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By Timothy D. Backstrom and Lisa M. Campbell

On September 19, 2018, the California Department of Pesticide Regulation (DPR) proposed a regulation to designate chlorpyrifos as a toxic air contaminant (TAC).  DPR states that this proposal is being presented “after an extensive period of scientific and public review.”  The proposed rule is based on a final evaluation issued in July 2018, in which DPR’s Human Health Assessment (HHA) Branch determined that chlorpyrifos meets the quantitative criteria for designation as a TAC.  To make that determination, DPR utilized an inhalation reference concentration (RfC) based on new animal studies with chlorpyrifos that reported neurodevelopmental effects at exposure levels well below the threshold for acetylcholinesterase (AChE) inhibition.  More information on DPR’s final TAC evaluation is available in our blog item "California DPR Releases Final Toxic Air Contaminant Evaluation for Chlorpyrifos."  In August 2018, DPR posted the Scientific Review Panel on TAC’s findings on chlorpyrifos and the Director’s Proposed Determination Concerning Chlorpyrifos as a TAC.

DPR is providing a 45-day public comment period (until November 9, 2018) on the proposed regulation to list chlorpyrifos as a TAC.  Written comments may be submitted to .(JavaScript must be enabled to view this email address).  In addition, DPR is holding a hearing to receive oral comments on this issue on November 8, 2018, at 2:00 p.m. (PT) at the California Environmental Protection Agency headquarters, 1001 I Street, in Sacramento, California.  DPR states that it anticipates that the proposed regulation to list chlorpyrifos as a TAC will be effective in 2019.  Even though DPR is proposing to list chlorpyrifos as a TAC, DPR states that “possible mitigation measures to protect human health and the environment will be considered through a subsequent process involving consultation with other state and local agencies including the Office of Environmental Health Hazard Assessment (OEHHA) and the California Air Resources Board (CARB).”

Commentary

The U.S. Environmental Protection Agency (EPA) previously issued a determination that the default 10X safety factor for infants and children established by the Food Quality Protection Act (FQPA) should be retained for chlorpyrifos.  This determination was based primarily on epidemiology studies that purported to show adverse neurodevelopmental outcomes in humans at exposure levels below the threshold for AChE inhibition, but the methodology used in these epidemiology studies has been harshly criticized by the pesticide industry.  In contrast, the DPR TAC proposal is predicated on a determination that new animal studies with chlorpyrifos report neurodevelopmental effects below the threshold for AChE inhibition, and DPR views the epidemiology studies utilized by EPA to make its FQPA determination as providing corroboration for the animal data.  At this juncture, it is not clear how EPA will characterize the new animal data concerning chlorpyrifos.  In any case, questions are likely to remain concerning EPA’s use of data concerning chorpyrifos to establish the FQPA safety factor for other organophosphate (OP) pesticides.

More information on chlorpyrifos issues and California DPR regulations is available on our blog.


 

By Lisa M. Campbell and Timothy D. Backstrom

In July 2018, the California Environmental Protection Agency’s Department of Pesticide Regulation (DPR), Human Health Assessment (HHA) Branch, issued its final toxic air contaminant (TAC) evaluation of chlorpyrifos.  This final TAC evaluation updates the December 2017 draft evaluation of chlorpyrifos as a TAC for the Scientific Review Panel (SRP) which updated the August 2017 draft and was reviewed by the SRP on TACs, and incorporates certain changes based on SRP recommendations.  As part of their review of the December 2017 draft, the SRP recommended “additional and detailed review of developmental neurotoxicity studies, in particular recent in vivo animal studies as well as a more in depth analysis of human effects of chlorpyrifos” and “that DPR reevaluate the critical endpoints, the associated [(uncertainty factors (UF)], and the resulting [reference concentrations (RfC)] and [reference doses (RfD)] for each endpoint.”

DPR determines that a pesticide is a TAC for a non-cancer adverse effect if the projected air concentrations associated with use of the pesticide are more than one tenth of the inhalation RfC established based on animal toxicity and epidemiology data.  In the draft TAC evaluation for chlorpyrifos, DPR utilized the threshold for red blood cell acetylcholinesterase (AChE) inhibition in humans and a target margin of exposure (MOE) of 100, including a factor of 10 intended to account for potential neurodevelopmental effects below the threshold for RBC AChE inhibition.  In the final TAC evaluation for chlorpyrifos, DPR increased the MOE for AChE inhibition to 300, based on deficiencies in the human inhalation parameters used to model the threshold for AChE inhibition.

In addition, the final TAC evaluation establishes a new No Observed Effect Level (NOEL) for neurodevelopmental effects in animal studies with chlorpyrifos reported at exposure levels well below the threshold for AChE inhibition.  Based on this NOEL, DPR has derived a new inhalation RfC for neurodevelopmental effects, using a standard MOE of 100 consisting of 10X for interspecies sensitivity and 10X for intraspecies variability.  This new inhalation RfC based on neurodevelopmental effects in animal studies is about one-half the revised inhalation RfC based on the threshold for AChE inhibition.  Because the modeled spray drift air concentrations for chlorpyrifos are more than one tenth of this new inhalation RfC, DPR concludes “that chlorpyrifos meets the criteria to be listed as a TAC pursuant to the law of California.”

Commentary

In the final TAC evaluation for chlorpyrifos, DPR concluded that there is sufficient evidence from animal studies to establish a new NOEL for neurodevelopmental effects, which is well below the level that has been shown to cause AChE inhibition in the same animals.  Although the U.S. Environmental Protection Agency (EPA) has previously issued a determination that the default 10X safety factor for infants and children established by the Food Quality Protection Act (FQPA) should be retained for chlorpyrifos, this determination was based on epidemiology studies that purported to show adverse neurodevelopmental outcomes in humans at exposure levels below the threshold for AChE inhibition.  The methodology used in these epidemiology studies has been harshly criticized by the pesticide industry.  DPR views these epidemiology studies as providing corroboration, but the new DPR risk assessment is predicated instead on DPR’s view that animal studies with chlorpyrifos report neurodevelopmental effects below the threshold for AChE inhibition.  The DPR risk assessment based on these animal studies uses a standard MOE of 100.  How EPA may or may not view DPR’s conclusion is not known.  In light of the August 9, 2018, decision by the U.S. Court of Appeals for the Ninth Circuit (Ninth Circuit) directing EPA to proceed with revocation of all tolerances and cancellation of all registrations for chlorpyrifos, the effect of the DPR conclusion on EPA actions is not clear.  Nevertheless, it is worth noting that, because the mechanism by which chlorpyrifos would cause such neurodevelopmental effects is unknown and is below the level that causes AChE inhibition, any presumption by EPA that other organophosphate (OP) pesticides may cause the same type of effects will likely be vigorously disputed by industry on scientific grounds.  

Please see our blog item Ninth Circuit Directs EPA to Revoke all Tolerances and Cancel All Registrations for Chlorpyrifos for more information on the Ninth Circuit’s August 9, 2018, decision.