Arsenic bioaccumulation and speciation in the filter-feeding clam Tapes philippinarum in the Venice and Marano lagoons (Italy)

A study on arsenic bioaccumulation in the Manila clam Tapes philippinarum was carried out in two coastal lagoons of the northern Adriatic Sea, the Venice and the Marano lagoons, where this bivalve species is a key product of the local mollusc farming activity. In addition, Manila clams are collected illegally in different areas of the Venice lagoon located close to a highly polluted industrial zone. Arsenic content and speciation were determined in transplanted clams placed in nylon nets in the studied sites at two different tidal heights, and grown from spring 2003 to winter 2005, when they reached the commercial size. Within this growth period, clam samples were collected three times, together with bottom sediments and suspended particulate matter (SPM). The aim of the study was to investigate the relationship between arsenic environmental concentrations and bioaccumulation in clams, and to achieve a better evaluation of the possible risk posed to the human population exposed to arsenic through clam consumption, by quantifying the individual levels of the various arsenic compounds in clam tissues. The results seem to indicate different patterns of arsenic accumulation by clams in relation to contamination in sediments and SPM in the two lagoons, with a higher bioaccumulation at Marano (up to about 60 mg/kg d.w.), despite the lower arsenic levels found in the abiotic matrices, whereas for the Venice lagoon sites As concentrations were below 30 mg/kg d.w. In addition, the relative abundance of the various arsenic compounds in clams collected in the different sampling sites allowed to advance some hypotheses about arsenic uptake and metabolism in this bivalve filter-feeder. A major role seems to be played by the physiological status of clams and by accumulation through the diet, since the two lagoons present differences in terms of environmental and contamination conditions, and of phytoplancton availability.