1

Conference Call with Pyrethroid Working Group on Pyrethroid Ecological Risk 

Assessment – Meeting Summary 

Thursday, June 27, 2013; 10:00 am – 12:00 pm 

Participants

Pyrethroid Work Group (PWG): 

Dick Collier (Landis International) 

Alex Porges (Landis International) 

Jeff Giddings (Compliance Services International) 

Jeffrey Wirtz (Compliance Services International) 

Dean Desmarteau (Waterborne Environmental, Inc.) 

Chris Holmes (Waterborne Environmental, Inc.) 

Gregg Hancock Waterborne Environmental, Inc.) 

Paul Hendley (Phasera, Ltd.) 

Michael Winchell (Stone Environmental, Inc.) 

Scott Jackson (BASF Corporation) 

Kevin Henry (Syngenta Crop Protection) 

Russell Jones (Bayer CropScience) 

Michael Dobbs (Bayer CropScience) 

Environmental Protection Agency (EPA or Agency): 

Environmental Fate and Effects Division

Mah Shamim 

Keith Sappington 

Michael Lowit 

James Hetrick 

Reuben Baris 

Steve Wente 

Rosanna Louie-Juzwiak 

Dana Spatz 

Jose Melendez 

Donna Judkins 

Biological and Economics Analysis Division

Jonathan Becker 

Pesticide Re-evaluation Division

Monica Wait 

Molly Clayton 

Tracy Perry 

Garland Waleko 

Laura Parsons 
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Carissa Cyran 

Patricia Parrott 

Kevin Costello 

Background

The Pyrethroid Working Group (PWG) is a group of pyrethroid technical registrants that 

represents the following 9 pyrethroid cases: bifenthrin, cyfluthrins, cypermethrin, cyahalothrins, 

deltamethrin, esfenvalerate, fenpropathrin, permethrin, and tefluthrin. The Environmental 

Protection Agency (EPA or Agency) has met several times previously with the PWG regarding 

its plans to conduct and submit probabilistic ecological risk assessments for these pyrethroids. 

Summaries of these meetings can be found in the general pyrethroid docket on 

www.regulations.gov under docket id number EPA-HQ-OPP-2008-0331. 

Presentation

The meeting began with a brief overview of the probabilistic ecological risk assessments the 

PWG plans to conduct for the 9 represented pyrethroids. 

The PWG then presented details on its plans to conduct, by December 2013, the following for 

the represented pyrethroids: 

 a review of use information on end use product labels 

 exposure modeling of synthetic pyrethroids

 a comparative sediment degradation study 

 a national scale assessment of erosion and drift potential 

 modeling of pyrethroid exposure in urban receiving waters 

 a residential use and usage survey 

 a monitoring database 

 a sensitivity analysis of the aquatic invertebrate Hyalella azteca

The meeting concluded with a brief discussion of potential future EPA-PWG interactions. 

Discussion

In previous discussions with PWG on its plans for conducting probabilistic ecological risk 

assessments (see the summary of the March 27, 2013 meeting, available in the pyrethroid 

docket), EPA explained that any significant change to EPA’s risk assessment methodology 

would need to undergo extensive peer review, and EPA must consider the timeframe allowed for 

pyrethroid risk assessments during registration review. Therefore, EPA anticipates conducting 

risk assessments for all pyrethroid active ingredients following the Agency’s standard policies 

and procedures. On June 26th, EPA reiterated that the Agency will review all data and risk 

assessments submitted by the PWG and anticipates that in particular the monitoring database and 

analysis of use information on registered product labels will be useful in informing the upcoming 

registration review risk assessments. 
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Planned PWG Submissions

Anticipated Timeline for PWG data and assessment submissions to EPA 

Item Topic Estimated 

Submission 

Dates 

1 Review of pyrethroid end use product labels September 2013 

2 Survey of professional applicators on residential uses of 

pyrethroids 

September 2013 

3 Conceptual models of pyrethroids in sediments, and comparison 

of receiving water simulation models to the conceptual models 

August 2013 

4 Determination of partition coefficients for 9 pyrethroids in natural 

and artificial sediments (laboratory report) 

