Potentially toxic trace elements in bee pollen collected around a former municipal waste deposit site

Potentially toxic trace elements (PTTEs) pose a risk to living organisms. We used honey bees (Apis mellifera) to explore differences in PTTE contamination levels between two study sites. Two apiaries with five bee colonies each were studied: The experimental apiary was located at a former waste deposit site (Witzwil, Switzerland), and the control apiary was 4.5 km away in the neighboring area (Bellechasse, Switzerland). Pollen was collected from colonies from May to August 2022 and 2023, and we developed an analytical method to assess 22 PTTEs. We quantified 19 PTTEs in at least one of the pollen samples (n = 80), with maximal levels recorded for Mn (298.8 mg/kg), B (95.1 mg/kg), Zn (63.4 mg/kg), Cu (19.2 mg/kg), Rb (17.7 mg/kg), Ba (11.1 mg/kg), and Sr (3.2 mg/kg). Most notably, site-specific and seasonal variations were observed. For example, in June, pollen at the Witzwil site had statistically significant higher average concentrations of PTTEs-Mn (204.6 ± 53.1 mg/kg), Rb (13.9 ± 2.3 mg/kg), Ba (6.7 ± 2.2 mg/kg), and Ni (1.8 ± 0.4 mg/kg)-than the Bellechasse apiary, with Mn (74.2 ± 67.1 mg/kg), Rb (5.6 ± 2.0 mg/kg), Ba (4.4 ± 2.5 mg/kg), and Ni (1.1 ± 0.5 mg/kg). By contrast, the levels of several PTTEs (e.g., Mn, Ba, and Ni) were similar in July and August in both apiaries. For maximal Cu, Cd, and Cr levels in pollen, we expect no increased acute oral toxicity to adult honey bees above the expected mortality levels.