6.21 Visit the page describing the assessment of the Reference Dose (RfD) for chronic oral exposure: ( documents/subst/0209_summary.pdf) for the chemi- cal atrazine. Atrazine is a popular herbicide: tens of millions of pounds of atrazine are applied to vegeta- tion in the United States annually, and, is a wide- spread drinking water contaminant. (a) What are the NOAEL and RfD for atrazine, and to which response do these doses refer? (b) Assume the follow- ing additional toxicity data points: LOAEL-5 mg/ kg/day (affects 5% of population); LD50-15 mg/ kg/day; other data points-22 mg/kg/day (affects 75% of population), 30 mg/kg/day (affects 95% of population). Draw a dose-response curve for these data. (c) What is the approximate slope of the curve? (d) Now consider applying atrazine to your lawn and assume that there are babies in the household that like to eat grass. What is the maximum amount of grass that a baby can eat safely in a day? Assume the follow- ing conditions: baby weight ~10 kg, residual atrazine concentration on grass from one application is ~0.01% (where 1% = 10,000 ppmm). (e) Given these results from part (d), does spraying your lawn with atrazine

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