Biotests using unicellular algae and ciliates for predicting long-term effects of toxicants

Test systems for predicting long-term effects with the freshwater algae Chlamydomonas reinhardi and Scenedesmus subspicatus and the ciliate Tetrahymena pyriformis were evaluated with respect to the following reference chemicals: atrazine, bromacil, diuron, methyl parathion, lindane, 3,4-dichloroaniline, pentachlorophenol, cadmium, copper, and the volatile 1,2-dichloropropane. In growth-inhibition tests under static conditions the algae revealed a higher sensitivity to the toxicants than the ciliate except for lindane and methyl parathion. Comparison of the impairment of photosynthetic efficiency (EPR, NOEC 24 hr) with the inhibition of growth (NOEC 72 hr) of S. subspicatus revealed a higher sensitivity of the EPR parameter for inhibitors of the photosynthesis. A flowthrough system was developed for long-term tests and testing of volatile and instable substances. Under flowthrough conditions C. reinhardi was more susceptible to the chemicals than under static test conditions, except for pentachlorophenol. Due to the high volatility, 1,2-dichloropropane was only tested in the flowthrough system. The data obtained from these toxicity tests provide information about effects on organisms representing different levels of the aquatic food web, possessing differences in sensitivity against toxicants. The presented flowthrough system allows the testing of volatile and instable chemicals, problematic in static test systems, and the EPR parameter is suitable for the early characterization of chemicals acting as specific inhibitors of the photosynthetic electron transport chain.