Quantification of Pesticide Residues in Retail Samples of Cowpea - Vigna unguiculata (L.) Walp

Abstract

Quantification of pesticide residues in retail samples of food is one way to determine the level of human exposure to these chemicals and hence their potential health hazards. The study was aimed at quantifying the level of some known pesticides in retail samples of Vigna unguiculata (L.) Walp. (Cowpea) from two cropping seasons. Five cultivars of cowpea from two different harvest seasons (2016/2017 and 2017/2018) were purchased from Ogige Market, Nsukka, Enugu State, Nigeria. The cowpeas were identified based on city/state where they were cultivated. Two foreign samples were also purchased from London, UK. The pesticide residues were determined using gas chromatography coupled with electron capturing detector (GC-ECD). The results showed that the retail samples of cowpea contained residues of one or more organochlorines and organophosphates. The levels of post-harvest pesticides, 2, 2-dichlorovinyl dimethyl phosphate (DDVP) in 2016/17 season (0.02 μg/g) exceeded the international permissible standards (0.01 μg/g). The levels of the pre-harvest pesticides, glyphosate was low in both seasons (0.01 μg/g) when compared to the international permissible standards (0.1 μg/g).  The DDVP was not detected in the two foreign samples. HCB (Hexachlorobenzene), α-HCH (alpha-Hexachlorocyclohexane), Chlorpyrifos, g-chlordane, t-nonachlor, p-p’-DDT (Dichlorodiphenyltrichloroethane), p-p’-DDE (Dichlorodiphenyldichlo-rowthylene), and p-p’-DDD (Dichlorodiphenyldichloroethane) were detected in the cowpea from two cropping seasons despite being banned from agricultural use. This could be due to the additional application of pesticides during storage of the cowpeas. The findings concludes that the levels of some of the residues exceeded the safety limits while some were below the safety limits, suggesting that some of samples of the cowpea were not safe for human consumption as bioaccumulation, persistence, and toxicity of these residues was likely to pose serious health risks to the consumers. Generally, cowpea from the 2016/17 season contained higher pesticide residues than those from the 2017/18 season.