Bioaccumulation of heavy metals in a gastropod species at the Kole wetland agroecosystem, a Ramsar site

Abstract

Heavy metal concentrations were evaluated in the Pila globosa tissues and the adjacent aquatic environment of the Kole wetland agroecosystem, a Ramsar site, southwest coast of India. Metal concentrations were analyzed to assess the spatial distribution, contamination levels, bioaccumulation potential, and potential risk to the human population and the migratory birds that forage the wetland agroecosystem. The recorded concentrations of heavy metals in P. globosa tissues and the aquatic environment followed the hierarchal order: Fe > Cu > Mn > Cr > Zn > Ni > Cd > Pb mg/kg and Fe > Zn > Ni > Cr > Mn > Pb > Cu > Cd mg/L, respectively. Elevated levels of heavy metals were recorded in the P. globosa tissues than the adjacent aquatic environment thus, highlighting their potential for bioaccumulation. The recorded concentrations of heavy metals in the P. globosa tissues exceeded the permissible limits for Fe, Cu, Mn, Ni, Cr and Cd at several sampling sites. However, in the aquatic environment, the concentrations of all heavy metals were within the permissible limits except for elemental Ni. Inter-elemental correlations between the P. globosa tissues and the aquatic environment recorded antagonistic associations that inhibit metal co-accumulations between the biotic and the abiotic environments. Source identification based on Principle Component Analysis revealed dynamic modes of variability for heavy metals, indicating agro-pesticides and fertilizers as the likely source of heavy metal contamination. Among heavy metals, greater bioaccumulation capacity was recorded for Cu, a moderate for Fe, and comparatively less bioaccumulation for Mn, Zn, Pb, Cr, and Ni. The health risk assessment based on the Target Hazard Quotient and Hazard Index revealed potential toxicity risk to the human population and the migratory birds including the transcontinental migrants that forage the Kole landscapes. Finally, the study emphasizes on long-term monitoring and surveillance programs to identify the multiple stressors most probably, the point sources of contamination and the diffuse sources along the Central Asian flyway for migratory birds to ensure protection of the threatened species and reduce the risk to the human population. Vulnerability to heavy metal toxicity shows that the Kole wetland agroecosystem, a Ramsar site for transcontinental migrants is likely at risk due to heavy metal bioaccumulation in gastropods, hence, requires urgent retrospection. The results of the study highlight that the biosorption potential of P. globosa, can be utilized for bioremediation of metal-contaminated wetlands and agroecosystems.