Assessment of metal enrichment and their bioavailability in sediment and bioaccumulation by mangrove plant pneumatophores in a tropical (Zuari) estuary, west coast of India.

Sediment collected from the estuarine mangroves of the Zuari estuary and Cumbharjua canal were analyzed to assess the concentration, contamination and bioavailability of metals. Mangrove pneumatophores were also analyzed to understand the metal bioaccumulation in mangrove plants. The results indicated the variation of metal concentrations in sediment along the estuary was attributed to changing hydrodynamic conditions, type of sediment and metal sources. Further, speciation studies revealed that Fe, Cr, Co, Ni, Cu and Zn were mainly of lithogenic origin and less bioavailable while high Mn content in the sediment raised concerns over its potential mobility, bioavailability and subsequent toxicity. The mangrove plants exhibited difference in metal accumulation due to variations in sediment parameters and metal availability, in addition to difference in plant species and tissue physiology that affect metal uptake. Moreover, the mangrove plants reflected the quality of the underlying sediment and can be used as a potential bio-indicator tool.

Geochemistry and bioavailability of mudflats and mangrove sediments and their effect on bioaccumulation in selected organisms within a tropical (Zuari) estuary, Goa, India.

Metals are non-degradable in the aquatic environment and play a vital role in estuarine biogeochemistry but could also be detrimental to associated biota. A comparative evaluation of the trace metal concentrations (Fe, Mn, Zn, Cu, Ni, and Co) was carried out in the Zuari estuary, Goa during the post-monsoon season of 2013 at six locations, each representing three mangrove and three mudflat regions. In addition, fractionation of trace metals in sediments was performed to provide information on the mobility, distribution, bioavailability and toxicity. Special attention was paid to the marine mollusks viz. bivalves and gastropods that are extensively used as bio-indicators in coastal pollution. Considering the percentage of metals in the sequentially extracted fractions, the order of mobility from most to least bioavailable forms was Mn > Zn > Cu > Ni > Co > Fe. Mn maintained high bioavailability (average around 60%) in Fe-Mn oxide and carbonate bound forms indicating that Mn is readily available for biota uptake. The bioavailability of Fe was on an average of around 6% whereas other metals like Cu, Zn, Ni and Co were around 19% to 34%. When the bioavailable values were compared with standard Screening Quick Reference Table (SQUIRT), Zn showed higher toxicity level and bioavailability in the lower estuary. On the basis of calculated Bio Sediment Accumulation Factors (BSAF's), overall trend in bioaccumulation was in the order of Cu > Zn > Mn > Ni > Co > Fe. Metal Pollution Index (MPI) computed was higher for gastropods than bivalves.

Impact of industrial effluents on geochemical association of metals within intertidal sediments of a creek.

Metal speciation studies were carried out on three intertidal core sediments of the industrially impacted Dudh creek located along west coast of India. Metals indicated a drastic increase in the bioavailable fraction towards the surface of the cores, suggesting an increase in anthropogenic metal input in recent years as compared to the past. Also, when compared with Vaitarna estuary and Khonda creek of Thane district, the speciation of metals in Dudh creek sediments was observed to have been highly modified in recent years. High concentrations of metals associated with bioavailable fractions therefore suggested a risk of toxicity to sediment associated biota of Dudh creek.

Speciation of metals and their distribution in tropical estuarine mudflat sediments, southwest coast of India.

Two sediment cores collected from a mudflat sedimentary environment of Swarna estuary (S3) and Gurpur estuary (MF6), representing the middle estuarine region, Karnataka, India, were investigated to understand bioavailability of metals and their toxicity. The subsamples were analyzed for sand, silt, clay, organic carbon and total metal concentration of Aluminum (Al), Iron (Fe), Manganese (Mn), Nickel (Ni), Zinc (Zn), Copper (Cu), Cobalt (Co) and Chromium (Cr) at 2 cm intervals. Sediments (average) are relatively coarser in Gurpur estuary whereas silt, clay, organic carbon along with the studied metals (except Mn and Cu) is noted to be higher in the Swarna estuary. Significant correlations were observed of Al, Fe with finer sediments and most of the trace metals in both the cores indicating a mainly lithogenic source. Further, metal speciation analysis carried out for Fe, Mn, Ni, Zn, Cu, Co and Cr on selected samples of both the cores indicated that Fe was largely associated with the residual fraction with 93 ± 0.5% in Gurpur and 84 ± 6% in Swarna estuary. The concentration of studied metals in the residual fraction in the sediments of Gurpur estuary was in the order Mn(90 ± 5%)>Cr(85 ± 1%)>Ni(72 ± 5%)>Zn(69 ± 3%)>Cu(57 ± 5%)>Co(55 ± 2%) and; Cr(80 ± 7%)>Mn(77 ± 10%)>Ni(76 ± 7%)>Zn(67 ± 10%)>Cu(67 ± 10%)>Co(50 ± 7%) in Swarna estuary. When the total (bulk) metals were compared with the Sediment Quality Values (SQV) following Screening Quick Reference Table (SQUIRT), Co values of both the cores fell above Apparent Effect Threshold (AET) values. When the sum of the average bioavailable fractions in sediments was considered, Co values exceeded the AET in core S3 (Swarna estuary). When the variations are viewed with depth, bioavailability of Mn, Ni, Cu and Co in Gurpur estuary indicated anthropogenic addition in recent years whereas in Swarna estuary most of the studied metals showed diagenetic remobilization and diffusion to the water column from surface sediments. Metal speciation study indicated no harm to the aquatic life, except of Co, in Swarna estuary wherein it posed a high risk of toxicity to organisms associated with the sediments.

