The bee’s knees: neonicotinoid insecticides in bee pollen quantitated in record times

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  • Published: Jul 15, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: HPLC
thumbnail image: The bee’s knees: neonicotinoid insecticides in bee pollen quantitated in record times

The birds and the bees

Bees are the unsung heroes of agriculture. Lured to the bright lights, sweet nectar and appetising aromas wafted by botanical sirens, these black-and-yellow-striped workhorses buzz from plant to plant, inadvertently carrying a fertilising payload.

Bees are the unsung heroes of agriculture. Lured to the bright lights, sweet nectar and appetising aromas wafted by botanical sirens, these black-and-yellow-striped workhorses buzz from plant to plant, inadvertently carrying a fertilising payload. As they feast on the sugary nectar, pollen released from the stamen—the male reproductive organ of a flower—rubs off onto bees. These unsuspecting mules then raid nearby and distant flowers, where the pollen in turn rubs off onto the stigma—the female reproductive organ of a flower. The plant is fertilised, and seed-bearing fruits develop—all good for farmers, unless opportunistic pests feast on crops intended for consumption by humans.

Caterpillars, for example, are known bingers of cabbage, munching their way through the foliar profits in the process. In the battle of farmers vs. nature, crops are frequently sprayed with insecticides in the hope of eradicating these pests. For this, the so-called neonicotinoid class of insecticides is preferred. Neonicotinoids have a broad spectrum of efficacy, are taken up by both the roots and leafs of plants, and have a propensity to dwell within the plant. These insecticides, however, do not discriminate in the insects they kill.

Bees acting for the benefit of plants and farmers are not immune to the toxicity of insecticides. ‘Exposure to neonicotinoid insecticides,’ Valverde and colleagues warn, ‘has been identified as one of the potential factors involved in the sudden decline in adult honeybee population, commonly known as colony collapse disorder.’ Whether these insecticides are planted into the soil, and subsequently absorbed and secreted by the leaves, or sprayed directly on to the leaves, residues of neonicotinoids end up in the pollen of plants, and eventually within the communal beehive larders, scientists have found.

QuEChERS

In response to the existential threat that insecticides pose to bees, and the earnest consequences to our crops that rely on their wings for pollination, the European Union has restricted the use of a few neonicotinoids for a two-year trial. Accordingly, an accurate method for their quantitation in bee pollen could therefore aid in the policing of these adulterants, whilst also providing the tools for scientists to further study the link between neonicotinoids and the decimation of bees. And that's exactly what the Spanish scientists set out to achieve.

QuEChERS means quick, easy, cheap, effective, rugged and safe. These are the characteristics kept in mind when devising this bee pollen sample prep method, keeping in line with current trends. Downstream of this quick sample prep, seven neonicotinoids—acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam—were quantitated with a method based on UHPLC coupled to quadrupole time-of-flight mass spectrometry (qTOF).

First, pollen components cleansed of interfering matrices were loaded onto a C18 fused-core type column—never before applied in the analysis of bee pollen or neonicotinoids—and separated over a slightly acidic, 6.5 minutes, aqueous-to-organic gradient. Next, resolved components were ionised immediately with high-voltage electrosprays and the resulting ions were monitored as they are split post collision (MRM).

Buzz test

The test was put through its paces in a series of drills, designed in line with international validation guidelines. For this, a range of twenty commercial bee pollens were obtained from Spanish regions known to use neonicotinoids—all of which were subsequently deemed ‘blank’ in the laboratory.

First of all, the ‘QuEChERS’ extraction was quick, easy and effective, yielding 91 to 105% recovery of 5 to 500 ng of neonicotinoids previously spiked into a gram of blank bee pollen. What’s more, the highly complex, protein-and-lipid pollen matrices had no influence on the chromatograms of blank, unfortified pollens, and standard and matrix-matched calibration were comparable.

With qTOF MS/MS, their method affords linearity from 2.1/4.0 upwards to 500 ng per 1-gram nugget of bee pollen. Limits of detection were slightly lower—from 0.6 to 1.3 ng/g depending on the compound being tested—potentially paving the way for the policing of these adulterants. Measurements of three quality control standards spanning the breadth of the test’s quantitative ability were achieved with 94 to 106% accuracy and the same measurements taken over three consecutive days were achieved with acceptable precision.

Through fastidiously tinkering with numerous configurations of sample prep and LC-based separation, the authors have achieved the quantitation of seven neonicotinoids in record time. However, the authors are under no illusion as to where their debt is owed. ‘The usefulness of a recently commercialised core-shell technology based column,’ the authors conclude, ‘...has been demonstrated.’

Related Links

Electrophoresis. 2016, EarlyView article, 2016. Valverde et al.. Fast determination of neonicotinoid insecticides in bee pollen using QuECHERS and ultra high performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry.

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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