Methods for growth inhibition toxicity tests with freshwater algae

Abstract

A critical review of batch-culture freshwater algal toxicity test methods (algal growth inhibition tests) is presented. Interlaboratory comparisons have revealed that the results from such tests can vary a great deal, in some cases by more than three orders of magnitude. The potential causes of variability are the physical/chemical experimental parameters. Algal tests, however, need not be very strictly standardized in order to be reproducible if tests are appropriately conducted and the experimental parameters are understood and controlled. Many algal toxicity data reported in the literature seem to have been generated from tests performed with an excessively high biomass and under poor gas-exchange conditions, the combination of which will cause an insufficient supply of carbon dioxide leading to high pH levels and sometimes even to mass-transport (carbon dioxide)-limited linear growth. Poor gas-exchange conditions will prevail unless the test flasks are shaken or aerated continuously. Literature data on the toxicity of chemicals to algae should therefore be used only with careful evaluation of the test method involved.