1

OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

 WASHINGTON, D.C. 20460

 

DP Barcode: 374620

PC Code: 035301, 035302, 129820 

December 16, 2010 

MEMORANDUM

SUBJECT: Drinking water assessment for ground and aerial application of bromoxynil on 

grass grown for seed and ground application of sorghum.

TO: Bethany Benbow

Herbicide Branch

Registration Division

Cassi Walls,

Risk Assessment Branch 3

Health Effects Division

FROM: Tiffany Mason, Environmental Engineer

Environmental Risk Branch II

Environmental Fate and Effects Division

THRU: Brian Anderson, Chief

Environmental Risk Branch II

Environmental Fate and Effects Division

Jean Holmes, DVM, MPH, Risk Assessment Process Leader

Environmental Risk Branch II

Environmental Fate and Effects Division 

R. David Jones, Ph.D., Senior Agronomist

Environmental Risk Branch II

Environmental Fate and Effects Division
2

CONCLUSIONS

This drinking water assessment is for a mixture of bromoxynil octonoate (PC Code 035302), 

bromoxynil heptanoate (PC Code 128920), and pyrasulfotole (PC Code 000692) for two new 

uses on grasses grown for seed and sorghum. The risk assessment considers the use of 

bromoxynil octanoate and bromoxynil heptanoate as proposed on the supplemental label for 

Huskie Herbicide (EPA Registration Number 264-1023). Since bromoxynil heptanoate is 

chemically and physically similar to bromoxynil octanoate (one carbon difference in the ester 

side chain) and both esters rapidly degrade to bromoxynil phenol (aka bromoxynil, PC Code 

035301), all calculations have been performed in terms of bromoxynil. Pyrasulfotole, another 

registered product on the proposed label, is evaluated in a separate assessment and will not be 

evaluated in this assessment. This assessment replaces the revised drinking water assessment for 

the use of bromoxynil on cotton completed August 11, 1997. Although those numbers were 

higher, the model versions used for that assessment have been superseded and the guidance has 

been updated.

Bromoxynil is a selective herbicide used for pre- and post-emergent weed control for certain 

broadleaf weeds in wheat, barley, conservation reserve program acres (CRP), grass grown for 

seed, oats, rye, sorghum (grain and forage), and triticale. This assessment is for two use patterns: 

grass grown for seed and sorghum. These use patterns have been previously registered for 

bromoxynil, however, this new product contains bromoxynil and pyrasulfotole (PC Code 

000692) and requires reassessment of the use patterns for drinking water exposure. The proposed 

new use for grasses grown for seed has a maximum label-specified use rate per year of 2 

applications (30 ounces per acre per year formulation or approximately 0.57 lb a.i. [bromoxynil] 

per acre per year), 30 days apart, at the rate of 0.15 oz of formulated product/acre (approximately

0.286 lb. a.i. [bromoxynil phenol]/acre). The proposed new use for sorghum has a maximum 

label-specified use rate per year of 2 applications (32 ounces per acre per year formulation or 

approximately 0.61 lb a.i. [bromoxynil phenol] per acre per year), 11 days apart, at the rate of 

0.16 oz of formulated product/acre (approximately 0.305 lb. a.i. /acre). 

Based on the proposed application rate and the environmental fate properties of bromoxynil, 

surface and ground water contamination may occur. The estimated environmental 

concentrations (EECs) generated by the FIRST model are listed below.

For drinking water derived from surface water, the acute and chronic concentrations to be used 

are 11.5 μg/l and 0.19 μg/l for the ground use on sorghum (Table 1).

For drinking water derived from ground water, the SCI-GROW model estimates bromoxynil 

concentrations of 1.33 ng/l for the ground use on sorghum (Table 1). Ground water numbers 

were not generated in the previous drinking water assessment performed August 11, 1997. The 

SCI-GROW value that should be used for acute, chronic, and the cancer risk assessment is 3.26 

ppb for the revised cotton assessment. 
3

Table 1. Tier I EEC's for Bromoxynil for the aerial use and ground use on grasses grown for 

seed and ground use on sorghum using FIRST and SCI-GROW models.

