R6 PM Bioavailability
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in 324-326

(AND-1117-578329) The influence of seasonal variations on the distributions of bioavailable PCBs and OC pesticides by using passive sampling devices in the Willamette River, Oregon.

Sethajintanin, D¹, Anderson, K¹, Grove, R², ¹ Oregon State University, Corvallis, OR, USA² USGS, Corvallis, OR, USA

ABSTRACT- Although the distributions of organochlorine compounds have been well investigated worldwide, very few studies have actually investigated the temporal transport of their bioavailable fraction which is more relevant to their toxicity, mobility and degradation processes. The present study focused on the spatial and temporal occurrence of bioavailable organochlorine pesticides and polychlorinated biphenyls (PCBs) within the surface water of a contaminated harbor to promote a more complete understanding of organochlorine contamination characteristics. Semipermeable membrane devices (SPMDs) were intensively deployed within the main river adjacent to various land uses of the lower Willamette River, Oregon including Portland Harbor superfund site in summer and fall during 2001-2004. An increase of estimated bioavailable DDTs (sum of p,p′-DDT, p,p′-DDD, and p,p′-DDE) concentrations was strongly affected by the local historic productions of DDTs and seasonal changes in river conditions. The dominance of bioavailable p,p′-DDD and high p,p′-DDD: p,p′-DDE ratios observed during periods of low precipitation, low river flow suggest direct inputs of p,p′-DDD and possible favoring conditions for reductive dechlorination of p,p′-DDT to p,p′-DDD. The estimated bioavailable concentrations and daily loads of PCBs and dieldrin increased during periods of high precipitation, high river flow, especially during episodic rainstorms. Similarity of PCB congener profiles and PCB homolog ratios at the industrial area and at the urban/residential area suggests the local sources of PCBs at the industrial area are important enough to significantly increase the concentrations of bioavailable PCBs in surface water but not to substantially change composition relative to surface water inputs from upstream. In addition, seasonal exceedances of the bioavailable organochlorine concentrations over the national and the Oregon water quality criteria suggest the potential impacts associated with seasonal changes of bioavailable organochlorine distributions in surface waters and the significances of consideration of realistic temporal and site-specific conditions in risk assessment and water quality management.

Key words: Willamette River, bioavailability, organochlorine contaminants, seasonal influence