Tag Archives: methylmercury

Where in the World is Mercury? Part 2: Ocean and Fish

By: Noelle Selin

Our previous posts have addressed mercury in the atmosphere, global reservoirs such as oceans and soils, fish and human hair. Since oceans and fish are so important to global mercury exposure, I thought it would be useful to highlight sources of more information about mercury concentrations there. Two recent major studies have been released looking at the mercury problem in aquatic systems. Both of these are being presented at INC-5.

The Biodiversity Research Institute and IPEN, a non-governmental organization involved in the negotiations, have collected worldwide data on so-called “hotspots” of mercury concentrations in fish and human hair samples. The report, available here, found that mercury contamination is ubiquitous in marine and freshwater systems along the world. The report compares fish mercury concentrations from around the world to U.S. EPA human health advisory guidelines. Depending on the country, between 43 to 100% of fish sampled exceeded guidelines; in Japan and Uruguay, concentrations were so high that no consumption was recommended. These guidelines are for one fish mean per month.

From BRI-IPEN report: % of fish samples above health thresholds

Look for Alice Alpert’s interview with Biodiversity Research Institute’s David Evers, who’s here in Geneva, to be posted soon on our blog.

Another key report came out of the Coastal and Marine Mercury Ecosystem Research Collaborative (C-MERC), brought together by the Toxic Metals Superfund Research Program at Dartmouth College. The report analyzed and synthesized the current science on mercury sources  in seafood, and explored ecosystem responses to potential emissions controls.

The report found that mercury pollution is on the rise. In response to emissions controls, methylmercury in open ocean fish would only begin to decrease within several years to decades, while fish in coastal systems could respond over many decades to centuries. In other words, these effects are very long lasting. An interview with Celia Chen, who co-authored the report, was conducted here at INC-5 by Amanda Giang and is posted below.

The Curious Life of a Mercury Atom

by Bethanie Edwards

Hi, a mercury atom here. I’m currently floating in a water bottle of a delegate at the INC5 mercury negotiations in Geneva. As you know, the global community is coming together this week to negotiate ways to prevent my release into the environment. How exactly do I and my fellow mercury atoms make it into the environment to begin with? Let me share my experience with you.

For much of my life I was just a mercury atom sharing electrons with my best friend, a sulfur atom, deep in the earth as cinnabar. My potential toxicity was masked by my rosy appearance. I was expecting to spend my entire life nestled away in the Earth’s crust. But suddenly, I was startled, a loud persistent thud getting closer and closer. It was 1500 AD, and Spanish miners had just dug me out of my lithospheric home in the mountain-sides of Almaden, Spain. That’s when I began my journey, contributing to the 350,000 metric tons of mercury that humans have released into the environment over the last 4000 years.

Illustration from Erker (1574)

Illustration from Erker (1574)

After traveling to a monastery, monks began heating me up. I could feel my bond with sulfur dissipating; I was entering the vapor phase. I was collected in a distillation bulb as I evaporated, separated from the cinnabar. Little did I know, I’d soon be forced into a new partnership (albeit a brief one).

Once condensed into my liquid state and mixed with sluice from gold panning, my affinity for binding with other metals led me to bind together with all of the gold in the river bed sluice, separating the gold from the rock. When the rock was discarded the monks begin heating me up again, ending my short amalgamation with gold. However, this time as I vaporized, I escaped into the atmosphere.

The vapor pressure of mercury is very high, so I floated all the way into the upper troposphere and caught a wind current to the North Pole. Along the way I met a few other mercury atoms. Most of them had found their way into the atmosphere after weathering into rivers and then evaporating, or after being emitted from the eruption of a volcano. I bummed around in the Arctic troposphere for about 6 months.  As I recall, there were quite a few bromine atoms around. I ran into one, lost a few electrons, and then stuck to it. Then we began falling through the atmosphere, luckily there was snow to break our fall. There I waited until summer, when the snow began to melt and I was washed into a fjord.

