2

comments were often written verbatim while other times they were summarized, as required. 

EFED’s purpose of the document is to respond to technical/science-related questions and 

comments. Comments of a regulatory nature will be addressed in the Final Work Plan (FWP).

The Agency appreciates the submitted information on monitoring data on permethrin

concentrations in water and sediment provided by the California water quality boards and 

associations. This information will be used as appropriate in the Registration Review ecological

risk assessment for the chemical, as well as the data on use and usage submitted by McLaughlin 

Gormley King Company and the Permethrin Data Group II.

The comments were addressed in the following order (Table 1): 

Table 1. Submitters of Comments on the “Environmental Fate and Ecological Risk 

Assessment Preliminary Problem Formulation in Support of Registration Review for 

Permethrin”

Abbreviation Submitter

CRWQCB CV California Regional Water Quality Control Board, Central Valley Region

CRWQCB SFB California Regional Water Quality Control Board, San Francisco Bay Region

CASQA California Stormwater Quality Association

Tri-TAC Tri-TAC

NAFA National Alfalfa & Forage Alliance

MGK McLaughlin Gormley King Company

PDGII Permethrin Data Group II
3

Submitter: California Regional Water Quality Control Board, Central Valley Region

1. CRWQCB CV Comment: The 2010 Clean Water Act §303(d) listings in Central Valley, CA 

contains 13 stream segments (10 in urban sites and 3 in agricultural sites) that exceed water quality 

standards due to pyrethroids in the sediments that are toxic to Hyalella azteca. This list was recently 

partially approved by the Agency and will be approved “shortly” following the resolution of unrelated 

additional listings. Permethrin has been implicated as a contributor to the toxicity observed. While all 

the pyrethroid-impaired bodies of water are in Sacramento, open literature articles document the presence 

of pyrethroids all throughout CA.

EFED Response: EFED has confirmed that the §303(d) listings were partially agreed upon with 

the Agency (letter from Alexis Strauss, Director of Water Division, Region IX, to Tom Howard, 

Executive Director of State Water Resources Control Board). The Agency’s Region IX sought

public comments and a final decision was issued by October 11, 2011 (letter from Alexis Strauss, 

Water Division Director to Tom Howard, State Water Resources Control Board (see the 

following site: http://www.epa.gov/region9/water/tmdl/california.html which was accessed 

10/21/2011). EFED will include information on 303(d) listings in the Registration Review 

ecological risk assessment. However, the preliminary EFED problem formulation for permethrin

reflected the current list of 303(d) impaired bodies of water. As mentioned in the problem 

formulation, ten additional bodies of water were in draft form and not yet finalized.

2. CRWQCB CV Comment: An attachment was provided with a list of pyrethroid retail products 

available based on a July, 2005 shelf survey of San Francisco Bay area warehouse and hardware stores. 

For permethrin, there were around 32 products on the list.

EFED Response: EFED will consider these and other permethrin containing products at the time 

of the Registration Review ecological risk assessment.

3. CRWQCB CV Comments: The board provided open literature and other articles as attachments:

Attachment 2: “Statewide Investigation of the Role of Pyrethroid Pesticides in Sediment Toxicity in 

California’s Urban Waterways,” a literature article by Holmes et al. 2008 (Environ. Sci. Technol. 2008, 

42, 7003–7009).

Attachment 6: “Sediment Toxicity in Agricultural Areas of California and the Role of Hydrophobic 

Pesticides,” a literature article by Weston et al. 2008 (published in: Synthetic Pyrethroids: Occurrence and 

Behavior in Aquatic Environments. Gan, J., Spurlock, F., Hendley, P. and Weston, D. (editors). American 

Chemical Society Symposium Series 991, American Chemical Society, Washington, D.C. pp. 26-54,

2008).

Attachment 7: “Monitoring Urban Pesticide Runoff in Northern California, 2009 – 2010,” a recent article 

by Ensminger & Kelley 2011 (Report 264, CA EPA, CA Department of Pesticide Regulation, 

Environmental Monitoring Branch, Surface Water Protection Program, July 2011, 34 pp.)

Attachment 8: “Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal 

Freshwater Estuary,” a literature article by Grimaldo et al. 2009 (Marine and Coastal Fisheries: 

Dynamics, Management, and Ecosystem Science 1:200–217, 2009).
4

Attachment 9: “Urban and Agricultural Sources of Pyrethroid Insecticides to the Sacramento-San Joaquin 

Delta of California,” a literature article by Weston & Lydy 2010 (Environ. Sci. Technol. 2010, 44, 1833–

1840).

Attachment 12: “Aquatic Toxicity Due to Residential Use of Pyrethroid Insecticides,” a literature article 

by Weston et al. 2005 (Environ. Sci. Technol. 2005, 39, 9778-9784).

EFED Responses: The Agency appreciates the submission of the above referenced studies. 

Some of these and other publications were initially considered in the preparation of the Problem 

Formulation for permethrin. Further review of open scientific literature and other relevant 

articles will be conducted as part of the Registration Review ecological risk assessment.

4. CRWQCB CV Comments: Tables containing permethrin sediment monitoring data were submitted:

Attachment 3: “Urban creek sediments sampled in the East Bay, CA.” Permethrin, sampled in six sites 

ranged from undetected (U) to 56.0 ng/g or equivalent to 0-0.99 toxic units (TUs).

Attachment 4: “Urban creek sediments sampled in and around Nashville, TN.” Permethrin was sampled

in 14 sites and detected in four of them at concentrations ranging from undetected (U) to 12.73 ng/g or 0-

0.05 TUs.

Attachment 14: “Urban creek sediments sampled in and around Sacramento, CA.” Permethrin, sampled 

in 11 sites was detected in all but one of the sites. Concentrations ranged from undetected (U) to 171.3 

ng/g or 0-0.42 TUs.

EFED Response: The Agency appreciates the submission of these report tables. They provide 

information on the prevalence of permethrin in sediment samples in California and will be 

considered at the time of the Registration Review ecological risk assessment.

5. CRWQCB CV Comment: The following documents were submitted: “Water Quality Criteria 

Report (WQC) for Permethrin” (Fojut, Rering & Tjeerdema, 2011), Appendix B1 (Data Summary Sheets) 

and “Responses to Public Comments and Peer Reviews” (Attachments 5, 10 and 11

“Aquatic life in the Sacramento River and San Joaquin River basins should not be affected

). This 

comprehensive report was prepared by U.C. Davis for CRWQCB CV, dated September 2011. A 

multiplicity of ecological effects studies were evaluated and classified using specified data evaluation 

criteria. Factors such as bioconcentration, sediment and air concentrations, and possible impact of other 

pesticides were evaluated and considered. In brief, the description of the final criteria is as follows:

unacceptably if the four-day average concentration of permethrin does not exceed 0.002 μg/L (2 

ng/L) more than once every three years on the average and if the one-hour average concentration 

does not exceed 0.01 μg/L (10 ng/L) more than once every three years on the average. Mixtures 

of permethrin and other pyrethroids should be considered in an additive manner.” 

EFED Response: The Agency also appreciates the submission of the report, as it contains a 

comprehensive review of open literature aquatic toxicity studies and information on species 

sensitivity distributions for permethrin and mixtures with other pyrethroids. As indicated in the 

Problem Formulation document, the Agency may further describe risks in the upcoming assessment

using methods such as the species sensitivity distributions analogous to those in the submitted report.

Submitter: California Regional Water Quality Control Board, San Francisco Bay Region
5

6. CRWQCB SFB Comment: Pesticides used in accordance with label directions are causing toxicity 

in our urban water bodies. For example, Kirker Creek recently was listed under Clean Water Act §303(d) 

as impaired by pyrethroids. Permethrin was found in sediments of two out of six Bay area creeks 

sampled, at concentrations up to 12.2 μg/kg, and found to contribute to toxicity in those creeks.

EFED Response: As indicated above, EFED will include relevant information on 303(d) listings 

in the Registration Review ecological risk assessment. However, the preliminary EFED problem 

formulation for permethrin reflected the current list of 303(d) impaired bodies of water at the time 

of its issuance.

7. CRWQCB SFB Comment: Based on our understanding of the current schedule, the Office of 

Pesticide Programs and Office of Water (OPP/OW) common effects assessment methodology will be 

available in time to use for this risk assessment. We support use of this updated methodology. To protect 

aquatic life designated uses, it is important that exposure periods and exposure frequencies used in 

ecological effects assessments include time periods consistent with those used by OW.

EFED Response: At this time, the OPP/OW common effects methodology framework is under 

development and a time line to include an integrated methodology in OPP's risk assessment 

process has not been established. The focus of the OPP/OW common effects methodology project 

has been on characterizing effects of stressors on aquatic organisms. OPP appreciates 

CRWQCB's comment about consideration of duration of exposure. EPA will consider this 

comment in the continued development of the common effects methodology.

8. CRWQCB SFB Comment: CRWQCB SFB encourages the EPA to develop a set of urban scenarios 

that better represents realistic urban pesticide use and runoff conditions. The current urban impervious 

surface scenario, which uses a 0.25-acre residential lot scenario, does not adequately represent today’s 

urban environment. Urban watersheds, where pesticides including permethrin are used in a variety of 

applications, have mixed uses that include dense residential with small lot sizes, multifamily, and 

commercial land uses – these all have significantly more impervious area per acre than the current urban 

impervious surface scenario. In addition, urban soils are highly compacted. The current scenario 

underestimates the mass of pesticide runoff in urban areas.

EFED Response: The justification of the use of a 1⁄4-acre residential lot was based on a past

American Housing Survey (AHS), dated 2006; however, in this response it is updated with data 

from the latest “American Housing Survey of the U.S.: 2009,” from the Census Bureau (AHS), 

which was accessed 9/30/11 at the following site: 

http://www.census.gov/housing/ahs/data/index.html. The latter survey was issued in March 2011,

and covers data for the year 2009. In order to test the assumption of the 1⁄4-acre lot as the best 

representation for residential housing, the AHS data for suburban homes that list total number of 

houses by lot size and by square footage of house was evaluated (Table 1- 3 at the AHS website 

above, was provided as an Excel spreadsheet entitled “Size of Unit and Lot–All Housing Units”). 

