Relationships between metallothioneins and metal accumulation in the whelk Thais clavigera

Whelks Thais clavigera were collected from field populations containing different concentrations of metallothioneins (MTs) or were pre-exposed to aqueous or dietary Cd in the laboratory to result in differential body MT concentrations. Cd, Hg and Zn uptake from the dissolved phase, assimilation efficiency from the dietary phase, and body burden were subsequently quantified. MT concentrations in whelks collected from 11 sites in the coastal waters of Hong Kong were significantly correlated with Cd body concentrations, but were not correlated with Cu and Zn body concentrations. There was a clear relationship between the dissolved Cd exposure and the resultant MT levels in the animals, but no such relationship was found following dietary exposure to Cd. The assimilation of Cd and Hg increased in whelks originating from impacted field populations with higher MT levels and following inducement of MTs by pre-exposure to dissolved or dietary Cd. Zn assimilation was comparable in the field populations with different MT levels, but decreased in groups with higher MTs following pre-exposure to Cd, presumably due to the saturation of MTs by Cd binding, and thus less MT binding sites were available for Zn. MTs may thus play an important role in metal assimilation. In contrast to dietary assimilation, metal uptake from the dissolved phase in whelks was unaffected by MT body concentrations. Dissolved uptake appears to be largely a physico-chemical process and is little affected by the intracellular physiological changes made by the animals. Given the ubiquity of MTs in marine animals and the importance of dietary sources in metal accumulation, the influence of MT should be considered in interpreting body metal concentrations, and the use of MTs as biomarkers of metal contamination should be treated with caution.