Surface Water Ground Water

Use Pattern Peak EEC (ug/L) Annual Mean EEC (ug/L) Peak and Mean EEC

----------------------- ug/L--------------------------- ng/L

Grasses for Seed 10.2 0.17 1.24

Sorghum 11.5 0.19 1.33

Revised Cotton Numbers

Cotton 4.34 0.07 3.26 

Environmental Fate Summary

Surface and ground water contamination may occur from the common degradate (bromoxynil 

phenol aka bromoxynil) of the two ester bromoxynil formations (bromoxynil octanoate and 

bromoxynil heptanoate), as opposed to the esters themselves. Since bromoxynil heptanoate is 

chemically and physically similar to bromoxynil octanoate (one carbon difference in the ester 

side chain) and bromoxynil octanoate rapidly degrades to bromoxynil (t1/2 ≈ 2.1 days), it is 

believed that bromoxynil heptanoate would behave similarly. Therefore, all calculations have 

been performed in terms of bromoxynil instead of the esters.

There is no evidence that bromoxynil degrades by abiotic hydrolysis at any measured pH (MRID 

41892901) or by photolysis (MRID 42234301, 41920401). Residues of bromoxynil appear to be 

moderately mobile to highly mobile in with three out of four soil-water partitioning coefficients 

(Kd ) less than three (MRID 110429) and appear to have no significant correlation with the soil 

organic carbon content. The field dissipation studies show that bromoxynil residues dissipated 

with half-lives of 1 to 14 days and were not detected below 15 cm soil depth (MRID 41653701, 

43071001) indicating that leaching is not an anticipated route of dissipation, likely due to the 

rapid degradation rate. 

Surface and ground water contamination may occur from the common degradate (bromoxynil 

phenol, aka bromoxynil) of the two ester bromoxynil formations (bromoxynil octanoate and 

bromoxynil heptanoate), as opposed to the esters themselves. Since bromoxynil heptanoate is 

chemically and physically similar to bromoxynil octanoate (one carbon difference in the ester 

side chain) and bromoxynil octanoate rapidly degrades to bromoxynil (t1/2 ≈ 2.1 days), it is 

believed that bromoxynil heptanoate would behave similarly. Therefore, all calculations to

determine acute toxicity has been performed in terms bromoxynil octanoate, and chronic toxicity

has been performed in terms of bromoxynil instead of the esters.

Abiotic Hydrolysis

Hydrolysis of bromoxynil octanoate is base-catalyzed with half-lives of 34.1 days at pH 5, 

11.5days at pH 7, and 1.7 days for pH 9. The hydrolysis products were 3,5-dibromo-4-
4

hydroxybenzonitrile(referred to as bromoxynil (phenol)), and 3,5-dibromo-dihydroxycyclohexadienylnitrile. Bromoxynil(phenol), which is stable to hydrolysis, increased throughout 

the study, reaching maximumconcentrations at 30 days of 35%, 77%, and 76% at pH 5, 7, and 9, 

respectively. The degradate 3,5-Dibromo-dihydroxy-cyclohexadienylnitrile concentrations 

reached maximum concentrations of 10.4%,10.7%, and 7.9% at pH 5, 7 and 9, respectively, but 

declined from those values by the end of the study,indicating that it was not stable to hydrolysis. 

(MRID41892901).

In another study bromoxynil octanoate hydrolyzed with calculated half-lives of 43 days at pH

5,28 days at pH 7, and 1.5 days for pH 9. Hydrolysis of bromoxynil butyrate (an ester of 

bromoxynilwhich is currently not being registered) is base-catalyzed with calculated half-lives of 

44 days at pH 5,52 days at pH 7, and 1.1 days for pH 9. Bromoxynil (phenol) was the hydrolysis 

product for both theoctanoate and the butyrate. It was stable to hydrolysis at pH 5, 7, and 9. The 

study was consideredacceptable. (MRID 00130424).

Aqueous Photolysis 

Bromoxynil octanoate degraded with a calculated photolytic half-life of 4.6 days at pH 5. 

Eachphotoperiod consisted of 12 hours of light (artificial - xenon arc lamp) and 12 hours of 

darkness.Bromoxynil octanoate was stable in the dark controls with a 110.7-day half-life. In the 

irradiatedsamples there were 3 major degradates: 4-cyano-2-bromophenyl octanoate (maximum 

meanconcentration of 13.9% at day 3), bromoxynil (phenol) (maximum mean concentration of 

53.4% at day30), and phenyl carbamate (maximum mean concentration of 26.6% at day 2). 

