Relationship between metallothioneins and metals in a natural population of the clam Ruditapes decussatus from Sfax coast: a non-linear model using Box-Cox transformation

Cadmium, copper and zinc were determined concomitantly with metallothionein -like proteins (MTLPs) in the subcellular fractions of Ruditapes decussatus digestive gland. This study covered 4 months and aimed to evaluate the eff ect of metal pollution and other factors such as sex, size and reproductive state on MTLP levels. Copper concentrations did not vary with month, howev er Cd and Zn concentrations showed high levels during August. Organisms sho wing low cadmium concentrations presented the highest cadmium percentages i n the soluble fraction (SF) containing MTLPs. However for high cadmium conc entrations, the insoluble fraction (IF) was implicated in cadmium associati on. MTLP levels varied according to the month, the sex and the size of the organisms. A non-linear model based on the Box-Cox transformation, was prop osed to describe a positive and a significant relationship between MTLPs an d the studied metals. A model including sex and size showed that these two factors affected MTLP levels, but were less important than metals. Males of R. decussatus showed higher significant correlations between MTLP levels a nd cadmium than females. Moreover, the effect of size and reproductive stat e on MTLP levels was less perceptible in males than in females. As a result , MTLPs in males of R. decussatus could be proposed as suitable biomarker f or detecting metal contamination. (C) 1999 Elsevier Science Inc. All rights reserved.