Hermetically Sealed


Mercury is an element with interesting physical properties, but unpleasant toxicology. It is the only metal that is a liquid throughout the room temperature range (it melts at -39 C). It is somewhat volatile, and while its metallic form is mostly insoluble in water, but is readily converted to the highly soluble organometallic compound methylmercury through biological action. Methylmercury accumulates in tissues, thus its concentration increases as one moves up the food chain: the mercury concentration in algae is likely to be close to the background concentration in the water (controlled by diffusion), while the concentration will be higher in the fish that eat the algae, and even higher in the predatory fish that eat those fish, and so on all the way to your dinner table. Mercury in either its elemental or alkylated forms is a neurotoxin and nephrotoxin - that is it can cause permanent brain and kidney damage. The description of symptoms of acute poisoning suggests that it may damage other organs as well, as if the first two weren't bad enough.

Why the science lesson? Mercury is slowly being phased out of many industrial processes. Another significant use is in lighting technology. Fluorescent lamps including CFLs, as well as the ubiquitous bluish-white mercury-vapor streetlights use mercury as both a conductor and an emission medium; in the near future though, these will be phased out as mercury-free LED lighting becomes more prevalent. This is good news - less mercury scattered around the country and the world means fewer releases and less exposure (yes I know about coal and I'll mention that later). However, the unintended consequences of these trends is that there is a large quantity of elemental mercury with few uses currently controlled by the Federal government. They plan to store it semi-permanently either against the possibility that it might be needed at some time in the future as a "strategic material", or that they have no other available option. The problem is that they seem to be planning to store it in liquid form. It does not take the imagination of a Charles Dodgson or a Neil Gaiman to consider the possibility that the containment system for a hazardous substance might be imperfect.

So what do we do? Are we stuck with 4400-plus tons of toxic waste? Remember that mercury is an element, that means that in the absence of nuclear reactions or other high-energy physics (which I am not suggesting as a course of action) it is eternal. Fortunately, there is no solution. (That was a chemistry joke). How is it that mercury exists naturally without saturating the ecosphere? It is tied up in insoluble minerals, primarily mercuric sulfide (HgS), also known as cinnabar or vermillion. (Pedantically, the mineral is cinnabar, and when it is synthesized or ground and then used as a pigment it is called vermillion.) Knowledge of the synthesis of vermillion from mercury and sulfur is over a thousand years old. Why then, do we not convert most or all of this stored mercury into this stable and much less hazardous form? While cinnabar is still toxic, the mineral does not flow, it does not release mercury vapor (below 580 C), and it has limited solubility in water (0.0125 mg/liter). Granular cinnabar could be safely stored indefinitely in drums in a concrete structure (no fires) on inland high ground (no floods) with a very low risk of a release that would endanger any living thing. I admit that it is not a perfect solution, and that there is still some small risk, but I believe that mineralizing the stored mercury would yield the greatest reduction in risk of any proven available technology.

After reaching this conclusion, one then has to ask: why aren't we doing this? It seems to me to be related to which parts of the government are responsible for this policy. EPA clearly indicates that immobilization technology exists; I suspect that if they were in charge, they would follow a course of action similar to the one that I have suggested. The problem is that the mercury is in the custody of DOD and DOE. As of 2003, DOD claimed that "bulk treatment and disposal of elemental mercury is not viable at this time". A possible translation of this statement is that "there is no operating facility to which we can ship this and forget about it", which to my knowledge is true - the facility to mineralize the mercury would have to be built, and there might need to be some development work to scale up the process. But is it not a better use of our money to not only render the mercury as safe as possible, but also to build the infrastructure for doing so in the future should the need arise again, than to sit on it until people downstream of the facility start getting sick and then run around saying that no-one could have predicted this tragedy? I'm predicting it...here and now. Let's get it done right from the beginning.

PS
This alas, does not solve the problem of environmental mercury. Even if we eliminated all industrial and commercial uses of mercury, a very large quantity (150 tons/yr from all sources) of mercury is added to the environment through the burning of coal: the coal contains small amounts of mercury-containing minerals which are broken down by the heat of combustion, releasing the mercury as a vapor.

PPS
This was initially brought to my attention in a news report from the-news-agency-that-shall-not-be-named-or-cited, fortunately I was able to find plenty of uncontaminated sources.