Mercury exposure from compact fluorescent lights

A commenter on a previous post asked about potential mercury exposure from broken compact fluorescent lights (CFLs). There are also various stories floating around the internet (such as this one) about the dangers of mercury in CFLs. So I thought I’d take the opportunity to look at how much mercury someone could be exposed to from a broken CFL, and whether there were any risks from that level of exposure.

A CFL typically contains about 4 mg of mercury (according to US EPA); a lot of newer CFLs contain 1 mg or less. I’ll look at the worst-case exposure, so let’s go with 4 mg of mercury in a bulb. In reality that mercury isn’t going to all be in the air right away – the evaporation rate of mercury is about 56 micrograms per hour per square centimetre – but figuring out the rate at which it enters the air requires assumptions about the area covered by the spilled mercury, temperature, pressure, etc. To keep things simple and to make sure I’m considering the absolute worst case, I’ll assume that all of that mercury instantly volatilizes.

After the mercury is released into the air, two things are going to happen. First, it will spread out, occupying a larger volume of air. Second, air movement in and out of the room will remove mercury over time. So let’s look at a couple of specific scenarios:

1. Let’s assume that right after the bulb breaks a person bends down to pick up the pieces. To keep the math simple I’ll say the mercury has spread into a volume of 1 m3 at this stage – large enough that the person’s head is within the affected volume and representing pretty much a worst-case exposure. In reality the mercury concentration within this 1 m3 volume would be highest right next to the floor (presuming the broken bulb is on the floor) and decreasing as you go up, but again to keep it simple and look at an absolute worst-case I’ll simplify things and pretend the mercury is evenly mixed over that entire 1 m3. The resulting concentration would be 4 mg mercury per m3 air. This concentration would not last very long at all and represents a worst-case instantaneous exposure.

2. If the CFL bulb broke in a fairly standard-sized bedroom (around 3 m x 3 m x 2.4 m, or 21.6 m3 – I’ll round down to 20 m3), then over time the mercury would mix throughout the volume of the room, with an average concentration of 4/20 = 0.25 mg/m3. However, air is also going to move in and out of the room (and the house). Even at the low end in winter with windows closed, an air exchange rate of about 1 air change per 3 hours is fairly conservative, so about 1/3 of the mercury would be removed after every hour. Therefore after 1 hour the concentration would be 0.17 mg/m3, after 2 hours it would be 0.11 mg/m3, after 3 hours it would be 0.074 mg/m3, and so on.

These concentrations are probably unrealistically high, since I’ve assumed all of the mercury instantly volatilized. A more realistic concentration would consider the evaporation rate (56 μg/h/cm2). The volume of 4 mg mercury would be about 0.0003 cm3; if it formed a hemispherical drop (probably a reasonable approximation) the exposed surface area would be about 0.017 cm2. Assuming room temperature and sea-level atmospheric pressure, the concentration in the bedroom would peak at about 0.0003 mg/m3 (again based on mixing throughout the bedroom; concentrations would be higher if you put your head right next to the mercury on the floor).

So now we have a very conservative prediction of how much mercury could be in the air under worst-case conditions. What does this mean in terms of potential for effects? The infamous National Post story I mentioned above talked about a Maine Department of Environmental Protection employee comparing concentrations measured in a bedroom to a state exposure limit of 0.0003 mg/m3. This exposure limit is actually the US Environmental Protection Agency “reference concentration” (RfC). However, if a Maine DEP employee really was using this value here, that employee is utterly incompetent or at least unqualified for that sort of assessment – it is a completely inappropriate value to use. The RfC is a conservative estimate of the average concentration you could be breathing in over your entire life without expecting any adverse effects. I’ve seen some other evaluations use occupational exposure limits – again this isn’t ideal, since they’re based on a worker being exposed every day over their working career.

The Agency for Toxic Substances and Disease Registry compiled data on short-term exposures to mercury vapours. The data on short-term human exposures are fairly limited, but measurable effects were associated with very high mercury exposures (of the cases where concentrations were known, they exceeded 40 mg/m3). There are also some animal studies using short-term exposures; generally effects were only observed at concentrations above about 27 mg/m3. The one exception is developmental toxicity; there were a couple of animal studies showing that when pregnant rats were exposed to concentrations as low as about 0.05 mg/m3 over 6 or 7 days at a key stage of foetal brain development, their offspring were hyperactive and showed effects on spatial learning.

