Chapter 7

Dose-response assessment


You have found anti-androgenic activity in a wastewater treatment plant effluent, and it was as high as flutamide (molecular weight 276.2 g/mol) equivalents Flutamide-EQbio of 4.8 μg/L. Then, you decided to measure the concentrations of various strong anti-androgenic compounds. Two of them, megestrol acetate (molecular weight 342.7 g/mol) and progesterone (molecular weight 314.5 g/mol), were present in the sample at concentrations of 0.19 and 0.69 ng/L, respectively. You searched in the literature and learnt that these levels are typical for occurrence of these compounds in wastewater treatment plant effluents. Therefore, you measured anti-androgenic activity of megestrol acetate, progesterone and flutamide in in vitro bioassays. Megestrol acetate, progesterone and flutamide had following EC50 values: 10.7, 19.3, and 656.1 nM, respectively. Determine the contribution of megestrol acetate and progesterone to the total anti-androgenic activity of the sample. Which conclusion(s) can be drawn based on the information provided?
(Note: Have a look at Chapter 8 for BEQchem and Chapter 13 for iceberg modelling to solve the question.)

You tested two water samples, one from a wastewater treatment plant influent and one from the matching effluent with a bioassay for estrogenicity, e.g., ER CALUX or ER GeneBLAzer (bioassays are explained in Chapter 10). The influent had high cytotoxicity with an IC10 of REF 0.5 and the effluent had an IC10 of REF 50. The EC10 for the activation of the estrogen receptor was REF 5 in the effluent but the activation was masked by cytotoxicity in the influent. Can you make any conclusions about the removal of estrogenic chemicals by the treatment plant?

The cytotoxicity burst is a phenomenon, where close to cell death many stress responses but also nuclear receptors are activated, which would lead to false positive results that are not triggered by specific activation of these pathways or nuclear receptors but rather by nonspecific toxicity or indirect effects. The cytotoxicity burst phenomenon has been reported for single chemicals only. Do you think it can also be observed for mixture of micropollutants as they occur in water samples? What is your practical advice to deal with such issues?