percent chance of excess lung cancer from a lifetime exposure to radon at the danger level of 4 picocuries of radon per liter of air. The International Commission on Radiological Protection is less stringent, recommending a danger level of 15 picocuries per liter of air for existing structures. The EPA also claims that 20 to 30 percent of the houses monitored over the past 2 years had radon above the EPA danger level. If these numbers are correct and representative of the whole country, the environmental risk is enormous—but epidemiological studies done on the general population have not demonstrated excess risk. Nevertheless, there must a be a significant number of houses in the country containing radon at or above the present control level in uranium mines. These houses should be identified for remedial action.

High household radon levels can be generated from very-low-radium-bearing but very permeable soils. Conversely, high radium levels are not always dangerous if soil permeability is poor. A more direct approach to evaluating hazard is the simple and cheap measurement of household radon levels, as urged by the EPA. Such determinations should be made in those areas of homes that are occupied much of the time, instead of little-used basements and storage areas. There is already significant mandated compliance as more and more jurisdictions and mortgage lending institutions require that the radon level be determined—just as a termite inspection is required—before a house can be sold or mortgaged.

In summary, ongoing direct determinations of household radon levels make any further geological effort to identify high-risk areas redundant. The role of the earth science community is probably limited to urging more people to voluntarily monitor their household radon levels and to pointing out that, in the past, too much emphasis was placed on soil radium concentrations and too little on soil permeability. High-radium soils may not lead to radon hazards in the home, and low-radium soils do not guarantee safety.

Zinc

A final example of poorly thought-out control measures for potentially hazardous geological materials is the standard recently set by the EPA for zinc mill and mine effluent. The agency set the allowable zinc content of mill effluent at 0.2 parts per million and the allowable zinc content in mine effluent at 0.5 parts per million. Throughout the U.S. central zinc-mining districts, the ambient groundwater contains an average of about 1.5 mg of zinc per liter, or 1.5 parts of zinc per one million parts of water.

Not surprisingly, removal of zinc from the groundwater used as influent was not feasible. As a consequence, the affected mines and mills were shut down; cleanup to the standards set by the EPA is costing huge amounts of money; and zinc supplies must be sought elsewhere, often outside the United States. At the same time, zinc supplements are fed to livestock in those same districts to promote growth, development, and healing. Zinc deficiencies lead to skin lesions, retarded growth, hair loss, emaciation, and loss of appetite in livestock and humans. To meet the minimum requirement for zinc, a person would have to drink 100 liters of EPA-standard mine effluent per day.

Agriculture

Concentrations of population require vast networks to provide even minimal needs, including food and fiber. The production of these commodities in rural environments stresses natural equilibria. Agriculture annually moves more mass and influences a greater area on the Earth than all other human endeavors combined. The chemical input to the environment through agriculture is tremendous; as populations rise, agricultural activity increases, as do its chemical byproducts. During 1988 the use of fertilizer in the United States alone exceeded 10 million tons of nitrogen, 31 million tons of phosphate rock, and 4.6 million tons of potash. The rest of the world used several times those quantities. It is paradoxical that the success of solid-earth scientists in finding and developing potash and phosphate deposits for fertilizer manufacture has helped generate the problems of agricultural waste now being addressed by some of their colleagues. While domestic and industrial disposal of phosphate detergents is controlled to improve the quality of streams, agriculture puts 10 times the controlled amount of phosphate into the environment. Long-lived persistent organic-chemical pesticides and herbicides, and their trace contaminant dioxin enter the groundwater system daily. Tillage and overgrazing foster dramatically increased erosion by water and wind and are major contributors to desertification. The ancient technique of slash-and-burn clearing of tropical forests is front-page news today. The effects of wholesale forest burning are widely dispersed, and so are a challenge to evaluate. The practice is difficult to influence directly because so many individuals in developing countries are economically



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