I. Health hazards
Invasion route: inhalation, ingestion and percutaneous inhalation.
Health hazard: Xylene can irritate eyes and upper respiratory tract, and can anesthetize central nervous system at high concentration.
Acute poisoning: Inhalation of high concentration in a short time can cause obvious irritation to eyes and upper respiratory tract, congestion of conjunctiva and pharynx, dizziness, nausea, vomiting, chest tightness, weakness of limbs, confusion and stumbling gait. In severe cases, restlessness, convulsions or coma may occur, and some of them may have hysterical attacks.
Chronic effects: long-term exposure to neurasthenia syndrome, irregular menstruation of female workers, dry skin, chapped skin and dermatitis of workers.
NFPA704 rated PX as a "health hazard" of 2, which is equivalent to diethyl ether [3].
Second, toxicological data and environmental behavior.
Toxicity: It belongs to slight toxicity.
Acute toxicity: LD50 1364mg/kg (mouse vein)
Reproductive toxicity: The lowest toxic concentration (TDL0) of rats in 24 hours (taking medicine on the 7th ~14th day of pregnancy) is 1500mg/m3, which is embryonic toxicity. [4]
Pollution source: Xylene is an important chemical raw material. Wastewater and waste gas from organic synthesis, synthetic rubber, paint and dye, synthetic fiber, petroleum processing, pharmacy and cellulose, as well as unsealed production equipment and ventilation in the workshop are the main sources of xylene in the environment. Overturning, leakage and fire during transportation and storage can also cause accidental pollution accidents. [4]
Metabolic degradation: in humans and animals, except for 3% ~ 6% inhaled xylene, all three isomers of xylene are metabolized into corresponding benzoic acid (60% o-xylene and 80% ~ 90% m-xylene), and then these acids react with glucuronic acid and glycine. In this process, a large amount of o-benzoic acid is combined with glucuronic acid, while p-benzoic acid is almost completely combined with glycine to generate corresponding methylhippuric acid, which is excreted. At the same time, a small amount of corresponding xylenol (phenol) and 3- hydroxy -2- methylbenzoic acid hydride may be formed (less than 2%).
Residue and accumulation: In occupational contact, xylene mainly enters the body through respiratory tract. For all isomers of xylene, the vapor absorbed by the lung is the same, the total amount is 60% ~ 70%, and this absorption amount is relatively constant during the whole contact period. Xylene solution can penetrate the whole skin with an average absorption rate of 2.25? G/(cm3 min) (range 0.7 ~ 4.3? G/(cm3 min)) is absorbed, and the transdermal absorption of xylene vapor can be ignored compared with direct contact with liquid. The residual and accumulation of xylene is not serious. As we said above, in the presence of NADP (transferase II) and NAD (transferase I), xylene entering human body can generate methylbenzoic acid, and then combine with glycine to generate methylhippuric acid, which is almost completely excreted in 18 hours. Even the 3%-6% xylene remaining in the lungs after inhalation is exhaled within 3 hours after contact (half-life is 0.5 ~ 1 hour). The residual detection of xylene exposure is mainly to determine the content of methylhippuric acid in urine, and it is also suggested to determine the content of xylene in our gas or blood, but the result of the latter is often inaccurate. Because methylhippuric acid does not exist naturally in urine, and because it is almost a residual xylene metabolite, it is the best confirmation of xylene contact test to determine its existence. Xylene can exist in drinking water for a long time. When the concentration of xylene in tap water is 5mg/L, its odor intensity is equivalent to Grade 5, and the unique odor of xylene will not disappear until July and August. When the odor intensity is Grade 3, it takes 4 to 5 years. The odor of xylene in river water is kept for a short time, which is related to the initial concentration, and can generally be kept for 3 to 5 years.