The application of the passive sampling technique diffusive gradients in thin-films (DGT) to the measurement of uranium in natural waters

摘要

This thesis describes the application of a passive sampler, Diffusive Gradient in Thin Films (DGT), to the measurement of uranium in natural waters. Four resins (Chelex-100, manganese dioxide [MnO2], Diphonix® and Metsorb) were trialled with the DGT device. In freshwater environments, the Metsorb accumulated uranium in line with the DGT equation for 7 d with an acuracy of 75%; Chelex-100 did not accumulate uranium past 2 d; MnO accumulated up to 75% of that predicted by the DGT equation for 4 d; and the Diphonix® accumulated uranium for 7 d with an accuracy of ~100%. None of the resins tested in this study accumulated uranium in a marine setting in line with DGT predicted values past 2 d.The application of DGT to regulatory environmental monitoring schemes was investigated with Metsorb. The Metsorb DGT devices were deployed for 7 days at a time over a 6 month period at two freshwater field sites. Fluctuations in water chemistry were monitored and the size of the diffusive boundary layer (DBL) was measured. The uranium accumulated by the Metsorb DGT showed close agreement with the grab samples. The size of the DBL was found to be significant, particularly in low flow conditions.This study showed that DGT could be used as a tool to both monitor radioncludes in the environment, and to obtain information on the speciation and organic interactions. The lability of uranium-humic acid complexes was also examined in this study. Initial data shows that the uranyl-humic complex is labile in low pH environments, but becomes increasingly kinetically limited the higher the pH and the higher the humic acid:uranium ratio. Data is also presented on the penetration parameter of the uranyl ion into the resin gel layer, and how this can be used to indicate lability. Lability is important in determining bioavailability and potential toxicity of uranium.