Ecotoxicity – Daphnia magna: Motility inhibition test (ISO 6341: 2013 standard or OECD 202: 2004 guideline).
This test determines the acute toxicity to Daphnia magna that may contain soluble chemicals or chemicals that can be maintained in a stable suspension or dispersion. Likewise, it can be carried out with industrial or residual effluents, treated or untreated after decantation, filtration or centrifugation, with surface water or with groundwater. The test determines the concentration that immobilizes 50% of the daphnids exposed to the test sample after 24 hours and 48 hours, providing the parameters EC50-24h and EC50-48h (depending on the requirements of users or national authorities, one or another exposure time may be required).
In the definitive test, the daphnids are exposed to five test concentrations, in 4 replicates, to determine the percentage of inhibition at each test concentration and the EC50-24 h and EC50-48 h are calculated. According to the ISO 6341 standard, at least 3 concentrations with an immobilization percentage between 10 and 90% must be included in the final test, while according to the OECD 202 guideline, the concentration that causes immobilization of 0% and 100% of the daphnids must be included. Positive and negative controls are also included in the test. If the client does not have information on the toxicity of the sample to determine the definitive test concentrations, the performing of a preliminary test can be requested, with one replica, where the daphnids are exposed to a series of widely spaced concentrations and the range of concentrations over which the definitive test will be carried out.
The standards include the possibility of peforming a limit test for biological testing of chemical substances, using a single test concentration, 100 mg/L (or the maximum concentration at which the product is soluble or forms a stable dispersion in water). Nevertheless, if the result of this test indicates that the percentage of immobilization is greater than 10%, the full test should be performed. During the tests, the concentration of dissolved oxygen and pH should be measured. If possible, the method to quantify the chemical substance to be tested should be provided (cost not included in the cost of the test).
To carry out the tests, the following information must be provided to the laboratory: test to be evaluated (definitive test, preliminary and definitive test or limit test), the concentrations to be tested (except when the preliminary test is requested), the nature of the product and its solubility. Test solutions should preferably be prepared by dissolving the test substance in water. The use of other solvents, emulsifiers or dispersants should be avoided. If the use of a solvent other than water is required, an additional control of the solvent must be carried out.