Human activities, whether at sea, on land or along the human-made coastline may cause chronic and diffuse pollution in the marine environment that represents 75% of the global marine pollution. The use of bioindicators is particularly relevant from a biological point of view if the directly measured concentrations reflect the bioavailable fractions in the marine environment. The Mediterranean Sea is an enclosed basin with an average depth of 1,500 m, with short ventilation and residence time. The Mediterranean Sea has relatively warm and salty waters, due to the Mediterranean climate and its enclosed nature. A coastal–open ocean gradient might dominate over such a basin scale gradient, leading to coastal site-specific planktonic characteristics. The Mediterranean mussel is a shellfish species that is widely distributed in the coastal waters of the eastern Atlantic-Mediterranean waters. Marine species represent a powerful model for risk–benefit assessment.