BLACK CARBON AND ORGANOCHLORINES IN COASTAL SEDIMENTS FROM PAKISTAN: LEVELS, SOURCES, RELATIONSHIP AND MASS INVENTORY

Abstract

Black carbon (BC) is considered as carbonaceous geosorbent which may play a major role in the fate and distribution of organic pollutants. Levels of total organic carbon (TOC) and black carbon (BC) were determined together with those of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in the selected coastal sites along the Arabian Sea from Pakistan. The results showed that the total concentration of TOC, BC, ∑OCPs and ∑26PCBs were ranged between 0.3−2.9 % dw, 0.06−0.25 % dw, 0.9−107 ng g-1 dw and 6.2−1206 ng g-1 dw, respectively. Pearson Correlation Analysis revealed stronger association of BC (r=0.26−0.89) with OCPs and PCBs instead of TOC (r=0.06−0.69). Moreover, regression analysis showed that BC is a better descriptor of sedimentary concentrations of ∑HCHs (57 %), ∑DDTs (70 %), heptachlor (64 %), HCB (78 %), tri-CBs (70 %), tetra-CBs (81 %), penta-CBs (79 %), hexa-CBs (69 %) and heptaCBs (61 %) while TOC did not show any role in describing organochlorine contaminants in the study area. Black carbon burial fluxes (Fburial) were found in the range of 183–766 µg cm-2yr-1. The sediment deposition fluxes (D) for ∑OCPs and ∑26PCBs were 1.7 and 4.9 t yr-1. While the sediment mass inventories (I) indicated the presence of 13.1 and 37 metric tons of ∑OCPs and ∑26PCBs, respectively in the coastal belt of Pakistan. Risk assessment using internationally established sediment quality guidelines indicated significant ecotoxicological risks of organochlorines for coastal area of Pakistan