Climate change could release large reserves of mercury, increasing health risks

Is the article of high quality?

“It is of high scientific quality, as it rigorously describes the current state of knowledge regarding the mercury cycle. A notable innovation is the attention it pays to ‘legacy mercury’ in relation to current mercury emissions—that is, it focuses on the large reservoir of mercury that has accumulated over centuries in various environmental strata (soil, ocean, sediments, permafrost).”

How does the article fit with existing evidence?

“It fits perfectly, as it demonstrates that mercury concentrations have decreased in some regions thanks to the Minamata Convention, which limits emissions. However, this finding aligns with evidence that a significant portion of the mercury circulating in the environment comes from historical deposits. The article highlights that climate change alters key processes such as wildfires, permafrost thaw, changes in atmospheric and oceanic circulation, runoff, and microbial methylation, all of which directly influence the mobilization and bioaccumulation of mercury. For all these reasons, the success of emission reduction policies could be limited by the effects of global warming on the biogeochemical cycle of mercury.”

What are the implications? 

“The implications for public health and environmental management are extremely significant.” 

What is the risk posed by the relationship between climate change and the mercury cycle? 

“There is a risk that the amount of mercury available in the environment will increase, but there is also a significant risk that the formation of methylmercury—the most toxic chemical form that biomagnifies throughout the food chain until it reaches high concentrations in large fish and, consequently, in humans—will be facilitated and accelerated. This could pose a major health problem for populations that depend on fish consumption, especially Amazonian indigenous communities affected by artisanal gold mining, as well as indigenous communities in Arctic regions.” 

Are there any significant limitations that should be taken into account? 

“That’s right; some of the mechanisms described are still uncertain, certain climatic processes act in opposite directions, and the predictions are based on models that do not fully represent the interactions between the various environmental compartments (atmosphere, oceans, soils, and ecosystems). Furthermore, there are few time series of the metal in soils, waters, and biota that would allow us to validate the predictions.” 

Is the article of good quality?

“Yes”.

How does it fit in with the existing evidence?

“It is a timely review, based on literature data, of the risk of mercury mobilisation through various processes linked to climate change. In fact, back in 2015 we already pointed out that the warming of mountain ranges would lead to the re-emission of organic pollutants that had been trapped by low temperatures; as temperatures rise, these would return to the air and create an additional source of pollution. This was published in the journal Atmospheric Chemistry and Physics, volume 15, pages 6069–6085 (2015). It did not concern mercury but organochlorine compounds; however, the mechanism by which they were reintroduced into the environment was the same.”

What are the implications?

“It highlights yet another potential problem arising from climate change.”

What is the risk associated with the link between climate change and the mercury cycle?

“As the article states, climate change may lead to increased mercury poisoning amongst the population.”

Are there any significant limitations that need to be taken into account?

“I believe the statement ‘Warm ocean temperatures can reduce the solubility of mercury by increasing kinetic energy, forcing dissolved gaseous mercury out of the ocean into the air’ is highly speculative. At higher temperatures, more mercury will also dissolve; incidentally, mercury is highly insoluble in water and is generally associated with suspended particles in it.”