Subcellular partitioning of elements and availability for trophic transfer: Comparison between the Bivalve Cerastoderma edule and the Polychaete Diopatra neapolitana

Metal transference through food-chain can constitute a serious problem, particularly in coastal systems, where macrobenthic organisms are often exposed to metal contamination. Previous studies have shown that the elements accumulated in macrobenthic organisms can either be precipitated or soluble in the cells. Whilst differences in the subcellular distribution between fractions are described for Cd, Cu and Zn, little is known for other elements such as As, Pb or Hg, despite their toxicity. The present study compared the subcellular partitioning of several elements in two different macrobenthic species, the bivalve Cerastoderma edule and the polychaete Diopatra neapolitana, and the potential that each element has to be trophically available was determined. There were differences in element accumulation between the two species: D. neapolitana presented a higher concentration of Zn and As while, C. edule accumulated more Al, Ni and Pb. The results obtained for the soluble fraction showed that the elements in higher concentration were, for both species, Al and Zn. In addition to these two elements, Cu, Cd, Cr and As concentrations in this fraction were higher in D. neapolitana than in C. edule, although the bivalve presented higher Ni levels. These results give a good estimate of the amount of elements more readily available to be trophically transferred. The relative amount of metal present in the soluble fraction may indicate more clearly the ability of each species to cope with each element and thus their propensity to allocate subcellular elements, regardless of the environment that it inhabits. The percentage of elements in the soluble fraction showed that C. edule had a high predisposition to compartmentalise As and Cd in the trophically available fraction, given that the other elements were preferentially in the insoluble fraction. In contrast, D. neapolitana distributes metals and As more evenly throughout both fractions. As our study simultaneously evaluated the different elements, this gave a more precise idea of the real contamination that passes to higher trophic levels, especially in the elements that have high toxicity and which had not yet been evaluated (Hg, Pb, and As). This shows that contamination of the food webs of an ecosystem is not only dependent on its chemical contamination, but also on the organisms at each trophic level.

► Cerastoderma edule and Diopatra neapolitana as indicators of sediment contamination. ► Species variability in metals (Cd, Zn, Hg, Ni, Cu, Pb, Al and Cr) and As accumulation. ► Total element concentration accessible for assimilation (soluble fraction).