ARSENIC has been known for centuries to be a poisonous substance. Human populations can be exposed to arsenic via 3 major routes: skin contact, inhalation, and ingestion. There have been numerous studies linking airborne arsenic exposure with excess cancers of the skin, respiratory system, and other internal organs in a variety of occupations (e.g., copper smelter workers exposed to arsenic as a byproduct,) German vineyard workers who use arsenic-containing pesticides, (11, 12) factory workers in plants in which arsenical insecticides are produced (13, 14). In several studies, investigators have shown that the latency period for arsenic-induced lung cancer may be as brief as 10-19 yr, (13)but in some cases may exceed 35 yr. (13,15,16) Elevated relative risks for non-respiratory cancers (e.g., cancers of the urinary tract, gastrointestinal tract, liver) have also been observed in smelter workers in the United States, Japan, and Sweden, as well as in Japanese refinery and mine workers. (15,17-19) In addition, researchers have identified a wide range of systemic effects resulting from arsenic inhalation. For example, arsenic-exposed workers in copper smelters (4,9,19,20) and orchards (21) have an elevated risk of mortality from cardiovascular disease.

Communities in certain geographic areas worldwide are exposed to high levels of arsenic in their drinking water. Studies of communities in Taiwan, Bangladesh, Chile, and Argentina have reported a strong association between high waterborne arsenic levels (up to 1,120 [micro]g/l) and mortality resulting from lung, liver, bladder, kidney, prostate, and skin cancers. (22,26) A dose-response relationship between skin cancer and the arsenic content of drinking water was also observed in Taiwan. (27) In additional studies in Taiwan, investigators found increased mortality for vascular disease, ischemic heart disease, and diabetes. (28, 29) In studies of populations exposed to drinking water containing lower levels of arsenic (~100 [micro]g/l) than those reported from Taiwan, Chile, and Argentina, researchers have generally failed to find similar adverse effects.

The results of these occupational and community studies have generated concern that populations living near arsenic-emitting industrial plants may be at an increased risk of mortality from lung and bladder cancers, as well as from other conditions. Several studies have addressed these concerns, but different conclusions have been reached regarding the adverse health effects from exposure to ambient arsenic. (35-40)

During the past 30 yr, studies have been completed of residents in Pierce County, Washington, in the United States. These residents were exposed to arsenic emissions from a local copper smeher, and some of the residents worked at the smelter. The American Smelting and Refining Company (ASARCO) operated a copper smelter in the town of Ruston, Washington, from the late 1890s until the smelter was closed in 1985. The ASARCO smelter was a specialty smeher--one of the few in the world that processed high-arsenic copper ores to produce both copper and arsenic. In the 1970s and 1980s, soil and ambient air arsenic concentrations in the community were measured and were found to increase with increasing proximity to the smeher stack. Soil arsenic concentrations ranged from 140 to 1,600 mg/kg of soil, depending on the distance from the smelter. (41) Ambient air sampling, conducted in 1974, revealed the same uniformly increasing arsenic concentrations as were seen in the soil. The highest air concentrations were observed south and southwest of the smelter. (42)

ASARCO also conducted several cohort mortality studies of its workers. (1,2) Those studies--like other studies of copper smelter workers--showed an elevated risk of lung cancer. Despite the abundance of occupational studies and environmental monitoring data, few human health studies have been conducted on the population living in the Ruston and north Tacoma neighborhoods closest to the smelter. Consequently, health risks to these communities remain unclear. Frost et al. (43) examined lung cancer risk for the period from 1935 to 1969 among women who resided near the smelter, (43) but no evidence of elevated lung cancer incidence was discovered. A second case-control study, using a group selected from the same population, adjusted for latency and exposure level, suggested possible health effects in the highest exposure group; however, this finding was not statistically significant and may have resulted from chance. In other limited studies conducted by the Washington State Department of Health, birth weights, birth defects, hearing loss, and school attendance were examined. (44)

The long-term health effects of exposure of children to ambient arsenic are of particular interest, inasmuch as children not only inhale airborne arsenic, but may also ingest arsenic-contaminated soil. Despite children's potentially higher risk, none of the studies cited previously were focused on this subpopulation. In studies conducted in the 1970s and early 1980s, investigators found increased arsenic levels in the hair and urine obtained from children who resided near the smelter; these levels decreased with increasing distance from the smeher stack. (44-46) Thus, children who lived near the smeher were exposed to high ambient arsenic levels from the time the smeher began production. These levels were even higher during earlier time periods, when there were few environmental regulations controlling the output of arsenic from the smelter stack.