With a total of 130,112,000 total units reported nationally for all suburban areas, 25,008,000 units 

(the largest class at 19%) were on lots between 1/8 acre and 1⁄4 acre, while 17,825,000 units (the 

third largest class at 14%) were on lots between 1⁄4 acre and 1⁄2 acre. Overall, these two lot size 

categories cover 33% of all housing units. The second largest class was for units between 1 to 5 

acres (15%) and the fourth largest class was for units less than 1/8 acre (11%). Overall, the 

median lot size was 0.26 acre. The vast majority of the houses were one unit structures, with 

95,216,000 units (73%). This analysis suggests that the 1⁄4-acre lot is a reasonable approximation 
6

of suburban pesticide use. As indicated in the Problem Formulation, “Alternative assumptions 

for percent impervious surfaces, percentage of use site treated, and percentage of overspray may 

be considered in order to characterize the assumptions of the ecological risks assessment in the 

context of the individual exposure assessment and risk conclusions.” EFED may evaluate further 

CRWQCB SFB’s comment and may determine whether additional scenarios are needed.

9. CRWQCB SFB Comment: The board’s comment attachment is a Final Project Report entitled

“Investigations of Sources and Effects of Pyrethroid Pesticides in Watersheds of the San Francisco 

Estuary.” (Lowe S., B. Anderson, and B. Phillips, 2007, Final Project Report: Investigations of Sources 

and Effects of Pyrethroid Pesticides in Watersheds of the San Francisco Bay Estuary. Proposition 13 

PRISM Grant # 041355520, SFEI Contribution #523, San Francisco Estuary Institute, Oakland, CA; 269 

pp.)

EFED Response: The Division appreciates the submission of this report. EFED will include all 

relevant information derived from the report at the time of the Registration Review ecological 

risk assessment.

Submitter: California Stormwater Quality Association

10. CASQA Comment: It is essential that the registration process adequately consider potential water 

quality impacts, so that such impacts are prevented before they result in CWA Section 303(d) impaired 

waters listings.

EFED Response: At the time of the Registration Review ecological risk assessment, all relevant 

303(d) listings will be considered.

11. CASQA Comment: CASQA encourages EFED to follow refinements to the existing modeling 

approach for urban impervious scenario:

1. Recognize applications to urban land uses within the conceptual model, and separately 

include “landscaped” (pervious) areas and “impervious” areas as urban source categories, at a 

level equivalent to agricultural soil (shown currently as “Soil” on the conceptual model 

diagram).

2. Recognize that within urban areas, pesticides are often applied directly and intentionally to 

impervious surfaces, and that applications to impervious surfaces are considered to be the 

controlling factor in urban runoff contributions to receiving water toxicity. The model 

discussion in the Problem Formulation currently seems to consider pesticide applications to 

impervious surfaces to be the unintended result of spray drift only.

3. The computational methods should distinctly account for appropriate wash-off fractions from 

urban impervious surfaces vs. landscaped (pervious) surfaces; discussion of impervious 

surface runoff coefficients was provided in a fact sheet that was attached to the comments 

(see below).

4. Account for the distinct physical characteristics of urban storm drainage conveyance systems, 

which rapidly convey water and pollutants to receiving waters.

EFED Responses: EFED points out that as part of the risk mitigation in the revised Permethrin 

Re-registration Eligibility Decision (RED, USEPA 2009, Document ID EPA 738-R-09-306, 

available at http://www.epa.gov/oppsrrd1/REDs/permethrin-red-revised-may2009.pdf and 
7

accessed 10/21/2011), for products to be used in and around buildings and other structures (i.e., 

likely having impervious surfaces): “All outdoor applications must be limited to spot or crackand-crevice treatments

treatment to soil or vegetation around structures; 

except for the following allowed uses:

applications to lawns, turf, and other vegetation; and,

applications to building foundations, up to a maximum height of 3 feet.

Other than applications to building foundations, all outdoor applications to impervious surfaces 

such as sidewalks, driveways, patios, porches and structural surfaces (such as windows, doors, 

and eaves) are limited to spot and crack-and-crevice applications, only.”

Thus, legal pyrethroid applications over impervious surfaces have been limited to a high extent.

1. The Problem Formulation shows applications over impervious surfaces in its conceptual model 

(not just soil or pervious surfaces). Modeling will include currently published categories of 

impervious areas in different urban areas of the country (based on NLCD) in order to establish a 

range of EECs from highly dense residential areas with high ratio of impervious to pervious 

surfaces to low density residential areas with low ratio of impervious to pervious surface).

2. Labeled pesticide application will be categorized into two categories and modeled separately. 

The suggested categories are: applications where drift is the main source for pesticide reaching 

impervious surfaces (e.g., labeled application to turf or landscaped areas), and direct application 

to impervious surfaces.

3. For direct applications over impervious surfaces, the portion of the pesticide “available for run 

off” is directly related to wash off factors established for various types of impervious surfaces 

(e.g., asphalt, concrete and others). The fraction of the rate (percent or %) used for impervious 

surface modeling will be equal to that expected to be washed off from the type of impervious 

surfaces. At the present time, EFED is reviewing a washoff study for cypermethrin submitted by 

the Pyrethroid Working Group (PWG, MRID 48072902), and another study that included 17 

pyrethroid products, including permethrin formulations will be submitted by the PWG in the near 

future. Both studies may

4. Storm drains (i.e., pipe conveyances designed to collect and transport surface stormwater through 

drainage inlets), convey the water through closed conduits to receiving waters. Conduit systems 

are often comprised of different material types, lengths, shapes, and sizes of storm drain pipes. 

Furthermore, they are connected by structures such as manholes, junction boxes, etc. This type of 

structure is not contemplated in the combination of residential (or rights-of-way) plus impervious 

scenarios. EFED may explore alternative ways to address this issue.

be used to characterize the washoff potential from impervious surfaces if 

appropriate.

12. CASQA Comment: CASQA encourages OPP to pursue development of a protocol for quantitative 

assessment of cumulative impacts of pesticide mixtures, as this appears to be a significant factor 

contributing to the observed toxicity in urban creeks.

EFED Response: EPA understands the desire for developing a risk assessment protocol that 

specifically addresses cumulative impacts of pesticide mixtures, such as the pyrethroids. As 

indicated in the Preliminary Problem Formulation document, the Agency believes that conducting 

a prospective (i.e., predictive) ecological risk assessment of pesticide mixtures would require a 

substantial amount of information regarding the temporal and spatial extent of pesticide usage 

within a watershed, which is currently lacking. This information is needed to accurately predict 

(or screen) pesticide concentrations in a waterbody because different pesticides will be applied at 

different times and locations within any given watershed. In addition, a watershed-based model 

would also need to be developed and reviewed for this particular application in order to capture 
8

the temporal and spatial dynamics of multiple pesticide uses and applications. Although a 

prospective cumulative ecological risk assessment methodology is subject to these and other 

challenges related to exposure and effects assessment, the Agency believes that available 

monitoring data for pyrethroids do offer some potential to evaluate cumulative ecological risk in a 

retrospective manner, as suggested in the Preliminary Problem Formulation document. The 

Agency will consider monitoring data of pyrethroid mixtures, such as concentrations in 

sediments, in the context of their potential to provide insight into ecological risks of pyrethroid 

mixtures to the extent that simplified assumptions regarding their combined toxicity (additivity) 

are scientifically supported. 

13. CASQA Comment: CASQA requests that the work plan be modified to indicate OPP’s intent to 

work with OW and to utilize the outcomes of the common effects assessment methodology project in

permethrin registration review. To facilitate integration with OW regulatory programs, they request that 

the work plan be modified to provide exposure estimates for time periods consistent with those used by 

OW in addition to the time periods ordinarily used by OPP.

EFED Response: See response to similar comment from CRWQCB (Comment #7) above.

14. CASQA Comment: CASQA urges OPP to continue to obtain and incorporate the extensive amount 

of new information being generated by CDPR through its pyrethroid reevaluation process.

EFED Response: The Agency encourages both CASQA and the registrant to submit all 

available useful information for consideration for the Registration Review ecological risk 

assessment. The Agency has been actively working with CDPR to coordinate its Registration 

Review with CDPR pyrethroid reevaluation process. This includes review of protocols and 

studies that are submitted by the registrant to CDPR.

15. CASQA Comment: Attachment: “Impervious Surface Coefficients: A Tool for Environmental 

Analysis and Management,” California Office of Environmental Health Hazard Assessment.

According to the attachment, a set of impervious surface coefficients, representing the average amount of 

impervious cover (IC) in each of the major land use categories (LUCs) in CA, have been developed. ICs

were based on data collected from Sacramento, Irvine, and Santa Cruz, and they reflect the average 

percent of IC for any single LUC. When combined with information on the total area of each LUC, the 

total amount of IC within any defined area can be estimated. Data are provided for ten Commercial/

General LUCs and the percent impervious surface coefficients (ISCs) range from 2% for open space to 

91% for heavy industrial. Residential ISCs are calculated using a regression equation. Finally, four 

categories of road ISCs range from 47% for rural to 96% for suburban. Using these data, the IC (e.g., 

acres) can be calculated for current or future IC for a developed (or to be developed) area.

EFED Response: EFED appreciates this submission, and it will be evaluated for potential use to 

characterize the percentages of impervious surface cover for various residential, industrial and/or

rural scenarios.

Submitter: Tri-TAC
9

16. Tri-TAC Comment: Permethrin from products for pets, for the treatment of fabrics and for head 

lice treatment can reach Publicly Owned Treatment Works (POTWs). Based upon these uses, it appears 

that the fate of permethrin is likely in water and solid emissions (i.e., biosolids) from POTWs. Effluent 

from the POTW will typically be discharged into creeks, rivers, estuaries, or the ocean. The receiving 

bodies of water may have little flow (i.e., “effluent dominated” waters). Recycled wastewater has 

growing use for irrigation, toilet flushing, industrial use, and groundwater recharge. Biosolids may be 

reused in agriculture or in urban gardens or disposed of in landfills.

