Gradient of suspended particulate matter hastens the multi-interface partition dynamics of atrazine and its...

Herbicides are ubiquitous pollutants in estuaries because of the increased demand for food and the need for intensive agricultural systems worldwide. Multi-interface partitioning processes are inadequate for the degradation products of herbicides, especially in sediment-laden river estuaries with intensive water and sediment partitioning. Therefore, the partition characteristics of atrazine and its degradation products at the surface water-suspended particulate matter (SPM), surface water-surface sediment, and SPM-surface sediment interfaces in a typical sediment-laden river estuary were analyzed, the dominant environmental factors were described, and the related mechanisms were explored. The results showed that the partitioning priority of atrazine and its degradation products was surface water > SPM > surface sediment. The partition coefficients of these three interfaces were significantly correlated. The primary degradation products and desisopropylhydroxyatrazine tended to partition into the SPM, and desethyldesisopropylatrazine tended to partition into the surface sediment. Canonical analysis and structural equation modeling indicated that temperature, salinity, sediment pH, and SPM concentrations were the main influencing factors. In the sediment-laden river estuary, the SPM concentration was the most dominant factor. The partition coefficients increased exponentially when the SPM concentration was <150 mg/L at the SPM-surface sediment interface, leading to a rapid shift in the interface proportion of atrazine and its degradation products. In the context of climate change and human activities, the SPM concentration in the estuary was decreasing, which hastened the release potential for atrazine and its degradation products from the estuarine sediment. The investigation of the partition traits of organic degradation pollutants promotes the understanding of the multi-interface transport processes in estuaries.