TN.

42013304	Hoberg, J.R. et al.  1991d.  Busan 77 - Toxicity to the
Freshwater Bluegreen Algae Anabaena flos-aquae.  Report No. 91-4-3726. 
Study performed by Springborn Laboratories, Inc. for Buckman
Laboratories, Inc., Memphis, TN.

42013305	Hoberg, J.R. 1991e.  Busan 77 - Toxicity to the Freshwater
Green Algae Selenastrum capricornutum.  Report No. 91-4-3732.  Study
performed by Springborn Laboratories, Inc. for Buckman Laboratories,
Inc., Memphis, TN.

42038101	Hoberg, J.R.  1991f.  Busan 77 - Determination of Effects on
Seed Germination, Seedling Emergence, and Vegetative Vigor of Ten Plant
Species.  Report No. 91-3-3695.  Study performed by Springborn
Laboratories, Inc. for Buckman Laboratories, Inc., Memphis, TN.

42479601	Putt, A.E. et al. 1992.  Busan 77 – Chronic Toxicity to
Daphnids (Daphnia magna) Under Static Renewal Conditions.  Report No.
92-7-4343.  Study performed by Springborn Laboratories, Inc. for Buckman
Laboratories, Inc., Memphis, TN.

 “Environmental Exposure Assessment for Releases of Bromonitrostyrene
from Once-through Cooling Water Systems,” memorandum to David Bays,
EPA OPP/AD, from Joshua Cleland and Keith Drewes, ICF International,
April 26, 2007.   Also, see “Environmental Exposure Assessment for
Releases of Busan 77 From Once-through Cooling Water Systems,”
memorandum to Norm Cook, EPA OPP/AD, from Siroos Mostaghimi, EPA OPP/AD,
July 27, 2007.

 The E-FAST2 model is available from EPA at   HYPERLINK
"http://www.epa.gov/opptintr/exposure/pubs/efastdl.htm" 
http://www.epa.gov/opptintr/exposure/pubs/efastdl.htm  and documentation
is available at   HYPERLINK
"http://www.epa.gov/opptintr/exposure/pubs/efast2man.pdf" 
http://www.epa.gov/opptintr/exposure/pubs/efast2man.pdf .

 Petrie, R. and K. Montague.  2006.  “Ecological Hazard And
Environmental Risk Assessment Chapter, Alkyl Dimethyl Benzyl Ammonium
Chloride (ADBAC).”  PC Code 069105, CASE No.: 0350, U.S. Environmental
Protection Agency, Office of Pesticide Programs, Antimicrobials
Division.  August, 2, 2006. 

 A 7Q10 stream flow is the lowest seven-day average stream flow over a
ten year period.

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