Tuesday, November 05, 2013

Pulling Teeth

The Minamata Convention on Mercury  is a first step toward ending human addition of mercury to the environment.  Minamata, a city in Japan, had the misfortune of becoming synonymous with mercury poisoning when the mercury waste from Chisso Chemical's production of acetaldyhyde there resulted in then mysterious neurological damage to fishermen, their families and those who ate fish caught in the adjourning bay.  While the source of the illness was found, not before much damage had been done, and those severely impacted were identified, there is still controversy about how many people were sub-critically impacted

"There are still many unresolved issues," says Masanori Hanada, a social policy specialist who heads the Open Research Center for Minamata Studies, attached to Kumamoto Gakuen University.

Among them: finding ways to identify patients with less severe mercury poisoning symptoms, and figuring out how low-level or early-life exposure is affecting people as they age. There are also fierce, ongoing battles over who should be counted among the victims of Minamata disease, who could number just a few thousand or up to 100,000—depending on who is counting.
Since many were affected when young, this is not just a question of finding minor problems
One part of the challenge, critics of the current system say, is that screening for signs of methylmercury poisoning was done several years after the crisis and in a piecemeal way. Another is that even people who were exposed to biologically harmful levels may not be aware they have symptoms. "I cannot distinguish by feel whether I'm touching someone's hair or their shirt," says Hajime Sugimoto, a 52-year-old, third-generation Minamata fisherman who lived in Tokyo and worked odd jobs during the ban on fishing. He says he also cannot tell when he has his hands in cold water. But when he was a child, "I thought this was just normal."

To help identify other such "quiet" victims, a team led by Shigeru Takaoka, a physician at the private Kyoritsu Neurology and Rehabilitation Clinic in Minamata, has been doing its own surveys. At the International Conference on Mercury as a Global Pollutant in Edinburgh in July, they reported finding extensive signs of methylmercury poisoning in more than 1000 people living on the coast of the Shiranui Sea, which contains Minamata Bay. "These people are not like the victims seen in the [famous] photographs, but they are Minamata disease patients," Takaoka says.
And, of course, as with lead poisoning, even "minor" damage, taken over a large number of people can be major.  In the case of lead, lead pipes, lead paint, and tetraethyl lead are legacy issues which can be mitigated by removal.  Lead solder is being replaced slowly.

Mercury will be more difficult. First, because emission from coal is a large source (that is most of the fossil fuel emission shown in the figure).  In theory at least, scrubbers could handle that.  Most difficult will be getting a handle on what is called artisanal mining.  With the surge in the price of gold, millions (Eli never exaggerates, estimates are 15 million) are trying to earn a living panning for gold in South America, Africa and Asia.

The process is simple, toss some mercury into the ore, form an amalgam between the gold and the mercury and then vaporize the amalgam freeing the gold in the pan, but pushing the mercury into the atmosphere. In addition the slurry with traces of mercury has to be discarded somewhere.  Neutral mercury atoms are not the problem, nor is the amalgam, like in most of our teeth, where it is locked up, but the damage is on deck when the mercury oxidizes, or becomes incorporated into organic compounds, which it will, sooner or later.
 Most mercury released to the atmosphere is in the gaseous elemental (Hg0) form, which has a long atmospheric lifetime (6 to 12 months), allowing hemispheric-to-global mixing and transport before deposition. Elemental mercury reacts with atmospheric oxidants such as bromine to form the highly water-soluble divalent mercury species (HgII) that is rapidly deposited to terrestrial and aquatic ecosystems. Some of this mercury is reduced back to Hg0 and reemitted to the atmosphere; the remainder cycles through soils and the oceans over time scales ranging from decades to many centuries until it is resequestered in the lithosphere (4).
How can this be dealt with?  Given the poverty of the miners, the only way will be to find better methods of separating the gold from the ore.  Such methods exist, but habits are hard to break and the equipment (which can be pretty simple) will almost certainly have to be provided to them.

But wait, there is more, of course, being bunnies, you knew there was more, and you probably thought that it might have something to do with climate change.  If things heat up, reactions occur more rapidly, so in a warming world, the conversion of atomic mercury to other forms will speed up.  Increased precipitation will wash soluble inorganic mercury into aquatic systems and soils.  To the extent that there is a  CO2 fertilization effect, well there will be more inorganic/organic mercury found in soild.

And then there is the Comstock lode. Fires in the Western US are on the increase due to bark beetle infestations and higher summer temperatures in general.  Hmm.  Right where the silver and gold mining finds of the 19th century.  While the mercury based methods for separating gold and silver from ores have been replaced in many cases and, of course, it is easier to control emissions from large facilities given regulations, that was not the case in the 19th Century
The Carson River Mercury Site includes mercury-contaminated soils at former mill sites, mercury contamination in waterways adjacent to the mill sites, and mercury contamination in sediments, fish and wildlife over more than a 50 mile length of the Carson River, beginning near Carson City, Nevada and extending downstream to the Lahontan Valley. Contamination at the site is a legacy of the Comstock mining era of the late 1800s, when mercury was imported to the area for processing of gold and silver ore. Ore mined from the Comstock Lode was transported to mill sites, where it was crushed and mixed with mercury to amalgamate the precious metals. 
and, of course, other gold and silver rush sites across the Americas.  Jerome Nriagu has a paper on that


Lionel A said...

Ah! Yes.

The unexpected consequences of opening Pandora's Box.

Then, amongst others, there is cadmium





waiting in the wings to bite us back.

a_ray_in_dilbert_space said...

Tom Lehrer's The Elements:

There's antimony, arsenic, aluminum, selenium,
And hydrogen and oxygen and nitrogen and rhenium
And nickel, neodymium, neptunium, germanium,
And iron, americium, ruthenium, uranium,
Europium, zirconium, lutetium, vanadium
And lanthanum and osmium and astatine and radium
And gold, protactinium and indium and gallium
And iodine and thorium and thulium and thallium.

There's yttrium, ytterbium, actinium, rubidium
And boron, gadolinium, niobium, iridium
And strontium and silicon and silver and samarium,
And bismuth, bromine, lithium, beryllium and barium.

There's holmium and helium and hafnium and erbium
And phosphorous and francium and fluorine and terbium
And manganese and mercury, molybdenum, magnesium,
Dysprosium and scandium and cerium and cesium
And lead, praseodymium, and platinum, plutonium,
Palladium, promethium, potassium, polonium, and
Tantalum, technetium, titanium, tellurium,
And cadmium and calcium and chromium and curium.

There's sulphur, californium and fermium, berkelium
And also mendelevium, einsteinium and nobelium
And argon, krypton, neon, radon, xenon, zinc and rhodium
And chlorine, carbon, cobalt, copper,
Tungsten, tin and sodium.

These are the only ones of which the news has come to Harvard,
And there may be many others, but they haven't been discovered.