Structure of peroxisomes and activity of the marker enzyme catalase in digestive epithelial cells in relation to PAH content of mussels from two Basque estuaries (Bay of Biscay): Seasonal and site-specific variations

The aim of the present work was to study the seasonal as well as the site-s pecific variations in the structure of peroxisomes and in the activity of t he peroxisomal marker enzyme catalase in digestive epithelial cells of muss els to validate the potential use of these parameters as early biomarkers o f environmental organic pollution in estuarine ecosystems. For this purpose , mussels were sampled monthly for 14 months in two Basque estuaries (Bay o f Biscay) with different degrees of pollution. Stereological procedures wer e applied to detect changes in peroxisome structure, and microspectrophotom etry was used to quantify changes in catalase activity. The animals from th e two studied sampling sites presented differences in polycyclic aromatic h ydrocarbon (PAH) burdens, mussels from Plentzia generally showing lower tot al PAH contents than mussels from Galea. The peroxisome structure of the an imals from the two estuaries suffered seasonal variations that were of diff erent kind and intensity in both sites. In this way, a strong peroxisome pr oliferatory response was found in mussels sampled in Plentzia during the su mmer months, while mussels from Galea presented few variations along the ye ar. Catalase activity behaved similarly in the animals sampled in the two e stuaries, with higher values in spring. It appeared that mussels exposed ch ronically to PAHs and other pollutants, such as those from Galea, lost thei r ability to respond to this exposure in terms of peroxisome proliferation. In contrast, mussels collected in Plentzia effectively responded to an inc reased bioavailability of organic pollutants during the summer by increasin g peroxisome volume and surface and numerical densities in digestive epithe lial cells. However, these increases were transient because elevated PAH bo dy burdens detected in mussels sampled in Plentzia in autumn were not accom panied by a peroxisome proliferatory response. Further studies are needed b efore changes in peroxisomal structure and in the activity of catalase coul d be used as early biomarkers to assess environmental quality in pollution monitoring programs like the Mussel Watch.