(MRID 42234301 and 41920401).

Soil Photolysis

Bromoxynil octanoate degraded with a calculated photolytic half-life of 2.6 days in the 

irradiatedsamples (artificial - xenon arc lamp) and 3.6 days in the dark control. The 3.6 day

half-life in the darkcontrols suggests other degradation processes such as hydrolysis or microbial 

metabolism, wereoccurring. (MRID 41920402).

Aerobic Soil Metabolism

[Cyano labeled 14C]-bromoxynil octanoate degraded in a sandy loam soil with a calculated halflifeof 2 days. The major degradate was CO2 which accounted for 64.28% of the applied 

radioactivity at 90 days. (MRID 42234302 and MRID 41897701). Bromoxynil (phenol) 

exhibited half-lives of 51 hr in sandy loam and 31 hr in loam soils (MRID 00142958). (MRID 

42234302, 41897701 and 00142958).

Anaerobic Aquatic Metabolism

Bromoxynil octanoate degraded in a sandy loam sediment with a calculated half-life of 3.7 

daysbased on the results obtained over the first 14 days of the experiment. The degradate 4-

hydroxybenzonitrile reached a maximum concentration of 45.52% by Day 14 before decreasing 

to 0.14% at 26 weeks. Bromoxynil (phenol) was also formed, reaching a maximum 

concentration of48.5% by day 7, then decreasing to 3.5% at 8 weeks. (MRID 42234303 and 

41892902).
5

Aerobic Aquatic Metabolism 

Bromoxynil octanoate degraded with a half-life of <12 hours when treated sandy loam soil 

wasflooded with pond water which was aerobically incubated in the dark at approximately 25 

C.Bromoxynil octanoate was 87.64% of the applied at time 0 and declined to undetectable levels 

by 48hours posttreatment. The major nonvolatile degradates were bromoxynil (phenol), phydroxybenzonitrile, 3-bromo-4-hydroxybenzonitrile, and 3,5-dibromo-4-hydroxybenzoic acid. 

Thedegradate bromoxynil (phenol) was 6.59% of the applied immediately posttreatment, 66.47% 

at 12hours, 78.77% at 48 hours posttreatment, 39.68% at 168 hours, and 2.39-4.56% at 336 

through 720 hours. (MRID 42364901).

Unaged Soil Column Leaching 

[14C]Bromoxynil OctanoateBromoxynil octanoate was mobile in columns of sand, sandy loam, 

and loam soils that weretreated at 228.9 g/column with phenyl ring-labeled [14C] bromoxynil 

octanoate and leached with 50.8cm of a 0.005 M calcium chloride solution. Residues were 

distributed throughout the length of eachsoil column and ranged from 2.7-18.2% of the applied 

in the leachates from the sandy loam-1, sandyloam-2, and loam soil columns; and from 52.4-

58.9% in the leachates from the sand soil columns. Inthe 0-7 cm segment of the columns for 

sandy loam-1, sandy loam-2 and sand soil, the recoveries wereapproximately 31-43%, 31-35%, 

and 13%, respectively. (MRID 42271101).

Aged Bromoxynil Octanoate Residues 

Aged bromoxynil octanoate (2,6-dibromo-4-cyanophenyl octanoate) residues were not mobilein 

columns of four soils and an aquatic sediment that were treated with bromoxynil octanoate that 

hadbeen aerobically aged (aerobic half-lives of 28-100 hours) and then leached with 50.8 cm of a 

0.01 Mcalcium chloride solution. Residues in the sandy loam, loam, clay loam, and aquatic 

sediment columnswere concentrated in the segment composed of the aged soil and the segment 

immediately beneath it:14C in the leachates was 0.27% of the applied. Residues in the sand soil 

columns moved slightly morethan in the other soils, but remained concentrated in the upper two 

segments of the columns (top 10cm); any 14C-residues in the leachates were [14C]-carbonates 

and were 3.50-3.58% of the applied. (MRID 42271101 and 43775001).

Adsorption/Desorption Batch Equilibrium

Bromoxynil octanoate was found to be mobile in sandy loam soil with pH 7.2 and 1.1% 

organicmatter. The Kd was 7.0 (Koc=1,003). The study was considered supplemental and did 

not satisfy datarequirements because the study authors failed to show that the aerobic soil 

metabolism half-life of thesandy loam soil was much greater than the equilibration time of 24 

hours in the batch equilibrium study (MRID #00116557 and 00114338). However, this data 

requirement is fulfilled using the agedand unaged column leaching studies (GLN 163-1; MRID 

42271101 and 43775001).

