EVALUATION OF A PHYTOPLANKTON TOXICITY TEST FOR WATER-POLLUTION ASSESSMENT AND CONTROL

A suggested standard test protocol for the short term C-14 assimilation algal toxicity test method (photosynthesis inhibition test) has been evaluated with natural phytoplankton and cultures of the marine diatom Skeletonema costatum. A number of test technical factors as well as the variability in the sensitivity of natural phytoplankton have been investigated, using potassium dichromate as a reference toxicant in all tests. Some supplementary experiments were carried out with pentachlorophenol and with an industrial effluent. The sensitivity of the test increased with increasing incubation time, but for practical reasons 6 hours of incubation time is recommended. The method showed good reproducibility. The sensitivity of natural phytoplankton, however, varied considerably, both between sampling locations and with time. For testing of effluents it was found necessary to measure the CO2 alkalinity and correct for changes in the specific C-14 activity caused by the deviating alkalinity of the effluent. Advantages and disadvantages of using natural phytoplankton or cultured algal species in toxicity tests for water pollution assessment and control are discussed. Tests with natural phytoplankton are not suitable for use in effluent control schemes or for similar regulatory purposes because their sensitivity is too variable. However, such tests are considered realistic indicators of the actual acute toxic effects on the phytoplanktonic community of a receiving water body. Laboratory tests with cultures of Skeletonema costatum are reproducible and can be performed all year round and are therefore well suited for regulatory uses.