The World Health Organization (WHO) released the fourth edition of Guidelines for Drinking-water Quality in July, 2011. In this edition, the drinking-water guideline for uranium (U) was increased to 30 μg L~(-1) despite the conclusion that "deriving a guideline value for uranium in drinking-water is complex, because the data [from exposures to humans] do not provide a clear no-effect concentration" and "Although some minor biochemical changes associated with kidney function have been reported to be correlated with uranium exposure at concentrations below 30 μ L~(-1) these findings are not consistent between studies" (WHO, Uranium in Drinking-water, Background document for development of WHO Guidelines for Drinking-water Quality, available: http://www.who.int/water_sanitation_health/dwq/ chemicals/uranium_forcomment_20110211_en.pdf, accessed 13 October 2011). This paper reviews the WHO drinking-water guideline for U, from its introduction as a 2 μg L~(-1) health-based guideline in 1998 through its increase to a 30 μg L~(-1) health-based guideline in 2011. The current 30 μg L~(-1) WHO health-based drinking-water guideline was calculated using a "no-effect group" with "no evidence of renal damage [in humans] from 10 renal toxicity indicators". However, this nominal "no-effect group" was associated with increased diastolic blood pressure, systolic blood pressure, and glucose excretion in urine. In addition, the current 30 μg L~(-1) guideline may not protect children, people with predispositions to hypertension or osteoporosis, pre-existing chronic kidney disease, and anyone with a long exposure. The toxic effects of U in drinking water on laboratory animals and humans justify a re-evaluation by the WHO of its decision to increase its U drinking-water guideline.
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