Despite the extensive transport of chemicals at sea, there is current lack of knowledge of the fate and effects of many of them on the marine biota. The current regulation that follows the GESAMP-MARPOL classification is mainly based on ecotoxicity assessment from fresh water based studies. Repetitive spills in marine coastal environment from tanker ship loaded with several thousand tonnes of chemicals raised concern about whether the existing freshwater data location can be used to predict the behaviour and the environmental effects of contaminants in marine surroundings. There is a general lack of information of the fate of chemicals at sea. A deviating pattern in marine environment from that in freshwater may have significant consequences for the counteracting actions taken to fight the spill, on staff working on the site of spill as well as on marine life present in the vicinity of the accident. In the present article, an environmental effect study of styrene was conducted as part of the ECOPEL program. We report some biological effects of styrene in laboratory-exposed marine organisms. Styrene was continuously supplied at a nominal concentration of 2mg L(-1) over 7 days to both mussels (Mytilus edulis) and fish (Symphodus mellops). At the end of this period, DNA damage was assessed by the Comet assay performed on blood (fish) and haemolymph (mussel) cells. In mussels, the lysosomal membrane stability was additionally assessed by the neutral red retention time assay (NRRT). Significant biological responses were observed over the studied period in both organisms with these two tests. Hence, the results favour the use of a biomarker-based approach to assess the health conditions in case of spill.