The Mediterranean sea is polluted by numerous substances considered to be environmentally and toxicologically most significant, namely hydrocarbon compounds, persistent toxic substances, heavy metals, radioactive materials.
Long-lived top predators in marine ecosystems, and particularly cetaceans, are most exposed to toxic effects and more vulnerable to the accumulation of high concentrations of anthropogenic contaminants, many considered Persistent, Bioaccumulative, and Toxic (PTB)
Cetaceans’ pollutant burden is high, amassing important concentrations of toxic substances in their tissues, even passing them to infants through mother’s milk.
Immunosuppression and Sterility
There is still no evidence that chemicals contaminants are causing direct mortality of cetaceans; however, some of them certainly cause immune and reproductive dysfunction. For example, the immunosuppressive effects of organochlorine compounds such as polychlorinated biphenyls (PCBs) in mammals suggested that these substances impaired immune responses and increased the severity of the outbreak.
Organochlorine compounds are also known to be endocrine-disrupting chemicals.
The continued accumulation of debris in the marine environment represents a growing global issue and a major threat to marine biodiversity. From the benthic environment to the pelagic zone, the whole spectrum of marine habitats is under pressure from its effects. It has the potential to affect all trophic levels and for impacts to travel through the food chain, from planktonic microorganisms through to marine megafauna.
Marine litter includes any manufactured or solid waste entering the marine environment irrespective of the source. It can be categorized into several diverse classes of material including plastics (soft, foam, nets, ropes, buoys, monofilament line and other fisheries-related equipment, smoking-related items such as cigarette butts or lighters), metal (drink cans, bottle caps, pull tabs), glass (buoys, light globes, fluorescent globes, bottles, etc), paper, rubber, and cloth.
The impacts on marine mammals are diverse and may include entanglements and ghost fishing, ingestion with consequent intestinal blockage, malnutrition and poisoning, blockage of filter-feeding mechanisms from small particulate plastic debris, physical damage until the death of marine animals.
84% of sperm whales beached in Italian seas between 2008 and 2019 had plastic fragments in their stomachs, with the extraordinary finding of as much as 22 kilos of plastic in the female beached in Olbia in early 2019 (see photo above, © Seame Sardinia). The cause is the large cloths used for agriculture, bags, filaments derived from the fragmentation of plastic, which accumulate in their stomachs.
Plastic can degrade to microscopic pieces . Microplastics (MPs – generally defined as fragments less than 5 mm in dimension) floating on the Mediterranean Sea have reached 115.000 particles per km2.
Due to the high sorption capacity for hydrophobic organic chemicals, the adherent chemicals can be transported by microplastics traveling long distances. Microplastics can serve as carriers of persistent organic pollutants in marine ecosystems.
Planktonic plastic loaded in organic pollutants can easily be mistaken for prey and upon ingestion the pollutants bioaccumulate. A wide range of organisms, from plankton to larger vertebrates such as whales, may ingest microplastics but impacts to organisms and the environment are largely unknown.