What are the Dangers of Lead Paint?

Lead can be inhaled through breathing, food and water, and absorbed through the skin. There is no threshold for the toxic effect of lead, that is, lead is toxic in the body. Therefore, "zero blood lead" has become the target of clinical control of childhood lead poisoning.

Environmental levels of lead exposure and human exposure

The average lead concentration in seawater around the world is 0.03 g / L, and fresh water is 0.5 g / L. The average lead content in the rural atmosphere is 0.1 g / m ³ , and the lead concentration in the urban atmosphere ranges from 1 to 10 g / m ³ . The average background value of lead in soil and rocks in the world is 13 mg / kg. The background value of soil lead content in China is high in the south and low in the north, with an average of 24.6mg / kg in Beijing and 72.57mg / kg in Hainan. The lead content range, arithmetic mean and geometric mean of vegetable soil in Beijing were 13.2-78.8mg / kg, 30.3mg / kg and 28.7mg / kg, respectively.

The sources of lead in the urban atmosphere in China are diverse, and the contribution of automobile exhaust accounts for a considerable proportion. In the 1990s, 80% of lead in Beijing's atmosphere came from automobile exhaust. During driving, 25% to 75% of tetraethyl lead is discharged into the air. Generally, the lead content of automobile exhaust gas is 20-50mg / m ³ , and the maximum can reach 100mg / m ³ . The use of leaded gasoline was banned in Shanghai at the end of 1997. In the first half of 1998, the atmospheric lead content in the urban area decreased from the annual average of 0.329x10 ^-3 mg / m ³ in 1997 to 0.234x10 ^-3 mg / m ³ . It was 28.9%. However, the atmospheric lead pollution in many cities is a compound type, and the lead content in the atmosphere has not decreased significantly after the promotion of unleaded gasoline.

Factory lead pollution is mainly spot-shaped, with irregular concentric circles spreading around the operating area and pollutant emissions. It can be roughly divided into the following layers: The air lead concentration at the operation site is 0.1 17.4mg / m ³ , which is 3 1417 times higher than the standard; the factory atmosphere is 0.012 0.8mg / m ³ , which is 8 532 times higher than the standard; The polluted area (0 3000m range) Atmospheric 0.0012 0.24mg / m ³ , 0 159 times higher than standard, surface water 0.24 18.3mg / kg, soil 20 6525mg / kg, grain 0.1 11.86mg / kg.

Because lead in water, soil, and air is absorbed by organisms and transferred to organisms, the average range of lead content in various plant foods worldwide is 0.1 to 1 mg / kg (dry weight), and the lead content in food products The average is 2.5mg / kg, and the average lead content of fish body ranges from 0.2 to 0.6mg / kg. The crustaceans and molluscs in some coastal contaminated areas even have lead levels of more than 3000mg / kg. The lead content range, median value, arithmetic average value, and Box-Cox average value of Beijing vegetables were 0.1-654.5 g / kg, 51.3 g / kg, 80.9 g / kg, and 48.7 g / kg FW, respectively. Based on the "Sanitary Standards for the Limit of Lead in Foods", the comprehensive exceeding rate is 9.2%; the lead concentrations of vegetables in Beijing's local and exposed areas are significantly higher than those of commercially available vegetables and protected vegetables; leaf beets have the highest resistance to lead pollution, Followed by cucumber, winter melon, Chinese cabbage, eggplant, shallots, tomatoes and cabbage, and Yunjia beans, radishes, peppers and cabbage are the least resistant to lead pollution.

The lead content of tea has increased year by year. For example, the lead content of Longjing tea was 0.63mg / kg in 1996, 0.74mg / kg in 1997, 0.87mg / kg in 1998, and 2.11mg / kg in 1999, which has exceeded the national standard (2mg / kg). The main reason for the unsatisfactory commercial teas is the excessive lead content, which is related to the excessively strict standards in China.

In newly renovated houses, the lead concentration in indoor air is generally significantly higher than outdoors, and some are as high as 2.7-90 g / m ³ , which is dozens of times more than outdoor. A survey showed that lead content in household dust can reach 561 g / g, which is even higher than that in park soil. The lead content of indoor dust in Beijing kindergartens was 73.3 g / g, which was also higher than the outdoor content.

