Geochemical fractionation of trace elements in sediments of Hugli River (Ganges) and Sundarban wetland (West Bengal, India).

A sequential extraction procedure was carried out to determinate the concentrations of 11 elements (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in different geochemical phases of sediments collected along the Hugli (Ganges) River Estuary and in the Sundarban mangrove wetland, eastern coastal part of India. The chemical speciation of elements was determined using the three-step sequential extraction procedure described by the European Community Bureau of Reference. Total metal concentration was determined using a microwave-assisted acid digestion procedure. Metal concentrations were near the background level except for As for which a moderate pollution can be hypothesized. The mobility order of the metals was: Cd > Mn > Cu > Zn > As > Co > Pb > Ni > Fe > Cr > Al. The highest percentage of Cd (>60%) was found in the most labile phase. Residual fraction was prevailing for Fe, Cr and Al, while Pb was mainly associated with the reducible fraction. Data were compared with Sediment Quality Guidelines to estimate the relationship between element concentrations and adverse biological effects on benthic community, finding the possibility of some toxic effects due to the presence of As in the entire studied area and Cd, only in Calcutta.

Using proteolytic enzymes to assess metal bioaccessibility in marine sediments.

In this work we tested two proteolytic enzymes (trypsin and pepsin) to evaluate metal bioaccessibility in marine sediments. Some working conditions were studied, in particular incubation time, enzyme concentration and solution/solid ratio, and metals release mechanisms were investigated using both untreated and denatured enzymes. The results obtained with trypsin and pepsin were compared with each other and with results from proteinase K extraction, carried out on the same sediment samples, following a procedure reported in the literature. Moreover, a comparison with the first step of BCR sequential procedure was made. Metal orders of mobility determined with the different enzymes and with acetic acid were compared with the one defined by the enrichment factors in the gut fluids of deposit-feeder organisms. The overall picture suggests that proteinase K has a better capability of reproducing natural phenomena and is therefore more suitable to determine metal bioaccessibility in marine sediments, when the target of the investigation is deposit-feeder organisms.