An estrogenic municipal effluent decreased fathead minnow reproduction to a near stop

Municipal wastewater treatment plants (WWTPs) release endocrine disrupting chemicals (EDCs) which can impact aquatic species' reproduction (e.g., decrease fecundity). As bioassays can quantify the cumulative effect of mixtures, such as effluents, this study proposes a two-Tier bioassay-based approach to assess EDCs in WWTP effluents. The first Tier is composed of the human receptor transactivation assay for estrogen (hERα) and androgen (hAR), and the Tier 2 comprises an abbreviated 7-day fish short-term reproduction assay (FSTRA; OECD TG 229) in fathead minnow (Pimephales promelas). The approach was assessed on a municipal effluent (12.5, 25 and 50% v/v) and compared to the standard 21-day FSTRA and chemical analysis. The first Tier detected mainly estrogenic activity at 6.7-51.5 ng/L of estrogen equivalent (EEQ). The 7-day FSTRA of Tier 2 was able to capture the same arrest in reproduction in the 50% v/v treatment as the 21-day FSTRA. Moreover, around halfway of the 21-day FSTRA, the 12.5% v/v treatment led to a reproduction arrest similarly to the positive control (12.5% v/v + 40 ng/L of 17α-ethinylestradiol (EE2)). During the 21-day experiment, bisphenols, nonylphenol and 19 pharmaceuticals were detected. Altogether, the results indicate the Tier 1 methodology was robust to identify potential endocrine disruptive activity of the effluent, while the Tier 2 was able to detect reproduction arrest without a clear mechanism of action. Overall, this two-Tier approach provides an initial framework to assess EDCs levels in WWTP effluents, which will help inform on the risk of complex mixtures to protect aquatic ecosystems.