Radionuclide distribution in soil and undecayed vegetative litter samples in a riparian system at the Savannah River...

The aim of this study is to comprehensively investigate radionuclide concentrations in surface soil and un-decayed vegetative litter along four stream systems (i.e. Fourmile Branch, Lower Three Runs, Pen Branch, and Steel Creek) at the Savannah River Site (SRS), Aiken, South Carolina. Soil and litter samples from systematically spaced 12 pairs (contaminated or uncontaminated) of plots along the four streams were analyzed for 16 distinct radionuclide activities. Lower radionuclide concentrations were observed in soil and litter samples collected along Pen Branch compared to the other 3 streams. The anthropogenic radionuclide with the highest activity was ¹³⁷Cs in soil (10.6-916.9 Bq/kg) and litter (8.0-222.3 Bq/kg), while the naturally occurring radionuclides possessing the highest concentration in the samples were ⁴⁰K (33.5-153.7 Bq/kg and 23.1-56.0 Bq/kg in soil and litter respectively) and ²²⁶Ra (55.6-159.9 Bq/kg and 30.2-101.8 Bq/kg in soil and litter respectively). A significant difference (p < 0.05) of radionuclide concentrations between paired-plots across four streams was observed for ²⁴¹Am, ¹³⁷Cs, ²³⁸Pu, ²³⁹Pu, and ²²⁶Ra in both contaminated and non-contaminated samples. ¹³⁷Cs and uranium isotopes had the highest litter-to-soil correlation in contaminated (rho = 0.70) and uncontaminated plots (rho = 0.31-0.41), respectively. ⁹⁰Sr was the only radionuclide with higher radioactive concentrations in litter (12.65-37.56 Bq/kg) compared to soil (1.61-4.79 Bq/kg). The result indicates that 1) historical discharges of anthropogenic ¹³⁷Cs was the most important contributor of radiation contamination in the riparian environment at SRS, 2) ⁹⁰Sr was the only radionuclide with higher concentration in litter than in soil, and 3) no apparent pattern in deposition density in soil or litter along downstream was observed for the radionuclides measured in this study.