As the summer progressed in the fjord, phytoplankton bloomed and then died. The bacterial populations began to grow exponentially and, before I knew it, the bacteria had used up all the oxygen. When bacteria deplete all the oxygen gas in an environment, they move on to using other molecules to make a living. Once they started using sulfate (SO42-), my old friend sulfur re-entered the picture. I bound with it and, not too long afterward, one of those bacteria sucked me into her cell. I’m not sure if the bacterium was just interested in the sulfur that I was attached to, or if she found me to be too toxic, but—to my horror—the bacterium quickly tore away the sulfur and stuck me with a methyl group.

Now, I’m not trying to be prejudiced against carbon, but it’s really not a good influence on me. I have enough toxicity problems on my own. And when I’m bound to an organic carbon, I can’t resist diffusing into organisms, be it fish, shellfish, or humans.  That is exactly what happened. After the water that I was residing in was re-oxygenated, a fish came along and I entered its body through the gill tissue, and as I was a methylmercury molecule by then, I wasn’t the only one to do so.

Eventually my fishy friend’s luck ran out; a fisherman caught him and cooked him up for dinner. I stayed inside the fisherman until he lived out his days and was cremated, and I was released back into the atmosphere.

I felt bad for the poor fellow but I was perfectly happy to be back in the atmosphere. I was looking forward to seeing the Arctic again. But to my surprise, I started falling to the Earth very shortly after being emitted. It must have been all the soot that I was associated with. I was deposited on the forest floor. As the seasons turned and leaves fell and decayed, I became buried in the soil. The rains came and went, but I stayed in the forest getting buried millimeter by millimeter deeper into the soil with each passing year. Until the day the fires came, that is.

Sometimes forest fires burn so hot that they scorch the soil. When this occurs, volatile elements like me can be vaporized and released into the atmosphere. While I will admit I was sequestered in the soil for quite a while, I did not expect to see so many other mercury atoms when I returned to the atmosphere. I met mercury atoms that had found their way to the atmosphere after being in fillings in people’s mouths, atoms that used to reside in light bulbs, several atoms that were used recently in gold mining in the depths of the jungle, and of course the atoms that were released from coal.

This time when I met and bound with a bromine radical, I was in the atmosphere over the Swiss Alps. Since Switzerland is a temperate region, it took much longer to get deposited than it had when I was in the Arctic. However, I eventually landed in the waters of the Alps and ultimately made it into the water bottle of an INC5 delegate.

Since I am one of 1.5×1015 mercury molecules in this water bottle alone, I sure do hope that they agree upon and sign a treaty with teeth!


Forms of Mercury: Beyond the Silver Liquid

By: Noelle Selin

It seems a bit strange to hear delegates at an intergovernmental negotiation on mercury discussing how to define “mercury.” Doesn’t the periodic table define it? Not only is mercury an element, but it’s also the reason why we’re all here in Geneva to negotiate an agreement. But defining exactly what is being addressed by the treaty is a critical issue – especially since mercury exists in many different forms in the environment.

Mercury in its liquid form is most  familiar.

Mercury in its liquid form is most familiar.

The chair’s draft treaty text defines mercury as “elemental mercury”. Elemental mercury is the liquid substance that many people recall when they think of mercury. In the atmosphere, most mercury is in elemental form, but it is a gas rather than a liquid. Elemental mercury is often abbreviated as Hg(0).

Another definition in the convention is “mercury compounds,” which addresses forms of mercury other than elemental mercury. What other forms of mercury are there?

Methylmercury is of particular concern, because it is the toxic form of mercury found in fish. Mercury is converted to methylmercury in aquatic systems by sulfate- and iron-reducing bacteria. For more on the health effects of methylmercury, see our earlier post.

