STATUS OF PESTICIDES AND DEGRADATION PRODUCTS IN SOIL AFTER CLEAN-UP OF STOCKPILES AND TREATMENT WITH SODIUM HYDROXIDE AT A FORMER STORAGE SITE IN KOROGWE, TANZANIA

Abstract

The status of pesticide residues in soil samples collected from a former storage site one year after clean-up of stockpiles and treatment with NaOH was investigated. The analytes were extracted from samples by pressurized fluid extraction using n-hexane:acetone (75:25) mixture. Clean-up of extracts was conducted by using silica gel and alumina with 3% H2O and the extracts were eluted with hexane:dichloromethane (1:1). Extra clean-up was performed through C18 SPE cartridges using acetonitrile as the eluting solvent. Labelled internal standards were used for identification and quantification. Analysis of the analytes was performed using a high resolution GC–MS. The dominant contaminants detected and their highest concentrations were 4,4'-DDT 423000 mg/kg dw, 2,4'-DDT 56200 mg/kg dw, 4,4'-DDD 41000 mg/kg dw, 2,4'-DDD 1300 mg/kg dw, 4,4'-DDE 30200 mg/kg dw and 2,4'-DDE 3000 mg/kg dw. The concentrations of total DDT ranged from 3 to 560000 mg/kg dw, with an average of 77000 mg/kg dw. Other compounds such as HCHs, pentachlorobenzene, hexachlorobenzene, pentachloroanisole, heptachloroepoxide, aldrin, dieldrin, endosulfan-II and methoxychlor were also detected, but their contamination status was attributed to environmental sources. The results indicated that the vertical movement of the compounds was very slow and that no significant degradation had occurred to the DDT residues in soil, implying risks and concerns for public health and the environment.