Protection of human health from mixtures of radionuclides and chemicals in drinking water

Risk- and safety-based scales were critically evaluated during the development of a common scale for evaluating health risks from contaminated drinking water. Many of the risk models used by different agencies were unrealistic, since regulatory toxicology depended on model-based, data-poor, analysis of extreme events whose predictive validity was difficult to evaluate, and used absolute methods which ensured safety but at the expense of realism. Relative methods were developed to evaluate the realism of these absolute methods used by the regulatory agencies. All pollutants were assumed to contribute to toxic effect, and relative potencies were linked to the most credible standards. Data-intensive, model-poor methods (RASH (Rapid Screening of Hazard) chemical scoring system) were used to transfer experience from well-studied chemicals to a new chemical, providing good relative precision. Pollutants were then compared with common foodstuffs (GRAS baseline concentrations), ambient radiation background (GRAS equivalent values), or utility-pure drinking water (GRAS (generally recognized as safe) baseline concentrations). Results from the development of risk specific concentrations and GRAS-equivalent index values for radionuclides to humans are tabulated. Groundwater samples from 2 wells, T-92 and T-257, from inside a radioactive low-level, solid waste disposal area showed that measured concentrations exceeded statutory concentrations for 11 of 25 pollutants listed. Results from the development of a risk-based composite hazard index and a composite-Gras index for the 2 water samples are tabulated and compared. The measured concentrations at the site were also compared with U.S. EPA standards.