Residue from potentially harmful pesticides has been discovered in 75 per cent of honey sampled from around the world, according to a study conducted by Swiss scientists that was published in the journal Science in October 2017.
The researchers sampled 198 different honeys sourced from every continent, excluding Antarctica, testing for the presence of five unique neonicotinoid pesticides that are frequently applied to crops. These insecticides are so efficient that by 2008, they accounted for one quarter of the global insecticide market – and that rate continues to increase.
According to the study, these neonicotinoids are absorbed by plants and transported to all organs – including flowers, resulting in contaminated pollen. Increasing evidence suggests that large-scale use may lead to significant environmental impacts, leading scientists to start investigating the chemical’s impact on landscapes around the world.
“Despite increasing research efforts to understand the patterns of neonicotinoid uses and their effects on living organisms, we lack a global view of the worldwide distribution of neonicotinoid contamination in the environment to evaluate the risk,” the study states.
To help determine the potential risk of current contamination levels, citizen scientists from around the world sent individual samples of locally produced honey to the researchers’ laboratory in Switzerland. According to the study, the residue level of pesticides found in honey provides a measure of possible contamination in the surrounding landscape.
“Many of our samples were from very remote regions,” said Professor Edward Mitchell with the University of Neuchatel in Switzerland, who co-authored the study. “We also aimed to (include) isolated oceanic islands, and places in central parts of continents far away from industrial areas.”
Mitchell said positive samples were found even in many of those remote locations, but the highest levels of these pesticides were detected in honey produced in North America, Europe, and Asia. Samples where the source of the product could not be verified were excluded from the study.
Of the samples collected, 30 per cent contained a single pesticide and 45 per cent revealed at least two, and up to five different kinds of neonicotinoid. The six samples collected from Australia most commonly showed trace amounts of thiamethoxam – a pesticide that was temporarily banned by the European Union in 2013, as a result over ongoing concerns related to colony collapse.
Since the level of contamination present in the honey samples was determined to be “below the maximum-residue level authorized for human consumption” by the European Union, researchers noted these findings may not directly impact human health – but they could be causing harm to bees and other pollinators.
“There are increasing concerns about the impact of these systemic pesticides on honey bees and wild bees,” the report concluded. “The average concentration (discovered in the honey samples) lies within the bioactive range, causing deficits in learning, behaviour, and colony performance.”
For a decade, researchers have been studying the concept of colony collapse, after beekeepers in the United States found thousands of hives that had been completely abandoned by bees. So far, studies have pointed to a variety of factors that contribute to this phenomenon, including sub-lethal levels of pesticide ingestion by bees.
“Large-scale losses of honey bee colonies represent a poorly understood problem of global importance,” reads a study published in PNAS in October 2013 that examined neonicotinoids and insect immunity in honey bees. “A stronger impact of pathogens in honey bees exposed to neonicotinoid insecticides has been reported, but the casual link between insecticide exposure and the possible immune alteration of honey bees remains elusive.”
While none of the tested honey samples were found to have levels of pesticides that are known to have “marked detrimental effects” on bees, Mitchell said the presence of these neonicotinoids are a significant cause for concern – even at lower levels.
“These pesticides are so incredibly toxic that they have a considerable effect at concentrations that are barely measurable,” he said. “The contamination confirms the inundation of bees and their environments with these pesticides, despite some recent efforts to decrease their use.”
Colony collapse has not been discovered in Australia to date, but both Europe and North America have been seeing increased rates of bee mortality over the winter. In the United States, a national beekeeping databased recorded that throughout the winter of 2015-16, more than 28 per cent of bee colonies were lost.
“Given the increasing use of neonicotinoid pesticides in the different regions of the world, despite partial bans such as the one implemented in the EU, it is reasonable to expect contamination to have increased over time,” the study states. “Total bans, such as the one soon to be implemented in France, may reverse this trend in the future.”
In 2016, France passed a law that will see the banning of all neonicotinoids by the year 2018.
The debate regarding neonicotinoids has primarily focused on bees and pollinators, but a study published in Frontiers in November 2016 examined the impacts and potential threats of these pesticides on aquatic environments.
“There is urgency in assessing the advantages and disadvantages of the widespread use of this class of insecticides, so as not to repeat the mistakes of the past,” the study states.
The findings were determined to be “of concern.” While a minimal number of aquatic species are impacted in areas with urban runoff, up to 40 per cent of local species were discovered to be “seriously affected” by runoff coming from agricultural lands. In the Sydney basin, 14 per cent of species are being affected in streams that receive water from turf farms.
Residues of neonicotinoids in soil have increased over the years, especially in countries where there is an extensive history of using seeds treated with the chemical imidacloprid.
“This accumulation results primarily from the fact that 80 to 90 per cent of the insecticide in the coated seeds and granules remains in the soil at the end of the cropping season,” notes the report. “Most of the residual chemical would remain in the applied field, from where it moves readily into ground waters.”
The report concludes that the “overall biodiversity of the aquatic communities is negatively affected” by the pesticides – particularly mayfly, caddisfly, and stonefly nymphs, which are responsible for the shredding of debris found at the bottom of bodies of water. While the debris would likely still undergo microbial degradation, this process would be much slower, and would produce undesirable by-products including sulfides and methane.
“The combined impacts by neonicotinoids and other pollutants could gradually poison the surface waters in many parts of the world,” the study states. “Solutions must be found soon if we are to save the biodiversity not only of aquatic ecosystems, but all other ecosystems linked by the food web.”
While the new study did conclude that according to current knowledge, consumption of honey is not thought to harm human health, the evident impacts of neonicotinoids on vertebrates – including humans – may indicate that our regulations could use an update.
“Although the impact of the measured concentrations of neonicotinoids in honey on vertebrates, including humans, is considered negligible, a significant detrimental effect on bees is likely for a substantial proportion of the analyzed samples,” reads the study.
The “sub-lethal” effects attributed to neonicotinoids include growth disorders, reduced efficiency of the immune system, neurological and cognitive disorders, and respiratory and reproductive function. The effects of exposure to multiple pesticides, the study adds, are only recently being explored – and are suspected to be stronger than individual effects.
“We urge national agriculture authorities to make the quantities of neonicotinoids and other pesticides used on their territories publicly available and also professionally available to epidemiologists at a much higher geographical resolution to enable correlative studies between local events and pesticide load,” the report concludes.
An exploration of alternative pest control options was published in January 2015. Drawing from examples of pest control in Italian maize production and Canadian forestry, the report illustrates other techniques for developing an integrated pest management strategy that may offer reduced risks to affected plants and animals.
These options include diversifying crop rotations, altering the timing of planting, tillage, and irrigation, using less sensitive crops in infested areas, applying biological control agents, or turning to other reduced risk insecticides.
“Continued research into alternatives is warranted,” the study concluded, “but equally pressing is the need for information transfer and training for farmers and pest managers, and the need for policies and regulations to encourage the adoption of integrated pest management strategies and their alternative pest control options.”