Evaluating farmers knowledge in pesticide handling and determining pesticides levels in maize after various processing methods and different storage conditions
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Post-harvest pesticides applied to consumable foodstuffs usually pose a serious but silent threat to human and livestock health. Some pesticides accumulate slowly in various strata of the ecosystem causing irreparable damage to the environment and wildlife. In Kenya huge quantities of these pesticides are used to preserve maize grains during storage. The amount of pesticide residues consumed through maize grains and its products depend on ambient storage conditions of grains, the nature of the active compound of particular pesticide and the processing technique of the grains before consuming. The purpose of this study was to investigate the effects of ambient storage conditions on the concentrations of pesticide residues in post-harvest maize grains and to evaluate the extent to which the consumer is exposed to these pesticides. The research involved a field survey that assessed the knowledge, attitudes and practices of the community regarding the safe use of pesticides (occupational exposure). The study also analyzed the residual concentrations of pesticides in stored maize grains and some of its processed products (milling fractions) such as white flour and whole meal flour. Gas chromatographic method using flame ionization detector (FID) was used for quantization of pesticide residues of two organophosphates (malathion, piriminiphosmethyl) and one synthetic pyrethroid (permethrin) in maize grains and its milling fractions. Three parameters were measured: level of pesticides in two maize milling fractions (whole meal and white flour) and level of pesticide residue that remained on maize grains after various cleaning processes (hulling, waterwash, detergent wash), extent of health risks associated with consuming maize grains and flour treated with pesticides (dietary exposures) and persistence of pesticide residues in maize grains stored under simulated storage conditions (temperature, light and relative humidity). The maize grains samples for the simulated storage were initially treated with 0.3mgkg -I permethrin, 3.9mgkg -1, pirimiphosmethyl and 3.92mgkg-1 malathion prior to storage and portions analysed at regular intervals for the pesticide residues. Data was analysed by SPSS and Genstat version 6.1 computer software. Field survey information indicated that more than 95% of farmers in Chilchila do not practice safety precautions during pesticide formulation and application. After six months of simulated storage, at ambient temperatures averaging 22 c and 55% RH the level of the initial residues that persisted on the maize grains was 63.3% permethrin, 64% pirimiphosmethyl and 56% malathion. The rates of dissipation of the pesticide from the maize grains decreased with storage time and followed a biphasic pattern for all storage conditions. Applying first order reaction kinetics, the following halflifes were obtained at the ambient storage conditions of the study area: maize grains treated with permethrin had 130 days; maize grains treated with pirimiphosmethyl had 77 days and the maize grains treated with malathion had 30 days. This trend was repeated for all the other storage conditions, giving a persistence order of permethrin followed by pirimiphosmethyl then malathion. Mean residue concentrations in whole meal were 1.7 mgkgl, 1.3mgkg-1 and 0.16mgkg-1 for pirimiphosmethyl, malathion and permethrin respectively. All these residue levels were above the ADI level for each pesticide. Results for white flour indicated mean residue levels of 0.54mgkg -1, for pinmiphosmethyl, 0.53 mgkg-1, for malathion and 0.06 mgkg -1 for permethrin, while hazard index analysis for maize grains, whole meal and white flour gave values greater than one for malathion and pirimiphosmethyl. The hazard index analysis was less than one for permethrin. These two observations meant that, the organophosphate pesticides (malathion and pirimiphosmethyl) occurred at levels risky to human consumption in all food products analysed while the pyrethroid pesticide (permethrin) occurred at a safe level for human consumption.