Adsorption/desorption and mobility of carbofuran in soil samples from Kenya.

Abstract

Carbofuran (2,3-dihydro-2-2-dimethyl-7-benzofuranyl-Nmethylcarbamate) is a very effective systemic and contact insecticide and nematicide used against a wide range of agricultural pests (Aquino and Pathak, 1976; Caro et al., 1973). Though less persistent than most organochlorine pesticides, carbofuran is more toxic to animals, it is very soluble in water and tends to degrade faster under flooded soil conditions (Caro et al., 1973; Venkateswarlu et al., 1977; El-Zorgani et al., 1980). The adsorption and desorption characteristics which determine the movement of pesticides through the soil profile, their bioavailabiltiy, microbial degradability and persistence depend upon the soil properties such as organic matter content, clay content and the physical/chemical properties of the pesticide i.e. size, shape, solubility in water, pK values and polarity (Wondimagegnehu and Foy, 1986; Calderbank, 1989). In Kenya, carbofuran is used extensively against rice pests in paddy fields and because of its acute toxicity the fate of its residues in terms of their persistence and mobility is of great concern (Anonymous, 1985; Plimmer, 1980). The aim of this study was to investigate the adsorption/desorption and mobility of carbofuran in samples of soil collected from the Ahero and Chiromo areas of Kenya. MATERIALS AND METHODS The two soils used in this study were collected from two different agricultural regions of Kenya i.e. the lowland heavy, sandy soils of the Kano Plains at Ahero and the red, silt loam soils from Chiromo in Nairobi. A third soil was a standard sandy soil obtained from the Institute of Ecological Chemistry, GSF, Munich. The composition and physical characteristics of the three soils are presented in Table 1. The soil samples were air-dried in the laboratory, ground with mortar and pestle and sieved through a 2 mm mesh.