Neonicotinoids in Three quarters of the world's honey

Three quarters of the world's honey is laced with neonicotinoid insecticides, a new study has shown this week.

In a scientific first, Edward Mitchell, from Neuchâtel University, in Switzerland, has analysed nearly 200 honey samples collected from around the world with the help of citizen scientists in every continent (except Antarctica!).

The analysis, presented in Science this week, looks at the levels of neonicotinoid pesticides, dubbed "neonics", present in the honey. Three quarters of the samples tested contained at least one neonicotinoid, and hearly half contained multiple neonic species, although the concentrations detected were not judged to be a threat to human health. The levels present were, however, within the biologically active range for insects.

Neonicotinoids are currently the most widely used class of insecticides worldwide. Sprayed on, or applied to seeds, they are taken up and distributed throughout the plant, and they also accumulate in nectar and in pollen.

This means that pollinators, like bees, have the potential to fall victim to off-target exposure to the agents, and this, some scientists are warning, might account for the global decline noted among some pollinator species in recent years. Researchers estimate that 90% of the neonics applied to a crop plant ultimately end up in the soil where they have the potential to enter wild flower species growing along field boundaries. 

If this is the case, then initiatives like the recent EU partial ban on neonic use in pollinator-visited crop plants may, in fact, be fruitless if the agents can still find their way into pollinator's food chains through so-called secondary routes in the soil.

But the extent to which this is occurring isn't known, and this was the stimulus that triggered the Swiss team to set up their global honey study. 

Samples from the US tested positive for at least one neonic 86% of the time, Asia about 80% of the time, Europe 79% and Oceania about 70%. Neonics work by mimicking the action of certain neurotransmitters in the insect brain, and the concentrations detected in the honey would certainly be high enough to cause behavioural and memory problems for bees that consumed it.

"This study shows that pollinators are globally exposed to neonicotinoids, at concentrations shown to be harmful to bees," say the Swiss team. "The fact that 45% of our samples showed multiple contaminations is worrying and indicates that bee populations throughout the world are exposed to a cocktail of neonicotinoids." The group conclude by urging policy-makers to make available data on local use of neonic so that more rigorous correlations can be sought.

It's not good news for humans either. Apart from potentially jeopariding the US$400 billion that pollinators contribute in economic terms each year, the fact that these chemicals have turned up in honey is making some people uneasy about what else might be in our food that we are not testing for. "It makes one wonder what other chemicals might also be there," questions Dundee University neuroscientist Chris Connolly.