Radium-226 in Magela Creek, northern Australia: Application of protection limits from radiation for humans and biota

C. Sauerland¹, P. Martin² and C. Humphrey¹

¹ Environmental Research Institute of the Supervising Scientist, Darwin, NT 0801, Australia,e-mail: Claudia.Sauerland@deh.gov.au
² Agency's Laboratories Seibersdorf, International Atomic Energy Agency, 1400 Vienna, Austria, e-mail: P.Martin@iaea.org

Abstract

In the context of protecting the environment from the effects of ionizing radiation associated with uranium mining, the alpha-emitting radium 226 is the uranium progeny of most interest as it is known to bioaccumulate and confers a high effective dose to biota. For the Ranger uranium mine in northern Australia, total radium 226 activity concentrations were determined in water samples from Magela Creek both upstream and downstream of the mine over two years. Those data were evaluated within three different frameworks and were found to comply with respective limits: human dose estimations, site-specific guideline `trigger' values for ecosystem health (derived from the distributional properties of values from a reference (upstream) dataset) and estimations of absorbed dose to freshwater mussels residing in Magela Creek (long-lived organisms with high rate of uptake and exposure). We propose that the currently-used, human-dose limit of 10 mBq.L^-1 be applied to the difference of the wet season arithmetic means calculated for the upstream and downstream locations. In addition, the statistically derived trigger values (e.g. a moving 80 percentile of upstream data) could be used to assess if radium 226 measured downstream of the uranium mine has resulted in an additional dose to biota.