§ 16.33. Nonthreshold effects (cancer).

 (a)  A nonthreshold effect is defined as an adverse impact, including cancer, for which no exposure greater than zero assures protection to the exposed individual. Thus, in contrast to the threshold concept discussed in §  16.32 (relating to threshold level toxic effects), the nonthreshold approach to toxics control is based upon the premise that there is no safe concentration of the toxic.

 (b)  The Department has determined that the regulation of carcinogens from a water quality perspective in accordance with the procedure specified in the following subsections will adequately and reasonably protect human health.

 (c)  The Department accepts the evaluation and extrapolation modeling used by the EPA to quantitate the carcinogenic risk of particular chemicals. Cancer risk level criteria are, therefore, adaptations of the EPA’s cancer potency (slope) factors. Criteria based on cancer risk levels are average lifetime exposure values.

 (d)  The Department’s water quality toxics management program controls carcinogens to an overall risk management level of one excess case of cancer in a population of one million (1 x 10-6). Expressing this another way, the probability of an individual getting cancer from an ambient water exposure to a carcinogen is increased by a factor of one in one million. This level appears to be protective of human health to a significant degree when compared to other risks encountered in life.

 (e)  The Department uses a 1 x 10-6 cancer risk level as specified in §  93.8a(d) (relating to water quality criteria for toxic substances). Attainment of this risk level is predicated on exposure that includes drinking 2 liters of water and ingesting 17.5 grams of fish per day over a 70-year lifetime, except as provided in §  16.61(b)(2) (relating to special criteria for the Great Lakes Systems). Bioaccumulation of carcinogenic toxics in edible portions of fish are accounted for by use of bioaccumulation factors (BAFs).

 (f)  The Department will use the following guidelines in establishing criteria for nonthreshold toxics:

   (1)  The determination as to whether a substance is a carcinogen will be its identification by the EPA.

   (2)  For toxics for which (cancer potency) slope factors have been developed as evidenced by listing on IRIS the Department will either use the EPA developed criteria or will develop criteria based upon these potency factors using the Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (EPA-822-B-00-004, October 2000) and the National Recommended Water Quality Criteria (EPA-822-H-04-001, 2004), as amended and updated or EPA’s Standard Toxicological Procedures outlined in Exhibit 3-2 of the Water Quality Standards Handbook, Second Edition, EPA 823-0-94-005A, August, 1994, as amended and updated.

   (3)  For carcinogens or suspected carcinogens for which cancer potency (slope) factors have not been developed, the Department will use an additional margin of safety (factor of 10) with threshold toxicity data to develop a protective health criterion.


   The provisions of this §  16.33 adopted March 10, 1989, effective March 11, 1989, 19 Pa.B. 1059; amended April 9, 1993, effective April 10, 1993, 23 Pa.B. 1727; amended December 26, 1997, effective December 27, 1997, 27 Pa.B. 6817; amended November 17, 2000, effective November 18, 2000, 30 Pa.B. 6111; amended May 15, 2009, effective May 16, 2009, 39 Pa.B. 2523. Immediately preceding text appears at serial pages (271872) to (271873).

Cross References

   This section cited in 25 Pa. Code §  16.61 (relating to special provisions for the Great Lakes System).

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