Lead Environmental Exposure

Respiratory inhalation, food and water intake, transdermal absorption. specifically is:

Inhale

There was a significant positive correlation between the lead content in the atmosphere in the polluted area and the blood lead concentration in children. When the average atmospheric lead content in Shanghai decreased from 0.329mg / m ³ to 0.234mg / m ³ , the rate of children's blood lead concentration exceeded the standard decreased from 37.8% to 25.7%. In newly renovated housing, the lead concentration in indoor air is generally significantly higher than that in the outdoor, and the lead dust content in the workers' housing of lead industrial enterprises is also higher.

Passive smoking.

Dietary intake

The main sources are:

Lead in the atmosphere is deposited directly in grains and vegetables. The average daily intake of vegetable lead by adults and children in Beijing is 16.6 g and 13.6 g.

Excessive soil lead levels contaminate food. For example, grains and vegetables in contaminated soil areas have excessive lead levels, and lead content in tea leaves is also potentially dangerous. The results of lead leaching studies vary widely, ranging from almost no leaching to 10.0% to 42.79%.

Indoor lead dust contaminates food in the kitchen. Many workers in lead industry enterprises wear work clothes home after work, or have no habit of taking a bath immediately. Therefore, it is easy to bring lead dust in the workplace to the home and pollute the home environment. Pakistan reported that children whose parents were contaminated with lead in the workplace had an average blood lead content of 159 g / L, and children in the control group had an average blood lead concentration of 126 g / L. Children whose family members work in battery factories have an average blood lead concentration of 180 g / L.

The production process uses lead-containing substances to contaminate food. Puffed foods such as popcorn and preserved eggs contain a large amount of lead. The food of Guangzhou lead pollution source is mainly preserved eggs, the average content of which exceeds the national standard limit value of 1.2 to 8.0 times.

Contamination of food stored in leaded glaze containers. Use colored bowls to contain acid foods (orange juice, etc.). Drink 100mL per day based on the average dissolved lead content. The intake of lead is 26g (porcelain bowl) or 3.6g (imitation porcelain plastic bowl). .

When packing food in food bags, prevent the words, pictures or trademarks on the plastic bags from coming into direct contact with the food (churros, hawthorn cakes, pickles, etc.). Because the color ink of printed characters and pictures contains a lot of lead. Words and pictures on food bags reported that lead content was as high as 46 g / cm ² . According to domestic reports, the printed plastic bags with words or pictures are 25cmx20cm, which can dissolve 28.8g of lead. The printed and painted plastic film is 20cmx30cm, which can dissolve 78.6g of lead.

Skin contact absorption

A variety of cosmetics contain lead, which is used in eye makeup care creams with a lead content of 16% to 80%. A study by Fesalabao in Pakistan showed that 80% of the 20 bottles of Surma had a lead content> 65%, and children used it twice a week, with an average blood lead of 154.8 g / L and a control group of 126.6 g / L . Israel: The blood lead concentration of infants used is 112 g / L, which is higher than 43 g / L for non-users. The mother uses Kohl brand, the infant blood lead concentration is 52g / L; without the user, the infant blood lead concentration is 28g / L.

Children are a sensitive group harmed by lead pollution. In addition to food, water, and air, children's exposure to lead is through hand-mouth intake. The EPA reported in 1986 that the main sources of lead intake for 2-year-olds were: 47% of food, 45% of dust, 6% of drinking water, and 1% of air and soil. 97% of lead absorbed by 2-year-old children in the UK passes through the digestive tract and only 3% passes through the respiratory tract. Studies in China have found that 90% to 98.5% of the daily intake of lead in children in Beijing passes through the gastrointestinal tract, and 1.5% to 10.0% passes through the respiratory tract. After the lead reaches the digestive tract, adults can absorb about 11%, and children can absorb up to 30% to 75%.

School supplies and toys are important ways for children to consume lead. Most of the children's school supplies and appliances supplied on the domestic market are painted with paint, and paint contains a certain amount of lead, which is more harmful to children. If according to the international maximum allowable amount (250mg / kg), children bite a toy that complies with national standards, swallow 5g of the paint layer of the toy, and intake 12.5mg of lead.

