The effects of fluid motion on toxicant sensitivity of the rotifer Brachionus calyciflorus.

Standardized methods for estimating the toxicity of anthropogenic compounds to aquatic organisms frequently fail to consider key elements of the test organisms' environment. Aquatic organisms exist in a fluid environment, and fluid dynamics may have an important influence on the response to toxicants. Rotifers are one of the three major groups of zooplankton and have been increasingly utilized in standardized toxicity testing. However, like other toxicity tests, assays with the species Brachionus calyciflorus are performed under static conditions in the absence of fluid motion. We investigated how fluid motion modifies pentachlorophenol (PCP) toxicity to B. calyciflorus using 24 h acute and 48 h reproductive toxicity tests. Estimates of PCP LC50s and reproduction EC50s in static conditions decreased from 738 and 1082 microg l(-1), respectively, to as low as 262 and 136 microg l(-1), respectively, in fluid motion. Flow analysis indicated that increased toxicant sensitivity can occur at ecologically relevant levels of fluid motion. Mechanistic studies indicated that fluid motion/toxicant interactions may result from the ability of fluid motion to cause shear stress, alter toxicant uptake, and/or alter the bioavailability of food. As fluid motion may have an important effect on the life histories of a wide variety of aquatic organisms, fluid motion/toxicant interactions may be an important consideration in other standard test organisms. These results raise questions about the accuracy of ecological risk assessments based on toxicity data from static conditions.