Laboratory Volatility and Field Volatility 

This data requirement was waived based on the low vapor pressure (1.39 x 10 -6 mm Hg) and 
6

estimated Henry’s Law Constant (9.76 x 10 -8 atm-m3 /mol). (EFGWB # 91-0200-0199, 

1/17/91).

Fish Accumulation 

[14C]Bromoxynil octanoate residues accumulated in bluegill sunfish continuously exposed to 

[14C]bromoxynil octanoate at 1.3-4.7 g/L. The maximum bioconcentration factors were 63x for 

edible tissue, 400x for inedible tissue, and 230x for whole fish. Depuration occurred with 85-

97% of theaccumulated residues eliminated by Day 14. (MRID42277301-a and 42277301-b).

Terrestrial Field Dissipation 

Bromoxynil, spray applied at 0.56 kg ai/ha to plots planted in wheat, dissipated with observed 

half-lives (DT50) of approximately 14 days from a Sorrento silt loam soil in California and 1 day

from a Norfolk sandy loam soil in North Carolina. At both sites, bromoxynil octanoate residues 

were not detected below the 0-15 cm soil depth indicating leaching was not an important route of 

dissipation. In San Juan Bautista, California, air temperatures ranged from 39o to 96oF and the 

soil temperatures(10-cm depth) ranged from 55o to 77oF . The field plots in California were 

irrigated with 30.5 mm of water to supplement the limited rainfall before day 20. In Clayton, 

North Carolina, air temperatures ranged from 19oto 35o C and soil temperatures (10-cm depth) 

ranged from 23oto 30o C. Total rainfall during the study was 245 mm; therefore, irrigation was 

not applied to field plots. Results of a freezer storage stability study indicate there was no 

significant degradation of either bromoxynil octanoate orbromoxynil (phenol) in the California 

or North Carolina soils used in the field studies. (MRID 41653701 and 43071001).

Nitrification Inhibition

Bromoxynil has been shown to inhibit nitrification in soils (Frear, 1976). Nitrification is defined 

as the oxidation of reduced nitrogen (e.g., ammonium) by bacteria (Nitrosomonas, Nitrobacter 

species) to nitrate through the intermediate product, nitrite (Brady and Weil, 1996). Various 

environmental factors such as soil reaction (acidity and alkalinity), aeration, moisture, carbon 

sources, temperature and nutrient availability influence the nitrification process. For certain 

environmental conditions, commercially-available nitrification inhibitors (Dwell®, N-Serve®) 

are used in production agricultureto temporarily slow conversion of ammonium fertilizers to 

nitrate because nitrate can be lost through leaching or denitrification. In the environment, 

adaptation to nitrification inhibitors, such as bromoxynil, is demonstrated by the increasing 

bromoxynil concentrations that are needed to cause 50% inhibition(Frear, 1976). In addition, 

these adaptation studies support the observation that microbial-mediatedmetabolism (aerobic soil 

metabolism half-lives of 31-51 hours; field dissipation half-life of 1-14 days) is an important 

process for degradation of bromoxynil in soils; therefore, nitrification inhibition would generally 

occur only on a temporary basis. Thus, nitrification inhibition by bromoxynil does not appear to 

be a concern.

Table 3. Summary of Bromoxynil Environmental Fate Properties
7

Study Value and unit

Major Degradate

Minor Degradates MRID # 

or 

Citation

Study 

Classification, 

Comment

Abiotic Hydrolysis

Half-life1= 

pH 5 = 34.1-43 days

pH 7 = 11.5-28days

pH 9 = 1.1-1.7 days

3,5-dibromo-4-

hydroxybenzonitrile,

3,5-dibromo-dihydroxycyclohexadienylnitrile(10.7%),

Bromoxynil Phenol (76%)

MRID 

41892901

00130424

Acceptable

Direct Aqueous 

Photolysis

Half-life1= 

4.6 days (pH 5, 12 hrs of 

darkness)

4-cyano-2-bromophenyl 

octanoate (max mean 

concentration 13.9%), 

Bromoxynil phenol (max 

mean 53.4%),

Phenyl carbamate (max mean 

26.6%)

