John P. Hassett

Mirex – Photomirex Relationships in Lake Ontario

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 ( 0.10) 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.

A Screening-Level Mass Balance Analysis of Mirex Transport and Fate in the Oswego River

Abstract A mass balance approach was used to evaluate the fate of mirex in the Oswego River. The objectives of this research were 1) to assess the magnitude and extent of mirex contamination in the Oswego River, 2) to quantify the transport, fate, and distribution of mirex in the river, and 3) to estimate mirex export to Lake Ontario via the Oswego River. Field data collected as part of a 1990 Oswego River Mirex Study, in addition to other existing data, were used to develop a water quality model describing the transport and fate of chlorides, total suspended solids, and mirex in the Oswego River from Fulton to Lake Ontario. Long-term and short-term loading scenarios were evaluated to assess the possible magnitude of the initial mirex discharge to the Oswego River in 1965 as well as the subsequent export resulting from a given loading. Field data and model results suggest that a short-term mirex discharge occurring in the mid-1960s cannot account for the water column concentrations observed in 1990 or the mirex mass in Lake Ontario sediments attributable to the Oswego River. Similarly, field data and model results suggest that resuspension of the 1990 in-place mirex mass cannot account for the water column mirex concentrations observed in 1990. This suggests that there may be a continuing mirex source to the Oswego River. Based on the 1990 field data, the estimated Oswego River mirex inventory was 10 kg and export to Lake Ontario averaged 42 g/day.