The contribution of metal/shell-weight index in target-tissues to metal body burden in sentinel marine molluscs. 1. Littorina littorea

Accumulation and tissue distribution of Cu and Zn in target organs of Littorina littorea have been investigated. Weight changes in particular organs were associated with either Cu or Zn exposures and therefore, metal/shell-weight indices were used instead of metal concentrations to investigate metal accumulation and mobilisation. A regulatory mechanism was observed on exposure to low levels of Cu, but regulation did not occur between 8 and 80 μg Cu/l seawater. Conversely, Zn was well-regulated up to a concentration of 80 μg Zn/l seawater. View the MathML source index increased linearly at increasing Zn exposure levels and decreased linearly at increasing Cu exposure levels. The gills are not target tissues reflecting environmental levels of either Cu or Zn, however, copper levels were elevated in gills after exposure to 80 μg Cu/l seawater for 29 and 41 days. On the other hand, the highest concentration of Cu in the kidney was found after exposure to 8 μg Cu/l seawater for 41 days. Higher exposures resulted in lower Cu concentrations. According to metal/shell-weight indices, Cu and Zn were not significantly accumulated in the digestive gland/gonad complex (DGGC) until a certain threshold value was reached (exposure level > 400 μg·day/l). On the other hand, DGGC weight was significantly reduced and, concomitantly, Zn and Cu concentrations raised. However, the metal concentration values increased beyond those resulting simply from a weight reduction. In conclusion, dissimilar mechanisms performed by different cell types in the different organs, together with metal-induced weight changes, would account for the existence of different patterns of metal accumulation and tissue distribution. It is therefore suggested that the suitability of winkles as indicators of Cu and Zn pollution should be reconsidered on the basis of measurements of metal burdens at tissue and cell levels.