Tri-TAC is concerned about potential effluent toxicity to aquatic organisms from pyrethroid 

discharges to POTWs, as found in Weston & Lydy (2010),1

POTWs are subject to National Pollutant Discharge Elimination System (NPDES) permits 

under the Federal Clean Water Act.

whom found pyrethroids and toxicity 

to H. azteca in secondary and tertiary POTW effluent samples.

EFED Response: Evaluation of E-FAST’s “down-the-drain” (DTD) module results indicated

that for the high end scenario, the stream dilution factor (SDF) is 1.00, which appears to be the 

minimum allowed value. The SDF is the volume of the receiving stream flow divided by the 

volume of the wastewater treatment facility effluent flow. The high end scenario (or 10th

percentile) concentration represents small receiving streams. A SDF of 1.00 represents “effluent 

dominated” surface bodies of water. These results may be compared against SDFs on the order 

of 20-24 for the average (50th percentile) concentration that represents midsized stream flows. 

Currently, EFED is conferring with Office of Pollution Prevention and Toxics (OPPT. the office 

that developed the model) to depict and select representative EECs more accurately.

Regarding the issue of biosolids, EFED stated in the Problem Formulation that, “The Agency is 

actively evaluating the extent to which ecological risk from permethrin via land application of 

biosolids should be addressed in its forthcoming environmental fate and ecological risk 

assessment and by extension, any additional data that may be required.”

The Agency acknowledges the concern about non-compliance with the Federal Clean Water Act 

(CWA). OPP is actively working with the Office of Water (OW) in harmonizing the 

methodologies for risk assessment and development of OW’s water quality criteria to address 

some of these concerns.

17. Tri-TAC Comment: Tri-TAC supports the use of Agency’s standard tool for DTD assessments, 

Exposure and Fate Assessment Screening Tool (E-FAST) Version 2.0, but has concerns with the way that 

OPP has applied the model. Tri-TAC recommends that the anticipated refinements to the model that are 

mentioned in the review be incorporated in the DTD assessment. In the past, OPP and OW have used 

different exposure periods and exposure frequencies in their ecological effects assessments. If these 

factors are not being addressed in the OPP/OW Common Effects Assessment Methodology project, we

request that OPP work with OW to develop a means of avoiding regulatory inconsistencies. One option 

would be to modify OPP pesticide runoff models to provide exposure estimates for multiple time periods, 

including time periods consistent with those used by OW.

EFED Response: See response to similar comment from CRWQCB above (Comment #7).

 1 Weston, D. P. and M.J. Lydy. (2010). Urban and Agricultural Sources of Pyrethroid Insecticides to the 

Sacramento-San Joaquin Delta of California. Environ. Sci. Technol. 44: 1833–1840.
10

18. Tri-TAC Comment: Available POTW monitoring data for other pyrethroids should be extrapolated 

to provide input into E-FAST for the DTD assessment. If influent, effluent, and biosolids POTW 

monitoring data are not available in time for the permethrin risk assessment or if available data are 

insufficient to account for the variety of POTW treatment processes and operational parameters utilized 

nationwide, EPA should use conservative assumptions for permethrin removal during wastewater 

treatment in the DTD assessment.

EFED Response: EFED may use available monitoring data in the Registration Review 

ecological risk assessment. [See also response to next comment (Comment #19).] However, the 

Division has also requested a bench scale POTW treatability study for permethrin. It is expected 

that the study will provide information about removal of permethrin from POTWs. As indicated 

previously in the problem formulation, “Part of the design of this study will need to address 

factors that the commenters present (such as the effect of differences in POTW design and 

operation on removal efficiencies) to the extent practicable. This may involve differences in 

experimental conditions and/or the use of POTW simulation models to address these concerns. 

The ability to extrapolate the bench scale results to results from available POTW monitoring data 

will also be evaluated.”

19. Tri-TAC Comment: A potentially valuable study is currently in development for POTW 

monitoring in collaboration among the PWG, CDPR and Tri-TAC in CA. Tri-TAC requests including 

this study in the Agency’s review.

EFED Response: EFED believes that this comment refers to the influent/effluent monitoring 

that CDPR requested for eight pyrethroids undergoing Reevaluation. In March 31, 2011 the 

Agency submitted comments on the proposed POTW sampling protocol to CDPR. The findings 

of this study will be evaluated in the upcoming Registration Review ecological risk assessment.

20. Tri-TAC Comment: Land application is a frequently used method for recycling biosolids. Since 

pyrethroids adsorb strongly to organic matter, a portion of permethrin entering POTWs will likely 

partition into biosolids. As such, the permethrin environmental risk assessment should address biosolids 

as well as effluent. The analysis of this partitioning has largely been missing from prior studies. We have 

heard that the Agency is open to including this component of your review and are pleased.

EFED Response: Regarding the assessment of biosolids it was stated in the problem 

formulation that “[t]he Agency is actively evaluating the extent to which ecological risk from 

permethrin via land application of biosolids should be addressed in its forthcoming environmental 

fate and ecological risk assessment and by extension, any additional data that may be required. 

As part of this evaluation, OPP is working closely with the Office of Water which regulates land 

application of biosolids under the Clean Water Act.”

21. Tri-TAC Comment: Acute and chronic toxicity data for freshwater and estuarine/marine fish and 

invertebrates are necessary to perform the DTD and biosolids assessments. Tri-TAC recommends that 

EPA issue data requirements for permethrin that fill any gaps in available data. The data requirements for 

permethrin should mimic the data requirements for pyrethroids undergoing registration review, which are 

the minimum necessary for a scientifically sound environmental risk assessment.

POTWs need the Agency’s assistance to protect surface water from contamination from pesticides. 

POTWs are required by NPDES permits to meet effluent toxicity standards; however, our agencies do not 
11

have the authority to directly regulate the use of pesticides. Tri-TAC requests that necessary aquatic 

toxicity data be obtained and the DTD assessment and a biosolids assessment be performed as part of 

EPA’s registration review for permethrin.

EFED Response: Similar to other pyrethroid problem formulations, the toxicity data requested 

for permethrin follow the Part 158 Ecological Effects data requirements. Based upon by 

permethrin’s physical properties, use patterns and previously demonstrated toxicity to aquatic 

organisms, additional data was requested in the problem formulation for acute effects of the 

technical product to freshwater invertebrates (Hyalella azteca), oysters and aquatic plants, as well 

as chronic toxicity information for the technical product on estuarine/marine invertebrates in the 

water column and benthic freshwater and estuarine/marine invertebrates. In addition, acute 

toxicity information on permethrin for freshwater invertebrates (Hyalella azteca) and freshwater 

fish are requested for an end-use product with the synergists PBO and MGK. These requested 

studies will supplement the currently available acute information on permethrin technical and 

end-use product toxicity (without PBO or MGK) to freshwater invertebrates (Daphnia magna), 

estuarine/marine invertebrates, freshwater and estuarine/marine fish and the chronic effects of 

permethrin technical to freshwater invertebrates and freshwater fish. Therefore, EFED believes 

the necessary aquatic toxicity data are being requested for the forthcoming registration review of 

permethrin. 

It is also noted again that the DTD module of E-FAST is not designed to evaluate 

estuarine/marine fish and invertebrate risks. This module was designed to address only 

freshwater receiving bodies of water. 

Regarding biosolids please refer to the response to Tri-TAC’s Comment #16 above.

Submitter: National Alfalfa & Forage Alliance

22. NAFA Comment: Permethrin is a critically important insect management tool which has broad 

spectrum control of a number of alfalfa hay and seed pests including, alfalfa weevil, aphids (pea, blue 

alfalfa, alfalfa, and spotted), caterpillars (alfalfa, armyworms, cutworms, loopers) and lygus bug. It is an 

integral part of alfalfa and alfalfa seed producers’ ability to control these insect pests. NAFA goes on to 

list the advantages of permethrin which are: it has a low mammalian toxicity, it has a short pre-harvest 

interval, and it is inexpensive if generic brands are used.

EFED Response: The issue of the weight carried out by permethrin’s costs and benefits is 

outside the scope of EFED. The response to this comment is deferred to PRD.

Submitter: McLaughlin Gormley King Company

23. MGK Comment: The submitter provided a letter with an appendix summarizing maximum use 

rates and use sites by product type for MGK permethrin products. The Appendix A is entitled 

“Permethrin Product Use Site and Rate Summary for McLaughlin Gormley King Company.” The table 

indicates the maximum rates and limitations (e.g., retreatment interval if available) for the following 

sample uses:
12

Indoor surface treatment; indoor broadcast for total release fogger; indoor space spray; outdoor 

premises treatment (turf, building surface treatment and fire ant); on animal (e.g., livestock, 

horses, ponies, dogs, cats, poultry, sheep); wood destroying pest; livestock premise treatment; 

residential systems; clothing repellent; lice and louse eggs, bedbugs; carpet upholstery broadcast; 

plants, home gardens

Furthermore, a provided Excel file had two spreadsheets with product descriptions, and maximum rates 

for each one. The documents also give which active ingredients are formulated with permethrin in MGK 

products. Information for around 29 products is provided.

EFED Response: EFED appreciates MGK’s submission. It appears that it will be helpful in 

determining use rates for many of the uses to be assessed in the Registration Review ecological 

risk assessment.

Submitter: Permethrin Data Group II

The PDGII divided its comments into two separate submissions or parts, which are identified as a and b.

a. Permethrin Data Group II Comments on the Permethrin Registration Review

24. PDGII Comment - PDGII will conduct and submit new studies to support the following 

requirements:

• 835.1230 Batch Equilibrium Adsorption/Desorption; 

• 835.2240 Aqueous Photolysis

• 835.4300 Aerobic Aquatic Metabolism

• Non-guideline Leachability from Treated Wood

• Non-guideline POTW Treatability Study

EFED Response: EFED concurs with PDGII on the submission of the newly conducted studies.

