Permafrost locks in tons of mercury–until it thaws

The Minamata Convention on Mercury is now in force.  But is it enough?

Not widely reported last year was an event which may eventually be seen as one of the most important international  agreements since the Paris Agreement on climate change in 2015.

The Minamata Convention on Mercury came into force on 16 August 2017 after 50 countries deposited their ‘instruments of ratification, acceptance, approval or accession’ with the United Nations. Both Canada and the USA signed up in 2013—the year the convention was adopted in Kumamoto, Japan.

It’s called the Minamata Convention after the horrendous tragedy that unfolded in the 1950s when as many as 50,000 people in Japan were affected by mercury poisoning when a factory was discovered to have been discharging waste containing high concentrations of methylmercury into Minamata Bay.  Over 2000 people with severe forms of the disease, including many children, suffered brain damage, paralysis, and delerium.

Toxic stuff

Mercury is extremely toxic—so much so that the World Health Organisation (WHO) considers it one of the top ten chemicals or groups of chemicals of major public health concern.

The stated objective of the Convention is to protect human health and the environment from anthropogenic emission and release of mercury and mercury compounds.

Human foetuses are most susceptible to the toxic effects of mercury. Methylmercury exposure in the womb–probably due to the mother eating fish and shellfish—adversely affects a baby’s growing brain and nervous system.  The primary health effect is impaired neurological development. Cogntive thinking, memory, attention, language, and fine motor and visual spatial skills, may all be negatively affected.

Communities that rely on subsistence fishing are the second group most a risk–a group would include many First Nation communities in northern Canada.

The WHO reported in 2017 that among “selected subsistence fishing populations”, between 1.5 and 17 children per thousand showed cognitive impairment and mild mental retardation caused by the consumption of fish containing mercury.

But in fact, anyone who eats seafood is at risk.

Blood work

In the US, a nationwide study of blood samples in 2000 showed that 15% of women of childbearing age had blood mercury levels that would cause them to give birth to children with mercury levels exceeding the EPA’s maximum acceptable dose for mercury—a dose established to limit the number of children with mercury-related neurological and developmental impairments.

Researchers at that time estimated that as many as 600,000 children were born in the US each year with blood mercury levels high enough to impair performance on neuro-developmental tests and cause lifelong loss of intelligence.

Unfortunately the Minimata Convention won’t reduce emissions of mercury right away: participating countries have until 2022 to implement ‘best available technology’ to reduce emissions from new sources of mercury; and until 2027 to implement best available technology on existing sources of mercury.

And the worst of those existing sources are coal-fired power plants.

In 2010 coal was responsible for the emission of about 475 tons of mercury worldwide, the majority of which was from power generation and industrial boilers. This amount is roughly 40% of total anthropogenic emissions.  In the US, coal-fired power plants account for about 42% of all anthropogenic mercury emissions in the US.

Mercury vapor can be removed from coal-fired power plants using a variety of pollution control technologies—but not completely. The mercury that is removed is then deposited in the solid waste products, mostly fly ash, from the power plant. Impoundments, slag heaps, tailings ponds, and tips, are never  permanent repositories of toxic pollutants. Once coal is mined and burned, one way or another, the mercury will find its way into the environment–and eventually into the food chain.

The only surefire way to stop mercury emissions from coal is to shut down the coal-fired power plants.

And then shut down the mines.

How about switching to natural gas?

Good try.

A bridge to nowhere

Natural gas is also a fossil fuel—just like coal and crude oil.  All fossil fuels contain mercury. The mercury in natural gas is removed in the processing plant that cleans up the gas for consumers.  But mercury is a element.  You can’t destroy it. You can bind it into compounds that may keep it out of the air—but once transformed into methylmercury, it will eventually find its way into streams, rivers, and the ocean. And then into fish and shellfish.

But the changing climate may render the Minamata Convention in its present form irrelevant.

An article this month in the journal Geophysical Research Letters presented the results of a survey of mercury levels  in permafrost soils in North America. They estimate that the amount of natural mercury stored in permafrost in the Northern hemisphere contains twice as much mercury as the rest of all other soils, the atmosphere, and ocean combined.

This mercury has been locked up in frozen tundra soils for millenia.

But the permafrost is melting.

Air temperatures in the Arctic have risen faster that anywhere else on the planet. Average temperatures in the permafrost have increased by over 5°C since the 1980s.

In 2016, permafrost temperatures were the highest on record at the majority of Arctic observation sites. In some places this has pushed the temperature above freezing, meaning that soils that may have been frozen for thousands of years have begun to warm and decompose. Microbial decay will resume and and release mercury to the environment.

Friends for life: Hg & GHG

Not only mercury is released from the warming soils.  Arctic permafrost also holds substantial amounts of old, geologic methane in subsurface reservoirs.  As the permafrost thaws, it may open up pathways for the methane to migrate to the surface. A study conducted in the Mackensie Delta in 2016 found that where the permafrost was discontinuous, emissions of methane were 13 times greater than the emissions typically measured from methanogenic bacteria in the soil.

So the warming climate is producing potentially severe environmental impacts that were not envisaged a few years ago. As the Arctic warms and permafrost soils start to thaw, carbon dioxide, methane, and mercury will all be released to the environment.

The carbon dioxide and methane emissions will strongly reinforce the continuing trend towards higher global temperatures; while the emissions of mercury into the environment will trigger a potentially serious health problem for First Nation communities.



For a deeper dive:

See : Permafrost carbon bomb may be more of a slow burn, say scientists.

See the article on terrestrial permafrost by Romanovsky et al. in the Arctic Report Card 2017 at

See : Methane seeps out as the Arctic permafrost starts to resemble Swiss cheese. This article summarizes the findings of the report in Nature by Katrin Kohnert et al.: Strong geologic methane emissions from discontinuous terrestrial permafrost in the Mackenzie Delta, Canada. Nature Scientific Reports 7, Article number: 5828 (2017).

World Health Organisation key facts : Mercury and health.

Geophysical Research Letters:

For the text on the Minamata Convention on Mercury, see:

Physicians for Social Responsibility : Coal’s assault on human health.



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