Since childhood, many have been told how dangerous it is to break a mercury thermometer, because the toxic fumes of a quickly evaporating substance can cause serious damage to health. We decided to check how justified such warnings are.
The question “what to do if the thermometer breaks” worries many Internet users, so official authorities share their explanations on this topic (such materials can be found, for example, on the official website of the mayor and government of Moscow mos.ru, on sites EMERCOM of the Russian Federation And Rospotrebnadzor), and various media (RIA Novosti, RBC, TV channelScience"). Especially those asking worries probability get poisoned spilled from thermometer mercury, as well as questionhow long it is forbidden go into room, Where crashed thermometer.
Mercury is a so-called transition metal, and at room temperature it is a heavy, silvery-white liquid. Mercury and many of its compounds poisonous, they have a toxic effect on the nervous, respiratory, digestive and immune systems, and can also damage the kidneys, skin and eyes. WHO classifies this metal as one of the top ten chemicals that pose a danger to humans.
Exists three forms of mercury: elemental (or metallic), inorganic, and organic (represented, for example, by toxic methylmercury). They differ in the degree of toxicity and effects on humans. The mercury thermometers we are used to contain elemental mercury, while a household measuring device usually contains located 1 g of mercury.
From the outside world, substances enter the body in three main ways: they are eaten, inhaled, or they come into contact with the surface of the skin.
Eating mercury from a broken thermometer is absolutely not dangerous, since the body absorbed less than 0.1% of absorbed mercury. Moreover, the medical literature describes a stunning happening: a man intentionally swallowed 220 ml (3 kg) of liquid mercury; when seeking medical help, he complained of tremors, irritability and fatigue, but doctors did not find any lesions in the gastrointestinal tract or kidneys, while extremely high concentrations of the metal were recorded in the blood and urine. Most of the mercury left the man's body through the intestines over the next ten days, and laboratory tests returned to normal after another ten months. For comparison, death is caused by the consumption of only 250 g of such a familiar product as salt. But eating the contents of 3000 thermometers is not capable of killing a person. IN reference book The "Toxicological Profile of Mercury" prepared by the US Department of Health and Human Services, in the section "Fatal Cases", does not describe any poisoning by ingestion of pure mercury, only its various compounds.
At the same time, organic mercury compounds are extremely dangerous if used systematically. Methylmercury is the most toxic - it is formed when elemental mercury interacts with various microorganisms. Its main source is fish and seafood, which accumulate this compound during their lives. The larger the fish, the greater the chance that its meat contains high concentrations of methylmercury. The most high-profile case of methylmercury poisoning fixed in Japan, where an acetic acid plant discharged liquid waste, including inorganic mercury, into Minamata Bay from 1932 to 1968. Fish and shellfish that lived in coastal waters and accumulated methylmercury in their bodies were the basis of the diet of the local population. The victims complained of numbness and weakness in the legs and arms, a constant feeling of fatigue, ringing in the ears, blurred vision and hearing, slurred speech and clumsiness. In the most severe cases, those poisoned went crazy, paralysis and death occurred. This methylmercury poisoning was called Minamata disease. True, there is no risk of its development due to a broken thermometer - in order for methylmercury to form from elemental mercury, necessary special microorganisms and algae that could process it and that live not in apartments or private houses, but at the bottom of large bodies of water.
The second potential way mercury can enter the body is through inhalation of its vapor. Mercury starts evaporate already at a temperature of +16 ° C, therefore advice trying to reduce the temperature in the room where the thermometer has broken is completely justified. The body absorbs inhaled vapors in much higher concentrations than the stomach absorbs - about 80% of the vapors fall into the lungs, and from where they are carried throughout the body by the blood flow. However, it’s too early to panic: it can lead to death will lead only inhalation of 2.5 g of mercury vapor, that is, you need to break at least three thermometers at the same time in an unventilated room and remain there for some time.