In addition to elemental mercury, atmospheric mercury also exists as divalent mercury. Divalent mercury, also referred to as Hg(II), is formed when elemental mercury has undergone a chemical reaction of oxidation, losing electrons. In the atmosphere, Hg(II) can bind with other elements, but scientists don’t yet know exactly what these forms are. The chemical form of Hg(II) in the atmosphere could be HgCl2, HgBr2, Hg(OH)2, or HgO. The leading candidate is HgCl2, [give the name for this?], but this is a topic of current research. When Hg(II) is measured in the atmosphere, it is referred to as reactive gaseous mercury. Forms of mercury found in the ocean include both Hg(0) and Hg(II).

Emissions from different sources release different forms of mercury. Emissions from the surface ocean and land are in the form of elemental mercury. Anthropogenic sources, such as coal power plants, can release both Hg(0) and Hg(II). This is important because the two forms of mercury have different environmental behavior.

Hg(0) lasts for a long time in the atmosphere (6 months to a year), meaning that it circulates around the globe and can travel long distances. Hg(II) can easily rain or settle out after only a few days in the atmosphere, which means it is more likely to enter the environment nearby its source. Thus, reducing Hg(II) emissions will have important local benefits, compared with reducing Hg(0), which has important global benefits.

The behavior of mercury in the environment, however, is complex. Thus, we need to use computer models [pdf] to determine how mercury changes form and travels after it is emitted. These models use the chemical and physical properties of mercury in its various forms to estimate where mercury will travel over time. Mercury deposited to the environment as Hg(II) can return to the atmosphere as Hg(0). Additionally, Hg(0) can react (oxidize) to form Hg(II) in the atmosphere, and Hg(II) can then reduce back to Hg(0). In other words, mercury can change its form. This can occur anywhere in the atmosphere, even when it is being released from power plant plumes [pdf]. Ultimately, all mercury released continues to cycle through the environment for centuries, contributing to the global mercury legacy.

Many of these reactions are not well understood by scientists, so the transport and fate of mercury in the environment is a topic of significant ongoing research.

Benefit estimates and other health effects from mercury

By: Amanda Giang

When I’m not in glamorous Geneva, and instead in my much-less-glamorous cubicle in Cambridge, MA, I work on assessing the benefits of reducing mercury emissions. The bulk of these benefits are related to improved health—reviewed in our earlier post. Discussion on the health impacts of mercury normally focus on neurologic effects—and with good reason. These effects often have devastating impacts on the lives of victims, and heavy social and economic costs—even when we’re talking about subtle IQ loss from fetal exposure to methylmercury.

What’s more, we have a large body of scientific evidence that helps us understand these neurologic effects, and that can help guide policy decisions about preventing them. But, focusing on just neurologic effects may not tell the whole story. There may be other—though considerably more uncertain—health effects from mercury exposure that have serious policy implications. A large part of my research is about how to include these uncertain health effects in estimating benefits from reduced mercury emissions.

Of these uncertain effects, cardiovascular impacts may be the most important, and also the least uncertain. A growing body of evidence suggests that there may be a causal relationship between methylmercury and cardiovascular disease (coronary heart disease, heart attacks, increased blood pressure). Scientists still aren’t sure why mercury might promote heart attacks; one hypothesis is that it causes oxidative damage.

A committee convened by the US EPA recently decided that there was enough evidence, at least for heart attacks, to warrant including this health effect in future benefit assessments for mercury regulation.* Taking into account mercury-related heart attacks is important because the “cost” of a heart attack—personal, social, and economic—is very high; particularly if a heart attack leads to a fatality. In one of the first studies to include heart attacks in its calculations of costs and benefits, 80% of the benefits associated with reduced mercury exposure ($8.6 billion/year in the US) were due to reduced heart attacks.

If, through further research, it turns out there is a causal relationship between mercury and heart disease, then this week’s mercury treaty might be even more socially beneficial than countries initially thought. This was the case when the US regulated sulfur dioxide in the 1990s. Originally, the focus during the policy’s development was on environmental benefits from reduced acid rain. However, it later emerged that reducing sulfur dioxide has huge health benefits (an unexpected $70 billion/year!). As the science develops, we’ll see whether this will play out for mercury as well.

