The analysis of 198 honey samples measured the concentration of five most commonly used neonicotinoids - acetamiprid, clothianidin, imidacloprid, thiacloprid and thiamethoxam.
Findings revealed 75% of the honey contained at least one of the five pesticides. Of this figure, 86% of North American samples were contaminated, followed by Asians (80%) and Europeans (79%).
30% of all samples contained only one neonicotinoid, 45% contained between two and five, and 10%, four to five.
Worryingly, two of the samples contained five neonicotinoids in quantities exceeding standards authorised for human consumption
“We show that, according to current standards, the vast majority of the samples studied do not concern consumers' health for the five pesticides studied," said principal author Edward Mitchell, a professor at the Soil Biodiversity Laboratory at the University of Neuchâtel in Switzerland.
Neonicotinoids are used mainly on large-scale crops (maize, rapeseed and beetroot), against insect pests, which alter the nervous system, causing paralysis and death.
These substances pass into the pollen and nectar of the flowers that eventually go on to form honey.
Additional findings by the team found the total concentration of the five measured neonicotinoids was, on average, 1.8 nanograms per gram (ng/g) in contaminated samples and reached a maximum of 56 ng/g over all positive samples
Maximum residue levels (MRLs) authorised in food products in the European Union (50 ng/g for acetamiprid, imidacloprid, and thiacloprid and 10 ng/g for clothianidin and thiamethoxam) were not reached for any tested neonicotinoid.
While these pesticide levels pose no urgent concern for humans, the situation could well become more critical in the future.
"With more than 350 synthetic pesticides used in Switzerland that can degrade into even more compounds, the metabolites and combinations are therefore endless, making any study complete illusory," said Dr Mitchell.
We are therefore limited to short-term research, often focused on the only 'active' compound. Thus, we do not take into account the adjuvants (other molecules included in the commercial formulation) or the presence of metabolites, sometimes as toxic, if not more than the 'active' compounds themselves."
Previous studies report a broad range of occurrence and concentrations of neonicotinoids in honey.
In a British study, 16 out of 22 samples were positive for clothianidin, but for all of these samples the measured concentrations, all below 0.02 to 0.82 nanograms per gram (ng/g), were below the detection limit of a Serbian study (1.0 ng/g) in which no sample tested positive.
A long-awaited pesticide review by the European Food Safety Authority (EFSA), due at the start of this year, has been delayed until this autumn.
The re-evaluation, looking at the safety of three neonicotinoid pesticides, clothianidin, thiamethoxam and imidacloprid, which have already received temporary bans by the EU on its use on some crops in 2013.
Earlier this year, the UN were critical of pesticide use commenting that to implement adequate food and health required measures to eliminate harmful pesticides.
“Corporations have the responsibility to ensure that the chemicals they produce and sell do not pose threats to these rights.
“There continues to be a general lack of awareness of the dangers posed by certain pesticides, a condition exacerbated by industry efforts to downplay the harm being done as well as complacent Governments that often make misleading assertions that existing legislation and regulatory frameworks provide sufficient protection.”
Published online ahead of print: DOI: 10.1126/science.aan3684
“A worldwide survey of neonicotinoids in honey.”
Authors: E. A. D. Mitchell et al.