Contaminant pathways in Port Curtis: Final report - OzCoasts

Contaminant pathways in Port Curtis: Final report7: Antioxidant enzymes as biomarkersChapter 7 Antioxidant enzymes as biomarkers ofenvironmental stress in oysters in Port Curtis7.1 IntroductionThe screening level risk assessment of contaminants in Port Curtis (Apte et al.2005) found that concentrations of metals in sediments and dissolved metals inthe waters were generally below levels of regulatory concern. However,concentrations of a variety of metals were significantly enriched in marine biota incomparison with organisms sampled at reference sites. Studies prior to this hadalso flagged concentrations of some metals, in particular, copper and zinc in mudcrabs (Andersen & Norton 2001) and copper in seagrass (Prange 1999) andfiddler crabs (Andersen et al. 2002), as potentially anomalous in Port Curtisrelative to background levels. The demonstration of bioaccumulation of acontaminant, however, does not necessarily mean that organisms will displayadverse effects. There is a need to demonstrate a link between exposure and anadverse biological response.Biomarkers are biochemical, physiological or histological changes that measuresublethal effects of, or exposure to, toxic chemicals (Weeks 1995; Luebke et al.1997), and generally but not exclusively pertain to a response at a specific organ,cellular or subcellular level of organisation (O'Halloran et al. 1998). These cellularand molecular responses can be used as early warning signals of environmentalstress, before whole organism effects become apparent (Regoli et al. 1998).Environmental pollutants generally cause an increase in peroxidative processeswithin cells, causing oxidative stress (Winston & Giulio 1991; Cheung et al. 2001;Nusetti et al. 2001). Lipid peroxidation (LPO) has often been used as a biomarkerof environmental stress, reflecting damage to cell membranes from free radicals(Ringwood et al. 1999). The extent of damage caused by oxyradical production isdependent on antioxidant defences, which include antioxidant enzymes and freeradical scavengers, such as glutathione (Doyotte et al. 1997). Therefore,antioxidant enzymes are some of the most common biomarkers used inenvironmental monitoring (Regoli et al. 1998).The enzymes usually respond rapidly and sensitively to biologically activepollutants (Fitzpatrick et al. 1997). Some of the most commonly used antioxidantenzyme biomarkers include catalase (CAT) and glutathione-s-transferase (GST)(Winston & Giulio 1991; Regoli & Principato 1995; Regoli et al. 1998). Glutathione(GSH) is often used in biomarker studies, as it is an overall modulator of cellular80