Critical evaluation and further development of methods for testing ecotoxicity at multiple pH using Daphnia magna and Pseudokirchneriella subcapitata

To meet the requirements of risk assessment legislature regarding the ecotoxicity of ionizing compounds, the present study attempts to establish easy, robust methods for testing ecotoxicity at various pH levels. An overview is given of the buffering methods found in the literature. This is supplemented by a series of experiments where toxicity and ability to stabilize pH of seven common buffering compounds was tested on Daphnia magna and Pseudokirchneriella subcapitata. We consider a buffer applicable at a given concentration if the pH drift is below 0.2 pH units, and if there are no toxic effects. Twenty-four- and 48-h acute toxicity tests with D. magna were carried on a series of organic buffers with pH monitoring. Based on the experimental results it is possible to give recommendations for buffer concentrations for use in toxicity testing with D. magna at pH levels in the range of pH 6.0-7.8 for 48 h exposure, and pH 6.0-9.5 for 24 h exposure. Forty-eight- and 72-h growth inhibition tests with P. subcapitata were carried out, and recommendations for buffer concentrations at pH 7.5 and 8.0 are made for both 48 and 72 h of exposure.