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While strolling through the Twin Cities, you might spot a monarch or swallowtail butterfly drifting gracefully through patches of blooming flowers, dusting themselves with pollen.
Scientists have found that some butterfly species are picking up more than just pollen.
In new research, University of Minnesota scientists discovered that some butterfly species are absorbing doses of lead beyond what occurs naturally.
Butterflies play a crucial role in ecosystems, as they pollinate plants and can indicate how healthy the insect population is overall. Principal investigator Emilie Snell-Rood says if lead pollution harms butterflies, it also could threaten the environment for other invertebrates.
Snell-Rood and the paper’s lead author, Lindsey Kemmerling, have studied butterflies for the past few years.
Only recently, Snell-Rood said that she and Kemmerling’s team have begun to measure how much lead pollution these butterflies are carrying in their bodies — and what that could mean for their survival.
“We’ve been doing a lot of work trying to think about how heavy metal pollutants move through urban ecosystems,” Snell-Rood said. “They are an important part of urban food webs, they’re of conservation concern, and they’re also really good indicators of overall health.”
The team launched a two-year field study across the Twin Cities.
Over the study’s duration, their team collected 535 butterflies from 38 sites, using lead exposure data from the Minnesota Department of Health.
At sites that ranged from urban farms and community parks to residential areas, researchers gathered not just butterflies, but soil, plants and air samples.
Through their measurements, Snell-Rood and Kemmerling’s team were able to conclude that some butterfly species, like the Cabbage White, had over 12,000 units of lead in their body, a concerning amount for an invasive species that would be more adaptable. Some species had lower amounts, such as the Northern Pearly Eye, with as little as 2 units of lead.
Digging deeper through their data, Snell-Rood and Kemmerling were able to find a correlation between lead levels and smaller wing sizes. Smaller wings can hamper butterflies’ ability to elude predators, find food or migrate.
Snell-Rood and her team believe that the main way their butterfly specimens have been exposed to lead is through contact with airborne particles, or soil.
A butterfly absorbs lead if it lands on contaminated ground as an adult or crawls through dirt at its larval stage. Butterflies may also pick up lead particles suspended in the air from waste incinerators and dust.
Soil becomes contaminated with lead when lead paint peels off the outside of older buildings and mixes with the soil. Soil can also be contaminated by factories and construction. A lead level of around 220 units is considered the threshold before negative effects were observed in butterflies, according the U researchers’ paper.
The only way to get rid of the lead contamination is to dig up the soil and safely dispose of it.
Snell-Rood says that her team’s findings add to a harsh reality.
“Butterflies and other insects are in a huge decline. So, thinking about whatever we can do to help insect populations is important,” she said.
Since the 1970s, the Environmental Protection Agency has tried reducing lead pollution and regulate the manufacture of products that contain lead. But Snell-Rood says that lead is still a problem because contaminated areas are not being treated properly.
“There’s this idea that led was a problem of the past,” Snell-Rood said. “But it’s still in the soil, it’s still in the air, and we’re still finding it in butterflies.”
Snell-Rood says that while lead is still lingering in the Twin Cities, removing it entirely could be nearly impossible.
Monarch butterfly expert Karen Oberhauser, says it’s not the lead that will kill the butterflies, but the loss of habitats.
“The problem of lead-contaminated soil would not be the thing that would drive butterflies to extinction,” the emeritus professor at the University of Wisconsin said. “It is the loss of habitat and climate change. Lead is just one thing in what we call ‘death by a thousand cuts.’”
But she has a solution, one that can be done right in your community.
"The thing that we can do is to both preserve habitat and build new habitat,” Oberhauser said. “That habitat can be in our yards, between agricultural fields, in protected parks, along roadsides, power lines and railroad tracks, are all valuable places.”
Snell-Rood and Kemmerling’s team hope that their research will push Minnesota lawmakers to create soil remediation and lead-reduction policies that'll help humans as well as the insects in the shared environment.
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