A. Hamzachaffai et al., METALLOTHIONEIN-LIKE PROTEIN - IS IT AN EFFICIENT BIOMARKER OF METAL CONTAMINATION - A CASE-STUDY BASED ON FISH FROM THE TUNISIAN COAST, Archives of environmental contamination and toxicology, 33(1), 1997, pp. 53-62
The aim of this work was to assess the relative importance of natural
fluctuations in metallothionein-like protein (MTLP) levels associated
with the sexual status of fish versus fluctuations due to metal exposu
re. In order to see fluctuations due to metal exposure, comparisons we
re made on the same fish species Scorpaena porcus sampled in polluted
and unpolluted sites. The hermaphrodite fish Serranus scriba and Scorp
aena porcus, in which sexes are separate, were compared at the unpollu
ted site to see fluctuations caused by the sexual status. In both spec
ies, metals and the MTLP levels were determined in the gills and liver
. In these organs, Cd, Cu, and Zn distributions were examined in diffe
rent fractions: the insoluble fraction (LF) and the cytosol divided in
to thermolabile compounds (HDF) and the heat stable compounds includin
g MTLP. MTLP levels were higher in the liver (3.09 mg/g in S. porcus,
1.59 mg/g in S. scriba) than in gills (0.13 mg/g in S. porcus, 0.40 mg
/g in S. scriba). For Scorpaena porcus, metals and MTLP levels varied
with sex, whereas in Serranus scriba, which is a hermaphrodite species
, inherent variations were also observed. At the polluted site, MTLP,
Cd, and Cu concentrations in the gills of S. porcus increased but the
supplementary metals were not associated with the heat stable compound
s including MTLP. At this site, hepatic MTLP bound more metals than at
the unpolluted site, but its binding capacity was not sufficient to a
void the binding of metals to the insoluble and the heat denaturable f
ractions. In light of these results and in spite of its hermaphrodism,
it is questionable whether to consider S. scriba as a good candidate
for biomonitoring based on MTLP. S. porcus could be useful for this pu
rpose only if the MTLP capacity in binding metals is not exceeded. The
MTLP could be considered as a biomarker only if it is investigated in
relatively unpolluted sites.