ECOSYSTEM TO SUBCELLULAR LEVEL EFFECTS OF CONTAMINATION FROM ABANDONED MINES ON ORGANISMS IN THE METHOW RIVER, WASHINGTON, U.S.A

A three-year multidisciplinary study was conducted on the relationship between mine waste contamination and responses in fish and invertebrates in the Methow River on the eastern slopes of the North Cascade Mountains in Washington State, U.S.A. Ore deposits in the area were mined for gold, silver, copper and zinc until the early 1950’s. Contamination impacts have been observed at ecosystem, community, population, individual, cellular and subcellular levels. An above-and-below-mine approach was used to compare potentially impacted to control sites. Although the dissolved metal concentrations in the Methow River were below the limits of detection, concentrations of Cd, Cr, Cu, Ni, Pb and Zn were from 2 to 9 times higher than background levels (p < 0.02) in sediments below the mine. The periphyton matrix with entrained sediments also contained higher concentrations of metals compared to background levels as did the whole-body metal content of the caddisfly larvae Ecclisomyia, a grazing aquatic invertebrate. Midgut epithelial cells from larvae exposed to contaminated sediments, examined by transmission electron microscopy, revealed the accumulation of electron-dense metals as granules in their mitochondria. Granules were also found in mitochondria of juvenile trout in the Methow River below the mine. Metal specific stains suggest either Pb or Cu is accumulating in the cartilage of trout gill filaments. Exposed trout in the Methow River showed reduced growth and increased mortality compared to controls. This study shows that contaminated sediments cause adverse biological effects even where the corresponding surface water meets water-quality based criteria.