POLONIUM-210 IN GROUNDWATER AND ITS POTENTIAL HEALTH EFFECTS

An investigation of a childhood-leukemia cluster in Lahontan Valley in Northern Nevada by the USGS and University of Nevada Reno lead to the discovery that more than one third of the private wells in the valley had concentrations of the radioisotope ²¹⁰Po that exceeded 0.55 Bq/L. ²¹⁰Po is a naturally-occurring alpha emitter that strongly binds to sediments and, because of this, levels in ground-water exceeding 0.1 Bq/L are extremely rare. The greatest concentration in Lahontan Valley, 6.6 Bq/L, is the fourth highest concentration reported for the USA. The temporal and spatial distribution of leukemia cases in Lahontan Valley groundwater suggested a viral cause of the cluster and that ²¹⁰Po exposure in drinking water was not consistent with it being a direct cause of the cluster.

²¹⁰Po is the last unstable isotope in the ²³⁸U decay series and is classified as a Group 1 human carcinogen. Unlike Radium-226 and Lead-210, which accumulate in the bones, ²¹⁰Po accumulates in soft tissues such as the liver and spleen. It also accumulates in the ovary and can kill primary oocytes at low doses. The ovary may be the critical organ in determining the lowest injurious dose for ²¹⁰Po because of its radiosensitivity and tendency to accumulate ²¹⁰Po. It also accumulates in the yolk-sac of the embryo and in fetal tissues where exposure to a single alpha particle may damage or kill critical stem cells.

Exposure to ²¹⁰Po in groundwater in both private and municipal drinking-water supplies has gone on for decades before the exposure was discovered. Private and stock-water wells are not regulated or monitored for radioactivity and tests on public water-supplies missed ²¹⁰Po because the Gross Alpha Radioactivity test used to determine compliance in the US with the MCL has serious problems with ²¹⁰Po.