Spatial and temporal patterns of radiocesium contamination in mosquitofish, Gambusia holbrooki (Girard, 1859), inhabiting a nuclear reactor cooling reservoir

Whole body concentrations of radiocesium (137Cs) were determined for 772 mosquitofish (Gambusia holbrooki) collected from three locations on the Pond B reservoir of the US Department of Energyʹs Savannah River Site in July and November 1991, and February and April 1992. Seasonal, site-, and sex-related differences in 137Cs concentrations were tested for significance, and results compared with those reported for mosquitofish collected from the same locations in April 1987. Results from 1991 to 1992 showed that 137Cs concentrations were higher in mosquitofish collected in February for both sexes at all sites. After accounting for differences in body size, males generally had higher concentrations than females across seasons and sites. Site-related differences were not the same as those found in April 1987. Results from the present study suggest that 137Cs concentrations in mosquitofish undergo a seasonal cycling pattern, and that caution should be used when interpreting data collected from a single season, year or sex.