Archives of Environmental Contamination and Toxicology

, Volume 19, Issue 4, pp 518-522

First online:

Expression of results from growth inhibition toxicity tests with algae

  • Niels NyholmAffiliated withWater Quality Institute

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Results from six growth inhibition toxicity tests with the freshwater green algaeSelenastrum capricornutum andScenedesmus subspicatus have been analyzed, using both biomass measurements and estimates of the specific growth rate to quantify the toxic response. For exponentially growing cultures, biomass derived effective concentrations (EC's) decrease with time, but reach asymptotic values in the course of some days. The final (asymptotic) values are smaller than EC figures derived from growth rates, and the differences are greater, the smaller the slope of the dose response curve. EC50 values differed by up to a factor of 5. The examples presented are in agreement with a previously presented mathematical analysis. The author recommends that standard test protocols for routine testing should prescribe the use of some appropriate measure of the specific growth rate-rather than the biomass-as the response variable.