By Bernadine A. Bonn
USGS Water-Resources Investigations Report 99-4107, 61 pages, 9 figures, 14 tables, 4 appendices
Concentrations of trace elements in Tualatin Basin sediments and fish tissue, including arsenic, chromium, copper, lead, mercury, nickel, selenium, and zinc, were generally similar to those found in the Willamette Basin and were toward the lower end of the range of national concentrations.
No exceedances of U.S. Environmental Protection Agency (USEPA) Tier 1 sediment screening values for any trace element were observed in the Tualatin Basin. Concentrations of chromium, copper, and nickel exceeded USEPA Tier 2 screening values at all sites in the basin. Copper and nickel concentrations were highest at the background sites and probably were related to basin geology.
Polyaromatic hydrocarbons (PAHs) were detected more frequently in Tualatin Basin sediment than in either the Willamette Basin or the Nation. The higher frequency of PAH detection in the Tualatin Basin probably occurs because of the large number of urban sites in the basin. When detected, however, PAH concentrations in the Tualatin Basin sediments were similar to those observed elsewhere.
In general, few organochlorine pesticides were detected in bed sediment or tissue in the Tualatin Basin. Chlordanes and p,p'-DDE were commonly detected in both sediment and fish tissue. Dieldrin was also commonly detected in fish tissue. Correlations of concentrations in bed sediment with those in tissue were poor for most elements and weak, at best, for organochlorine compounds. Concentrations of organochlorine compounds in tissue usually exceeded those in bed sediment concentrations by at least tenfold.
Contamination patterns that were consistent with urban sources-high concentrations of PAHs, lead, and some phthalates-were found at Ash Creek at Greenburg Road, Fanno Creek at Nicol Road, Fanno Creek at Denny Road, and McKay Creek at Hornecker Road.
High levels of organochlorine pesticides in both sediment and fish tissue were found at two sites in largely residential areas (Fanno Creek at Nicol Road and Fanno Creek at Denny Road). Concentrations of total chlordane, dieldrin, and p,p'-DDE in sediment at these sites exceeded USEPA Tier 2 screening values. Concentrations of total chlordane in fish tissue exceeded both the National Academy of Science/National Academy of Engineering (NAS/NAE) guidelines and the New York State criteria. Organochlorine concentrations were much lower downstream of these sites where the land use changed to light industrial; concentrations of trace elements, however, increased.
The most contaminated bed sediment found in this study was collected from the most urban site (Beaverton Creek at Cedar Hills Boulevard). USEPA sediment screening values were exceeded for four organochlorine pesticides, six polyaromatic PAHs, two phthalates, p-cresol, and eight metals (including arsenic, cadmium, lead, and mercury). Levels of polychlorinated biphenyls in the few fish found at this site exceeded the NAS/NAE guidelines for fish tissue.
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