Tracing microplastic (MP)-derived dissolved organic matter in the infiltration of MP-contaminated sand system and its disinfection byproducts formation

•First report of tracking optical features of MP-DOM in MP-contaminated sandy soil.•Contamination with UV-aged MPs led to enhanced DOM in sand infiltration.•Unique spectroscopic signatures remained stable despite environmental interferences.•DBP precursors in sand infiltration originate from MP contamination in systems.