Antioxidant enzymes as biomarkers of environmental stress in oysters in Port Curtis

The estuarine embayment of Port Curtis is Queensland's largest multi-cargo port and the fifth largest port in Australia. It supports major industries in the Gladstone area including the world's largest alumina refinery and Australia's largest aluminium smelter. Because the estuary is one of the Coastal CRC's three key study areas, research by the CRC contaminants team focused firstly on identifying contaminants of concern in a screening-level risk assessment. Although enrichment of some metals in marine organisms was recorded, subsequent projects focused on assessment of organism health to determine if environmental harm had occurred. There was a need to demonstrate a relationship between exposure to a contaminant and an adverse ecological effect. The objective of the current study was to examine the use of biomarkers as a measure of pollution-induced stress in oysters (Saccostrea glomerata) transplanted into Port Curtis from a clean area. Biomarkers are defined as a biological response that can be related to exposure to an environmental contaminant. In a broad context they can include measuring such endpoints as reproduction and growth, or behavioural changes; however, the biomarkers chosen in this study measured effects at a cellular level. Exposure to pollutants causes the production of potent oxidants and free radicals capable of damaging important cell components such as proteins and DNA. In response, the cell initiates antioxidant enzyme systems and produces free radical scavengers in order to prevent cellular injury and maintain cell homeostasis. The induced biomarker response can then be measured and related to measured concentrations of the contaminant the oyster is exposed to.