Steven J. Hamilton James C. Schmulbach Kevin J. Buhl 1993 <p><span>Two chronic toxicity tests were conducted in which </span><i class="EmphasisTypeItalic ">Daphnia magna</i><span> were either continuously or intermittently exposed to bromoxynil octanoate (BO; as Buctril</span>^®<span>) for 28 d. In the intermittent exposure test, daphnids were exposed to daily pulses of BO with 24-h mean concentrations equal to those in the continuous exposure test, and the peak concentrations were three times the 24-h mean values. After 28 d of continuous exposure to BO, survival of daphnids was reduced at 80 μg/L, whereas mean number of young per adult, intrinsic rate of natural increase, and mean weight of adults were all reduced at ⩾40 μg/L. Intermittent exposures to daily pulses of BO for 28 d caused reduced survival of daphnids at 24-h mean concentrations ⩾40 μg/L and reduced mean number of young per adult, intrinsic rate of natural increase, and mean weight of adults at 24-h mean concentrations ⩾20 μg/L. The estimated geometric mean-maximum acceptable toxicant concentrations of BO based on 24-h mean nominal values were 28 μg/L for continuous exposures and 14 μg/L for intermittent exposures. These results demonstrated that continuous-exposure studies may not be adequate in assessing herbicide toxicity to aquatic biota when concentrations fluctuate temporally.</span></p> application/pdf 10.1007/BF00212126 en Springer Chronic toxicity of the bromoxynil formulation Buctril® to <i>Daphnia magna</i> exposed continuously and intermittently article