MRID 

42234301

41920401 Acceptable

Soil Photolysis Half-life1= 

2.6 days (irradiated 

sample, 3.6 days in dark 

control)

Bromoxynil phenol (99%)

MRID 

41920402 Acceptable

Aerobic Soil 

Metabolism

Half-life1= 2 days, 

sandy loam

Bromoxynil phenol:

Half-life1= 31-51 days, 

loam soils

CO2 (64.28%)

Bromoxynil phenol (44.59%)

3-bromo-4-hydroxybenzamide 

(0.42%) 

3,5-dibromo-4-

hydroxybenzamide (5.41%)

3,5-dibromo-4-hydroxybenzoic 

acid (0.37%)

MRID 

42234302

41897701

00142958

Acceptable

Anaerobic Soil 

Metabolism Half-life1= 3.7 days

4-hydroxybenzonitrile 

(45.52%),

Bromoxynil phenol (48.5%)

MRID

42234303

41892902

Acceptable

Aerobic Aquatic 

Metabolism 

Half-life1= < 12 hrs 

Bromoxynil phenol (78.77%),

p-hydroxybenzonitrile 

(25.6%),

3-bromo-4-

hydroxybenzonitrile (12.10%),

3,5-dibromo-4-hydroxybenzoic 

acid (12.0%)

MRID

42364901 Acceptable

Anaerobic Aquatic 

Metabolism 

Half-life1= 3.7 days Bromoxynil phenol (48.48%),

4-hydroxybenzonitrile 

(46.32%),

3-bromo-4-

hydroxybenzonitrile (nominal)

MRID 

42234303

41892902

Acceptable

Solid-water 

distribution 

coefficient (Kd)

Kd = 

7.0 L/kg (sandy loam, 

pH 7.2, 1.1% organic 

matter)

Not reported MRID 

00116557

00114338

42271101

43775001

Supplemental

Organic-carbon 

normalized 

KOC = 

1,003 L/kg (sandy loam, 

Not reported MRID 

00116557 Supplemental
8

Study Value and unit

Major Degradate

Minor Degradates MRID # 

or 

Citation

Study 

Classification, 

Comment

distribution 

coefficient (KOC)

pH 7.2, 1.1% organic 

matter)

00114338

42271101

43775001

Soil Column 

Leaching

Residues very mobile in 

sand, sandy loam, and 

loam soils, 2.7 – 18.2% 

radioactivity remained in 

soil column and 52.4 –

58.9% recovered in 

leachate. 

CO2 (12.1%),

Bromoxynil phenol (found in 

sandy loam soil and lechate-% 

not reported),

3-bromo-4-

hydroxybenzonitrile (found in 

lechate only-% not reported)

MRID 

42271101

43775001

Acceptable

Volatility from Soil 

(Laboratory)

No Study No Study No Study Waived

Terrestrial Field 

Dissipation

Bromoxynil octanoate:

No study

Bromoxynil phenol:

Dissipation Half-life1,2= 

14 days (silt loam soil in 

CA), 1 day (sandy loam 

soil in NC)

CO2 (33.6%),

3,5-dibromo-4-

hydroxybenzamide (21.6%),

3,5-dibromo-4-

hydroxybenzoic acid (34.8%)

MRID 

41653701

43071001

Acceptable

Aquatic Field 

Dissipation

No Study No Study No Study No Study

Bioconcentration 

Factor (BCF)

Bluegill sunfish (63 x for 

edible tissue, 400x for 

indedible tissue, 230x 

for whole fish)

Bromoxynil phenol (79%, in 

fish tissue)

MRID 

42277301-

a

42277301-

b

Acceptable

Abbreviations: wt=weight

1Half-lives were calculated using the single-first order equation and nonlinear regression, unless otherwise specified.

2The value may reflect both dissipation and degradation processes.

*Degradates less than 10% are considered minor degradates unless deemed of toxicological concern. All minor and major 

degradates above were not included in modeling calculations because they do not appear to be of toxicological conern. The 

esters and the phenol are much more toxic with the esters being an order of magnitude (in some cases) more toxic than the 

phenol.

