Residential applicator exposure assessment

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14.8.2. Risk assessment of residential exposures to chlorpyrifos

Chlorpyrifos is an organophosphorous insecticide that causes toxicity by inhibiting AChE in both insect and mammalian nervous systems. The EPA completed a comprehensive chlorpyrifos exposure and risk assessment in 2000 EPA, 2000d. The patterns of use most common in indoor environments for control of pests were crack-and-crevice or spot applications and general surface treatments. Chlorpyrifos applied in homes by these methods vaporized after application, contaminated indoor air and led to secondary inha- lation exposure. Secondary dermal exposure was most likely from general surface treat- ments, leading to incidental exposures, especially among children. The effect that was considered adverse by the EPA, which was common to all exposure routes, was inhibi- tion of cholinesterases not only AChE. An AEL equal to 1000 was considered acceptable, because it took into account what was considered to be young animals’ greater sensitivity to the toxic effects of chlorpyrifos. It should be noted that most residential exposure assessments done for chlorpyrifos were Tier 1 assessments. SOPs and Pesticide Handlers Exposure Database PHED data were used in these evaluations. For a few scenarios, studies were available on environmental and biomonitoring, enabling the EPA to refine some of the exposure values.

14.8.2.1. Residential applicator exposure assessment

Three residential applicator exposure assessment scenarios were evaluated: 1. paint-brush applications to surfaces 2. spot treatments with low-pressure hand sprayers 3. outdoor hose-end applications to lawns and shrubs. Residential applicator data were unavailable, and the following assumptions were taken into consideration in performing the assessment. • Dermal and inhalation exposures were combined, because cholinesterase inhibition was the toxicological end-point of concern in both cases. • The average BW of an adult is 70 kg. • The application of chlorpyrifos is made according to the label directions. • Applicators wore short-sleeved shirts and no gloves. • Exposure is short-term one day to one month after application. • When data were unavailable, surrogate unit exposures were based on PHED data. • The AEL is 1000. The daily dermal dose, inhalation dose and total MOS are defined as follows. Pesticides: risks and hazards 518 magnitude of exposures by the principal routes and their significance in the light of patterns of application use, we provided below examples from EPA exposure evaluations and the public literature. In these evaluations, residents who apply pesticides are called handlersor applicators , while non-applicator housing residents are called residential bystanders. Quantifying exposure to pesticides from the oral, inhalation, and dermal routes is essen- tial to risk characterization and management. The margin of safety MOS is defined as the ratio of the NOAEL, derived from relevant toxicity studies, to the actual estimated, calculated or measured exposure. An acceptable exposure level AEL is a MOS derived by dividing NOAELs by factors, called uncertainty factors or safety factors by different bodies, that are applied to overcome uncertainty. This chapter uses the term uncertainty factor UF. AELs are identified as such because the uncertainty factor has been applied and represents a benchmark regulation based on the level of human health concern. A MOS calculated from actual data is referred to as MOS in this chapter. Note that the EPA uses the term margin of exposure MOE instead of MOS. Also, it uses MOE UF instead of AEL. When performing risk assessments, uncertainties arise from the possibility of differen- ces in toxicological responses between people and test animals interspecies responses, differences within the human population intraspecies responses and, where applicable, within subgroups of human populations. UFs are applied to account for these differen- ces, in the absence of evidence to the contrary, as follows. • People are assumed to be 10 times 10x UF more sensitive to the adverse effects of a pes- ticide than tested animals. • An additional 10x UF is added to account for human intraspecies responses. In the United States, an additional factor known in the United States as the Food Quality Protection Act FQPA factor is added by default, assuming that if not otherwise demonstrated children are 10 times 10x UF more sensitive than adults to the adverse effects of pesticides. If all three UFs are applied, multiplying them together yields an AEL for residential set- tings equal to 1000, and this AEL is used often in the United States for Tier 1 risk assess- ments. AEL values less than 1000 may be used if data exist to refine the assessment. An AEL of 1000 means that it is only acceptable to allow a person to be exposed daily to a pes- ticide amount that is 1000x less than the level at which no adverse effects were observed in laboratory animals – that is, the AEL is 1000 or more. Therefore, an acceptable AEL may range in value from 100 to 1000 or more, depending on the amount and quality of toxicity and exposure data available to refine the risk assessment. Chlorpyrifos and pyrethrin exposures and risks, as assessed by the EPA, are described below EPA, 2000d, 2006b. For these compounds, the acute and sub-chronic toxicity end- points are described in Table 14.2. Public Health Significance of Urban Pests 521

14.8.2.4. Incidental hand-to-mouth oral exposure