Characterization of atrazine removal from stormwater runoff in bioretention cells with different modified fillers

Atrazine and its toxic degradation product, deethylatrazine, enter water bodies through surface runoff and leaching. They pose potential threats to aquatic ecosystems and human health. Therefore, it is crucial to reduce the impacts of atrazine and deethylatrazine on water environments by implementing source-control measures for stormwater runoff. This study constructed slag-modified loess-based bioretention cells (SC group) and zeolite-modified loess-based bioretention cells (ZC group) to examine the effects of drought periods and influent atrazine concentrations. Results showed that the SC group achieved significantly higher atrazine removal efficiencies (96.0%-98.4%) than the ZC group (89.9%-95.1%). Prolonged drought periods had opposite effects: effluent atrazine concentrations decreased in the SC group (22.2-1.2 µg/L) and increased in the ZC group (16.8-158.2 µg/L). When influent concentration increased from 10 to 100 µg/L, removal efficiency in the SC group decreased from 97.2% to 77.8%, while in the ZC group, it increased from 42.6% to 84.2%. Effluent atrazine concentrations from the SC group (0.3-67.9 µg/L) were consistently lower than those from the ZC group (2.5-99.5 µg/L) at all depths. The highest concentrations of atrazine and deethylatrazine in the effluent, as well as the greatest accumulation of atrazine in the filler, occurred in the upper layer (0-10 cm). This study clarifies the removal efficiency and transport characteristics of atrazine in bioretention cells with different fillers during drying-wetting cycles, offering practical guidance for optimizing the systems.