An international study has found 75 per cent of honey across the globe is contaminated with neonicotinoid pesticides.
The concentrations of neonicotinoids (NNIs) detected in study are below the amount is below the level authorised by by the European Union for human food and animal feed products.
Some experts say the findings highlight the risk to pollinator populations from NNI use, particularly bees. But opinions remain divided on the links between NNIs and bee health.
The peer reviewed study, A worldwide survey of neonicotinoids in honey, took 192 samples from honey in all continents, including Australia and New Zealand, except Antarctica.
The samples were tested for five common NNIs, which are often used for seed and herbicide treatments in Australian broadacre agriculture. The findings were published in the journal Science.
The study found that in 34 per cent of honey samples the pesticides were detected at concentrations known to be detrimental to bees. Around 10pc contained four or five different neonicotinoids; 30pc contained a single NNI; and 45pc contained two or more.
Concentrations were highest in European, North American, and Asian samples. Multiple contaminations were most common in North America, Asia, and Europe and least frequent in South America and Oceania.
UK-based Rothamsted Research plant ecologist Dr Jonathan Storkey agreed with the assertion of the studies authors that pesticides accumulated in the environment and hives is a “serious” environmental concern that likely contributes to pollinator declines, but cautioned against outright bans of NNIs.
“There is no suggestion in the paper of a risk to human health, however, the levels recorded (up to 56 ng/g) lie within the bioactive range that has been shown to affect bee behaviour and colony health – scientists showed earlier this year that levels of less than 9 ng/g reduced wild bee reproductive success.”
An over-reliance and imprudent use of NNIs had contributed to the situation but the alternatives, namely multiple sprays of synthetic pyrethroids, pose a potentially worse risk, Dr Storkey said.
“Rather than seeking an outright ban, research should focus on developing strategies for limiting the use of neonicotinoids across crop rotations, using all the principles of integrated crop management as well as integrating additional foraging resource into the landscape for pollinators to reduce the exposure of hives.”
University of Dundee reader in neurobiology Dr Chris Connolly said the findings are “alarming”, even though the relatively low levels of NNIs detected in honey are not likely to be lethal to bees.
“However, the levels detected are sufficient to affect bee brain function and may hinder their ability to forage on, and pollinate, our crops and our native plants,” he said.
“Clearly, the use of neonicotinoids need to be controlled. Their widespread use on crops is due to their prophylactic use, as insurance against the possibility of future pest attack.”
Hutton Institute senior ecological scientist professor Nick Birch said it was unfortunate that the study lacked information on other types of pesticides that may present in these samples, given we know that bees react to cocktails of pesticides encountered in landscape scale foraging.
“For example, scientists recently demonstrated that a commonly encountered fungicide doubles the toxicity of certain NNIs when they are encountered together,” Dr Birch said.
“This implies, as other studies have shown, that multiple stressors (eg ‘pesticide cocktails’) could have an effect on bees if exposure is sufficient over time and space.”
Dr Birch said other studies have recently noted pesticide exposure varies by country and does not fully explain any negative NNI effects on bees.
“Other factors such as non-contaminated food sources in the region and regional bee disease pressure play a part and can mitigate the negative impact of NNIs.
“Future risk management strategies for bees and other pollinators should be able to reduce impacts of NNIs via suitable monitoring mitigation measures; for example, offsetting any negative impacts of pesticides by prudent management of pesticide use and by providing a disease-free and food-rich habitat for bees and other pollinators.”
Rothamsted Research weed ecologist Dr Paul Neve said the impact of chronic bee exposure to NNIs had not been determined, and difficult to perform, large scale epidemiological studies are needed to address the question.
“We need to remain open-minded and base decision-making relating to pesticide regulation on a strong science base, acknowledging that pesticides can have unacceptable negative impacts, but not forgetting their large role in securing productive harvests.”