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Towards a Cleaner Marine Environment 3. No limits to marine pollutionVarious chemicals, which can affect and harm the marine environment, are constantly flowing into the sea. These substances mainly originate in human activities, from our everyday housekeeping, to agriculture, industry, traffic and energy production. This pollution does not solely come from Denmark, but also from other countries. Perhaps the smoke from Danish chimneys ends up in the Gulf of Bothnia, while the Baltic Sea receives, for instance, contaminated river water and atmospheric fallout from East Europe. If our efforts are to be successful, the pollution of the sea must be curbed also at the international level. Fortunately, many substances that end up in the sea are innocuous in the environment, as micro-organisms and other natural processes degrade them rapidly. They can, however, disturb the balance between the different animal and plant species. But other substances - even at extremely low concentrations - only degrade with difficulty and are suspected of harming animal life and people. The environmental authorities' monitoring of the marine environment obviously keeps an eye on the most dangerous substance groups, for instance heavy metals and such poorly degradable organic substances as PCBs (polychlorinated biphenyls), pesticides, softeners for plastics, TBT (tributyltin) and the PAHs (polyaromatic hydrocarbons). Fewer heavy metals in Danish harbours The sea is primarily contaminated by heavy metals through atmospheric fallout and discharges from urban areas and industry. Once in the sea, most of the heavy metals become bound to particles in sediment. But a small quantity becomes dissolved in the water and can spread widely in marine food chains. Cadmium and mercury are the two heavy metals that accumulate in this way, and they are toxic to aquatic organisms and humanity alike. Heavy metals also occur naturally in the environment. Such natural occurrences are called the background levels. Our goal for the Danish marine environment is to reduce the concentrations of heavy metals to values close to the background levels. Fortunately, sampling reveals that, with the exception of cadmium, concentrations of heavy metals are dropping in Danish waters and, in many places, are approaching their background levels. Certain places, such as Øresund and a few of the inner fiords, still exhibit levels high enough to affect aquatic organisms. Spotlight on PAHs from oil PAHs are substances that occur in oils and are formed during the combustion of fossil fuels (coal, oil and gas). Oil spills from shipping, oil extraction and spillage from industrial processes at sea are the main sources of PAHs in the marine environment, although about a quarter of the sea's PAHs originate in land-based combustion processes. Many PAHs are acutely toxic to aquatic organisms and other types of PAH can act as carcinogens and cause changes in the genetic material of man and animals. Most aquatic organisms can, however, metabolise the substances and excrete their metabolites, which limits the extent of their accumulation in the food chain. Monitoring of PAHs in our coastal waters shows that the general PAH level is low. But levels harmful to fish and small animals have been found in fiords, where water exchange only occurs slowly, or where major point sources of contamination are located. For this reason, the environmental authorities have redoubled their efforts to prevent the occurrence of all types of oil pollution in our waters.
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