Highway to brood cell: bumblebees ingest and transfer tire wear particles more frequently than polystyrene microplastics

Abstract Pollinators like bumblebees are exposed to microplastics (MP) pollution during foraging. After returning to the colony foragers may subsequently spread MP in the nest or transfer ingested MP to larvae during cooperative brood care. Experimental studies have shown that MP can exert negative effects on hymenopteran pollinators, such as impaired cognition or increased mortality. However, as physical and chemical properties of MP depend on for instance polymer type, effects of MP and also their transfer within colonies may be polymer-specific. Currently research has predominantly focused on standard MP types like polystyrene (PS-MP). However, especially in urban environments tire wear particles (TWP) constitute a major MP source. We thus compared the uptake and transfer of PS-MP and the environmentally relevant TWP within colonies of the buff-tailed bumblebee Bombus terrestris. B. terrestris colonies were provided with sugar water spiked with 0.4% w/v PS-MP or TWP for four weeks, after which we examined the gut system of workers and larvae and the whole body of pupae, as well as honeypot contents and wax for the presence of MP using stereo microscopy. We show that TWP were significantly more frequently ingested by workers, transferred to larvae, and incorporated into nesting materials than PS-MP. We suggest that bumblebees fail to recognise TWP as pollutants, potentially due to their rough surface, which may facilitate ‘masking’ of the particles by a coating of sugar water. Given the widespread presence of TWP in human-altered landscapes and the higher frequency of uptake they may pose a much greater risk than PS-MP. Our findings highlight the need for comparative studies on health effects of different environmentally relevant MP types.