Sobol sensitivity analysis for risk assessment of uranium in groundwater.

The exposure to uranium (U) in the natural environment is primarily through ingestion (eating contaminated food and drinking water) and dermal (skin contact with U powders/wastes) pathways. This study focuses on the dose assessment for different age-groups using the USEPA model. A total of 156 drinking water samples were tested to know U level in the groundwater of the study region. Different age-groups were selected to determine the human health impact due to uranium exposure in the residing populations. To determine the relative importance of each input, a variance decomposition technique, i.e., Sobol sensitivity analysis, was used. Furthermore, different sample sizes were tested to obtain the optimal Sobol sensitivity indices. Three types of effects were evaluated: first-order effect (FOE), second-order effect (SOE) and total effect. The result of analysis revealed that 17% of the samples had U concentration above 30 µg l-1 of U, which is the recommended level by World Health Organization. The mean hazard index (HI) value for younger age-group was found to be less than 1, whereas the 95th percentile value of HI value exceeded for both age-groups. The mean annual effective dose of U for adults was found to be slightly higher than the recommended level of 0.1 m Sv year-1. This result signified that adults experienced relatively higher exposure dose than the children in this region. Sobol sensitivity analysis of FOE showed that the concentration of uranium (Cw) is the most sensitive input followed by intake rate (IR) and exposure frequency. Moreover, the value of SOE revealed that interaction effect of Cw - IR is the most sensitive input parameter for the assessment of oral health risk. On the other hand, dermal model showed Cw - F as the most sensitive interaction input. The larger value of SOE was also recorded for older age-group than for the younger group.

Spatial distribution of uranium and basic water quality parameter in the capital of Bihar and consequent ingestion dose.

Investigation of presence of Uranium (U) in groundwater/drinking water is an active are of research due to its chemical and radiological toxicity as well as long-term health effects. The current study had the objective of estimating U as a naturally occurring radioactive element in groundwater samples and assessment of ingestion dose, when groundwater is the source of drinking water. The random sampling method was chosen for the collection of samples based on population density. The estimation of U was done using LED fluorimeter. Statistical tools were applied to analyze the data and its spatial distribution. The U concentrations in three blocks of urban Patna were well below the permissible limits suggested by different health agencies of the world. A correlation test was performed to analyze the association of U with other physiochemical parameters of water samples. It was found that the sulfate, chloride, calcium, hardness, alkalinity, TDS, salinity, and ORP were positively correlated, whereas fluoride, phosphate, magnesium, dissolved oxygen, and pH were negatively correlated with U concentrations. The ingestion dose due to U, occurring in groundwater, was found to vary from 0.2-27.0 µSv y-1 with a mean of 4.2 µSv y-1, which was well below the recommended limit of 0.1 mSv (WHO WHO Chron 38:104-108, 2012).Therefore, the water in this region is fit for drinking purposes.