Background levels of lead, zinc, nickel, chromium, copper, and manganese in soils and in four classes of vegetation have been estimated from collections that were made in remote areas presumed to be free from inorganic contamination. The trace-metal content of soils and plants varies widely in different geologic provinces of the United States; in those areas of high natural mineralization, additions of metals from man-made pollution may compound a possible hazard. Results of sampling in urban areas show that contamination of vegetation by gasoline lead can be expected for at least 1000 ft back from transportation lanes, and that the lead burden is increasing greatly with time. Ore-treatment plants can also be a source of air contamination for several miles downwind and several thousand feet in other directions. Soils of naturally high metal content in a mining district may be further contaminated with both major and minor elements from smelting operations. Recent studies show that volatile elements are released directly to the air from ore deposits in place. Concentrations of mercury, for instance, may be as much as 20 times background for several hundred feet in altitude over ore deposits in which mercury occurs as a relatively minor constituent.

The source of inorganic pollution in surface drainage and also in ground water is commonly geologic, as rivers may be contaminated from coal and metal deposits in place and also from mining and smelting operations.

More information of the type illustrated should be accumulated and made available to scientists who are working in environmental health, and, in particular, to those involved in the pollution problem. Only by these means can we provide a scientific basis for the enactment of realistic and effective legislation for pollution control.