5 October 2023

Pesticides persist in bee pollen, study says


An Irish study shows that pollen from several bee species retains traces of toxic substances from neonicotinoids. And researchers are concerned

by Matteo Cavallito


Pollen from several bee species in Ireland has traces of pesticides. A worrisome phenomenon in the face of the fallout on the pollination services provided by these insects. This is highlighted by a study by Trinity College Dublin and Dublin City University carried out in some agricultural fields in the country and whose results were published in the journal Science of the Total Environment.

“The work raises concerns about the potential wide-spread exposure to multiple chemicals from two pesticide categories (fungicides and neonicotinoid insecticides) and indicates that different bee species may be exposed differently to pesticides,” says a statement released by Trinity College.

The research

“Where crops are treated with pesticides, bees are likely to be exposed to a range of chemical compounds in a variety of ways,” the researchers explain. The extent of the effects of these substances on different bee species depends largely on the concentrations and type of exposure. The investigation tried to quantify the presence of the selected pesticides in pollen from rapeseed and fava bean crops.

“Sampling was performed in 12 sites in Ireland and our results were compared with the pollen loads of honey bees and bumble bees actively foraging on those crops in those same sites,” the study continues.

“Most detections originated from compounds that were not recently applied on the fields. Samples from B. napus fields were more contaminated compared to those from V. faba fields. Crop pollen was contaminated only with fungicides, honey bee pollen loads contained mainly fungicides, while more insecticides were detected in bumble bee pollen loads.”

Eyes on neonicotinoids

Definitely relevant is the presence of neonicotinoids, insecticides chemically related to nicotine that are particularly toxic to bees. “The highest number of compounds and most detections were observed in bumble bee pollen loads, where notably, all five neonicotinoids assessed (acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam) were detected despite the no recent application of these compounds on the fields where samples were collected,” the study continues.

Azoxystrobin, boscalid and thiamethoxam together constituted the most prevalent pesticide combination in pollen. The results, the study points out, “raise concerns about potential long-term bee exposure to multiple residues and question whether honey bees are suitable surrogates for pesticide risk assessments for all bee species.”

Pesticides are particularly persistent

One area of particular concern among scientists is the presence of the five neonicotinoids tested in bumblebee pollen but not in crop pollen. “Some of these pesticides, known to be particularly toxic, had not been applied in the fields we sampled for at least three years,” said Elena Zioga, PhD Candidate in Trinity’s School of Natural Sciences and first author of the just-published journal article.

“This shows either that they persist for a long time in the field edges, where wildflowers grow, or that bees collected neonicotinoid-contaminated pollen from beyond the sampled fields,” she added.

Overall, the statement stressed, the research findings raise significant concerns about potential widespread exposure to multiple pesticides. The simultaneous presence of insecticides and fungicides, moreover, poses an additional danger. In fact, previous studies have shown that combining these different products can increase their overall toxicity.