Particulate Matter from Coal-fired Power Plants: Three Reasons Why it Might Not Harm Health. Laura C. Green, Ph.D., D.A.B.T, Cambridge Environmental, Cambridge, Massachusetts 02141

When analyzing, regulating, or otherwise addressing fine particulate matter (such as PM2.5) in ambient air, it is typically assumed that all forms of PM2.5 are equally toxic. This simplifying assumption cannot be correct, and may lead to wildly inaccurate analyses, misguided policies, and other unintended consequences. Herein we focus on the widely held assumption that particulate matter emitted and/or derived from the coal-fired power plants triggers attacks of asthma. For three types of reasons, we find that this assumption is unlikely to be true. First, we consider the pathophysiology of the disease, asthma, and find that some specific chemical and biological forms of air pollution are known or expected to exacerbate the disease, while other forms are not. Second, we consider the toxicology of the main constituents of PM2.5 due to power plants, and find that these constituents are not toxic at ambient air concentrations. Third, we consider the epidemiologic associations between particulate matter in ambient air and asthma attacks in populations, and find that they tend to be plagued by confounding (which occurs when true and false causes of disease co-vary) and/or by the "ecologic fallacy" (which is that associations derived from observations on populations may not apply to individuals). Taken together, considerations of pathophysiology, toxicology, and epidemiology indicate that associations between power-plant derived particulate matter and asthma attack rates cannot be characterized as causal. More broadly, epidemiologic studies also link sulfate levels in ambient air with populational rates of lung cancer. If this association were causal, sulfate would be more carcinogenic to the lung than inhaled arsenic or inhaled emissions from coke ovens. For several reasons, explored herein, this seems implausible.

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