Evaluation of persistent hydrophobic organic compounds in the Columbia River Basin using semipermeable-membrane devices

Persistent hydrophobic organic compounds are of concern in the Columbia Riv er because they have been correlated with adverse effects on wildlife. We a nalysed samples from nine main-stem and six tributary sites throughout the Columbia River Basin (Washington and Oregon) for polychlorinated dibenzo-p- dioxins, dibenzofurans, polychlorinated biphenyls, organochlorine pesticide s, and priority-pollutant polycyclic aromatic hydrocarbons. Because these c ompounds may have important biological consequences at aqueous concentratio ns well below the detection limits associated with conventional sampling me thods, we used semipermeable-membrane devices to sample water and achieved parts-per quintillion detection limits. All of these compound classes were prevalent within the basin, but concentrations of many analytes were highes t in the vicinity of Portland-Vancouver, indicating that the Willamette sub basin - and perhaps the urban area in particular - is an important source o f these compounds. Data collected during basin low-flow conditions in 1997 and again during basin high-flow conditions in 1998 indicate that in-stream processes such as dilution by relatively clean inflows, and flow through i sland hyporheic zones may be important mechanisms for attenuating dissolved concentrations of hydrophobic compounds.