Overall, a broken CFL bulb won’t result in mercury concentrations in air anywhere near as high as the concentrations at which effects on humans or even animals have been observed. However, given that mercury is a known developmental toxin, and since concentrations could be higher very close to the spill or after disturbance (e.g. during cleanup), it’s probably not a bad idea for pregnant women to avoid cleaning up broken CFL bulbs if possible; there probably wouldn’t be an effect but it doesn’t hurt to err on the side of caution if possible.

The commenter I mentioned at the beginning of this post mentioned a different scenario where her husband drove in a car for 3 months in winter with a case of broken bulbs. A study of air exchange rates of stationary vehicles suggests between 1 and 3 exchanges per hour with windows closed and no ventilation, or between 1.8 and 3.7 exchanges per hour with windows closed and the fan on recirculation; a compact car has an interior volume of about 3 m3. If the case had 12 CFLs, that would be a total of 48 mg of mercury potentially released; if it was released all at once this would result in an initial concentration of about 16 mg/m3 which would rapidly decrease. Again this mercury probably would not be volatilized to the air all at once though. Rather mercury would be released gradually over time. It’s honestly almost impossible to calculate the likely concentrations, particularly without knowing things like the temperature, how the car was used, etc. If we assume room temperature (e.g. the heater was on) and that each bulb resulted in a hemispherical mercury drop as described above, then a concentration as high as about 0.004 mg/m3 could be calculated, but there are so many assumptions and unknown variables that I wouldn’t want to rely on that number. The concentration probably isn’t in the range where short-term effects are likely, but there are so many unknowns I wouldn’t feel comfortable making predictions about long-term effects, particularly if the driver was spending long periods of time in the car.

14 Responses to Mercury exposure from compact fluorescent lights

  1. CFLs do save energy, but they also contain small amounts of mercury. It is important for consumers to realize that CFLs and fluorescent bulbs contain mercury and require special handling. The mercury vapor can be detrimental to handlers’ health—from those involved with handling new bulbs to people involved with storing, packaging and shipping used lamps. Mercury vapor, which can be absorbed through the skin or inhaled, can cause neurological damage, and when it gets into water, it can enter the food chain through fish. Read more about the dangers of mercury exposure here:

    If a bulb is broken or burns out, it should be properly cleaned up and recycled—it should not be disposed of in landfills. To reduce the risk for mercury vapor exposure, CFLs and fluorescent lamps should be safely handled, stored and transported to recycling facilities in a package that is proven to effectively contain hazardous mercury vapor. Find out more about how to minimize environmental risks and safely package CFLs here:
    If a bulb breaks, consumers can learn more about clean-up procedures here:

  2. ashartus says:

    I was tempted to not approve this comment (it was flagged by the spam filter and is a thinly-disguised ad for a commercial product), but decided to let it through in the interests of free speech and open discussion.

    The mercury in CFLs is not enough to be a health concern in most circumstances, as detailed in the post. I also followed up on the links; really they were more related to commercial fluorescent lamps and not CFL bulbs, though there isn’t that much more mercury in a commercial lamp. However, the study referenced on these pages about mercury concentrations from broken bulbs was really poorly designed and would significantly over-predict concentrations due to the use of a sealed chamber, which doesn’t reflect real-world conditions (it would be one thing if the study acknowledged this limitation , but it doesn’t – possibly since it was funded by manufacturers of special packing for fluorescent bulbs who have a vested interest in people thinking a broken bulb will result in hazardous concentrations…). Another example of why acceptance in a peer-reviewed publication does not guarantee a high quality study.

  3. johnwhitelaw says:

    Thank you for posting a thoughtful and informed analysis of the actual health risks associated with CFLs!

