Tracking chiral polychlorinated biphenyl sources near a hazardous waste incinerator: Fresh emissions or weathered revolatilization?

Abstract

The Swan Hills Treatment Centre (SHTC), located in central Alberta, is the primary facility in Canada for incinerating polychlorinated biphenyls (PCBs). Past studies have shown significant contamination by PCBs and other pollutants of the immediate surrounding region. However, it is unclear whether the major source of contamination to the region's atmosphere is historical release incidents or long-term emissions. To answer this question, concentrations of PCBs and enantiomer fractions of several PCB congeners were determined in soil and air, via polyurethane foam passive samplers, over several seasons between 2005 and 2008. Concentrations in both media were highest for samples collected closest to the SHTC, demonstrating a concentration profile typical of a point source. Enantiomer analysis revealed racemic profiles in air for all congeners, while soil was significantly nonracemic for PCB 95, indicating significant microbial degradation of this congener. However, the primary source of this congener, and likely others, in the surrounding atmosphere is recent and continual releases from the SHTC, rather than the release of weathered PCBs previously deposited to local soils. In addition, enantiomer compositions for PCBs 95 and 149 yielded minimum biotransformation half-lives of 25 and 97 years, respectively, suggesting an expected gradual decline in the region's PCB load once fresh inputs cease.