Spatial and temporal distribution of polychlorinated biphenyl residues in tropical soils

Abstract

Polychlorinated biphenyls (PCBs) in tropical soil samples from the Central Region of Ghana, and their variation with the soil characteristics were assessed. The soil characteristics of seventy eight samples were first determined. The PCBs was extracted with (1:1) hexane : acetone mixture, and then the extract treated with concentrated H2SO4, 5% KMnO4 and copper. The extract was finally eluted from a silica gel column with hexane:dichloromethane (97:3v/v), and the PCBs analyzed using a gas chromatograph equipped with 63Ni electron capture detector (GC-ECD model CP 3800). The composition of PCBs homologous in the soils followed the order:hexa-PCBs (31.89%) > pentaPCBs (23.98%) > tri-PCBs (18.47%) > tetra-PCBs (13.67%) > hepta-PCBs (11.99%).The PCB congener profile in the study area was PCB 28 > PCB 153> PCB 138 > PCB 52 > PCB 101> PCB 180 > PCB 118.The mean concentration of the PCB congeners (dry matter basis) was PCB 28, 2.27± 2.436;PCB 52, 1.84 ± 2.27;PCB 101, 2.17± 2.52 µg/kg;PCB 118, 0.83± 0.89 µg/kg;PCB 138, 0.99 + 0.91µg/kg; PCB 153, 1.18 ± 1.11µg/kg and PCB 180, 1.18 ± 1.19 µg/kg. The mean concentrations of ΣPCBs were 9.15± 0.52 µg/kg for the surface soils (0 -10 cm), 7.55± 0.56 µg/kg and 7.82 ± 0.5 µg/kg for the 10 -20 cm and 20 -30 cm sub-surface soils respectively. Significant but weak correlations were observed between PCBs and the soil pH, moisture, and exchangeable base. The coefficient of determination for all significant correlations was between 6.6% and 18.75%