Water Resources Summary

A. Monitoring 

Below (Table 2) is a summary of monitoring data found on bromoxynil from the USGS 

NAWQA surface and ground water database 

(http://infotrek.er.usgs.gov/apex/f?p=136:1:0::NO:::) and California Department of Pesticide 

Regulation (CDPR) surface water database 

(http://www.cdpr.ca.gov/docs/emon/surfwtr/surfcont.htm). 
9

The NAWQA database had taken 7,218 samples for bromoxynil across the United States. It is 

believed that these samples represent bromoxynil phenol, but cannot be verified since USGS did 

not differentiate between bromoxynil phenol, bromoxynil octanoate, bromoxynil heptanoate, or 

bromoxynil butyrate. Out of 7, 218 samples, there were 54 confirmed detections ranging in 

concentration from 0.001 μg/L to 6.1 μg/L. Of those 54 detections, 40 were samples taken from 

streams, 8 from ground water sources, 4 from waste water treatment effluent, and 1 from a water 

distribution system. The rest of the samples were below the detection limit.

The California Department of Pesticide Regulation (CDPR) database looked for both bromoxynil 

and bromoxynil octanoate. Out of 531 samples and approximately 29 sites, taken from February 

8, 1993 to January 6, 2005, 192 were for bromoxynil octanoate, and 339 were for bromoxynil. 

There were two detections, one for bromoxynil and one for bromoxynil octanoate. Both 

occurred on May 9, 1997 in Yolo County, CA with a concentration of 0.06 μg/L. It is possible 

these two detections at the same location, date, and concentration could be the same bromoxynil 

compound. 
10

Table 2. Surface and Groundwater detections of Bromoxynil from CDPR and USGS NAWQA databases.

USGS NAWQA Database**

River Basin Site Type Code* State and County USGS Staion ID Place Name Concentration μg/L

Allegheny and Monongahela Basins ST PA - ALLEGHENY 3049646 Deer Creek Near 

Dorseyville, Pa

0.07

Williamette Basin ST OR - CLACKAMAS 14202000 Pudding River At 

Aurora, Or

0.03

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.0032

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.0043

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.0059

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.006

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.0074

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.0086

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.0096
11

USGS NAWQA Database**

River Basin Site Type Code* State and County USGS Staion ID Place Name Concentration μg/L

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.0344

Williamette Basin ST OR - MARION 14201300 Zollner Creek Near 

Mt Angel, Or

0.0409

Williamette Basin ST OR - MULTNOMAH 14211720 Willamette River 

At Portland, Or

0.0043

White, Great and Little Miami River Basins ST IN - HAMILTON 395743086030501 White R, W Bank, 

1 Rmi Us 116th St 

At Fishers In

0.0041

Upper Mississippi River Basin ST MN - CARVER 5330000 Minnesota River 

Near Jordan, Mn

0.02

Upper Illinois River Basin ST IL - LA SALLE 5553500 Illinois River At 

Ottawa, Il

0.02

South Platte River Basin ST CO - WELD 6753990 Lonetree Creek 

Near Greeley, Co.

6.1

San Joaquin-Tulare Basins ST CA - MERCED 11273500 Merced R A River 

Road Bridge Nr 

Newman Ca

0.0132

San Joaquin-Tulare Basins ST CA - STANISLAUS 11274538 Orestimba Cr At 

River Rd Nr Crows 

Landing Ca

0.0132
12

USGS NAWQA Database**

River Basin Site Type Code* State and County USGS Staion ID Place Name Concentration μg/L

Lower Illinois River Basin ST IL - PIATT 5572000 Sangamon River At 

Monticello, Il

0.002

Lower Illinois River Basin ST IL - SCOTT 5586100 Illinois River At 

Valley City, Il

0.0095

Eastern Iowa Basins ST IA - JOHNSON 5454500 Iowa River At Iowa 

City, Ia

0.0008

Eastern Iowa Basins ST IA - JOHNSON 05465500 Iowa River At 

Wapello, Ia

0.02

Eastern Iowa Basins ST IA - TAMA 5464220 Wolf Creek Near 

Dysart, Ia

0.22

Central Nebraska Basins ST NE - DOUGLAS 6800500 Elkhorn River At 

Waterloo, Nebr.

