Report No FR/D0011
EFFECTS OF AMMONIA ON FISH PHASE II -
Ammonia is highly toxic to fish and is released to fresh waters by agricultural and industrial activities. Water quality standards for ammonia e.g. 25 µg l-1 NH3 (95 percentile) for salmonids (EIFAC, 1970), have in the past been derived from mortality studies. However unfavourable chronic physiological and sublethal effects may be caused by lower concentrations of ammonia.
The objective was to assess sublethal effects of ammonia on sensitive fresh water species such as wild populations of salmonids, especially at early stages of the life cycle which are regarded as most vulnerable, with the aim of recommending water quality standards for ammonia.
Laboratory experiments were based on relevant ammonia and pH values obtained from field data. Techniques were developed to detect sublethal responses of fish to ammonia including measurement of sodium fluxes (unidirectional influx and efflux). The rates of these fluxes control body sodium balance. The method is non invasive and measures perturbations in sodium balance of fish provoked by the presence of pollutants in the water.
Future standards for ammonia should be based not solely on NH3 but on total ammonia. Previous recommendations suggested that unionised ammonia levels should not exceed 25 µg l-1 and total ammonia 1 mg l-1. However our study suggests that even these levels may be too high to prevent chronic sublethal effects on salmonids, particularly wild populations.
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