Dripping Poison

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The European Food Safety Authority (EFSA) has carried out reviews of the neonicotinoid pesticides thiamethoxam, imidacloprid and clothianidin in order to assess the possible risks posed by these systemic insecticides to bees. These reviews helped underpin the decision by the European Commission to ban the three active ingredients from certain applications for a period of two years. In particular, the reviews identified shortcomings and gaps in the available data which prevented an holistic and exhaustive risk assessment from being carried out. One key uncertainty identified by EFSA in each case related to the role of guttation fluid exuded by commercial crop plants as a potential source of the chemicals to bees when they used it as a water source for themselves or for thecolony as a whole.

The use of neonicotinoid insecticides as seed treatments and granules applied to soil is known to lead to these chemicals being present in the guttation fluid of various crop plants. Although the literature on this subject is sparse, the research carried out to date indicates that the neonicotinoids may be present at high concentrations. In order to investigate this phenomenon further, Greenpeace undertook a study of guttation fluid produced by maize plants grown in field conditions in Hungary, which according to the farmer had been treated with two different commercial seed treatment products. One field had been planted with seeds treated with Poncho®, with clothianidin as the active ingredient, while the other had been planted with seeds treated with Cruiser®, with thiamethoxam as the active ingredient. Samples of guttation fluid were sampled from each field over a number of days and analysed using UPLC-MS/MS techniques.

The results of the analyses revealed significant concentrations of neonicotiniod pesticides present in guttation fluid. Up to 11 709 μg/l of clothianidin was present in the fluid from the Poncho-treated seeds, while up 55 260 μg/l of thiamethoxam was present in the fluid from Cruiser-treated seeds. In addition, the Cruiser-treated plants also exuded upto 9651 μg/l of clothianidin, most likely as a degradation product of the primary active ingredient used on the seeds.