Sorption and resistant desorption of atrazine in typical Chinese soils.

Atrazine is one of the most commonly used herbicides and is produced and used in large quantity worldwide. In the present study, the sorption and desorption of atrazine in five typical Chinese soils were examined. The sorption of atrazine followed the conventional linear isotherm reasonably well, indicating that sorption was driven largely by hydrophobic partitioning into soil organic matter. However, strong resistant desorption (desorption hysteresis) was observed for all five soils. The desorption data could be well modeled with several biphasic sorption/desorption isotherms that include a quasi-Langmuir or a Freundlich term to account for the nonlinear sorptive property associated with the desorption-resistant fraction. Experimental observations in the present study are consistent with studies reported in the literature and with our previous work with other hydrophobic organic compounds and different sorbents. These observations suggest that physical entrapment within porous soil matrix was likely the predominant mechanism controlling the observed desorption resistance. The unique characteristics associated with the resistant-desorption fraction have important implications for risk assessment of atrazine-contaminated soil/sediment and should be taken into account in the regulation, management, and remediation of atrazine-contaminated sites.