Bioavailability of heavy metals and polycyclic aromatic hydrocarbon in long-term sewage-drained soils of Tamil Nadu

Heavy metals and organic contaminants are reported in sewage discharged sites. Screening and assessment of their toxic concentration in soils of the discharged sites of major cities in Tamil Nadu, India have been carried out in the present study. The major cities included Coimbatore (Ukkadam; U), Madurai (Avanaiyapuram; A), Tiruchirappalli (Rettamalai; R), Nesapakkam (N) and Koyambedu (K) Chennai Corporation. The total aquaregia-extractable concentrations of cadmium, chromium, lead and nickel were measured and found to be highest in U, followed by A, R, N and K. Their potential bioavailabilities were quantified in the following order: Cd - N > U > K > R > A; Cr - N > A > K > R > U; Pb - N > K > R; U > A; Ni - N > K > R > U > A. Bioavailable Factor was found to be highest for Cd in U (2.9%-83%) followed by Cr in N (1.1%-62.3%) and Ni in (1.70%-52.7%) N. With regard to organic contamination, the major pesticides belonged to 13 organochlorine, 10 organophosphate and 8 synthetic pyrethroids reported below detectable concentration. Among the 16 US EPA priority poly aromatic hydrocarbon (PAHs) only 15 were detected. However, PAHs were found to be less than the permissible concentration for soils (0.3 mg kg(-1)) in sewage-contaminated sites. The results show that there is potential risk of transfer of heavy metals to higher trophic level of the food chain.