PAHs sorption to biochar colloids changes their mobility over time

•Adsorption of PAHs reduced the negative surface charge of biochar colloids over time.•Transport of biochar colloids with PAHs was highly related to PAHs adsorption kinetics.•Adsorption of PAHs onto the outer biochar surface decreased the mobility of biochar colloids.•Diffusion of PAHs to the biochar inner pores slightly affected the mobility of colloids.