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Anaerobic potentiation of copper toxicity and some environmental considerations.

The toxicity of copper is substantially greater when the metal ions is applied to cells under conditions of anoxia than under aerobic conditions. The increase in toxicity occurs because Cu(II) is reduced to Cu(I) which is stable under anoxia and is more toxic than the oxidized species. This effect has been observed in mammalian cells in tissue culture and in bacteria. Anoxic potentiation of copper toxicity has also been observed in algal, fungal and yeast cells. The reduction of Cu(II) has been demonstrated by electron paramagnetic resonance spectrometry. The appearance of Cu(I) has been observed by means of specific colorimetric reagent. The reduction of Cu(II) to Cu(I) is not dependent upon concomitant metabolism and requires only a supply of sulphydryl groups. Microorganisms that are responsible for two anaerobic processes of economic importance to humans, the digestion of sewage sludge in effluent treatment plants and the digestion of food in ruminant animals, may be exposed to high concentrations of copper. The environmental consequences of this exposure are discussed.