Tag Archives: mercury forms

Mercury NOMADSS travel to Smyrna, TN!

Greetings from sunny Smyrna, TN, where for the last few weeks we (Noelle Selin, Amanda Giang and Shaojie Song) have been participating in a mission to measure mercury and other pollutants in the atmosphere. NOMADSS is the title of the airplane-based campaign, which stands for “Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks.” It’s part of the larger Southeast Atmosphere study that’s investigating air quality in the southeast U.S. this summer. We are using our models to predict where we’re likely to find pollution, and to interpret data from the last several days to guide planning.

If you’re interested in following all of the science going on this summer, check out the Southeast Atmosphere Study home page, follow @SAS_Operations on twitter. There’s also a great blog on another component of the Southeast Atmosphere Study, the Southern Oxidant and Aerosol Study. Stay tuned for further updates from the field!

For mercury-specific updates, stay tuned to #MITMercury.


Bioamplification, Bioaccumulation and Bioconcentration

By: Julie van der Hoop

The confusion between bioamplification, bioaccumulation and bioconcentration is understandable. Yesterday, delegates asked for a clarification and explanation as to how this happens. These terms are not interchangeable, though they are often used as if they were. This post should clarify the situation.


Bioamplification (or biomagnification, as the picture shows) refers to an increase in the concentration of a substance as you move up the food chain. This often occurs because the pollutant is persistent, meaning that it cannot be, or is very slowly, broken down by natural processes. These persistent pollutants are transferred up the food chain faster than they are broken down or excreted.

In contrast, bioaccumulation occurs within an organism, where a concentration of a substance builds up in the tissues and is absorbed faster than it is removed. Bioaccumulation often occurs in two ways, simultaneously: by eating contaminated food, and by absorption directly from water. This second case is specifically referred to as bioconcentration.

So, what have we learned? Bioconcentration and bioaccumulation happen within an organism, but biomagnification occurs across levels of the food chain. An example: phytoplankton and other microscopic organisms take up methylmercury and then retain it in their tissues. Here, mercury bioaccumulation is occurring: mercury concentrations are higher in the organisms than it is in the surrounding environment. As animals eat these smaller organisms, they receive their prey’s mercury burden. Because of this, animals that are higher in the food chain have higher levels of mercury than they would have due to regular exposure. With increasing trophic level, mercury levels are amplified.

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.