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**UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

**WASHINGTON D.C., 20460**

**OFFICE OF**

**PREVENTION, PESTICIDES AND**

**TOXIC SUBSTANCES**

PC Code 128825

> DP Barcode D311012

**[MEMORANDUM]{.underline}**

**DATE:** February 7, 2006

**SUBJECT:** Tier I Estimated Environmental Concentrations of Bifenthrin
for the Use in the Human Health Risk Assessment.

**TO:** Shaja Brothers, Risk Manager Reviewer

Sidney Jackson, Risk Manager Reviewer

BeWanda Alexander, Risk Manager Reviewer

Daniel Rosenblatt, Risk Manager #5

George LaRocca, Risk Manager #13

Registration Division (7505C)

**AND:** Karen Whitby, Branch Chief

Registration Action Branch I

Health Effects Division (7509C)

**FROM:** José Luis Meléndez, Chemist

ERBV, Environmental Fate and Effects Division (7507C)

**THROUGH:** Jean Holmes, DVM, Acting Chief

> Environmental Risk Branch V

Environmental Fate and Effects Division (7507C)

This memo presents the Tier I Estimated Surface Drinking Water
Concentrations and Estimated Ground Water Concentrations (EDWCs) for
Bifenthrin, calculated using the Tier I aquatic models FIRST and
SCI-GROW, respectively, for use in the human health risk assessment.

The Estimated Drinking Water Concentrations (EDWCs) for bifenthrin were
calculated based on a maximum application rate of 0.5 lb a.i./A/season.
The acute drinking water concentration in surface water is 0.0140 ppb of
bifenthrin, based on applications of the chemical to lettuce. The
cancer/chronic drinking water concentration is 0.0140 ppb (based on
applications of lettuce, highest application rate). The SCI-GROW
generated EDWC is 0.00300 ppb of bifenthrin, which is recommended for
use, both for acute and chronic exposures. Because of the very low
solubility of bifenthrin, the EDWCs did not exceed 0.0140 ppb (the
solubility of bifenthrin).

Table 1 provides a summary of the Tier I modeled drinking water
concentrations. Should there be a need for additional refinements, the
EFED can perform a Tier II aquatic assessment, for surface waters.

**[EXECUTIVE SUMMARY]{.underline}**

Bifenthrin (chemical name Number range
CHAPTER2-methylbiphenyl-3-ylmethyl
(*Z*)-(1*RS*,3*RS*)-3-(2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethylcyclopropanecarboxylate,
CAS# 82657-04-03, PC code 128825)Number range CHAPTER is a synthetic
pyrethroid insecticide. Its structure has three rings, two phenyl rings
attached to each other by a single bond, and a cyclopropyl ring. The
chemistry of bifenthrin may be dictated by its ester moiety; however,
laboratory studies show that it is relatively stable. The molecule has
some chiral centers, and a double bond that brings isomer possibilities.

Number range CHAPTERBifenthrin is a neural toxic insecticide acting
through direct contact and ingestion, having a slight repellent effect.
The primary biological effects of bifenthrin and other pyrethroids on
insects and vertebrates reflect an inhibition of the correct firing of
neurotransmitter deliver signals from one cell to another via nerve
membrane inhibition of the voltage-gated Ca^2+^ channels coupled with a
stimulatory effect on the voltage-gated Na^+^ channels (sodium ion
channels). All pyrethroids act as axonic poisons, affecting both the
peripheral and central nervous systems, and share similar modes of
action. Pyrethroids, including bifenthrin, stimulate repetitive action
in the nervous system by binding to voltage-gated sodium channels,
prolonging the sodium ion permeability during the excitatory phase of
the action potential. This action leads to spontaneous depolarizations,
augmented neurotransmitter secretion rate and neuromuscular block, which
ultimately results in paralysis of the insect.

This is a Tier I screening assessment using Tier 1 aquatic models
SCI-GROW and FIRST, and maximum application rates for bifenthrin, with
minimum application intervals. It was found that the worse case scenario
was lettuce for bifenthrin, with the highest application rate, and the
highest PCA. There are no major degradates for bifenthrin; therefore, no
degradates were modeled in this assessment. The major uncertainty with
respect to this assessment appears to be the problem with the extremely
low solubility of bifenthrin. The hydrolysis, aqueous photolysis and
batch equilibrium studies were performed in the presence of unusually
high concentrations of acetonitrile.

The proposed uses involved in this action are the following IR4
tolerance petitions: leafy brassica greens, tuberous and corm
vegetables, dried shelled peas and beans, cilantro and okra, and an
application to amend the label to include tobacco (refer to highlighted
section of Table 2).

