6.21 Visit the page describing the assessment of the

Reference Dose (RfD) for chronic oral exposure:

(https://cfpub.epa.gov/ncea/iris/iris_documents/

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