On July 20, 2016, the U.S. Environmental Protection Agency (EPA) issued a memorandum attaching minutes from the April 19-21, 2016, FIFRA Scientific Advisory Panel (SAP) meeting, Transmittal of Meeting Minutes of the April 19-21, 2016 Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP or Panel) Meeting Held to Consider and Review Scientific Issues Associated with “Chlorpyrifos: Analysis of Biomonitoring Data.”  This SAP was convened to advise EPA regarding the evaluation of biomonitoring chlorpyrifos data from epidemiology studies conducted by the Columbia Center for Children’s Environmental Health (CCCEH).

The minutes indicate that the SAP has significant concerns with EPA’s proposal to use the biomonitoring chlorpyrifos data from the CCCEH epidemiology studies to establish a point of departure (PoD) for chlorpyrifos risk assessment.  The minutes state:  “Because many uncertainties cannot be clarified, the majority of the Panel does not have confidence that the Columbia Center for Children’s Environmental Health (CCCEH) cord blood data on chlorpyrifos concentrations can accurately be used in quantitative risk assessment to determine a Point of Departure (PoD).”  A major source of uncertainty cited by the FIFRA SAP is “the lack of verification and replication of the analytical chemistry results that reported very low levels of chlorpyrifos (pg/g),” because EPA had to impute a finite quantitative value to “a large fraction of cord blood samples included in the analyses presented with levels below [level of detection (LOD)].”  Moreover, some SAP members “thought the quality of the CCCEH data is hard to assess when raw analytical data have not been made available, and the study has not been reproduced.”

The SAP also, however, stated that “both epidemiology and toxicology studies suggest there is evidence for adverse health outcomes associated with chlorpyrifos exposures below levels that result in 10% red blood cell (RBC) acetylcholinesterase (AChE) inhibition (i.e., toxicity at lower doses).”  Nevertheless, it agreed with EPA that “applying additional safety factors to the AChE PoDs to account for a possible noncholinergic mode of action (MOA) would be problematic because of challenges in justifying any particular value for such an adjustment.”

Of note, the SAP concluded that it would be appropriate to use a “10X intra-species extrapolation factor” in any analysis based on the cord blood data.  It also identified other sources of uncertainty that should be considered in such an analysis, including “the inability of single measures of chlorpyrifos concentration in blood to provide information regarding source, frequency, duration and magnitude of exposure, and how these exposures are linked to specific outcomes measured in the CCCEH study participants.”  Although EPA suggested in a Status Report filed in the chlorpyrifos litigation pending in the Ninth Circuit Court of Appeals on June 29, 2016, that the FIFRA SAP might recommend a “hybrid approach” that EPA could use in lieu of a PoD based on AChE inhibition, thereby altering the prior EPA analysis for chlorpyrifos, the SAP minutes do not include a recommendation for such a hybrid methodology.

Commentary

Given the concerns expressed by the SAP regarding EPA’s proposal to derive a PoD from cord blood biomonitoring data collected in the CCCEH epidemiology studies, it may be unlikely that EPA will further pursue this specific approach.  It is less clear whether EPA will be inclined to propose any further adjustments to its existing risk assessment for chlorpyrifos, which utilizes a PoD based on animal AChE data, along with intra-species and inter-species uncertainty factors and an additional Food Quality Protection Act (FQPA) 10X factor.  EPA’s decision to retain the special FQPA factor in its risk assessment for chlorpyrifos will remain controversial, because it is based on an assessment of the value and significance of several epidemiology studies for chlorpyrifos that many in the pesticide industry strongly dispute.  The discussion in the minutes of the uncertainties resulting from the refusal of the CCCEH investigators to provide underlying raw data may provide further support for arguments by industry that EPA should not predicate risk assessments on the epidemiology studies for chlorpyrifos before obtaining and reviewing these data.