This report review the potential harmful substances which are organized by WHO and FAO and UNEP. Following review by GESAMP XV, New York, 25-29 March 1985 the Working Group met again in November 1985 and finalized the combined draft document on arsenic, mercury and selenium. Final approval was subsequently obtained from GESAMP XVI, London, 17-21 March 1986. This publication has been prepared and issued in conformity with that decision.