Assessment of organochlorine insecticide residues in cowpea grains and dried yam chips in selected markets in Ile-Ife, Osun State
The study established the presence and determined levels of organochlorine insecticides residues in samples of cowpea grains and dried yam chips sold in wholesale markets in Ile-Ife and ascertained whether the residue levels were above their respective permissible levels; with a view to assess the likely dietary intake of organochlorine insecticide (OC) residues in these food items which are widely consumed by the people of Ile-Ife and its environs, and be able to ascertain the safety of the food items for human consumption. Five (5) samples each of cowpea grains and dried yam chips were collected from randomly selected traders in each of the wholesale markets, making a total of ten samples per food product. All samples were analyzed for residues of organochlorine insecticides to determine the presence and levels of residues in the sampled cowpea grains and dried yam chips using Gas Chromatography with Electron Capture Detector (GC-ECD) after the extraction and cleanup of all samples. Data were analyzed using descriptive statistics, correlation and Principal Component analysis (PCA). The results showed that all the cowpea grains and dried yam chips samples from the two markets contained various sub-group of OCs which included chlorinated benzenes, cyclodienes and dichlorodiphenylethanes. The predominant chlorinated benzene, cyclodiene and dichlorodiphenylethane compounds in cowpea grains from the two markets were γ-BHC (lindane), heptachlor and DDD (a DDT metabolite). Eighty five percent and 90% of OCs detected in cowpea grains sampled from Odo Ogbe and Better Life markets respectively had their mean concentration (mg/kg) greater than the EU-MRLs. While, in the dried yam chips sampled from the two markets, δ-BHC (an isomer of γ-BHC) was predominant. The predominance of two cyclodiene compounds, heptachlor (0.264 ± 0.038 mg/kg) and aldrin (1.050 ± 0.908 mg/kg), were observed in the dried yam chip samples from Odo Ogbe and Better Life markets respectively. Methoxychlor (0.039 ± 0.006 mg/kg) and DDD (0.141 ± 0.038 mg/kg) were the predominant dichlorodiphenylethane compounds in the dried yam chip samples from Odo Ogbe and Better Life markets respectively. Seventy five percent and 95% of OCs detected in dried yam chip samples from Odo Ogbe and Better Life markets respectively had their mean concentrations (mg/kg) above the EU-MRLs. The results also revealed that a strong correlation existed among a number of OC insecticide residues suggesting a common origin. Principal Component Analysis (PCA) results of cowpea grain samples from Odo Ogbe and Better Life markets accounted for 10 and 8 OCs respectively, causing variation in the 20 OCs detected; while the results of the dried yam chips from Odo Ogbe and Better Life markets accounted for 9 and 6 OCs respectively, responsible for the variations in the 20 OCs detected. The study concluded that Better Life market in general, recorded higher OC residues in the foodstuff samples than in those from Odo Ogbe market; and that levels of OC insecticide residues in cowpea grains and dried yam chips sampled from the two markets were generally above the EU-MRLs, suggesting that the foodstuffs were not safe for human consumption.