Passive sampling devices as biological surrogates for evaluating seasonal bioavailability of hydrophobic organic contaminants in surface water

The seasonal distribution of bioavailable organochlorine contaminants in surface water and the potential environmental factors influencing their bioavailability were evaluated. The study was carried at the lower Willamette River at Portland Harbor, Oregon where surface water runoff varied according to season. Bioavailable water concentrations of DDTs and PCBs were determined using a polyethylene membrane containing passive sampling device (PSD), known as semipermeable membrane device (SPMD). Our findings indicated that the influence of river seasonality on the bioavailable distributions of organochlorine contaminants was compound- and site-specific. Bioavailable SigmaDDTs concentrations were strongly affected by the local historic use of DDTs and seasonal changes in river conditions. The dominance of bioavailable p,p'-DDD and large DDD/DDE ratios observed during low flow condition in summer suggest redistribution of p,p'-DDD into the water column and conditions favoring reductive dechlorination of p,p'-DDT to p,p'-DDD. In contrast, bioavailable dieldrin and SigmaPCB concentrations were significantly increased during high flow condition in fall, especially during episodic rainstorm events. While a discernable seasonal pattern for PCBs was observed along the 18-mile stretch study area, the seasonal pattern of dieldrin was only apparent at the sampling site downstream of an agricultural creek with historical use of dieldrin. The increase in bioavailable PCB concentrations and daily loads coincident with high precipitation and sewer overflows in fall suggested a significant contribution of PCBs from precipitation input and urban storm water discharges to the surface water. Seasonal bioavailable concentrations of organochlorine compounds exceeded the national and the Oregon water quality criteria revealing the significance of considering realistic seasonal and site-specific influences on bioavailable organochlorine distributions when performing risk assessments. In addition, we developed the triolein-free polyethylene lay flat tubing (LFT) as an alternative in situ PSD. The LIFT proved reliable and had the same benefits as SPMD, but was simpler, inexpensive and lacked interference from the triolein impurities. The LFT tended to accumulate compounds with high log Kow faster than SPMD. LFT sampling rates were estimated and modeled for 33 target analytes, including PAHs, PCBs, and organochlorine pesticides. The successful determination of field derived data illustrates the effectiveness and reliability of LFT for environmental monitoring.