The Use of Geochemical Speciation Modelling to Predict the Impact of Uranium to Freshwater Biota

Abstract

Uranium is the prime potential contaminant in mine waste waters that may be released from the Ranger Uranium Mine (RUM) into the receiving waters of the Magela Creek, Alligator Rivers Region, Northern Australia. The potential ecological impact of the migration of uranium, that would result from an elevation in its concentration above background, in the Magela Creek downstream of the RUM, has been experimentally investigated by integrating biomonitoring with geochemical speciation modelling. The freshwater bivalve Velesunio angasi, abundant throughout the Magela Creek catchment, was exposed to a variety of uranium concentrations in a synthetic Magela Creek water, at four pH levels (5.0, 5.3, 5.5 and 6.0), in the presence (3.05 and 7.50 mg l{sup -1}) and absence of a model fulvic acid (FA), and its behavioural response was measured. Speciation modelling, using the HARPHRQ code, provided evidence that UO{sup 2+}{sub 2} and UO{sub 2}OH{sup +} are the uranium species most responsible (ca. 96%) for eliciting an adverse behavioural response when UO{sup 2+}{sub 2} is assigned twice the toxic effect of UO{sub 2}OH{sup +}. This finding rejects the notion that biota respond specifically to the sum total of inorganic uranyl species. (orig.)