I’ve been puzzling for a while about why the areas with the most power plants aren’t the areas with the worst levels of mercury pollution. Why aren’t the areas downwind from the power plants heavily polluted? I keep running across curious statements like “There was no obvious relationship between large-mouth bass or yellow perch fish tissue mercury concentrations and their locations relative to prevailing wind patterns and the incinerators” (source). In that regard I came across a critically important paper. The paper starts with what to me is a most surprising statement.
But before I get to that, a short digression. There are a couple kinds of mercury emitted by power plants, by forest fires, and by your automobile, for that matter. Well, actually three kinds, but there’s very little particulate mercury coming from any of those sources. The two kinds are “divalent” and “elemental”.
Elemental mercury (written as “Hg0”) means what you’d think, atoms of mercury vapor. Because it doesn’t bind with much and it is insoluble, it has a fairly long atmospheric half-life, on the order of a year or so. Elemental mercury is what forms the background mercury levels that are present everywhere in the atmosphere.
Figure 1. Areas in the US where fish have high levels of mercury. White areas have not been tested. EPA threshold as safe to eat is 0.30 ppm (two lightest shades of red). From the EPA’s Mercury Maps (PDF)
The other kind of mercury, divalent mercury (written as HgII), exists in the form of compounds like mercuric chloride (HgCL2). Because these compounds are both water-soluble and chemically reactive, they come out of the atmosphere quickly through deposition by precipitation. In addition, they come out slowly as elemental mercury is slowly changed into divalent mercury in the atmosphere. And as a result of all of these kinds of atmospheric mercury, plus mercury naturally in the soils, we end up with mercury in the fish.
To summarize: elemental mercury is added to the background mercury and doesn’t settle out near the power plant. Divalent mercury is reactive and water-soluble, so it rains and precipitates out near the power plant. And the problem is that analysis of the emissions from the smokestack of coal-fired power plants show on the order of 25% more divalent mercury than elemental mercury. Which sounds like bad news for those living downwind from our power plants.
With that as prologue, here’s the opening statement that I found so surprising, from a paper called “Modeling Mercury in Power Plant Plumes”.
First, the Mercury Deposition Network (MDN) data (1) along a west-to-east transect from Minnesota to Pennsylvania show no significant spatial gradient in annual mercury (Hg) concentrations in atmospheric precipitation although the Ohio Valley includes several large Hg emission sources located, under prevailing wind conditions, upwind of Pennsylvania.
Say what? No hot spots for mercury downwind of several large power plant mercury emission sources? How come I haven’t heard of that?
So I wandered off to the Mercury Deposition Network, where I found a couple more surprising maps.
Figure 2. Total Mercury concentration in the atmosphere in 2010. Units are nanograms per litre. The red “hot spot” in the center of the US reflects the natural mercury coming from deserts and croplands, as I discussed in “The EPA’s Mercurial Madness” SOURCE
As an aside, the EPA and other scientists claim that much of the mercury in the atmosphere is “recycled” anthropogenic mercury. They say the natural emissions are in large part just man-made emissions being re-emitted. I certainly would hope that Figure 2 would put a stop to those claims. The main and overwhelming source of atmospheric mercury in the US is the natural mercury in the soils.
OK, another surprise for me. We’ve seen where the sources are and what’s in the air. Now, let’s see what gets deposited in the rain and snow. Figure 3 shows the wet deposition map for the US in 2010.
Figure 3. Mercury wet deposition rates for the US. Units are micrograms per square metre of surface. SOURCE
Note that strangely, this is kind of a weather map. Why is it a weather map? Well, for example I live on the coast not far north of San Franciso Bay. I was amazed to see that I live in an area of relatively high mercury deposition. Why?
The answer is, because when the moist air sweeps in off the Pacific and hits the coastal mountains, it rains. And when it rains, I get showered with natural mercury from the ocean. Further inland on the east side of California, you can see the western slopes of the Sierra Nevada mountains painted in red. They get the moisture that doesn’t fall on the coastal ranges. And since they are much higher, they pretty much wring the moisture (and the mercury) out of the air, leaving Nevada with little mercury deposition.
