Occurrence, distribution, and ecological risk of heavy metals and persistent organic pollutants (OCPs, PCBs, and PAHs) in surface sediments of the Ashtamudi wetland, south-west coast of India

Abstract

Monitoring heavy metals (HM) and persistent organic pollutants (POP) has become more important recently, as they pose serious threats to tropical aquatic ecosystems. The Ashtamudi wetland a Ramsar Site in the southwest coast of India must be monitored due to the intense urbanisation and anthropogenic activities that occur in the nearby areas of this wetland. This study aims to identify potential sources of POPs (OCPs, PCBs, and PAHs) and HM in the surface sediments of Ashtamudi wetland, as well as to assess their ecological risk. The enrichment factor (EF), contamination factor (CF), degree of contamination (CD),geo-accumulation index (Igeo), pollution load index (PLI), and sediment quality guidelines (SQG) were used as pollution indices. The average concentrations of HM were Iron (39582.52 mg/kg) > manganese (365.92 mg/kg) > Zinc (91.39 mg/kg) > nickel (49.36 mg/kg) > Copper (31.47 mg/kg) > lead (21.21 mg/kg) > Cadmium (0.73 mg/kg). The concentrations of HM detected during the study were on par with or even higher than the other coastal systems. Several areas of the Ashtamudi wetland are extremely enriched and moderately to considerably contaminated with cadmium (EF and CF indices). Nickel exceeds the ERM (Effects Range Median) in some sampling stations. The Ashtamudi wetland has not been seriously contaminated by organochlorine pesticides (2.03 to 2.45 μg/kg) and polychlorinated biphenyls (0.26 to 0.35 μg/kg). Sediments are moderately contaminated with polycyclic aromatic hydrocarbons (202.81–158.23 μg/kg) from urban emission sources of Kollam. These results can be used as a reference point for future research on organic contaminants in Indian wetlands and highlight the need for effective controls of micro pollutants.