John Wiley & Sons, Ltd.

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

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Six freshwater species (Chlorella sp., Lemna aequinoctialis, Amerianna cumingi, Hydra viridissima, Moinodaphnia macleayi and Mogurnda mogurnda) were exposed to 4, 8 & 24‐h Mg pulses in natural creek water. Mg 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 IC50s, and comparing to continuous exposure data from a previous study, the increase in toxicity with increasing exposure duration from 4‐h to continuous (72 h to 144 h) ranged from ∼two‐fold for Chlorella sp. and H. viridissima to >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 ∼4 × more sensitive (based on IC50s) than <6 h old neonates. Species sensitivity distributions were constructed for the 4, 8 and 24‐h pulse durations, from which 99% species protection guideline values (95% 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 SETAC

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