Distribution of persistent organic pollutants in aggregate fractions of a temperate forest and semi-rural soil

The fate of persistent organic pollutants (POPs) and their interactions with aggregates of forest soils are not completely understood. Our objectives here were to quantify the distribution of different POPs in water-stable aggregate fractions and to study their influence on soil organic carbon (C-org) content. Soil samples were taken from a forest-site, Gogerddan (G) and a semi-rural site, Hazelrigg (H) in Great Britain, from 0-2 and 2-5 cm and 0-4 and 8-12 cm soil depth, respectively. POPs analyzed were PAHs, PCBs, total DDT, PBDEs and HCB. The bulk soil analysis showed that the concentration of POPs was significantly higher (p <= 0.05) in forest site G than in semi-rural site H, particularly at the surface soil levels compared to the subsurface soil depths in both sites. Total concentrations of PCBs and PAHs of both sites were positively correlated with C-org contents. POPs concentrations and C-org, N-t contents of forest site G were significantly higher (p <= 0.05) in water-stable macro aggregates (> 0.25, > 1, > 2 mm) than the micro aggregates (> 0.053 mm). The POP concentrations of all aggregate fractions after normalizing to their respective C-org content were increased due higher contamination and strong sorption by C-org. These results showed a strong effect of C-org on the partitioning of organic pollutants to soil aggregate size fractions. The present study affirms the ecological significance of forest soils act as a potential sink of POPs. In summary, our results suggest that aggregate fractions may promote soil C storage and act as a potential POP sink in surface soil without increasing their concentration in the aggregate fraction of subsoil.