Adsorption, desorption and degradation of α‐endosulfan in tropical soils of Thailand

Abstract

The adsorption, desorption, and degradation of endosulfan (1,2,3,4,7,7‐hexachlorobicyclo[2,2,l]‐2‐heptene‐5,6‐bisoxymethylene sulfite) in two major tropical soils from Thailand were studied. Each soil‐type, Rangsit lowland soils (Rangsit series) and Phrabat upland soils (Pakchong series), were sub‐divided into surface or plow layer, 0–20 cm depth, and subsoils, 20–40 cm depth. Adsorption was determined using 24 h batch equilibrium, with five different concentrations of ¹⁴C labelled endosulfan ranging from 1.04 to 16.64 ng/mg soils. Adsorption coefficient values (K_ads) as by Freundlich's model ranged from 0.02 to 0.20. Higher adsorption coefficients were measured in Rangsit soils as compared to Phrabat soils. Desorption as attributed to hysteresis was also measured. Desorption coefficient values (Kj_es) were higher than adsorption (K_ads) in each study. Degradation of endosulfan was through microbial process. Little abiotic degradation was measured in sterile soil sample. Measured degradation rates were highest in Phrabat plow layer and subsoil. However, total degradation after 98 days was less than 20 % of initial application rate. Results indicate that applied endosulfan would be persistent or slow to degrade in the soils studied.

Key words:

• α‐endosulfan
• tropical soils
• adsorption
• desorption
• degradation
• pesticide

Notes

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