Human Pesticide Exposure Assessment – Simazine
Abstract
This exposure assessment document is written as an integral part of the Department’s risk characterization document for the active ingredient simazine. Simazine is a selective pre-and post-emergence herbicide used primarily for the control of broadleaf and grassy weeds in soil where almonds, apples, avocados, blueberries, corn, established Christmas trees, grapes, and other crops are or will be planted, and in non-cropped areas such as around buildings, lawns, and rights-of-way. Simazine is an organic compound of the s-triazine family. Its mode of herbicidal action is through inhibition of photosynthesis. During the five-year period between 2006 and 2010, there was one (1) illness reported in California as having an association with simazine use in combination with other pesticides, with the case occurring in an occupational setting and involving eye irritation as the only symptom. Available metabolism studies showed that a di-N-dealkylated metabolite appeared to be the major degradate in rats with a range from 1.6% of the applied (gavage) dose at 0.50 mg/mL to 18% at 50 mg/mL, tending to suggest that the rate of simazine metabolism in the rat may be dose-dependent. A study on dermal absorption of atrazine in humans was also submitted, from which a daily absorption of 6% was concluded to be an appropriate surrogate and sufficient for calculating the dermal doses of simazine in humans. In the present exposure assessment, the potential exposures to simazine were considered for 14 exposure scenarios subsumed under 6 major subpopulations including applicators, human flaggers, mixer/loaders, mixer/loader/applicators, homeowner users, and nonusers as well as bystanders. Reentry exposures for fieldworkers were deemed insignificant and hence not assessed quantitatively, as simazine is a herbicide used primarily for the control of weed seeds with a very short application window. No chemical-specific data on human exposure to simazine were available. The potential exposures to simazine for the subpopulations were thereby estimated from (considering the use of) surrogate exposure data, such as those available in the nonchemical-specific PHED (Pesticide Handlers Exposure Database) or those specifically on atrazine, a herbicide very similar to simazine in structure, functions, and uses. For short-term exposure lasting 1 to 7 days, the highest calculated absorbed daily dosage (ADD) was 5.5 mg per kg of body weight (BW), that estimated for aerial mixer/loaders preparing liquid simazine while wearing normal work clothes and gloves. For intermediate-term (a.k.a. subchronic) exposure (i.e., for 8 to 90 days), the highest calculated ADD was 1.4 mg/kg BW, also for the same handler group. For nonuser residents as well as for children with normal (or pica) mouthing behavior, the estimated aggregate ADD from short-term or subchronic exposure was <0.14 (or <0.16 for pica) mg/kg BW.