title: The effect of calcium and magnesium ratios on the toxicity of copper to five aquatic species in freshwater.
abstract: While it is generally accepted that water hardness affects copper toxicity, the major ions that contribute to water hardness (calcium [Ca] and magnesium [Mg]) may affect copper toxicity differently. This is important because the Ca:Mg ratio in standard laboratory-reconstituted waters often differs from the ratio in natural surface waters. Copper toxicity was assessed for five different aquatic species: rainbow trout (RBT), fathead minnow (FHM), Ceriodaphnia dubia, Daphnia magna, and an amphipod (Gammarus sp.) under different Ca:Mg ratios (4:0, 3:1, 1:1, 1:3, and 1:4 mass basis) at a common hardness (180 mg/L as CaCO3) and alkalinity (120 mg/L as CaCO3). Copper toxicity increased at lower Ca:Mg ratios for RBT but increased at higher Ca:Mg ratios for D. magna. Fathead minnows (<24 h old) were more sensitive to copper in 1:1 Ca:Mg waters compared to 3:1 Ca:Mg waters. The toxicity of copper did not vary under different Ca:Mg ratios for Gammarus sp., C. dubia, and 28-d-old FHM. The effect of Ca:Mg ratios on copper toxicity changed for D. magna in softer water (90 mg/L as CaCO3) compared with hard water studies.
authors.affiliation: ENSR, Fort Collins, Colorado 80521, USA. rnaddy@ensr.com
authors.forename: Rami B
authors.initials: RB
authors.lastname: Naddy
authors.forename: William A
authors.initials: WA
authors.lastname: Stubblefield
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: May
authors.forename: Scott A
authors.initials: SA
authors.lastname: Tucker
authors.forename: J Russell
authors.initials: JR
authors.lastname: Hockett
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry*; D003300:Copper / Q000633:toxicity*; D003445:Crustacea; D003530:Cyprinidae; D003621:Daphnia; D007928:Lethal Dose 50; D008274:Magnesium / Q000737:chemistry*; D017686:Oncorhynchus mykiss; D014867:Water / Q000737:chemistry; D014873:Water Pollutants / Q000633:toxicity*
chemical_list: D014873:Water Pollutants; D014867:Water; D003300:Copper; D008274:Magnesium; D002118:Calcium