**Table 1. Maximum Tier I Estimated Drinking Water Concentrations
(EDWCs) for drinking water risk assessment based on aerial application
of bifenthrin on lettuce**.

  ------------------- -------------------- --------------- ---------------
  **DRINKING WATER    **USE (rate          **MAXIMUM       
  SOURCE (MODEL       modeled)**           ESTIMATED       
  USED)**                                  DRINKING WATER  
                                           CONCENTRATION   
                                           (EDWC) ( ppb)** 

  Groundwater         Lettuce (0.5 lb.     Acute and       0.00300
  (SCI-GROW)          a.i./A/season)       Chronic         

  Surface water       Lettuce (0.5 lb.     Acute           0.0140
  (FIRST)             a.i./A/season)                       

                      Lettuce (0.5 lb.     Chronic         0.0140
                      a.i./A/season)                       
  ------------------- -------------------- --------------- ---------------

**[PROBLEM FORMULATION]{.underline}**

*This is a Tier I drinking water assessment that uses modeling and
available monitoring data to estimate the groundwater and surface water
concentrations in drinking water source water (pre-treatment) resulting
from pesticide use on sites that are highly vulnerable. This initial
tier screens out chemicals with low potential risk* *and allows OPP to
focus resources on more refined risk assessments for chemicals which
potentially present more significant risks. This drinking water
assessment will report potential exposure concentrations for the human
health dietary risk assessment and provide a clear and transparent
description of how those concentrations were determined.*

**[ANALYSIS]{.underline}**

**Use Characterization**

Table 2 is a summary of all agricultural use patterns for bifenthrin.
The highlighted uses are those proposed new ones. The use information
was obtained from the current label for Capture 2EC Insecticide/Miticide
and the proposed labels for the same product.

**Number range CHAPTERTable 2. Summary use information for bifenthrin,
based on Capture 2EC Insecticide/Miticide label (EPA Reg. No.
279-3069)**

  ---------------------------------------------------------------------------------------------------------
  **USE**       **SINGLE APP. **NUMBER OF **SEASONAL   **INTERVAL   **APP.      **INCORPORATION   **PHI**
                RATE (lbs.    APPS.**     APP. RATE    BETWEEN      METHOD**    DEPTH (inches)**  
                a.i./A)**                 (lbs.        APPS.                                      
                                          a.i./A)**    (days)**                                   
  ------------- ------------- ----------- ------------ ------------ ----------- ----------------- ---------
  Cotton        0.1           5           0.5          3            Ground or   0                 14
                                                                    aerial                        

  Corn          0.1           3           0.3          As necessary Ground or   0                 30
                                                                    aerial                        

  Sweet corn    0.1           2           0.2          As necessary Ground or   0                 1
                                                                    aerial                        

  Succulent     0.1           2           0.2          Not          Ground or   0                 3
  peas and                                             specified    aerial                        
  beans                                                                                           

  Brassicas     0.1           5           0.5          7            Ground or   0                 7
                                                                    aerial                        

  Canola,       0.04          2           0.08         14           Ground or   0                 35
  Crambe,                                                           aerial                        
  Rapeseed                                                                                        

  Cucurbits     0.1           3           0.3          7            Ground or   0                 3
                                                                    aerial                        

  Eggplant      0.1           2           0.2          7            Ground or   0                 7
                                                                    aerial                        

  Lettuce, head 0.1           5           0.5          7            Ground or   0                 7
                                                                    aerial                        

  Caneberries   0.1           2           0.2          One          Ground or   0                 3
                                                       pre-bloom    aerial                        
                                                       and one                                    
                                                       post-bloom                                 

  Artichoke     0.1           Not                      15           Ground or   0                 5
                              specified                             aerial                        

  Peppers       0.1           2           0.2          7            Ground or   0                 7
                                                                    aerial                        

  Hops          0.1           3           0.3          21           Ground or   0                 14
                                                                    aerial                        

  Pears         0.2           3           0.5          30           Ground or   0                 14
                                                                    aerial                        

  Citrus        0.25          2           0.5          Early and    Ground      0                 1
                                                       late season                                

  Tomatoes      0.08          4           0.32         10           Ground      0                 1

  Spinach       0.1           4           0.4          7            Ground or   0                 40
                                                                    aerial                        

  Grapes        0.1           1           0.1          N/A          Ground or   0                 30
                                                                    aerial                        

  Leafy         0.1           4           0.4          7            Ground or   0                 7
  Brassica                                                          aerial                        
  Greens                                                                                          

  Tuberous and  0.3 in furrow 3           0.5          21           Foliar      0                 21
  corm          at planting                                         treatment                     
  vegetables    and 0.1                                             not                           
                foliar                                              specified                     

