Immune biomarker and hydrocarbon concentrations in carpet shell clams ( Ruditapes decussatus ) collected from a Mediterranean coastal lagoon

Immunological alterations may be used as ecotoxicological biomarkers to detect and monitor biological effects of chemical contaminants in polluted environments. The main goal of this study was to assess the immunotoxic effects of hydrocarbon contamination in the soft tissues of carpet shell clams ( Ruditapes decussatus ) sampled from the South Lagoon of Tunis (Tunisia). Sediments and clams were collected from four locations, three of which were located within the polluted South Lagoon of Tunis (S1, S2 and S3) whereas the other was a clean site on the Mediterranean coast. Total hydrocarbons were extracted from the clam tissues and sediments and fractionated into aromatic and nonaromatic hydrocarbons. The status of the clam immune system was assessed by measuring the total haemocyte count (THC) and the phenoloxidase, lysozyme and esterase activities in haemolymph samples from the clams. Hydrocarbon analysis revealed that pollution levels in the South Lagoon of Tunis were high and spatially variable. Phenoloxidase activity was inhibited in clams sampled at sites S1, S2 and S3 compared to clams at the control site, while lysozyme and esterase activities and THCs were higher in the clams at the polluted sites than in those at the control site. Moreover, the biomarker responses indicated that S3 was the most polluted site in the South Lagoon of Tunis. The results of the present study clearly show that suitable biomarkers can be useful tools for biomonitoring in the study area.