Document pe17jZ9qbEEgm78nwzpQ9LjNa

October 22,1990 Some interesting details in the recent Benzene NESHAP. The twafnumerical criteria EPA lyod ao a-firsfltep" in the procsswere of no greater than approximately ' 10"4, assuming 70 years exposure. Pi Dtecting the "greatest number of persons to an individual lifetime risk" less than 10*^ (99% of peof le within 50 kilometers tp <10*6). "A pri nciple that accompanies th ;se numerical (goals is that while the Agency can e$tablish them as fixed numbers, the state of the art of risk assessment does not enable numerical risk estimates <5 be made with comparable confit lence. Therefore, judgment must be us id in deciding how numerical risk estimates are considered/with respect :o these oals- As discussed below, uncertainties arising freon such factors as the lads of knowledge about the Hology of cancer causation and gaps in data must be 'weighed along with other public health considerations" (page 6). A two step process is used as outlined in Vinyl Chloride. Step 1 is to establish the risk based acceptable level (IQ-4) Stej 2 is to determine margin of ss afety to de dde . . whether to redi "risks even further."(page 13 my emphasis):-- In the first step "The EPA will generally presume that if the risk to that individual is no higher than approximately 1 to 10 thousand, that risk level is considered acceptable and EPA then considers the other health and risk factors to complete an overall judgment on acceptability. The presumptive level provides a benchmark for judging the acceptability of maximum individual risk ("MIR"), but does not constitute a rigid line for making that determination." (page 8) "It is an estimate of the upperbound of risk based on conservative assumptions, such as continuous exposure for 24 hours per day for 70 years. As such, it does not necessarily reflect the true risk, but displays a conservative risk level which is an upperbound that is unlikely to be exceeded. The Administrator believes that an MIR of approximately 1 in 10 E/S'd TSt>9 9)S 081 "ItOIWOHO MOQ WdZS: 0 96, 60 100 -2- thousand should ordinarily be the upper end of the range of acceptability (page 8-9)". "Pamculai attentrai will also be accorded to the weight of evidence presented in the ris|K assessment of potential human inogenicity or'ckher health effects of pollutant. While the same nun erical risk/may be estimated for an exposure to a poll atant judge/ to >e a knoWn human carcinogen, and to a pollutant cons dered a possiblt humaiy carcinogen based on limited ^rdmal test data, th4 same Weight cannot bt accorded to both estimates. In 'considering the potential Public healaj^ffects of the two pollutants, the Agency's judgment on amenability, including the MIR, will be influenced by tng^reater weight of evidence for the known human carcihdgen (page 10)". tl e distributionpf risks in the lation, iiicidende, the/cience pohcyaslumptions and jodajea with thesriskymeasures/,and-tfieweight oT'evidence Pollutant ish^rmful to health are all important factors to be considered te acceptability judgment (page 11-12)". E/E'd TSt-9 9)S E08T "ItOILO-Q MOQ WdZ:E0 96, 60 IDO