Ship Wastewater Discharges Cause Nutrient Input

The aim of the survey conducted by VTT was to investigate the scope of ship wastewater nutrient inputs in the Baltic Sea. The results indicated that ship wastewater only makes up a small part of the total loading, being 0.04 % for nitrogen and 0.3 % for phosphorus. Compared with wastewater discharges, the amount of eutrophicating nitrogen entering the Baltic Sea with ship exhaust gases each year is substantially higher. At the turn of the millennium, 6 % of the nitrogen fallout in the Baltic Sea was caused by exhaust emissions from ships.

However, the environmental impact of ship wastewater is much more severe than suggested by mere percentages in that most of its nutrients are in a form biologically exploitable by algae. Most wastewater nutrients enter the Baltic Sea in summer, at which point algae have already depleted most of the nitrogen and phosphorus having dissolved into run-off water in spring. Wastewater discharges also have local harmful effects on heavily trafficked shipping routes. The wastewater released into the sea also contains pathogens, heavy metals and organic compounds harmful to aquatic organisms.

The results are being utilised in the work of the Maritime Group of the Helsinki Commission, HELCOM Maritime. HELCOM Maritime works to prevent any pollution from ships including deliberate operational discharges as well as accidental pollution. The working group also aims to assign the status of a special area to the Baltic Sea through the IMO's agreement. The status involves the requirement that the nutrient loading caused by ship wastewater discharges must be limited in the area.

VTT's survey is based on information obtained from port facilities, shipping companies and reference literature. It was concerned with passenger ships, cruise ships and cargo vessels, but not recreational vessels. The share of ship traffic wastewater discharges causing eutrophication in the Baltic Sea was investigated by VTT for the first time in 2007 and an update was published this year. The investigation was financed by the Finnish Maritime Administration.