Benzylalkyldimethylethyl　ammonium　compounds　(BAC)　and　polyvinyl　chloride　microplastics　(PVC　MPs),　as　the　frequently　detected　pollutants　in　wastewater　treatment　plants　(WWTPs),　have　attracted　more　concerns　on　their　ecosystem　risks.　Therefore,　this　study　investigated　how　the　sulfur　autotrophic　denitrification　(SAD)　system　responded　to　the　single　and　joint　stress　of　PVC　MPs　(1,　10　and　100　mg/L)　and　BAC　(0.5,　5　and　10　mg/L).　After　100　days　of　operation,　the　presence　of　10　mg/L　BAC　led　to　obviously　inhibitory　effects　on　system　performance　and　microbial　metabolic　activity.　And　the　additions　of　PVC　MPs　or/and　BAC　stimulated　the　proliferation　of　intracellular　resistance　genes　(RGs),　whereas　exposure　to　BAC　increased　the　abundances　of　extracellular　RGs　and　free　RGs　in　water　more　significantly.　Compared　to　the　joint　stress,　BAC　single　stress　resulted　in　higher　abundances　of　free　RGs　in　water,　which　further　increased　the　risk　of　RGs　propagation.　Moreover,　the　interaction　between　mobile　genetic　elements　and　extracellular　polymeric　substances　further　increased　the　spread　of　RGs.　Pathogens　might　be　the　potential　hosts　of　RGs　and　enriched　in　SAD　system　and　plastisphere,　thereby　leading　to　more　serious　ecological　risks.　This　study　will　broaden　the　understanding　of　the　environmental　hazards　posed　by　PVC　MPs　and　BAC　in　WWTPs.　©　2024　Elsevier　B.V.