Session Title: Higher Tier Risk Assessment for Chlorfenapyr
July 1, 1999
In December of 1994 the Office of Pesticide Programs received a request for a FIFRA Section 3 Registration for the use of the pyrrole insecticide chlorfenapyr on cotton. The Environmental Fate and Effects Division (EFED) has conducted a series of increasingly refined ecological risk assessments to respond to this registration request. The purpose of this SAP session is to obtain SAP input on the results of completed risk assessments and to obtain guidance on potential further refinements.
The first ecological risk assessment, conducted in 1994, was qualitative in nature and based solely on the limited data available in support of an experimental use permit application for chlorfenapyr. This risk assessment was conducted pursuant to emergency use requests (FIFRA Section 18). In this assessment, EPA found that the acute levels of concern were exceeded for birds, fish, and aquatic invertebrates. The assessment concluded that birds were expected to be at high acute risk (no chronic toxicity data were yet available) and the exceedance of the levels of concern warranted a refined risk assessment.
In 1995, OPP conducted a screening level risk assessment of the use of this compound on cotton. In this assessment, EPA estimated chlofenapyr residues in wildlife food items based on assumptions of maximum application rates and frequencies of application and no dissipation (this was a typical EFED screening level risk assessment). The assumption of maximum application rate and frequency of application combined with the assumption of no dissipation meant that EPA's estimates of residues on avian food items would be relatively high and that avian exposure would, accordingly, also be estimated to be relatively high. In this assessment, EPA concluded that chlorfenapyr was persistent and risk quotients for acute toxic effects exceeded high risk level of concern by 20X and chronic effects level of concern by 504X. Aerial application of chlorfenapyr was concluded to also present a high acute risk to aquatic organisms.
In 1996, OPP refined the avian exposure component of its ecological risk assessment to rely on mean or typical assumptions of chlorfenapyr residues in wildlife food items rather than estimates based on maximum application rates and frequencies of application. Both the 1995 and 1996 assessments assumed no dissipation of chlorfenapyr residues in food items. In this assessment, EPA found that avian acute risk quotients exceeded the acute high risk level of concern by factors ranging from 0.5X to 6X (depending on application rate) and chronic levels of concern were exceeded by factors of 4x to 53X.
In 1997, OPP further refined the avian risk assessment to account for potential residue dissipation. However, food item residue dissipation data was not available, and the 1997 risk assessment relied on environmental fate data to estimate the fate of residues in the soil as a surrogate for the fate of residues in wildlife food items. In this refinement, EPA found that soil half-life assumptions of 2 to 4 years resulted in modeled soil concentrations that exceeded the 0.5 ppm dietary avian reproduction effects threshold for multiple years.
Subsequent to the 1997 refinement of the avian risk assessment, the registrant provided the Agency with data regarding the residues of parent chlorfenapyr in vegetation, seed, and insects over time to address the need for dissipation of residues in wildlife food items. In addition, new data were supplied for aerobic soil metabolism and field soil dissipation of chlorfenapyr that indicated the persistence of chlorfenapyr in soils was less than previously assumed. OPP's 1998 further refinement of the avian risk assessment incorporated registrant-supplied data regarding measured chlorfenapyr residues in wildlife food items, avian species assemblages in cotton agro-environments, and selected biological characteristics of these avian species as they relate to dietary exposure and effects data for selected passerine species. Although OPP's techniques for assessing avian exposure and effects were modified from historic practice in order to incorporate the measured residue data, the avian risk assessment generally followed current EFED risk assessment approaches. In addition to refinements in the avian risk assessment, OPP's 1998 assessment included refinements in the aquatic risk assessment. The 1998 assessment includes the use of the MUSCRAT probabilistic model for aquatic exposure as well as effects data for sediment-dwelling invertebrates.
EFED recognizes the limitations of the Division's current deterministic approach and the potential utility of a probabilistic approach in helping risk assessors and risk managers to better understand the potential magnitude and severity of ecological impacts. EFED is, in fact, actively engaged through the ECOFRAM initiative in a substantial effort to develop probabilistic risk assessment methods, approaches, and tools for purposes of ecological risk assessment of pesticides. However, at present EFED lacks peer reviewed guidance and standard operating procedures for probabilistic ecological risk assessments of pesticide use. EFED is looking for guidance on next steps in further refining its chlorfenapyr avian risk assessment using more probabilistic techniques and, where data and validated methods are limited for purposes of probabilistic risk assessment, suggestions for further refining its deterministic assessment of avian risk from the use of chlorfenapyr on cotton.
- Recognizing the limitations of the current deterministic risk
assessment approach employed by EFED and the absence of adequately
developed probabilistic ecological risk assessment methods for
pesticides, EFED is seeking SAP input regarding the current agency
risk assessments use of available data to characterize the risks
of chlorfenapyr use on cotton to birds using cotton agro-environments.
- Although ECOFRAM has recently released draft technical reports on terrestrial and aquatic probabilistic methods for assessing pesticide risks, EFED recognizes that implementation of the tools and methods suggested in these reports will require substantial time and effort. Further, while EFED's concerns for chlorfenapyr are centered on potential avian reproduction impairment, the ECOFRAM documentation is centered primarily on acute mortality endpoints for birds. Consequently, EFED is requesting guidance from the SAP on appropriate interim measures to take to begin implementation of probabilistic techniques in the assessment of chlorfenapyr avian reproduction risks. EFED is also seeking SAP opinion on whether the existing data (residues, biology, and effects) can support the use of probabilistic assessment techniques within acceptable margins of uncertainty.