Analysis and quantification of the levels of insecticide residues in maize sold in South Eastern Nigeria

Abstract

Pesticides are important in reducing losses caused due to insect pest both in the field and storage but the dangers associated with its use including problem of residues is of serious public health concern. Maize grains treated with insecticide in order to prevent insect pest attack are healthy and safe for consumption if the active ingredients of such insecticides are within the maximum residue level (MRLs) set by regulatory bodies. Assessing the contamination of cereals and their manufactured products with pesticide residues is a topic of global importance, and monitoring studies are needed to analyse residues at trace levels. This study investigated the levels of insecticide residues in maize sold in South East Nigeria. Maize grains presumed to be treated with insecticides were collected from four different maize sellers each from five major markets across the South East to analyse and quantify the level of presence or absence of residues on the samples. The maize samples were sorted out by removing stones and other unwanted material from the samples. 30.0g of each sample was grinded into smaller particles to produce a uniform sample maize powder. Extraction was performed according to the methods of Sharif et al. (2006). The milled samples of maize were properly mixed and 2.0g was weighed into a 20.0ml sample vial. Anhydrous sodium sulphate (1.0g) was added and mixed with the sample to absorb any moisture present. The sodium sulphate was previously heated at 650⁰C for one hour and stored in a desiccator. Ethyl acetate (10.0ml) was added to the vial. The mixture was vortex mixed for 5 minutes and then allowed to stand for 45 minutes. It was mixed again and centrifuged for 5 minutes at 2500rpm. The supernatant was carefully transferred into a flask. The residue was further extracted twice as described above, using 10.0 ml ethyl acetate each time. The supernatants were combined and reduced to about 1ml under a gentle stream of nitrogen gas at 36⁰C. For the clean-up, solid phase extraction cartridges (florisil, 500mg/6ml) were used. The analysis of maize samples for pesticide compounds was performed on a Gas Chromatography –Mass Spectrometry (GC-MS), an auto sampler and a split-splitless injector. Among the pesticide compounds analysed for residue in maize grains in Enugu, Abia, Imo, Anambra and Ebonyi State respectively, lindane (0.06,0.13,0.05,0.05,0.05mg/kg) (organochlorine), dichlorvos (0.36, 1.09,0.51,0.51 and 0.53mg/kg) (organophosphate) and carbofuran (0.23mg/kg) (carbamate) absent in Enugu, exceeded their maximum residue levels (MRL) of 0.02, 0.1and 0.05mg/kg respectively set by pesticide regulatory bodies. The result shows that occurrence of pesticide residues (dichlorvos, lindane and carbofuran) in the maize samples which exceeded its MRLs could be considered serious threats to human health. An investigation into continuous monitoring and stringent regulation of pesticide residues not only limited to maize grains but also on other food and products are recommended.