Comparison of the EC50s of algal toxicity tests calculated by four methods

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Abstract
EC50s (calculated concentrations that would inhibit growth by 50%) of 21 pesticides in unicellular algal toxicity tests were calculated by straight‐line graphical interpolation, moving average interpolation, prohibit analysis, and the binomial method. EC50s of 18 tin compounds were calculated by graphical interpolation, moving average, and probit methods. Results from a total of 187 tests were analyzed. The EC50 values were essentially identical when calculated by each method. Although moving average and probit analyses allow calculation of confidence intervals, there is doubt that they can be used with the quantitative data of algal toxicity tests. In the absence of confidence intervals, only the calculated EC50 is used to express relative toxicity, and straight‐line graphical interpolation, a simple and rapid method, may be used in lieu of more complex statistical methods.