The main flow of air in the US is from west to east. As a result, the hot spot over the southwestern US precipitates out in the central US. It is aided by moist air flowing in from the Gulf of Mexico during some months. This can be seen all along the Gulf Coast. Florida, like where I live, is another victim of oceanic mercury poisoning.
Finally, to return to the surprising statement I started with, in Figure 3 the blue arrow shows the prevailing winds blowing over the power plants in the Ohio River Valley towards Pennsylvania. If it is the case that the majority of the mercury emissions are divalent mercury, then why is there no trace of them raining out along the way as we’d expect?
The authors look at several different possibilities. Their final conclusion? (emphasis mine)
A sensitivity study of the impact of the Hg dry deposition velocity shows that a difference in dry deposition alone cannot explain the disparity. Similarly, a sensitivity study of the impact of cloud chemistry on results shows that the effect of clouds on Hg chemistry has only minimal impact. Possible explanations include HgII reduction to Hg0 in the plume, rapid reduction of HgII to Hg0 on ground surfaces, and/or an overestimation of the HgII fraction in the power plant emissions.
We propose that a chemical reaction not included in current models of atmospheric mercury reduces HgII to Hg0 in coal-fired power plant plumes.
This has large implications for the regulation of power plants. All the big power plants in the Ohio River Valley aren’t increasing the mercury deposition towards Pennsylvania. The mercury is being converted into elemental mercury along the way somewhere, so it’s added to the background mercury rather than raining out near the power plants.
In fact, where I live, on the pure clean Pacific coast with lots of sea breeze, I get more mercury pollution than they get around Pennsylvania despite all the coal-burning power stations just upwind from them.
And that, dear friends, was a very big surprise … when’s the EPA gonna step in to save me?
Does this mean mercury is not a poison? By no means, mercury is a bad thing, and it’s everywhere … it just shows the story has lots of tricks and turns.
Always more to learn,
w.
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Willis: “Elemental Mercury” is Hg, not HgO. HgO is Mercury Oxide. I guess you wanted to put Hg° (Hg0 with the “zero” as superscript, which is a correct way to describe metals in their elemental form). Just for clarification, it was misleading for me in the first moment.
Might I respectfully suggest that non-chemists be careful about the use of chemical nomenclature. Hg toxicology is heavily dependent on chemical speciation and there is no such chemical as either methylmercury or ethylmercury despite the gay abandon with which such terms are used.
These entities are ions better expressed as MeHg+ or EtHg+. The toxicology of these ionic species is entirely dependent on the counterion to which they will always be attached in nature. If this is a simple halogen such as chlorine or bromine then you have methylmercuric chloride which is highly toxic readily absorbed through the skin and has a very high bioaccumulation potential. This is the substance that was released from the acetaldehyde plant at Minamata in Japan which accumulated in fish and resulted in the poisoning of the Japanese population in 1956. Similar organomercury compouds were used as seed dressings in the 1960s and 70s and misuse of which produced the much larger death toll in Iraq.
However, as mentioned in a previous comment Hg is very easily bound to S’ groups in proteins and this is how MeHg+ is found in normal fish tissues i.e as MeHgS-Protein compounds. As such the toxicology is very different to that of simple organomercury compounds such as MeHgCl. Breaking the Hg-S bond in the protein in order to release the toxic MeHg+ ion is very dificult and reference to Westoo’s original analytical method to determine the organic mercury content of fish clearly demonstrates the highly aggressive chemical treatment of the tissue taht was necessary to release the Hg in a form that could be measured.
So beware a little knowledege can be a dangerous thing……
Willis, this article would make more sense to newcomers if you changed the “I” to “Anthony” below Article 3 where it mentions “I live on the coast not far north of San Franciso Bay.” It is not immediately obvious that this post has two authors. — John M Reynolds
The estimated lifetime of elemental mercury in the atmosphere is around a year as another poster has noted. That means there is a global dispersion of airbourne mercury and local hotspots are due to deposition of soluble mecuric compounds from oceans/lakes more than from coal fired power plants.
