Organo-halogenated contaminants (OHCs) in the sediments from the Soan River, Pakistan: OHCs(adsorbed TOC) burial flux, status and risk assessment

In this study, regression analysis revealed that TOC is the principal factor in controlling the fate of organo-halogenated contaminants (OHCs: PCBs, PBDEs, OCPs) in Soan River, Pakistan. The OHCs(adsorbed TOC) burial flux (OHCs(adsorbed TOC)Bf; mg/cm2·yr) was calculated in the following ranges: ∑ PCBs (0.07-0.31), ∑ PBDEs (0.005-0.029), ∑ HCHs (0.015-0.046) and ∑ DDTs (0.007-0.039). Apart from OHCs(adsorbed TOC)Bf, the levels of OHCs were in the following order: PCBs > DDTs > PBDEs > HCH > Chlordane > HCB. PBDEs and PCB congener patterns showed following order respectively: BDE-149 > -153 > -18 > -138 > -44 and PCB-149 > -153 > -18 > -138 > -44. DDT isomers and metabolites' pattern were p,p′-DDT > p,p′-DDD > p,p′-DDE > o,p′-DDT > o,p′-DDD > o,p′-DDE and HCHs were β-HCH > α-HCH > γ-HCH > δ-HCH. PBDE composition had similarities to penta-BDE and DE-71 mixtures and PCBs with commercial products Aroclor-1254 and -1260. (DDE + DDD)/∑ DDTs and p,p′-DDT/p,p′-DDE suggested the recent input of DDTs in sediments while α/γ-HCH indicated past usage of lindane and technical mixtures. Risk assessment suggested that Soan River and its tributaries are potentially at risk against most of the OHCs.