0.0432

Central Columbia Plateau-Yakima River Basin ST WA - BENTON 461032119194900 Drain At Badger 

Road, Mile 8.8

0.0069

Central Columbia Plateau-Yakima River Basin ST WA - BENTON 12510500 Yakima River At 

Kiona, Wa

0.0081

Central Columbia Plateau-Yakima River Basin ST WA - FRANKLIN 12473740 El 68 D Wasteway

Near Othello, Wa

0.02
13

USGS NAWQA Database**

River Basin Site Type Code* State and County USGS Staion ID Place Name Concentration μg/L

Central Columbia Plateau-Yakima River Basin ST WA - KITTITAS 465640120265700 Johnson Drain At 

South Ferguson 

Road

0.0171

Central Columbia Plateau-Yakima River Basin ST WA - WHITMAN 13351000 Palouse River At 

Hooper, Wa

0.013

Central Columbia Plateau-Yakima River Basin ST WA - WHITMAN 13351000 Palouse River At 

Hooper, Wa

0.007

Central Columbia Plateau-Yakima River Basin ST WA - WHITMAN 13351000 Palouse River At 

Hooper, Wa

0.006

Central Columbia Plateau-Yakima River Basin ST WA - WHITMAN 13351000 Palouse River At 

Hooper, Wa

0.0041

Central Columbia Plateau-Yakima River Basin ST WA - YAKIMA 12505450 Granger Drain At 

Granger, Wa

0.0076

Central Columbia Plateau-Yakima River Basin ST WA - YAKIMA 12505450 Granger Drain At 

Granger, Wa

0.0096

Central Columbia Plateau-Yakima River Basin ST WA - YAKIMA 12505450 Granger Drain At 

Granger, Wa

0.0122
14

USGS NAWQA Database**

River Basin Site Type Code* State and County USGS Staion ID Place Name Concentration μg/L

Central Columbia Plateau-Yakima River Basin ST WA - YAKIMA 12505450 Granger Drain At 

Granger, Wa

0.023

Central Columbia Plateau-Yakima River Basin ST WA - YAKIMA 12505450 Granger Drain At 

Granger, Wa

0.0233

Central Columbia Plateau-Yakima River Basin ST WA - YAKIMA 462018120075200 Jd 32.0 Upstream 

Of Dr 2

0.0367

Central Columbia Plateau-Yakima River Basin ST WA - YAKIMA 462023120075200 Dr 2 At Yakima 

Valley Highway 

Near Granger, Wa

0.006

Central Columbia Plateau-Yakima River Basin ST WA - YAKIMA 462046120065600 Dr 2 At Vanbelle 

Road

0.0473

Upper Snake River Basin GW ID - BONNEVILLE 433021112001001 02n 38e 16bcc1 0.0088

Upper Snake River Basin GW ID - MINIDOKA 424617113421901 07s 23e 36daa1 0.0054

Upper Snake River Basin GW ID - TWIN FALLS 423115114290401 10s 17e 29dcd1 0.0447

Tennessee River Basin GW TN - BEDFORD 353211086271201 Bd:L-41 0.0162

Santa Ana River Basin GW CA - RIVERSIDE 340033117204001 002s004w07l001s 0.0061
15

USGS NAWQA Database**

River Basin Site Type Code* State and County USGS Staion ID Place Name Concentration μg/L

Puget Sound Basin GW WA - UNSPECIFIED 490040122240501 092g.008.2.2.2-91-

12

0.0005

Lake Erie-Lake Saint Clair Drainage GW MI - HILLSDALE 414520084374800 Ag059-9 0.02

Apalachicola-Chattahoochee-Flint River Basin GW FL - JACKSON 305137085060301 Nwfwmd 

80'Tot/65'Cased 

Well

0.0005

Ozark Plateaus FA-WTP AR - STONE 355453092061301 Finished Water 

Near Allison

0.0016

Northern Rockies Intermontane Basins FA-WTP WA - SPOKANE 12424000 Hangman Creek At 

Spokane Wa

0.2837

Northern Rockies Intermontane Basins FA-WTP WA - SPOKANE 12424000 Hangman Creek At 

Spokane Wa

0.0275

Mississippi Embayment FA-WTP LA - TENSAS 315913091154900 Lake Bruin [Finish] 

Nr St Joseph, La

0.0115

Lake Erie-Lake Saint Clair Drainage FA-WDS OH - DEFIANCE 411645084230502 Maumee River At 

