Description:
Rainbow trout, mountain whitefish and large-scale suckers taken from 4 different localities along the Spokane River (eastern Washington) during July, August and October of 1999 were analyzed for three heavy metals (lead, zinc and cadmium) by Manchester Laboratory for the Washington State Department of Ecology. Most of the analyses were done on filets (the part typically consumed by humans), however a few whole specimens were tested as well. Metal contents are reported in milligrams of metal per kilogram of fish (mg/kg), which is an equivalent unit to parts per million (ppm). A couple of redundant analyses indicate crude uncertainties in reproducibility of at least 14 ppm for zinc, .07 ppm for lead, and .01 ppm for cadmium.
The source of the heavy metals is upstream from Spokane in the Coeur d'Alene mining district of northern Idaho, one of the richest mining districts in the US and also one of the most heavily contaminated. Acid mine drainage directly from shafts and adits, and from leaching of metal rich mine tailings (waste rock), as well as metal-rich discharges from smelters, have contaminated many streams, rivers and lakes in the Spokane/Coeur d'Alene watershed. Metals are both dissolved in the river water and found as minute particles, and can enter the food web at various stages.
The graph shows a strong positive linear correlation between lead and zinc content in whole fish, regardless of fish type. One could use this relationship to predict the zinc content of a fish based on its lead content, thereby increasing the efficiency of the analytical program; you only have to analyze for lead.
Does this relationship support the contention that fish in the Spokane River are contaminated in the same way from the same source?