December 2013 

5 Measured pyrethroid concentrations in US surface waters and 

sediments 

September 2013 

6 Tier 2 and refined agricultural exposure modeling and risk 

estimation 

December 2013 

7 Sensitivity analysis and probabilistic modeling with the SWMM 

exposure model 

December 2013 

8 National vulnerability assessment December 2013 

9 Exposure modeling for pyrethroids in flowing water December 2013 

10 High-resolution landscape-level exposure analysis for pyrethroids 

in selected watersheds 

December 2013 

11 Modeling pyrethroid runoff from urban residential areas September 2013 

12 Analysis of pyrethroid aquatic toxicity data [SSDs, acute-tochronic ratios, isomers, formulation, freshwater/saltwater, etc.] September 2013 

13 Toxicity of cypermethrin [and bifenthrin] to Hyalella azteca from 

laboratory cultures and natural populations 

August 2013 

14 Bioassessment studies December 2013 

15 Review of aquatic mesocosm studies December 2013 

16 Modeling effects of pyrethroids on aquatic invertebrate 

populations and potential indirect effects on salmon 

December 2013 

17 Nine separate higher-tier aquatic risk assessments March 2014 – 

January 2016 

Future EPA-PWG Interactions

EPA plans to meet with the PWG following the submission of the items listed above. 

The first of EPA’s preliminary risk assessments for the represented pyrethroids (deltamethrin) is 

scheduled for completion in March 2015. The last of the PRAs for the represented pyrethroids 

(tefluthrin) is scheduled for completion in January 2017. 



6/27/2013

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Conceptual Model Refinements to Support 

Exposure Modeling for Synthetic Pyrethroids 

- Implications for Data Development, Exposure 

Modeling and Toxicity Studies

Presentation to EPA EFED on June 27, 2013.

Paul Hendley (Phasera Ltd.) 

on behalf of the Pyrethroid Working Group (PWG)

Outline

 Conceptual models

 Largely covered by existing EPA conceptual models

 Some pyrethroid-specific factors require conceptual model refinement.

 Aquatic Exposure modeling

 Certain pyrethroid-specific issues are not addressed by current EXAMS model

 Resulting PWG non-spatial exposure modeling deliverables

 Model input selection

 USEPA SAP and ORNL comments

 PWG efforts to address these
6/27/2013

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Pyrethroid Reg Review Aquatic Conceptual Models

Pyrethroid Characteristics that Impact Exposure - 1

 Adsorption to organic matter is exceptional

 Remarkably high Koc – 1,000,000 – 4,000,000 L/kg (SPME)

 Only recently measurable at these extremes – early guideline studies underestimates

 Impacts partition in water bodies, uptake into organisms and bioavailability in 

presence of particulates and dissolved organic matter

 Equilibrium Partition Approach (DiToro) – i.e. bioavailable fraction drives eco-toxicology

 Runoff entry/sedimentation process algorithms critical for aquatic exposure models

 Biotic degradation is relatively rapid – ester cleavage via enzymes

 Unlike many other high Koc compounds, degraded and excreted by organisms

 Therefore limited bioaccumulation potential
6/27/2013

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Pyrethroid Characteristics that Impact Exposure - 2

 Adsorption/desorption exchange behavior is relatively rapid

 Unlike many other high Koc compounds, bound material re-equilibrates quite 

rapidly between environmental compartments and is therefore available for 

microbial degradation in soils and sediments

 Faster than expected half lives in soil & sediment

 Combined adsorption/degradation behavior results in additional 

aquatic dissipation (e.g. plant surface uptake degradation, Leistra (2003), Hand et 

al (2001) & biofilm dissipation, Allan et al (2005))

 Overall system dissipation rate is faster than expected in microcosms

 Additional degradation routes remove chemical from the system

Current PRZM-EXAMS Model & Pyrethroids

 All eroded chemical enters pond – but no sediment or runoff water 

 PRBEN% (50%) of chemical immediately perfectly mixed in top 5cm sediment

 Remaining (100-PRBEN%) enters water column - treated like spray drift entry

 Suspended solids in water column unchanged at 30 ppm despite heavily or 

lightly erosive runoff event

 No sedimentation occurs in pond with time, no overflow of sediment laden water

 No sediment deposition occurs in model, each yearly total mass of eroded 

chemical is added to the same 5 cm volume of sediment – build up possible

 Logic and study data show these are not reasonable assumptions

 Especially for eroded pyrethroids - almost exclusively sediment bound

 EPA has recognized this

 “In cases where chemicals have appreciable stability in the environment, the EXAMS 

pond model will tend to overestimate the concentration in pond sediments“ (page 54 of 

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf.)

