Bees may be at risk from commonly used weedkillers, Irish scientists find

Bees can become exposed to EU’s most common herbicide via wildflower nectar

Bees may be at risk from exposure to glyphosate – an active ingredient in some of the EU’s most commonly used weedkillers – via contaminated wildflower nectar, according to research by Irish scientists.

The weedkiller is shown to contaminate plant pollen and nectar of “non-target plant species”; providing the latest evidence supporting the case for its curtailment.

Residues of glyphosate have previously been found in nectar and pollen collected by bees foraging on plants that have been selectively targeted with weedkiller, but this is the first time it has been reported in unsprayed wildflowers growing near sprayed fields. The study was conducted by scientists at Trinity College Dublin and Dublin City University.

While glyphosate is intended to only kill plants it has been shown to harm the digestive systems of honeybees and bumblebees, which makes them more vulnerable to infections, and it may have other negative consequences.


“This is the first time glyphosate is reported in unsprayed wildflowers under conventional farming conditions,” said Elena Zioga, a PhD candidate at TCD School of Natural Sciences and lead author of the research, which was published in the journal Heliyon.

“While we need more research to find how much higher glyphosate concentrations would be in directly sprayed plants, we know wild bees and honeybees will visit the contaminated wildflowers to collect pollen and nectar,” she added. “They will thus be exposed to glyphosate and that could impact their health and the critical pollination service they provide.”

Glyphosate is the most frequently used weedkiller within the EU and is widely used in other parts of the world. “The residues we found in nectar in this study exceeded the European maximum permitted levels of glyphosate in honey and honeybee products, which suggests they could be harmful to honeybees and those eating the honey,” Ms Zioga said.

The European Commission is re-evaluating glyphosate, primarily because of human health concerns, with results due later this year. It has been or will soon be banned in at least 10 countries, and at least 15 others have restricted its use. Farmers in Germany must stop using it completely from 2024. In Ireland only half of glyphosate’s use is on farms. The rest is in amenity areas, parks and golf courses.

While regulators worldwide have determined glyphosate to be safe, Bayer has settled nearly 100,000 US lawsuits for $10.9 billion, denying claims that Roundup – its trade name – caused cancer.

This latest study sampled farmed fields of oilseed rape and nearby growing blackberry wildflowers in seven different locations in east and southeast Ireland.

In three of these locations, glyphosate residues were found in pollen and nectar of the blackberry flowers within a week after spraying took place. When the weedkiller was used as “a pre- or post-emergence spray” on oilseed rape crop (two months before sampling), no residues were detected.

“Knowing that bees may be exposed to glyphosate residues in the environment makes it important that more research takes place to assess the glyphosate impact on more bee species,” Ms Zioga said.

“We recommend the immediate investigation of glyphosate as a desiccant [to dry weeds quickly] before harvesting crops to better understand how this impacts non-target flowering plants growing near crop fields to enable a greater evidence base for evaluation of the renewal of market authorisation for glyphosate in the EU.”

This research was supported by the Department of Agriculture, Food and the Marine.

Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times