I asked before about a thermometer that I broke yesterday. To summarize, I broke a mercury thermometer in my bedroom, which is a place where is difficult to have sure that I get rid of all mercury, but I cleaned the large amount without touching it.

However, I have more specific questions now. I discovered that I, by my lack of attention, have spread mercury along the house. I found a very tiny drop (really difficult to see) on the floor near to my desktop, which is in the living room, not in my bedroom. I also found a few same little drops in the bedroom, but it was really tiny. So, since I can assume that I will not be able to get rid of all mercury now, I have the following question:

  • How much time mercury takes to evaporate?

I think that wait the mercury to evaporate it is the only way that I can get rid of them now. Also, I have to say that I live in a country which doesn't have a service to check the amount of mercury in the air of the house neither get rid of the mercury.


I found what maybe is more mercury tiny drops under a table in living room, but this time I tried to estimate the size of the possible drops.

Three really tiny mercury beads

Three really tiny mercury beads (zoom in if you could not clearly see the white points)

enter image description here

I know is it difficult to see, but I placed a piece of adhesive tape on the floor, which has the same size as my thumb's nail (about 1.4cm).

I don't know if is a good way to measure something, but I cut one of the three beads in a imagem editor and placed copies of it from on side until another. It takes about 30-40 copies to made the path. So, 1.4cm/30 results in each bead being at least about 0.47mm.

So, with this information, how many of that beads are needed to make the air dangerous?

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    $\begingroup$ The risk and recommendations are a bit OT here, but the rate of evaporation that is to be expected is interesting. The vapour pressure of Hg at 300K is around 1 Pa. $\endgroup$ – Karl May 4 '20 at 6:37
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    $\begingroup$ I deleted the third one to fit better to the rules. Sorry for that. $\endgroup$ – Mycroft May 4 '20 at 13:00
  • $\begingroup$ You really should find a good way to decontaminate. Letting it disappear by evaporation is akin to saying "let me breath dangerous levels of mercury vapour for a decade". We don't "let it evaporate" even in a well ventilated laboratory: we clean it up as fast as possible. $\endgroup$ – matt_black May 5 '20 at 15:32
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    $\begingroup$ @karl even a 0.1g drop is enough to contaminate the air in a large house (say 500 cubic meters) above the minimal safe level for the best part of a year (crudely). So evaporating slowly is not a big gain. $\endgroup$ – matt_black May 5 '20 at 17:17
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    $\begingroup$ Sulphur powder (flowers of sulphur) is normally used to clear up mercury spills. You could try to get some (Amazon sell it) , just liberally spread it over the spill area, rub it into cracks etc. $\endgroup$ – porphyrin Oct 31 '20 at 7:40

I found this statement in a paper about $\ce{Hg}$ contamination from dental work:

The evaporation rate of elemental mercury at room temperature ($\pu{20 ^\circ C}$) is approximately $\pu{50 \mu g\:cm-2h-1}$ (range of $\pu{40-60 \mu g\:cm-2h-1}$).

They cited the following work as a source for that number:

Gary N. Bigham, Wanyu R. Chan, Manuel Dekermenjian, Ali Reza, "Indoor Concentrations of $\ce{Hg}$ Vapor Following Various Spill Scenarios," Environmental Forensics 2008, 9(2-3), 187-196 (https://doi.org/10.1080/15275920802121975)

German regulations (as an example) say that 0.035 µg/l of metallic mercury vapour in air pose no risk under lifelong exposition, and 0.35µg/l can be harmful under long (months?) exposition for some people. The math is full of imponderables, esp. the actual amount that was spilled and size of drops.

Swiss officials https://www.toxinfo.ch/quecksilberhaltige-fieberthermometer say that a single broken fever thermometer can lead to intoxications, but the risk can usually be averted by collecting as much as possible and ensuring proper, regular ventilation.

The following publication suggests that a properly cleaned up spill from a fever thermometer should become undetectable within several weeks, but the airborne Hg concentration can be significant in that time, and regular ventilation is highly recommendable.

E. Martin Caravati et al. Elemental mercury exposure: An evidence-based consensus guideline for out-of-hospital management, Clinical Toxicology 2008, 46:1, 1-21, https://doi.org/10.1080/15563650701664731

But one thing is quite clear: A single, large blob that you miss (under furniture, wooden floorboard etc.) can stay for a very long time, and lead to potentially harmful concentrations in the air. There are a lot of reports about little mercury puddles that were found under floorboards during laboratory renovations, even decades after the last mercury instrument had been thrown out.

  • $\begingroup$ I have sure the tiny drops that I have mentioned weren't bigger than 1mm. $\endgroup$ – Mycroft May 4 '20 at 13:33
  • $\begingroup$ Well, are they gone by now? $\endgroup$ – Karl May 4 '20 at 20:15
  • $\begingroup$ Actually, no. I just found a couple of tiny drops near to my desktop (which is not the area that I broke the thermometer). They were about 1mm each. $\endgroup$ – Mycroft May 5 '20 at 0:27
  • $\begingroup$ @Karl your calculations are way, way out. I reckon that drop would take years to evaporate and this corresponds to my experience of mercury in a lab. It is likely that lots of small particles will persist and lead to dangerous levels of mercury vapour in a domestic environment (if you ever vacuum the carpet you will make this much worse). Even in labs with good ventilation we take major precautions to clean up mercury spills by, for example, sprinkling everything with flowers of sulfur). $\endgroup$ – matt_black May 5 '20 at 15:24
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    $\begingroup$ I have read the most high amount of mercury that a fever thermometer has is 3g, and the most are in 0.7g and 1.5g. $\endgroup$ – Mycroft May 5 '20 at 18:14

As the comments in the other post say, there is no need to worry. You'll probably get more mercury and in a more dangerous form by eating fish and seafood and even more if you should smoke. To stay on the safe side, open the windows in your house from time to time, as you probably are doing anyway.

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    $\begingroup$ +1 for your nick. :-) $\endgroup$ – Karl May 4 '20 at 9:18
  • $\begingroup$ Totally disagree. Small mercury droplets dispersed widely indoors will lead to worrying levels of mercury vapour in the air and this will persist for years and will be worse if you ever vacuum as this disperses the particles into smaller droplets and puts them in a warm environment. Gas utilities (whose domestic meters used to use mercury in valves which occasionally spilled) have been prosecuted for this. $\endgroup$ – matt_black May 5 '20 at 15:29
  • $\begingroup$ Please see the official guidelines by NHS (UK) nhs.uk/common-health-questions/… $\endgroup$ – imalipusram May 6 '20 at 6:12
  • $\begingroup$ @imalipusram Those guidelines cover both thermometers and mercury-containing CFL bulbs or fluorescent tubes. But bulbs don't contain enough mercury to cause long term contamination. Thermometers do. And their advice on broken thermometers isn't not to worry: it is to contact experts who know how to decontaminate things like carpet. $\endgroup$ – matt_black May 8 '20 at 14:00

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