Studies on the toxicity of ammonia, nitrate and their mixtures to guppy fry

Using guppy fry as the test fish the individual and joint toxicities of ammonia and nitrate were estimated in static tests at constant pH and temperature. The 72-h lc₅₀ values were 199 and 1.26 mg 1⁻¹ −N for potassium nitrate and free ammonia, respectively. The toxicities of mixtures of the two were additive except at very low ammonia to nitrate ratios. Watson's equation, a disinfection law relating toxicant concentration to survival, was applicable to both toxicants. The applicability of Chick's law and other kinetic models to fish toxicity was also evaluated.