Sustainability in Environment ISSN 2470-637X (Print) ISSN 2470-6388 (Online) Vol. 8, No. 4, 2023 www.scholink.org/ojs/index.php/se 1 Original Paper Concentrations of Pesticides Residues in Grain Sold at Selected Markets of Southwest Nigeria Modupe Abeke Oshatunberu 1* , Adebayo Oladimeji 2 , Sawyerr Olawale Henry 1 , Opasola Afolabi Olaniyan 1 & Morufu Olalekan Raimi 1&3 1 Department of Environmental Health, Faculty of Pure and Applied Science, Kwara State University, Malete, Kwara State. Nigeria 2 Department of Zoology, Faculty of Pure and Applied Science, Kwara State University, Malete, Kwara State. Nigeria 3 Department of Environmental Management and Toxicology, Federal University Otuoke. Bayelsa State, Nigeria Received: March 22, 2023 Accepted: August 16, 2023 Online Published: September 02, 2023 doi:10.22158/se.v8n4p1 URL: http://dx.doi.org/10.22158/se.v8n4p1 Abstract The objective of this work is to determine the concentration of the identified pesticide in grains commonly used by farmers, and which are available directly from the open markets in the Nigerian market. The research was carried out at Kwara State University (Kwara State) and Afe Babalola University (Ekiti State) research laboratory. A total of twenty-four (24) samples were collected in the frame of this preliminary study within the month of August and September 2021. Pesticide residues were quantified through a multiresidue method using a varian 3800/4000 Gas Chromatograph Mass Spectrometer (GC/MS). The simultaneous measurement of four classes of pesticides by gas chromatography-mass spectrometry (GC/MS) approach using sample preparation on QuEChERS-citrate, was developed and validated. The results frequently showed high specific contamination, which makes sense given the target market and dietary diversity in the area. This study found that grains purchased from particular markets in southwest Nigeria contained numerous pesticide residues. The MRLs set by the EU or FAO/WHO or both were surpassed by 17 out of the total 27 pesticides reported in this work in at least one grain, despite the fact that there was no published codex MRLs for some pesticide residues in some grains. These residues were classified among the four pesticides classes: carbamates, organophosphates, organochlorines, and pyrethroids. In actuality, 90% of the mainly banned organochlorine pesticides exceeded MRLs. Thus, this study revealed higher concentration levels of organo-chloride pesticides and organo-phosphate pesticides in grain samples