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?
Johnson, A. (2000), Results from Analyzing Metals in 1999 Spokane
River Fish and Crayfish Samples; Washington State Dept. of Ecology