DEVELOPMENT OF HEALTH CRITERIA FOR SCHOOL SITE RISK ASSESSMENT PURSUANT TO HEALTH AND SAFETY CODE SECTION 901(g): PROPOSED CHILD-SPECIFIC REFERENCE DOSE (chRD) FOR SCHOOL SITE RISK ASSESSMENT - Chlorpyrifos

REFERENCES-A child-specific reference dose (chRD) at 0.0001 mg/kg-day for chlorpyrifos has been established in this document pursuant to Health and Safety Code Section 901(g). Health and Safety Code Section 901(g) requires the Office of Environmental Health Hazard Assessment (OEHHA) to identify chemical contaminants commonly found at school sites to be of greatest concern based on child-specific physiological sensitivities, and to develop numerical health guidance values (HGVs) for these chemical contaminants for use in the assessment of risk at proposed or existing California school sites. Chlorpyrifos, O,O-diethyl-O-(3, 5, 6-trichloro-2-pyridinyl)-phosphorothioate, is a broad-spectrum organophosphate insecticide. Despite the cancellation of its registration for most home, lawn and garden use by U.S. EPA since 2000, chlorpyrifos continues to be one of the most commonly used pesticides, and the potential risks to children are still of concern to OEHHA. Inhibition of cholinesterase by its active metabolite chlorpyrifos oxon was once considered the lone mechanism of chlorpyrifos neurotoxicity. However, there is now evidence that chlorpyrifos directly targets events that are specific to the developing brain and that are not related to the inhibition of cholinesterase, including: inhibition of DNA synthesis, impairment of cell acquisition and differentiation, interactions with neurotrophic factors, interruption of cell signaling cascades, and alteration in synaptic function. Based on our review of the existing literature, OEHHA concluded that there are age-related differences in the susceptibility to chlorpyrifos. Young animals are more sensitive to chlorpyrifos than adults. OEHHA also concluded that both cholinesterase and non-cholinesterase-related mechanisms contribute to the differential susceptibility between young and adults. The deficits may be manifested immediately after the exposure, or appear later in life. OEHHA proposes a chRD of 0.0001 mg/kg-day for chlorpyrifos based on both cholinesterase inhibitions in dogs and rats and supporting information on cognitive deficiencies in rats. Health and Safety Code (HSC) Section 901(g) requires the Office of Environmental Health Hazard Assessment (OEHHA), in consultation with the appropriate entities within the California Environmental Protection Agency, to identify those chemical contaminants commonly found at school sites and determined by OEHHA to be of greatest concern based on child-specific physiological sensitivities. HSC Section 901(g) also requires OEHHA to annually evaluate and publish, as appropriate, numerical health guidance values (HGVs) for five of those chemical contaminants until the contaminants identified have been exhausted. HGVs established by this mandate are intended for use in the assessment of risk at proposed or existing California school sites. At this time, OEHHA focuses …