Sorption characteristics and contribution of organic matter fractions for atrazine in soil

Purpose Atrazine, as one of most widely applied herbicides in the world, caused significant concern due to long-term threat to the environment and risk for human health. Soil organic matter (SOM) is considered as one of the most important soil component controlling the transport and fate of contaminants in soil/water environments. Therefore, it is important to explore the sorption characteristic as well as distribution of atrazine among different SOM fractions in their respective soils. Materials and methods To further our understanding in this area, various SOM fractions (humic acid1 (HA1), humic acid2 (HA2), humin (HM)) were sequentially extracted using Na 4 P 2 O 7 and NaOH from two kinds of agricultural soils, and batch sorption experiments for atrazine onto extracted SOM fractions were examined. Results and discussion Atrazine sorption isotherms were nearly linear and were well-fitted to the Freundlich equation with nonlinearity factors ( n ) ranging from 0.887 to 0.977. The sorption capacity of atrazine by the extracted SOM fractions followed the order HA1 > HA2 > HM, and the organic carbon normalized distribution coefficients (log K OC ) were significantly related to (N + O)/C ratios of the extracted SOM fractions, demonstrating that the polarity of SOM fractions dominates atrazine sorption by polar interaction (e.g., H bonding). The relative contributions of different SOM fractions to the overall sorption of atrazine depend on their sorption capacities of atrazine and relative contents in the SOM, and the combined contribution of HA fractions in their respective soils was higher than that of HM although their lower content in SOM. Conclusions The results in this study indicated the important roles of SOM polarity and the HA fractions in the sorption of atrazine by the investigated soils.