Pennsylvania Code › Title 25 - ENVIRONMENTAL PROTECTION › Part I - Department of Environmental Protection › Subpart A - Preliminary Provisions › Article II - Statements of Policy › Chapter 16 - WATER QUALITY TOXICS MANAGEMENT STRATEGY-STATEMENT OF POLICY › Subchapter A - GUIDELINES FOR DEVELOPMENT OF CRITERIA FOR TOXIC SUBSTANCES AND WATER QUALITY CRITERIA FOR TOXIC SUBSTANCES › GUIDELINES FOR DEVELOPMENT OF HUMAN HEALTH-BASED CRITERIA › Section 16.33 - Nonthreshold effects (cancer)

Current through Register Vol. 54, No. 28, July 13, 2024
(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 toxic substances). Attainment of this risk level is predicated on
						  exposure that includes drinking 2.4 liters of water and ingesting 22.0 grams of
						  fish per day over a 70-year lifetime. 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.