from oil, gas, or nuclear energy. Most of the accident risk with coal is associated with deep mining and rail transportation. (The latter, of course, is not uniquely associated with coal.) The health of workers in the mines has been notoriously poor in the past and has led to special congressional legislation to provide benefits that now total more than $1 billion/yr. A conscientious program to improve mine safety and hygiene, especially by enforcing current regulations, and to improve railroad safety could materially improve the situation. The rising percentage of surface mining in the total of production should also tend to reduce the risk of accident and disease.

EMISSIONS

A great variety of pollutants that may affect human health as well as plant and animal life are released from the combustion of fossil fuels, especially coal. These include sulfur and nitrogen oxides, carbon monoxide, hydrocarbons, particulates, and heavy metals (in trace amounts). Local air pollution containing these substances at high levels and in varying proportions is known to have increased the incidence of discomfort and disease (especially of the respiratory system), and even death. The intent of the national ambient air quality standards is to render negligible the morbidity and certainly mortality (or so-called “premature death”) from emissions.

Whether or not the standards have been set at the most efficient levels (adequately protective of health, but not needlessly restrictive or costly), and whether all toxic substances requiring regulation have been specified are topics under very active discussion and investigation. The standards themselves must be reviewed, by law, every 5 years and revised if necessary. Current interest centers on several pollutants: sulfur and nitrogen oxides, carbon monoxide, hydrocarbons, particulates, and heavy metals. Since the particulates (now regulated) comprise a spectrum of sizes, of which only those below 2 µm in size can reach the lungs, it is thought that respirable particulates may be the true measure of toxicity. A standard for sulfates had been proposed in addition to the current one for sulfur dioxide. Sulfate is a constituent of the particulates, however, so that it might be an indirect measure for them. In any event, the acidity of the atmosphere does depend on its sulfate (and nitrate) content. Hydrocarbons and heavy metals are also associated with the particulates. In setting standards, the question of whether there are thresholds (exposure levels below which there are no significant health effects from pollutants) is important. In general, standards are based on all available evidence, including that for any type of induced discomfort, promotion or induction of disease, and possible genetic effects. As a practical matter, a level at or



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