Chiral Signatures Show Volatilization from Soil Contributes to Polychlorinated Biphenyls in Grass

Enantiomer fractions (EFs) of PCB 95 and concentrations of PCBs 28/31, 52, 101, 118, 138, 153, and 180 were determined in air. Samples were taken at similar to 14 day intervals on a vertical gradient at an urban background site in Birmingham U.K. in summer 2009 (114 days) and spring 2010 (84 days). EFs in air at 3 cm height were nonracemic (average 0.453 (2009) and 0.468 (2010)) and differed significantly (p<0.05) from the racemic EFs in air at 10, 40, 90, and 130 cm. EFs in soil (average 0.452 (2009) and 0.447 (2010)) closely matched those in air at 3 cm, while those in grass (average 0.468 (2009) and 0.484 (2010)) were intermediate between those in soil and the racemic EFs in air at >= 10 cm. This implies that at the study site, PCBs volatilize from soil to an extent discernible only at the soil: air interface, and that PCBs in grass arise due to foliar uptake of volatile emissions from soil. Atmospheric concentrations of Sigma PCBs increased significantly (p < 0.05) with increasing height. Combined with the chiral signature data, this suggests the influence of PCB emissions from soil on airborne concentrations decreases with altitude, while that of emissions from the built environment increases.