Predicting the bioavailability of sediment‐bound uranium to the freshwater midge (<italic>Chironomus dilutus</italic>) using physicochemical properties.

Abstract: Assessment of uranium (U)‐contaminated sediment is often hindered by the inability to accurately account for the physicochemical properties of sediment that modify U bioavailability. The present goal was to determine whether sediment‐associated U bioavailability could be predicted over a wide range of conditions and sediment properties using simple regressions and a geochemical speciation model, the Windermere Humic Aqueous Model (WHAM7). Data from a U‐contaminated field sediment bioaccumulation test, along with previously published bioaccumulation studies with U‐spiked field and formulated sediments, were used to examine the models. Observed U concentrations in <italic>Chironomus dilutus</italic> larvae exposed to U‐spiked and U‐contaminated sediments correlated well (<italic>r</italic>2 > 0.74, <italic>p</italic> < 0.001) with the WHAM‐calculated concentration of U bound to humic acid, indicating that humic acid may be a suitable surrogate for U binding sites (biotic ligands) in <italic>C. dilutus</italic> larvae. Subsequently, the concentration of U in <italic>C. dilutus</italic> was predicted with WHAM7 by numerically optimizing the equivalent mass of humic acid per gram of organism. The predicted concentrations of U in <italic>C. dilutus</italic> larvae exposed to U‐spiked and U‐contaminated field sediment compared well with the observed values, where one of the regression models provided a slightly better fit (mean absolute error = 18.1 mg U/kg dry wt) than WHAM7 (mean absolute error = 34.2 mg U/kg dry wt). The regression model provides a predictive capacity with a minimal number of variables, whereas WHAM7 provides additional complementary insight into the chemical variables influencing the speciation, sorption, and bioavailability of U in sediment. The present results indicate that physicochemical properties of sediment can be used to account for variability in U bioavailability as measured through bioaccumulation in chironomids exposed to U‐contaminated sediments. <italic>Environ Toxicol Chem</italic> 2018;37:1146–1157. © 2017 SETAC [ABSTRACT FROM AUTHOR]