Health Risk Assessment for Uranium in Groundwater - An Integrated Case Study Based on Hydrogeological Characterization and Dose Calculation

The uranium mining and milling facilities of Caetité (URA) is the only active uranium production center in Brazil. Operations take place at a very sensitive semi-arid region in the country where water resources are very scarce. Therefore, any contamination of the existing water bodies may trigger critical consequences to local communities because their sustainability is closely related to the availability of the groundwater resources. Due to the existence of several uranium anomalies in the region, groundwater can present radionuclide concentrations above the world average. The radiological risk associated to the ingestion of these waters have been questioned by members of the local communities, NGO’s and even regulatory bodies that suspected that the observed levels of radionuclide concentrations (specially Unat) could be related to the uranium mining and milling operations. Regardless the origin of these concentrations the fear that undesired health effects were taking place (e.g. increase in cancer incidence) remain despite the fact that no evidence - based on epidemiological studies - is available. This paper intends to present the connections between the local hydrogeology and the radiological characterization of groundwater in the neighboring areas of the uranium production center to understand the implications to the human health risk due to the ingestion of groundwater. The risk assessment was performed, taking into account the radiological and the toxicological risks. Samples from 12 wells have been collected and determinations of Unat, Thnat, 226Ra, 228Ra and 210Pb were performed. The radiation-related risks were estimated for adults and children by the calculation of the annual effective doses. The potential non-carcinogenic effects due to the ingestion of uranium were evaluated by the estimation of the hazard index (HI). Monte Carlo simulations were used to calculate the uncertainty associated with these estimates, i.e. the 95% confidence interval for Hazard Index and Effective dose estimation. No significant radiological related health effect could be attributed to the ingestion of this water by members of the local community. The calculated doses, for example, were below the internationally recommended limit of 1mSv/y to members of the public to be adopted in the regulation of planned exposures. This limit corresponds to an excess lifetime cancer risk of 4.0 x 10-3. However, if the non-carcinogenic effects of uranium are to be taken into account, it was observed that the ingestion of water from some of the investigated wells would be associated with a hazard index above unity indicating a potential risk for an adverse health effect. In the case of uranium these effects would be mainly associated with primarily damage to kidney, although it is also dependent on several factors, including physicochemical form and solubility. The regulatory implications of these findings will also be discussed in the paper.