Plastic waste in the seas

One of the biggest news items on contamination has been the presence of huge amounts of plastics in many areas of world's oceans. One of the greatest sources of plastics are plastic bags - carelessly handled by people. Eighty to ninety % of plastic contamination in the seas comes from coastal areas. Plastics in the coast float up to several thousand kilometers from the disposal point in sea currents.

Plastics are very stable. That is the major reason, why they have become so intensively used. However, abiotically they are slowly degraded to small plastic particles, microplastics, in sunlight and the presence of oxygen. Biologically, bacteria, which are able to use plastics as food source, have evolved. Plastics are made from oil. Thus, oil-eating bacteria have developed to plastic-eating bacteria. They are much more effective at tropical temperatures than in cold. Thus, both oil and plastic pollution are a longer-lasting problem in the arctic than tropical areas.

Although the toxic compounds of oils are also those of many plastics, the major biological effects of plastics are caused by the influence of plastic particles on digestion. Microplastics are virtually undigestible and often clog the digestive tract of animals which eat them. (And this is what most animals do, as plankton-eating animals do either not recognize the difference between real edible animals and undigestible plastic particles or eat animals with digestive tract filled with plastic particles). As the real food cannot then be digested the animals cannot get energy required for living. Consequently, it is presently estimated that millions of birds and fish die annually because of the disturbances in digestion caused by the plastics, and the number of dead invertebrates is much greater.