Comparative Biochemistry and Physiology Part C 123 (1999) 153 – 163 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 A. Hamza-Chaffai a, *, J.C. Amiard b , R.P. Cosson b a Uniersite de Sfax, IPEIS, BP 805, Sfax 3018, Tunisia b EP61 -CNRS -ISOMer, 1 rue Gaston Veil, 44035 Nantes, France Received 15 May 1998; received in revised form 23 February 1999; accepted 3 March 1999 Abstract 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 effect of metal pollution and other factors such as sex, size and reproductive state on MTLP levels. Copper concentrations did not vary with month, however Cd and Zn concentrations showed high levels during August. Organisms showing low cadmium concentrations presented the highest cadmium percentages in the soluble fraction (SF) containing MTLPs. However for high cadmium concentrations, the insoluble fraction (IF) was implicated in cadmium association. 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 proposed to describe a positive and a significant relationship between MTLPs and 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 and cadmium than females. Moreover, the effect of size and reproductive state 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 for detecting metal contamination. © 1999 Elsevier Science Inc. All rights reserved. Keywords: Biomarker; Biomonitoring; Box-Cox transformation; Cadmium; Copper; Metallothionein-like proteins; Pollution; Ruditapes decussatus ; Zinc 1. Introduction Biomonitoring based on biomarkers is a recent con- cept relying on the interaction between a toxic chemical and a biological receptor in a living organism [23,26]. This new approach allows the detection of the pollutant effect at the cellular level. To be efficient, a biomarker should have an early warning capacity, a certain specifi- city and other criteria as mentioned by some authors [15,27]. Among the biomarkers proposed in monitoring pro- grams, there are metallothioneins (MTs), which are low molecular weight, heat stable proteins of extremely high sulphur and metal content [25]. These proteins are found in various tissues of vertebrates and inverte- brates, and have been identified in most living organ- isms [2,14,18]. Marine invertebrates synthesis MTs having biochemical characteristics and functional prop- erties similar to those of vertebrates [42]. Bivalves exposed to pollutants accumulate various contaminants by mechanisms related to their filter-feed- ing habits. They are able to accumulate toxic metals in their organs to relatively high levels without any appar- ent detrimental effects. Many studies established a rela- tionship between MT synthesis and metal pollution in * Corresponding author. Tel.: +216-4-614109; fax: +216-4- 614109. 0742-8413/99/$ - see front matter © 1999 Elsevier Science Inc. All rights reserved. PII:S0742-8413(99)00023-7