Toxic metals distribution, seasonal variations and environmental risk assessment in surficial sediment and mangrove plants (A. marina), Gulf of Kachchh (India)

Highlights: • Seasonal variation of heavy metals in plants and sediment were assessed. • Toxic metals in sediments were found in higher concentrations, Fe, Mn, Sb, Ti were higher among all the metals. • Contamination indices demonstrate that sediments are extremely contaminated by metals, chiefly from Sb and As. • Ecological risk assessment indicates about 72% of sites come under higher risk. • A. marina efficiently translocates Cu, Pb, Fe, As, Zn, Ni, Sr, Mn and shows high bioaccumulation potential for Pb, Cu, Mo, Zn. Toxic metal pollution in the coastal ecosystem is becoming a serious problem, particularly in developing countries as a result of the industrial revolution. In recent years, mangroves are continuously contaminating with toxic metals and receiving global attention due to its toxicity, non-degradability, abundance, subsequent bioaccumulation, and biomagnification through successive trophic levels. This study aims to investigate the toxic metal content and pollution status in mangroves surface sediment and plants. Results showed that toxic metals in sediments were higher than natural background levels indicate anthropogenic sources. Fe, Mn, Sb, Ti found higher in concentration among all toxic metals, and site 9, 15, 18, 19, 21, 31 found the highest total metal load. Contamination indices like enrichment and contamination factor, geo-accumulation index, suggest minimal to extremely high level of contamination, and sediments have found extremely contaminated with Sb and As. Contamination degree and modified contamination degree suggest very high degree of contamination at all sites. Pollution load index indicates significant deterioration of sediment quality. Ecological risk and potential ecological risk index also indicate about 72% of sites come under higher ecological risk. Toxic metal in Avicennia marina was found higher in root than leaf. High bioconcentration factor has observed for Pb, Cu, Mo, Zn. Translocation factor for Cu and Zn at all sites, and As, Ni, Pb, Fe, Sr, Mn at some sites indicate high-efficiency in plants for toxic metal translocation.