Man has always considered the sea as a “natural drain”, but for millennia this has not caused very serious damage. Today, however, compared to a hundred years ago, the situation has changed a lot: the world population has more than tripled and is concentrated in urban areas, often located near the coasts; hence the human-made organic discharges are considerably increased.
The number of industries has skyrocketed and the range of their products has expanded: man-made chemicals that are hardly degradable (plastic, nylon, detergents) and which in some cases also contain very toxic metals (such as mercury, nickel, zinc , chromium). The pollution caused by these substances has harmful effects on marine organisms and on the animals that feed on them, such as birds and humans.
Agriculture also plays its part in polluting the waterways and the sea. Huge quantities of residues of chemical fertilizers, insecticides and pesticides arrive here every year, producing extremely harmful effects on flora and fauna, with serious dangers also for humans; effects that do not remain localized in the unloading areas, but are often felt at considerable distances.
Another form of sea pollution is that due to oil. It arrives in the sea for different causes: leaks from the pipes of coastal refineries, accidents involving large oil tankers, abusive washing of oil tankers’ tanks offshore. Oil forms floating spots on the sea surface and causes a decrease in oxygen in the water. Many marine organisms, which breathe oxygen dissolved in water, die and birds suffer serious consequences when they run into these spots: getting their feathers dirty they have difficulty flying and floating and also ingest contaminated food. Tourism and fishing are also severely damaged.
Thermoelectric and nuclear power plants, which often arise right in coastal areas, pour into the sea, directly or through rivers, the water used in the cooling systems that have a high temperature compared to that of sea water. This form of pollution, called thermal pollution, has serious consequences on aquatic organisms that are unable to withstand excessive changes in temperature. Sea pollution is a global problem. The pollutants do not remain in the area where they are discharged but, carried by the currents, they make their harmful effects felt even at great distances. This does not mean that economic development must be stopped, but only that it is necessary to pay extreme attention to the phenomena that occur in the sea and to the effects induced by certain human activities, making every effort to control the most harmful ones, if one wants to maintain and properly use this enormous source of resource, to the benefit of all humanity!