Wildflowers could be absorbing toxic metals from soil in urban areas and passing toxins on to pollinators, a study has found.

Researchers from the University of Cambridge found that common plants including white clover and bindweed, which are vital forage for pollinators in cities, can accumulate arsenic, cadmium, chromium and lead from contaminated soils.

These metals have been found in previous studies to damage the health of bees and other pollinators, which feed on the contaminated nectar. This leads to reduced population sizes and death. Even low metal levels in nectar can hinder bees’ learning and memory, which degrades their foraging abilities.

The contaminated soils tend to be on land previously used for buildings and factories, which have leached these pollutants into the land. The scientists who carried out the study are now recommending that urban areas are tested for contaminants and potentially cleaned before wildflowers are planted.

The study, published in Ecology and Evolution, was carried out in the post-industrial US city of Cleveland, Ohio, which has more than 33,700 vacant lots left as people have moved away from the area. It was once a hub for iron and steel production, as well as oil refining and car manufacturing. These are all industries that potentially contaminate land with trace metals.

The researchers extracted and tested nectar from a range of self-seeded flowering plants that are popular with pollinators, and were found growing across the city. Lead was consistently found at the highest concentrations, but different species of plant accumulated different amounts and types of metals.

The bright blue-flowered chicory plant (Cichorium intybus) accumulated the largest total metal concentration, followed by white clover (Trifolium repens), wild carrot (Daucus carota) and bindweed (Convolvulus arvensis).

Cities worldwide face metal contamination in soils, and the level of contamination usually increases with the age of the city. Sources include cement dust and mining.

But people should not be discouraged from planting wildflowers for bees, the report authors said.

Dr Sarah Scott, from the University of Cambridge’s Department of Zoology and first author of the report, said: “It’s really important to have wildflowers as a food source for the bees, and our results should not discourage people from planting wildflowers in towns and cities.

“We hope this study will raise awareness that soil health is also important for bee health. Before planting wildflowers in urban areas to attract bees and other pollinators, it’s important to consider the history of the land and what might be in the soil – and if necessary find out whether there’s a local soil testing and cleanup service available first.”