Anthropogenic sources emitt around twice as much mercury (elemental and soluble) as natural surces overall. This is most notable where local industrial sources have generated Hg II compounds with beluga tusks now containting over 10x as much mercury now as they did in pre-industrial times.
It would be very hard to make a case for NOT regulating industrial mercury emissions. They are NOT harmless, they are exceeding natural exposure by around 100% and are cummulative in the food chain. This essay does nothing to refute the need to regulate mercury emissions. The vauge ‘handwaving’ about the sampled deposition rates are arguements for the complexity of the deposition process and the inadequacy of the monitering system, not a basis for the industry to deny the need for emission controls.
Figure 2 shows an improvement in the mercury levels around quite a few of the power stations, or is this just an artifact in the digitisation of the map?
Arthur Dent, alas, there is a little problem with your thiol trapping thesis. It is true that methylmercury(1+) does react with thiols (and selenols), displacing a proton. However, it is not locked away. Cysteine is the normal protein thiol species, and when the protein is digested within or outside the cell, you still have Cys-S-Hg-CH3 or Cys-S-Hg(+). Our amino acid transporters are unable to spot the difference between Cys and Cys-S-Hg-CH3 or Cys-S-Hg(+).
These two conjugated cysteine conjugates are also toxic, the former disrupting methionine pathways and the latter attacking mitochondria.
Willis Eschenbach says:
April 2, 2012 at 1:58 am
That’s what I thought too, but I looked into it a couple years ago and it turns out they used HgNO3 (or would it be Hg(NO3)2? Haven’t checked.)
Page with properly serious tone: http://www.cas.org/newsevents/connections/hatter.html
Page with Lewis Carroll tone: http://corrosion-doctors.org/Elements-Toxic/Mercury-mad-hatter.htm
The chemical triggers connection along hair protein cause it to kink and shrink, an important step of the felting process.
jmrsudbury says:
April 2, 2012 at 3:25 am
Clue 1: Anthony lives in Chico. That’s inland.
Clue 2: Willis was at the dinner yesterday.
One aspect to consider is microbial transformation. It’s not suprising to me to find that the majority of HgII is found is areas upstream from water bodies, as it is in water where microbial transformation of Mercury occurrs. Bacteria play a crucial role in methylating mercury, thus converting it from inorganic to organic. The organic form is what is incorporated into the food chain.
There is no doubt that Coal Fired plants increase Mercury load, but this load is mistakenly being identified as “natural” or elemental, simply because it is not raining out as HgII. As the elemental mercury slowly precipitates out of the atmosphere, a good portion deposits in water, and it is in water where the problems occurr. After methylation, the newly formed HgII is taken up in evaporation and then rains out. This is why your pristine west coast has such high mercury deposition, because the transformation occurs in the pacific.
I haven’t looked at the studies, but the more relevant marker would be the change in Hgii presipitation or change in methyl mercury concentrations in fish populations. I would expect, given the slow deposition rate of Hg0 that is becomes well mixed in the atmosphere, and thus, any increases resulting from coal fired plants would be noticed on a time scale.
From my ever useful “Nature’s Building Blocks” by John Elmsley . .
Minamata Bay in Japan was a case of mercury poisoning in the 1950’s. A local chemical company had discharged about 100 tonnes of mercury a year for 30 years into the bay. The bugs in the silt were eaten by the fish resulting in them containing 0.2% of their mass in mercury.
People ate the fish and about 10 000 folk were crippled with Minamata disease. Once the cause was figured out the factory implemented a mercury recovery process and banned fishing in the bay. No new cases were reported.
The real number here is 3000 tonnes of mercury resulting in fish being 0.2% mercury. Nanograms don’t really measure up.
Humans take up about 3 micrograms a day by way of food that gathers mercury from the soil. This is not considered harmful.
We have in our system . .
Blood 8 p.p.b.
Bone 0.5 p.p.m
Tissue 0.2-0.7 p.p.m.
