Cambridge researchers warn of hidden risks in city soil as wildflowers growing in contaminated areas expose pollinators to harmful metals like lead and arsenic

A new study has raised fresh concerns over pollinator health in urban areas, revealing that wildflowers growing in contaminated soils can absorb toxic metals and pass them on to bees through their nectar.

Researchers from the University of Cambridge found that common urban wildflowers such as white clover, bindweed, and chicory can accumulate heavy metals including arsenic, cadmium, chromium, and lead from polluted soils. When bees forage on these plants, they ingest the toxic substances — posing a potential threat to their health and survival.

The study was conducted on post-industrial sites in Cleveland, Ohio, where past activities like steel manufacturing, oil refining, and automobile production have left a legacy of soil contamination. “Metal contamination is an issue in cities worldwide, and the levels usually rise with the age of the city,” said the researchers. The metals in question stem from sources such as cement dust, mining residues, and industrial emissions.

Among the findings, Chicory (Cichorium intybus) had the highest total metal concentration and White Clover (Trifolium repens) showed the highest levels of lead in nectar, lead emerged as the most prevalent metal across all nectar samples, followed by chromium, cadmium, and arsenic.

The implications for pollinators — especially bees — are significant. Previous research has shown even low levels of heavy metals in nectar can affect learning, memory, and foraging efficiency in bees, ultimately contributing to population declines and higher mortality. Yet, despite the findings, the researchers emphasized the importance of urban wildflowers for pollinators.

“It’s really important to have wildflowers as a food source for bees,” said lead author Sarah Scott, of the University of Cambridge’s Department of Zoology. “Our results should not discourage people from planting wildflowers in towns and cities.” Instead, the study calls for greater awareness and caution when planting in urban areas, urging assessments of historical land use and soil quality to prevent unintentional harm to pollinators.

The research also adds to a growing body of evidence linking pollinator decline — estimated at over 50 per cent in the past 50 years — to habitat loss, climate change, pesticide use, and now, soil contamination. As cities continue to expand and repurpose former industrial land for green spaces, the study underscores the need for responsible urban greening that supports, rather than endangers, vital insect populations.