The activity of humans has significantly raised the levels of mercury in the atmosphere. These levels have gone up about seven times since 1500 CE, when the modern era began. A new method was developed to accurately assess mercury emissions from volcanoes, which are thought to be the single largest natural source of mercury emissions. This work determined that before people started injecting the atmosphere with mercury, there was an average of about 580 megagrams (Mg) of mercury in the atmosphere. By 2015, however, the level of mercury in the atmosphere was estimated to be around 4,000 Mg, or about 7 times more than what would be expected due to natural conditions. The findings have been reported in Geophysical Research Letters.
All of that excess mercury comes from a few places, including coal-fired power plants, the incineration of waste, mining, and other industries. It's also toxic.
"Methylmercury is a potent neurotoxicant that bioaccumulates in fish and other organisms, including us." If we can learn about the natural mercury cycles that are driven by volcanic emissions, it shows where the baseline is, and helps us create policies that can lower mercury emissions. It also helps us to reveal how human activities are impacting the environment, said senior study author Elsie M. Sunderland, a professor at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).
Mercury in the atmosphere can be difficult to measure because the levels are fairly low; only a single nanogram of mercury might be found in one cubic meter of air, for example. These levels are not possible to detect with satellite technology, which is used to measure other emissions. Unfortunately, even very low amounts of mercury might be detrimentally affecting humans and animals.
In this study, the scientists solved the detection problem by assessing levels of sulfur dioxide, which are a primary part of volcanic emissions. While this is not a direct way to measure mercury, it was used by the researchers as a proxy to show when and where volcanic emissions of mercury were probably happening. Sulfur dioxide ratios in volcanic plumes were used to determine the levels of mercury that volcanoes naturally released. Additional atmospheric modeling indicated how that mercury moved around the world.
"The nice thing about sulfur dioxide is that it's really easy to see using satellites," said first study author Benjamin Geyman, a graduate student at SEAS.
The study suggested that mercury seems to move a long way from where it is initially released, and mixes into the atmosphere. However, only a small percentage of ground-level mercury concentrations in most parts of the globe can be attributed to volcanic emissions. In some areas, like the Ring of Fire in the Pacific, or the Mediterranean, a higher rate of volcanic emissions makes the natural release of mercury harder to track.
Hawaii, for example, has higher natural variations in mercury levels over time compared to a place like Boston, noted Geyman. But this work shows how volcanoes are connected to atmospheric mercury levels, and could help us understand how people affect long-term trends in mercury levels in the air, ocean, and places like fish. "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."
Sources: Harvard John A. Paulson School of Engineering and Applied Sciences, Geophysical Research Letters
