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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Yep, in every home too. Dozens of little 5mg Hg hand grenades. Compact fluorescent light globes, whoever came up with that idea has had more than a background dose.
The elevated concentrations of mercury about the west coast of the US might also be coming from the soils, as the young volcanoes in the region would also increase the amount of natural mercury. Mercury is higher in various fluids and rocks within volcanic terranes.
Not surprised, plenty more “everyone knows”.
Good post.
Mods: an update pls
Another masterly bit of work by Willis.
Which needs to be published far more widely.
The EPA has turned into some sort of ravenous monster. I was always afraid of the UN taking over the world, but their incompetence always reassured me.
But now I fear the EPA! With unlimited power, answering to no-one, flinging national economies this way and that with joyful abandon, and with only a token hat tip to logical thought processes, it is a far more powerful and dangerous beast.
Thank you very much for this contribution.
I’d heard sometime back about more than one “kind” of mercury and that one is dangerous but the other isn’t (within reason). I’ve also overdosed on EPA stupidity. JunkScience.com had a really great one about a Chinese pollution study with grunge numbers an order of magnitude higher than the new EPA danger numbers but that completely gutted the EPA’s estimated death count from particulates.
Now, is there a case for long term suspension of the mercury? could the stuff be going to Africa? In fact, some dust and pollen apparently cross the Atlantic, so I’m wondering if we’re not just shipping the stack garbage further than might be thought. Anyone got any info on that idea?
Steve from Rockwood says:
April 1, 2012 at 5:19 pm
Good point that the national sampling grid shown in these plots is not of sufficient density to detect any hot spots that might occur near large coal-fired power plants. However, I have reviewed a few studies that looked at soil and vegetation samples in a dense pattern around power plants. These studies found no hot spots, but that was a few years ago, so perhaps later studies found some evidence of hot spots. I have not had time to look through EPA’s references for the rulemaking. Presumably if there were convincing data showing hot spots near power plants, EPA would have presented it as support for the rulemaking.
The EPA with its linear, no-threshold concept of heavy metal toxicity. Plus, postage-stamp the mapped area, take the pattern out of context, and you get as much alarm as you wish. And change the colour scheme to emphasize the highest level, however low it is.
You cannot get the whole country behind a national program unless the whole country feels threatened. The EPA with its 50-year message of pollution threatening the nation (now the world), is trying to get the national response it needs for federal power and regulation. Everyone pays for some people’s problem or some people’s potential problem. It’s a war mentality gone viral.
Or they are intentionally trying to poison us with mercury so we become infertile. http://en.wikipedia.org/wiki/Young%27s_syndrome
The maps above have a mid range value of 10 micrograms/m^3. if a Compact Fluorescent Bulb has 5 mg, that is 5000 micrograms. To dilute that to below 10 ug/m^3, you need about 500 m^3 of air, but that would be a room of 3 m by 6 m by 28 m, or a room (or house!) with 1800 sq ft with 10 foot ceilings.
Which points out one of the major problems with the EPA and their pollution control efforts. Modern technology can detect various chemicals at orders of magnitude smaller quantities than can be shown to have any medical consequences. Those low thresholds of detections also must include error bars.
If you are detecting a contaminate at nano grams / liter, what is the precision of that measurement? At those low concentrations the difference between being detectible and nothing is very small. That suggests that the inherent noise in the data is probably very large.
How many samples were taken at each location, over what time period? What was the scatter in those measurements? Are those values the peak value detected, the median or average of multiple measurements or just a single measurement at some point in time?
Just because it is detectable and measurable, does not necessarily mean it is hazardous. Just like nuclear radiation, many assume a linear relationship with exposure and harm for chemical exposure, but what if toxic chemicals have a threshold below which the body copes with no negative consequences? What if like selenium at very low doses mercury is harmless or even essential. Without understanding those aspects of biological action the gross concentration may or not mean anything at all.
How far below the minimum threshold of detectable clinical biological consequences are these measurements? Are these levels 10x or 100x or 1000x times smaller than doses that are indistinguishable from no exposure?
With many heavy metals the method of absorption is as or more important than the gross level of exposure. A metal as a citrate for example might be orders of magnitude more soluble and biologically more reactive than the same metal in the form of an oxide or other compound form.
Some forms might be easily excreted with no biological action and other easily absorbed and captured by the tissue and biological processes.
