UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

MEMORANDUM 

September 3, 2014 

PC Code: 109709 

DP Barcode: 422414 

SUBJECT: Response to Public Comments on the Preliminary Ecological Risk Assessment for 

Metofluthrin. 

TO: Veronica Dutch, Chemical Review Manager 

Risk Management and Implementation Branch 5 

Pesticide Re-evaluation Division (7508P) 

THROUGH: Dana Spatz, Branch Chie~ ~ ..... ..........,~-... 

~ 

Environmental 

Environmental 

Risk 

Fate and 

Bra~~Effects ~ 

Division (7507P) 

FROM: ¥ ov""Melissa Panger, Ph.D., Senior Biologis~ .... "\: 

James Wolf, Ph.D., Environmental Scientist ()tAAt')tuK iA)~ 

Environmental Risk Branch 3 tl--- -..... 

Environmental Fate and Effects Division (7507P) 

The Metofluthrin Preliminary Work Plan (PWP) dated June 21,2013, and published in docket 

number EPA-HQ-OPP-2012-0105 summarized the preliminary conclusions made in the April 

16, 2013 ecological risk assessment and endangered species effects determination. For all 

currently registered outdoor uses of metofluthrin (PC code 1 09709), metofluthrin is released into 

the air as a vapor through passive dissipation, heat-driven or fan-driven evaporation. The 

ecological risk assessment conducted for the PWP for metofluthrin addressed potential risks 

associated with deck strips (~200 mg a.i./strip), personal fans (~15 mg a.i./device), and candles 

(~200 mg a.i./device)]. Following the PWP, a new use was proposed and assessed for a tabletop 

mister (up to ~726 mg a.i./device). All ofthe currently registered outdoor use products 

containing metofluthrin are used to repel mosquitos in outdoor areas (e.g., backyards, patios, 

decks, and campsites). In the assessments for the currently registered outdoor uses, risks to 

aquatic and terrestrial organisms were not expected. There is also an indoor registered use for 

metofluthrin to control bedbugs. An ecological risk assessment for the indoor bedbug use has 
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not been conducted due to the expected limited exposure to non-target wildlife and plants from 

this use (see below for details). 

The Preliminary Work Plan requested public comment on the ecological risk assessment / 

endangered species effects determination. Comments were received from the San Francisco Bay 

Regional Water Quality Control Board (SFBRWQCB) (8/26/2013), the Central Valley Regional 

Water Quality Control Board (8/26/2013), and the California Stormwater Quality Association 

(CASQA) (8/23/2013). These comments were reviewed by the Environmental Fate and Effects 

Division (EFED) and responses to the comments were provided on November 18, 2013. Since 

EFED’s latest response to comments, additional comments on the metofluthrin registration 

review have been received, including additional comments from the CASQA (8/4/2014) and the 

SFBRWQCB (August 1, 2014), submitted during comment period for proposed interim decision. 

The most recent comments from CASQA and the SFBRWQCB are very similar to the comments 

submitted by these groups earlier in the registration review comment period. No new data or 

analyses were provided in the most recent comments received. The primary concerns related to 

the ecological risk assessment are: 

1. The environmental risk assessment should consider that some fraction of the mist will 

deposit on outdoor surfaces where it can then be transported to storm drains or directly to 

water bodies. 

2. The outdoor misters and indoor bedbug treatments are likely to cause and/or add to the 

pyrethroid toxicity in urban waterways. 

3. Environmentally significant amounts of metofluthrin will be released to indoor drains 

during washing of linens that have covered treated mattresses and of clothes worn by 

people using the mister and the clip-on vaporizer. 

4. Aquatic toxicity data for known sensitive species, i.e., Hyalella Azteca, Americamysis 

bahia, Chironomus dilutes, and Leptocheirus plumulosus should be required and 

incorporated into the risk assessment. 

The potential for risk to non-target organisms from pesticide exposure depends on many factors, 

most notably the toxicity of the chemical, its fate properties, its use pattern(s), and its expected 

concentration(s) after use. Specific chemicals, even within the same class of chemicals, can vary 

dramatically from each other in respect to these factors. One fate parameter that varies 

significantly among pesticides within the pyrethroid chemical class is photostability. First 

generation and Type 1 synthetic pyrethroids tend to be much less photostable than Type 2 

pyrethroids. For example, less photostable pyrethroids (like metofluthrin) can break down in 

sunlight with half-lives of an hour to hours, while more photostable pyrethroids can have 
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photolysis half-lives in the tens (and sometime hundreds) of days (Spurlock and Lee 2008). This 

has impacts on their use patterns – for example, the less photostable pyrethroids, like 

metofluthrin, are not used in agriculture. After reviewing the new comments received and 

reconsidering the specific toxicity profile for metofluthrin, its specific fate properties, its 

currently registered uses (both indoor and outdoor), and its expected environmental 

concentrations, EFED still feels that the risks to nontarget organisms from the use of 

metofluthrin are low. Responses to the specific concerns received are provided below: 

1. The environmental risk assessment should consider that some fraction of the mist 

will deposit on outdoor surfaces where it can then be transported to storm drains or 

directly to water bodies. 

