Seawater Inhibition of Nitrite Toxicity to Chinook Salmon

Crawford, Richard; Allen, George

Abstract: "The relative toxicity of nitrite to chinook salmon fingerlings (Oncorhynchus tshawytscha) in both freshwater ([Ca++] = 32 mg liter-1) and natural seawater (32.5‰, [Ca++] = 396 mg liter-1) was measured by 48-h static bioassay. The percentage of hemoglobin oxidized to methemoglobin was also determined. In freshwater, the 48-h median lethal nitrite concentration was 19 mg liter-1. In natural seawater, 1,070 mg liter-1 nitrite caused only 10% mortality in 48 h. In freshwater with 27 mg NO2- liter-1, 44% methemoglobin occurred with 70% mortality. In natural saltwater with 815 mg NO2- liter-1, 74% methemoglobin occurred with 10% mortality. Adding calcium sulfate to the freshwater decreased the toxicity of nitrite but did not reduce methemoglobinemia. Nitrite in calcium-free artificial seawater (100 mg NO2- liter-1) was highly toxic but did not induce appreciable methemoglobinemia. Adding calcium to this medium decreased the acute toxicity of nitrite. These results suggest nitrite toxicity mortalities resulted from a cause(s) other than methemoglobinemia. The presence of another antagonistic ion(s) in seawater to nitrite toxicity is also suggested."