Organochlorine pesticides and polychlorinated biphenyls (PCBs) are synthetic organic chemicals that have been linked to reproductive problems in aquatic invertebrates, fish, birds, and mammals. PCBs were used in the manufacture of electrical equipment, such as capacitors and transformers. Use and manufacture of PCBs and the pesticides chlordane, DDT, dieldrin, and toxaphene have been restricted or banned in the United States since the late 1980s or earlier, but they are still present in aquatic systems because of their environmental persistence. Similarly, many trace elements have important anthropogenic sources and are toxic at high concentrations; however, they also can have natural geologic sources, and some are essential for biological function. Organochlorine pesticides, PCBs, and trace elements are more likely to be associated with sediment or incorporated into tissue than to be dissolved in water. Thus, bed sediment and aquatic biota were used to evaluate general levels of occurrence and spatial distributions of these constituents.
Of 27 organochlorine compounds analyzed both in bed sediment and aquatic biota during 1992-95, 19 were detected in sediment, and 14 were detected in biota. The most common compound in sediment and biota was p,p'-DDE, a degradation product of DDT, which was used extensively to control insects from about 1940 until its ban in 1972. Concentrations of p,p'-DDE were detected at 45 percent of sites where bed sediment was collected and at 63 percent of sites where aquatic biota were collected. Detections were about equally divided among basins with predominantly agricultural, urban (residential, commercial, industrial), and mixed land uses. Detections were more common in biota than in sediment.
The most common organochlorine compound was p,p'-DDE, a degradation product of DDT. |
The largest concentration of p,p'-DDE in bed sediment (120 micrograms per kilogram dry weight) was found in upper Johnson Creek east of Portland, where the basin is mostly agricultural. This value is higher than reported for the agricultural Central Columbia Plateau Basin, Washington (Gruber and Munn, 1996), but it is less than one-tenth the maximum concentration reported for the Yakima Basin, Washington, where DDT contamination in runoff from agricultural land has been documented (Rinella and others, 1992; 1993).
Total PCBs were detected at 11 percent of sites where bed sediment was collected, but detections were reported for 32 percent of sites where aquatic biota were collected. All sediment and biota with PCB detections were from streams draining areas with strong urban influences.
Recommended concentration guidelines for protection of aquatic life from organochlorine pesticides and PCBs in bed sediment are summarized by Gilliom and others (in press). Criteria for protection of fish-eating wildlife have been recommended by the National Academy of Sciences and National Academy of Engineering (NAS/NAE) (1973). Chlordane and its component compounds (six sites), and DDT and its degradation products (six sites) accounted for 94 percent of exceedances of recommended guidelines in bed sediment. Ten of 47 sites exhibited exceedances; two agricultural, one urban, and one urban/industrial basin accounted for 77 percent of the exceedances. Organochlorine pesticide and PCB concentrations in fish tissue from 17 sites did not exceed the NAS/NAE criteria.
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Most organochlorine compounds were detected more frequently in aquatic biota than in bed sediment. |
The highest lead concentrations in bed sediment were found in urban streams. |
Arsenic, cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc are of particular interest in the Willamette Basin because they are potentially toxic to aquatic organisms and are widespread by-products of human activities (Rickert and others, 1977). Of these, median chromium and nickel concentrations in bed sediment showed no obvious differences for streams draining forested, agricultural, urban, or mined areas.
Lead concentrations in bed sediment were significantly higher for streams draining urban areas than for streams draining other land uses. Median lead concentrations from urban areas were 50 µg/g (micrograms per gram) dry weight; the highest value was 240 µg/g dry weight from Beaverton Creek--an urban stream in the Portland area. Median values for all other land uses were 14 µg/g dry weight or less. Common lead sources in urban environments include batteries, dyes, and paints. Much of the lead probably also was contributed by leaded gasoline, which is no longer sold but is persistent in the environment. Distributions of cadmium, silver, and zinc in relation to land use were similar to that for lead.
Mercury concentrations in bed sediment were highest downstream from an abandoned mercury mine. |
Mercury concentrations in bed sediment generally decreased downstream from the Black Butte Mine. The affected area includes Cottage Grove Reservoir (located on the Coast Fork Willamette River), where a mercury advisory warning of health risks from consumption of fish has been in effect since 1979 (Newell and others, 1996). Mercury concentrations as high as 1.79 µg/g wet weight have been reported for fillets from largemouth bass collected in this reservoir (Allen-Gil and others, 1995; Newell and others, 1996). In February 1997, the Oregon Health Division issued a mercury advisory for consumption of smallmouth bass, largemouth bass, and northern squawfish from the entire main stem Willamette River, including the Coast Fork to Cottage Grove Reservoir; a separate advisory was issued for consumption of all fish from Dorena Reservoir, which also is located in the Coast Fork Basin.
Guidelines for protection of aquatic life from trace element concentrations in bed sediment have been recommended by Environment Canada (1995). The most commonly exceeded guidelines were for nickel (12 sites) and chromium (15 sites), which occur naturally at high concentrations in basaltic rocks (Parker, 1967), such as those found in much of the Willamette Basin. The next most commonly exceeded guidelines were for arsenic (eight sites) and mercury (six sites); four of the mercury exceedances were for samples collected downstream from the abandoned Black Butte Mine. Zinc and lead concentrations exceeded guidelines at four and three sites, respectively, and no exceedances were found for cadmium or copper. Exceedances for at least one trace element occurred at 26 of 52 sites.
Although fewer samples of aquatic biota than bed sediment were collected for analysis of trace elements, results in relation to land use generally were similar. No well established guidelines were available for evaluating risks of trace elements in aquatic biota to fish-eating wildlife.
Mercury concentrations in bed sediment were higher in urban areas than in forested or agricultural areas (left). Mercury concentrations were highest below the Black Butte Mine, and they generally decreased downstream (right).
Twenty sites were sampled both for bed sediment and aquatic biota, and 32 additional sites were sampled for bed sediment only (p. 25).Site locations are shown on the land use map on page 24.The sites reflect important land uses in the basin, including forested (12 sites), agricultural (10 sites), urban (12 sites), mixed (14 sites), and mined (4 sites). Samples were collected following protocols given by Crawford and Luoma (1993) and Shelton and Capel (1994).
Bed sediment samples to be analyzed for trace elements were wet sieved through a 62-micrometer nylon cloth; samples for analysis of organochlorine pesticides and PCBs were passed through a 2-millimeter stainless-steel sieve. Aquatic biota samples were mostly composites of 6-10 sculpin (whole body) or 35-50 Asiatic clams (soft tissue only). Livers from carp, largemouth bass, and largescale suckers were analyzed for trace elements at three sites.
Analyses were performed by USGS laboratories in Denver, Colorado, following procedures described by Arbogast (1990), Foreman and others (1995), Leiker and others (1995), and Hoffman (1996).
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Sculpin (left) and Asiatic clams (right) were the main species analyzed.
