Fig. 3 presents (S)-Crizotinib concentration of the Σ14drug residues in the three phases A) for each sampling site and B) for each river. The concentration of drug residues was found to vary strongly whatever the sampling site. In the dissolved phase, concentrations of Σ14drug residues were lower than 1 μg L− 1 except for the Don station in the Deûle River. The highest concentration was recorded at Don (1290 ± 193.5 ng L− 1), followed by Férin (800 ± 120 ng L− 1) and Erquighem-Lys (654 ± 98 ng L− 1) (Fig. 3A). The total concentrations of drug residues associated to SSM were always lower than 30 ng L− 1, much lower than in the dissolved phase. Although low levels of drug residues were detected in the water column of the Scarpe River, their concentrations were detected at high level in the sediment (Fig. 3B). The highest concentration of drug residues was found in Nivelles (station located in the Scarpe River) with 60.7 ± 9.1 ng g− 1 dw followed by Zingem located along the Scheldt (27.8 ± 4.2 ng g− 1 dw) and Don along the Deûle River (26.9 ± 4.0 ng g− 1 dw).