Chiral PCB Signatures in Air and Soil:  Implications for Atmospheric Source Apportionment

Abstract

Enantiomeric fractions (EFs) of chiral PCBs 95, 136, and 149 were measured in samples of topsoil and outdoor air at one urban and one rural location in the U.K. West Midlands between early 2001 and early 2002. While EFs in air were essentially racemic, those in topsoil indicated appreciable enantioenrichment of the second eluting enantiomer for PCB 95 and the (+) enantiomer for PCBs 136 and 149. This suggests (i) that essentially all atmospheric PCBs at both sites arise from racemic (i.e, primary) sources, rather than volatilization from soil and (ii) that appreciable enantioselective degradation of the monitored PCBs in topsoil occurs. This is one of only two reports of enantioselective degradation of PCBs in soil worldwide and is particularly noteworthy as it is occurring at PCB concentrations (e.g., 5.9 pg g(-1) for PCB 136) that are typical of the U.K. and other industrialized countries. The extent of enantioselective degradation in this study for PCBs 95 and 136 is consistent with those reported for soils in the Greater Toronto area (GTA). In contrast, enantioselective degradation of PCB 149 observed in this study is--while consistent with that reported for U.K. lacustrine sediments--in excess of that observed in either the GTA soil study or in U.S. lake sediments.

Chirality as an Environmental Forensics Tool

“…Such observations are consistent with the hypothesis that soil microbial degradation of PCBs occurred slowly (i.e. on a timescale of years to decades) but appreciably over time [156,182,183]. Chirality is thus the only feasible method to detect such biodegradation.…”

“…Chiral PCB EFs in rural UK topsoils contained nonracemic PCBs 95, 136, and 149 (respective EF ranges of 0.39-0.45 using Equation (4.4) on Chirasil-Dex, 0.52-0.53, and 0.50-0.54) at pg/g concentrations [182]. Soils closer to the city of Birmingham had more racemic EFs [183].…”

“…capacitors, transformers, construction materials) may also contribute to atmospheric contamination [316,317]. The use of PCB atropisomers for source apportionment was first demonstrated by Robson and Harrad [182], who observed that nonracemic soil EFs for PCBs 95, 136, and 149 were statistically different from racemic EFs of all three congeners in the overlying air. In contrast to chiral OC pesticides, the source of atmospheric PCBs was thus not due to volatilization from the soil, but from emission of unweathered PCBs remaining in use.…”

Can polychlorinated biphenyl (PCB) signatures and enantiomer fractions be used for source identification and to age date occupational exposure?

“…The Enantiomeric Fractions (EFs) of CBs 95, 136 and 149 were analysed according to the method of Robson and Harrad (2004), using an Agilent 7890 gas chromatograph coupled to a Micromass AutoSpec Premier high resolution mass spectrometer (GC-HRMS) tuned to greater than 10000 mass resolution. The two most abundant isotopes of each enantiomer were recorded in Selected Ion Recording Mode (SIR).…”

Risks and Management of Dioxins and Dioxin-like Compounds in Baltic Sea Fish: An Integrated Assessment

“…There are data suggesting that primary sources contribute significantly to present emissions, along with those from PCBs accumulated in the environment (Robson and Harrad 2004). In addition, dlPCBs originate from other products including pigments (Litten et al 2002) as well as combustion sources.…”