EFFECT OF MICROBES ON THE UPTAKE OF CO-60, SR-85, TC-95M, I-131 AND CS-134 BY DECOMPOSING ELM LEAVES IN AQUATIC MICROCOSMS

We used decomposition of elm leaf discs as a model system to determine the uptake of Co-60, Sr-85, Tc-95m, I-131 and Cs-134 from freshwater by detritus and the role of microbes in this process. Two treatments w ere used: a microbially enhanced (ME) treatment and a microbially inhi bited (MI) treatment. The ME treatment involved the addition of a micr obial inoculum, collected from a beaver pond, and nutrients (5 mg P l( -1) as K2HPO4 and 20 mg N l(-1) as (NH4)(2)SO4) to the water to enhanc e microbial growth. The MI treatment involved sterlizing the leaf disc s and water with gamma irradiation (1.7 Gy s(-1) for 4 h) and the addi tion of a fungicide (100 mg l(-1) of nystatin) and bactericide (3.0 mg l(-1) each of streptomycin and penicillin) to the water. The Co-60, T c-95m, I-131 and (CS)-C-134 concentrations of the elm leaf discs were greater (P<0.05) in the ME treatment than the MI treatment, whereas th e Sr-85 concentration was higher in the MI treatment. The increase in the Tc-95m, I-131 and Cs-134 concentration of leaf discs with time in the ME treatment suggests microbes played an important role in uptake. Uptake of these radionuclides by the leaf discs points to the potenti al importance of detritus in the accumulation of radionuclides. This c ould subsequently result in the transfer of radionuclides to higher tr ophic levels by the detritus-food web.