Correlation between the morpho-cytohistochemistry of the outer mantle epithelium ofAnodonta cygneawith seasonal variations and following pollutant exposure

Abstract

Seasonal and experimental conditions induce morphological and cytochemical variations in the outer mantle epithelium (OME) of the freshwater bivalve Anodonta cygnea, probably influencing the shell calcification mechanism. In this study, OME samples were taken from untreated animals in autumn, winter, spring and summer as well as from animals exposed to divalent metals (cadmium, chromium, lead, copper and zinc) and pesticides (setoxidim and dimethoate) and observed by light microscopy. The present results showed that OME cells have larger cell volumes and increased amounts of secreted macromolecules during spring and summer than in autumn and winter. This correlates with higher shell calcification rates in spring and summer and lower shell calcification rates in autumn and winter. The experiments showed that incubation with pollutants for 8 months dramatically reduced the cellular volume so that the density of cytoplasmic material appeared higher that in the control samples. The pronounced changes in OME cells suggest a significant decrease in secretory activity following exposure to toxic agents and this has implications for the shell calcification process.