ABSTRACT
F. B. EDDY* AND E. M. WILLIAMS** *Department of Biological Sciences, University of Dundee, Dundee DDI 4HN,•
**Nuffield Department of Anaesthetics, The Radcliffe Infirmary, University of Oxford, Oxford OX2 6HE
Revised by F. B. Eddy and E. M. Williams
Nitrite occurs naturally in fresh waters as a result of nitrification of ammonia and denitrification of nitrate, and its concentration can be enhanced by partial oxidation of ammoniacal discharges. Nitrite is toxic to vertebrates including fish and a principal effect is the conversion of haemoglobin to methaemoglobin which is incapable of oxygen transport although there are circulatory and tissue effects as well. The toxic species is the nitrite ion (NOD which is believed to enter the blood via the branchial chloride/bicarbonate exchange, and fish such as salmonids with high chloride uptake rates are more susceptible than those with low chloride uptake rates, for example carp. Nitrite toxicity is strongly aleviated by chloride and the concentration ratio of these ions is of great importance in assessing toxicity. Short term and long term toxicity data for a variety of fish species are presented. There are no field data on fish populations in waters where nitrite was the only pollutant. However, extensive field surveys indicated that in waters with a mean chloride concentration of 25 mg/I good salmon fisheries were associated with concentrations of nitrite below 50 µg/I N • NO2 , good coarse fisheries below 100 tig/I N • NO2 .