Larry
By way of some reassurance, we all have a heavy metal detoxification system in our livers. It’s a set of proteins called metallothioneins, that are rich in sulfur amino acids. Sulfur is very effective at attaching permanently to mercury.
So, most of the mercury we eat ends up being trapped by the metallothioneins in the liver and permanently hidden away. The mercury never moves and never leaves the liver (until we die), and doesn’t get into the rest of our body.
Metallothioneins are also very effective at trapping other toxic heavy metals, such as cadmium.
The fact that we all have well-developed metabolic heavy metal traps shows that these metals have always been in our diets. The metallothioneins are evolutionary answers to perpetual heavy metal exposure over long evolutionary times.
Plants have similar proteins, developed for the same reason: heavy metals are in soils and have always been in soils. Plants evolved the proteins to defend themselves against heavy metal toxicity, from time immemorial.
That’s not to say we shouldn’t be careful about emissions. But it is to say that we’re well-equipped to protect ourselves from small chronic exposures.
Actually, Willis, if you live north of SF Bay and east of Clear Lake, you’re living in cinnabar country. Cinnabar is mercuric sulfide (HgS). There are large surface outcroppings all over that area. Plus hot springs. Some of the creeks are full of dissolved mercury that has washed off the outcrops.
I’ve been to Wilbur Hot Springs a number of times, in that area. The local hot creek washes down off the hills and the shores are rimed yellow with elemental sulfur. Bacteria live on the sulfur, and scads of black flies graze on the bacteria. Old cinnabar mine shafts dot the hills, with poorly blockaded entrances. Some of them still sport rusty equipment.
South of San Jose are the old Almaden mines, where cinnabar was mined for the mercury to use for gold production. Lot’s of surface outcrops there, too.
Apart from the cinnabar, of course, there’s the poison oak. Of the two, I tend to be more cautious of the poison oak. One should never, ever, take a leak after even a hint of a bare possibility of maybe having touched a plant. Lady-folk have a distinct advantage there.
I was a kid back before the advent of fluoridation, so by the time I was a teen I had a bunch of silver-mercury amalgam fillings. After fluoridation set in, nationally the number of cavities declined, and thus the number of amalgam fillings went down. As modern resin fillings improved, even fewer amalgam fillings, less mercury to leach from our teeth into the body.
We’re told that mercury affects intelligence, and yet, the national IQ has declined since the 50’s. Could it be that a little mercury is like a little radiation, essentially harmless?
Willis says “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.”
First of all Willis, excellent article in my opinion… very well done.
However in regards to what is in the “”. While it is clear that Hg, especially organic mercury, can lead to poor health and/or be fatal in high enough concentrations, I think what your data clearly shows is that at the current levels of environmental Hg concentrations, Hg is not poisonous. Are you sick? Your neighbors? Do you know ANYONE in your area that has died or is sick due to Hg poisoning from air or eating to much fish? I also think it clearly shows that the Hg EPA rules in effect for the past 20 years are quite sufficient for dealing with Hg emmissions from power plants. The new rules being implented will not save lives or make people healtthier. In fact they will have just the opposite effect as it drives up the cost of energy (which increases the cost of EVERYTHING) and lowers the standard of living for all. Lower standards of living leads to more sickness and death.
As one who enjoys gold dredging as a hobby the part realy missing from all the other studies I have seen is a inventory of natural deposets of what ever they are doing a study on. In SW WA USA they would like to blame on the old minors but the only time we pick up Mercury is when dredging on a low grade Cinnabar ore vains or deposit of sands from that ore body. The natural geological events of erosion and large events like the Missoula flouds have spread sands of ore deposits hundreds of miles away with out even looking at where anchent rivers once where that are no long around. Man made may be more because of road cuts through ore bodies and the rock used to build roads and pave them. The hazmat from road cuts and building makes the EPA wories a BIG JOKE with a little understanding of mining geology.
Hazard Summary-Created in April 1992; Revised in January 2000
Mercury exists in three forms: elemental mercury, inorganic mercury compounds (primarily mercuric chloride), and organic mercury compounds (primarily methyl mercury). All forms of mercury are quite toxic, and each form exhibits different health effects.
Acute (short-term) exposure to high levels of elemental mercury in humans results in central nervous system (CNS) effects such as tremors, mood changes, and slowed sensory and motor nerve function. Chronic (long-term) exposure to elemental mercury in humans also affects the CNS, with effects such as erethism (increased excitability), irritability, excessive shyness, and tremors. Human studies are inconclusive regarding elemental mercury and cancer.