* NOTE: In the US, part of the regulation making process involves assessing the costs and benefits of regulation.

Mercury’s Health Effects

by Alice Alpert, Ellen Czaika, and Amanda Giang

Pathways to exposure

Although these negotiations are explicitly focused on creating an environmental treaty, mercury’s major significance is its toxicity to humans. When you think about mercury, you probably picture a mercury thermometer. In a thermometer, you can literally see the silvery mercury in its bulb – this is liquid, elemental mercury. If you are absent minded and accidentally drop that mercury thermometer on the bathroom floor, the mercury will spills and form into beads. Although it’s not a good idea to touch this mercury, it is also not easily absorbed by the digestive system in this form.

The more pernicious way for this mercury to enter your body is if it vaporizes, which happens to a small amount of the liquid mercury at room temperature. If you inhale the vapor it can easily pass from your lungs into your blood stream and damage tissues. In fact, vacuuming up the spilled mercury can increase its vaporization and therefore the danger.

In truth, most people will not be exposed to mercury in this form. Instead, people working in chlor-alkali production, mercury mining and refining, thermometer production, dentistry, and in the production of mercury-based chemicals are at increased risk. Although measures have been taken to limit occupational exposure to mercury, many workers may continue to be at risk. Similarly, artisanal or small-scale gold miners are routinely exposed to mercury vapor at very high levels, in the process of burning the mercury-gold amalgam used to extract gold from ore. Indeed, miners and their communities often exhibit clear signs of mercury poisoning.

Another important pathway for mercury exposure is through eating seafood. In fact, according to the World Health Organization (WHO) (Section 2.4, paragraph 128), for many people this is the main pathway for human exposure to methylmercury. Exposure happens through the process of bioaccumulation and biomagnification. In brief, mercury is methylated to methylmercury (CH3HgX) by bacteria in the ocean and then accumulates in fish and marine mammals. Long-lived predatory fish at the top of the food-chain, such as swordfish, tilefish, shark, and tuna, can accumulate dangerously high concentrations of mercury. The US EPA lists guidelines for safe consumption of fish. Women who are pregnant or who could become pregnant should be especially careful about eating mercury contaminated fish because the mercury can be harmful to the developing fetus.

In addition, exposure could happen through dental amalgams. Elemental mercury is used in dental amalgam, and it can be ingested or its vapors can be inhaled. This is a contentious issue in the negotiations. The American Dental Association and the US Environmental Protection Agency state that mercury in dental amalgam is safe, while a report by the WHO (p.11) states that dental amalgam is a significant source of mercury exposure in those who have mercury fillings. We encourage you to look into the reports if you are concerned about this issue. For a solid overview of all pathways, see the WHO report on mercury exposure.

How and why does mercury make us so sick?

The most serious effects of elemental mercury vapor concern the nervous system, including tremors, erethism (a neurological disorder characterized by irritability and shyness), insomnia, muscle weakness, and memory loss. At especially high concentrations, the kidneys, thyroid, and pulmonary system can be affected. Similarly to elemental mercury, mercury in its organic form, methylmercury, has serious neurological effects, including neurobehavioral deficits, neuronal loss, loss of muscle movement, hearing loss, paralysis, and death.

Why is mercury so toxic for the nervous system? There are two specific processes: first, elemental mercury and methylmercury can easily cross the blood-brain barrier and once in the brain, can be oxidized to the mercuric ion (Hg2+), which cannot cross back across the barrier. Instead, mercury is trapped in the brain, where the second process begins, neurotoxin by excitotoxicity. What? Okay, we’ll slow down and explain these multi-syllabic words: in studies of rats, Hg2+ inhibits glutamine and glutamate transport, causing receptors for these molecules to become overexcited. This causes a large influx of the calcium ion into the cell, which activates enzymes that can lead to the neuron’s death, and thus the serious neurological effects. This second process is the reason why mercury is so toxic.

