About the Spokane River fish data
Rainbow trout, montain whitefish and largescale suckers taken from 4 different localities
along the Spokane River (eastern Washington) during July, August and October of 1999 were analyzed for lead 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 .07 ppm for lead.
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.
Mean lead content of filets are highest for rainbow trout and lowest for mountain whitefish,
with suckers in between. Standard deviations are high compared to the mean value, indicating a lot of variability.
Perhaps some of this variability is due to age; the older the fish, the more lead it may have accumulated. Size
of the fish might be used as a proxy for age to test this assumption.
Mean lead contents of whole fish are highest in suckers and lowest in whitefish (though the
number of analyses is very small). The mean lead content of whole fish is very much larger than the corresponding
filet, indicating that lead is concentrated in tissues other than filets (probably bones and fat).
Lead can cause health problems, especially in children. Are these levels cause for concern?
What part of the fish would you eat?
Reference: Johnson, A. (2000), Results from Analyzing
Metals in 1999 Spokane River Fish and Crayfish Samples; Washington
State Dept. of Ecology report #00-03-017.
Web Site: http://www.ecy.wa.gov/biblio/0003017.html