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ANALYSIS

Three-quarters of honeys contain neonicotinoids, known for bee decline
Monday, 09 October, 2017, 08 : 00 AM [IST]
Neuchâtel
Three quarters of the honeys produced around the world contain neonicotinoids, a family of pesticides known for its role in the decline of bees. This was the conclusion of a study published in the prestigious journal Science recently by an interdisciplinary group of the University of Neuchâtel (UniNE) and the Botanical Garden of the City of Neuchâtel.

However, the measured concentrations of neonicotinoids remain below the maximum permitted levels for human consumption.

Neonicotinoids occupy one-third of the market share of pesticides, mainly on large-scale crops (maize, rapeseed and beetroot), against insect pests, which alter the nervous system, causing paralysis and death.

As these substances pass into the pollen and nectar of the flowers, the bees swallow them when they forge. Now, honey is nothing but the result of the transformation, by the bees, of the nectar in reserve of food. Hence the relevance of measuring the quantities of neonicotinoids.

During this research conducted between 2015 and 2016, scientists analysed 198 honey samples from around the world. They measured the concentration of five most commonly used neonicotinoids (acetamiprid, clothianidin, imidacloprid, thiacloprid and thiamethoxam).

The collection of honeys used results from an action of citizen science initiated by the Botanical Garden of the City of Neuchâtel. “All these samples were given to us,” explained its director Blaise Mulhauser.

“They were taken at random from the travel of more than 100 donors. We have just oriented our choices so as to favour honeys of small producers, or at least of well-defined regions, in order to obtain the best geographical representation,” she added.

With the large quantities of nectar, it harvests each year, the bee has been used as an elegant way to probe the presence of pesticides in our environment.

“A bee fetches nectar up to a distance of 12km from its hive, thus covering a considerable area,” said Alexander Aebi, teacher and researcher in agroecology, UniNE, and beekeeper.

This work was made possible thanks to UniNE’s UniNet Platform of Analytical Chemistry (NPAC).

“We have tools that can detect traces of neonicotinoids in complex matrices like honey. These molecules can be quantified with excellent precision at concentrations of the order of one part per ten billion or less,” said Gaétan Glauser, head, NPAC.

Results
Seventy-five per cent of the honey contained at least one of the five substances sought. This rate varied considerably from region to region - 86 per cent of North American samples were contaminated, followed by 80 per cent of the samples from Asia and 79 per cent of those from Europe. The lowest share of contaminated samples came from South America (57 per cent).

In detail, 30 per cent of all samples contained only one neonicotinoid, 45 per cent contained between two and five, and 10 per cent four to five.

The measured doses did not exceed the standards authorised for human consumption for each individual substance.

But for two of the samples containing the five neonicotinoids at a time, the total concentrations exceeded this standard.

“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 Edward Mitchell, professor, Soil Biodiversity Laboratory, and principal author of the article.

However, the situation is more critical for bees. “Our study demonstrates that they are exposed worldwide to concentrations of neonicotinoids that have important effects on their behaviour, physiology and reproduction,” said Alebi.

In addition to the actual dose of individual neonicotinoids, the effect of organisms (bees, human beings, etc.) may be on the presence of several toxic substances at the same time, commonly called the cocktail effect. The question remains broadly open.

“With over 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,” observed 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,” he added.
 
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