  4. Randi says:

    Thank you for writing such an informative article. I hope you have time to respond to my query. We brought home a package of 1 CFL from my mom’s 5 days ago – we brought it home in a bag with stuffed animals, coloring books, crayons for my 2 and 4 year old. When we got home I put the package on a high shelf in the kitchen – not realizing it was broken! It sat up there for 5 days, no ventilation at all. Last night my husband went to get the light bulb and a few tiny shards and dust fell out of the package! We immediately cleaned the whole kitchen with wet paper towels. But if the package broke in transit, could it have contaminated everything in the bag and the car? And if so, how should we proceed? I threw all the stuff out, but only after the kids played with the stuffed animals and books all over the house. Again, the package appeared closed but when picked up, a few small shards and dust fell out and room was unventilated for 5 days. Could the package have contained the vapor or would a slit be enough for it to escape? We are beyond worried about how it might have affected our kids and how the particles may have been spread through our house. Also, your article is the first I’ve found that has mentioned cars. If it broke in the car, would the kids have been harmfully exposed and do they continue to be? We were driving at night when it happened with the windows closed and the heat on. Thank you so much for your time.

    • ashartus says:

      If it was just one CFL I wouldn’t be too worried. Even if the other stuff in the bag was contaminated,there probably wasn’t enough mercury to have an effect. Remember that mercury is a naturally occurring substance and we are all exposed to a certain amount every day – it’s when we get abnormally high exposures that there are problems. For a single CFL, I think your steps were more than adequate (I probably would’ve just washed the stuffed animals, not thrown everything out). There isn’t really enough mercury in a CFL to be of concern for anyone except possibly pregnant women and very young babies (and even there it’s more precautionary). A single CFL breaking in a car shouldn’t be a problem – the case I mentioned in the article was about an entire case of them breaking.

  5. Thank you so much for your well written, informative and level headed article. I broke a CFL bulb last night and it was my son who showed me how to clean it up properly. But all day today I have remained uneasy and I’ve left the front door open (the bulb broke in the foyer) in 16F degree weather with the heat off (to keep it from circulating throughout the rest of the house) in an effort to air out the foyer. Of course I did this last night as well for 2.5 hrs. Overkill maybe? lol! Thank you again. You have made me feel much better.

  6. John says:

    Very good article, i would really appreciate it if you could give your opinion on a few questions I have. Have you ever read the Maine CFL study ?
    They actually broke bulbs and measured the mercury vapor levels. Do they seem dangerous to you?

    Some of the scenarios break the OSHA .1 mg/m3 ceiling (not to be surpassed ever) could this cause poisoning to a child?

    There doesn’t seem to be a reference level other than the 300 ng/m3, nothing for residential with children around so I see why they used it but I see why you say it is too low a level to use for a short term exposure.

    Also the SHER reviewed the study and determined there was a low risk to an adult but they punted when determining risk to a child because “no studies exist” and they say they can’t determine risk because children may ingest elemental mercury after bulb is cleaned up on contaminated dust through hand to mouth actions. This sounds really scary to me. Could you give me some perspective on the risk of this to a child playing in the area that a cfl broke in? Maybe a comparison or two?

    Also how far could contamination go in our home. The first cleanup instructions I read said (health canada) nothing about being able to contaminate clothing or other things with mercury but as I kept reading i found other instructions that say you can contaminate your clothing and your washing machine, but by the time we read that it was days later so i dont know what is contaminated. Will all our clothing be contaminated?

    We vacuumed when my toddler broke one. And brought me a little piece of it (and i was 5 feet from him but not looking that direction) and none of us left the room for 5-10 minutes until after it was vacuumed up and I read online that we were not supposed to have vacuumed and we were supposed to have evacuated. We then opened windows, shut off the heat and left the main floor for an hour or so and took showers. How bad was this for my kids? Especially since my toddler went close enough to pick up a piece when the vapor levels would have been the highest? Plus we don’t know what we touched after touching the bulb with bare hands because we didnt know at first it was this toxic. Did we contaminate other things? Also we wiped down the floor with wet cloth’s later that night but we were in there walking around the rest of the day before this after only having vacuumed. Did we spread it to other rooms on our socks?

    How contaminated is our home?

