Summary
Pentachlorophenol (PCP), a biocide used frequently in the wood preservation industry, is present at detectable levels in many bodies of freshwater (Jones 1981). Because of its wide use and the possibility of contamination of non-target organisms much is known about its chemistry, pharmacology, and toxicology (see Rao 1978). A review of fish life-cycle toxicity tests suggests that embryo-larval and early juvenile stages are among the most sensitive for most toxicants (McKim 1977). However, in this respect less seems to be known about the effects of PCP on the early life stages of fish although Borthwick and Schimmel (1978) have reported on 96 h LC50 studies on some estuarine animals, while Chapman and Shumway (1978) and Hodson and Blunt (1981) have studied the effects of PCP on the developmental and early alevin stages of Salmo gairdneri. The latter two studies demonstrate the toxic nature of PCP to these early life stages of a cold water fish. In this paper we report on the toxicity of PCP to various life-cycle stages of a warm water species, the largemouth bass (Micropterus salmoides). Also, using long term exposures to low concentrations of PCP, we determine the highest PCP concentration which causes no significant increase in mortality.
Methodology
Acute toxicity tests, in the form of 96 h LC50 determinations, were carried out in static water that was changed daily while chronic toxicity tests were made using a continuous flow proportional dilution apparatus; Eleutheroembryos were collected from male defended nests in Lake Opinicon and were held in running water aquaria at the Queen's University Biology Station, Chaffey's Locks, Ontario, Canada. Once the free-swimming stage was reached the fry were redistributed amongst several holding aquaria or placed under experimentation. In this study all fry were aged from the date that 50% of the eleutheroembryos of an aquarium became free swimming. Fry in the holding aquaria were fed 3 times daily on live zooplankton from fertilized rearing pools and live brine shrimp nauplii. Experimental fry were fed only brine shrimp nauplii 3 times daily. Frozen brine shrimp were provided once the fry were large enough to eat them. All holding and experimental containers were cleared of accumulated debris at frequent intervals. The I00 L holding aquaria were made of grey-painted wood with one glass side. All holding aquaria were supplied with continuously flowing lake water (alkalinity 65 mg/L as CaC03, Smol 1983; pH = 7.7) and a natural photoperiod, whereas the aquaria at the main campus laboratory were kept under a 12 h light - 12 h dark photoperiod and received dechlorinated municipal water (alkalinity 67 mg/L (as CaC03) and pH 7.2) at 25C.
To prepare the concentrated PCP stock solution 500 mg of reagent grade pentachlorophenol (lot no. I02F-0044, Sigma Chemical Co., St. Louis, MO. U.S.A.; purity 99% by G.C.; contaminants not identified) was dissolved in 10.0 ml of 1.0 N NaOH solution which was diluted with distilled water to a total volume of 1.0 L. The 96 h LC50 determinations were carried out in static PCP-treated water that was aerated and changed daily. The ratio of fish to water volume was kept at 120 mm total fish length per 1.0 L of test solution. At least 10 individuals were tested at each concentration. The fry selected for the LC50 trials were reared and tested at 25~ LC50 trials were carried out periodically over the summer (see Table I) to test for changes in the LC50 as fry grew older and larger. Throughout a trial the containers were checked frequently and dead individuals removed o and measured. The temperature of 25 C was chosen as a constant test temperature since it is well below the upper lethal o temperature and near the temperature optimum (27 C) for growth of bass fry (Straun 1961).