Abstract
Development of an unconventional test method involves usually the comparison of biological responses under a variety of test conditions. The quality of these biological methods relies on an appropriate experimental design. The Daphnia magna heartbeat rate as a physiological endpoint for assessing aquatic pollution has been of minor interest so far; nonetheless, this could be an early and sensitive indicator of the harmful effect of micropollutants. Our aim was to set up the optimal experimental design of the heartbeat rate test. The studied factors were the composition of the test medium, the age of the test organism, and the exposure time, at triclosan concentrations between 0.2–2000 μg/L. According to the evaluation of test results the optimal test condition for the heartbeat rate test assumes tap water as test medium, 10-day-old test organisms and 48 h exposure time.
Highlights
As the whole set of experiments was repeated twice, this yielded a total of 16 datasets with altogether approx. 800–1000 heartbeat rates each coming from three successive measurement of an individual
The test organisms were not incubated individually but in sets of ten which was very convenient from the experimental point of view but resulted in heartbeat rates that were not independent from each other
Due to the subtle effects of pharmaceuticals and personal care products (PPCP) chemicals measured by conventional ecotoxicity methods at environmentally relevant concentrations their effects are underestimated and there is a high demand for new, more sensitive environmental ecotoxicity tests
Summary
The cladocerans Daphnia spp. have been established as useful test systems in environmental toxicology but usually the classical endpoints (immobilization and lethality) are applied for impact assessment of toxic substances [8,9,10,11]. Studies applying the D. magna heartbeat rate endpoint to investigate the environmental effects of chemical substances and environmental samples were targeting concentrations that cannot be considered environmentally relevant [15,16,17]. The D. magna heartbeat rate test described by Fekete-Kertész et al [18] was established for studying the physiological effect of micropollutants (Na-diclofenac, 17β-estradiol, paracetamol, triclosan and metazachlor) on freshwater ecosystems. The heartbeat rate test gives quantifiable results of the effect of micropollutants at environmentally relevant concentrations, the available scientific literature contains scarce information about using this endpoint for especially ecotoxicological purposes
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