Quantifying historical releases of radium-226 from Canadian mining operations to freshwaters

Abstract

A common misconception is that radium-226 (Ra-226) is released into receiving waters exclusively by uranium mines and mills. In fact, Ra-226 is routinely analyzed in mining effluent across various sectors. Using data reported under the Canadian Metal and Diamond Mining Effluent Regulations, Ra-226 releases from mine effluent were evaluated for the period of 2014–2022. Final treated effluent concentrations ranged from 0.2 to 7800 mBq/L. Data were grouped by mining sector as being either precious metals, base metals, ferrous metal, non-ferrous metals, uranium ore, or diamonds. Mean Ra-226 concentrations were highest for non-ferrous metal mines (51.9 mBq/L), followed by base metal (31.6 mBq/L), diamond (23.8 mBq/L), uranium (22.0 mBq/L), precious metal (15.0 mBq/L), and ferrous metal mines (11.0 mBq/L). Mean concentrations for non-ferrous, base metal, diamond, and uranium mining sectors exceeded the upper tolerance limit (UTL) for natural background concentrations (21.7 mBq/L), calculated using reference data from Northern Saskatchewan. Median concentrations, however, were below the UTL for all sectors, indicating episodic high Ra-226 releases likely influenced by variations in the uranium content of the ore bodies. This study demonstrates that Ra-226 activity concentrations in final treated effluent from uranium mining operations are lower than those from other mining sectors, challenging the perception that uranium operations are the primary source of Ra-226 releases.