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Toxicity of magnesium pulses to tropical freshwater species and the development of a duration-based water quality guideline

Authors

  • Alicia C. Hogan,

    Corresponding author
    • Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of Sustainability, Environment, Water, Population and Communities, Darwin, Northern Territory, Australia
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  • Melanie A. Trenfield,

    1. Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of Sustainability, Environment, Water, Population and Communities, Darwin, Northern Territory, Australia
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  • Andrew J. Harford,

    1. Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of Sustainability, Environment, Water, Population and Communities, Darwin, Northern Territory, Australia
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  • Rick A. van Dam

    1. Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of Sustainability, Environment, Water, Population and Communities, Darwin, Northern Territory, Australia
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Address correspondence to Alicia.Hogan@environment.gov.au.

Abstract

Six freshwater species (Chlorella sp., Lemna aequinoctialis, Amerianna cumingi, Hydra viridissima, Moinodaphnia macleayi, and Mogurnda mogurnda) were exposed to 4-h, 8-h, and 24-h Mg pulses in natural creek water. Magnesium toxicity to all species increased with exposure duration; however, the extent of increase and the nature of the relationship differed greatly between species. Based on median inhibitory concentrations (IC50s), and compared with continuous exposure data from a previous study, the increase in toxicity with increasing exposure duration from 4 h to continuous (72–144 h) ranged from approximately 2-fold for Chlorella sp. and H. viridissima to greater than 40-fold for A. cumingi. Moreover, the form of the relationship between Mg toxicity and duration ranged from linear or near-linear to exponential for different species. The life-stage at which M. macleayi was exposed was important, with cladocerans pulsed at the onset of reproductive maturity being approximately 4 times more sensitive (based on IC50s) than younger than 6-h-old neonates. Species sensitivity distributions were constructed for the 4-h, 8-h, and 24-h pulse durations, from which 99% species protection guideline values (95% confidence limits [CLs]) of 94 (6.4–1360) mg/L, 14 (0.5–384) mg/L, and 8.0 (0.5–144) mg/L Mg, respectively, were derived. These values were plotted against exposure duration (h) and polynomial interpolation used to derive a guideline value for any pulse duration within the range assessed. Environ Toxicol Chem 2013;32:1969–1980. © 2013 Commonwealth of Australia. Environmental Toxicology & Chemistry © 2013 SETAC

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