Exposure assessment to pesticide residues and trace metals related to the consumption of imported onions (Allium cepa) in Senegal

In Senegal, the onion is one of the most consumed vegetables because it is used in all salty culinary preparations. The objective of the study was to assess the contribution of imported onions to exposure to pesticide residues and metallic trace elements. Composite samples of onions were taken in the seven largest markets of Dakar: Thiaroye, Keur Massar, Castors, Cambérene, Rufisque, Tilène and Dalifort. The metallic trace elements were determined by the ICP-AES, type Agilent Technology serial number AU 14110053 of 2014, while pesticide residues were detected and quantified by gas chromatograph, type Agilent Technology 6890A serial CN10721019, equipped with an Electron Capture micro-Detector with serial number 022423. The average content of the composite samples in lead (Pb) (778.22 µg/kg) was 7 to 8 times higher, in cadmium (Cd) (12.43 µg/kg) 5 times lower than the maximum residue limits determined by the European Union and the Codex Alimentarius, while the average concentration of aluminum (Al) was 13570 µg/kg. Twenty four (24) pesticide residues were tested. The average concentrations of some pesticides banned in European Union (EU) exceeded the maximum limits set by them. In fact, they are more than hundred (100) times higher for Prophenophos (2088.16 µg/kg), 25 times for Fenthion (508.01 ppb), 7 times for Tetramethrin (72.56 µg/kg), 2.5 times for Parathion methyl (50.16 ppb), 2 times for Dichlorvos (19.12 µg/kg), and 1.4 times for Endrin (14.26 µg/kg). The Dimetoate and the Malathion, although authorized, were found in onions at concentrations 25 times (250.8 µg/kg) and 2 times (40.71 µg/kg), respectively higher than the maximum limits set by the EU. Only the average content of Chlorpyrophos (4.13 µg/kg), Bifenthrin (2.99 µg/kg), Lambda Cyhalothrin (7.30 µg/kg) and Cypermethrin (8.095 ppb) were in accordance with the EU regulations. The results of the exposure assessment reveals that the calculated daily consumption of 0.158 kg of these onion samples by a 60 kg average body weight Senegalese adult would provide 56% of the Toxicological Reference Value for lead, 25% for aluminum, 66% for Dimetoate, 63% for Dichlorvos, 28% for Dieldrin, 19% for Fenthion, 18% for Endrin and Prophenophos and 13% for Parathion-methyl. This study reveals that the imported onion contributes to the exposure of the Senegalese adult to eight (8) phytosanitary active substances and three (3) metallic trace elements. Thus, the health risk cannot be ruled out and it is important to set up a monitoring plan for the imported onion.