  7. B Barnes says:

    The scenario I would like to have input with regards to is as follows:
    The cfl bulb is in a fixture which refines a person to climb a ladder and reach over his or her head to change the bulb. while doing so the bulb breaks causing the powder in the bulb to shower down in the face of the person changing the bulb. It gets in the person’s open eyes, open mouth and is breathed into the person’s lungs. Thus the exposure is a) absorption into the system via direct contact with the eyes, b) ingestion by mouth, c) absorption via lungs both at initial breath as the powder was in the air while the person looked upwards toward the light fixture as the bulb broke and subsequent breaths as the powder is on the person’s skin of the face, lips, hair, hands, arms, clothing and d) absorption through the skin of the person’s face, neck, hands and arms.

    What level of exposure could a person receive in this scenario?

    I experienced this specific scenario and had a number of symptoms that followed. Bad taste in my mouth like I was constantly sucking on pennies. An intense wave of nausea about to minutes after the exposure that lessened only slightly but never went away for days for which I ultimately required prescription nausea medicine, A nearly immediate loss of motility lasting 4-6 weeks. The only way I could eliminate stool was by ingesting the OTC liquid used to cleanse in preparation for a colonoscopy plus miralax plus a prescription medication for constipation plus high fiber content foods plus a fiber supplement AND regular use of FIeet’s anemas.

    Eventually the bad taste went away and normal motility returned. I continue to have waves of intense nausea or more mild nausea that lasts for several days.

    The exposure happened on Feb 13 and today is May 18.

    • ashartus says:

      I don’t think it would be easy to calculate the exact exposure (and I definitely don’t have time these days which is why this blog is pretty much inactive). Maybe a worse case assumption would be that the entire mercury content of the bulb (1 to 4 mg) enters the body. For an average-sized adult (around 70 kg) that would be about 0.015 to 0.06 mg per kg body weight. That’s kind of in what I consider a grey area – there aren’t any reliable studies showing clear effects in humans or animals at that level of short-term exposure but given the limitations in the available studies and protecting for people who might be unusually sensitive it’s a higher exposure than we’d normally allow in public health situations. The actual exposure would probably be quite a bit lower than that but not easy to figure out exactly.

  8. Rambosteeler says:

    Simply wonderful blog! Very informative and relieving esp for a hypochondriac like me.

    I had a broken cfl incident about 3 weeks ago. I was changing the bulb in my room of the new apartment, which had nothing but this floor lamp with an extended arc arm ( of which I was changing the bulb). The bulb then broke and a few shattered pieces fell on the carpeted floor. I was about 1 to 1.5 feet away from the bulb when it broke and not in line of shatter spill. At that time, I wasn’t aware of the risk and hence didn’t bother to move out of the room. I just picked up the shattered pieces from the carpet floor and the bulb itself (which never fell down and was still in my hand) and disposed them after a short while. I visually inspected carefully for any glass pieces and made sure there was nothing visible at least to the naked eye. I don’t remember the windows being open, but they may just have been a little open with the blinds closed. I didn’t vacuum the carpet then because I didn’t have a vacuum cleaner in my new apartment and not because I thought it was harmful (I didn’t know it was harmful then). Not knowing, I slept that night in the same room, with A/C on and left the next day on some work out of town for three weeks with window and door of my room closed (The A/C was on though since my roommates were there). I returned on last Sunday (24th) and slept in the same room with door open. Only yesterday my roommate told that it was harmful when I casually mentioned it to him. I feared the invisible shattered powder would still be there (without having any way to confirm if it was actually there), I decided to vacuum up the entire floor with small suction fixture of the vacuum cleaner just to be safe. Only then I read that vacuuming was really bad on the EPA website. I have since then been extremely worried, and could not sleep all night thinking that vacuum cleaner would have spread the vapours all across the room. I would be really grateful if you could please tell me if I am ok to continue on in this room or inform the landlord to get the carpet changed. I’m really worried now thinking if I’ll have any long term effects. Please give me your thoughts on this. Thanks!

  9. Stephanie says:

    I had two energy lights break over my head. dust was everywhere . not sure if breathed in or not. recieved about 25 or more small cuts and one large cut on bottom of foot requiering five stiches. should i be concerned

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