Bioaccumulation and heat shock proteins in marine mussels (Mytilus galloprovincialis) exposed to zinc pyrithione

We investigated the biological fate and the effects of the organic biocide zinc pyrithione (ZPT) in comparison to inorganic Zn on the marine mussel Mytilus galloprovincialis, commonly widespread on hard bottoms of confined habitats such as harbours and marinas, where ZPT may be released in consequence of the use of antifouling paints and also become a source of Zn contamination. In particular, our aim was to highlight the pattern of accumulation of Zn both in his organic and inorganic form in the gills and in the digestive gland of the mussels and to assess whether a short term exposure to ZPT at sublethal doses could lead to the activation of repair mechanisms as highlighted by an increased expression of the early stress indicators hsp27, hsp60 and hsp70. ZPT has been introduced as a replacement for organotin compounds, which have recently been banned from antifouling treatments, but it has received little attention due to the lack of sufficient analytical methods for its determination in environmental matrices. ZPT is marketed as being an environmentally neutral, non-persistent compound based on the fact that it easily photolyses and rapidly degrades when exposed to direct sunlight (t½<1 hour). However, the analytical methods so far used measure the disappearance of the original biocide and not a reduction in total toxicity. Few studies have examined the toxicity of ZPT to marine non-target organisms. ZPT resulted very toxic to the crustacean Nitocra spinipes, with LC50 varying between 180 and 340 μg/l, underlining that ZPT can potentially be highly toxic towards marine organisms other than the fouling ones. To minimize oxidative damage and to cope with stressors, eukaryotic cells utilize a variety of protective mechanisms, including the expression of an assortment of proteins which are collectively referred to as “stress proteins”. HSPs showed to be a useful biomarker, in particular to detect early effects due to low level- or short term-exposures. Because of his ubiquity the marine mussel Mytilus galloprovincialis is widely used as a sentinel organism for the assessment of pollution in coastal environments. Monitoring its wellness is extremely important when harmful xenobiotic compounds are suspected to reach non-target species, as a consequence of submarine maintenance works or aquaculture-related treatments.