Fig. 4

Mixture toxicity based on the sum of toxic units (TU) in Daphnia spec. for 57 analyzed chemicals (a, data from [140]) and mean and standard error of the mean of EC₅₀ values for baseline toxicity, determined with the Microtox assay (b), and of dioxin-like activity, determined with the yeast dioxin screen (c), in water samples from the river Horloff. Dashed arrows mark the outflow of the last of the four small wastewater treatment plants (WWTPs) downstream of site 4 in the upper reach of the Horloff and of the WWTP Wölfersheim downstream of site 19. The solid arrow marks the outflow of the large WWTP Hungen-Utphe downstream of site 14. Hatched bar: reference site 16 in the space-for-time-substitution approach to account for differences to sites 17 and 18 within the restoration section (dark green bars) and to transect sites (light green bars) downstream of the restoration section