Acute toxicity of nitrite to crayfish Procambarus simulans in varied environmental conditions

Abstract

In low chloride (≤5 mg litre −1), neutral pH water, resistance times to 50% death of crayfish Procambarus simulans to environmental nitrite concentration were highly significantly correlated (r = -0·953) in an inverse, double logarithmic fashion. The best fit regression equation equalled: log time ( h) = 2·64−0·84 log nitrite concentration (mg litre −1). This model predicts resistance times to 50% death for 24,48, 72 and 96 h of 31·5, 13·8, 8·6 and 6·1 mg of nitrite litre −1. Increases in environmental chloride concentration to 300 mg litre −1 ameliorated the toxicity of nitrite. At a lower pH (5·6) resistance times decreased slightly and the protective efficacy of chloride ions was reduced. These results indicate that P. simulans possesses an intermediate tolerance of nitrite relative to fish species and that chloride ions act as antagonists to nitrite ions (NO 2 −) at monovalent ion uptake sites, but apparently do not compete with the uptake of the uncharged nitrous acid (HNO 2) molecule.