URANIUM IN OHIO SURFACE WATERS: GEOGENIC AND FERTILIZER DERIVED SOURCES

Large-scale fertilizer application has led to huge perturbations in many global biogeochemical cycles. The impacts on the nitrogen and phosphorus cycles are the most acknowledged and studied, but other global elemental cycles are also greatly augmented by modern agricultural practices. Fertilizers are commonly mined from rocks that contain trace elements such as uranium (U) that remain in the final product. Its mobilization during agricultural, hydrological, and biogeochemical processes can degrade environmental quality beyond just agricultural environments, such as surface water and groundwater. There is no defined “safe” level of U, and while the US EPA limit is 30 ppb (126 nM), estrogenic effects are observed in mice far below that level. Uranium has been shown to accumulate in agricultural soils where P-fertilizers are applied, and associated groundwaters are also affected. However, there is little evidence of effects on surface waters. Our previous work hypothesized that elevated U concentrations in rivers draining row crop agriculture in Ohio are due inorganic P fertilizers, but the story is complicated by glacial history. Agriculture is dominant in the glaciated portion of the state of Ohio, which is covered in glacial till. The unglaciated portion is dominated by forested lands. We combined new stream water data collected from Ohio rivers during early summer runoff and fall baseflow with archived surface soil and surface water data from the US Geological Survey and performed spatial analyses using bedrock, surficial geology, mining activities and land cover datasets. We found that elevated uranium concentrations in surface waters in the unglaciated portion of the state are associated with surface mining activities. Mean concentrations in the glaciated portion (8 nM) were significantly higher than the unglaciated portion (3 nM), and concentrations are twice as high during early summer runoff than baseflow, and are not correlated with lithology. We present ²³⁴U/²³⁸U data as a possible tracer to differentiate between uranium sourced from fertilizer and geogenic sources. We hypothesize that soluble U anion complexes are rapidly mobilized from soil pore water to receiving surface waters through abundant agricultural tile drains in Ohio.