The acute and chronic toxicity of ammonia to marine fish and a mysid

Abstract

The acute toxicity (96-hr LC50) of un-ionized ammonia to mysids (Mysidopsis bahia) and larval inland silversides (Menidia beryllina) was influenced by pH and salinity in a species specific manner. With mysids, NH₃ was most toxic at pH 7.0 and less toxic at pH 8.0 and 9.0. In contrast, NH₃ toxicity to inland silversides was greatest at pH 7.0 and 9.0 and lowest at pH 8.0. A drop in salinity from 31 g/kg to 11 g/kg uniformly increased toxicity to mysids over this pH range. In contrast, in silversides at 11 g/kg, NH₃ toxicity was less at pH 7.0, greater at pH 8, and slightly less at pH 9, relative to the toxicity at 31 g/kg. Temperature had no significant effect on the acute toxicity of un-ionized ammonia with acclimated mysids tested at 18, 25 and 32.5°C, but did have a small effect with acclimated larval sheepshead minnows (Cyprinodon variegatus) tested at 13, 25 and 32.5°C. The chronic toxicity value (the geometric mean of the highest no-effect concentration and lowest effect concentration) at pH 8.0, 25°C and 31 g/kg salinity is 0.061 mg NH₃/L for inland silversides and 0.232 mg NH₃/L for mysids; the acute: chronic ratio is 21.3 and 7.2, respectively.