Assessing metal contamination using bumblebees and honey bees – Complementary roles in biomonitoring

Metal pollution poses a significant risk to ecosystems and public health, which is why effective monitoring tools are needed. Honey bees (Apis mellifera) are often used as biomonitors due to their large foraging range and ease of sampling. However, as they are domesticated, eusocial insects with perennial colonies, they may not be representative of all bee species. In this study, the bufftailed bumblebee (Bombus terrestris), a native wild pollinator with distinct ecological characteristics, is evaluated as a complementary or alternative biomonitor. Bumblebees forage over shorter distances and have a more diverse diet, offering the potential for higher spatial resolution in pollution studies. Honey bee and bumblebee colonies were sampled near Aachen, Germany. Bumblebees showed higher concentrations of S, Cu, Zn, As, Se, Mo and Ba compared to honey bees. Honey bees had higher concentrations of Al, K, Ca, Rb, Cd, Sn and Cs compared to bumblebees. Bumblebees generally collect more nutrient-rich food, which is confirmed by the higher proportion of essential and beneficial elements in bumblebees (S, Cu, Zn and Se) compared to honey bees (K and Ca). Contamination indices showed similar pollution levels for most elements, although bumblebees showed localized pollution sources. Both species are effective biomonitors: honey bees provide broader area assessments, while bumblebees offer finer spatial resolution and operate at lower temperatures. Together, they enable a multi-level monitoring approach, with honey bees indicating general pollution trends and bumblebees detecting local sources.