  Dried shelled 0.1           2           0.2          Not          Ground or   0                 14
  peas                                                 specified    aerial                        

  Dried shelled 0.1           3           0.3          Not          Ground or   0                 14
  beans                                                specified    aerial                        

  Tobacco       0.1 at        Not                                               0                 N/A
                transplant,   specified                                                           
                and 0.05                                                                          
                foliar                                                                            

  Cilantro      0.1           5           0.5          7            Ground or   0                 3
  (coriander)                                                       aerial                        

  Okra          0.1           2           0.2          7            Ground or   0                 7
                                                                    aerial                        
  ---------------------------------------------------------------------------------------------------------

Capture 2EC Insecticide/Miticide is an emulsifiable concentrate. It may
be applied by ground, air or ULV methods. The label imposes certain
restrictions (buffer zones) to protect bodies of water, accordingly: 25
ft for ground applications, 150 ft for aerial applications and 450 ft
for ULV applications. There is also a granular formulation for use on
corn at plant (granules are incorporated into the top one inch of the
soil) or foliar (as granules).

The use pattern selected for drinking water modeling was lettuce. It has
the maximum application rate (maximum number of applications) with the
maximum PCA.

**Fate and Transport Characterization**

Table 3 provides a summary of the major physical, chemical,
environmental fate and transport properties of bifenthrin.

**Number range CHAPTERTable 3. Summary of physical/chemical and
environmental fate and transport properties of bifenthrin**.