Twenty-three kinds of toys tested in our country found that seven of them (30.4%) of the paint on the surface of toys contained soluble lead exceeding the standard. Among the 9 types of pencils, 6 types (66.7%) of lead content exceeded the standard, and the highest one exceeded the standard by 4.12 times. Half of the 12 kinds of school supplies exceeded the lead content, and the brown and black paint layers of the desks and chairs with the highest content exceeded the standard by 36.7 times. The lead content of textbooks and color covers exceeded the standard by 13.6 times. The absorption rate of soluble lead in gastric juice of young children is as high as 76%, which is prone to lead poisoning. New Zealand eliminated the use of lead paints and coatings and other measures, which reduced the human blood lead concentration by 42% between 1978 and 1985.

Environmental exposure toxicity threshold for lead

There is no threshold for the toxic effect of lead, that is, lead is toxic in the body. Therefore, "zero blood lead" has become the target of clinical control of childhood lead poisoning. In 1991, the US National Centers for Disease Control defined children's lead poisoning as follows: As long as children's blood lead levels exceed 100 g / L, children's lead poisoning can be diagnosed regardless of the corresponding clinical symptoms and signs and changes in biochemical indicators. Based on the serious harm of lead to the human body, at present, developed countries such as Japan and Canada have adopted 60 g / L as the standard for diagnosing lead poisoning in children.

Biological effects of lead environmental exposure

Comparison of metabolic kinetics of lead environment in animals and humans

Absorption / distribution / excretion

Absorption: Under production conditions, lead and its compounds mainly enter the human body through the respiratory tract in the form of dust, smoke or vapor, and a small amount can be ingested through the digestive tract. Lead and its inorganic compounds cannot be absorbed through intact skin. The deposition and absorption rate of lead in the lung is generally 30% to 50%, the absorption rate in the gastrointestinal tract is 7% to 10%, and it can reach 45% on an empty stomach. The absorption rate of lead through the respiratory tract and digestive tract is significantly higher in children than in adults. The human body ingests trace amounts of lead from food, water, and air daily, and daily intake of 100 to 300 g of lead from diet.

Distribution: More than 90% of lead in blood is combined with red blood cells, and about 10% is in plasma. Lead in plasma consists of two parts, one is the more active soluble lead, mainly lead hydrogen phosphate (PbHPO ₄ ) and lead glycerol phosphate, and the other part is plasma protein-bound lead. The lead that enters the blood is distributed in all tissues and organs of the body with blood circulation in the early stage, and the soft tissues are higher in liver, muscle, skin, and connective tissue, followed by lung, kidney, and brain. A few weeks later, about 90% was stored in the bone. Bone lead initially existed in an unstable form and later in the form of insoluble lead orthophosphate [Pb ₃ (PO ₄ ) ₂ ]. Bone lead can be divided into two parts, one is in a more stable state, and the half-life is about 20a. The other part is metabolically active, with a half-life of about 19 days, which can be quickly transferred to blood and soft tissues, and bone lead maintains a dynamic balance with lead in blood and soft tissues.

Excretion: The metabolism of lead in the body is similar to calcium. Any factor that can promote the storage or discharge of calcium in the body can affect the storage and discharge of lead in the body. A high-calcium diet is conducive to the storage of lead in bones. When calcium deficiency, infection, hunger, alcohol consumption, trauma, fever, and acid-base disorders caused by taking acidic drugs can lead bone to the blood, it can often lead to lead poisoning. Symptoms appear or worsen. Lead in the body is mainly excreted by the kidneys through the urine, followed by metabolism and its products

