Chronic toxicity of a pure and technical grade pentachlorophenol toDaphnia magna

Abstract

Chronic toxicity test procedures (static, with renewal) were used to determine the chronic toxicity of sublethal concentrations of a technical formulation of pentachlorophenol (PCP) and pure pentachlorophenol toDaphnia magna. Test organisms 48+-12 h old were exposed for their entire lifespan (i.e., until death) to 0.01, 0.05, 0.1 and 0.5 mg technical PCP/L and 0.01, 0.087 and 0.1 mg pure PCP/L. Criteria used to assess chronic toxicity were mean time to appearance of the primiparous instar in the brood chamber, mean number of days to release of the first brood, mean number of broods produced per female, mean brood size per female, mean number of reproductive days, mean number of young produced per reproductive day per female and survivorship.

Pentachlorophenol differentially affected maturation and reproduction but not survivorship or longevity. Mean number of broods produced per daphnid, length of the reproductive period, longevity and survivorship were insensitive criteria relative to mean time to appearance of the primiparous instar, time to release of first brood, brood size, and number of young produced per daphnid per reproductive day. Generally, there was little difference in toxicity of the three concentrations of pure PCP, for they significantly reduced mean brood size and rate of reproduction of young and significantly but differentially affected maturation.

Technical PCP, at the highest concentration of 0.5 mg/L, significantly reduced mean brood size and the rate of production of young, and significantly delayed both time to appearance of the primiparous instar and release of the first brood. When differences in toxicity occurred, generally, pure PCP was more toxic than comparable concentrations of technical PCP. Although enhanced maturation was observed there was no compensatory reproduction.

Similar conclusions regarding maturation and survivorship would have been derived from this study had it been terminated after the standard 21 d; however, the conclusions would have been different for reproduction. Only the highest concentration of technical PCP reduced brood size, the rate of production of young and total number of young produced per daphnid in 21 d. Only pure PCP at 0.05 mg/L caused daphnids to produce significantly fewer broods and, although the mean brood size was significantly larger than those in the controls, the mean number of young produced in 21 d was significantly reduced. These results differ substantially from those based on the entire life-cycle study and one of the most obvious differences is the much lower rates of young production in the entire life cycle study (2.41–3.03 young per daphnia per reproductive day) opposed to the first 21 days of the study (5.13–7.5 young per daphnia per reproductive day).