+-------------------+-------------------+------------+---------------+
| **PARAMETER**     | **VALUE(S)        | **SOURCE** | **COMMENT**   |
|                   | (units)**         |            |               |
+===================+===================+============+===============+
| Chemical Name     | 2-methylbi        | --         | IUPAC name    |
|                   | phenyl-3-ylmethyl |            |               |
|                   | (*Z*)-(1*R        |            |               |
|                   | S*,3*RS*)-3-(2-ch |            |               |
|                   | loro-3,3,3-triflu |            |               |
|                   | oroprop-1-enyl)-2 |            |               |
|                   | ,2-dimethylcyclop |            |               |
|                   | ropanecarboxylate |            |               |
+-------------------+-------------------+------------+---------------+
| Molecular Weight  | 422.87 g/mol      | --         | --            |
+-------------------+-------------------+------------+---------------+
| Solubility (22    | 1.4x10^-5^ mg/L   | Laskowski  | --            |
| ^o^C)             |                   | 2002       |               |
+-------------------+-------------------+------------+---------------+
| Vapor Pressure    | 1.8 x 10^-7^ mmHg | Tomlin, C. | --            |
| (25 ^o^C)         |                   | editor     |               |
|                   |                   | 1994.      |               |
+-------------------+-------------------+------------+---------------+
| Henry's Law       | 7.2 x 10^-3^      | \- -       | Estimated     |
| constant          | Atm-m^3^/mol      |            | from vapor    |
|                   |                   |            | pressure and  |
|                   |                   |            | water         |
|                   |                   |            | solubility.   |
+-------------------+-------------------+------------+---------------+
| pKa (20 ^o^C)     | NA                | \- -       | --            |
+-------------------+-------------------+------------+---------------+
| Octanol-Water     | 3.00x10^6^        | Laskowski  | --            |
| Partition         |                   | 2002       |               |
| Coefficient       |                   |            |               |
|                   |                   |            |               |
| (K~OW~)           |                   |            |               |
+-------------------+-------------------+------------+---------------+
| Hydrolysis        | Stable            | ACC:       | Stable at all |
| Half-life         |                   | 251728,    | pHs.          |
|                   |                   | MRID:      |               |
| \[pH 5, 7, 9; (25 |                   | 132539.    |               |
| ^o^C)\]           |                   |            |               |
+-------------------+-------------------+------------+---------------+
| Aqueous           | Relatively stable | ACC:       | Samples were  |
| Photolysis        |                   | 264642.    | not buffered  |
| Half-life         |                   |            | and contained |
|                   |                   |            | 30%           |
|                   |                   |            | acetonitrile  |
|                   |                   |            | as cosolvent. |
|                   |                   |            | Natural       |
|                   |                   |            | sunlight was  |
|                   |                   |            | used.         |
+-------------------+-------------------+------------+---------------+
| Soil Photolysis   | t~1/2~ = 147 days | ACC:       | Natural       |
| Half-life         | and 98.5 days for | 264642.    | sunlight in   |
|                   | cyclopropyl and   |            | New Jersey,   |
|                   | phenyl labels,    |            | silt loam     |
|                   | respectively.     |            | soil used.    |
|                   |                   |            |               |
|                   | Corrected         |            |               |
|                   | half-lives are    |            |               |
|                   | 147 days and 106  |            |               |
|                   | days (no          |            |               |
|                   | significant       |            |               |
|                   | degradation in    |            |               |
|                   | dark control for  |            |               |
|                   | cyclopropyl       |            |               |
|                   | label)            |            |               |
+-------------------+-------------------+------------+---------------+
| Aerobic Soil      | [Soil Cyclopropyl | MRID:      | \- -          |
| Metabolism        | Ph                | 141202,    |               |
| Half-life         | enyl]{.underline} | 254411,    |               |
|                   |                   | 532540,    |               |
| (days)            | SL 132 115        | 251728,    |               |
|                   |                   | 254401,    |               |
|                   | SiL 250 156       | 073225,    |               |
|                   |                   | 073174,    |               |
|                   | SiCL 129 96.8     | 251278.    |               |
+-------------------+-------------------+------------+---------------+
| Anaerobic Soil    | Stable            | MRID:      | \- -          |
| Metabolism        |                   | 264642     |               |
+-------------------+-------------------+------------+---------------+
| Anaerobic Aquatic | NA                | \- -       | --            |
| Metabolism        |                   |            |               |
|                   |                   |            |               |
| Half-life         |                   |            |               |
+-------------------+-------------------+------------+---------------+
| Aerobic Aquatic   | NA                | \- -       | \- -          |
| Metabolism        |                   |            |               |
|                   |                   |            |               |
| Half-life         |                   |            |               |
+-------------------+-------------------+------------+---------------+
| Organic Carbon    | 131,000, 239,000, | MRID:      | --            |
| Partition         | 302,000, 275,000  | 254401.    |               |
|                   | mL/g~OC~ for the  |            |               |
| Coefficient       | S, SL, SiL and    |            |               |
| (K~OC~)           | SiCL,             |            |               |
|                   | respectively      |            |               |
+-------------------+-------------------+------------+---------------+
| Soil Partition    | 992, 4192, 5430,  | MRID:      | --            |
| Coefficient       | 3690 mL/g         | 254401.    |               |
| (K~d~)            |                   |            |               |
|                   | for the S, SL,    |            |               |
|                   | SiL and SiCL,     |            |               |
|                   | respectively      |            |               |
+-------------------+-------------------+------------+---------------+
| Terrestrial Field | [Site             | MRID:      | \- -          |
| Dissipation       | Half-l            | 264642,    |               |
|                   | ives]{.underline} | 42339203,  |               |
| Half-life         |                   | 42339201,  |               |
|                   | Champaign, IL 192 | 42334167,  |               |
|                   | days              | 41673103,  |               |
|                   |                   | 41673101,  |               |
|                   | Fresco, CA 345    | 41671302.  |               |
|                   |                   |            |               |
|                   | Madera, CA 155    |            |               |
|                   |                   |            |               |
|                   | Imperial County,  |            |               |
|                   | CA 228            |            |               |
|                   |                   |            |               |
|                   | Tifton, GA 122    |            |               |
|                   |                   |            |               |
|                   | Marion, AR 78     |            |               |
|                   |                   |            |               |
|                   | Fresno, CA 193    |            |               |
|                   |                   |            |               |
|                   | Champaign, IL 118 |            |               |
|                   |                   |            |               |
|                   | Champaign, IL 126 |            |               |
|                   |                   |            |               |
|                   | Marion, AR 121    |            |               |
|                   |                   |            |               |
|                   | San Joaquin,      |            |               |
|                   | Fresno DT~50~ 35  |            |               |
+-------------------+-------------------+------------+---------------+
| Aquatic Field     | Dallas County,    | MRID:      | \- -          |
| Dissipation       | Orville, Alabama  | 40981803,  |               |
|                   |                   | 40981805,  |               |
| Half-life         | Residues of       | 40981808,  |               |
|                   | bifenthrin were   | 40981812,  |               |
|                   | found in the      | 40981814,  |               |
|                   | sediments of the  | 40981815,  |               |
|                   | pond during the   | 40981816,  |               |
|                   | 12 months period  | 40981817,  |               |
|                   | after             | 40981818,  |               |
|                   | application;      | 40981819.  |               |
|                   | there was no      |            |               |
|                   | discernable       |            |               |
|                   | pattern of decay. |            |               |
+-------------------+-------------------+------------+---------------+

Number range CHAPTERBifenthrin is a synthetic pyrethroid. Its structure
has three rings, two phenyl rings attached to each other by a single
bond, and a cyclopropyl ring. The molecule has some chiral centers, and
a double bond that bring isomer possibilities. According to the Capture
2EC Insecticide/Miticide label, a minimum of 97% consists of cis isomers
(see figure in the Appendix).

