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