WP6 Sediment Chemistry
Room 18A/B, Level 4
2:10 PM - 5:30 PM, Wednesday, 12 November 2003
Chair: van Metre, Peter ,
(456) The Influence of Clay Minerals and Soil Organic Matters on the Hydrolysis of 
-Endosulfan.
Hengpraprom, Sarunya1, Lee, Cindy1, Coates, John1, 1 Clemson University, Anderson, SC, USA
ABSTRACT- Organic matter is a significant contributor for adsorption of pesticides in soil; however, in some cases mineral surfaces may play an important role in the retention of these compounds. Numerous studies have also reported the ability of mineral surfaces to catalyze hydrolytic reactions. Therefore, in an effort to better understand the hydrolysis of -endosulfan in solid matrices, adsorption of -endosulfan by mineral surfaces needs to be investigated. Using batch experiments, the influences of clay minerals (kaolinite and montmorillonite) on the sorption and hydrolysis of -endosulfan were studied. The experiments were conducted at pH 8 and 2 temperatures (25 and 45oC). The samples were equilibrated (end over end) in the dark up to 48 hours. Supernatants and pellets were extracted to determine the concentration of -endosulfan at each sampling time. The Freundlich sorption coefficient, Kf, determined from isotherms with clays demonstrated a greater sorption of -endosulfan on montmorillonite than kaolinite. The greater sorptive capacity of montmorillonite is likely due to its 2:1 layer structure and higher surface area. Compared to the homogeneous system, the formation of the hydrolysis-byproduct, endosulfan-diol, was less in the system containing kaolinite and water than in water only, indicating that kaolinite inhibited the overall rate of hydrolysis of -endosulfan. In contrast, in the system containing montmorillonite, the formation of the endosulfan-diol was greater than in the system containing water only, indicating that montmorillonite enhanced the overall rate of hydrolysis. The presence of soil organic matter suspensions appeared to reduce the catalytic activity of montmorillonite and delay the overall rate of degradation of -endosulfan.
Key words: Clay minerals, -endosulfan, HYdrolysis, Adsorption