 Dirk Young currently developing a revised SWC model based on variable volume 

pond and related concepts to tackle these (& other) potential problems
6/27/2013

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Aquatic Model algorithms important for pyrethroids 

 Variable pond water volume

 Suspended & eroded sediment deposition

 Relevance of 5 cm assumption

 Burial of Sediment chemical with deposition

 Variable suspended solids/algae concns.

 Pore water/ water column mixing

 Consideration of dissolved organic carbon

 Pore water/water column mixing factors

 Variable Plant poplns. – plant uptake factor

 Flowing water – residue exchange removal 

 Flowing water – reducing exposure duration

 Sediment bioturbation (biological mixing)

 Data to support organic matter concns.

 Sediment bulk density data to estimate pore 

water/sediment distributions

 Sediment entry improvements

 More realistic PRZM erosion scenarios – max T loss

 Incorporate VFSmod for reduction of sediment entry

 Estimation of irrigation related erosion for West USA

Factor EXAMS -

standard

EXAMS AGRO SWC* 

(VVWM)

Variable pond water volume N Y Y Y 

Suspended & eroded sediment deposition N N Y

Relevance of 5 cm assumption N

Burial of Sediment chemical with deposition N N Y Y

Variable suspended solids/algae concns. N N N N

Pore water/ water column mixing Y Y

Consideration of dissolved organic carbon Y Y Y Y

Pore water/water column mixing factors N N

Variable Plant poplns. – plant uptake factor N Y N

Flowing water – residue exchange removal N Y Y ?

Flowing water – reducing exposure duration N Y Y ?

Sediment bioturbation (biological mixing) N Y ?? ??

Data to support organic matter concns. N N N ??

Sediment bulk density data to estimate pore 

water/sediment distributions

N NN N

Sediment entry improvements N Y N Y?

Current Aquatic Receiving Water Model Capabilities

PWG Conclusion: No ideal model available, EXAMS does not address pyrethroids suitably

* SWC (VVWM) 

model still in αdevelopment 

stage - exact 

capabilities not 

yet fully defined
6/27/2013

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Selection of aquatic exposure models

 All agree that EXAMS (current version) is unsuitable

 Only SAP reviewed model that attempts to deal with some of the 

key pyrethroid–specific issues is AGRO

 Appears to meet “best available” criterion – especially for static water bodies

 SWC status – under revision due to Waterborne pyrethroid model findings

 PWG notes EPA concerns over AGRO and wishes to know more details of EPA 

plans for alternative approach for pyrethroid risk assessments.

 Recent EPA white paper review

 Sediment burial – needs to be included - long term source of contamination

 PWG agrees conceptually but believes that EXAMS/AGRO estimates of 

concentration will be maxima (due to dilution, dispersion) for epi-benthos

 Scour/re-suspension – flowing water issue – high flow events – large dilution

 Farm ponds – require digging out to make room for new events

 Model conservatism elements that should be included

 Several EPA/SAP comments on use of whole water body dissipation constants

PWG Plans for Crop Exposure Modeling

 Tier 2 modeling – due to start when label info collection completed (Sept 2013)

 PRZM-EXAMS – “Yellow Book” standard scenarios for key crops

 Inputs – available data for AI’s generally selected via US EPA approaches

 Tier 2+ modeling – due to start when label info collection completed (Sept 2013)

 AGRO (depends on SWC (VVWM) status/capabilities) with standard scenarios for key crops

 Corresponding AGRO (or SWC) pyrethroid specific input parameter sensitivity analysis

 CA lettuce (drift driven) and MS cotton scenarios (drift/runoff) as baselines

 Inputs – best available chemical inputs for racemic AI’s and refined scenario inputs 

 full list can be supplied

 Additional Modeling efforts

 Uncertainty analyses – examine assumptions & key factors not covered by current models

 Wind speed/direction probability analyses for key pyrethroid SAMSON locations

 Comprehensive probabilistic exposure assessment covering most sensitive variables

 Flowing water modeling to account for sediment transport/runoff & drift exposure durations

 Others: e.g. Comparison with monitoring data exemplifying other dissipation routes

 Spatial - National Scale Erosion and Drift Potential

 Spatial - High Resolution Modeling of higher exposure potential watersheds
6/27/2013

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Non-Spatial PWG Crop Modeling Deliverables

 Tier 2 

 Use label info, input data info, model files, AI comparative tables, report covering key crops and all 

