The researchers studied floodplain soils along Germany’s Lahn River and found that quaternary ammonium compounds (QACs)—common disinfectants—have accumulated in the soil for over a century. These chemicals likely entered the soil through floods, attached to suspended particles and microplastics. Some concentrations exceeded levels considered harmful to ecosystems. The study highlights that QACs are persistent pollutants and may pose long-term environmental risks in floodplain areas.