Lead acts on various organs of the whole body, mainly involving the nervous system, blood system, digestive system, and kidneys. Lead can affect many biochemical processes in the body, the mechanism of which has not been fully elucidated. Porphyrin metabolism disorder is one of the more serious and early changes in lead poisoning. The effect of lead on the blood system is because it inhibits a series of thiol-containing enzymes necessary for porphyrin metabolism, leading to impaired hemoglobin synthesis. Lead mainly inhibits õ-amino-y-ketovalerate dehydratase (ALAD), fecal porphyrinogen oxidase and ferrous complexase, and also inhibits õ-amino-y-ketovalerate dehydratase (ALAS) and feces Porphyrinogen decarboxylase and so on. After ALAD is inhibited, the formation of porphyllogen by õ-amino-y-ketovaleric acid (ALA) is blocked, and ALA in the blood increases and is excreted by the urine. Inhibition of faecal porphyrinogen oxidase inhibits the oxidation of faecal porphyrinogen III to protoporphyrin IX, which increases faecal porphyrin in blood and urine. After the ferrous complex enzyme is inhibited, protoporphyrin IX cannot bind with divalent iron to form heme. At the same time, erythrocyte free protoporphyrin (FEP) increases, which can combine with zinc in erythrocyte mitochondria to form zinc protoporphyrin (ZPP), and red blood cell zinc protoporphyrin (ZPP) also increases. Due to hemoglobin synthesis disorders, compensatory proliferation of young red blood cells in the bone marrow.

In addition to the direct effects of lead on the nervous system, in addition to increased ALA in the blood, it can enter the brain tissue through the blood-brain barrier, competing with y-aminobutyric acid (GABA) for GABA receptors on the postsynaptic membrane, resulting in Competitive inhibition. GABA exists in the pre-synaptic and post-synaptic mitochondria of the central nervous system. GABA inhibition interferes with the function of the nervous system, and changes in consciousness, behavior, and neurological effects occur. Lead can also affect the metabolism of catecholamines in the brain, significantly increase high vanillic acid (HVA) and vanillyl mandelic acid (VMA) in the brain and urine, eventually leading to toxic encephalopathy and peripheral neuropathy. Lead can inhibit the activity of alkaline phosphatase and ATPase in the intestinal wall, make the smooth muscles of the intestinal wall or arterial wall convulsions, and intestinal ischemia cause abdominal colic.

Lead can affect the function of renal tubular epithelial mitochondria, inhibit the activity of ATPase, cause renal tubular dysfunction or even damage, reduce the renal tubular reabsorption function, and also affect the glomerular filtration rate.

Interaction with drugs

Increased lead levels and magnesium deficiency can contribute to the onset of attention deficit hyperactivity disorder (ADHD). Interaction analysis showed that the effects of blood lead and blood magnesium are antagonistic to each other in the pathogenesis of ADHD.

In vivo and in vitro effects of lead exposure

Under in vitro culture conditions, exposure to low concentrations of lead (0.01 mol / L) induces tumor necrosis factor-a (TNF-a) overproduction in the neurocollagen cell line U-373MG. In addition, C57BL / 6 mice can induce the expression of TNF-a in neural collagen cells and nerve cells in the brain of mice after intraperitoneal injection of a lead acetate solution containing 12.5 g / kg of body weight. TNF-a may stimulate astrocyte proliferation or cause neuronal cell death, and such conditions are generally considered to be related to pathological astrocyte death and demyelinating effects. Although lead causes cells to express TNF-a, in vitro culture status, analysis of the proliferation rate of U-373MG cells and the results of detecting the number of apoptosis with iodoprodil staining, or using terminal transferase (TdT) X-dUTP-mediated terminal deoxynucleotidyl transferase labeling (TUNEL) staining directly analyzed the number of apoptotic neurons and collagen cells in mice after lead treatment, which showed that lead did not directly inhibit cell growth or cause cell death. Apoptosis. Similarly, treating mice (10 mg / kg body weight) or cell line U-373MG with bacterial endotoxin (LPS) did not directly inhibit cell growth or cause apoptosis. Although the impact on cell survival will vary somewhat depending on experimental conditions. In addition, after U373MG cells were exposed to lead acetate at different concentrations, such as 0.01 mol / L to 10 mol / L, Western blot was used to detect the modification of MAPK series proteins. It can be found that the phosphorylation of Raf, MEK, MAPK and other signaling proteins It rises as the lead ion concentration increases. After treatment with MAPK kinase function inhibitor PD98059, lead-induced TNF-a expression was inhibited. Lead does not cause I-kB phosphorylation at any concentration, while bacterial endotoxin causes I-kB phosphorylation. Lead and bacterial endotoxin have different signaling pathways in the collagen cell line U373MG ^[1] .

