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Comparative Toxicity of Hypochlorous Acid and Hypochlorite Ions to Mosquitofish
Author(s) -
Mattice J. S.,
Tsai S. C.,
Burch M. B.
Publication year - 1981
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1981)110<519:ctohaa>2.0.co;2
Subject(s) - hypochlorous acid , chemistry , chlorine , hypochlorite , toxicity , environmental chemistry , sodium hypochlorite , nuclear chemistry , inorganic chemistry , biochemistry , organic chemistry
We examined the relative toxicity of hypochlorous acid (HOCl) and the hypochlorite ion (OCl − ) by exposing mosquitofish Gambusia affinis for 1 hour to predominantly free residual chlorine (FRC) at six levels of pH following a 7‐day acclimation to the test pH. Median lethal concentrations (LC50), in terms of total residual chlorine (TRC), increased with increasing pH, ranging from 0.41 mg/liter at pH 6.05 to 1.28 mg/liter at pH 8.42. Because of the influence of hydrogen ion concentration on dissociation of HOCI, the percent of FRC present as HOCl is about 97% and 13%, respectively, at the low and high pH. Cursory examination of toxicity of monochloramine (NH 2 Cl) and mixtures of NH 2 Cl and dichloramine (NHCl 2 ) suggested that their contributions to toxicity were negligible at the concentrations existing at any test pH. Free residual chlorine concentrations at the LC50 for each pH were fitted to a theoretical model derived from an assumption that toxicities of HOCl and OCl − were additive. More than 99% of the total variability was explained by the model, providing strong support for the assumption. Hypochlorous acid is about four times as toxic as OCl − .