In Brennn10's Compact Fluorescent Instructable there was a short discussion about the amount of mercury contained in CFL bulbs. The same topic came up in a mailing list I read, and there was some interesting analysis worth sharing.Statement:The Stranger (the Seattle weekly) has a column called "Dear Science" where the typically quite intelligent author argued that CFL bulbs weren't all that "better" for the environment because inevitable improper disposal put more mercury-n-shit into the environment. So unless you got all your power from a mercury spewing coal plant, you shouldn't use CFL's . And Seattle, getting a majority of it's power from hydro, shouldn't use CFL's.This was called into question for being selective analysis that encourages an attitude of "there's not currently a solution, so keep doing what you're doing", and elicited the following response:Just so I can bore everyone with what I think is the current level of knowledge about mercury and CFLs, here's some of the current information.NRCan did a study on how much mercury is actually in CFLs, and compares them to other typical consumer sources (e.g., watch batteries--if you throw one of them out, you've throw out five times as much mercury as in a CFL):http://oee.nrcan.gc.ca/energystar/english/consumers/questions-answers.cfm#mercuryAfter reading this, I actually worked out these numbers for myself on how CFL savings compare to mercury releases a few months ago. Of course, this is all more environmental destruction brand X vs. brand Y discussion that was being talking about.I was curious about what the numbers work out to, so I went to dig for some data; this is what I came up with.In 1999, about 1.75 trillion kWh were generated by coalEnergy Information Administration Annual Energy Review 1999, Figure 26In 1999, 47.8 tons/year of mercury emissions came out of coal-fired power plants.Source: U.S. EPA, Office of Air Quality Planning and Standards.1999 National Emissions Inventory for Hazardous Air Pollutants.http://www.epa.gov/ttn/chief/net/1999inventory.html#final3haps.This calcs out to a figure of 0.025 mg mercury per kWhAssuming 5 mg mercury per CFL, the equivalence point is about 200 kWh--a CFL would need to save 200 kWh before getting tossed in the trash. A quick calculation shows that this is about how much a CFL saves in half a year, if it were run 24-7: 75 W for an incandescent; 25 W for an equivalent CFL = 657 vs. 219 kWh/year, or 438 kWh/year difference.Of course, this assumes that the coal mercury emission rate is the same as it was in 1999; I'm not sure if measures have been taken since then to reduce mercury emissions. Also, this is assuming that 100% of the power saved by the CFL would be generated by coal-fired power plants. But even with that assumption, coal is such a large fraction of the power generation (typically about half)--it would jump from six months to a year, instead. Of course, this period gets longer assuming a realistic duty cycle, but still, those numbers all seem to pencil in below typical installed lifetimes of CFLs.Finally, there's a article from Home Energy magazine (behind a subscriber link), where somebody did a similar calculation with more current numbers, I think.http://www.homeenergy.org/article_full.php?id=457&article_title=Understanding_CFLsHome Energy MagazineNovember/December 2007Understanding CFLsby Richard Benware"Although the use of CFLs is steadily spreading, public understanding about how to dispose of them responsibly has not kept pace."Life Cycle BenefitsIn order to disprove the myths about CFLs, let's begin at the beginning. When CFLs are created, manufacturers dose the bulb with a small amount of mercury. This mercury, when electrically stimulated, releases UV light, which subsequently reacts with a phosphor coating to create visible light. Thus mercury is an essential part of every CFL; without it, the bulbs would not produce light. The typical dose of mercury is about the size of a pen tip, and these doses have been getting smaller and smaller. One reason for this is that the laws resulting from the Restriction of Hazardous Substances (RoHS) Directive have made it illegal for CFLs in Europe to contain more than 5 milligrams (mg) of mercury.In the United States, there are no such laws limiting the amount of mercury in lightbulbs as yet, but members of the National Electrical Manufacturers Association (NEMA) have voluntarily agreed to limit the amount of mercury in the CFLs that they produce to 5 mg for bulbs of up to 25 watts and 6 mg for bulbs of 25 to 40 watts. The average CFL on store shelves today contains about 4 mg of mercury, and nearly all the CFLs in production contain less than 5 mg. The mercury used in all the CFLs produced in the United States represents 0.18% of the mercury used in all U.S. products andindustrial processes.CFLs do not release mercury as long as they are intact. In fact, they reduce net mercury emissions in the environment by conserving energy. For every kWh of electricity used by consumers, the average power plant emits over 1.5 lb of pollutants. If a 75W incandescent is replaced by an 18W CFL, the CFL will use 456 kWh less energy than the incandescent over its 8,000 hour lifetime. The Emissions and Generation Resource Integrated Database (eGRID) contains data on the emissions of the average power plant. Using eGRID's information to calculate the average emissions per kWh, we find that this single CFL has prevented the release of 2.72 lb of sulfur dioxide, 1.05 lb of nitrogen oxide, 5.67 mg of mercury, and over 700 lb of CO2.It is important to note that these are the reductions from the average U.S. power plant. The eGRID data show that, on average, nonbaseload emissions tend to be dirtier. And in addition to reducing emissions, CFLs save money for the consumer. The Energy Information Administration (EIA) gives a 2006 average residential electricity cost of $.1008/kWh. Using the example given above, and basing our calculation on this figure, we find that a consumer would save about $46 on energy over the lifetime of the CFL.When these bulbs finally do reach the end of their useful life, there are several pathways they can take. In the best-case scenario, the bulbs are recycled. Recycling rates are increasing, thanks to state regulations -- California and Minnesota have banned altogether throwing CFLs in the trash -- and improved consumer awareness. In 1999, it was estimated that only 15% of all fluorescent lightbulbs were recycled. Currently, that number has increased to around 25%, with higher levels in commercial applications. Since an average of 98.9% of the mercury is successfully recovered in the recycling process, this pathway generates minimal emissions.Even the CFLs that are discarded in the trash are unlikely to release much of their mercury. Although most of them break under current trash disposal methods, some remain unbroken, and will not release any mercury. But those that do break are not likely to release much mercury. EPA estimates that only 0.2% of the remaining mercury in a spent bulb is elemental vapor. The rest of the mercury is in the glass, the phosphor coating, and the electrodes of the bulb. Mercury absorbed in these areas is not readily released. In fact, an EPA study found that only 6.8% of the total mercury in a broken bulb will be released. Since the average bulb on the market today contains only 4 mg of mercury, it will release only about 0.27 mg, even if it breaks when it is thrown in the trash.The only disposal option that could lead to the release of any significant amount of mercury is incineration. Today, many incinerators have advanced mercury control technologies. CFLs disposed of in such incinerators would release up to 90% of their mercury, but those emissions would then be removed by these technologies. Incinerators without these technologies are not capable of removing the mercury. But even after accounting for all of the emissions that occur via all of the routes listed above, CFLs represent a mere 0.01% of total U.S. mercury emissions annually.It is important to note that even if CFLs released all of their mercury, the environment would still be better off than it would be if nobody used CFLs. This is true because the average power plant releases 5.67 mg of mercury to power each 75W incandescent bulb. In short, replacing incandescents with CFLs is a great way to save energy, reduce mercury emissions, and save money (see "Discounting CFLs").