Combined toxicity of free chlorine, chloramine and temperature to stage I larvae of the American lobster Homarus americanus

The differential effects of free chlorine and chloramine on stage I larvae of the American lobster Homarus americanus have been investigated in continuous flow bioassay units. Applied chloramine was more toxic than corresponding concentrations of applied free chlorine to lobster larvae with estimated lc₅₀ values at 25° of 16.30 mg/l applied free chlorine and 2.02 mg/l applied chloramine. The synergistic effect of temperature on the toxicity of both free chlorine and chloramine has also been demonstrated. Exposure to applied free chlorine at 20° resulted in no significant mortality of test organisms, whereas exposure at 30° resulted in an estimated lc₅₀ value of 2.50 mg/l. Applied chloramine was considerably more toxic with an estimated lc₅₀ value at 20° of 4.08 mg/l and at 30° of 0.56 mg/l.The action of each toxicant appeared to be an alteration of standard metabolic activity as revealed by changes in respiration rates during and after exposure to applied free chlorine and chloramine. Initial respiratory stress was detected during exposure to 0.05 mg/l applied chloramine and 5.00 mg/l applied free chlorine. Reductions in respiration rates 48 h after exposure were observed with exposure to all concentrations tested, similar results being obtained following exposure to 0.05 mg/l applied chloramine and 0.10 mg/l applied free chlorine. These results are indicative of the need for information in addition to that obtained in standard bioassays for an adequate assessment of chlorine toxicity.The apparent chlorine demand of the seawater used in this study was determined after removal of particulate and dissolved organics and ammonia. Approximately 18% of the applied level of free chlorine and chloramine was recovered as residuals, measured by amperometric titration; however, no reason for this low recovery has been determined. Until it has been established that undetected chlorine and chloramine in seawater do not result in the production of toxic compounds, both applied and residual levels should be reported in toxicity studies.