title: Aquatic toxicity of magnesium sulfate, and the influence of calcium, in very low ionic concentration water.
abstract: The toxicity of magnesium sulfate (MgSO(4)), and the influence of calcium (Ca), were assessed in very soft freshwater (natural Magela Creek water [NMCW]) using six freshwater species (Chlorella sp., Lemna aequinoctialis, Amerianna cumingi, Moinodaphnia macleayi, Hydra viridissima, and Mogurnda mogurnda). The study involved five stages: toxicity of MgSO(4) in NMCW, determination of the toxic ion, influence of Ca on Mg toxicity, toxicity of MgSO(4) at an Mg:Ca mass ratio of 9:1, and derivation of water quality guideline values for Mg. The toxicity of MgSO(4) was higher than previously reported, with chronic median inhibition concentration (IC50)/acute median lethal concentration (LC50) values ranging from 4 to 1,215 mg/L, as Mg. Experiments exposing the 3 most sensitive species (L. aequinoctialis, H. viridissima, and A. cumingi) to Na(2)SO(4) and MgCl(2) confirmed that Mg was the toxic ion. Additionally, Ca was shown to have an ameliorative effect on Mg toxicity. For L. aequinoctialis and H. viridissima, Mg toxicity at the IC50 concentration was eliminated at Mg:Ca (mass) ratios of < or =10:1 and < or =9:1, respectively. For A. cumingi, a 10 to 30% effect persisted at the IC50 concentration at Mg:Ca ratios <9:1. The toxicity of MgSO(4) in NMCW at a constant Mg:Ca ratio of 9:1 was lower than at background Ca, with chronic IC50/acute LC50 values from 96 to 4,054 mg/L, as Mg. Water quality guideline values for Mg (to protect 99% of species) at Mg:Ca mass ratios of >9:1 and < or =9:1 were 0.8 and 2.5 mg/L, respectively. Magnesium can be toxic at concentrations approaching natural background levels, but toxicity is dependent on Ca concentrations, with exposure in very low ionic concentration, Ca-deficient waters posing the greatest risk to aquatic life.
authors.affiliation: Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of the Environment, Water, Heritage and the Arts, P.O. Box 461, Darwin, Northern Territory 0801, Australia.
authors.forename: Rick A
authors.initials: RA
authors.lastname: van Dam
authors.affiliation: Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of the Environment, Water, Heritage and the Arts, P.O. Box 461, Darwin, Northern Territory 0801, Australia.
authors.forename: Alicia C
authors.initials: AC
authors.lastname: Hogan
authors.affiliation: Edith Cowan University, Centre for Ecosystem Management, Joondalup, Western Australia 6027, Australia.
authors.forename: Cherie D
authors.initials: CD
authors.lastname: McCullough
authors.affiliation: Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of the Environment, Water, Heritage and the Arts, P.O. Box 461, Darwin, Northern Territory 0801, Australia.
authors.forename: Melanie A
authors.initials: MA
authors.lastname: Houston
authors.affiliation: Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of the Environment, Water, Heritage and the Arts, P.O. Box 461, Darwin, Northern Territory 0801, Australia.
authors.forename: Chris L
authors.initials: CL
authors.lastname: Humphrey
authors.affiliation: Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Australian Government Department of the Environment, Water, Heritage and the Arts, P.O. Box 461, Darwin, Northern Territory 0801, Australia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Harford
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002708:Chlorella / Q000187:drug effects; D033361:Cladocera / Q000187:drug effects; D005618:Fresh Water / Q000032:analysis; D006829:Hydra / Q000187:drug effects; D008278:Magnesium Sulfate / Q000633:toxicity*; D011786:Quality Control; D012908:Snails / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical; D008278:Magnesium Sulfate; D002118:Calcium
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