Mercury crucially effects developing fetuses. In the same way that methylmercury can cross the blood-brain barrier, it can also pass through the placenta from a mother to her fetus and then to the developing fetus’ brain. As a neurotoxin, methylmercury can also damage its nervous system, and in fact mercury has lasting negative effects when fetuses are exposed to concentrations at levels that are only 10%-20% of toxic levels for adults.

Babies born to women who consumed significant amounts of methylmercury while pregnant display symptoms similar to cerebral palsy, including delayed walking and talking, altered muscle tone and reflexes. Tragically, these impairments are permanent and affected will suffer from these impairments for their entire life. In fact, recently published research estimates that IQ reductions due to chronic, low-level fetal mercury neurotoxicity costs the European Union alone € 8-9 billion euros per year. Clearly, there are significant social and economic impacts from mercury exposure, particularly for the young.

Dinner…with a side of mercury?

by Julie van der Hoop

Worldwide, fish consumption is the main source of human exposure to methylmercury, a highly toxic form of mercury that biomagnifies up the food chain [1]. Accordingly, a fair amount of media attention has focused on mercury content in fish as a potential public health threat [2]. In an effort to protect consumers, US state and federal agencies have set guidelines for limiting consumption of fish that tend to be high in levels of methymercury (these guidelines are particularly important for pregnant women and women of childbearing age, as fetal exposure to methylmercury can create long-term developmental impacts). Additionally, health advisories are available online to help consumers avoid consuming types of fish that are particularly high in mercury and other toxins.

In light of these health concerns, it is no surprise that one of the aims of a global mercury treaty is to, through reducing mercury emissions, ultimately reduce the levels of toxic methylmercury in fish and shellfish.

Should we eat fish?

Fish are often touted for their great nutritional profile: they’re low in fat, with high-quality protein and an added dose of vitamins. The American Heart Association recommends at least two 3-ounce servings of fish per week to obtain beneficial omega-3 fatty acids. However, balancing the risks of mercury consumption and the benefits of fatty acids can be difficult for both consumers and those faced with the task of setting advisories.

Some studies are now urging consumers to weigh the risks and benefits of eating certain types of fish. In terms of what to avoid, shark and swordfish shouldn’t make it to your plate, not even for a single meal per month. The health benefits of fishes such as tilapia, pollack, flounder, shrimp, trout, herring, salmon, canned light tuna, and cod generally outweigh their potential mercury concentration cons [3]. That being said, other contaminants (e.g., persistent organochlorines in farmed salmon) and fishery sustainability (e.g., depletion of many cod stocks) are additional concerns worth considering when planning your meals.

Will fish mercury levels ever decrease?

It’s uncertain when—and whether—you’ll be able to enjoy all-you-can-eat sushi without thinking about how much mercury you’re consuming. However, recent research is helping us better understand how changes in mercury emissions could affect the future methylmercury content in fish.

In a new study, researchers added mercury to an experimental lake to learn how quickly it was incorporated into fish and to track what happened when mercury-addition stopped. Good news: concentrations of methylmercury in lake fish decreased much faster than previously thought. As reported by Susan Bence this week, researchers working on the project believe that reductions in mercury emissions could lead to a fairly rapid decrease in fish mercury levels in certain ecosystems. How fast these levels will decrease, however, will vary depending on where the fish are caught.

Still, mercury cycles through the environment very slowly, and even if we can restrict future emissions to current level, this will not reduce the global mercury burden. A major cut in mercury emissions is needed to reduce methylmercury concentrations in marine fish: as a recent report by Chen et al. shows, cutting mercury emissions by about 40% could lead to a 16% decline in mercury concentrations in fish in the North Atlantic Ocean.

What should you do in the meantime?

To help guide you in your fish dining decisions, check out the EPA’s online guidelines for eating and selecting fish and shellfish, as well as the consumer guides and apps available from groups such as NRDC and the Sierra Club. Still, what might matter most in is not the species of fish, but where it was caught [4]. Informing ourselves as consumers is increasingly important – whether it be for concerns over sustainability or mercury consumption.