Simazine cumulative exposure

Exposure assessments characterize the water, diet, and herbicide handling exposure pathways for atrazine and simazine (Sielken et al, 1996, 1998). For each exposure pathway, the chemical-specific doses (mg/kg/day) from each relevant route (ingestion, inhalation, and dermal) are summed. The total chemical-specific dose for each exposure pathway is characterized separately, and then these doses are aggregated by summing over the multiple exposure pathways. The pathway-specific and aggregate assessments are performed separately for atrazine and simazine. In addition, because atrazine and simazine are assumed to have a common mechanism of toxicity, a cumulative exposure assessment is performed combining the doses of atrazine and simazine. 

Because Equation (31.4) is mathematically equivalent to either Equation (31.5) or (31.6) (shown below), the formula for MOEatrazine simazine in Equation (31.4) is of the proper form - namely, a benchmark dose corresponding to a known amount of toxicity, divided by a cumulative dose from exposure that reflects the relative toxicity of the cumulated chemicals. 

The cumulative margin of exposure (MOE) for atrazine and simazine is calculated by using the following equation ... 

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