Monday, September 15, 2008

New EPA sulfur dioxide science assessment is bad news for coal and oil

US EPA scientists have quietly released a new scientific assessment of the dangers posed by sulfur dioxide (SO2) in the air:

It’s very clear from the scientific evidence that tougher pollution standards are needed to protect people with asthma, children, and senior citizens. In particular, the EPA assessment points to the need for a new short-term standard to limit sulfur dioxide emissions.

This is an argument for further cleanup of existing coal-fired power plants, as well as an argument against building new coal-fired plants.

Not surprisingly, the electric power and oil industries have already begun tossing up arguments against any effort by EPA to set tougher new standards. (Oil refining is another source of sulfur dioxide emissions, as are the paper and smelting industries, among others. For some comments, see at )


The EPA’s “integrated science assessment” concludes that

Collectively, the human clinical, epidemiologic, and animal toxicological data
are sufficient to conclude that there is a causal relationship between
respiratory morbidity and short-term exposure to SO2. Observed associations
between SO2 exposure and an array of respiratory outcomes, including respiratory
symptoms, lung function, airway inflammation, AHR, and ED visits and
hospitalizations from the human clinical, animal toxicological, and
epidemiologic studies, in combination, provide clear and convincing evidence of
consistency, specificity, temporal and biologic gradients, biological
plausibility, and coherence.
Human clinical studies consistently demonstrate
respiratory morbidity among exercising asthmatics following peak exposures (5-10
min) to SO2 concentrations ≥ 0.4 ppm, with respiratory effects occurring at
concentrations as low as 0.2 ppm in some asthmatics. In the epidemiologic
studies, the SO2-related respiratory effects were consistently observed in areas
where the maximum ambient 24-h avg SO2 concentration was below the current 24-h avg NAAQS level of 0.14 ppm (see Tables 5-4 and 5-5). Potentially susceptible
and vulnerable subgroups include asthmatics, children, older adults, and
individuals who spend a lot of time outdoors at increased exertion levels.
In addition to respiratory morbidity related to short-term exposure to SO2,
studies of other health outcomes and exposure durations were also evaluated in
this ISA. The evidence is suggestive of a causal relationship between short-term
exposure to SO2 and mortality. The evidence linking short-term SO2 exposure and
cardiovascular effects, and morbidity and mortality with long-term exposures to
SO2 is inadequate to infer a causal relationship.

The American Lung Association has long argued that EPA should set a new short-term standard to protect those living near power plants and other sources of SO2 emissions. The EPA last reviewed the air standards for sulfur dioxide in 1996. The agency has announced a schedule under which it would propose a new standard (or, improbably, propose no change in current standards) by next July.

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