Arsenic speciation in tissues of the Mediterranean polychaete Sabella spallanzanii

Arsenic toxicity is strictly related to its chemical form and marine organisms are known to accumulate this element mostly as organoarsenic nontoxic molecules. Contrasting with this general trend, the presence of moderately toxic to toxic arsenic compounds recently has been reported in some polychaete species, showing a completely different profile of represented chemical species. In this work the presence and distribution of arsenic were characterized in the Mediterranean polychaete Sabella spallanzanii, by analyzing total levels in different tissues and subcellular fractions and the occurrence of various arsenical compounds. Further investigations on arsenic accumulation in S. spallanzanii were based on the capability of this species to regenerate the branchial crown both in laboratory and field conditions. Though basal levels of arsenic in the thorax were similar to those already described for most polychaetes and invertebrate species, branchial crown revealed a remarkable accumulation of this element with concentrations higher than 1000 microg/g. Arsenic mainly was localized in a soluble form within the cytosol and dimethyl-arsinate (DMA) appeared the most represented chemical species. Experiments on bioaccumulation of arsenic in regenerating branchial crowns confirmed the environmental origin of this element and the time-dependent appearance of various As compounds suggested a methylation pathway more than a degradation process for the elevated content of DMA. The accumulation of this moderately toxic compound in the more vulnerable tissues of the polychaete might represent an antipredatory strategy, as indicated by some feeding trials where fish ate the thorax but rejected the branchial crowns.