Mechanisms of acute and chronic waterborne nickel toxicity in the freshwater cladoceran, Daphnia magna.
We present evidence that Mg2+ antagonism is one mechanism for acute toxicity of waterborne Ni to Daphnia magna. Acutely, adult D. magna were exposed to either control or 694 microg Ni L(-1) as NiSO4 in moderately soft water (45 mg L(-1) as CaCO3; background Ni approximately 1 microg Ni L(-1)) for 48 h without feeding. Chronically, adults were exposed to either control or 131 microg Ni L(-1) for 14 days (fed exposure). These concentrations were approximately 65% and 12%, respectively, of the measured 48-h LC50 (1068 microg Ni L(-1)) for daphnid neonates in this water quality. The clearest effect of Ni exposure was on Mg2+ homeostasis, as whole-body [Mg2+] was significantly decreased both acutely and chronically by 18%. Additionally, unidirectional Mg2+ uptake rate (measured with the stable isotope 26Mg) was significantly decreased both acutely and chronically by 49 and 47%, respectively, strongly suggesting that Ni is toxic to D. magna due at least in part to Mg2+ antagonism. No impact was observed on the whole-body concentrations or unidirectional uptake rates of Ca2+ during either acute or chronic Ni exposure, while only minor effects were seen on Na+ and Cl- balance. No acute toxic effect was seen on respiratory parameters, as both oxygen consumption rate (MO2) and whole-body hemoglobin concentration ([Hb]) were conserved. Chronically, however, Ni impaired respiratory function, as both MO2 and [Hb] were significantly reduced by 31 and 68%, respectively. Acutely, Ni accumulation was substantial, rising to a plateau between 24 and 48 h of approximately 15 microg g(-1) wet weight--an increase of approximately 25-fold over control concentrations. Mechanisms of acute toxicity of Ni in D. magna differ from those in fish; it is likely that such mechanistic differences also exist for other metals.
Pane
Eric F
EF
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada. michanderic@yahoo.com
Smith
Clint
C
McGeer
James C
JC
Wood
Chris M
CM
D000818:Animals; D003621:Daphnia; D005260:Female; D007474:Ion Exchange; D007928:Lethal Dose 50; D008274:Magnesium / Q000493:pharmacokinetics; D009532:Nickel / Q000494:pharmacology / Q000633:toxicity*; D014867:Water / Q000737:chemistry; D014873:Water Pollutants / Q000494:pharmacology / Q000633:toxicity*
D014873:Water Pollutants; D014867:Water; D009532:Nickel; D008274:Magnesium