Sorption and desorption hysteresis of widely applied triazine and phenylurea herbicides were studied for river sediments. Organic carbon normalized sorption coefficient (KOC) values for all herbicides were significantly higher for the sediment from the downstream region of the river vs. the upstream sediment. On the basis of the measured KOC values, the triazine herbicides can be arranged in the following order: terbutryn>terbuthylazine>ametryn>atrazine. Among the phenylurea herbicides, chlorotoluron exhibited higher sorption than isoproturon (K OC values of 137 vs. 60 and 228 vs. 125 L/kg for the upstream and downstream sediments, respectively). Moreover, chlorotoluron exhibited lower desorption potential as compared with isoproturon (apparent hysteresis index values were 0.2-0.3 for chlorotoluron vs. 0.6-0.9 for isoproturon, measured with the upstream sediment). High sorption affinity of chlorotoluron to the sediments is probably due to stronger H-bonding interactions of the herbicide molecules with the sorbents. For both phenylurea herbicides, desorption hysteresis increased with decrease in sorbed amount. This behavior was opposite to the hysteresis trend observed for the triazines. The Cl-triazines (atrazine and terbuthylazine) exhibited higher desorption hysteresis than the S-triazines (ametryn and terbutryn). Therefore, the apparent hysteresis index values calculated for the Cl-triazines were lower than the values of S-triazines (about 0.4 and 0.7, respectively). Based on the relative strength of H-bonding interactions of Cl- and S-triazines with formate anion and on the desorption hysteresis data we suggest a gradient-derived hole-filling sorption mechanism for the triazine herbicides with the river sediments.
Bibliographical noteFunding Information:
This research was supported in part by The Max Deutsch Foundation for Water Research. The authors thank Dr. Baoshan Xing (Dept. of Plant and Soil Sciences, University of Massachusetts) for performing the solid-state 13 C NMR measurements, and Adi Oren, Ziva Hochman and Ya’ara Rimon for their assistance during sediment sampling and sorption–desorption experiments.
- Phenylurea herbicides