Tank cleaning and its impact on the marine environment

Report, 2022

Every year, the seas around Sweden are trafficked by chem- and product tankers that collectively transport hundreds of millions of tons of liquid chemical substances and products in bulk. When ships carry different types of chemicals, the tanks must be cleaned after unloading, before the new product is loaded. The aim of this pre-study was to assess tank cleaning from a marine environment perspective and to review current applicable regulations.
Legal discharges of wash water and chemicals from operational tank cleaning of vessels cause an increased pressure on the marine environment. There are currently no statistics on where and when tank cleaning is performed in Swedish sea areas, but based on observations from aerial and satellite surveillance, and traffic intensity of tankers from AIS data, some areas can be identified as probable areas for discharges. Several of these areas border or overlap with designated protected areas, for example according to Natura 2000. Current regulations, mainly within the IMO MARPOL Annex II, related to discharge of tank cleaning residues are intricate and leave room for different interpretations. In addition, there is no comprehensive statistics available on the substances that are loaded and unloaded in Sweden. Further, the statistics that are available often contain errors which contribute to major uncertainties in the possible assessment of effects in the marine environment as a result of tank cleaning.
Today, very few of the substances transported in liquid bulk, can with certainty be classified as totally harmless. The regulations should therefore be reviewed and in the absence of reliable statistics and scientific evaluations, all substances discharged in connection with tank cleaning should be classified as hazardous substances. There is consensus within HELCOM that the pressure on the marine environment from hazardous substances in the Baltic Sea must be reduced, which strengthens arguments for applying the precautionary principle and consider a ban of discharges from tank cleaning at sea.
There are various advanced tank cleaning procedures to reduce the residual volume in the tanks. In accordance with previously published results, there is considerable potential for improvement in reducing the concentration of hazardous substances in the environment, by reviewing requirements for extended application of state-of-the-art cleaning procedures. In order to reduce the impact on the marine environment from tank cleaning, as well as
the environmental impact of shipping in general, increased collaboration between the relevant transport and environmental management authorities and other actors such as ports, ship operators and industries is required. Although there is already an ongoing cooperation within marine environment management, there is a lack of harmonization between the regulations for pollution prevention from ships versus the environmental objectives
formulated by the management side.