Formaldehyde, colorless gas. It has a special pungent smell, and the relative density of gas is 1 and 067 (air is 1). The relative density of liquid is 0,815 (-20℃), the melting point is -92℃, and the boiling point is-19,5℃. Soluble in water and ethanol. The concentration of aqueous solution is usually 35%~40%. Formaldehyde gas is mixed with air to form an explosive mixture, and the ignition temperature is about 300℃. Used as pesticides and disinfectants, and also used to make phenolic resin, urea-formaldehyde resin, vinylon, urotropine and dyes. It is prepared by dehydrogenation or oxidation of methanol under the catalysis of metals such as silver and copper.
Formaldehyde can combine with NH2 group in protein to form formyl protein, and its reaction speed is significantly affected by PH value and temperature. Gaseous formaldehyde has a strong stimulating effect on mucosa. Formaldehyde aqueous solution can denature protein and is widely used as a bactericide. In animal experiments, the oral LD50 of rats is 800 mg/kg, and that of guinea pigs is 240 mg/kg. For the human body, the initial low concentration stimulates the eye mucosa, and the slightly higher concentration stimulates the upper respiratory tract, causing cough and chest tightness. At the same time, there will be a special feeling of oppression on the forehead, which will cause mucosal ulceration and then cause lung inflammation. After inhaling formaldehyde, it causes loss of appetite, anorexia, emaciation, weakness and insomnia; Frequent contact may cause allergies. And can cause skin tissue ulcer. Formaldehyde has an anesthetic effect on the central nervous system.
The effects of formaldehyde on human health include abnormal sense of smell, irritation, allergy, abnormal lung function, abnormal liver function, abnormal immune function, affected central nervous system and damaged intracellular genetic material, which is a suspected carcinogen. Among them, smell and stimulation are the most sensitive, so its main harm is the stimulation to mucosa. Formaldehyde is easily absorbed through the respiratory tract, but rarely through the skin. 93% formaldehyde inhaled through the nose stays in the nasal tissue. When inhaled in high concentration, there will be severe irritation and edema of respiratory tract, increased respiratory resistance, decreased respiratory frequency, eye irritation and headache. The following table lists the acute irritation caused by short-term exposure to formaldehyde.
Acute Stimulation of Human Body Caused by Short-term Exposure to Formaldehyde
Human health impact
Concentration level of formaldehyde in air/(mg/m3)
coverage area
median
Olfactory threshold
0.06~ 1、2
0. 1
Eye irritation threshold
0.0 1~ 1、9
0.5
Pharyngeal stimulation threshold
0. 1~3、 1
0.6
Eye irritation
2.5~3、7
3. 1
Tears (exposure for 30 minutes)
5.0~6、2
5.6
Strong tear (left side exposed)
12~25
17.8
Life-threatening: edema, inflammation, pneumonia
37~60
37.5
die
60~ 125
125
Formaldehyde entering the body is metabolized very quickly, immediately oxidized to formic acid, and then quickly oxidized to CO2, exhaled from the lungs, and part of formic acid is excreted from the urine. Therefore, after inhaling formaldehyde, the concentration of formaldehyde in the blood did not increase.
Repeated inhalation of small doses of formaldehyde can induce allergic reactions and asthma; Direct skin contact with formaldehyde can cause allergic dermatitis, pigmentation and necrosis.
In vitro detection results of various mammalian cells show that formaldehyde can induce gene mutation, damage DNA, lead to DNA breakage and protein cross-linking, and inhibit RNA synthesis. However, the results of the whole animal experiment are contrary to those of the in vitro experiment. The main reason may be that formaldehyde is metabolized quickly in the body, and the tissues far away from the contact organs are rarely affected by direct formaldehyde except the organs that are in direct contact with formaldehyde.
Experimental animals exposed to high concentration inhalation can cause nasal squamous cell carcinoma. Population epidemiological survey shows that exposure to formaldehyde will increase the risk of nasal, nasopharyngeal and oral cancer. The International Centre for Research on Cancer (LARC) lists formaldehyde as a suspected carcinogen for human beings.