Hemond, third from left, with students, collecting sediment in Thoreau’s bog.
PHOTO: COURTESY OF THE RESEARCHERS
He would likely be troubled to learn that today in a wetland named for him, MIT biogeochemist Harold Hemond PhD ’77 is extracting the airborne metals released by industrialized society, including rare earth elements (REEs), increasingly indispensable in consumer electronics, computers, and clean energy technologies.
For Hemond, William E. Leonhard Professor in the Department of Civil and Environmental Engineering, the presence of these substances in Thoreau’s Bog—a body of water he has studied for four decades—is an opportunity to anticipate and perhaps prevent problems as society changes its chemical footprint: “We need to be proactive in understanding what kind of impacts we are making,” he says. Hemond’s research is part of a novel investigation, supported by MIT’s new Environmental Solutions Initiative (ESI), into the potential effects of REEs on the environment and humans.
“Use of these materials has gone up tenfold in a decade, but there’s been very little testing of their toxicity,” says John Essigmann SM ’72, PhD ’76, the William R. and Betsy P. Leitch Professor in Residence, whose lab straddles the departments of chemistry and biological engineering. “Many materials released in large amounts in the past, like asbestos, DDT, and lead in gasoline, seemed very constructive at the time but ultimately proved destructive to biological systems.” Along with Bevin Engelward, professor of biological engineering, Essigmann became Hemond’s partner on the ESI grant through the activities of the MIT Center for Environmental Health Sciences.
Essigmann and Engelward are studying how these new environmental chemicals might affect human health. This means closely examining Hemond’s bog sediments, which date further back in time as they increase in depth. The sediments are vital records of atmospheric emissions, since this bog is fed exclusively by rainwater.
Measurements by the Hemond Lab reveal a host of REEs, likely released in large part by metal smelting processes. According to a preliminary chronology, these elements barely registered in 1900, but grew through the century and spiked to hundreds of parts per billion by mid-century. Then they began to decline, Hemond says: “Our working hypothesis is that increasing industrial activity put more of these chemicals in the air, and then the 1970 Clean Air Act helped reduce their presence.”
While this appears reassuring, Essigmann finds reason for concern. The bog reflects historic, regional atmospheric concentrations of REEs, so concentrations in regions lacking air regulations, or regions with aggressive mining and manufacturing practices, might currently be much higher. With expanding global use and discard of products incorporating REE-based technologies, concentrations could rise again as REEs find their way into the environment at unprecedented levels.
One element from Hemond’s bog samples drew Essigmann’s particular attention: cerium, now turning up as a fuel additive to make diesel engines burn more efficiently and at lower temperatures. This epitomizes why Essigmann calls REEs “a double-edged sword.” He explains, “On the one hand cerium oxide particles are good for the environment and sustainability, but on the other it’s been discovered that they escape from tailpipes, and we have to worry about the health consequences if we breathe them.” Using technology developed in the Engelward laboratory for measuring DNA damage, Essigmann’s preliminary research indicates that while these particles alone are not very toxic, hydrogen peroxide produced by the body’s inflammatory response to small particles can combine dangerously with cerium oxide. Together, says Essigmann, “they produce a very harsh chemical byproduct that breaks DNA.”
Before drawing conclusions about health impacts, Essigmann and Engelward await ongoing testing by Hemond, which will try to correlate concentrations of REEs taken from air samples with those from rain-fed bogs. “We will be able to tell you based on what you see in a bog anywhere in the world how much people breathe of REEs at any given time,” says Essigmann. Using concentrations typical in countries manufacturing REEs, Essigmann hopes to pursue further tests with these compounds using mouse models. If these experiments demonstrate lung damage, he believes the work might influence regulatory policy.
“Think of our work as due diligence,” says Hemond. “We want to be ahead of the curve this time.”