Just for fun, scientists hosting a bee exhibit at a Swiss botanical garden a few years ago asked visitors, friends and colleagues to send them honey pots from around the world. They soon had more than 200 samples from bees on six continents, a honey resource that has yielded a groundbreaking study on global pesticide use.

"We thought it was cool to have a collection, and once we realized the treasure that we were building, we thought we could make use of this," said Edward Mitchell, a soil biologist at Switzerland's University of Neuchatel and the scientific director at the city of Neuchatel's botanical gardens.

The team of researchers led by Dr. Mitchell analyzed the honey for five kinds of neonicotinoid pesticides, a popular chemical linked to the declines in populations of bees and other pollinators.

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"We thought that having a global map of these concentrations and contaminations of honey by these pesticides would be extremely useful," Dr. Mitchell says. "Such a map didn't exist."

The tests revealed 75 per cent of the honey samples were contaminated by at least one variety of the pesticide used in agriculture, flower growing and even flea collars worn by pets, according to the research to be published on Thursday in the journal Science.

"We were shocked by this figure," Dr. Mitchell says by phone from New Zealand, where he is on sabbatical.

All contamination levels were below the amounts regulations permit for human consumption. But almost half of the samples had a pesticide concentration above the minimum level known to have detrimental effects on bee health. These effects include impaired learning or memory, which negatively impacts bees' abilities to remember the path to and from the hive, reducing their effectiveness at collecting food and ultimately harming the health and resilience of a hive.

"It just shows us that they are used almost everywhere in the world. It's really amazing," he says. "Bees, by collecting nectar up to 10 or 12 kilometres around the hive, they really are good sensors of contamination of pesticides in the environment."

Neonicotinoid pesticides (neonics) are among the most widely used in Canada and around the world. The nerve agents are absorbed by plants, rendering them toxic to insect pests. But non-target species, including honeybees, wild bees and other pollinators, are also affected by the chemicals. Studies have shown the chemicals affect bees' survival by hurting their abilities to forage, reproduce and ward off pathogens.

Forty-five per cent of the honey samples were contaminated by more than one kind of neonicotinoid, a finding Dr. Mitchell says is alarming because little is known about how bees are affected by combinations of the nerve agents.

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The study looked at four samples from Quebec and three from southern British Columbia. All B.C. samples had four or five neonicotinoids while the samples from Quebec – from producers near Rimouski, Lac St. Jean and Sherbrooke – had between two and five neoncotinoids.

Eighty-six per cent of the North American samples had neonicotinoids, compared with 80 per cent in Asia, 79 per cent in Europe and 57 per cent in South America.

The honey samples tested by Dr. Mitchell came from areas with intensive, modern agricultural practices such as British Columbia and Belgium as well as from less-developed or remote regions with hives not close to crops.

Amro Zayed, a biology professor at Toronto's York University who has studied the effects of neonics on honeybees, said the results are remarkable because they show neonicotinoids are being found in places where their use has undergone little examination, if any. "I think the study shows the use of neonicotinoids is very pervasive. I was actually pretty shocked when I saw the study," Dr. Zayed says.

Honeybees collect nectar from plants to make honey, which becomes a colony's main source of food through the winter. Eating pesticide-laced honey through winter could negatively affect the bees' abilities to stay warm enough to survive and reproduce, he says.

"Honeybees are social and the honey is the communal fridge, and the fact the communal fridge is poisoned means, depending on how long it stays in the honey, we might have several generations of bees that are fed contaminated honey. The levels are small … but other researchers have found that even at these small levels you could still have an effect on bee health," Dr. Zayed says.

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Lisa Gue, a researcher at David Suzuki Foundation, an environmental group, said the findings reinforce concerns pollinators are at risk from the widespread use of pesticides, despite some governments' attempts to restrict their use.

The Canadian government has proposed to ban the neonic imidacloprid over concerns its seepage into groundwater is harmful to aquatic insects. The government is also reviewing the approval of two other neonics, thiamethoxam and clothianidin. Ontario farmers face restrictions on their use of neonics on corn and soybean crops.

"It's not a secret that the chemicals are toxic to bees. It says so right in the registration. The question is about exposure," Ms. Gue says by phone from Ottawa.

Although there have been similar studies of honey, this is believed to be the first one to look at a global sampling using highly precise chemical analysis tools, Dr. Mitchell says.

Dr. Mitchell's department at the Swiss university is still getting deliveries of honey from far-flung pastures. He plans to use it for more studies on other pesticides. "We're hanging on to it because there's more we can do. People are continuing to give us samples."