25. 835.4100 Aerobic Soil Metabolism – PDGII proposes to submit this study utilizing cold parent 

material (as opposed to radiolabeled material).

EFED Response: Paragraph (e)(1) of the OCSPP 835.4100/835.4200 guidance for Aerobic and 

Anaerobic Soil Metabolism studies specifically indicates that the use of a radiolabeled material is 

recommended “for studying the pathway of transformation and for establishing a mass balance.” 

[Emphasis was added.] Thus, in order to establish a pathway, pattern of formation and decline of 

the degradates, and obtain suitable mass balances, EFED recommends that the test material be 

radiolabeled.

26. 835.4200 Anaerobic Soil Metabolism – PDGII believes that a new anaerobic soil metabolism study 

will not give substantial new information because the previous study shows persistence of permethrin 

under anaerobic conditions. Furthermore, the anaerobic aquatic metabolism that PDGII will submit 

should be more relevant to surface water exposure estimates.
13

EFED Response: These studies are required for the proper characterization of the environmental 

fate of permethrin in anaerobic soils. Based on the characteristics of permethrin (which binds 

tightly to soils and sediments), it seems unlikely that the chemical would reach subsurfaces to a 

high degree; however, permethrin has aquatic uses and thus potential to reach anaerobic soils due 

to adulticide treatment. The single available study lasted only 60 days of anaerobic incubation, a 

period during which permethrin decreased from 81.7% AR to 68.1% AR (decreasing only 13.6% 

AR during this period, and making the half-life highly unreliable) (the required anaerobic period 

is one year). Also, both trans-DCVA and m-PBA increased throughout the study. Additional

degradation half-life information and data about these degradates are needed.

27. 835.4400 Anaerobic Aquatic Metabolism – PDGII suggests the submission of two ongoing studies 

that are being performed for CDPR.

EFED Response: EFED agrees with the submission of two CDPR studies.

28. 835.6100 & 835.6200 Environmental Chemistry Methods (ECMs) and Independent Laboratory 

Validations (ILVs), for Soil, Water and Sediment – PDGII is proposing to use the following two 

available studies to support this data requirement: 47053001 and 47053002.

EFED Response: As indicated in the problem formulation, EFED will evaluate these two studies 

for their suitability and determine their acceptability for soil, water and sediment.

29. 850.1010 Acute Toxicity Freshwater Invertebrates and 850.1020 Acute Toxicity H. azteca (using 

highest ratios of PBO and MGK-264) – It appears that there are some inconsistencies in comparing the 

summary document and the problem formulation. PDGII asks for clarification on this data requirement.

EFED Response: Acute water column toxicity data on permethrin technical and typical end-use 

products (TEPs) with PBO and MGK-264 are requested for H. azteca, using Guideline 850.1020 

(Gammarus acute toxicity test guideline) as the basis for conducting the tests. As appropriate 

modifications to the 850.1020 guideline will be necessary for testing of H. azteca, the registrant is 

encouraged to submit a protocol to the Agency prior to conducting the acute test of H. azteca.

30. 850.1025 Oyster Acute Toxicity Test (shell deposition); 850.1075 Acute Freshwater Fish 

Toxicity (TEP) (using highest ratios of PBO and MGK-264); 850.1350 Aquatic Invertebrate LifeCycle (saltwater); 850.2100 Avian Acute Oral Toxicity Test (passerine species): The PDGII indicated 

that they will conduct and submit these studies.

EFED Response: EFED concurs with PDGII on the submission of the newly conducted studies.

31. 850.4100 Seedling Emergence and 850.4150 Vegetative Vigor– A waiver for this data requirement 

was submitted based on the fact that FMC (original registrant for permethrin) generated efficacy data for 

numerous crops. No phytotoxicity was observed to alfalfa, asparagus, beans, cabbage, sweet and field 

corn, cucumber, lettuce, pepper, plum, potato, pumpkin and tomato. PDGII does not believe that a new 

study would generate additional useful data.
14

EFED Response: Among other data quality requirements, these terrestrial plant studies would 

need to address the potential adverse effects examined in our typical seedling emergence and 

vegetative vigor studies, such as germination, growth and phytotoxic damage. Also, the studies 

must demonstrate that permethrin was applied at or above the maximum labeled application rates 

with a minimum 14-day post-application observation period. The field trials recently submitted to 

the Agency are designed for residue chemistry (OCSPP Series 860 Guidelines). Although these 

data do provide additional lines of evidence regarding the potential phytotoxic effects of 

permethrin, the studies do not meet the same objectives as a standard seedling emergence and/or 

vegetative vigor study. In addition, the 8 major and 149 minor permethrin plant incidents that 

have been reported indicate that plant damage may occur following use of this chemical. Data 

that will provide quantitative information on the potential effects of permethrin exposure to 

terrestrial plants, including any inhibition of germination, reduction in growth and observed 

phytotoxicity, are needed for the upcoming ecological risk assessment. 

32. 850.4400 Aquatic Plant Growth (aquatic vascular plant toxicity), Tier II – Another waiver for 

this data requirement was submitted. PDGII indicates that the above mentioned studies indicated no 

phytotoxicity to numerous crops and also argues that only small amounts of permethrin would reach 

adjacent bodies of water because permethrin does not have aquatic uses and such amounts would not be 

bioavailable to macrophytes because permethrin binds to sediments.

EFED Response: Similar to the response for Comment #31 above, these field trials do not 

address the same questions as our standard aquatic plant toxicity tests. Data that will provide 

quantitative information on the potential phytotoxic effects of permethrin exposure to aquatic 

vascular plants, including any reductions in growth or observed phytotoxicity, are needed for the 

upcoming ecological risk assessment. 

Regarding the aquatic uses for this chemical, EFED confirms that permethrin does have aquatic 

uses (as a mosquito adulticide). In addition, chemicals that bind to sediments still have the 

potential for exposure to aquatic plant root systems, as well as contact with the shoot portions of 

macrophytes in the form of dissolved and particulate organic matter.

33. 850.5400 Aquatic Plant Growth (algae) Tier II – PDGII is evaluating existing studies to determine 

if they meet the data requirement and will submit them at the time of the DCI.

EFED Response: Once submitted, EFED will evaluate these studies for their suitability 

according to current guideline requirements.

b. Comments on EPA’s Summary Document and Problem Formulation Supporting Registration Review

35. PDGII Comment: Labels from FMC, Valent, and United Phosphorus were reviewed and were 

considered representative of the majority of the agricultural, residential and professional labels, so a 

subset of all registered uses was reviewed. This approach should be robust for the purposes of a 

screening level assessment, because the other registered use labels should essentially be copies of FMC, 

Valent, or United Phosphorous labels, with the same use rates, interval between applications, and seasonal 

rates. No dust formulation labels were reviewed in PDGII’s analysis. However, of the 9 registered dust 

formulations, they found that all are labeled for home lawn and garden use only, so the extent of exposure 

to them is expected to be much less than if they were agricultural uses, as EPA’s table implies.
15

EFED Response: A substantial subset of labels was utilized to prepare the use and usage 

information in the LUIS report. The labels evaluated represent all use patterns, maximum single 

application rates, and all formulation types. EFED did not intend to “imply” that the extent of 

exposure of any of the uses was greater or smaller than others. The table presented the maximum 

rates if available for all agricultural and non-agricultural uses. For the uses that are limited to 

home and gardens only, EFED currently has a specific scenario (residential), which is run in 

tandem with the impervious scenario to derive suitable EECs.

36. PDGII Comment: EPA states that the Label Use Information System (LUIS) report and Usage/

Label Use Reports for Permethrin were based on a partial listing of labels due to the large number of 

permethrin labels. Section 3 labels or major producers’ labels, along with all State and Local Needs 

(SLN) labels were incorporated in the LUIS report. However, that report is not included as an appendix 

to the Problem Formulation or in the Registration Review docket, making it difficult to evaluate the 

information presented in the Problem Formulation. EPA states that these data represent major uses for 

this chemical. PDGII believes that EPA’s approach of identifying “representative” agricultural and nonagricultural labels will not be acceptable to the Services. A more detailed analysis and summary of all 

permethrin labels may be needed if formal consultation on endangered species is requested by EPA.

EFED Response: This approach was used in the past for endangered species risk assessments 

(e.g., the California Red Legged Frog/San Francisco Bay and the Valley Elderberry Longhorn 

Beetle permethrin assessments). As said above, the LUIS report was based on a subset of labels

that account for all the chemical’s uses. Permethrin has over 700 product labels of which a 

substantial subset was extracted. In general, the full LUIS report is not included in the docket, 

but it includes all use patterns, maximum single application rates, and all formulation types.

37. PDGII Comment: EPA does not state the objectives of its summary of the permethrin uses, but it is 

expected that the information is to be used to support a screening-level ecological risk assessment, as well 

as any refinements that might be needed for an endangered species effects determination. The critical

information for these activities would include: an evaluation of the inherent risk to non-target organisms 

of the different formulations (e.g., granular, sprays, and dusts) and associated application sites and 

methods; and a summary of mitigation measures on the labels.

EFED Response: EFED acknowledges that identifying and tabulating all the multiplicity of 

uses of permethrin is challenging. The referenced section of the Problem Formulation is an 

“overview” of use and usage of permethrin, but the complete use and usage is given in the LUIS 

report. EFED stated in the document the main mitigation measures that were imposed in the 

labels, which resulted from the Reregistration Eligibility Decision (e.g., buffer zones and 

vegetative buffer strips). In the upcoming Registration Review ecological risk assessment, EFED 

will not only account for these measures of mitigation, but also include differences which result 

from applications of different formulations, use sites, and application methods.