Studies conducted on bifenthrin indicate that it is persistent under
most conditions and bioaccumulative. It appears that a major route of
degradation is aerobic metabolism. Bifenthrin is relatively stable to
hydrolysis at all pH's. It is relatively stable to aqueous and soil
photolysis and degrades slowly under both aerobic and anaerobic soil
metabolism conditions (half-life range 97-250 days in 3 soils, and
relatively stable, respectively). Bifenthrin is relatively immobile in
four soils tested (K~OC~ range 131,000 to 275,000). Field studies show a
pattern consistent with the laboratory studies, with relatively high
persistence (half-lives ranging from 78 to 345 days in 10 field trials)
and low mobility of the chemical in soil. In aquatic environments, it
appears that residues of bifenthrin persist in pond sediments (and in
the water column) for extended periods (at least 12 months of
monitoring). No major metabolites were observed (\>10% of the applied)
in any of the laboratory studies. The high octanol/ water partition
coefficient suggests that bifenthrin will bioconcentrate in aquatic
organisms. Bifenthrin was highly bioaccumulative in fish with slow
depuration. The very low water solubility and hydrophobic nature of
bifenthrin leads to strong soil adsorption and a tendency to partition
to sediment in aquatic systems.

Bifenthrin has a vapor pressure of 1.8x10^--7^ mmHg, water solubility of
0.0140 ppb, and an estimated Henry's law constant of 7.2x10^-3^
atm-m^3^/mol. Based upon its Henry's law constant and vapor pressure,
bifenthrin is expected to have a moderate to low potential for
volatilization from soil and water surfaces. Bifenthrin's potential for
volatilization is reduced significantly because it adsorbs strongly to
soils, suspended solids, sediment and organic matter in the water
column. A laboratory volatility study showed a maximum volatility at
40°C of 5.07x10^-4^ μg/cm^2^ hr (average at 14 days), a relatively low
value.

Bifenthrin can be spray applied by ground or aerially on agricultural
settings. A buffer region is label recommended; however, under a high
end drift scenario, substantial amounts of the chemical can reach
adjacent bodies of water via spray drift. Furthermore, substantial
fractions of the applied bifenthrin should be available for runoff for
several weeks to several months. Due to its low solubility (0.014 ppb)
and high level of binding it appears that bifenthrin would remain bound
to the soils during run-off events, and that the chemical would reach
surface waters if the run-off event is accompanied by erosion. Once
bifenthrin reaches surface water, the fate of the chemical is of concern
since bifenthrin is very toxic to fish and aquatic invertebrates. The
Agency believes that bifenthrin, due to its high level of binding, would
remain bound to the sediments and would dissolve only very slowly into
the water column. Organisms that live near the sediments may be
particularly at risk. The sediments may serve as reservoirs of
bifenthrin, where it will persist.

A supplemental aquatic field dissipation study employing a site in
Alabama showed that bifenthrin in aquatic environments (a pond) persists
for extended periods of time. It was found throughout the 12 months of
monitoring after the last pesticide application, that residues were
observed in the water column and in the sediment, with no clear pattern
of decline.

On the other hand, bifenthrin is not likely to reach subsurface soil
environments or ground waters. Various terrestrial field dissipation
studies confirm that bifenthrin remains mostly in the upper soil level.

Due to the slow dissipation pathways for bifenthrin, no transformation
products were observed to be higher than 10% of the applied in any of
the laboratory studies.

The major uncertainties with respect to the environmental fate studies
on bifenthrin are related to the extremely low solubility of bifenthrin
and the problems found when the registrant performed these studies. The
hydrolysis, aqueous photolysis, and batch equilibrium studies were
performed in unusually high concentrations of acetonitrile. The
cosolvent may have had an effect on the results. Furthermore, the batch
equilibrium studies were performed at a single concentration (a
Freundlich isotherm was not developed). The EFED had to rely on a single
point result.

Table 4 is a summary of degradate formation for bifenthrin. Note that,
because bifenthrin is relatively stable or dissipates very slowly in all
studies, no major transformation products (≥10% of the applied) were
observed.

[]{.mark}

**Table 4. Summary of degradate formation from degradation of
bifenthrin**.

  -----------------------------------------------------------------------------
  **STUDY TYPE**    **SOURCE**   **DEGRADATE and                  
                                 MAXIMUM                          
                                 CONCENTRATION**                  
  ----------------- ------------ ------------------ ------------- -------------
                                 **DEG1 (%          **DEG2 (%     **DEG3 (%
                                 applied)**         applied)**    applied)**

  Hydrolysis        ACC: 251728, NO hydrolysis                    
                    MRID:        product exceeded                 
                    132539.      10% of the applied               
                                 during the study.                

