Characterisation of Neonicotinoid Insecticides in the Cocoa-producing Owena River Basin of Nigeria by a QuEChERS Method Coupled to Liquid Chromatography-Tandem Mass Spectrometry

Neonicotinoids (hereafter called “neonics”) are systemic insecticides used for the protection of agricultural crops. However, their dispersion in nature has been the subject of global concern due to reports of adverse effects on some living organisms. One of the applications of neonics in Nigeria is to protect the cocoa cash crop.

Previous studies on pesticide-related pollution in Nigeria focused mainly on organochlorines, but research on neonics is sparse, and the knowledge gap needs to be filled. This work aimed at confirming the presence of four neonics, namely, imidacloprid, thiacloprid, acetamiprid, and thiamethoxam, within the Owena River Basin.

Neonics were extracted from cocoa-growing soil, river water, and sediments by a modified QuEChERS method, followed by clean-up of the extractant by dispersive solid phase extraction and analysis by an optimized liquid chromatography/tandem mass spectrometry analytical procedure. The overall performance of these developed methods was then evaluated by set criteria.

The Limit of Detection (LOD) and Limit of Quantitation (LOQ) ranged from 0.0005 to 0.002 μg/g and 0.002 to 0.005 μg/g, respectively. The recovery for the four target analytes exceeded 75% across all matrices from laboratory-prepared samples. It was discovered that the average concentrations of three of the four neonics of interest in the individual media were: 10.34 nmol/g in cocoa-producing soil, 1.03 nmol/g in river sediment, and 1.08 nM (1.08 x 10^-3 nmol/g) in surface river water. No imidacloprid was identified in any of these three environmental compartments.

The concentration of neonics in the river water, i.e., 0.23 µg/L (230 ng/L), is identical to that of the maximum value recommended in the Canadian Water Quality Guidelines for the Protection of Freshwater Aquatic Life.