The use of biomarkers in bivalves has gained significance as a reliable method for the assessment of the presence and effect of contaminants in aquatic ecosystems. However, it is important to note that the biomarkers respond not only to contaminant loadings and bioavailability but also to environmental stress. Therefore, the association between biomarkers and contamination/pollution should be conducted cautiously as the environmental factors also affect their response. These factors should be integrated into the assessment of the response of the biomarkers. The potential impact of effluents from an urban wastewater treatment plant (UWWTP) on the Ruditapes decussatus clam specimens located 1.5 Km away in a surrounding area was evaluated. After one month of exposure, three biomarkers were analyzed, namely lipid peroxidation (LPO), acetylcholinesterase (AChE) and electron transport system (ETS). These parameters were also determined for a control group purchased from a local nursery, which had no influence from UWWTP, in order to compare the results obtained from both groups. The in situ physicochemical characterization of the exposure site (temperature, salinity, pH and dissolved oxygen) was evaluated together with nutritional parameters, morphometric measurements and condition index. The biochemical analysis showed that the activity levels of AChE fluctuated from 4.0 to 4.6 nmol/min g protein and that of LPO from 101.5 to 248.9 nmol MDA/g protein. Also, the ETS activity levels were in the range of 27.2 to 30.2 nmol O2/min g protein. The lipid peroxidation was found to be the most responsive biomarker toward the damage caused by environmental conditions on the clams.
