Risk assessment of bilge water discharges in two Baltic shipping lanes

Environmental concentrations and effects of bilge water contaminants in two Baltic Sea areas were estimatedfrom modelling of discharge rates and analytical data on bilge water from seven ships. Biodegradation of bilgewater oil was accounted for and annual water concentrations were estimated to peak in late spring, whichcoincides with the beginning of a period with extensive biological activities in the sea.

Concentrations on bilgewater metals were calculated both as water concentrations and as the annual contribution of metals to sediments.The predicted bilge water concentrations of oil and metal in the marine environment were estimated tobe 4 to 8 orders of magnitude lower than reported toxic concentrations. However, available toxicity data arebased on short term exposure and there is to date limited information on toxic effects of the small but chronicallyelevated contaminant concentrations derived from bilge water discharge and other operational shipping activities.