The Distribution of Endpoint Chronic Values for Freshwater Rotifers

Abstract :Several types of toxicity tests have been described using the freshwater rotiferBrachionus calyciflorus. Variation among different endpoints has not been described and compared to variation in toxicant sensitivity among rotifer species. Data is presented demonstrating that endpoint chronic values for pentachlorophenol are log-normally distributed with a mean of 251 µg/l PCP and a coefficient of variation of 12%. This compares to the distribution of rotifer species sensitivities, which is also log-normally distributed with a mean of 29 µg/l PCP and a coefficient of variation of 53%. Since the breadth of rotifer species sensitivity distribution is much greater, which endpoint that is measured is less important than making toxicity measurements on several species. This suggests that toxicity should be assessed using the simplest, fastest, and most inexpensive tests available. Toxkits are well designed to meet these needs and should play an expanding role in toxicity assessments in the future.