We report on the rates of decomposition of a group of N-methylcarbamate (NMC) pesticides (carbaryl, carbofuran and propoxur) under pre-determined tropical field conditions. Rates of decomposition for three NMCs were determined at pH 7.08 and T = 20 °C and pH 7.70 and T = 33 °C respectively, as follows: carbaryl (78 days and 69 days); carbofuran (143 days and 83 days) and propoxur (116 days and 79 days). Investigation on methods for removal of NMCs and their phenolic decomposition products shows that activated charcoal outperforms zeolite, alumina, diatomaceous earth, cellulose and montmorillonite clay in the removal of both NMCs and phenols from aqueous solution. Furthermore, metal complexation studies on the NMCs and phenols showed that Fe (III) forms a complex with isopropoxyphenol (IPP) within which the Fe:IPP ratio is 1:3, indicative of the formation of a metal chelate complex with the formula Fe(IPP)3.
Keywords: N-methylcarbamate pesticides; alkaline hydrolysis; metal chelates; sequestration; tropical aquatic systems.