Characterizing metal levels and their speciation in intertidal sediments along Mumbai coast, India.

The present study investigated the concentration, distribution and speciation of metals (Fe, Mn, Cu, Pb, Co, Zn and Cr) in sediments of Mumbai region. Pearson's correlation matrix and cluster analyses showed good association of metals with grain size and organic matter. Factor analysis applied to the speciation data helped to identify the role of different sediment fractions in metal retention. The environmental risks of metals, evaluated by sediment quality guidelines, revealed some contamination in the region. However, the Individual and Global Contamination Factors and the Risk Assessment Code, suggested low risk to the aquatic environment, except of Mn in the creek sediments.

Depositional environment and geochemical response of mangrove sediments from creeks of northern Maharashtra coast, India.

Present study provides results of trace metal distribution in mangrove sediment cores collected from macro-tidal Khonda and Dudh creeks of Northern Maharashtra coast, India. Most of the metals showed significant higher addition in Dudh creek (core DC) as compared to Khonda creek (core KC). However, Khonda creek sediments did show anthropogenic enrichment of Mn, Zn and Ni, while Dudh creek sediments showed anthropogenic enrichment of almost all the studied metals. Large difference in metal concentration between the two creeks was attributed to their proximity to industries. The higher Mn, Zn and Ni content in Khonda creek was mainly attributed to addition from domestic and agricultural wastes. While high deterioration of Dudh creek sediments was the outcome of addition from industrial effluents.

Distribution and speciation of selected metals in surface sediments, from the tropical Zuari estuary, central west coast of India.

Estuarine sediments are major reservoirs for the metals. Distribution and mobility of metals within estuaries depends strongly on their specific chemical form. In the present study, surface sediments from Zuari estuary, Goa were analysed by a sequential procedure for Fe, Mn, Cu, Zn, Cr and Co to determine their distribution in five geochemical phases (Exchangeable, carbonate, Fe-Mn oxide (reducible) organic bound (oxidisable) and residual). The total metal content, sand, silt, clay and organic carbon were also determined of the surface sediments. The total metal contents were found to be greater than the background concentrations of average shale values as well as to that of earlier studies indicating enrichment probably due to the anthropogenic origin of metals. The results obtained from sequential procedure showed that among the studied elements, Mn and Co are potentially available in the bioavailable fractions (exchangeable, carbonate and Fe-Mn oxide bound fractions) indicating their importance in toxicity whereas rest of the metals viz. Fe, Cu, Zn and to some extent Cr are largely available in residual phase although they are available in other fractions. The main source of metals to the estuary is mining and its associated activities in the study area. Chemical speciation by sequential extraction procedure has helped in assessing the mobility, bioavailability, diagenesis and toxicity of metals and hence giving a better insight into the ultimate fate of pollutants, which are introduced into the estuarine environment. To understand the risk of the metals to the sediment dwelling organisms the data were compared with the Sediment Quality Values (SQV) using SQUIRT. Also, correlation and Factor analysis were carried out to understand the associations of metals in the different fractions with sand, silt, clay, organic carbon and with other metals.

Environment quality at Maitri station in Antarctica.

A comprehensive study of air, water and soil quality was undertaken during the austral summer of 1999-2000 at the Indian Polar Research Station "Maitri" in compliance with the statutory requirements of the article 3 of Protocol on Environmental Protection to the Antarctic Treaty. The main objective of the study was to assess the impacts of various scientific programs and their associated logistic support facilities on the fragile ecosystem of Antarctica. Identification of major sources of pollution and quantification of pollutants in different environmental components were carried out through an extensive environmental monitoring program spread over a period of 5-7 weeks. Preliminary studies reveal that the levels of pollution are not alarming but there is scope for concern looking into the critical aspects of Antarctic environment and the carrying capacity of the environment surrounding Maitri station.