Barium (Ba) is a silvery white metal with a slight luster, and only soluble barium salts can cause acute poisoning. Barium and its compounds can enter the body from respiratory tract, digestive tract and damaged skin, and can also be killed by intravenous medication. Most of the barium ions in blood quickly transferred to muscles and bones within 24 hours, and then barium in muscles gradually decreased and barium in bones gradually increased, and the cumulative amount could reach 65% of the total absorption. Barium is excreted mainly through feces and urine, and barium in the mother can enter the fetus and nursing children through the placental barrier and milk. Barium ion can cause excessive stimulation and excitement to striated muscle, smooth muscle and myocardium, and eventually lead to paralysis; Barium changes the permeability of cell membrane, leading to hypokalemia. The toxic dose of oral barium chloride is 0.2~0.5g, and the lethal dose is 0.8 ~ 0.9g The early symptom of barium poisoning is gastrointestinal irritation. Paralysis may also occur in the future, including cyanosis of face, chills of limbs, cold sweat, muscle tremor, convulsions, paralysis of tongue muscles and throat and language disorder.
The harm of mercury to human health is related to its chemical form, environmental conditions and ways of invading human body. Metal mercury vapor is highly diffusive and fat-soluble, which can be completely absorbed by alveoli after invading respiratory tract and transported to the whole body through blood. Metal mercury in blood can enter brain tissue through blood-brain barrier, and then be oxidized into mercury ions in brain tissue. Because it is difficult for mercury ions to return to the blood through the blood-brain barrier, they gradually accumulate in brain tissue and damage brain tissue. Metal mercury in other tissues may also be oxidized to ionic state and transferred to the kidney for accumulation.
The clinical manifestations of chronic metal mercury poisoning are mainly nervous system symptoms, including headache, dizziness, numbness and pain in limbs, muscle tremor and dyskinesia. Inhaling a large amount of mercury vapor will cause acute mercury poisoning, and its symptoms are hepatitis, nephritis, proteinuria, hematuria and uremia. Acute poisoning is common in production environment, but rare in general living environment. The amount of metallic mercury absorbed by digestive tract is very small. Metal mercury ingested through food and drinking water generally does not cause poisoning.
Inorganic mercury compounds can be divided into soluble and insoluble. Insoluble inorganic mercury compounds are easy to precipitate in water. Although insoluble mercury compounds suspended in water can enter the gastrointestinal tract through people, they are difficult to be absorbed and will not cause harm to people. The absorption rate of soluble mercury compounds in gastrointestinal tract is also very low.
Methylmercury enters the human body mainly through food, and is easily absorbed in the human intestine and transported to various organs of the whole body, especially the liver and kidneys, of which only 15% reaches the brain tissue. However, methylmercury first damages the brain tissue, mainly the cerebral cortex and cerebellum, so it has clinical manifestations such as centripetal vision loss, dyskinesia, acrosensory disturbance and so on. This is different from the tremor caused by the invasion of metallic mercury into brain tissue. The brain damage caused by methylmercury is irreversible, so far there is no effective treatment, which often leads to death or lifelong illness (see Minamata disease).
It is predicted that mental illness will prevail in this century, because mercury poisoning mainly damages nerves, so mental illness may occur if the mercury content in the body is too high. In the 1970s, the incidence of mental illness in China was 3.2‰, rising from 2 1.56‰ in the early 20th century, accounting for about15 million people. The growth rate is very fast.
Mercury ion has a strong affinity with sulfhydryl groups in the body, so it can combine with substances containing the most sulfhydryl groups in the body, such as protein, and important enzymes involved in the metabolism of substances in the body, such as cytochrome oxidase, succinate dehydrogenase, lactate dehydrogenase and so on. The combination of mercury and sulfhydryl in the enzyme will inactivate the enzyme and endanger human health.
Mercury in the body mainly excretes urine and feces through the kidneys and intestines, so urine mercury examination has important reference value for the diagnosis of mercury poisoning.