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While laws to limit pollution have been around for decades, heavy metal pollutants like lead remain a problem in many areas. Lead and other metals in the soil or air can move through urban ecosystems, impacting the health of humans, plants and animals.

In a pair of new studies, one in Science of The Total Environment and the other forthcoming in Evolutionary Applications, researchers with the Minneapolis-St. Paul Long Term Ecological Research Program asked how this pollution might impact butterflies in greenspaces around the Twin Cities, and why some species may tolerate pollution better than others.

They also wanted to know whether butterflies were absorbing lead through their food sources or through more direct routes of exposure to contaminated soil or air.

The research sets the stage for a broader understanding of pollution risks in the Twin Cities, said author Emilie Snell-Rood, a professor in the College of Biological Sciences. "Butterflies can give us clues on routes of exposure and impacts not just on wildlife health, but also human health. Humans are just a part of the urban ecosystem."

The research team found:

• Butterflies in green spaces with elevated soil and air lead pollution carry high levels of lead in their bodies.
• Higher lead concentration correlated with smaller wing size across all species studied, suggesting lead exposure is somewhat stressful.
• Species that have larger ranges and an evolutionary history with plant toxins are more tolerant of lead. Butterflies that have been feeding on toxic plant families for millions of years may harbor adaptations for environmental stress that can protect them from lead pollution.

"We found correlations between lead and smaller wing size across all common butterfly species that we studied. Lead was mostly outlawed in the 1970s, yet we are still being exposed and experiencing consequences from this pollutant. And lead is just one pollutant," said postdoctoral researcher and project leader Lindsey Kemmerling.

"Recent research has shown that butterfly abundance has declined by over 20% in the last 20 years, a truly tragic number," said Kemmerling. "Testing why some species are better or worse at tolerating pollution can point us to which species might require the most urgent conservation support. Our work shows that species with smaller habitat ranges and species that don't feed on plants that contain natural toxins are likely the most vulnerable to pollution."

The research demonstrates that public health and species conservation go hand in hand, and shows where pollution mitigation efforts could be targeted locally. The team hopes that their continuing research will help them understand specific drivers of heavy metal pollution in some parts of the Twin Cities.