Silver Bay, on the Minnesota shore of Lake Superior, became the center of pollution control lawsuits in the 1970s when cancer-causing asbestos-type fibers, released into the lake by a Silver Bay factory, turned up in the drinking water of numerous Lake Superior cities. While pollution lawsuits have become common, Silver Bay was a landmark case in which a polluter was held liable for probable, but not proven, environmental health risks. Asbestos , a fibrous silicate mineral that occurs naturally in rock formations across the United States and Canada, entered Lake Superior in the waste material produced by Silver Bay's Reserve Mining Corporation . This company processed taconite, a low-grade form of iron ore, for shipment across the Great Lakes to steel-producing regions. Fibrous asbestos crystals removed from the purified ore composed a portion of the plant's waste tailings . These tailings were disposed of in the lake, an inexpensive and expedient disposal method. For almost 25 years the processing plant discharged wastes at a rate of 67,000 tons per day into the lake.
Generally clean, Lake Superior provides drinking water to most of its shoreline communities. However, water samples from Duluth, Minnesota, 50 mi (80.5 km) southwest of Silver Bay, showed trace amounts of asbestos-like fibers as early as 1939. While the term "asbestos" properly signifies a specific long, thin crystal shape that appears in many mineral types, both the long fibers and shorter ones, known as "asbestos-like" or "asbestiform," have been linked to cancer in humans.
Early incidences of asbestos-like fibers in drinking water probably resulted from nearby mining activities, but fiber concentrations suddenly increased in the late 1950s when Reserve Mining began its tailing discharge into the lake. By 1965 asbestiform fiber concentrations had climbed significantly, and municipal water samples in the 1970s were showing twice the acceptable levels defined by the federal Occupational Safety and Health Administration (OSHA). Lawsuits filed against Reserve Mining charged that the company's activity endangered the lives of the region's residents.
Although industrial discharge often endangers communities, the Silver Bay case was a pivotal one because it was an early test of scientific uncertainty in cases of legal responsibility. Cancer that results from exposure to asbestos fibers appears decades after exposure, and in a large population an individual's probability of death may be relatively small. Asbestos concentrations in Lake Superior water also varied, depending largely upon weather patterns and city filtration systems. Finally, it was not entirely proven that the particular type of fibers released by Reserve Mining were as carcinogenic as similar fibers found elsewhere. In such circumstances it is difficult to place clear blame on the agency producing the pollutants. The 200,000 people living along the lake's western arm were clearly at some risk, but the question of how much risk must be proven to close company operations was difficult to answer. Furthermore, the Reserve plant employed nearly all the breadwinners from nearby towns. Plant closure essentially spelled death for Silver Bay.
In 1980 a federal judge ordered the plant closed until an on-land disposal site could be built. Reserve Mining did construct on-shore tailings ponds, which served the company for several years until economic losses finally closed the plant in the late 1980s.
[Mary Ann Cunningham Ph.D. ]
Carter, L. J. "Pollution and Public Health: Taconite Case Poses Major Test." Science 186 (October 4, 1974): 31–6.
Sigurdson, E. E. "Observations of Cancer Incidence Surveillance in Duluth, Minnesota." Environmental Health Perspectives 53 (1983): 61–7.