Biological effect and chemical monitoring of Watch List substances in European surface waters: Steroidal estrogens and diclofenac – Effect-based methods for monitoring frameworks

•EU-wide diclofenac and steroidal estrogen monitoring was performed with LC-MS/MS and biotests.•Low estrogenicity and partly high COX-inhibition were found in the sampled surface waters.•Bioassays showed good screening function and applicability for investigative monitoring.•LC-MS/MS detection of EE2 remains challenging at its predicted no-effect level of 35 pg/L.•Standard addition tackled LC-MS/MS detection challenges.