Giving about 6 milligrams per person.
I guess the take away message is “keep calm and carry on”.
izen:
Your post at April 2, 2012 at 3:27 am consists solely of unjustified assertions that are denied by data in the above article. If you have contrary data then please state it. Otherwise, please withdraw your comment.
The important point is that Hg emissions are trivial when compared to natural sources. This is clearly demonstrated in the above article where it says;
“In fact, where I live, on the pure clean Pacific coast with lots of sea breeze, I get more mercury pollution than they get around Pennsylvania despite all the coal-burning power stations just upwind from them.”
Richard
PS
You may wish to consider changing your screen name from Izen. It always makes me think of Izal which was a cheap, abrasive and rather unpleasant toilet paper that used to common in the UK. Unless, of course, you also think that association is appropriate to your comments.
I find it strange that both Figure 2 and 3 show a power plant in Northwest Montana, right where Hungry Horse Dam sits. How error prone is power plant sighting? http://en.wikipedia.org/wiki/Hungry_Horse_Dam
Articles like these are the best form of informative science. I have learned so much about the various Hg chemical species, information that would have required serious study to find all of the various parts so clearly presented here.
From my point of view, most of us consider elemental Mercury dangerous, and ubiquitous, and Mercury in more chemically active states, an extreme hazard. At the same time, based on the excellent maps Willis has included, as well as the research papers, the EPA’s war against Hg is as close to Don Quixote as anything I can imagine.
Thanks again Willis!
Deanster:
I write to comment on your post at April 2, 2012 at 6:27 am, and I copy that entire post to avoid others needing to find it. It says;
“One aspect to consider is microbial transformation. It’s not suprising to me to find that the majority of HgII is found is areas upstream from water bodies, as it is in water where microbial transformation of Mercury occurrs. Bacteria play a crucial role in methylating mercury, thus converting it from inorganic to organic. The organic form is what is incorporated into the food chain.
There is no doubt that Coal Fired plants increase Mercury load, but this load is mistakenly being identified as “natural” or elemental, simply because it is not raining out as HgII. As the elemental mercury slowly precipitates out of the atmosphere, a good portion deposits in water, and it is in water where the problems occurr. After methylation, the newly formed HgII is taken up in evaporation and then rains out. This is why your pristine west coast has such high mercury deposition, because the transformation occurs in the pacific.
I haven’t looked at the studies, but the more relevant marker would be the change in Hgii presipitation or change in methyl mercury concentrations in fish populations. I would expect, given the slow deposition rate of Hg0 that is becomes well mixed in the atmosphere, and thus, any increases resulting from coal fired plants would be noticed on a time scale.”
Your assertion may (or may not) be correct concerning accumulation in the air of microbially transformed Hg compounds. And you may (or may not) be right that it is would be possible to “notice” a change to atmospheric loading by anthropogenically-derived Hg compounds.
But it does not matter whether you are right or not.
Firstly, biota vary for many reasons with time so – if you are right – a change to the atmospheric loading may be observed but (as with recent increase to atmospheric CO2 loading) there would be no way to definitively “notice” the anthropgenic contribution as being other than natural.
Secondly, and very importantly, the anthropogenic contribution to Hg emissions is so small relative to natural emissions that it can be considered to be trivial. Indeed, as the above article explains, the local variations in atmospheric Hg ARE trivial compared to the local differences in natural Hg emissions.
Hence, you provide an assertion that is plain wrong when you say;
“There is no doubt that Coal Fired plants increase Mercury load, but this load is mistakenly being identified as “natural” or elemental, simply because it is not raining out as HgII.”
There is much “doubt” because your assertion is constructed from a series of assumptions that have no supporting evidence. And your assertion would be trivial even if it were right because the emissions from the coal-fired plants are trivially small.
