Uptake and elimination of 137Cs in aquatic biota inhabiting a contaminated effluent canal

Radiocesium (¹³⁷Cs) is among the most prevalent and concerning radionuclide released from anthropogenic activities due to its relatively slow decay time and high bioavailability. Numerous studies have reported activity concentrations of ¹³⁷Cs in exposed biota, but few have assessed detailed toxicokinetics. The objective of our study was to quantify and compare the uptake and elimination of ¹³⁷Cs in aquatic taxa from multiple classes with different ecological roles inhabiting a canal contaminated from nuclear production activities on the Savannah River Site in South Carolina, USA. We tracked accumulation and elimination of ¹³⁷Cs in four understudied aquatic species: one aquatic macrophyte [American white water lily (Nymphae odorata), two benthic associated omnivorous species (American bullfrog (Lithobates catesbeianus) and red swamp crayfish (Procambarus clarkii), and one pelagic carnivorous fish (Eastern mosquitofish (Gambusia holbrooki)]. We monitored accumulation of ¹³⁷Cs from initial exposure until equilibrium for biota restricted within the canal and subsequently tracked elimination of ¹³⁷Cs over time by moving organisms from the canal to a nearby reference pond. Results indicated bullfrog tadpoles reached 95 % equilibrium in approximately 9 days, the fastest among the species evaluated. After bullfrog tadpoles, the next fastest time to equilibrium was achieved by red swamp crayfish (51 days) followed by mosquitofish (86 days). At equilibrium, bullfrog tadpoles were found to have similar ¹³⁷Cs activity concentrations to mosquitofish (3.16 and 3.57 Bq/g, respectively), and both were significantly higher than red swamp crayfish (1.77 Bq/g). For elimination, we found biological half-lives to range between 8 and 43 days with bullfrog tadpoles eliminating ¹³⁷Cs the fastest followed by water lilies, mosquitofish, and red swamp crayfish. Overall, we found the uptake and elimination of ¹³⁷Cs to vary widely among our studied species, but benthic organisms are not at an increased risk to accumulate ¹³⁷Cs compared to organisms in less frequent contact with the sediment.