Seasonal variation in radiocesium levels of largemouth bass (Micropterus salmoides): Implications for humans and sensitive wildlife species

To examine seasonal variation in levels of radiocesium (¹³⁷Cs) within largemouth bass (Micropterus salmoides; N = 589), fish were collected monthly over a one-year period from an abandoned reactor cooling reservoir. Month of collection, sex, age, and body mass (log transformed) were all significant factors influencing ¹³⁷Cs concentrations. Levels of ¹³⁷Cs reached a peak in late winter/early spring (February/March), and minimum values occurred in the fall (October). An asymmetric sawtooth model with a four- month period of increase and an eight-month period of decrease fit the data for monthly ¹³⁷Cs values significantly better than symmetric sinusoidal and sawtooth models. The mean concentration of ¹³⁷Cs for bass collected during all months was 7.09 Bq/g wet mass. All individuals examined, regardless of month, sex, age, or body mass, had ¹³⁷Cs levels (2.95-12.60 Bq/g) that were much higher than the maximum level (0.60 Bq/g wet mass) generally considered safe for human consumption. Radiocesium is relatively long-lived within this reservoir and will continue to remain an important issue in risk assessments for both humans and wildlife species.