From flowers to pollinators: Dietary exposure of honey bees, bumble bees and solitary bees to trace elements across European fields

Abstract

Trace elements are persistent contaminants that enter bee diets through pollen, nectar, soil-derived particles and atmospheric deposition, yet field-based exposure data for pollinator taxa remain limited. We examined 18 trace elements (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Se, U, V, Zn) in pollen stored by managed western honey bees (Apis mellifera), buff-tailed bumble bees (Bombus terrestris), and red mason bees (Osmia bicornis) from 128 apple orchards and oilseed rape fields across eight European countries. We assessed species-, crop- and landscape-related drivers of element accumulation in stored pollen and honey bee workers, and used these data to estimate dietary exposure and risk. Stored pollen showed crop- and species-specific differences in trace element levels. Red mason bee pollen contained several-fold higher concentrations than honey bee and bumble bee pollen, suggesting that honey bees may not be a suitable model for pollen-based exposure studies. Stored pollen from apple orchards contained higher Cu than that from oilseed rape sites, likely linked to Cu-based fungicide use. Landscape characteristics, including crop and urban cover, influenced element concentrations in stored pollen and honey bee workers. Acute risks were assessed for As, Cd, Cu, and Hg, and chronic risks for As and Cd. For elements with available toxicity endpoints, estimated dietary risk was negligible or low; for elements lacking such endpoints, risk could not be quantified despite exposure estimates. Higher exposure of solitary bees, together with scarce toxicity data, indicates that future studies should focus on establishing species-specific toxicity endpoints.