Acute exposure to inorganic mercury by the oral route may result in effects such as nausea, vomiting, and severe abdominal pain. The major effect from chronic exposure to inorganic mercury is kidney damage. Animal studies have reported effects such as alterations in testicular tissue, increased resorption rates, and abnormalities of development. Mercuric chloride (an inorganic mercury compound) exposure has been shown to result in forestomach, thyroid, and renal tumors in experimental animals.
Acute exposure of humans to very high levels of methyl mercury results in CNS effects such as blindness, deafness, and impaired level of consciousness. Chronic exposure to methyl mercury in humans also affects the CNS with symptoms such as paresthesia (a sensation of pricking on the skin), blurred vision, malaise, speech difficulties, and constriction of the visual field. Methyl mercury exposure, via the oral route, has led to significant developmental effects. Infants born to women who ingested high levels of methyl mercury exhibited mental retardation, ataxia, constriction of the visual field, blindness, and cerebral palsy.
DocM;
Evidently your mercenary nature overcame your editorial senses:
“They would then heat the amalgam, vaporizing the mercury and leaving the gold behind. This introduced huge amounts of gold into the environment.”
I think you said the vapors were Hg, not Au??
🙂
[Very good. I figure it wasn’t his mercenary nature that did it, it was the mercury fumes. I fixed DocM’s original for him, many thanks. -w.]
I wonder if this topic contains any clues as to the origins of Willis’ mercurial nature …
|8-0 !
John B., M.D. says:
April 1, 2012 at 6:30 pm
Thanks, Dr. John. Indeed organic mercury is highly toxic, and we should not forget that.
We should also not forget that with respect to the US, the sources (see Figure 2) are overwhelmingly natural.
w.
thingadonta says:
April 1, 2012 at 8:12 pm
Figure 3 shows where the mercury is precipitating from the atmosphere. It does not show mercury in the soil, from the volcanoes, or from mercury mine tailings.
w.
aired says:
April 1, 2012 at 8:23 pm
A good point indeed, aired. The sampling density is not enough to show an individual power plant. But the point of the scientific article I quoted from is that the sampling network should pick up Hg deposition downwind from the large number of coal-burning power plants and industrial furnaces in the Ohio River Valley. The fact that it does not argues strongly for the authors’ conclusion, that the HgII is getting reduced to Hg0 shortly after leaving the stack, and thus is widely diluted and added to the atmospheric background elemental mercury levels, rather than coming back to the downwind surface fairly quickly as divalent mercury.
w.
stpaulchuck says:
April 1, 2012 at 8:19 pm
A good question, chuck. The “residence time” for something in the atmosphere is generally measured as the length of time an average atom or molecule stays suspended in the atmosphere.
For elemental mercury (Hg0) that’s thought to be on the order of a year. So indeed, in that year it will circle the earth many, many times.
You are correct that we are indeed just shipping it far afield. The red area in Figure 3 where I live on the California coast and in the Sierra Nevada mountains shows that the ocean is a large source of mercury. This means mercury has been falling from the sky in those areas for millions of years. Florida has been the unlucky recipient of oceanic mercury poisoning for as long as the peninsula has existed.
And in addition to that mercury from the ocean, some of that red area in Figure 3 where I live is from the background atmospheric elemental mercury. So some of it is from diesel Mercedes in Brussels, some is from Chinese coal seam fires, and some is undoubtedly from the power plants in the Ohio River Valley. They don’t deposit their mercury between there and Pennsylvania as we thought. They deposit it on my house.
But look at the airborne concentration in Figure 2. As air passes over North America, it picks up a load of mercury, enough to turn the whole southwestern US red. Why? Wind over the desert. There’s natural mercury in those soils. When there is no vegetation to hold it down, wind-blown dust is common, and that dust puts mercury into the air.
Is that a good thing? Neither the mercury from the power plants nor the mercury from the Southwest deserts and arid regions are good things. No, absolutely not, hey, it’s my house they’re raining out on.
But will the EPA regs make a difference? Less than 1%. The amount of red in the picture will change by maybe half a percent … that’s lost in the noise. Look at Figure 2, the mercury load in the atmosphere. You’d have to pave from the Mojave desert in California right through to Texas to make a meaningful dent in the amount of mercury coming from the wind in the US deserts, the US power plants are nowhere near that league …
Meaningful change in power plant emissions, sadly, will have to occur in other countries than the US. Despite the huge amount of power generated from coal, we’re only 8% of global power plant mercury emissions.
w.
