Abstract
Water and sediment samples collected from the Lake Ontario system were analyzed for mirex and photomirex. Photomirex to mirex ratios (P/M) increased in the stratified surface layer of the lake from spring to autumn and in water from Oswego harbor. P/M ratios in the mirex source sediments (the Niagara and Oswego rivers) were very low (< 0.07) whereas higher P/M ratios were seen in the lake bottom sediments (> 0.10) and surface waters (> 0.30). The ratios in the St. Lawrence sediment and water were greater than 0.30. These findings are consistent with the hypothesis that photomirex in Lake Ontario is produced by the photolysis of mirex present in the surface waters. It is then partitioned between the water, sediments and biota.