Human emissions increased mercury in atmosphere seven times

Since around 1500 BC, the start of the modern era, human activities have led to a sevenfold increase in the amount of toxic mercury in the atmosphere, according to new research from Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS).

New method estimates pre-human mercury levels

The study, led by Fred Cawley, professor of environmental chemistry, and Elsie M. Sunderland, professor of Earth and planetary sciences, introduced a new method to accurately estimate the annual mercury emissions from volcanoes, the only natural source of mercury. Using this estimate and a computer model, the team was able to determine pre-human atmospheric mercury levels.

The researchers found that before human mercury emissions, the atmosphere contained an average of about 580 megagrams of mercury. However, a 2015 study estimated that atmospheric mercury levels were about 4,000 mg, roughly seven times higher than the natural state estimated in this study.

Human mercury emissions originate from coal-fired power plants, waste burning, industry, and mining. The study has been published in Geophysical Research Letters.

“Methylmercury is a potent neurotoxin that bioaccumulates in other organisms, including fish and people,” said researcher Sunderland. “Understanding the natural mercury cycle driven by volcanic emissions sets a baseline target for policies aimed at reducing mercury emissions and helps us understand the full impact of human activities on the environment.”

Despite its significant impact on human health, the amount of mercury in the atmosphere is relatively low, making it nearly undetectable via satellite. The researchers used sulfur dioxide, a key component of volcanic emissions, as a proxy for mercury.

Estimating volcanic mercury impact globally

The team reverse-engineered the amount of mercury attributable to volcanic eruptions using a compilation of mercury and sulfur dioxide ratios measured in volcanic gas plumes. They then used the GEOS-Chem atmospheric model to simulate how volcanic eruptions distribute mercury globally.

While mercury mixes in the atmosphere and can travel long distances from its source, volcanic emissions directly contribute to only a small percentage of ground-level amounts in most regions of Earth. However, in areas such as the Ring of Fire in South America, the Mediterranean, and the Pacific, volcanic mercury emissions make it difficult to detect human emissions.

This research is crucial for understanding the impacts of long-term mercury trends on humans, fish, air, and oceans. It is particularly important for correcting natural variability in volcanic impact in places where the impact is not negligible.

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