Since the dawn of the modern era around 1500 C.E., human activities have escalated the concentration of mercury in our atmosphere by a staggering sevenfold.
These alarming findings are the result of a study from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).
The research team, led by Professor Elsie M. Sunderland, developed a new method to accurately estimate how much mercury is emitted annually from volcanos, the largest single natural emitter of mercury.
The new technique combined an accurate estimation of volcanic mercury emissions with a computer model. This integration was crucial to reconstruct the atmospheric mercury levels before the influence of human activities.
Prior to human intervention in the natural cycle, the atmosphere contained approximately 580 megagrams of mercury.
Yet, by 2015, other independent studies assessing all available atmospheric data revealed that mercury content had soared to around 4,000 Mg. This sharp rise, almost seven times the natural baseline, is attributed to human-induced sources.
Emissions from coal-powered plants, industrial activities, waste incineration, and mining operations are the primary culprits.
“Methylmercury is a potent neurotoxicant that bioaccumulates in fish and other organisms – including us,” said Professor Sunderland.
“Understanding the natural mercury cycle driven by volcanic emissions sets a baseline goal for policies aimed at reducing mercury emissions and allows us to understand the full impact of human activities on the environment.”
However, despite mercury’s profound influence on human health, its atmospheric presence is minuscule. Detecting even a nanogram of mercury in a cubic meter of air via satellite is practically impossible.
The researchers needed to use another chemical emitted in tandem as a proxy. They focused on sulfur dioxide, a major component of volcanic emissions.
“The nice thing about sulfur dioxide is that it’s really easy to see using satellites,” said study first author Benjamin Geyman. “Using sulfur dioxide as a proxy for mercury allows us to understand where and when volcanic mercury emissions are occurring.”
Using mercury-to-sulfur dioxide ratios found in volcanic gas clouds, the team estimated the levels originating from volcanic outbursts. Subsequent application of the GEOS-Chem atmospheric model showed the dispersion of volcanic mercury on a global scale.
The study revealed that, despite mercury’s capability to integrate into the atmosphere and traverse vast distances, volcanic discharges only account for a minuscule fraction of ground level concentrations in most global regions.
However, specific regions, namely South America, the Mediterranean, and the Pacific’s Ring of Fire, manifest higher levels of volcanic mercury emissions, complicating the tracking of human-induced contributions.
“In Boston, we can do our local monitoring and we don’t have to think about whether it was a big volcano year or a small volcano year,” said Geyman. “But in a place like Hawaii, you’ve got a big source of natural mercury that is highly variable over time.”
“This map helps us understand where volcanos are important and where they aren’t, which is really useful for understanding the impact of humans on long-term mercury trends in fish, in the air and in the ocean. It’s important to be able to correct for natural variability in the volcanic influence in places where we think that influence may not be negligible.”
The study is published in the journal Geophysical Research Letters.
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