Sensitivity of different growth inhibition tests--just a question of mathematical calculation? Theory and practice for algae and duckweed.

Hazard assessment often needs to compare inhibition values of different test species and different test durations. But the three different methods to calculate inhibition in growth inhibition tests (final biomass, growth rate, area under the growth curve) may lead to very different and sometimes contradicting numerical sensitivities of the test species. This paper will depict why there are these different results and what consequences this has for the evaluation of results. Comprehensive discussion of different aspects will show that using growth rate may eliminate most of the problems occurring for comparisons between test species, different test times and different laboratories. The use of growth rate and the adaptation of toxicity levels maximises reproducibility, comparability and biological sensitivity of biotests.