38. PDGII Comment: EPA groups emulsifiable concentrate, water soluble bag and granules in one 

table; dusts are presented separately. The potential for offsite movement of the two spray formulations, 

the granule, and the dusts differ and it may be inappropriate to ignore these differences. The drift 

potential for granules is negligible, and if applied in-furrow, runoff will be markedly reduced. Spray 

formulations can be applied as a foliar spray or applied directly to the soil at planting, pre-emergence, or 

pre-plant incorporated, as is the granule. Other things being equal, a foliar spray application will have a 

greater potential for drift and runoff than a spray or granule applied to the soil. The granules can also be 
16

applied aerially, but other than being captured in corn whorls, should leave minimal residue on foliar 

surfaces. For a foliar application, some of the permethrin could reach the soil surface; adsorption to foliar 

surfaces will differ from that on soil surfaces and could modify runoff. It is recommended that EPA 

perform separate analyses for granular and spray formulations and for foliar and soil applied methods to 

ensure that appropriate estimates of residues and offsite movement are made.

EFED Response: EFED acknowledges the differences in the potential for offsite transport for 

different permethrin formulations and application methods and will consider the PDGII comment 

when assessing permethrin in the Registration Review ecological risk assessment. Generally, 

when a screening-level risk assessment is conducted, the most conservative scenarios are 

modeled. In addition, for endangered species assessments for Registration Review, different 

application methods and formulations, and possible refinements are also considered.

39. PDGII Comment: Some unusual or specialized labels allow treatment of many matrices, often with 

little indication of maximum treatment rates. It will be difficult for EPA to assess these, even with their 

experience, and more difficult for the Services to evaluate them. For many of them, no risk scenarios are 

available. One advantage is that labels do limit applications that might formerly have been made on 

impervious surfaces where urban and suburban runoff would have been a problem prior to those 

limitations; only spot or crack and crevice applications may be made to such surfaces. These products 

may be used as a residual surface treatment on walls and ceilings. Most of these are indoor uses. The 

outdoor uses are limited to the lower three feet of walls and directions specify that sprays are not to be 

made to the point where the material would run off from the treated site.

EFED Response: In past assessments, EFED has made estimates of the application rates for 

numerous unusual scenarios. EFED is aware of, and will consider the above stated mitigation 

measures at the time the Registration Review ecological risk assessment is done (noted also a

response to CASQA’s Comment #11 above).

40. PDGII Comment: Mosquitocide uses are intended to remain in the air for a significant period of 

time and not deposit out; while drift may be enhanced, deposition resulting from that drift will be 

reduced. Mosquito adulticides may be applied to the air column over a variety of crops, all of which are 

on permethrin agricultural labels, but the rate of 0.007 lb a.i./A is far lower than the maximum crop rates 

of 0.1 lb a.i./A and higher. Thus, the mosquito use of permethrin will not add, for all practical purposes, 

to the residues from crop applications of agricultural formulations. This public health use is only allowed 

under the authority of federal, state, local, or tribal governments and applicators must be certified or under 

the direct supervision of certified applicators.

EFED Response: Previous risk assessments have shown that there may be RQs that exceed one 

or more of the LOCs for the adulticide uses. It is important to reassess them with the most up to 

date label requirements. Despite that the application rate is low, multiple applications are allowed 

and the minimum interval between applications is only 1 day (high pest pressure). The seasonal 

application rate is 0.18 lb a.i./A. Furthermore, in addition to agricultural crop uses, adulticide 

applications are also allowed over regions that could have extensive impervious surfaces. EFED 

acknowledges the mosquitocide application restrictions (e.g., made by certified applicators).

41. PDGII Comment: Termiticide applications, which are very important for structural pest control, 

may present difficulties, but permethrin products are to be applied only by state licensed and trained 

individuals, injected well into non-saturated soils or covered, and not applied when precipitation is 
17

occurring, along with other provisions to reduce exposure away from treated areas. Other underground 

treatments such as to cables and other utilities, will have very limited potential exposure, other than to 

fossorial animals. Premise treatments, such as public health and other applications to a wide variety of 

structures, walls, and their immediate surroundings still require buffers to keep runoff away from water.

EFED Response: EFED acknowledges the above mentioned information and will evaluate it, 

along with labels for termiticide applications, for possible uses with potential for exposure to nontarget wildlife, such as fossorial and/or aquatic animals, aquatic plants, etc.

42. PDGII Comment: In the narrative following the Environmental Hazard Statements, EPA discusses 

the fact that permethrin labels require a 10-ft buffer zone around certain water bodies. However, the 

narrative does not indicate, as the agricultural labels do, that this 10 ft area is to be uncultivated so as to 

leave a vegetated buffer strip; vegetated buffer strips are more efficient at reducing runoff than a simple 

buffer zone that may or may not be bare ground. Furthermore, there is a specific statement for protection 

of bees. The labels for the crop applications have a wide range of specifications to reduce spray drift 

from ground or aerial applications. The language on the Pounce EC, WP, and even 1.5G labels is 

identical and covers wind speed and direction, temperature inversion, droplet size, as well as additional 

requirements for ground and air applications. The Permethrin Task Force suggests that EPA consider 

these measures when developing Estimated Environmental Concentrations (EECs) for permethrin. Also, 

these measures need to be considered by EPA and the Services if it is necessary to craft Reasonable and 

Prudent Alternatives and Measures for listed species.

EFED Response: EFED is aware of these mitigation measures and will consider them at the 

time of the ecological risk assessment is completed, as appropriate.

43. PDGII Comment: Ten representative Task Force labels were reviewed and summarized in tabular 

form to facilitate a comparison with EPA’s Tables 3.2 and 3.5. According to PDGII, it appears that the 

labels selected by EPA in Table 3.2 were substantially similar to the POUNCE 3.2 EC label.

PDGII compared the POUNCE 3.2 EC label with EPA’s Table 3.2 with the following findings: A 

difference between EPA’s tables and the POUNCE 3.2 EC label was that EPA often concluded that 

chemigation, airblast, and even soil incorporation application methods could be used. FMC’s crop-level 

descriptions usually specified ground or air, and perhaps airblast or ULV. There was general statement 

about the chemigation uses on the POUNCE 3.2 EC label, but this statement often did not tie back to the 

crop-level instructions. For example, EPA states that alfalfa could be treated by chemigation and by soil 

incorporation, but the POUNCE 3.2 EC label only mentions ground or air, and makes no mention of 

chemigation or soil incorporation. There were a few differences in the crops listed in EPA’s Table 3.2 

and the POUNCE 3.2 EC label. EPA includes anise, beans, Swiss chard, kohlrabi, okra, fennel, pecans,

raspberries, blueberries, and strawberries, rhubarb, and watercress, Christmas tree plantations, rights-ofway/fencerows/hedgerows, patios/patios and paved areas, and public health uses, which do not appear to 

be on the POUNCE 3.2 EC label. Some of these differences may be due to Section 24(c) labels, which 

were not reviewed for PDGII’s analysis. EPA does not limit the uses on collards and turnips to specific 

states, but the FMC label does. The Problem Formulation does not indicate which products were used to 

develop the table of non-agricultural uses. The rangeland use is on the POUNCE 3.2 EC label, with a 

specified rate of 0.01 lb a.i./A and is allowed only in the state of New Mexico. In contrast, EPA lists the

rangeland use in Table 3.2 as 0.1 lb a.i./A.

EFED Response: A comparison of POUNCE 3.2 EC label against EFED’s tables is not 

appropriate because the LUIS report summarized in the review incorporates several labels.
18

Inspection of the LUIS report indicated that both chemigation and soil incorporation are allowed 

application methods for alfalfa. Further, according to the report, anise, beans, Swiss chard, 

kohlrabi, okra, fennel, pecans, raspberries, blueberries, strawberries, rhubarb, watercress, 

Christmas tree plantations, rights-of-way/fencerows/hedgerows, patios/patios and paved areas, 

and public health uses are all registered uses for permethrin. EFED acknowledges that uses on

collards and turnips are restricted to specific states and confirms that the uses on rangeland 

include a maximum rate of 0.1 lb a.i./A, as stated in EFED’s table.

44. PDGII Comment: While usage data indicate considerable home and garden use, it should be noted 

that this use is typically spread out more than in agricultural areas because only some homeowners will 

use a particular product and only on limited parts of their property. Thus any off-site exposure would be 

much more limited than in agricultural areas. Use on lawns and landscaping plants would result in 

permethrin being adsorbed to plant materials, rather than to soils as in cropland areas, and thus less 

available to runoff on soil particulate matter. The commercial and other wide area urban uses of 

permethrin have labels that dictate no applications during rain and no spraying of plants or articles to the 

point of dripping or runoff, reducing the potential for transport of an adsorptive material. Labels limit 

applications to impervious surfaces to crack and crevice applications, and prohibit use in sewers or sewer 

drains.

EFED Response: The comment is acknowledged and will be considered at the time of the 

Registration Review ecological risk assessment (note also a response to CASQA’s Comment #11

above).

45. PDGII Comment: EPA has some very high use rates for termiticide treatments in the Table 3.5, and 

it is not clear how, for example, the 180 lb a.i./A use rate for pre-construction treatment was arrived at. 

On its face, a use rate this high would seem to imply considerable potential for exposure. But for the 

termiticide uses, the products are mixed with considerable amounts of soil and then covered and buried. 

Instructions require that treated areas must not be left open, and applications are not allowed when 

precipitation is occurring or when soils are frozen or saturated. Only persons licensed and trained are 

allowed to apply permethrin products as termiticides.

EFED Response: These rates were obtained directly from BEAD’s report and a footnote with a 

reference to the specific use was included in the Problem Formulation for unusually high 

application rates (e.g., used for soil treatment (preconstruction) or soil treatment (rodding) –

injection equipment). EFED acknowledges uses that may involve lower exposure potential and 

the measures of mitigation taken for of the termiticide uses. It is noted that these rates were 

obtained from BEAD's LUIS report. BEAD converts all application rates into lb a.i./A regardless 

of the labeled unit of measurement. EFED realizes that the pre-construction treatment with the 

mitigation referenced by PDGII is applied to buildings, structures, and their immediate 

surroundings only, and that the lb a.i./A unit measurement may not be appropriate for this use 

scenario. Additionally, EFED will consider the specific application restrictions when assessing 

the exposure from this use, which may result in lower exposure scenarios.

