Environmental fate of radiocesium in biota inhabiting a contaminated ecosystem on the U.S. Department of Energy's Savannah River Site.

Although biomagnification of radiocesium (137Cs) has been reported in food webs, most previous research has been limited to select trophic linkages. Few studies have included a comprehensive survey of fauna associated with aquatic, semi-aquatic, and terrestrial habitats within a single study framework. The objectives of this study were to advance our understanding of the dynamics of 137Cs accumulation within food webs by quantifying 137Cs activity across a wide range of biota found within a contaminated canal, as well as test the hypothesis that life-stage and body size influence 137Cs bioaccumulation in select herpetofauna. With extensive sampling across multiple taxa collected from a contaminated canal system and associated floodplain on the Savannah River Site, we assessed 137Cs activity and stable nitrogen isotopes for both aquatic organisms that were restricted to the contaminated effluent canal, and semi-aquatic organisms able to move freely between the contaminated canal and the adjacent uncontaminated terrestrial habitat. We found 137Cs activity to be highly variable among species, with evidence for and against biomagnification in semi-aquatic and aquatic organisms, respectively. Furthermore, 137Cs activity decreased with life stage and body size in bullfrogs (Lithobates catesbeianus), despite post-metamorphic bullfrogs having a more carnivorous diet compared to tadpoles, while cottonmouths (Agkistrodon piscivorus) retained similar 137Cs activity regardless of their age and size. Although evidence of biomagnification has been observed in some contaminated systems, results of our study suggest the extent to which 137Cs biomagnifies within food webs is context-dependent and likely influenced by a suite of biotic and abiotic factors. Further, our data indicate sampling of a broad suite of species and environmental attributes are needed to elucidate the fate and dynamics of anthropogenic pollutants within contaminated ecosystems.

Mercury Concentrations in the Two-Toed Amphiuma (Amphiuma means) and the Lesser Siren (Siren intermedia): Validating Non-lethal Sampling Methods in Southeastern Aquatic Salamanders.

The global decline of amphibians is a major conservation issue. Many stressors are recognized for this decline including exposure to environmental contaminants. Mercury (Hg) is an environmental contaminant that bioaccumulates in wildlife and can cause a variety of negative impacts across taxa, including amphibians. Amphiuma and Siren spp. can comprise a large portion of biomass within their respective ecosystems, and thus, likely serve as important predators or prey in wetland communities. However, due to their cryptic nature, little is known about their ecology, diet, and accumulation potential. We sought to validate a nonlethal sampling method to quantify total mercury (THg) in two enigmatic species of aquatic salamanders: the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia). We examined relationships between THg content in lethal (whole-body) and nonlethal (tail clip) samples. Tail clips were statistically significant predictors of whole-body THg (all p < 0.001), explaining 84-89% of variation in whole-body THg. Average whole-body THg (mg/kg) did not significantly differ between the two species (p = 0.97), and overall, they had similar whole-body THg content (S. intermedia = 0.330 ± 0.04, n = 18; A. means = 0.333 ± 0.07, n = 11). To our knowledge, these data represent the first reported Hg burdens in A. means and S. intermedia.

Mercury speciation, bioavailability, and biomagnification in contaminated streams on the Savannah River Site (SC, USA).

Water, sediment, and biota from two streams on the Savannah River Site were sampled to study mercury (Hg) biogeochemistry. Total and methyl- Hg (MHg) concentrations were measured for all samples, speciation models were used to explore Hg speciation in the water, and Diffusive gradients in thin films (DGT) were applied to indicate the vertical profiles of labile Hg (DGT-Hg). Trophic position (δ15N) was estimated for biota and used to establish MHg biomagnification model. The speciation model indicated Hg methylation in the water occurred on settling particles and the most bioavailable Hg species to bacteria were complexes of inorganic Hg and labile organic ligands. Correspondingly, dissolved organic carbon concentrations were positively related to MHg concentrations in the water. In the sediment, the sharp increase of DGT-Hg around the sediment water interface underscores the importance of this interface, which determines the differences in the accumulation and generation of labile Hg among different waterbodies. The positive correlation between sediment MHg and sulfate concentrations suggested possible methylation reaction by dissimilatory sulfate reducing bacteria in the sediment. The food web magnification factors of MHg were 9.6 (95% CI: 4.0-23.4) and 4.4 (95% CI: 2.5-7.7) for the two streams established with trophic data of biofilm, invertebrates, and fish. Meanwhile, DGT-Hg concentrations in the water were positively correlated to biofilm Hg concentrations, which can be combined with the MHg biomagnification model to generate a modified biomagnification model that estimate MHg bioaccumulation with only labile Hg concentrations in the water. With this approach, Hg accumulation in abiotic and biotic environmental compartments was connected and the different bioaccumulation patterns of Hg in different waterbodies were explained with both geochemical and biological factors.

Radiocesium (137Cs) accumulation by fish within a legacy reactor cooling canal system on the Savannah River Site.

The aquatic cooling canal system associated with a nuclear reactor built in the early 1950s received accidental releases of radiocesium (137Cs) from the reactor between 1954 and 1964, resulting in the dispersion of ~8.2 × 1012 Bq of 137Cs into the associated canals and ponds. The primary purpose of this study was to document concentrations of 137Cs in littoral zone fish currently occupying components of the cooling canal system, 3 canals and 2 impoundments, to determine how concentrations varied among these various components. Secondarily, we examined for potential influence of weirs within the canal system on concentrations in fish as well as the potential relationship between fish species and body size and on 137Cs concentrations in fish. We collected samples of sediment, biofilm, and fish from each component of the R-Reactor cooling system and compared 137Cs among sites and species in individual sites. Concentrations of 137Cs in sediments, biofilms and mosquitofish varied significantly among sampling areas with higher concentrations in RCAN1, a canal segment that was the closest to the reactor and received reactor effluent for a longer period than other components. Comparisons among other components of the cooling system, and species comparisons relative to presumed trophic positions and fish length were not consistent. However, littoral zone fish in the cooling canal system continue to bioaccumulate 137Cs >50 years after the original releases of contamination.

Accumulation of 137Cs by Carnivorous Aquatic Macrophytes (Utricularia spp.) on the Savannah River Site.

Plants are an important mode of transfer of contaminants from sediments into food webs. In aquatic ecosystems, contaminant uptake by macrophytes can vary by path of nutrient uptake (roots vs. absorption from water column). Carnivorous plants likely have additional exposure through consumption of small aquatic organisms. This study expanded on previous research suggesting that bladderworts (Genus Utricularia) accumulate radiocesium (137Cs) and examined for (1) a potential association between sediment and plant concentrations and (2) differences in 137Cs accumulation among rooted and free floating Utricularia species. A strong correlation was found between average 137Cs concentrations in all Utricularia species (combined) and sediments (rs = 0.9, p = 0.0374). Among three bladderwort species at common sites, Utricularia floridana, the only rooted species, had higher mean 137Cs concentrations than Utricularia purpurea, and U. purpurea had a greater mean 137Cs concentration than Utricularia inflata.