title: Ionoregulatory disruption as the acute toxic mechanism for lead in the rainbow trout (Oncorhynchus mykiss).
abstract: The mechanism for acute toxicity of lead (Pb) in rainbow trout (Oncorhynchus mykiss) was investigated at Pb concentrations close to the 96 h LC50 of 1.0 mg dissolved Pb l(-1) (0.8-1.4, 95% C.I.) determined in dechlorinated Hamilton city tap water (from Lake Ontario, hardness=140 mg l(-1) CaCO(3)). Tissue Pb accumulation associated with death was highest in the gill, followed by kidney and liver. Significant ionoregulatory impacts were observed in adult rainbow trout (200-300 g) fitted with indwelling dorsal aortic catheters and exposed to 1.1+/-0.04 mg dissolved Pb l(-1). Decreased plasma [Ca(2+)], [Na(+)] and [Cl(-)] occurred after 48 h of exposure through to 120 h, with increases in plasma [Mg(2+)], ammonia, and cortisol. No marked changes in PaO(2), PaCO(2), pH, glucose, or hematological parameters were evident. Branchial Na(+)/K(+) ATPase activity in juvenile trout exposed to concentrations close to the 96 h LC50 was inhibited by approximately 40% after 48 h of Pb exposure. Calcium ion flux measurements using 45Ca as a radiotracer showed 65% inhibition of Ca(2+) influx after 0, 12, 24 or 48 h exposure to the 96 h LC50 concentration of Pb. There was also significant inhibition (40-50%) of both Na(+) and Cl(-) uptake, measured with 22Na and 36Cl simultaneously. We conclude that the mechanism of acute toxicity for Pb in rainbow trout occurs by ionoregulatory disruption rather than respiratory or acid/base distress at Pb concentrations close to the 96 h LC50 in moderately hard water.
authors.affiliation: Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ont., Canada L8S 4K1. rogersjt@mcmaster.ca
authors.forename: J T
authors.initials: JT
authors.lastname: Rogers
authors.forename: J G
authors.initials: JG
authors.lastname: Richards
authors.forename: C M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000097:blood; D005880:Gills / Q000187:drug effects / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects*; D007854:Lead / Q000493:pharmacokinetics / Q000633:toxicity*; D007928:Lethal Dose 50; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D011188:Potassium / Q000097:blood; D014018:Tissue Distribution; D023382:Toxicity Tests, Acute; D014873:Water Pollutants / Q000493:pharmacokinetics / Q000633:toxicity*
chemical_list: D014873:Water Pollutants; D007854:Lead; D011188:Potassium; D002118:Calcium