From single chemicals to mixtures-Reproductive effects of levonorgestrel and ethinylestradiol on the fathead minnow.

•We characterised the reproductive responses of the fathead minnow to ethinyestradiol and levonorgestrel and a binary mixture of the two.•A new statistical approach was developed to analyse egg production during exposure experiments.•The concept of concentration addition was tested.•Plasma drug concentrations and the read across approach were used to guide the interpretation of the reproductive results.