Long term temporal and spatial changes in the distribution of polychlorinated biphenyls and polybrominated diphenyl ethers in Scottish soils.

Long term changes in polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) concentrations in soil from four transects across Scotland were measured in three surveys conducted between 1990 and 2007-9. Overall PCB level declined during this period (22.5 to 4.55 ng/g, p<0.001) but PBDEs increased (0.68 to 2.55 ng/g, p<0.001), reflecting the ban on PCB use in the 1980s while PBDE use increased until about 2004 when the use of penta-mix congener ceased in Europe. The proportion of lighter PCB congeners (28+52) present declined (p<0.001) primarily between 1990 and 1999. However, the proportion of lighter PBDE congeners (47+99) in the soil samples increased (p<0.01) from 1990 to 1999 and declined (p<0.001) thereafter, probably reflecting the introduction of legislation banning penta-BDE products and the degradation of lighter congeners and their translocation. PCBs were slightly higher in two southernmost transects but PBDE concentrations were significantly higher (p<0.001) in the two southern transects than in the two northern transects. This may reflect proximity to areas of high population and industrial activity. It is concluded that temporal and spatial changes in the distribution of PCBs and PBDEs reflect geography, physical processes and legislation.