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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C.,20460

OFFICE OF

CHEMICAL SAFETYAND

POLLUTION PREVENTION

PC Code: 109709

DP Barcodes: 4t527 8, 4tgL7 5

Response to Public Comments Received on the Preliminary Ecological Risk Assessment

and Endangered Species Effects Determination Conducted for the Registration Review

of Metofluthrin

May L5,20L4

MEMORANDUM

SUBJECT:

FROM:

TO: Linda Arrington, Branch Chief

Risk Management and lmplementation Branch V

Pesticide Re-evaluation Division (7508P)

The Metofluthrin Preliminary Work Plan dated June 2L, 2013 and published in docket number EPA-HQOPP-2012-0105 summarized the preliminary conclusions made in the April t6,2OL3 ecological risk

assessment and endangered species effects determination. The risk assessment noted that for the

currently registered uses, metofluthrin is released into the air as a vapor through passive dissipation,

heat-driven or fan driven evaporation, and that metofluthrin was expected to dissipate rapidly through a

combination of degradation and dilution by the large volume of air into which it is released.

Based on the available data, the currently registered use patterns, and conservative assumptions

regarding exposure, none of EPA's Levels of Concern were exceeded for fish, aquatic invertebrates,

birds, or mammals. Given the relatively limited area of effect around the metofluthrin dispensing

devices (up to 5 meters), the likely setting of use (i.e., in backyards and other areas around people), the

short half-life of metofluthrin in air (ranging from 1.7 to 1.9 hours), and the fact that the non-target

invertebrates would be exposed to the metofluthrin only by chance [unlike the target species (i.e.,

mosquitoes that track humans)1, the probability of impacting endangered invertebrates was low.

Further, the risk assessment concluded that due to a combination of low exposure and relative

insensitivity to the active ingredient (for many taxa), risks to non-target organisms were not expected.

Because direct adverse effects were not expected for birds, reptiles, amphibians, mammals, fish, or

aquatic invertebrates, and there was no reasonable expectation of effects to plants or terrestrial

invertebrates, a No Effects (NE) determination for all Federally-listed threatened/endangered species

was made for the currently registered uses of metofluthrin. This determination was supported by the

Office of Pesticide Programs' Science Policy Council/Risk Management Forum De Minimis Subgroup. lt

3;J;jffi:;,:lHlSHl,' rlrcf zDt/

Environmental Fate and Effects Division (75O7Pl
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was also determined that for the currently registered uses, no Habitat Modification was likely for 

designated critical habitats. 

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

(8/26/2013), and the California Stormwater Quality Association (8/23/2013). Comments from all three 

organizations were similar and are summarized below. Overall, the commenters felt that the data and 

modeling required of other pyrethroids undergoing registration review should also be required for 

metofluthrin, metofluthrin’s environmental risk assessment should include a quantitative assessment of 

the same level of rigor as the risk assessments for all other pyrethroids, and that all pyrethroids should 

be reviewed together as a group.

Summary of Comments

 Request that the de minimis environmental risk determination be rescinded and a full risk 

assessment be conducted. 

 Based on experience with other pesticides, the outdoor misters and indoor bedbug treatments 

are likely to cause and/or add to the pyrethroid toxicity in urban waterways.

 Metofluthrin should be considered cumulatively with the other pyrethroids because toxicity is 

additive within the class.

 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.

 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.

 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.

 Experimental photodegradation rates for air and surfaces are needed.

 An anaerobic sediment degradation rate is needed.

 Modeling of urban runoff from impervious surfaces and turf should be completed.

 Modeling down-the-drain pathways to wastewater treatment plants should be completed.

 Analytical methods for water and sediment matrices that detect metofluthrin at 

environmentally relevant concentrations should be required from the pesticide manufacturer.

 Water quality monitoring data should be required.

The Environmental Fate and Effects Division has carefully evaluated the comments received during the 

public comment phase of the registration review process for metofluthrin and continues to believe that 

the toxicity and environmental fate data for the compound, taken together with the registered uses 

strongly support the de minimis finding and the no effect determination. Even considering highly 

conservative exposure scenarios, we did not find exceedences of EPA’s levels of concern. 
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While we agree with the commenters that it is appropriate to schedule the evaluation of all the 

pyrethroids together as a chemical class (which we are doing in Registration Review), each chemical in 

this class has its own unique hazard and exposure profile, and thus risk. Therefore, consistent with 

EPA’s ecological risk assessment guidelines, it would not be appropriate to conduct the exact same type 

and level of risk assessment for all of the pyrethroids, because of the differences between them. 

Should the use pattern for metofluthrin change and/or expand, an updated risk assessment would be 

conducted, and the de minimis decision revisited.