  Aqueous           ACC: 264642. NO aqueous                       
  Photolysis                     photolysis product               
                                 exceeded 10% of                  
                                 the applied during               
                                 the study.                       

  Soil Photolysis   ACC:         NO soil photolysis               
                    264642..     product exceeded                 
                                 10% of the applied               
                                 during the study.                

  Aerobic Soil      MRID:        NO aerobic soil                  
  Metabolism        141202,      metabolism product               
                    254411,      exceeded 10% of                  
                    532540,      the applied during               
                    251728,      the study.                       
                    254401,                                       
                    073225,                                       
                    073174,                                       
                    251278.                                       

  Anaerobic Soil    . MRID:      NO anaerobic soil                
  Metabolism        264642       metabolism product               
                                 exceeded 10% of                  
                                 the applied during               
                                 the study.                       

  Aerobic Aquatic   .NA          \- -                             
  Metabolism                                                      

  Anaerobic Aquatic NA           \- -                             
  Metabolism                                                      

  Terrestrial Field MRID:        4'-OH-Bifenthrin                 
  Dissipation       40981803,    detected in                      
                    40981805,    certain studies.                 
                    40981808,                                     
                    40981812,                                     
                    40981814,                                     
                    40981815,                                     
                    40981816,                                     
                    40981817,                                     
                    40981818,                                     
                    40981819.                                     
  -----------------------------------------------------------------------------

No degradates were considered "major" ([\>]{.underline}10% of applied in
parent equivalents), nor were they flagged for further quantitation.
There is uncertainty with respect to the aqueous photolysis study, which
was conducted in the presence of 30% acetonitrile. Even though no
substantial photolysis was observed, it is not known if the cosolvent
may have affected the formation of transformation products.

**Drinking Water Exposure Modeling**

Models

SCI-GROW (Screening Concentration in Ground Water) is a regression model
used as a screening tool for ground water used as drinking water.
SCI-GROW was developed by regressing the results of Prospective Ground
Water studies against the Relative Index of Leaching Potential (RILP).
The RILP is a function of aerobic soil metabolism and the soil-water
partition coefficient. The output of SCI-GROW represents the
concentrations that might be expected in shallow unconfined aquifers
under sandy soils, which is representative of the ground water most
vulnerable to pesticide contamination likely to serve as a drinking
water source. (**Ref. 2**)

FIRST (FQPA Index Reservoir Screening Tool) is a screening model
designed by the Environmental Fate and Effects Division (EFED, 2001a) of
the Office of Pesticide Programs to estimate the concentrations found in
drinking water from surface water sources for use in human health risk
assessment. As such, it provides upper bound values on the
concentrations that might be found in drinking water due to the use of a
pesticide. FIRST is a single event model (one runoff event), but can
account for spray drift from multiple applications. Spray drift
(resulting in direct deposition of the pesticide into the reservoir) is
assumed to be 16% of the applied active ingredient for aerial
application, 6.3% for orchard air blast application, and 6.4% for other
ground spray application. FIRST is hardwired to represent the Index
Reservoir, a standard water body used by the Office of Pesticide
Programs to assess drinking water exposure (Office of Pesticide
Programs, 2002). It is based on a real reservoir (albeit not currently
in active use as a drinking water supply), Shipman City Lake in
Illinois, that is known to be vulnerable to pesticide contamination. The
single runoff event moves a maximum of 8% of the applied pesticide into
the reservoir. This amount can be reduced due to degradation on the
field and the effects of binding to soil in the field. FIRST also uses a
Percent Cropped Area (PCA) factor to adjust for the area within the
watershed that is planted to the modeled crop. The default agricultural
PCA is 0.87. (**Ref. 3 and 4**)

For volatile and semi-volatile compounds, Tier I modeling will tend to
over-estimate EDWCs because there are no parameters in SCI-GROW and
FIRST that explicitly take into account volatility (ie., no vapor
pressure input). Therefore, in reality, more of the compound will be
volatilizing than Tier I can account for. If drinking water levels of
concern are exceeded for over-estimated Tier I EDWCs, Tier II modeling
will be able to refine these EDWCs by including volatility
considerations.

*Modeling Approach and Input Parameters*

Table 5 provides the input parameter values used for modeling of
bifenthrin using SCI-GROW. Table 6 provides the input parameter values
used for modeling of bifenthrin using FIRST. As indicated earlier, no
degradates were included in the modeling because none exceded 10% of the
applied in the laboratory studies.

