Seasonal variation of histopathological and histochemical markers of PAH exposure in blue mussel (Mytilus edulis L.)

The aim of this work was to study seasonal variation of histopathological and histochemical markers in blue mussels (Mytilus edulis L.) exposed to pyrogenic PAH contaminants. Mussels were collected in January, June, September and October from a sampling site in the vicinity of the discharge from an aluminium smelter and from a clean reference site. Histopathological analysis was carried out on the digestive gland (DG) and the gonads, lipofuscin and neutral lipids were analysed in the DG. Clear responses in lipofuscin and neutral lipids were detected in the DG of mussels collected from the polluted site at some sampling times. Moreover, these mussels presented atrophy in digestive tubules and haemocytic aggregates in the gonad and DG. However, in all parameters studied, the magnitude of the response showed clear seasonal variation.

Research highlights
► The present study has demonstrated that lipofuscin and neutral lipids, together with histopathological analysis of gonads and digestive gland are useful biomarkers of stress caused by the pyrogenic PAHs.
► For more comprehensive biomonitoring programmes the sampling schedule should reflect seasonal variation in the selection of sampling months (reproduction cycle).
► The seasonal variation, combined with the health status and the reproductive stage of the organisms, needs to be considered during interpretation.
► The histopathology and histochemistry are suitable tools to be used in PAHs environmental monitoring programs.