Microplastics in the marine environment - A threat to marine biota?

Microplastics in marine environments are an emerging environmental problem of international concern. This review focuses on the sources, quantities and effects of microplastics, to assess whether or not they pose a threat to marine biota. Microplastics are ubiquitous in marine environments, and have been reported along shorelines, in surface waters, seabed sediments, watercolumn and in a wide range of biota, from the Arctic to Antarctic. Particularly high concentrations have been measured in sub-tropical ocean gyres, close to population centers and in enclosed seas, like the Mediterranean. Measurements over time have also revealed that the smaller fragments are increasing. These have more surface area per unit mass, and are therefore likely to exhibit more intrinsic toxicity. Their small size also makes them bioavailable to a much wider variety of organisms, than larger plastic debris. Microplastics can therefore act as a carrier of chemicals ( either adsorbed from surrounding seawater, or incorporated in the plastic ) to marine biota. Few field studies have attempted to investigate the effects of microplastic exposure, however, indications of harmful effects have been revealed in several laboratory studies. These include reduction in the function and health of zooplankton, hindered algal photosynthesis and accumulation in mussels, causing a strong inflammatory response. The potential impact on the base of the food chain represents a primary concern, as it could affect the productivity of the entire ecosystem.