Wildflowers on disused urban land may pose a risk to bee health due to the accumulation of harmful metals such as lead, arsenic, and chromium in their nectar, a recent study indicates. These metals, sourced from various activities like cement production and mining, are found in soil and are absorbed by the plants. Bees ingest these metals while feeding, which can adversely affect their learning and memory, their ability to forage, and ultimately, their population size.
According to the study published in the journal Ecology and Evolution, researchers extracted nectar from flowering plants found on unused land in Cleveland, Ohio, and detected substantial amounts of these metals. Dr. Sarah Scott, from the University of Cambridge's Department of Zoology and first author of the report, stated: “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.”
The study urges the testing of urban soils for contaminants before establishing wildflower habitats, and, if necessary, cleaning up polluted areas. Another recommendation involves managing wildflower species to limit flowering and reduce metal transfer to bees.
Scott emphasized, “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.”
The research was conducted in Cleveland, Ohio, a city with numerous vacant lots due to past industrial activities like iron and steel production. Results showed that plants such as chicory, white clover, and wild carrot accumulate different levels and types of metals, with chicory noted for accumulating the highest metal concentration.
The decline over the last five decades in wild pollinator populations, which facilitate the pollination necessary for food crops like apples and tomatoes, is largely attributed to habitat loss. Although factors such as climate change and pesticide use also contribute to this decline, Scott points out that small efforts like planting flowers in certain areas can aid pollinator conservation.
The USDA National Institute of Food and Agriculture primarily funded the research, signaling a need to better understand and mitigate risks to urban pollinators.