Metabolism of Ingested U and Ra

Abstract

The literature on metabolism of U and Ra for man relevant to deriving drinking water standards has been reviewed and summarized. Radium is well understood, but significant gaps remain in our knowledge about U metabolism. Limits should be based on an equilibrium model where a constant relationship between intake and organ burden is established, using the best and most likely metabolic parameters. For the skeleton we conclude that the best estimate of skeletal burden expressed in days equivalent intake are 25 days for 226Ra, 10 days for 228Ra, and 0.3 days for 224Ra. For long-lived isotopes of U, we chose 11 days, with a range between 1 and 35 days. The committee believes that intake of natural U in water should be limited by considerations of toxicity to the kidney, and we believe that the metabolic model of Spoor and Hursh with a modified gastrointestinal (GI) absorption (1.4%) should be used to infer kidney content. Our review and analysis of the world literature leads us to believe the average human GI absorption of U is most likely 1-2% and is probably reasonably independent of age or the mass of U ingested. Using a safety factor of 50-150, the committee recommends a limit of U in water of 100 micrograms/l in order to limit toxic effects in the kidney. One hundred micrograms/liter is equivalent to 67 pCi/l of long-lived alpha-emitting natural U isotopes. Further research into the distribution of U in the human body is desirable, especially at natural levels in kidney and skeleton, the time-dependent pharmacokinetics of U in animals, the GI absorption of U in man from water and food, toxicological and U distribution studies in animals under conditions of chronic oral U intake, and metabolic model error propagation.

Uranium analysis in some food samples collected from Bathinda area of Punjab, India

“…Like many trace metals the bioavailability of uranium in food may be influenced by the food's phytate (or fibre) content [19][20] and the presence of the low molecular weight ligands, such as citrate may promote uptake. Wrenn et al [21] reviewed uranium uptake factor across the range of average diets and suggested an uptake factor of 2% to 3%.…”

Potential Health Risks from Uranium in Home Well Water: An Investigation by the Apsaalooke (Crow) Tribal Research Group

“…Uranium exposure has been found to be positively associated with cytotoxicity biomarkers: increases in urinary albumin [8], glucose and calcium [2], β2-microglobulin and alkaline phosphatase [6]. Absorbed uranium not excreted via urine, accumulates primarily in the skeleton and kidney [4,43]. Exposure can increase cancer risk and lead to liver damage [44].…”

Gestão e avaliação de risco em saúde ambiental

“…Entretanto, para o urânio, a toxicidade química é maior que a radiológica, sendo os efeitos de toxicidade sistêmica o critério limitante no qual deve se basear o controle da exposição a este contaminante (Wrenn et al, 1985;Fisenne, Perry & Harley, 1988).…”