Acute but not fatal mercury vapor poisoning comes at a concentration of 0.13–0.80 mg/m3. Usually, mercury from a thermometer forms several rather large balls, taking the form of hemispheres on the floor, which, firstly, are quite easy to remove, and secondly, their evaporation area will not be the largest. However, let's consider the worst, albeit largely hypothetical, scenario: all the mercury has leaked out and broken up into droplets that are not visible to the naked eye. Human capable To distinguish objects up to 0.01 cm long with the naked eye, let’s take this value as the diameter of each drop. Let effective evaporation occur from two-thirds of the surface, since some part of the mercury hemisphere lies on the floor. Let's calculate the surface area of the entire sphere, and then the area of evaporation. The total area will be 3.14 * 10-4 cm2, and the evaporation area is 2.09 * 10-4 cm2.
Knowing the density of mercury and calculating the volume of one ball (0.52 * 10-6 cm3), you can find out its mass (7.07 * 10-6 G). Then you can calculate how many such drops the same 1 g of mercury from the thermometer will disintegrate into. It turns out that in the worst situation there will be 141,500 tiny particles of mercury on the floor with a total area of 45 cm2, and the area from which the metal evaporates will be 30 cm2. The evaporation rate of mercury at room temperature is 0.002 mg/cm2 per hour Thus, 0.06 mg of mercury will evaporate in the room within an hour.
If you look at the maximum permissible concentration (MPC) of mercury, established legally, namely 0.0003 mg/m3, then you may get the impression that there is a lot of mercury in the air and poisoning will soon occur. However, an important point is not taken into account here - the MPC value does not determine one-time consumption, but describes the impact over a period of time. Let's transfer our calculations to specific housing. Since mercury gas will spread throughout all rooms, the entire area should be taken into account, and not just the affected room. Let it happen in an apartment with an area of 60 m2 with a ceiling height of 2.7 m. The volume of such a room will be 160 m3. Since it is not sealed, natural air exchange will occur (in the case of open windows, it is faster, but even with closed windows, the air circulates both inside the house and from the street and penetrates outside). Let’s assume that the volume of circulating air per hour is 320 m3, that is, half the volume will change. Let's calculate the concentration taking into account these data and find that per hour in the worst case it is 0.00018 mg/m3, which is even lower than the dose prescribed by law. In other words, for acute poisoning, which occurs at a dose of 0.13–0.80 mg/m3, you will have to break more than 720 thermometers in the room.
Now let's try to calculate a long-term impact, for example a week. Let’s say a person who broke a thermometer does not leave the apartment for the entire week (according to the same worst-case scenario, all the metal scatters into particles invisible to the eye). It turns out that during this time about 0.03 mg of mercury will enter the body (in fact, even less, since over time the mercury will evaporate more slowly). This indicator is also lower than dangerous even in the most unfavorable case under consideration, so there is no reason to fear that due to a broken thermometer the apartment will become dangerous for a long time.
The third potential route of poisoning is the penetration of mercury through the skin. However, mercury is too dense a metal (13 times tighter water) and can't absorbed through the skin. At the same time, it can still evaporate from the surface of the skin and poison the body with its vapors. You should not pick up spilled mercury with your bare hands because the metal can penetrate into the bloodstream through cuts and other damage to the skin and negatively affect your health.
Thus, the fear of mercury poisoning due to a broken thermometer is exaggerated. It is indeed an extremely toxic metal when inhaled, but home thermometers contain it in very small quantities. To get a dose of mercury that can lead to acute poisoning, you will have to break more than one thermometer, not remove large drops and deliberately stay indoors. Another way is to deliberately inhale the vapor from the contents of three thermometers so that they completely enter the lungs. A swallowed ball of mercury cannot harm the body at all. There is also no great danger if mercury touches the skin - it can only be absorbed through its damaged areas.
Cover image: Mercury thermometer with many medical capsules and pills von Marco Verch via ccnull.de
Read on the topic:
- Hugh Aldersey-Williams. Scientific tales of the periodic table. An interesting history of chemical elements from arsenic to zinc. “Liquid Mirror (chapter on mercury)
- Why were cats dying in Minamata?
- Is it true that if you eat apples with seeds, you can get poisoned?
- Is it true that fluoride toothpastes are dangerous to your health?
- Is it true that you need to take iodine immediately after exposure to radiation to protect against infection?
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