Acute Toxicity of Monochloramine to Juvenile Chinook Salmon (Oncorhynchus tshawytscha Walbaum) and Ceriodaphnia dubia

Abstract

Abstract A comprehensive data set for the acute toxicity of monochloramine to juvenile chinook salmon, Oncorhynchus tshawytscha, and the aquatic invertebrate Ceriodaphnia dubia are presented. For exposures up to 10 days, the equation LC50 = 7244t-0.4525 (where LC50 = monochloramine concentration in μg/L for 50% lethality and t = time in minutes) can predict the LC50 value for monochloramine in juvenile chinook salmon and accounts for 94.4% of the variability in the experimental data. Predictions of acute toxicity were less reliable for concentrations in the range 0.5 mg/L to 0.8 mg/L since the time to 50% mortality (LT50) value varied substantially in this range. Post-exposure mortality occurred only with exposures of >0.67 mg/L monochloramine. Feeding fish immediately before and during acute monochloramine exposure created a large chloramine demand in test chambers. In all tests where fish were fed, measured monochloramine concentrations were below detectable levels (<10 μg/L) and no fish mortality occurred. Monochloramine toxicity to the freshwater invertebrate Ceriodaphnia dubia was studied with time-to-lethality tests at 26 different concentrations. The equation LC50 = 61600t-1.0748 predicted the LC50 value for monochloramine in C. dubia and accounted for 94.8% of the variability in the experimental data. The mathematical equations that describe the LC50 for juvenile chinook salmon and C. dubia were used as reference lines for the evaluation of relative monochloramine toxicity. Both juvenile chinook salmon and C. dubia were among the most sensitive fish and aquatic invertebrate species, respectively, C. dubia being more sensitive than juvenile chinook salmon for exposure durations >30 minutes.