46. PDGII Comment: There are numerous livestock and animal premise uses, including feedlots, where 

there may be heavy concentrations of livestock. A large proportion of animal treatments will be spot 

treatments, and indoor treatments of animals or premises. Outdoor agricultural premises will typically be 

associated with barns and other animal houses. While these may be made outdoors, they are not made in 

natural habitats, nor are they typically made near such habitats where most non-target organisms would 
19

occur. Use in feedlots would likely be insignificant relative to the waste products generated by the 

animals themselves. The most likely exposure scenario for threatened and endangered species would be 

livestock treated on rangeland or pastureland, which does occur, but is not the kind of area where either 

the livestock or the pests to be controlled are concentrated.

EFED Response: In the past, the Division has evaluated livestock uses for only a few chemicals. 

Based upon a preliminary screening-level assessment, EFED will determine whether further 

refinements to the proposed scenarios is warranted. 

47. PDGII Comment: Agricultural Usage –A limitation of EPA’s Screening Level Usage Analysis is 

that it does not explicitly consider the time trends of permethrin usage. To complement EPA’s 

agricultural usage analysis, usage data from Doane’s were obtained from FMC for 2010. Those data 

showed that the top 8 crops were: pistachios (23%), corn (16%), lettuce (10%), soybeans (10%), potatoes 

(7%), sweet corn (5%), almonds (4%), and spinach (4%). Celery made up 3% of the total, while peaches, 

cucumbers, pumpkins and alfalfa made up 2% of the total. Another 8 uses made up 1% of the total each, 

and 15 uses made up less than 1% of the total each. To further complement EPA’s agricultural usage 

analysis, data were obtained for 2007 to 2009 from the CA Pesticide Use Reporting (PUR) database

(http://calpip.cdpr.ca.gov/main.cfm ). These data are presented alphabetically by agricultural use in Table 

1 of the PDGII submission. Total permethrin agricultural use (as measured by pounds of active 

ingredient) decreased by 29% from 2007 to 2008, and increased slightly (4%) from 2008 to 2009. Each 

year, the top ten crops accounted for >90% of permethrin use. The highest use crop was pistachios (33-

40%), followed by almonds (11-14%), lettuce head (11-13%), lettuce leaf (10-12%), spinach (4-6%), 

celery (3-6%), corn (3-4%), walnuts (2-3%), tomatoes (1-3%), and onion (1-2%). A wide range of crops 

made up <1% of the total each.

EFED Response: The Division appreciates the submission of these data. It will aid to identify 

major agricultural crops of interest during the process of the Registration Review ecological risk 

assessment. EFED notes that one limitation of the usage data presented in PDGII’s table is that it 

includes only the state of CA.

48. PDGII Comment: Urban Usage – In its Problem Formulation, EPA did not perform an analysis for 

the urban usage of permethrin. Urban usage is broadly defined as essentially all nonagricultural pesticide 

usage, including applications to residences, commercial buildings, institutions, parks, golf courses, and 

rights-of-way, structural, landscape maintenance, public health, vertebrate, commodity fumigation, and 

regulatory. The most detailed data on nonagricultural permethrin use are available from the CA PUR. 

The PDGII provided information in Table 2 of the submission. The CA PUR data rely on responses from 

professional applicators, but permethrin is also purchased and used by homeowners. Information was 

summarized for 2007 to 2009 and data were presented alphabetically by nonagricultural use. Total 

permethrin non-agricultural use decreased by 11% from 2007 to 2008, and decreased by an additional 

29% from 2008 to 2009. Each year, structural pest control accounted for >90% of non-agricultural use. 

The next highest non-agricultural uses were landscape maintenance (6-9%), and public health pest control 

(<1-1%). All other non-agricultural uses made up <1% of the total each. Total permethrin nonagricultural use was 50 to over 100% higher than agricultural use, depending upon the year under 

consideration from 2007-2009.

EFED Response: The Division appreciates the submission of these data. It will help identify 

major non-agricultural uses of interest during the process of the Registration Review ecological 

risk assessment. It also helps to inform trends of usage of permethrin over time.
20

49. PDGII Comment: Ecotoxicity: EPA has not conducted a full analysis of the available data, 

including data available in its ECOTOX database and other sources. Drawing on the extensive database 

of the PWG, an analysis was conducted on the studies that EPA relied upon in the Problem Formulation, 

as well as additional studies that could be used in a refined assessment. The PWG database was also 

searched to distinguish studies that might be used to fulfill data gaps identified by EPA. Additional 

studies on non-target insects and on plants were also identified from EPA’s ECOTOX database. These 

studies could be relevant for performing a refined ecological risk assessment.

With regard to toxicity data for terrestrial insects, the Problem Formulation indicates that open literature 

toxicity data will be considered in the upcoming risk assessment. EPA also provides a rationale for 

exclusion of efficacy studies, but none for exclusion of non-efficacy studies. We note that the ECOTOX 

database includes median lethal dose (LD50) values for more than 70 other species of insects in addition 

to honeybees, which may be relevant to a refined assessment.

The Problem Formulation indicates that no terrestrial plant data are available to the EPA for permethrin. 

The ECOTOX database includes toxicity data for over 50 species of terrestrial plants, which may be 

relevant to a refined assessment.

Appendix H (ECOTOX Database for Permethrin) of the longhorn beetle risk assessment (EPA 2010) 

contains no studies from 2010. However, the current ECOTOX database does contain studies from 2010 

that most likely had not been entered into ECOTOX when Appendix H was compiled. The Permethrin 

Task Force requests that EPA continue to examine ECOTOX for new studies that may be useful for a 

refined risk assessment.

EFED Response: A full ECOTOX search will be conducted prior to the final risk assessment for 

Registration Review, and the available studies identified for permethrin will be evaluated for 

suitability in quantifying ecological risk of the chemical. EFED welcomes submission of any 

studies that the registrants believe may fulfill the data gaps for permethrin in the context of a data 

waiver request.

50. PDGII Comment: Using the PWG’s aquatic toxicity database, the data used by EPA in their

Problem Formulation were evaluated to insure that they were from reliable and relevant studies and that 

the endpoints were correct. The studies in the PWG’s aquatic toxicity database have been reviewed and 

evaluated for reliability and relevance. Based upon these evaluations, the Permethrin Task Force suggests 

that the 48-hour median effect concentration (EC50) of 0.075 μg/L for the Daphnia magna acute study 

(MRID 00043736), is more appropriate than the 96-hour EC50 of 0.039 μg/L presented in the Problem 

Formulation. According to test guideline OPPTS 850.1010, the purpose of the definitive test is to 

determine the 24– and 48–h EC50 values. 

Additionally, an acceptable study for the bluegill (Lepomis macrochirus) is available (Bentley 1974; 

MRID 00110657) and is more suitable for risk assessment than the supplemental study (Hill et al. 1976; 

MRID 00042128). The Bentley (1974) study is preferable since it used statistics to calculate the median 

lethal concentration (LC50) and reported the control performance (100% survival).

EFED Response: EFED agrees that the 48-hour EC50 value should be used for the acute study 

with Daphnia magna, instead of the 96-hour EC50 value (MRID 00043736). In this particular 

study, the test organisms were fed after 48 hours, and the control immobilization was greater than 

10% at 96 hours, indicating test organism stress that is not chemical-related (13% immobilization 
21

was observed in the negative control at 96 hours, compared to 0% immobilization in the negative 

control at 48 hours). 

Thank you for providing a review of available data for bluegill. We are aware of several strengths 

and limitations in the bluegill study referenced in the permethrin problem formulation (MRID 

00042128). Some of the study’s strengths include the use of measured concentrations, flowthrough conditions, the availability of raw data and use of concurrent controls. However, we 

recognize that some of study limitations include absence of control response reporting, relatively 

high co-solvent concentrations and use of graphical methods for LC50 determination. Some of 

these limitations can be addressed (such as recalculating statistics for LC50), but others do not 

appear to be repairable, such as use of high co-solvent concentration and lack of control data. The 

bluegill study suggested by the PDGII (MRID 00110657) is not considered useful for risk 

assessment purposes and was invalidated because the percent active ingredient of the test 

substance was not reported and water quality measurements were not taken during the study.

For the final risk assessment of permethrin, the Agency will re-evaluate its choice of the acute 

toxicity endpoint for freshwater fish in the context of all available information, including data 

from the open literature which have yet to be reviewed, and the associated strengths and 

limitations of the bluegill study used for risk quotient calculations in previous permethrin 

ecological assessments (MRID 00042128).

51. PDGII Comment: The Problem Formulation says the assessment will use the surrogate species 

approach, and that surrogate test species “are intended to be representative of broad taxonomic groups.” 

The surrogate species approach is the only option for ecological risk assessment because data are 

available for only a small number of species. However, the breadth of the taxonomic groups to which 

surrogate data are applied should be kept to a minimum. Species sensitivity is more similar for more 

closely related taxonomic groups, and becomes less similar with increasing taxonomic distance.

In the case of permethrin, for example, there is a wide difference in sensitivity between taxonomic groups 

of aquatic invertebrates. In particular, mollusks are much less sensitive than arthropods, and therefore, 

toxicological data for arthropods should not be extrapolated to mollusks. While it may be appropriate to 

lump all aquatic invertebrates into a single category in the initial stage of the assessment, risks to these 

two important groups should be clearly distinguished at the first level of refinement. This is especially 

important because of the large number of threatened and endangered species of mollusks. We note that 

the taxonomic categories in the Office of Pesticide Programs (OPP) Pesticide Ecotoxicity Database 

distinguish between crustaceans, insects, and mollusks, and that the data in the OPP Pesticide Ecotoxicity 

Database confirm the large difference in sensitivity of crustaceans and mollusks.

Other relevant and reliable studies that could be used in a refined risk assessment are presented in Table 4 

(freshwater) and Table 5 (marine) of PDGII’s submission. As evidenced by the assigned MRID numbers 

and EPA ratings, many of the studies in Table 4 and Table 5 have been rated by EPA and found to be 

Acceptable or Supplemental. The data presented in Table 4 and Table 5 will be useful in a refined aquatic 

risk assessment that accounts for all available, high-quality data, rather than only the lowest endpoints as

used in the screening-level assessment.