Richard
OK, you’re convincing me, Willis. A nicely done presentation, and it does make sense. It also makes it a headache to track mercury sources — if we eliminate power plants as significant anthropogenic contributors, second in line is human spills and industrial dumping — e.g. gold prospecting (increasing levels in specific rivers, which BTW might be a potential source of your mercury excess in CA even now — otherwise it is difficult to understand the inhomogeneity of levels along the CA coast is it not), paper mills, and mercury used elsewhere in industry that makes or made its way into waterways. I can easily believe that the US southwest is a source of mercury vapor, as there is a rather lot of cinnabar (and where it concentrates, mercury mines) mixed in with the native rock throughout much of the region, IIRC. Indeed, I think there are several mercury mines (started during the Gold Rush) in central and northern CA — another potential source of your hotspot.
So if we care (if we should care, and I still would personally prefer to keep my Hg levels as low as possible in spite of your compelling presentation that it is difficult to resolve damage from background noise for moderate levels of exposure:-) we should focus on mercury ores and natural earthbound mercury and direct dumping of industrial mercury compounds and native metal, not so much power plants. Or at the very least, we should demand a complete and compelling presentation of a scientific and economic case for regulation of mercury emission from power plant smokestacks.
rgb
****
Mike McMillan says:
April 1, 2012 at 9:37 pm
As modern resin fillings improved, even fewer amalgam fillings, less mercury to leach from our teeth into the body.
****
The amalgam is a metallic alloy. The mercury atoms are as “locked” in it as much as a chemical compound. Tiny amounts “released” won’t be elemental mercury, but amalgam (which is stable & nonreactive).
You can die of water intoxication if you drink too much of it. Who can say that some tiny trace amount of mercury cannot possibly be beneficial?
If the FDA existed before the discovery of the value of vitamin A is there any doubt they would have just labeled it a poison?
According to Wiki (a sometimes reliable source), liquid Hg is not particularly dangerous:
http://en.wikipedia.org/wiki/Mercury_poisoning
This accounts for how all kids used to handle quicksilver with no perceptible ill effects. Is the Hg in curly lightbulbs liquid and hence not particularly dangerous unless incinerated? Does it become vapor when lit, so that an accidentally broken lit bulb would be the biggest concern? Why does the EPA allow these things?
But then Wiki says that human sources are responsible for half of atmospheric Hg:
I would wonder about the effect of southwestern dust storms, most famously shown by the recent haboobs in Phoenix, on the prevalent mercury in the local soils. In La Paz county in southeast Arizona. Mercury bearing veins in the quartz around Quartzite, such as the Cinnabar Mine, have been a source of concentrated mercury predating European colonization of the area. Cinnabar ore was used as a pigment prior to be used in gold separation. The mercury was extracted from the ore by heating. I wonder how much mercury was released from surface deposits by the recent forest fires in northern Arizona…..
beng says: April 2, 2012 at 7:55 am
“The amalgam is a metallic alloy. The mercury atoms are as “locked” in it as
much as a chemical compound. Tiny amounts “released” won’t be elemental
mercury, but amalgam (which is stable & nonreactive).”
The chemical bond between mercury and silver is very weak – unlike most
chemical bonds in compounds.
The silver does greatly slow evaporation, etc. of the mercury. I think what
is useful is data on concentrations of mercury in people with lots of amalgam
fillings, vs. none.
I’ve no ideas about other states, but in California there are both large natural and historic sources for mercury in the soil, water, and fish. Major mercury mines are or were located in the Northern Coast Range for just one factoid. One of the them is just north of SR 20 on the way to Clear Lake from the Central Valley. There are also significant amounts of arsenic and selenium coming out of the ground in both the North and Southern Coast ranges. The primary historic source of mercury in the Central Valley is from the massive placer tailings from the California gold rush. Mercury was used to amalgamate gold in sluice boxes, and the major hydraulic mining companies used tons of mercury each year of operation. The mercury and coarse gold were collected from the sluices and the mercury was then distilled off the gold (and reused if it was properly done) to concentrate the fine gold. Metallic mercury is still washing out of those tailings. In the 1950s it was possible to collect mercury from the Sacramento River sand bars by panning (as in gold panning, but we were kids and mercury was far easier to find and more fun).
