Rapid toxicity screening tests for aquatic biota 1. Methodology and experiments with Daphnia magna

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Abstract
A promising new and rapid toxicity screening test was developed, the concept and principles of which are presented. The method consists of visual observation of in vivo inhibition of an enzymatic process, using a fluorescent substrate. Juvenile Daphnia magna was exposed to a toxicant dilution series for 1 h, after which the substrate was added and the enzymatic inhibition (absence of fluorescence) was observed visually, using a long‐wave UV light (385 mm). The 1‐h EC50 results of 11 pure compounds are presented and compared to the conventional 24‐ and 48‐h Daphnia magna EC50s. All 1‐h “fluorescence” EC50s were of the same order of magnitude and correlated very well with the 24‐ and 48‐h EC50s. The sensitivity and reproducibility of this cost‐effective screening test were compared to those of the Microtoxr̀ test. The scope for application and the potential of this new rapid toxicity screening test are evaluated.