The test solutions were shaken at 150 rpm, 25°C for 24 h to dissolve the BAC in water. The preparation of the test solutions is described in more detail in Section S4, SI. The test system was set up with 50 mL dechlorinated tap water (pH: ~8) under light-dark cycles of 16:8 h at 21°C, following the culture conditions. Food and aeration were not provided throughout the acute ecotoxicity test. The test solutions were not changed during the exposure. The acute toxicity test was performed for 48 h without shaking. After 24 and 48 h, immobilization of the daphnids was determined by gently shaking the water and checking their movement for 15 s. Cw of the BAC were measured just before adding D. magna and at the end of the 48 h acute toxicity test. In some toxicity tests, dissolved organic carbon (DOC) was measured before adding daphnids and at the end of the ecotoxicity test (further details in Section S5, SI). Water quality was measured before and after the acute toxicity test (see Table ). EC50 values were obtained based on the 2-parameter log-logistic model in the drm() function of the R-package drc (version R 4.2.2, R Core Team, 2022). For each exposure level, the arithmetic mean of the measured Cw at the start and end was used for the EC50 estimation.