Nothing like starting the week off by getting my BP raised – which is what happens whenever I am forced to think about the EPA and what they call science.
Thanks Willis.
(For helping remind people of the importance of being at least somewhat scientifically literate, so as to recognize when our nannys in government are overreaching.)
Sorry but the policy train has left the station. There is no stopping it now and the chase cars of lawyers and dealing-making Sierra Club will not be diverted by details and facts. It’s a storyline management thing.
Willis, EPA has already stepped in to save you. Just earlier this year, they released the “Utility MACT” rule that restricts emissions of mercury, trace acid gases (like HF and HCl) and fine particulate matter from power plants. It has been characterized as the most expensive environmental regulation ever issued. One source, http://junkscience.com/2011/12/15/utility-mact-600-million-in-costs-for-0-2-emissions-reduction/) says it will cost $600 million, EPA (http://www.usclimatenetwork.org/resource-database/assessment-of-epa2019s-utility-mact-proposal) says it will cost $10.9 billion per year. Per year! After a while you start talking about some real money, here. And coal plants are being shut down all across the country.
Although mercury is usually described in the media as a “potent, brain destroying neurotoxin,” actual EPA studies (from models, of course) say this rule prevents an average 0.9 I.Q. point decrease. This is not even measurable. So all of the benefit is from particulate emission reduction that has already been regulated, double counting the benefit. They do this all the time for the “sake of the children.”
Richard
“Your assertion may (or may not) be correct concerning accumulation in the air of microbially transformed Hg compounds. And you may (or may not) be right that it is would be possible to “notice” a change to atmospheric loading by anthropogenically-derived Hg compounds.
But it does not matter whether you are right or not.
Firstly, biota vary for many reasons with time so – if you are right – a change to the atmospheric loading may be observed but (as with recent increase to atmospheric CO2 loading) there would be no way to definitively “notice” the anthropgenic contribution as being other than natural.
Secondly, and very importantly, the anthropogenic contribution to Hg emissions is so small relative to natural emissions that it can be considered to be trivial. Indeed, as the above article explains, the local variations in atmospheric Hg ARE trivial compared to the local differences in natural Hg emissions.
Hence, you provide an assertion that is plain wrong when you say;
“There is no doubt that Coal Fired plants increase Mercury load, but this load is mistakenly being identified as “natural” or elemental, simply because it is not raining out as HgII.”
There is much “doubt” because your assertion is constructed from a series of assumptions that have no supporting evidence. And your assertion would be trivial even if it were right because the emissions from the coal-fired plants are trivially small.”
Richard
It’s true Richard, I have no way of separating out anthropogenic mercury from natural mercury, as there is no way to assertain the contribution of natural and anthropogenic to the inorganic pool of Mercury in the water.
All I’m saying, is that according to the paper, there apparently is some unknown mechansim wherein HgII gets converted to HgO. Once that conversion occurrs, the ability to track anthropogenic contributions becomes rather difficult. The premise of Anthony’s post is … hey .. look here … the high levels of HgII precipitation is not where the coal fired plants are, . therefore, the contribution of the coal fired plants must be negligible. I don’t necessarily agree with that. HgO, per the paper, has a resident time of 1 year. That’s plenty time for the emissions of coal fired plants to mix in the atmosphere, resulting in a pattern of deposition that will be unbiquitous, as opposed to correlating to the location of coal plants. Considering that the natural contribution of mercury to the system would be expected to be somewhat constant, a rise in HgII precipitation in places such as San Fransisco could very well be carrying a signal of increased HgO deposition in the ocean resulting from a power plant in Ohio. LIke I said, I haven’t looked at the data .. for all I know, HgII precipitation in San Fran has been constant for centuries … but if there is indeed a spike in HgII precipitation, there is a possibility that it is a response resulting from increased HgO deposition in the Pacific with origins in power plants thousands of miles away.
The main point I was making, is that Microbial Transformation of HgO to methyl mercury should not be ignored in this issue, as increases in HgO deposition will contribute to the HgII concentrations via microbial transformation.