title: Toxicity of magnesium pulses to tropical freshwater species and the development of a duration-based water quality guideline.
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.
authors.affiliation: Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of Sustainability, Environment, Water, Population and Communities, Darwin, Northern Territory, Australia. Alicia.Hogan@environment.gov.au
authors.forename: Alicia C
authors.initials: AC
authors.lastname: Hogan
authors.forename: Melanie A
authors.initials: MA
authors.lastname: Trenfield
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Harford
authors.forename: Rick A
authors.initials: RA
authors.lastname: van Dam
mesh_terms: D000818:Animals; D059001:Aquatic Organisms / Q000187:drug effects*; D029064:Araceae / Q000187:drug effects; D002708:Chlorella / Q000187:drug effects; D033361:Cladocera / Q000187:drug effects; D005618:Fresh Water; D006829:Hydra / Q000187:drug effects; D008274:Magnesium / Q000633:toxicity*; D008906:Mining; D010473:Perciformes; D011786:Quality Control; D012908:Snails / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D060753:Water Quality
chemical_list: D014874:Water Pollutants, Chemical; D008274:Magnesium
keywords: Episodic exposure; Intermittent exposure; Magnesium; Pulse; Water quality guidelines