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Background: 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. Objective: 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. Methods: 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. Results: 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. Conclusion: 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.

The Owena River Basin in Nigeria is an area of agricultural importance for the production of cocoa. To optimise crop yield, the cocoa trees require spraying with neonicotinoid insecticides (Imidacloprid, Thiacloprid Acetamiprid and Thiamethoxam). It is proposed that rainwater runoff from the treated area may pollute the Owena River and that these pesticides may thereby enter the human food chain via six species of fish (Clariasgariepinus, Clariasanguillaris, Sarotherodongalilaeus, Parachannaobscura, Oreochromisniloticus and Gymnarchusniloticus) which are cultured in the river mostly for local consumption. This work aims to establish a working method to quantify the likely levels of the insecticides in the six species of fish, firstly by undertaking a laboratory-based study employing the QuEChERS method to extract the four neonicotinoids from fish purchased in marketplace in the UK, spiked with known quantities of the pesticide and using liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS) as the detection method; secondly, by using these samples to optimise the detection method for very low levels of pesticides, then applying the optimised techniques to the analysis of three of each six species of fish taken from the Owena River. A significant benefit of this combined technique is that only small samples of fish are required. Success with this part of the study showed that very low concentrations of the insecticides could be detected in fish muscle. The third aim is to apply a simple quantitative risk assessment model using the data sets obtained, together with information about daily diet, human body weight and recommended safety limits of pesticides in food to illustrate how human health may be affected by the consumption of these fish. The multiple determinations of neonicotinoids in edible fishes in Nigeria are pioneer research and fill a gap in addressing the relationship between waterborne pesticides and food quality in the country. Fundamentally, this work is an exercise to demonstrate the applicability of the aforementioned instrumental method of analysis to fish muscle, which requires only a small sample size of fish; a large number of fish is not required for a proof of concept, in this case. Although not a monitoring programme for the whole Owena River Basin ecosystem per se, this work successfully demonstrates the technical feasibility of a system of chemical analysis and establishes the foundation for ecological surveys in the immediate future. Parameters involving exposures to xenobiotics in ecotoxicological modelling can now be expressed in terms of both mass and molar concentrations of a chemical in animal tissues if so desired.

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