Surfactant-enhanced desorption of atrazine and linuron residues as affected by aging of herbicides in soil

In the present work, we studied the efficiency of two surfactants, one anionic (SDS) and other non-ionic (Triton X-100), in the desorption of atrazine and linuron after 0, 3, and 9 months of soil-herbicide aging time. Batch desorption studies were conducted in soil-water and in soil-water-surfactant systems. The kinetic pattern of desorption was biphasic, a slow desorption following an initial fast phase. Both phases followed first-order kinetics. The desorption rate of the first phase (KI) was very low in water for both herbicides and always increased in the presence of surfactants. At zero time, KI increased 9- and 8-fold (atrazine), and 24- and 17-fold (linuron) in the presence of the two surfactants, respectively. Desorption rates decreased with the increase in the aging time in all three desorption systems. After 9 months of soil-herbicide aging time, DT25 for linuron was 6.85 h (SDS) and 41.7 h (Triton X-100) and for the atrazine it was only possible determine in SDS solution (17.2h). The amount of desorbed herbicide in the different systems varied from 35.6-12.5% (water), 87.9-46.2% (SDS), and 63.2-18.0% (Triton X-100) for atrazine and 8.02-3.94% (water), 69.9-41.3% (SDS), and 58.1-34.8% (Triton X-100) for linuron. The ratio of amount desorbed in surfactant solution and in water for the different aging times of the herbicides was greater for the desorption of linuron than that of atrazine. For both herbicides, it was always greater with SDS than with Triton X-100, and was higher when desorption of the residues aged for 9 months was carried out. The results indicate the interest of surfactants for increasing the desorption of atrazine and linuron from soils polluted with these compounds after a long aging time in the soil. Therefore, they indicate the possibility to use the pump-and-treat remediation technique for pesticides in soils with a long history of pollution. The enhanced desorption achieved will be governed by the hvdrophobic character of the herbicide, the nature of the surfactant used, the aging time, and the characteristics of soils.