Human effects from lead exposure

Lead is a toxic metal that can accumulate in human and animal and plant tissues. It mainly damages the bone marrow hematopoietic system and causes anemia; or damages the nervous system and causes peripheral neuritis. Population characteristics:

Adult lead poisoning: symptoms such as fatigue, mood depression, heart failure, abdominal pain, kidney deficiency, high blood pressure, joint pain, reproductive disorders, anemia, etc. Men can cause reduced sperm count, decreased activity, and morphological changes.

Lead poisoning in pregnant women: severe consequences such as miscarriage, underweight in neonates, dead babies, and infant dysplasia.

Children's lead poisoning: Appetite loss, stomach pain, insomnia, learning disabilities, constipation, nausea, diarrhea, fatigue, low IQ, and anemia.

Acute or subacute toxicity

Mainly caused by life, mostly due to misuse or excessive use of lead-containing prescriptions to treat asthma, epilepsy, deworming, abortion, etc. These lead-containing compounds such as lead, lead dan, lead cream, meditation monk, black tin Dan, Zhang Dan, etc .; also used tin pot wine, tin pot to hold wine; and mistakenly take lead powder for potato powder. Children abroad are often poisoned by eating peeled plasters such as toys and paint on walls and furniture. This onset of oral poisoning often has an incubation period, the short one being 4 to 6 hours, usually two to three days, and the longest one to two weeks, which is closely related to the intake dose and individual differences. Occupational subacute poisoning can also occur.

Clinical features: severe abdominal cramps, anemia, toxic liver disease, toxic kidney disease, multiple peripheral neuropathy. He showed dizziness, general weakness, sore muscles and joints, inability to eat, constipation or diarrhea, liver enlargement, tenderness in the liver area, jaundice, and increased blood pressure.

Laboratory tests: In addition to the obvious increase in lead poisoning indicators, bilirubin increased and ALT increased; red blood cells, white blood cells, and urobilinogen were seen in urine; hemoglobin and red blood cells were decreased.

Nervous System Examination: Gloves and socks-type sensation loss, muscle atrophy, and muscle weakness can be found at the extremities. In severe cases, lead palsy occurs, that is, vertical wrist, ptosis; lead toxic encephalopathy, severe headache, convulsions, delirium, convulsions, stiffness, and even coma. Individual patients may develop paralytic intestinal obstruction.

Chronic toxicity

Chronic lead poisoning has clinical symptoms of nervous, digestive, and blood systems.

(1) Nervous system: mainly manifested as neurasthenia, polyneuropathy and encephalopathy. Neurasthenia, one of the early and more common symptoms of lead poisoning, is manifested in dizziness, headache, general weakness, memory loss, sleep disturbance, dreaming, etc. Among them, dizziness and general weakness are the most obvious, but they are generally mild , Is a functional symptom. There are still many people with early lead poisoning, and the above symptoms are not obvious. Polyneuropathy can be divided into sensory, motor, and mixed types. The sensory type manifested as numbness of the extremities and glove-sock type sensory disturbance of the extremities. Sports-type performances include: muscle weakness, first the grip strength decreases, appear earlier and more common. Further development is muscle weakness, mostly extensor weakness. Muscle paralysis, also known as lead paralysis, is more common in the radial nerve innervation of fingers and wrist extensor muscles, also known as sagging wrist; fibula, total toe muscle, and extensor toe sarcoidus, also known as drooping Foot disease. Encephalopathy is the most severe lead poisoning. Symptoms include headache, nausea, vomiting, high fever, irritability, convulsions, drowsiness, mental disorders, coma and other symptoms, similar to seizures, meningitis, cerebral edema, psychosis or local brain damage syndromes. Due to the improvement of labor conditions in China, it is rare, but the incidence of children abroad is very high.

(2) Digestive system: mild patients show general gastrointestinal symptoms, and severe patients have abdominal cramps. Gastrointestinal symptoms include metallic taste in the mouth, loss of appetite, bloating and discomfort in the upper abdomen, abdominal pain and constipation, dry stools in the form of abacus beads, and refractory constipation before the onset of lead colic. Abdominal colic is a sudden attack, mostly in the umbilical cord, with paroxysmal exacerbations of persistent pain, ranging from several minutes to several hours each. Because the pain is severe and unbearable, he often bends over and bends his knees, and he is restless. He presses his abdomen to ease the pain. At the same time, she looked pale and had sweats all over her body, but she had vomiting. During the examination, the abdomen was flat and soft, with mild tenderness, no fixed tenderness point, decreased bowel sounds, and often accompanied by temporary elevated blood pressure and fundus arterial spasm.