Willis:
This is ‘déjà vu’ again. And history shows the scare poses a long-term threat.
I was working at the UK’s Coal Research Establishment (CRE) in the 1980s when ‘Acid Rain’ was Europe’s ‘big scare’. It was being claimed that sulphur oxides (SOx) emitted from coal-fired power stations in the UK and Germany were causing ‘waldsterben’ (i.e. forest death in Germany and Scandinavia). SOx is very water soluble and the solution forms a dilute acid.
It was argued that flue gas desulphurisation (FGD) was needed to prevent emissions of SOx from coal-fired power stations which caused ‘acid rain’ that was killing the forests. (We now know the forests were expanding at the time, but that was not then known).
FGD adds about 20% to the capital cost and about 10% to the operating cost of a coal-fired power station. This is a major increase to the cost of coal-fired electricity.
The matter gained great importance because coal was the major source of electricity generation in the UK and Germany, but France had adopted nuclear power as its major electricity generation source. So, enforced addition of FGD to coal-fired power stations would improve the commercial and industrial competitiveness of France relative to the UK and Germany (i.e. France’s major competitors).
But I observed that the spatial distribution of the acidity of rain was not consistent with the scare. There was no evidence of ‘waldsterben’ near power stations which is where ‘acid rain’ should have been greatest (SOx is VERY water soluble). Importantly, greatest acidity of rain was near outflows from major rivers. Emissions from UK and German power stations would be required to cross high-deposition zones near river outflows if they were to reach Scandinavia.
I suggested that the increased acidity of rain and its spatial distribution of deposition were consistent with an acceleration of the natural sulphur cycle in the North Sea. Excess nitrogenous and phosphorous agricultural fertiliser was being transported to the North Sea where it was increasing growth of phytoplankton such that they emitted more dimethyl sulphide (DMS). This would explain the observed spatial distribution of the increased acidity of rain. And the explanation was supported by the fact that North Sea phytoplankton had increased to such a degree that the phytoplankton were forming toxic algal blooms that were affecting shores.
Upon investigation it was discovered that the agricultural explanation was correct. France had a powerful farming lobby so the ‘acid rain’ scare was quietly forgotten. But by then Europe’s Large Combustion Plant Directive (LCPD) had been adopted as legislation to prevent SOx emissions from European power stations, and the jobs to impose and enforce the LCPD had been created.
The people fill those jobs need to justify their jobs so they keep reducing the emission limits decreed by the LCPD. The latest of these reductions is closing the UK’s remaining coal fired power stations in the next four years although the reason for the LCPD was disproved a generation ago.
Richard
PS
Please note that SOx emissions can be a problem especially near the emission sources. But the ‘acid rain’ scare and the LCPD are not relevant to this.
Jon Alldritt says:
April 1, 2012 at 10:38 pm
We’re nothing if not a full-service website. I can’t find such a map for the US, but here’s the cinnabar mines (crossed pick and shovel) in the Coastal Range of California.
SOURCE
Indeed, that’s what makes the large red area in the center of Figure 2, natural sources.
And if you look at Figure 3, you can see that like where I live in California, in Washington and Oregon the air from the ocean rains and snows out the mercury in the first two mountain ranges. So a main source of mercury in the soil and water is from the ocean.
This doesn’t let the old miners off the hook, though. From the source of the map above, it says:
Not a pretty picture …
Good luck with your gold dredging. When I was a young man I spent far too much of a summer underwater, wearing a hookah and running the business end of a 12 inch gold dredge in the Yuba river in the Sierra Nevada mountains. Found about an ounce … gold was $32 an ounce then … a 12 inch dredge, I just look back and shake my head, I was young and foolish.
w.
Heystoopidone says:
April 1, 2012 at 11:30 pm
Indeed, I can only agree and emphasize, all forms of mercury are toxic. Liquid mercury can be handled without harm, many of us did it as kids, although I wouldn’t advise it and you’d want to wash your hands well.
But the exact same elemental mercury we handled, when inhaled, is what drove the hatter mad …
w.
PS—If you don’t mind my saying, that’s an off-putting screen name. Seems like you are either calling me or yourself “stoopid”, and neither option is very pleasant. You might consider taking another name if you want your words to carry more weight.