PROCEDURE FOR DETERMINING CANCER INDEX FOR SIMULTANEOUS EXPOSURE TO MULTIPLE CARCINOGENS

Subpart 1. Cancer index. To evaluate simultaneous exposure for multiple carcinogens, a cancer index must be calculated using the procedure in this part. Subp. 2. Carcinogenic HRVs. For health risk values (HRVs) that have cancer endpoints, items A to C apply. A. A cancer index is determined for chemicals or defined mixtures of chemicals with an inhalation endpoint of cancer using the following equation: Cancer index = E C1 _ HRV C1 + E C2 _ HRV C2 + . + E Cn _ HRV Cn Where: (1) E Cn represents the measured or modeled ambient air concentration as expressed in units of micrograms per cubic meter (µg/m 3 ) of the first, second, through the n th carcinogen; and (2) HRV Cn represents the chronic HRV of the first, second, through n th carcinogen as expressed in units of micrograms per cubic meter (µg/m 3 ). B. A cancer index of one is equivalent to a cumulative HRV. A cancer index greater than one exceeds the cumulative HRV. Subp. 3. Carcinogenic MHRVs. For mixtures of multimedia health risk values (MHRVs) that have cancer endpoints, items A to C apply. A. A cancer index is determined for chemicals or defined mixtures of chemicals with an endpoint of cancer using the following equation: Cancer index = D C1 _ MHRV C1 + D C2 _ MHRV C2 + . + D Cn _ MHRV Cn Where: (1) D Cn represents the calculated lifetime averaged daily dose of the first, second, through the n th carcinogen as expressed in units of micrograms per kilogram of body weight per day (µg/kg-d); and (2) MHRV Cn represents the MHRV of the first, second, through the n th carcinogen as expressed in units of micrograms per kilogram of body weight per day (µg/kg-d). B. A cancer index of one is equivalent to a cumulative MHRV. A cancer index greater than one exceeds the cumulative MHRV.