Holgate Avenue F

0.0033

CDPR Surface Water Database - all samples taken in State of CA

Date of Sample Site Type Code County in CA Chemical Found Place Name Concentration μg/L
16

USGS NAWQA Database**

River Basin Site Type Code* State and County USGS Staion ID Place Name Concentration μg/L

May 9, 1997 SW YOLO bromoxynil

Colusa Basin Drain 

above Knights 

Landing 0.06

May 9, 1997 SW YOLO

bromoxynil 

octanoate

Colusa Basin Drain 

above Knights 

Landing 0.06

*SW: Surface Water, ST: Stream, GW: Ground Water, FA-WTP: Water-supply treatment plant, FA-WDS: Water-distribution system 

**USGS NAWQA database only stated bromoxynil. What form of bromoxynil was present is undetermined. The database did not provide a date of when the samples were taken 

either.
17

B. Surface Water

The Tier I screening models FIRST Version 1.1.1 (FQPA Index Reservoir Screening Tool) with 

Percent Crop Area adjustment factor was used to determine drinking water concentrations of 

Bromoxynil derived from surface water sources. 

Bromoxynil may move from the treated field to surface water or ground water through run-off 

shortly after application. Residues of bromoxynil are highly to moderately mobile in soil. Tier 

1 drinking water concentrations derived from surface water for bromoxynil was estimated using 

Version 1.1.1 of FIRST model. Input values for the FIRST model are reported in Table 3.

Table 3. FIRST Input Parameters for Bromoxynil aerial and ground use on grasses grown for 

seed and ground use on sorghum.

Parameter Input value Data Source/Rationale*

Application Rate (lbs ai/A) 0.286 

(grasses)

0.305 

(sorghum)

Label

Maximum No. of 

Applications/season

2 Label

Application Interval (days)

30 (grasses)

11 (sorghum)

Label 

Percent Cropped Area (as 

decimal) 

0.87 Default

Incorporation depth (inch) 0 Label

Kd 4.61

Average Kd from 4 soils (MRID 110429), range 

of 1.4 to 12.54

Aerobic Soil Metabolism Half-life 

(days)

3.00

Upper 90th percentile confidence bound on two 

values 

Is the pesticide wetted-in? No

Grasses: Aerial and Ground
18

Parameter Input value Data Source/Rationale*

Method of application

Sorghum: Ground

Solubility (ppm) 130 Product Chemistry

Aerobic aquatic t1/2 (days) 6.0 2 x (aerobic soil value)

Photolysis Half-life (days) 0 Stable (MRID 42234301, 41920401)

* Parameters were selected in accordance with the Proposed Interim Guidance for Input Values 

document, dated September 22, 2009.

It is important to note, that since bromoxynil heptanoate is chemically and physically similar to 

bromoxynil octanoate (one carbon difference in the ester side chain) and both esters rapidly 

degrade to bromoxynil phenol (aka bromoxynil), all calculations have been performed in terms 

of bromoxynil. 

C. Ground Water

SCI-GROW model (Screening Concentration in Ground Water Program (SCI-GROW) 

VERSION 2.3.0 was used to predict the maximum chronic and acute concentration of 

Bromoxynil derived from shallow ground water.

Bromoxynil is mobile, but has a short metabolic half-life in soil under aerobic conditions. 

Therefore, bromoxynil should not be a ground water concern in most environments. In the event 

that bromoxynil did reach ground water it is expected to degrade slowly due to microbial activity 

(faster under aerobic conditions than anaerobic conditions) but is rather persistent otherwise. 

Table 4 below summarizes the results of the screening level groundwater model, SCIGROW 

2.3.0, for bromoxynil.

Table 4. SCIGROW input parameters used to estimate Bromoxynil aerial and ground use on 

grasses grown for seed and ground use on sorghum.

Parameter Input value Data Source/Rationale*

Koc 192.1

Average Koc from 4 soils (MRID 

110429), 

Clay-loam: 228.6

Loamy-sand: 107.7

Loam: 193.3

Sandy-loam: 238.9
19

Parameter Input value Data Source/Rationale*

Application Rate (lbs ai/A) 0.286 (grasses)

0.305 (sorghum)

Label

Maximum No. of 

Applications/season

2 Label

Aerobic Soil Metabolism Half-life 

(days)

1.71

Mean value as per input 

parameter guidance. Half-lives 

2.13 and 1.29. (MRID 142958).