Monitoring of carbofuran residues in Laikipia and Isiolo districts in Kenya for ecological risk Assessment

Abstract

Granular carbofuran which was widely used to control agricultural pests in Isiolo and Laikipia districts was also misused by local farmers and pastoralists to kill predators leading to massive deaths of Gyps vultures through secondary pois,oning. In support of conservation efforts, this study was conducted to monitor carbofuran usage and its environmental contamination in the two districts and to establish potential routes of exposure to Gyps vultures' species. A survey was conducted to establish the level of carbofuran use and misuse by administering questionnaires to the farmers, pastoralists and the conservationists. Soil, water and zea mays leaves samples from selected farms as well as lion carcass and vulture tissues were solvent extracted and residues analysed by HPLC and confirmed by GC-MS. Survey data which was analysed by SPSS statistical package indicated that 67.5% of the farmers use carbamate pesticides and 16.8% of the respondents reported that carbofuran was intentionally used as a poison to kill predators. The residues analysis results were subjected to MST AT (ANOV A) statistical package and the mean concentration of 3-ketocarbofuran and 3-hydroxycarbofuran were found to be 0.199 ::l.~0.016and 0.087 ± 0.019 ppm, respectively, in vulture's crop content indicating carbofuran exposure. The vultures' feet and beak samples contained mean concentration ranges of 0.025-0.04 ppm (carbofuran), 0.185-0.0.24 ppm (3-keto-carbofuran), 0.59- 0.0.73 ppm (3-hydroxycarbofuran). The mean concentration of the residues of carbofuran, 3-ketocarbofuran and 3-hydroxycarbofuran found in plant samples ranged from 0.099-0.269, 0.145-0.641 and 0.196-0.499 ppm respectively in the study area The water samples contained mean concentrations of carbofuran, 3-ketocarbofuran and 3- hydroxycarbofuran in the ranges of 0.011-0.592, 0.068-0.525 and 0.118-0.0.646 ppm in Isiolo and Laikipia respectively, while dried soil sample mean concentrations ranged between 0.146-0.179, 0.484-0.313 and 0.433-0.694 ppm respectively in both districts. There was significant regional and seasonal variation in mean levels of residue in plants, water and soil sample taken in the wet and dry seasons with higher mean concentration recorded in wet season for carbofuran. .The levels showed extensive environmental 'contamination of the farms, rivers and plants around the conservancies. These mean levels of carbofuran residues obtained in the environmental matrices do not confirm them as potential routes of exposure but indicate the usage as well as level of contamination. Levels of residues in lion tissue demonstrate exposure before death and could possibly be the cause of death. Data gathered forms a basis to create awareness about toxicity of carbofuran and discourage its misuse.