EFED Response: It is EFED’s policy to select an acute and a chronic endpoint from the 

available test data within each of these very broad taxonomic groups for risk estimation. As a 

conservative measure, the selection is made from the most sensitive species tested within that 

organism group (see Overview of the Ecological Risk Assessment Process in the Office of 

Pesticide Programs, USEPA, 2004). Additional toxicity data within a broad taxonomic group can 
22

provide insight on relative species sensitivity within that group, and can be a useful tool for risk 

characterization. A summary of the lowest data endpoints was presented in the problem 

formulation. All available toxicity data for permethrin will be considered, as appropriate, in the 

upcoming Registration Review ecological risk assessment. In addition, the totality of aquatic 

toxicity data may be evaluated in the context of one or more species sensitivity distributions in 

order to provide additional characterization of ecological risk.

52. PDGII Comment: In the Summary, there is a requirement for study 850.1010 with a typical end-use 

product. The Summary appears to be silent about the species or the formulation to be tested. There is 

also a requirement for study 850.1020 to be done with H. azteca and combination products containing

piperonyl butoxide and MGK-264. In the Problem Formulation, there is a requirement for study

850.1010, and it is specified that this study should be done with H. azteca and combination products

containing piperonyl butoxide and MGK-264. There is also a requirement for study 850.1020 on page 82,

and a footnote 4 for this study on page 83. The footnote specifies that the test species should be H.

azteca, but is silent about the test substance. If study 850.1020 is done according to the requirements of

the Work Plan, it would seem that it is a duplication of 850.1010. The Permethrin Task Force requests

that EPA clarify the test species and test substance(s) for studies 850.1010 and 850.1020.

EFED Response: As listed in Table 7.2 of the problem formulation, the registrant has previously 

submitted studies for permethrin technical under Guideline 850.1010 with Daphnia magna as the 

test species (MRIDs 00043736, 00110662, 00110663). No additional studies with this guideline 

are requested at this time. Acute toxicity data on permethrin technical and typical end-use 

products with PBO and MGK-264 are requested for H. azteca, using Guideline 850.1020 as the 

basis for developing the tests. As appropriate modifications to the 850.1020 guideline will be 

necessary for testing of H. azteca, the registrant is encouraged to submit a protocol to the Agency 

prior to conducting the acute test of H. azteca.

53. PDGII Comment: In the Problem Formulation EPA raises concern about the potential for 

permethrin to bioconcentrate and to bioaccumulate in aquatic organisms and to biomagnify in terrestrial 

organisms. EPA raises these concerns based on permethrin’s octanol/water partition coefficient, the

bioconcentration factor (BCF) in the bluegill study, depuration rate from bluegills, and persistence in

water and sediment. In order to assess the potential for bioaccumulation, EPA will use its KOW (based)

Aquatic BioAccumulation Model, version 1.0 (KABAM). Although KABAM has been reviewed and

approved by EPA’s Scientific Advisory Panel, it is nonetheless a relatively recent addition to EPA’s suite

of models. It is suggested that the model outputs from KABAM be compared with all available and

relevant higher tier aquatic or terrestrial studies, as part of a model verification effort. KABAM should

not be used uncritically as the basis for a screening level assessment.

EFED Response: As indicated in the Problem Formulation (p. 66), the Agency will assess 

permethrin bioaccumulation using available bioconcentration and bioaccumulation studies in 

addition to KABAM. Such an approach, that couples measured and modeled estimates of 

bioaccumulation, was strongly endorsed by the Agency's FIFRA Scientific Advisory Panel 

meeting in 2008 (http://www.epa.gov/scipoly/sap/meetings/2008/october/minutes.pdf).

Furthermore, the Agency clearly recognized the role of biotransformation in pyrethroid 

bioaccumulation and indicated that KABAM-based estimates of bioaccumulation will consider 

available information on biotransformation rates of permethrin by aquatic organisms.
23

54. PDGII Comment: With regard to the development of EECs for the urban use, EPA has not 

provided very much detail on how the “impervious” and “residential’ scenarios were developed or 

verified. Many terms used in EPA’s discussion of these scenarios are apparently undefined. Considering

EECs for use around structures, EPA proposes to use its PRZM/EXAMS model, in a combination of 

scenarios that are described as “impervious” and “residential.” Given the extent of the urban residential 

uses of permethrin, and given what is known regarding contamination of urban water bodies by 

pyrethroids in general, arriving at appropriately conservative EECs will be critical for the permethrin risk 

assessment. The Problem Formulation document does not provide very much detail on the assumptions 

made in the impervious or residential scenarios, or any explanation for how these scenarios were 

developed or verified. EPA discusses how “alternative assumptions on percent impervious surfaces, 

percentage of use site treated, and percentage of overspray may be considered in order to characterize the 

assumptions of the ecological risk assessment in the context of individual exposure and risk conclusions.” 

Many of the terms used in this discussion are apparently not defined in the text of the Problem 

Formulation. Furthermore, it would appear that EPA has not, in fact, arrived at established assumptions 

for modeling of urban EECs. It is a concern when models that are apparently in development are used to 

support regulatory analyses.

EFED Response: Metadata files for the impervious, residential, and rights-of-way scenarios are 

available at: http://www.epa.gov/oppefed1/models/water/pe5_rlf.htm (accessed 10/21/2011). 

These files provide valuable information about these scenarios and their assumptions. Previous 

comments in this document additionally partially provide responses to the PDGII comment (e.g., 

Comment #8 and Comment #11).

55. PDGII Comment: The EFAST2 DTD screening level tool relies on simple inputs, such as 

production volume and fraction of the chemical removed during wastewater treatment, to estimate 

concentrations of chemicals in surface water that may result from household uses and disposal into 

wastewater. In order to parameterize EFAST2, EPA is requiring a POTW Treatability Study with 

technical permethrin. As several commenters have pointed out with regards to this requirement for 

bifenthrin, there is considerable variability in the performance characteristics of wastewater treatment 

plants. The study design should therefore aim to mimic a reasonable worst case for the fraction of 

permethrin removed by wastewater treatment. Also, the risk assessment itself should consider the 

bioavailability of permethrin in wastewater and biosolids. This consideration is especially relevant for a 

pyrethroid like permethrin because of the importance of dissolved organic carbon and sediment to the 

bioavailability of permethrin in other systems. These factors should be considered in developing any 

EECs for permethrin in wastewater or in biosolids. The bioavailability of permethrin in these matrices 

needs to be taken into account to arrive at appropriately conservative EECs.

EFED Response: As stated in the problem formulation, “[t]he Agency received comments from 

stakeholders with concerns regarding the value of a POTW Treatability Study and its 

representativeness of numerous treatment plant designs. EFED recognizes that such differences 

in plant design and operation may affect removal efficiencies, which is why it is proposing to 

require a POTW treatability study for permethrin, to support its EFAST2 down-the-drain 

modeling. EFED is currently working with the registrant on the design of this study to best meet 

the Agency’s environmental risk assessment needs. Part of the design of this study will need to 

address factors that the commenters present (i.e., the effect of differences in POTW design and 

operation on removal efficiencies) to the extent practicable. This may involve differences in 

experimental conditions and/or the use of POTW simulation models to address these concerns. 

The ability to extrapolate the bench scale results to results from available POTW monitoring data 

will also be evaluated. The forthcoming environmental risk assessment would address the 
24

uncertainty involved in the interpretation and extrapolation of results from the POTW treatability 

study to the national scale.”

The Agency acknowledges the substantial body of literature that indicates dissolved organic

carbon and particulate organic carbon can reduce bioavailability of highly hydrophobic chemicals 

such as permethrin. This effect is considered in the Agency's EECs developed using 

PRZM/EXAMS. In relation to E-FAST2, the Agency will consider the effect of organic carbon 

should it be necessary to refine model estimates. Furthermore, the Agency also points out the 

potential dual role that dissolved organic carbon (DOC) may have on pyrethroid bioavailability.

Specifically, while DOC is widely recognized as reducing pyrethroid bioavailability within an 

environmental compartment (such as water), it also may contribute to the dissolution and 

transport of pyrethroids between environmental compartments, such as from soils/ sediments into 

streams (Delgado-Moreno et al., 2010).2

 

56. PDGII Comment: With regard to EECs for the cattle treatment uses, EPA appears to be proposing 

that 100% of applied permethrin could wash off from treated cattle. Given the binding characteristics of 

permethrin, this assumption is likely to be unduly conservative, and should be refined. EPA also has to 

develop another novel EEC for the treatment of cattle with permethrin. EPA considers that there are two

possible scenarios by whereby permethrin can enter aquatic ecosystems after cattle are treated. The first 

scenario is that treated cattle can enter into a farm pond. The second scenario is that rainfall can wash the 

permethrin from the hair of the treated cattle, and permethrin could reach a farm pond via run-off. In both 

cases, EPA appears to be assuming that 100% of the applied permethrin will wash off from the treated 

cattle. Given the binding characteristics of permethrin to organic matter, this assumption seems overly 

conservative. It is suggested that data sources be examined to arrive at an appropriately conservative 

percent of washoff.

EFED Response: Regarding the EECs for cattle treatment, this is one representative use of the 

numerous uses of permethrin to treat animals. It appears to be one of the uses that could involve 

high exposure to aquatic habitats. Regarding the percent wash off of permethrin, EFED is open 

to evaluate further information provided by the registrant that could help refine its assessment. 

EFED believes that such studies may have been already provided to HED and if so, the registrant 

should cite them. In the absence of data, conservative assumptions will be made in the context of 

a screening assessment.

