Document ID: EPA-HQ-OPP-2010-0268-0007
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-06-01T04:00Z

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                               WASHINGTON, D.C.  20460
                                   OFFICE OF
                          PREVENTION, PESTICIDES AND
                               TOXIC SUBSTANCES

                                       
                               

								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

		

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  Although those numbers were higher, the model versions used for that assessment have been superseded and the guidance has been updated.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 ug/l and 0.19 ug/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.  

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-hydroxybenzonitrile(referred to as bromoxynil (phenol)), and 3,5-dibromo-dihydroxy-cyclohexadienylnitrile.  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 half-lifeof 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).

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), p-hydroxybenzonitrile, 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:[14]C 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 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 39[o]  to 96[o] F and the soil temperatures(10-cm depth) ranged from 55[o]  to 77[o] F .  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 19[o] to 35[o] C and soil temperatures (10-cm depth) ranged from 23[o] to 30[o] 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(R), N-Serve(R)) 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

Study

Value and unit

                                Major Degradate
                               Minor Degradates
                                       
                              MRID # or Citation
                         Study Classification, Comment

Abiotic Hydrolysis
Half-life[1] = 
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-dihydroxy-cyclohexadienylnitrile(10.7%),
Bromoxynil Phenol (76%)
MRID 41892901
00130424
Acceptable
Direct Aqueous Photolysis
Half-life[1] = 
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-life[1] = 
2.6 days (irradiated sample, 3.6 days in dark control)
Bromoxynil phenol (99%)
MRID 41920402
Acceptable
Aerobic Soil Metabolism
Half-life[1] = 2 days, sandy loam

Bromoxynil phenol:
Half-life[1] = 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-life[1] = 3.7 days
4-hydroxybenzonitrile (45.52%),
Bromoxynil phenol (48.5%)
MRID
42234303
41892902
Acceptable
Aerobic Aquatic Metabolism 
Half-life[1] = < 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-life[1] = 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 distribution coefficient (KOC)
KOC = 
1,003 L/kg (sandy loam, pH 7.2, 1.1% organic matter)
Not reported
MRID 00116557
00114338
42271101
43775001
Supplemental
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-life[1,2] = 
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
[1]Half-lives were calculated using the single-first order equation and nonlinear regression, unless otherwise specified.
[2]The 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).  

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 ug/L to 6.1 ug/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 ug/L.  It is possible these two detections at the same location, date, and concentration could be the same bromoxynil compound.   

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 ug/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
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
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
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
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
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 ug/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.

	

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 90[th] percentile confidence bound on two values 

Is the pesticide wetted-in?

No

Method of application
Grasses:  Aerial and Ground

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

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).