A range of pesticides, including neonicotinoids, have been found in the pollen of different bee species, according to Trinity College Dublin research.
The research, Trinity said, paints a worrying picture for the different species of bees that provide multi-million euro pollination services in Ireland each year.
The study looked at the potential widespread exposure to multiple chemicals from both fungicides and neonicotinoid insecticides.
It took into account residues in crop pollen at 12 sites in Ireland and in pollen collected from honey bees and bumble bees from the same sites.
PhD candidate in Trinity’s school of natural sciences Elena Zioga is the first author of the just-published journal article.
She said: "The results of this study are concerning on several levels. Of particularly great significance is the indication that different species seem to be exposed to pesticides differently based on the variation in the types and number of different pesticides found in pollen of honey and bumble bees respectively."
It is also very worrying, she added, that the five neonicotinoids that were looked for appeared in bumble bee pollen and 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."
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.
"Our work also showed that neonicotinoid detection increased when the presence of wild plants in bumble bee pollen increased and that is one of many things that require further investigation," she concluded.