AI’s

 Tier 2+ 

 Sensitivity study data and report

 Literature support, conceptual models, assumptions, input info, model files, AI comparisons, verification data, 

report covering key crops and AI’s

 Additional Modeling

 Details of approaches to Pyrethroid flowing water modeling examining probabilities of exposure 

duration 

 Assumptions, input/output data and report

 National hourly wind speed/direction probability assessment for all SAMSON stations

 Database and examples of application for drift probability assessment 

 Broader Probabilistic exposure assessment covering full set of sensitive variables

 Assumptions, input/output data and report

 Uncertainty analyses covering additional variables not accounted for in existing models

 Report and supporting literature/data

Model inputs – Koc and Sediment Degradation Rates

 Current data highly inhomogeneous

 Wide range of soils/sediments/ methods/ LOD’s/ lab capabilities

 Multiple data for individual products across time. Isomer issue

 Laskowski data selection–study quality based –differs from EPA current methods

 For sediment exposure potential modeling and assessing bioavailable fraction this 

makes AI-to-AI comparison difficult

 ORNL..little information on the desorption kinetics of the pyrethroids. ... lack of studies to 

define pyrethroid desorption kinetics with ..e.g., soil type, organic carbon (OC) content, pore 

water content.. however, a careful review of all existing data on soil-water partition 

coefficients for the pyrethroids is warranted. If this data review does not provide sufficient 

confidence in the use of current Koc Kow and Kd’s, a series of adsorption and desorption studies 

for the pyrethroids (other than cypermethrin) and in particular their degradates would reduce 

uncertainties associated with partition coefficients. It is suggested the studies be 

conducted by one laboratory thus generating a standard basis for comparison of the 

pyrethroids. 

 SAP. Careful examination of the Kow, Koc, and water solubility relationships should 

provide the necessary basis to determine whether the physical property data base is 

acceptable and the potential for using carbon normalization.
6/27/2013

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Koc Values in Tier 2/Tier 2+

Bifenthrin Cyfluthrin Cypermethrin

DeltamethrinEsfenvalerateFenpropathrin Lambda-Cyhalothrin Permethrin Tefluthrin

Henry’s Law Constant,

atm-m3/mole 7.2e-3 3.7e-6 3.4e-7 3.1e-7 1.4e-7 6.2e-7 1.9e-7 1.4e-6 5.2e-4 k

Soil Koc, mL/g

131000, 239000, 302000

275000a

Mean: 236750

124000, 180300, 

118000, 73500b

Mean: 123950

141,700-

mean value 

used in TII 

EDWCi

392000, 577000, 204000, 

460000c

Mean: 408250

85700, 

140000, 

141700, 

171700, 

375000, 

596200d

Mean: 

251717

23300, 

51100, 

22100, 

46200, 

29300

Mean:

34400

346000, 200000, 298000, 

724000, 209000, 270000, 

305000, 352000, 518000, 

110000f

Mean: 333200

60,900, 20, 900,

19,300, 20,500

25,500g

Mean:

29420

Range (158,000 to 

332,000)k 

Mean:

211,000k

Laskowski Koc 237000 124000 310000 704000 42500 326000 277000

LogKow 6.4a 5.97b 6.6n 6.4r 5.62d 6.00e 7.00 (gamma = 4.9)f 6.10g 6.50m

Soil photolysis T1⁄2, 

days

(see notes below)

Corrected (net 

photodegradation) halflives=147, 106; Mean = 

126.5a

5.6 b 55 q Stablec Stabled Stablee Stablef 106g Stable

Aqueous photolysis 

T1⁄2, days

Relatively Stablea

New study requested

4.5 (linear)

0.7 (nonlinear)b

Max: 4.5

36.2-used 

in TII 

EDWCi

2 labels: 64, 84 c

Mean: 74

6 (SSisomer)d Stablee

29.5, 36.9f

Mean=33.2

(value uncertain due to test 

subs. solubility)

80g Stablek

Aerobic soil T1/2, days

Mean + CL

Mean Values Based 

on 2 labels:

SL: 123.5, 

SiL: 203.0, 

SiClL: 112.9a

Mean+t90=200.2

73.5, 94.8b

Mean+t90= 116.9

Mean+t90= 

62 days 

used in TII 

EDWCi

Mean values by soil: 

