Neonicotinoids are among the most widely used pesticides in the world and imidacloprid, the first registered neonicotinoid, has been applied through seed coatings, sprays, soil drenches, and granules. Imidacloprid is transported from its point of application and has been detected in waters, soils, plants, and animal tissues. Furthermore, animals have been observed directly consuming seeds coated with imidacloprid, raising concern for its toxicity towards nontarget organisms. To better characterize exposure and possible toxicological endpoints, accurate and sensitive methods are necessary for the direct measurement of imidacloprid in biological tissues or food sources. Following the dosing of Japanese quail (<i>Coturnix japonica</i>) with imidacloprid-treated wheat seeds, plasma, liver, and fecal matter samples were analyzed by enzyme-linked immunosorbent assay (ELISA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Imidacloprid metabolites, including 5-OH-imidacloprid, imidacloprid-olefin, imidacloprid-urea, desnitro-imidacloprid, and 6-chloronicotinic acid were tested for cross-reactivity to antibodies in a commercial imidacloprid ELISA kit. The two major metabolites, 5-OH-imidacloprid and imidacloprid-olefin, showed cross-reactivities of 0.93 to 26%. Substantial cross-reactivities were not observed for the three other metabolites. Positive correlations were seen between ELISA and LC-MS/MS analyses, but there was poor agreement in concentrations. Plasma and fecal matter imidacloprid concentrations were higher by ELISA, whereas liver imidacloprid concentrations were higher by LC-MS/MS. Abundant metabolites artificially inflated ELISA results in plasma and fecal matter samples, whereas liver sample concentrations may be affected by extraction methods and/or matrix interferences. Matrix interferences were observed in analyses and were minimized by the application of matrix-matched calibration curves. ELISA was a useful screening tool for imidacloprid in these biological matrices, but the presence of cross-reactants confounded concentration results. Confirmation of ELISA results via more selective techniques (e.g. LC-MS/MS) is suggested in complex samples.

Evaluation of ELISA for the analysis of imidacloprid in biological samples: Cross-reactivities, matrix interferences, and comparison to LC-MS/MS

ACS Fall 2021

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