Neodymium (Nd) is one of 17 rare earth elements (REEs) and is classified as such due to chemical properties, occurrence in deposits, and concentration abundance for economic exploitation (Natural Resources Canada, 2013). REEs are a priority on the Canadian Critical Minerals List for their use in permanent magnets in application to sustainable technologies (Natural Resources Canada, 2022). There are currently no published Canadian environmental water quality guidelines for REEs. The goal of my research is to characterize exposure-effect relationships of Nd with freshwater rainbow trout (Oncorhynchus mykiss). Exposures were conducted at 12 °C in soft water (30 mg CaCO3/L, pH 7.0) similar to media used in aquatic toxicology research reported in literature to maximize metal bioavailability (Nautilus Environmental, 2021). Sample collection was at 12, 24, and 48 h, as well as 7, 14, 21, and 36 d. Physiological effects were hypothesized to demonstrate a damage-repair-acclimation response. Dissolved concentrations in the exposure solutions were ³ 91% of total. Initial acute exposures of O. mykiss to 48, 78, and 152 µg Nd/L were acutely lethal. Subsequent chronic exposures of O. mykiss to 5 and 10 µg Nd/L resulted in significant Nd bioaccumulation in gill, liver, and kidney but not muscle. O. mykiss plasma Na+, Cl-, K+, and glucose concentrations were unaffected by chronic Nd exposure. O. mykiss survived exposures of 5 µg Nd/L but experienced an initial and temporary loss of plasma Ca2+. A 10 µg Nd/L exposure resulted in significant O. mykiss mortalities, associated with disruptions of plasma Ca2+ (loss) and Mg2+ (increase). An exposure to 10 µg Nd/L (8 mg Ca/L) with added calcium (26 mg Ca/L) was protective against O. mykiss mortalities (all fish survived), bioaccumulation was significantly reduced compared to the exposure without added Ca. O. mykiss swimming performance was not significantly reduced following chronic Nd exposure. Findings of this study illustrate the acute and chronic toxicity of Nd and that O. mykiss can respond to exposure in a manner that is similar to other metals. This research was supported by NSERC (Alliance), Environment and Climate Change Canada, Stantec Inc and Nechalacho Resources/Vital Metals Inc.
Jane G Morgan (Thu,) studied this question.