SL (0.02 lb/A): 53.6, 

SL (0.20 lb/A): 52.6

SiL (0.02 lb/A):48.2, SiL 

(0.20 lb/A): 49.1,

Dubbs fine SL: 22.2, 

Alkaline AZ SL: 24.0c

Mean+t90=50.4

75d (SSisomer)

3xHL =225

152e

3xHL =456

(additional 

values in 

RED)

46.2, 31, 55, 26, 102, 12.2, 

14.5f

Mean+t90 = 57.9

3 x 37g (single value) =111

21.79, 22.95, 

17.37,

49.9 & 75.3k

Mean+t90 = 53.8

Laskowski Aerobic

Laskowki Anaerobic

96.3

425

11.5

33.6

27.6

55

24.2

28.9

38.6

90.4

22.3

276

42.6

???

39.5

197

Anaerobic soil T1/2, 

days

Mean + CL

Aerobic soil T1/2 x 2

Slow metabolism observed: 

75-79% of recovered was 

bifenthrin at 61 daysa

New study requested

30b

3xHL=90 NA

2 studies w/2 labels: 

Alk. SL: mean = 34; 

SL: mean = 44.8c

Mean+t90= 56.0

77 (SSisomer)d

186e

3xHL =558

107f

3xHL =321 204g >30 days

Bayer Sed – Aerobic

Bayer Sed- Anaerobic 100, >200, 100

>200,115, 106

4,15,4

26,24,22

4,18,5

35,28,27

12, 45, 14

100,68,60

19, 50,26

94,73,67

9, 63, 9

85,114,95

26, 60, 17,

84, 93, 62

3, 53, 3,

101, 64, 66

Comparative sediment degradation study

Very tight agreement 

between replicates.

Also a viable method 

for comparing isomer 

variant behaviors.
6/27/2013

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SPME and LLE Comparative Koc study

 One lab, nine AI’s, three sediments (same as ecotox), two methods

 Near-classic method - liquid-liquid extraction (LLE) Koc values 

 Includes chemical present adsorbed to particulates and DOC

 Solid Phase Micro Extraction (SPME) based – calculates Koc based on Free 

pyrethroid residues (i.e. bioavailable residues per EqP approach)

 Well described in literature (Jay Gan et al papers, CDPR, & others will be documented)

 As recommended by EPA SAP

 Study at 1:100 sediment:water ratio – will be repeated at higher ratio.

 Pyrethroid Koc’s extreme – methodology not easy (SAP & ORNL)

 Methodology refined and full protocol about to be signed

 Preliminary data shown

 Full reports due fall 2013

 Will be used to estimate

eco-tox endpoints

Kd LLE Koc LLE

Kd free 

SPME

Koc free 

SPME

Sediment A

#091312 Rep. 1 12804 640175 28727 1436343

#091312 Rep. 2 12728 636389 30448 1522398

#091312 Rep. 3 12690 634505 29626 1481316

PWG Model Input Data Generation Status

 PWG will submit comparative sediment degradation study to US EPA 

and use these data for risk assessment as best-available due to their 

comparative nature

 Use for all water body sediment degradation inputs

 PWG will submit comparative Koc study data (fall 2013) and will use 

these data as best available as above

 All nine AI’s, three sediments.

 LLE and SPME- based Koc results and associated supporting data

 Follow up study at Higher sediment:water concentration

 PWG is also generating a comparative Kow data set (due fall 2013)

 Will be used for input to accumulation and foodweb models (& AGRO)
6/27/2013

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Model inputs- Addressing SAP / ORNL comments

 One compound is not sufficient...Model all pyrethroid AI’s... – will be done at tier 

2/2+ level

 recommends that PWG measure the Kow for entire class using slow-stir [sic 

shake flask] method. Under way 

 Adsorption/binding is key for pyrethroids...Additional Koc sediment data 

needed.... Examine effect of solid water ratios... better understanding of 

sediment/suspended particle and plant material binding should be developed...3 

or 4 pyrethroids should be subjected to the same adsorption/desorption, water 

solubility, and toxicity tests.... At the same testing laboratory 

 Koc studies at different solid/water ratios for 9 AI’s in three sediments used for 

toxicity under way at same lab using same methods for LLE and SPME

 Solid phase microextraction (SPME).. a rapid and accurate approach for estimating 

bioavailable fraction of organic contaminants in water containing humics...

 SPME analyses underway for estimation of relevant Koc’s for ecotox study 

interpretation

 Other examples provided in white paper

The End