57. PDGII Comment: With regard to EECs for the ULV mosquito adulticide uses, it is suggested that 

EPA select realistic values for model inputs, such as number of applications per season, application 

interval, spray height, and nozzle type. It is further suggested that EPA draw on available laboratory and 

field studies for permethrin and other ULV mosquito adulticides. These studies would be used to verify 

model inputs and model outputs. There is considerable use of permethrin as a ULV treatment to control 

adult mosquitoes. In its Problem Formulation, EPA discusses the various models it plans to use to arrive 

at EECs for non-target organisms. However, that section is silent on how EPA plans to arrive at EECs for 

permethrin levels in water that might result from ULV applications. Contrary to conventional spray 

applications, the purpose of ULV applications is to create a fog or mist of droplets that remain suspended, 

so that adult mosquitoes come into contact with them.

 2 Delgado-Moreno, L, L. Wu and J. Gan. 2010. Effect of Dissolved Organic Carbon on Sorption of Pyrethroids to 

Sediments. Environ. Sci. Technol., 2010, 44 (22), pp 8473–8478
25

In the past, EPA has used the AGDISP (AGricultural DISPersal) model to calculate EECs, for example in

the effects determination for the Valley Elderberry Longhorn Beetle (VELB) assessment. There is

uncertainty in the applicability of AGDISP to ULV mosquito adulticide uses, and to the authors’

knowledge, predictions of AGDISP have not been compared with measured deposition or drift of any

ULV spray. There is a study relevant to the drift of ULV permethrin applications (Zhai & Groome 

[1995]; MRID 45486202). The results of this study should be compared, as possible, with model inputs 

and model-derived EECs for permethrin. Also, EPA has generally accepted the idea that, environmental 

conditions being equal, drift is primarily a function of the droplet size spectrum of the spray. Chemical 

specific factors are less important. There are several studies that show the drift and percent deposition of 

ULV applications. It is suggested that EPA compare any model-derived EECs for permethrin with the 

results of the literature studies on other ULV mosquito adulticides, as a verification step for the 

plausibility of the model results. The assumptions needed for AGDISP should be realistic. In the past for

other ULV adulticides, EPA has made non-representative assumptions about numbers of applications,

nozzle type, and the height at which the airplane flies. It is suggested that EPA plan to refine any 

AGDISP modeling that is designed to produce high-end estimates of exposure, by using realistic inputs 

for these variables.

EFED Response: In past EFED chapters for the Reregistration Eligibility Decisions of mosquito 

adulticides, the Division initially used conservative assumptions because labels for these 

chemicals were very open regarding application parameters. In the year 2005, PR Notice 2005-1 

was issued (see the following site accessed 10/11/2011 http://www.epa.gov/PR_Notices/pr2005-

1qa.htm). This notice imposed significant restrictions regarding application parameters for 

adulticides which will be taken in consideration, along with the label restrictions when the 

Registration Review ecological risk assessment is written.

A study comparing deposition of another pesticide (malathion) used as an adulticide was 

published in 2005.

3

The registrant-referenced 1995 study (Zhai & Groome) will be evaluated regarding application 

parameters and suitability of methods (e.g., droplet size spectrum, boom height, particularly if 

aerial applications were included), etc. to determine whether it provides useful information that 

may be used to refine developed EECs in the Registration Review ecological risk assessment. 

The application parameters should be comparable to the currently required ones, as per PR Notice 

2005-1.

58. PDGII Comment: EPA noted that standard laboratory tests and incident reports suggest that

permethrin has the potential to adversely affect honey bees. As such, EPA has held certain study

requirements “in reserve” as the data relating to honey bee risk and the methods for honey bee testing are 

being developed. In the Problem Formulation, EPA states that “information from standard laboratory 

tests and permethrin incident reports suggest the potential for risks to honeybees and other beneficial 

insects.” The Problem Formulation notes that in the assessment for the VELB, EPA also concluded that 

there are potential effects of permethrin on invertebrate pollinators of elderberry. However, due to 

several considerations, such as the non-systemic nature of permethrin, available information on residues 

in bees, pollen, and wax, and further development of pollinator risk assessment guidelines, EPA has 

decided to hold any further data requirements “In Reserve”. In the Problem Formulation, EPA 

 3 Mickle, R.E. 2005. Direct comparison of deposit from aerial and ground ULV applications of malathion with 

AGDISP predictions. REMSpC Report 2005-02. Study performed by REMSpC Consulting, ON, Canada and 

reported to Institut national de santé publique du Québec (INSPQ), Sainte-Foy (Québec), Canada. 83 pp. (accessed 

10/06/2011 at http://www.inspq.qc.ca/pdf/publications/483-DirectComparisonMalathion.pdf).
26

summarized the incident reports for terrestrial species that involved permethrin. The timeframe of the 

incidents is 1994 to the present. There are 3 incidents that involved permethrin and bees: I003826-028, 

I0209998-040, and I012515-004. The first 2 incidents were caused by accidental or intentional misuse. 

The third incident was rated as Possible, but the Legality of Use was rated Unknown. Permethrin has a 

wide variety of uses that could result in exposure of honeybees. Yet there have only been 3 incidents of 

bee mortality reported since 1994. Two of those incidents were some form of misuse, and the other one 

has an unknown legality of use. This seems to be a very small number of incidents for a widely used 

compound like permethrin. Furthermore, declines in our Nation’s bee colonies have prompted a high 

level of scrutiny of the causes for bee mortality. It seems likely that EPA’s concern about only a small 

fraction of incidents that occur are actually reported is much less likely for a high profile effect on 

honeybee colonies, which are tended and monitored closely by beekeepers. It is suggested the EPA keep 

these facts in mind as it decides what, if any, additional data may be required to gauge the effects of 

permethrin on pollinators.

EFED Response: EFED agrees that the nature and number of permethrin incidents that involve 

bees and other pollinators will be considered as part of any future decision regarding the need for 

additional data on pollinator effects or exposure. Because incident data are not systematically 

collected, a lack of incidents is not considered evidence that incidents do not happen. A single 

incident provides evidence that a labeled pesticide can result in an effect, such as a bee kill. The 

Agency will be considering the findings of the recent 2011 Pesticide Risk Assessment for 

Pollinators: Summary of a SETAC Pellston Workshop

(http://www.setac.org/sites/default/files/executivesummarypollinators_20sep2011.pdf), in 

addition to a forthcoming Scientific Advisory Panel on pollinator risk assessment, to determine 

the need for additional data.

59. PDGII Comment: EPA is requiring studies on the toxicity of combination products of permethrin 

with piperonyl butoxide and MGK-264, to evaluate the degree of enhancement these synergists cause. To 

do so, EPA is requiring that formulations containing the maximum ratio of synergist to permethrin be 

tested, because higher ratios of synergist to permethrin are expected to increase the degree of synergism. 

EPA further points out that the ultimate ratios of synergist to permethrin in the environment may differ 

from the ratios in the formulations, and may alter toxicity. It is suggested that EPA consider not only the 

ratio of synergist to permethrin, but also the absolute amount of the synergist. It is further suggested that 

EPA take into account that the degree of synergism may not be constant for low, intermediate, or high 

responses (e.g., lethal concentrations such as LC10, LC50, or LC90), even for the same ratio of synergist to 

permethrin.

It is well established that piperonyl butoxide and MGK-264 can cause greater than additive toxicity 

(synergism) of pyrethroids in general. EPA is requiring initial testing of formulated products containing 

the highest ratio of piperonyl butoxide or MGK-264 to permethrin, using H. azteca. This request is 

consistent with EPA’s evolving approach for evaluating the degree of synergism that occurs for other 

compounds synergized by piperonyl butoxide or MGK-264. The rationale for requesting the highest ratio 

of synergist to permethrin is that there is a positive correlation between that ratio and enhancement of 

toxicity. However, the degree of synergism can also be due to the absolute amount of the synergist, as 
27

well as the ratio (Wickham 1998).4 Also, the degree of synergism may not be uniform across the range of

responses (e.g., LC10, LC50, or LC90) (Holborn 1957).5

EPA notes that the ratio of synergist to permethrin that occurs in the environment may be quite different 

than the ratio that occurs in a formulated product, because the synergist and permethrin may have 

substantially different environmental fate properties. To address this concern, EPA will attempt to bridge 

results from ongoing “comprehensive” synergist testing being done at varying synergist to active 

ingredient ratios. If however, this comprehensive testing should prove to be insufficient to enable 

scientifically defensible bridging, EPA may apply a toxicity enhancement factor to address uncertainty 

regarding differences in synergist-to-permethrin ratios in the environment versus those tested in 

formulated products. If EPA does take this latter approach, it is suggested that not only the ratio of the 

synergist to permethrin be considered, but also the absolute amount of synergist. Furthermore, the degree 

of enhancement at toxicity levels relevant to risk assessment should also be kept in mind.

EFED Response: The Agency recognizes that the synergistic effect of PBO & MGK-264 on 

pyrethroid toxicity may be concentration and/or ratio dependent. The ongoing "comprehensive" 

synergist testing with pyrethrins and PBO is expected to provide additional insight into this 

issue. The Agency will consider all available evidence on the factors, such as the synergist to 

active ingredient ratios or absolute concentrations, that best enable bridging the results 

from combined synergist/pyrethroid toxicity tests to other pyrethroids and their application 

to ecological risk assessment.

60. PDGII Comment: The PDGII submitted a summary of ten labels from major producers of 

permethrin products for EFED (and BEAD)’s review. Besides the basic application parameters, the tables 

give comments under “other” category.

EFED Response: At the time of the Registration Review ecological risk assessment, EFED will 

evaluate the labels for the submitted products and verify any changes made during the time period 

if any, such as addition of a crop, or changes in application parameters (e.g., application interval, 

application rate and seasonal/yearly rate). EFED appreciates the submission of the summary 

tables for the ten permethrin products.

 4 Wickham J. 1998. The use of synergized pyrethroids to control insect pests in and around domestic, industrial, and 

food-handling premises. In Piperonyl Butoxide: The Insecticide Synergist, Jones DG, ed. Academic Press, London 

1998, pp. 239-260. 5 Holborn JM. 1957. The susceptibility to insecticides of laboratory cultures of an insect species. J. Sci. Food Agric 

8:182-188.