Metal enrichment and toxicity assessment through total and speciation of metals in lower and middle regions of tropical (Mandovi) Estuary, western coast of India.

The study aimed to understand the metal enrichment and toxicity in lower and middle regions of a tropical Mandovi Estuary, revealed metals dilution by coarser intertidal mudflat sediments in the lower estuary (downstream of the fishing jetty-core S). A relatively calm depositional environment prevailed at the middle estuary (core M) and also at the upstream of the jetty of the lower estuary (core L) facilitating deposition and enrichment of Mn and Zn in cores M and Mn, Cu and Co in core L. The distribution of trace metals in sediments was regulated by grain size, total organic carbon and Fe-Mn oxides. The potential contamination index indicated a moderate degree of metal contamination in sediments while the anthropogenic factor showed the signatures of human-induced activities in the enrichment of metals. The sequential extraction of metals showed bioavailability of Mn, Cu, Zn and Co. Fe-Mn oxide and organic/sulphide were key phases for the retention of bioavailable metals. The elevated level of these metals suggested possible toxicity to benthic biota, particularly from Mn (cores L and M) and Co (core L) according to the screening quick reference table.

Assessment of metal enrichment and contamination in surface sediment of Mandovi estuary, Goa, West coast of India.

Metal concentration in the sediments was determined to assess the metal enrichment and level of contamination in the Mandovi estuary. The metal distribution in the Mandovi estuary revealed preferential input through open-cast iron-ore mining, industrial, fishing, and agricultural activities. The heavy riverine runoff associated with high rainfall influenced the distribution of Mn, Zn, and Pb during monsoon season. In addition, sediment grain size and associated organic matter governed metal distribution in surface sediments. The role of grain size and organic matter along with Fe-Mn oxides in the distribution of metals was construed through correlation and factor analysis. Geo-accumulation index, contamination factor, and potential contamination index indicated contamination of surficial sediments of the Mandovi estuary with Cr and Pb.

Spring-neap tides influence on bioavailability of metals and bioaccumulation in edible biota of the Zuari (tropical) Estuary.

Role of spring and neap tides on metal bioavailability and bioaccumulation in edible biota was studied in the Zuari Estuary. Moderate to very high range of contamination factor for Fe, Mn, Cr, Zn, Cu, Cd, and Pb at one or more stations and tides suggesting their anthropogenic origin. The anthropogenic input of metals was supported by pollution load index. Relatively high bioavailable concentration of Fe, Mn, Cr, Zn, Cu, Cd, and Pb indicated their toxicity to biota. Total metal concentration, viz., Fe, Mn, Cr, Zn, Cu and Cd, and bioavailable content Mn, Cd, and Pb were higher during spring tide than neap tide at one or more stations which revealed their low mobility under flooded conditions. The above observation was well supported by higher concentration of Fe, Mn, Cr, Zn, Cu, and Pb in Polymesoda erosa at the middle estuary during neap tide than subsequent spring tide. Further, an increase in concentration of metals bound to certain bioavailable fractions toward the surface of the cores revealed their possible bioavailability to the biota with changes in the physicochemical properties of the Zuari estuary. Biota sediment accumulation factor revealed macro level accumulation of Cd and suggested its toxicity to marine biota.

Assessment of metal pollution and bioaccumulation of metals by edible bivalve Polymesoda erosa in the Zuari Estuary, west coast of India.

The mangrove sediment cores from middle and upper Zuari Estuary were studied for grain size, organic carbon, total and bioavailable metals (Fe, Mn, Zn, Pb) to evaluate the metal enrichment and pollution, along with the bioaccumulation of metals by edible bivalve Polymesoda erosa to understand the toxicity of metals. The distribution of metals varied between middle and upper estuary and was attributed to difference in metal source, hydrodynamics and/or post-depositional behavior. The pollution indices viz., contamination factor and pollution load index revealed metal pollution at both middle and upper estuary. Speciation of Mn, Zn and Pb indicated their bioavailability in sediments, and the application of screening quick reference table and risk assessment code suggested possible harmful effects of Mn on biota. The concentration of metals in Polymesoda erosa was more than the standard permissible limit, at both middle and upper estuary indicating metal toxicity to Polymesoda erosa and human health.

Assessment of metal enrichment and bioavailability in mangrove and mudflat sediments of the tropical (Zuari) estuary, west coast of India.

Mangrove and mudflat sediment cores at the confluence point of the Cumbarjua Canal and the Zuari River were collected and analyzed to assess metal enrichment and bioavailability, with the background of significant bioaccumulation reported in earlier studies within the Zuari Estuary, a recipient of open-cast mining waste containing Fe and Mn. Metals were enriched in mangrove and mudflat sediments due to additions from natural and anthropogenic sources. Contamination factor showed moderate degree of contamination of Fe, Mn, Cu, and Co in mangroves while of Fe, Mn, and Co in mudflats. Pollution load index suggested metal pollution in the sediments of the Zuari Estuary. Metal speciation study indicated largely lithogenic source of Fe (in mudflats), Cu, Zn, and Co, whereas abundant bioavailable Fe (in mangroves) and Mn (in both mangroves and mudflats) suggest their possible mobilization, preferential accumulation, and bioavailability. Further, sediment quality values indicated toxicity of bioavailable Mn and Co, and risk assessment code revealed medium risk of Mn to sediment associated organisms.