Discharges to sea

Discharges to sea

The main discharges to sea of environmental concern are associated with antifouling coating, ballast water, accidental and deliberate discharges of oil or oily water, and discharges of sewage and garbage.

Undesirable spreading of alien species has been described as the biggest threat to biodiversity and as the next big challenge for the shipping industry. The introduction of new species may cause irreversible altering of the ecological balance as well as affecting human health and industrial activities.

Release of TBT from anti-fouling paints is known to have a negative impact on several marine organisms. Based on this new use of TBT is now forbidden. As a consequence of this there has been an increase in use of ship-bottom paint with copper. It should then be noticed that some copper containing anti-fouling paints contain additives that recently has been given high attention e.g. in Norway. An example is Diuron (biocide) which is suspected to be carcinogenic.

Some estimates indicate a global discharge of oil to the sea of 2.35 Mton in 1990, where shipping accounts for 0.56 Mton, or 24 %. It has previously been estimated that over 70-80% of oil entering the sea from marine transportation is attributable to normal ship operations. However, this percentage will be highly dependent upon the occurrence or absence of large oil spills within the period for which the estimate is made. Operational oil pollution is estimated to have fallen from approximately 1.4 million tonnes to 0.57 million tonnes between 1981 and 1990. The two largest sources of oil entering the sea from marine transportation activities are due to operational tanker discharges and discharges of fuel oil sludge and machinery space bilge. The operational release is excepted to have decreased since 1989/90 due to IMO regulations requiring segregated ballast tanks (SBT), crude oil washing (COW), load-on-top (LOT) procedures and an oil discharge monitoring and control system to monitor the amount of oil discharged to sea. In addition, certain areas like the Mediterranean and Baltic Seas are designated as IMO Special Areas, and no oil discharges are allowed. However, the annual number of oil slicks between 1990 and 1998 attributable to illegal discharges in the North and Baltic Seas does not show a consistent decline.