This report is being published almost ten years after work started on the assessment of the environmental hazards of substances carried by ships. This work was undertaken initially as preparatory work for the development of the International Convention for the Prevention of Pollution from Ships, 1973 (MARPOL 73). A request was made by the SubCommittee on Marine Pollution* of the Inter-Governmental Maritime Consultative Organization (moo) with regard to questions related to the consideration of hazards which might arise through the accidental spillage of substances carried either in bulk or in packaged form, or through the operational discharge of tank washings by chemical tankers, whenever such discharges might -take place