Modulation of cupric ion activity by pH and fulvic acid as determinants of toxicity in Xenopus laevis embryos and larvae

  • Buchwalter D
  • Linder G
  • Curtis L
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An ion-specific electrode measured cupric ion activity modulated by fu lvic acid (FA) and pH in a series of modified Frog Embryo Teratogenesis Assa y-Xenopus (FETAX) toxicity assays. Hydrogen ion concentration was the primar y determinant of cupric ion activity, while FA played a smaller but signific ant role. Fulvic acid was a weak copper complexing agent at pH 5.50. At pH 5 .50 there was slight reduction of ionic activity and a subsequent attenuatio n of copper toxicity with 5.0 mg/L FA. At pH 7.50, FA also had a mild attenu ating effect on copper toxicity. At pH 6.50, copper was strongly complexed b y FA at total copper (TCu) concentrations below its pH-dependent solubility limit. AtTCu concentrations above the solubility limit FA enhanced toxicity. There was more cupric ion activity measured in the presence of 0.5 and 5.0 mg/L FA than without it at TCu concentrations above the solubility limit. Th e proposed mechanism for this behavior was FA action as a nucleation inhibit or. Under the chemical conditions of the pH 6.50 experiments, a stable super saturation of copper was formed, resulting in a more toxic aqueous matrix

Author-supplied keywords

  • Copper toxicity
  • Fulvic acid
  • pH

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