Residue concentrations of chlorpyrifos in french beans and soil and assessment of dimethoate and chlorpyrifos residue levels in french beans in Nairobi, kenya

Abstract

Residue concentration of applied chlorpyrifos in soil and French beans was determined in green house experiment, the residue levels of chlorpyrifos and dimethoate in French beans sold in Nairobi County were also determined and a survey to identify the most commonly used pesticides and their safety on farmers in Kiambu County was conducted in this study. Controlled and treated experiments were conducted in a green house on soil obtained from Kiambu County, Kenya. Samples from green house, open air markets and supermarkets were soxhlet extracted using organic solvents. Clean up was done using 8 % deactivated alumina and elution achieved by hexane solvent. Detection and quantification of dimethoate and chlorpyrifos was done by gas chromatograph-mass spectrometer (GC-MS). The survey in Kiambu County was achieved by using structured field questionnaires which were distributed to 64 respondents chosen randomly. The half life of chlorpyrifos dissipation was calculated using Langmuir-Hinshelwood kinetic model equation and regression curves were drawn to get the rate constant. Results obtained indicated that chlorpyrifos has a dissipation half-life of 3.05 days in French bean and 7.8 days in soil. Chlorpyrifos residue on the pre-harvest day was 0.05 mg/Kg which is the same as both the EU and Codex MRLs. All the samples analyzed from open air market and super market had below detection limit of both chlorpyrifos and dimethoate residue levels. A survey conducted in Kiambu County showed that fifteen pesticides were identified as commonly used. Out of the fifteen pesticides 7 % are classified as most hazardous according to WHO (2002) classification of pesticides. Farmers identified the following factors which determined the choice of a given pesticide: increased yield, cost effectiveness, suggested by NGOS, suggested by agrochemical dealers, sales agents and suggested by other farmers.Farmers within this region mostly obtained information on proper handling of chemicals from: government agricultural extension workers, non-governmental organizations (NGOS), radio, Agro- chemical industries and dealers. General knowledge among farmers about chemicals risks, safety, and chronic illnesses was low. Activities that increase environmental awareness and safety of pesticides should be initiated by the agrochemical firms, NGOs and both the local and national government. There are major pests problems in Kiambu County and therefore an active pest management programme is necessary to secure the harvest in the region. Results obtained from this study indicate that it’s important to monitor and ascertain the residue levels of pesticides in soil and horticulture. This gives information to be used in surveillance programs for pesticide residue levels in Kenya.