DIGESTIVE LYSOSOME ENLARGEMENT INDUCED BY EXPERIMENTAL EXPOSURE TO METALS (CU, CD, AND ZN) IN MUSSELS COLLECTED FROM A ZINC-POLLUTED SITE

This investigation was carried out to quantify changes in the structur e of the digestive lysosomes of mussels, Mytilus galloprovincialis, ex posed to sublethal concentrations of metals, in both field and laborat ory conditions. Digestive lysosomes were automatically measured in an image analysis system to calculate several stereological parameters (v olume density, surface density, surface to volume ratio, and numerical density) after the histochemical demonstration of beta-glucuronidase activity on cryotome sections. The field study revealed that increasin g environmental levels of bioavailable zinc (Zn) are associated with e nlarged digestive lysosomes in mussels living in their natural habitat . When these Zn-polluted mussels were depurated in clean seawater for short time periods (1-week acclimation plus 6 experimental days), the digestive lysosomal size was reduced significantly. After longer depur ation periods (over 20 experimental days), the stress due to laborator y handling provoked reduced numbers of large digestive lysosomes. On t he other hand, the subsequent laboratory exposure to Zn and to other m etals (copper, Cu, and cadmium, Cd) caused an enlargement in the diges tive lysosomes of Zn-polluted mussels beyond that produced by Zn-pollu tion in the field. In summary, the enlargement of digestive lysosomes reactive to beta-glucuronidase is a sensitive biomarker for non-specif ic environmental stress induced by sublethal concentrations of bioavai lable metals. In addition, we propose the four studied stereological p arameters, calculated by means of automated image analysis, as quick, reliable, and useful measurements of such lysosomal enlargement.