Human activities have led to the pollution of some of the remotest places in the world, a new study shows.
By examining ice cores taken from the Guliya ice cap in northwestern Tibet, researchers found that by measuring lead isotopes in dust-filled samples, they could detect a clear change in lead source levels present in the environment long after the Industrial Revolution.
While increases in the amount of lead could be found in ice core samples dated to the beginning of the Industrial Revolution, a significant change in its origin was noted beginning in 1974, when regulatory agencies in the U.S. began to institute strong emissions policies to curb dangerous overexposure to the metal. Though this caused a decrease in some types of gasoline use in some countries, other sources of lead emissions peaked later, said Roxana Sierra-Hernandez, lead author of the study and a senior research associate at The Ohio State University’s Byrd Polar and Climate Research Center.
“Our lead isotope samples date to about 36,000 years ago, a time when we know that no civilizations at the time were using lead – meaning that much of what we found is natural,” she said. “Now with this work, we can pinpoint anthropogenic lead and when they left a mark in the region.”
The study was published recently in the journal Communications Earth & Environment.
Millions of people rely on the glaciers in the Tibetan Plateau for life-sustaining water, but as global warming causes glaciers to retreat, those communities are put in jeopardy due to reduced water levels. What’s more, as glaciers continue to melt, the pollutants preserved inside them will also escape, said Sierra-Hernandez.
“Depending on the amount of pollution there is in the environment, it sinks into these glaciers,” she said. “If a glacier melts, that source of pollution can leak into nearby rivers.”
While small quantities of lead do originate from beneath the Earth’s crust, the bigger issue is lead put into the environment through human activity, she said. Prolonged exposure to the heavy metal can be toxic to humans, both when ingested or inhaled through contaminated food, water or air. It has been known to lead to a wide variety of health issues, including cancer, cardiovascular disease and fertility issues.
With more accurate data on what constitutes a natural lead baseline, researchers can get a better handle on how drastically humans have affected the environment and better prepare for these consequences, according to the research.
What also sets this study apart, said Sierra-Hernandez, is that the instruments and models the research team used were sensitive enough to discern the type of pollution the lead came from. They found that up until 2007, Chinese gasoline was the main source of the lead before those emissions decreased and emissions from coal and lead-zinc ores increased.
Overall, their work emphasizes a huge change in lead sources during the last few centuries, and offers a glimpse into how local pollution distributes globally, even to faraway glacial regions.
It’s an issue that likely won’t be solved by one country alone, noted the study. “Politicians need to be conscious enough to see that lead is still a concern and make policies that avoid emitting more of it, whether it’s from sources of coal or gasoline,” said Sierra-Hernandez.
Additionally, since lead isotopes can act like a fingerprint for unique chemical signatures, researchers can use them to track and investigate sources of pollution, opening a path for similar studies to analyze and compare polluted ice core samples from other glaciers around the world, said Sierra-Hernandez.
“Future studies can build on this study to compare modern and ancient pollution trends and better identify sources due to human activities,” she said. “It’s important to do more lead isotope studies. It’s hard and it’s time-consuming, but there’s so much to learn.”
Other co-authors include Elizabeth M. Griffith and Lonnie G. Thompson from Ohio State as well as Franco Marcantonio from Texas A&M University.
