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Questions Arising On Mercury In Compact Fluorescents
Patchw0rk F0g sends in an article from MSNBC on how some environmentalists are having second thoughts on compact fluorescent bulbs. Their relative energy efficiency is unquestioned. The problem is the mercury — enough in one bulb to contaminate 1,000 gallons of water, even in newer low-mercury bulbs. The EPA has an 11-step cleanup process to follow when you break a CFL in your home. The specialized recycling facilities that are needed are thin on the ground — about one per county in California, one of seven states where it is illegal to dispose of CFLs in the general waste stream.
1. Mercury oxide is as toxic as metallic mercury. The worst are mercury alkyls since they are the most readily absorbed
2. Mercury in filling is amalgamated with other metals and practically stable against leaching or vaporisation. Some studies have suggested you absorb more mercury by having old fillings drilled out than by leaving them in for a lifetime.
To put the whole problem with the CFB mercury in relation, 100 Million light bulbs at 5 mg each contain a total of 500 kg of mercury.
The EPA estimate for mercury emissions from coal fired power plants is 50,000 kg a year.
I'm aging rapidly, I bought a new game and had no idea if my machine was good for it.
Ladies and gentlemen, a bit of math.
Amount of mercury in 1 CFL light bulb: 5 milligrams (source: TFA)
Amount of energy saved by using a CFL bulb instead of incandescent, over the lifetime of the CFL:
10,000 hours * 75 watts * 75% energy savings = 0.6 megawatt-hours
(http://en.wikipedia.org/wiki/Compact_fluorescent_lamp#Lifespan)
Fraction of that energy that would be generated by coal-fired power plants: about 50%.
(http://www.eia.doe.gov/cneaf/electricity/epa/epat1p1.html)
Coal power plant energy savings: 0.3 megawatt-hours
Annual emission of mercury by US coal-fired power plants: 48 tons/year in 1999
(http://www.nescaum.org/documents/rpt031104mercury.pdf)
Power output of US coal-fired power plants: 1,900,000 gigawatt-hours in 1999 (about the same today)
Mercury emitted by coal plants: 48 tons / 19000000 GWh = 23 milligrams per megawatt-hour
Power-plant mercury emissions avoided by using a CFL bulb over its lifetime:
7 milligrams
So it's a wash. The amount of mercury in the bulb is roughly the same as what would be emitted by a coal-burning power plant, if you stuck with incandescent bulbs.
But the mercury in a CFL bulb is a lot easier to clean up than the stuff spewed into the atmosphere by power plants.
If you're talking about the unnatural color balance, then LEDs are no better than fluorescents. If you're talking about the flicker, then you are probably basing your experience on old fluorescent tube fittings that use a magnetic ballast at mains frequency (50-60Hz). Modern compact fluorescent bulbs use a high frequency electronic ballast that eliminates flicker completely.
This particular topic has been discussed at least once as an article on slashdot, and almost every energy related topic ultimately wanders onto mercury in fluorescent light bulbs.
However, here's the abbreviated facts (and I apologize I'm not going to go look up all the numbers again, but if you don't take my word for it, you can look the numbers up yourself):
A typical compact fluorescent light bulb has about 5 mg of mercury in it. All NEMA manufacturers voluntarily agreed to this a maximum. This is roughly as much as is contained in 50 cans of tuna. The FDA recommends consumers limit their intake of tuna to 1 serving per week, so that's about the same as a year's supply of tuna. So is this enough to be a health hazard? Not really.
First of all, the tuna contains the compound methylmercury, which is formed by bacterial action and bioaccumulates much more readily than elemental mercury. A greater portion of the latter passes through the body unretained. Secondly, you eat the tuna. Nobody eats a light bulb. Not to mention, the FDA recommendation is conservative, except in the case of children and pregnant women.
Generally, the lightbulbs don't get broken until disposal, and therefore completely contain the mercury, but if it does, it can safely be disposed of in the garbage. The EPA recommends that you not touch the pieces with your bare hands, so use a broom and put it in a bag. Most of that tiny amount of mercury is actually condensed on the phosphor that lines the bulb, and therefore fairly effectively immobilized, although it will slowly evaporate.
Is it an environmental hazard? Again, not really.
The EPA has calculated, based on the US's current power source mix, that the mercury contained in a CFL is more than offset by the power savings, which reduce the amount of mercury released into the atmosphere by burning coal. Additionally, don't forget that the mercury is trapped inside the bulb until broken. Even then it's at best a small concern. Most of the mercury in the environment is naturally occuring, although in specific areas industrial pollution has resulted in significantly elevated mercury levels.
Additionally, due precisely to disposal concerns, many CFL retailers have implemented recycling programs so you can drop off you dead CFL's and they will dispose of them properly. Not only that, but non-commercial users are actually allowed to dispose of fluorescent bulbs in the trash in most cities. Sound bad? The average US citizen produces about 4 pounds of landfill waste per day. Mix in half a dozen CFL's per year with the trash of an average household, and the amount of mercury ends up being about the same as natural occurs in the earth's crust.
Again, you don't have to believe me, but if you search around for the relevant information (natural abundance of mercury, trash produced per capita, USDA recommended limits on tuna intake, EPA datasheets on mercury and methylmercury, etc) you can verify everything I just wrote.
One thing that should be remembered about the current regulations for mercury are very strict in contrast to the levels associated with deterministic effects. This is perfectly natural since the natural occurrence of mercury is in such low concentrations. In fact almost all practical problems with mercury and how to deal with it are somehow linked to the inability to accurately measure it at the concentrations it begins to harm organisms.
Second, the speciation (division between different compounds) of mercury makes a huge difference in how the body absorbs it. The elemental form, found in old thermometers, switches and these CFL's, is practically biologically unavailable when liquid. There was a man in Taiwan who drank, IIRC, around a kilo without permanent effects. Oxidized mercury (HgCl2, Hg(NO3)2, and a few others) are also generally quite unavailable--several were used as syphilis medicine for quite some time--but led to a number of occupational hazards and poisonings. Mercury sulphide, on the other hand, is so unavailable that it's considered a "retirement path" in the mercury cycle. Among the variety of questionable Chinese medicine are "herbal balls," which have been found to contain up to 1.2 g (over a hundred CFL bulbs worth of mercury) of HgS. Finally, there are organic mercury compounds which are extremely toxic, but these are irrelevant except when they are produced by man in large quantities (though not necessarily on purpose) or when large amounts of inorganic mercury are available to anaerobic bacteria.
Almost all large-scale mercury poisoning has been due to the organic form entering the food supply.
However, though elemental, the form found in CFL's would most likely be vaporized if it got loose in your home. Vaporized elemental mercury is readily absorbed into the lungs, and can cross the blood-brain barrier, leading to temporary neurological effects in the few well-studied cases of household aspiration of the elemental form. Irritability and hyperactivity are typical symptoms.
Five milligrams is a good round number for the Hg content of a single CFL bulb. What is that for a person? 0.1 ppm? Well, the onset of symptoms in the victims of the Minamata disease (organic mercury poisoning) was a hair concentration of around 50 - 125 ppm (as mentioned, the margin of error on everything related to mercury is HUGE). Ca 100 ppm blood concentrations were found in the mothers of newborns in Iraq after an incident there with fungicide-laced grain in the 1970's. Again, uncertainty is the rule, and due to widely-varying affinities for heavy metals between different organs, there's very little one can predict in a given incident.
On a side note, while doing my thesis on a power plant mercury control system, I found my first grey hairs.