**Table 5. SCI-GROW (v2.3) input parameter values for bifenthrin use on
lettuce^1^**.

  -------------------------------------------------------------------------------
  **PARAMETER (units)**  **VALUE(S)**   **SOURCE**   **COMMENT**
  ---------------------- -------------- ------------ ----------------------------
  Maximum Application    0.1            Label.       --
  Rate (lb a.i./A)                                   

  Number of Applications 5              Label.       Represents most-conservative
  per Year                                           scenario in which the total
                                                     maximum rate per year is
                                                     applied in one application.

  Organic Carbon         257,000        MRID:        Represents the median value
  Partition Coefficient                 254401.      of four values ranging from
  (K~oc~; mL/g)                                      131,000 to 302,000 mL/g for
                                                     the parent compound.

  Aerobic Soil           130.5          MRID:        Represents the median
  Metabolism Half-life                  141202,      half-life of six values
  (days)                                254411,      available (132, 250, 129,
                                        532540,      115, 156, 96.8 days).
                                        251728,      
                                        254401,      
                                        073225,      
                                        073174,      
                                        251278.      
  -------------------------------------------------------------------------------

**^1^** Parameters are selected as per Guidance for Selecting Input
Parameters in Modeling the Environmental Fate and Transport of
Pesticides; Version I, February 28, 2002.

Number range CHAPTER**Table 6. FIRST (v1.0) input parameter values for
bifenthrin use on lettuce^1^.**

  -------------------------------------------------------------------------------
  **PARAMETER (units)**  **VALUE(S)**   **SOURCE**   **COMMENT**
  ---------------------- -------------- ------------ ----------------------------
  Application Rate (lb   0.1\`          Label.       --
  a.i./A)                                            

  Number of Applications 5              Label.       \- -

  Interval between       3              Label.       \- -
  Applications (days)                                

  Percent Cropped Area   0.87           \- -         National default.
  (decimal)                                          

  Soil Partition         275,000        MRID:        Represents the lowest
  Coefficient (K~d~;                    254401.      non-sand K~OC~ value among
  (mL/g) or K~OC~                                    four values ranging from
  (mL/g~OC~))                                        131,000 to 302,000 mL/g; the
                                                     K~OC~ model was utilized as
                                                     per recommendation of the
                                                     SAP..

  Aerobic Soil           176.4          MRID:        Represents the 90^th^
  Metabolism Half-life                  141202,      percentile of the upper
  (days)                                254411,      confidence bound on the mean
                                        532540,      of six half-life values:
                                        251728,      132, 250, 129, 115, 156,
                                        254401,      96.8 days; mean = 146.5
                                        073225,      days; std. dev.= 49.6 days
                                        073174,      
                                        251278.      

  Wetted in?             No             Label.       --

  Depth of Incorporation 0              Label.       --
  (inches)                                           

  Method of Application  Aerial spray   Label.       --

  Solubility in Water @  0.000014       Laskowski    --
  22 ^O^C, unbuffered                   2002         
  (mg/L or ppm)                                      

  Aerobic Aquatic        352.8          MRID:        No aerobic aquatic
  Metabolism Half-life                  141202,      metabolism data are
  (days)                                254411,      available and the pesticide
                                        532540,      is hydrolytically stable, 2X
                                        251728,      the aerobic soil metabolism
                                        254401,      half-life input value is
                                        073225,      used.
                                        073174,      
                                        251278.      

  Hydrolysis Half-life @ 0              ACC: 251728, Stable.
  pH 7 (days)                           MRID: 132539 

  Aquatic Photolysis     0              ACC: 264642  --
  Half-life @ pH 7                                   
  (days)                                             
  -------------------------------------------------------------------------------

**^1^** Parameters are selected as per Guidance for Selecting Input
Parameters in Modeling the Environmental Fate and Transport of
Pesticides; Version I, February 28, 2002

*Modeling Results*

**Table 7. Maximum Tier I Estimated Drinking Water Concentrations
(EDWCs) for drinking water risk assessment based on aerial application
of bifenthrin**.

  ------------------- -------------------- --------------- ---------------
  **DRINKING WATER    **USE (rate          **MAXIMUM       
  SOURCE (MODEL       modeled)**           ESTIMATED       
  USED)**                                  DRINKING WATER  
                                           CONCENTRATION   
                                           (EDWC) ( ppb)** 

  Groundwater         Lettuce (0.5 lb      Acute and       0.0140
  (SCI-GROW)          a.i./A/season)       Chronic         

  Surface water       Lettuce (0.5 lb      Acute           0.0140
  (FIRST)             a.i./A/season)                       

                      Lettuce (0.5 lb      Chronic         0.00300
                      a.i./A/season)                       
  ------------------- -------------------- --------------- ---------------

