Ocean pollution crisis
In eight of ten cases, pollutants identified in the sea originate from terrestrial sources. As industrial or household waste, they are either discharged directly into the water, escape from poorly functioning wastewater treatment plants, are washed from the fields and streets by rainfall from above, or are leached from landfills and garbage dumps into subterranean water channels or streams. Litter and plastics are also carried to the sea by the wind. The remaining input of pollution occurs directly at sea, as a result of fishing and aquaculture or from shipping.
Winds and ocean currents transport garbage and pollutants to the most inaccessible regions of the world’s oceans. Evidence of the pollution can be found on remote islands, in the polar sea ice and in deep ocean trenches.
Pollutants especially hazardous for marine biotic communities are those that are long-lived and that accumulate in the food webs. These are characteristic, for example, of the group of persistent organic pollutants (POPs), which includes many pesticides and industrial chemicals.
The consequences of contamination are manifold and are distinguished according to the species affected and pollutant concerned. Known environmental pollutants cause diseases such as cancer, evoke deformities and behavioural changes in marine organisms, impair reproduction in affected species and can cause death in contaminated individuals. As a rule, predators at the highest trophic levels are especially impacted by environmental pollutants. These include sharks, toothed whales and seals. Animals that come into contact with plastic waste are in danger of being trapped, or of ingesting the plastic and starving with a full stomach. At least 700 animal species have now been identified for which plastic in the ocean can be a deadly hazard.
The international community is attempting to limit the input of pollutants into the seas through a variety of international agreements as well as trans-regional and national regulations. The prohibition of selected persistent organic pollutants by the Stockholm Convention, for example, is delivering results. The concentrations of these pollutants in the sea are declining.
But in many other cases, politicians and scientists are facing the problem that regulatory authorities are not always fully informed about the chemicals that are used in popular products, or about the impacts these ingredients would have should they someday end up in the sea. In many cases, the risk analyses required for a ban on dangerous substances are only possible after excessive quantities of them have already been introduced into the ocean and researchers are able to demonstrate the links between pollutant input and ecosystem destruction.
An end to the crisis of marine pollution will not be possible until a large proportion of the households and businesses around the world are connected to functioning sewage and solid-waste management systems, until substances toxic to the environment and carbon-based plastics are replaced by biodegradable alternatives, and the use of chemicals and plastics is limited to closed-loop systems.
