Pollution
The Mediterranean Sea is polluted by numerous substances considered environmentally and toxicologically hazardous: hydrocarbon compounds, persistent toxic substances, heavy metals, and radioactive materials. The impact of pollutants is accentuated by the closed and oligotrophic nature of the basin.
Predators at the top of the food chain, and particularly cetaceans, are more exposed to toxic effects and more vulnerable because they accumulate high concentrations of anthropogenic contaminants, which are considered Persistent, Bioaccumulative and Toxic (PBT).
Cetaceans bear a high pollutant load, accumulate significant concentrations of toxic substances in their tissues, and transmit them to their newborns through breast milk.
There is still no evidence that chemical pollutants directly cause cetacean death; however, some among them certainly cause immune and reproductive dysfunction. For example, the immunosuppressive effects of organochlorine compounds such as PCBs have demonstrated that these substances impair mammalian immune responses and increase the spread of disease outbreaks.
Organochlorine compounds are also known to be endocrine-disrupting chemicals.
Marine Litter
The continuous accumulation of debris in the marine environment is a growing global problem and a serious threat to marine biodiversity. From the benthic environment to the pelagic zone, the entire spectrum of marine habitats is under pressure from its effects. It has the potential to affect all trophic levels, from planktonic microorganisms to marine megafauna.
Marine litter includes all generated or solid wastes that enter the marine environment, regardless of their origin. They can be classified into different classes of materials, including plastics (foam, nets, ropes, buoys, monofilament and other fishing-related equipment, smoking-related items such as cigarette butts or lighters), metal (e.g., drinks cans, bottle caps), glass, paper, rubber, and cloth.
The impacts on marine mammals are diverse: intestinal blockages caused by the ingestion of litter, malnutrition, and poisoning, blockage of filter-feeding mechanisms by small particulate plastic debris, physical damage, and death.
84% of sperm whales stranded in Italian seas between 2008 and 2019 had plastic fragments in their stomachs, with the remarkable finding of as much as 22 kilograms of plastic in the female stranded in Olbia in early 2019 (see photo above, © Seame Sardinia). The cause is the large polyethylene sheeting for agriculture, bags, and filaments derived from the fragmentation of plastic, which accumulates in their stomachs.
Microplastics
Plastics can degrade into tiny pieces. Microplastics (generally defined as fragments less than 5 mm in size) floating in the Mediterranean Sea have reached 115,000 particles per km2.
Because of the high adsorption capacity of hydrophobic organic chemicals, adhering chemicals can be transported by microplastics traveling long distances. Microplastics can act as carriers of persistent organic pollutants in marine ecosystems.
Planktonic plastics loaded with organic pollutants can be easily mistaken for prey, and after ingestion, pollutants bioaccumulate. A wide range of organisms, from plankton to larger vertebrates such as whales, can ingest microplastics, but the impacts on organisms and the environment are largely unknown.