Exposure to urban heavy metal contamination diminishes bumble bee colony growth

As a result of their industrial past, legacy cites often have elevated concentrations of soil heavy metal contamination. Metal pollution can have negative and prolonged ecosystem impacts, and bees that forage in these urban ecosystems are at risk of exposure. Legacy cities are known to support species rich bee communities, which highlights the importance of determining the impact of heavy metal contamination on wild bee health. We examined how oral exposure to concentrations of four metals found within the provisions of bees foraging within Cleveland, Ohio, USA influenced colony growth of Bombus impatiens Cresson (Hymenoptera: Apidae), a common species within legacy cities across the eastern United States. Colony weight and brood survivorship were compared among hives fed uncontaminated sucrose solution (hereafter nectar), nectar spiked with one metal (arsenic, cadmium, chromium, or lead), and nectar containing all metals, after 15 or 30 d of exposure within flight tents. Across both exposure periods, we found a significantly higher proportion of dead brood in metal exposed hives. Additionally, colonies fed all four metals had a significantly higher proportion of dead brood than those fed a single metal. Our findings illustrate that even low, environmentally relevant concentrations of metals collected by B. impatiens in legacy cities can negatively influence bee colony growth. We highlight the need to identify metal exposure routes for bees in contaminated landscapes to minimize risk and bolster conservation habitat initiative success.