Magazine article Issues in Science and Technology

Improve Chemical Exposure Standards

Magazine article Issues in Science and Technology

Improve Chemical Exposure Standards

Article excerpt

I certainly agree with Gwen Ottinger and Rachel Zurer ("Drowning in Data", Issues, Spring 2011) and the followup letter by Sarah A.Vogel (Issues, Summer 2011, p. 16) that it is a fundamental challenge to translate chemical concentration data into information that is meaningful to the public. However, both of these pieces include some incorrect information and miss key aspects of the issues.

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First, Ottinger refers to various ambient air standards and the fact that there is "no consensus on what constitute [s] a safe or permissible level." A casual reader could get the impression that all of the health-effects research that has been done to date has basically been useless in terms of relating con-centrations to health effects, which would be misleading. Although there is some variability in the underlying technical information, much of the variability in standards is because standards have different purposes and/or are applied to different situations. For example, contrary to what Ottinger and Zurer say, the federal Clean Air Act does not set ambient air standards for volatile organic compounds (VOCs); however, Clean Air Act regulations do set stack concentration limits for VOCs, for some industrial sources. Not surprisingly, if you are comparing stack concentration limits to ambient concentration limits, you are going to expect orders of magnitude differences, but these differences are not due to a lack of scientific consensus. They are due in part to the fact that they are applied to different locations (inside an exhaust stack versus in the ambient air) and in part because they are not both based on what is "safe." For example, some industrial equipment standards are based on what is achievable with available control technologies, which may be more or less than what someone deems to be safe. In addition, some air standards are not standards for what are safe levels in the ambient air, but are conservative standards used for issuing air pollution permits. In other words, the standards are for purposes of comparing the worst-case effects of a facility to a person standing at the facility's fence line for an extended period of time.

Second, it needs to be recognized that while identifying safe levels can and should be based on scientific information, there is also some political judgment involved. Although there are some health effects with thresholds, others do not have clear thresholds. For example, the default assumption for cancer risk is that the only concentration that corresponds to zero risk is zero. In addition, there are questions about how to address scientific uncertainty, how to extrapolate animal data to humans and account for the most susceptible humans, and how to extrapolate data that were taken at very high doses in order to produce a measurable effect down at the low doses. Vogel states that "what is safe for a 180-pound healthy man is not safe for a newborn, but our safety standards for industrial chemicals, except for pesticides, treat all humans alike." But this is incorrect, because many of the health-based air standards are in fact designed to be protective of the most sensitive individuals and do take children explicitly into account (OSHA standards are one obvious exception, because they are applicable to workplace conditions experienced by adults). …

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