*SCI-GROW concentration (ppb) represents the groundwater concentration
that might be expected in shallow unconfined aquifers under sandy soils.
Output is used for both acute and chronic endpoints.*

*FIRST concentrations (ppb) represent untreated surface water
concentrations.*

*The peak day concentration (over 30 years) is used for acute endpoints
and the annual average concentration (over 30 years) is used for chronic
endpoints.*

*The estimated concentrations provided in this assessment are
conservative estimates of concentrations in drinking water. If dietary
risks require refinement, higher tiered crop-specific and
location-specific models and modeling scenarios can be utilized.*

**Monitoring Data**

*Monitoring data usually provide different kinds of information than
modeling (e.g., monitoring reflects current use pattern, underestimates
frequency of occurrence, often misses peaks, inputs cannot be adjusted
as modeled ones can, usually done for purposes other than characterizing
exposure from a particular pesticide), and, consequently, tend to
complement the modeling rather than refine it. In general, a useful
interpretation of monitoring values requires in-depth assessment of the
data, which is beyond the scope of a Tier I assessment.*

**Drinking Water Treatment**

It is likely that primary treatment may reduce the levels of
cypermethrin due to its tendency to bind. However, there is no
information available at this time to determine the levels of reduction
(***Ref. 7***).

**[CONCLUSIONS]{.underline}**

The following can be concluded about bifenthrin:

-   This is a Tier I level analysis, refinements may be available should
    they be needed. The acute levels of surface drinking waters was
    0.0140 ppb, the chronic level of drinking waters was 0.0140 ppb of
    bifenthrin. The groundwater concentration of cypermethrin, suitable
    for acute and chronic is 0.000300 ppb. All the concentrations were
    limited by the solubility limit of bifenthrin. It was assumed that
    the maximum application rate was used on lettuce, with the minimum
    interval between applications. The major uncertainty is presence of
    acetonitrile in several of the laboratory experiments. Furthermore,
    the batch equilibrium constants were obtained at only one
    concentration (no Freundlich isotherms).

-   Despite the weaknesses of the data, this is considered a
    conservative (screening level) analysis.

APPENDIX

SCI-GROW and FIRST model output files.

RUN No. 1 FOR Bifenthrin ON Lettuce \* INPUT VALUES \*

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

ONE(MULT) INTERVAL Koc (PPTr) (%DRIFT) AREA (IN)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

.100( .474) 5 7 275000.0 14.0 AERIAL(16.0) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

(FIELD) RAIN/RUNOFF (RESERVOIR) (RES.-EFF) (RESER.) (RESER.)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

176.40 2 N/A .00- .00 352.80 352.80

UNTREATED WATER CONC (NANOGRAMS/LITER (PPTr)) Ver 1.0 AUG 1, 2001

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC)

CONCENTRATION CONCENTRATION

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

14.000 14.000

SCIGROW

VERSION 2.3

ENVIRONMENTAL FATE AND EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL

FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3

chemical:Bifenthrin

time is 1/18/2006 10:23:25

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Application Number of Total Use Koc Soil Aerobic

rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

0.100 5.0 0.500 2.57E+05 130.5

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

groundwater screening cond (ppb) = 3.00E-03\*

\*Estimated concentrations of chemicals with Koc values greater than
9995 ml/g

are beyond the scope of the regression data used in SCI-GROW
development.

If there are concerns for such chemicals, a higher tier groundwater
exposure

assessment should be considered, regardless of the concentration
returned

by SCI-GROW.

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Molecular structure of BIFENTHRIN.

![](media/image2.png){width="3.6354166666666665in"
height="3.8229166666666665in"}

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

**References:**

1.  Policy Establishing Current Versions of Exposure Models and
    Responsibility for Model Maintenance (11/06/2002)

2.  SCIGROW: Users Manual (11/01/2001, revised 08/23/2002)

3.  FIRST Users Manual (08/01/2001)

4.  FIRST: A Screening Model to Estimate Pesticide Concentrations in
    Drinking Water (05/01/2001)

5.  Guidance for Selecting Input Parameters in Modeling the
    Environmental Fate and Transport of Pesticides, Version II
    (02/28/2002)

6.  Number range CHAPTERUse of the Index Reservoir and Percent Crop Area
    in EFED Drinking Water Assessments (12/01/1999)

7.  The Incorporation of Water Treatment Effects on Pesticide Removal
    and Transformations in Food Quality Protection Act (FQPA) Drinking
    Water Assessments (10/25/2001)

8.  Laskowski, D.A. 2002. Rev. Environ. Contam. Toxicol. 174:49-170

9.  Tomlin, C. editor. 1994. The Pesticide Manual 10^th^ Edition.
    British Crop Protection Council and Royal Society of Chemistry, UK.