Influence of microplastic-associated biofilms on the bioavailability of a mixture of cadmium and benzo[a]pyrene by the analysis of biomarker gene expression in larval zebrafish

•BaP or Cd sorption to MPs reduces bioavailability of both contaminants.•MP-associated biofilm selectively influence biomarkers expression in Cd/BaP mix.•In presence of BaP, biofilm on MPs affects the transfer of Cd to aquatic environment.•Biofilms provide additional interactions sites for BaP compared to Cd.•Biofilm microbial communities include hydrocarbon-degrading bacteria.