The review conducted by EFED for the metofluthrin mister use did consider the potential for the 

deposition of metofluthrin on outdoor surfaces and its runoff to offsite water bodies (although it 

was not specifically modeled). The metofluthrin misters are small, tabletop misters (they are not 

the large, perimeter misters registered for some other pyrethroids). The misters contain a small 

percentage of metofluthrin (i.e., 0.23%) and each product contains at most 726 mg (0.0016 lb) of 

metofluthrin. Because the product is designed to keep the metofluthrin suspended in air (that is 

the only way it is efficacious against adult mosquitoes) and is designed not to release the product 

all at once (the product mists periodically over a several hour period), and because metofluthrin 

in air has a short half-life (<2 hrs.), only a small fraction of the applied metofluthrin is expected 

to deposit on outdoor surfaces. This combined with the limited use area, means that very little 

metofluthrin will be available for offsite transport from the mister use. 

2. The outdoor misters and indoor bedbug treatments are likely to cause and/or add to 

the pyrethroid toxicity in urban waterways. 

As discussed above, EFED does not agree that the outdoor mister use will cause pyrethroid 

toxicity in urban streams because of the low environmental exposure expected with this use (see 

above). 

Regarding the registered products for the indoor bedbug use, these products (which contain 

either 0.1 or 0.01% metofluthrin) can be sprayed on mattresses but cannot be sprayed directly 

onto bed linens (linens must be removed prior to the metofluthrin application). EFED does not 

typically conduct down-the-drain analyses for treated mattresses because of the limited exposure 

expected on linens. In the case of the metofluthrin bedbug use, EFED agrees that a down-thedrain analysis for the indoor, bedbug use is not warranted. EFED concludes that the 

concentration in urban waterways is expected to be minimal based on the low amount of 

metofluthrin applied to mattresses (0.00086 lb metofluthrin can be applied per 1,000 ft2

), the 

limited amount of metofluthrin expected to transfer from the mattress to the linens, and the 
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fraction of metofluthrin that is expected to persist and be available on the linens at the time of 

washing. Therefore, EFED does not agree that the indoor bedbug use will cause pyrethroid 

toxicity in urban streams because of the low exposure expected with this use. 

3. Environmentally significant amounts of metofluthrin will be released to indoor 

drains during washing of linens that have covered treated mattresses and of clothes 

worn by people using the mister and the clip-on vaporizer. 

As discussed above, EFED does not agree that environmentally significant amounts of 

metofluthrin will be released to indoor drains during the washing of linens that have covered 

treated mattresses (see above). 

Additionally, EFED does not agree that environmentally significant amounts of metofluthrin will 

be released to indoor drains during the washing of clothes worn by people using the mister and 

clip-on vaporizer. Again, EFED does not typically conduct a down-the-drain analysis for the 

washing of clothes not directly treated or impregnated with a pesticide due to the expectation of 

limited exposure potential. In the case of the mister and clip-on fan uses, only a small fraction of 

the metofluthrin released from the mister/fan is expected to persist on any surface (including 

clothes) after use – see above for the mister and the 2013 ecological risk assessment for the clipon fan use. Therefore, the amount of metofluthrin on clothing (if any) available for wash-off 

after the mister or fan use is expected to be minimal. 

4. Aquatic toxicity data for known sensitive species, i.e., Hyalella Azteca, Americamysis 

bahia, Chironomus dilutes, and Leptocheirus plumulosus should be required and 

incorporated into the risk assessment. 

Risk assessment involves a consideration of both hazard (toxicity) and exposure. Therefore, 

even for toxic compounds, if limited or no exposure is expected, the potential for risk is low. 

Because the expected environmental aquatic concentrations for the currently registered uses of 

metofluthrin are expected to be low, additional toxicity data are not needed to make the 

ecological risk conclusions at this time. However, if the use pattern for metofluthrin was 

expanded or changed in a way that would result in higher environmental concentrations, the 

request for additional toxicity data would need to be revisited. 

REFERENCES: 

Spurlock, F., and M. Lee (2008). Synthetic Pyrethroid Use Patterns, Properties, and 

Environmental Effects. Synthetic Pyrethroids. ACS Symposium Series, Vol. 991. Pp. 3 – 25. 

Washington, DC.