ABSTRACT

As effective as polychlorinated biphenyls (PCBs)     may be in achieving thermal stability as coolant in transformer oils; spills, decommissioning and poor handling of these transformer oils often results to contamination of PCBs on the environment. The attendant adverse effect of PCBs on the environment and humans has been of serious concerns. The residue levels of PCBs in soil of selected transformer maintenance workshops in Kaduna and Zaria metropolis, Kaduna State, Nigeria was determined. Two soil samples per site, one top-soil (0 – 5 cm) and one sub-soil (20- 30 cm), totalling fourteen (14) soil samples were collected in four (4) and three (3) different locations in Kaduna and Zaria metropolis respectively. Some soil physico-chemical properties such as particle size (sand, silt and clay) and total organic carbon (TOC) in the soil that may influence the dynamics of the pollutants was determined. In addition, the soil samples were analysed for residues of PCBs using the technique of gas chromatography-mass spectrometry (GC-MS). PCB concentrations were correlated (PEARSON) with the particle size and total organic carbon (TOC). The coefficient of variation of percent TOC was 45. The concentration of the PCBs measured showed significant correlation (P< 0.05) with TOC. PCB congeners CB 28, CB 52, CB 101, CB 153, CB 138 and CB 180 were detected at varied concentrations, occurring most frequently with highest sum PCB congeners of 8209.50 µg/kg at Arewa Metal Containers (AMECO) Kaduna, lowest sum PCB congeners of 0.81 µg/kg at Ahmadu Bello University (ABU) Main Campus, Samaru- Zaria, and absent at farmland near National Research Institute for Chemical Technology (NARICT), Zaria that serve as control. CB 153, CB 138 and CB 180 (hex- and hepta- chlorinated biphenyls) were dominant species in all the soil samples, accounting for more than 82 % and 68 % of total PCBs in the soil samples from Kaduna and Zaria respectively. The sum PCB congeners‘ residue levels down the soils in all the sites decreases due to soil binding effect and other weathering process. The percent hexa- and hepta- chlorinated biphenyls increased from top-soil to sub- soil except in AMECO. This finding reveals that higher molecular weight PCBs percolates down the soil which might offer an insight for ground water contamination. The measured Relative Retention Factors of all the samples were within the 6-11 percent (%) standard deviation retention time of the referenced standard PCB congeners, and was found satisfactory. The percent (%) recoveries of PCBs in topsoil and subsoil of AMECO, topsoil and subsoil of Mando are in the ranges of 83-145 % and 53-86 %, 52-92 % and 71-143 % respectively. The PCB residue levels in all the samples complied with the United Nations Environmental Programme (UNEP) set maximum limit of 50 ppm (50,000 µg/kg).

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