Search

for the poster presentation at CRF-ChemCYS 2022 conference.

Poster presentation

Oral presentation at the 15th International Symposium on the Interactions Between Sediments and Water (IASWS) conference.

Synthetic solutions of Rh and Pt at near neutral pH, as well as spiked natural waters are subjected to an ageing effect, which means that over time the speciation of the PGEs will be changed from their original composition due to aquation and hydrolysis, forming various hydroxy and aqua complexes. Due to slow ligand exchange reactions equilibrium speciation may not be rapidly attained. Ageing may affect the reactivity of the PGE solutions towards chelating resins used in the analysis of PGEs by Diffusive Gradients in Thin films (DGT). The aim of the study was therefore to investigate the performance of the chelating resins (Purolite S914 and S920 with thiourea and isothiourea functional groups, and IONQUEST® MPX-317 with a phosphine oxide thiourea functional group) for their applicability as a binding resin for DGT applications for Pt and Rh in natural waters using 17-day aged spiked solutions. Uptake kinetics experiments revealed that the direct uptake of Pt on the resins from aged solutions was fast and quantitative, whereas only 30% of Rh was directly bound on the resin. Likewise, much lower apparent diffusion coefficients were obtained for Rh in aged spiked river water (70% decrease) which can be explained by the formation of Rh(OH)3(s) which is not taken up by the resin gel. The addition of dissolved organic matter results in an increased solubilisation of Rh(OH)3(s) and an increased DGT labile fraction. The formation of Rh(OH)3(s) is less pronounced in seawater. For Pt, no species are formed which are not DGT labile. Thus, DGT accurately measures labile metal species in solution, discriminating labile from inert metal species.

The population resident in areas around the East African Rift System (EARS) is facing serious problems associated with the availability and quality of drinking water. Groundwater wells, boreholes and springs are the main sources of drinking water in these areas. These sources are, however, characterised by elevated fluoride concentration (> 1.5 mg/L), resulting from the interactions with the surrounding volcanic rocks. The high fluoride levels found in the groundwater are often associated with the presence of other naturally occurring potentially toxic elements (PTEs), such as As, Mo, U and V, which are known to cause adverse effects on human health. The occurrence of such PTEs in the groundwater on the populated flanks of Mt. Meru, an active volcano situated in the EARS, has not been previously reported. The objective of this study is to determine the concentrations and distribution of PTEs in groundwater on the flanks of Mt. Meru to assess the potential health hazards that extend beyond the known fluoride issues in the study area. A large set of PTEs (Al, As, Ba, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Se, Sr, Pb, U, V, W and Zn), physicochemical parameters and major elements were analysed in 48 groundwater samples sourced from wells, springs and tap water systems. To estimate the potential health risk associated with consumption of water with elevated concentrations of PTEs, chronic daily intake (CDI) and hazard quotient (HQ) were calculated. Preliminary results show that some of the water samples from the NE and SW flanks exceed the WHO tolerance limit for drinking water for some elements such as U (> 30 µg/L) and Mo (> 70 µg/L) as well as Na (> 200 mg/L) and K (> 50 mg/L). Estimated HQs indicate that such concentrations of Mo and U are not safe for consumption. Therefore, the continued drinking of water from these sources may result in serious health issues. Furthermore, the results show that some samples are characterised by total dissolved solids (TDS) values exceeding the permissible limits of WHO making the groundwater in the study area unsafe for drinking. The results presented in this paper are a part of a larger study on the groundwater quality in the Mt. Meru area and will serve to inform and direct exploitation of safe drinking water.

International audience

International audience