Microscale Toxicity Testing with Rotifers
Abstract :Toxicity tests are one of the essential tools for evaluating the effects of anthropogenic stress in aquatic ecosystems. Methods using microscale organisms have improved the speed, simplicity, and reduced the cost of making toxicity measurements. The size, ecology, and life cycle of rotifers makes them well suited for microscale assays and toxicity assessment. In the last five years the use of rotifers in routine toxicity assessment has dramatically increased, due primarily to the widespread availability of rotifer cysts and standardized protocols for performing tests. Development of new endpoints for rapid toxicity measurements are described, as well as their application to evaluating effluents, sediment and soil elutriates, and sediment pore waters. Most work has used 24 h acute tests with brachionid rotifers, but a standardized 2 d population growth test and a 7 d full life cycle test are available for estimating chronic toxicity. The chronic toxicity of several compounds has been evaluated and acute/chronic ratios of 0.9 to 33 reported. Behavioral assays of swimming are described that are based on computer tracking of rotifer movement. Methods for measuring ingestion rates are described using fluorescent microspheres and image analysis of single rotifers. Several substrates that are metabolised to fluorescent products have been used to measurein vivoenzyme activity. The reduction of enzyme activity with increasing toxicant exposure has been quantified in single rotifers with image analysis or in populations with a fluorometer. Results from changes in rotifer stress protein gene expression as a result of toxicant exposure are summarized. The need to relate biological effects at one level of organization to those at higher levels is discussed. Understanding how effects in population level processes like growth, predation, and competition translate into changes in community structure is especially critical. Several areas where rotifers could contribute to the understanding of how toxicants modify aquatic ecosystems are described.