Surface-catalyzed transformations of aqueous endosulfan.

Area of Science:

• Environmental Chemistry
• Environmental Science
• Chemical Kinetics

Background:

• Endosulfan is a widely used insecticide with alpha and beta isomers.
• Its degradation products include endosulfan diol, sulfate, ether, and lactone.
• Understanding degradation pathways is crucial for environmental risk assessment.

Purpose of the Study:

• To investigate the impact of various suspended solids on endosulfan hydrolysis and oxidation.
• To determine the kinetics of endosulfan hydrolysis in the presence of different surfaces.
• To elucidate the mechanism of surface-catalyzed endosulfan hydrolysis.

Main Methods:

• Experiments conducted in a 0.001 M NaHCO3 buffer at pH 8.15.
• Tested suspensions of sea sand, TiO2, alpha-Fe2O3, alpha-FeOOH, Laponite, and SiO2.
• Measured heterogeneous and homogeneous rate constants for endosulfan hydrolysis.
• Employed ab initio molecular orbital calculations (STO-6G) to study transition states.

Main Results:

• Most tested suspended solids (sea sand, TiO2, alpha-Fe2O3, alpha-FeOOH, Laponite, SiO2) catalyzed endosulfan hydrolysis to endosulfan diol.
• Suspended creek sediment significantly inhibited endosulfan hydrolysis.
• Beta-endosulfan hydrolyzed faster than alpha-endosulfan, attributed to a more stable transition state.
• Hydrolysis rates correlated with the tritium-exchange site density of the surfaces.
• Oxidation of endosulfan to endosulfan sulfate was not observed.

Conclusions:

• Surface properties of suspended solids play a critical role in the fate of endosulfan in aquatic environments.
• The mechanism likely involves surface coordination followed by nucleophilic attack.
• Further research is needed to understand the inhibitory effect of organic-rich sediments.