Analysis of Pesticide Residues in Maize and Beans Types in Lagos Markets

Ogah, C. O. (2008)

Thesis

Pesticides used in agriculture for the control of various pests often leave residues in foodstuffs and these have been shown to pose health hazards. Analysis of pesticide residues in food is one way to determine the level of human exposure to these chemicals and hence their potential human health hazards. Maize (Zea mays L.) and beans (Phaseolus vulgaris L.) samples purchased from different markets in Lagos State were analyzed for residues of organochlorine, organophosphate and carbamate pesticides. Analysis was done using gas chromatograph with mass spectrometric detector (GC-MS) after careful extraction and cleanup. Most of the maize samples (96%) were found to contain residues of one or more pesticides with concentrations ranging from 2.2-3951.0 μg/kg. The white types of maize contained higher concentrations of residues than the yellow types. Three classes of pesticides were detected in maize. All the samples of beans analyzed contained at least one pesticide residue (100% incidence). White beans were found to contain higher concentrations of residues than the brown types. The concentrations of organochlorine, organophosphate and carbamate pesticides residues in beans ranged from 2.3-1480.5μg/kg. The most commonly found residue among both maize and beans samples was the organophosphate, pirimiphos-methyl. Its percent occurrence was 43 in maize and 54 in beans. There was a decline in the mean levels of organochlorine pesticides in both maize (6.9-41.3μg/kg) and beans (4.8-39.7μg/kg) compared to the results of a previous similar study (10.0-93.0μg/kg for maize and 25.0-303.0μg/kg for beans). Maximum residue limits (MRLs) of the various pesticides were exceeded in up to 10% of samples of both maize and beans. The incidence of pesticide residues in maize and beans was found to be higher in some markets than others but mean concentrations were not different from market to market. The pesticide residue contents were decreased by boiling. Percent reduction ranged from 9 to 100. The extent of reduction was higher in the organophosphates (24-100%) and carbamates (20-100%) than in the organochlorines (9- 32%). The estimated total diet intakes (ETDIs) for most of the pesticides were well below their maximum permissible intakes (MPIs). On the other hand, the ETDIs for aldrin, dichlorvos and dieldrin exceeded their MPIs by 100%, 363% and 17% respectively. Conclusively, most of the maize and beans in Lagos markets contain pesticide residues at different levels and maximum residue limits were exceeded in about 10% of samples. There is therefore a need for more stringent monitoring of the use of pesticides in agriculture and food storage in Nigeria.

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