(3) Blood system: Lead mainly interferes with the hemoglobin synthesis process and causes changes in its metabolites, such as decreased blood AL-ALAD activity, increased urine 8-ALA, increased urine CP, increased blood FEP, ZPP, etc., which eventually lead to anemia, mostly Low pigmented normal red blood cell anemia.

(4) Other systems: Lead damage to the kidney is more common in acute, subacute lead poisoning or more severe chronic cases, and amino acid proteinuria, red blood cells, white blood cells and casts, and renal failure appear, suggesting toxic nephropathy with hypertension . Female workers are more sensitive to lead, especially during pregnancy and lactation, which can cause infertility, miscarriage, premature delivery, stillbirth and lead poisoning in infants. Male workers can cause reduced sperm counts, decreased activity, and morphological changes. It can also cause hypothyroidism.

Human health prevention and treatment measures for lead environmental exposure

Human exposure to lead environment

(1) Respiratory protection: Workers should wear dust masks.

(2) Eye protection: A safety mask can be used if necessary.

(3) Protective clothing: Wear work clothes.

(4) Hand protection: Wear protective gloves when necessary.

(5) Others: Smoking, eating and drinking are prohibited at the work site. After work, shower and change clothes. Conduct pre-employment and regular physical examinations. Maintain good hygiene.

Lead Environmental Exposure Health Monitoring

Conduct lead and regular health checks on lead workers to find employment taboos in time and to deal with patients with lead poisoning early.

Child lead poisoning

Childhood lead poisoning is a global problem. Lead poisoning has caused great harm to children's physical and mental health. In recent years, all sectors of society and the general public have paid great attention to this. China has carried out research and prevention of child lead poisoning in some areas since the 1980s, and has learned from foreign experiences, conducted useful explorations, and played a positive role in reducing the prevalence of child lead poisoning in China. In order to effectively prevent and treat children's lead poisoning, and in accordance with China's reality, to standardize the principles of prevention, diagnosis, classification and treatment of children's lead poisoning, the Ministry of Health has formulated the "Guidelines for the Prevention of Children's Hyperleademia and Lead Poisoning" and "Children's High Lead Principles of Classification and Management of Semia and Lead Poisoning (Trial)-Document of the Ministry of Health (Weifushefa [2006] No. 51).

Emergency Response

Cut off the fire. Wear a gas mask and general fire protective clothing. Collect with a clean shovel in a dry, clean, covered container, solidify with cement, asphalt, or a suitable thermoplastic material before discarding. If a large amount of leakage, collect and recycle or discard after harmless treatment.

(1) For leaking PbCl ₄ and Pb (ClO ₄ ) ₂ , all protective equipment such as gas masks should be worn. Mix with dry sand, pour it into a large amount of water in small batches, and put the diluted sewage into the wastewater system.

(2) For leaking PbO and Pb ₃ O ₄ , all protective equipment such as gas masks should be worn. Mix with dry sand and bury it in an open area; scrub the contaminated ground with soap or detergent, and put the diluted sewage into the wastewater system.

(3) For leaking PbF ₂ , all protective equipment such as gas masks should be worn. Sprinkle soda ash on the spill; rinse the contaminated ground with water, and dilute the sewage into the wastewater system.

(4) For leaking Pb (BrO ₃ ) ₂ , PbO ₂ and Pb (NO ₃ ) ₂ , all protective equipment such as gas masks should be worn. The contaminated ground is washed with water, and the diluted sewage is put into the waste water system.

(5) For leaked alkyl lead, use an incombustible dispersant to make an emulsion brush. If there is no dispersant, it can be absorbed by sand and poured into an open area for burial; the contaminated ground is washed with soap or detergent, and the diluted sewage is put into the wastewater system ^[1] .

Environmental Lead Disposal Methods

When the water body is polluted, it can be treated by neutralization, that is, adding lime milk to adjust the pH to 7.5, so that the lead is precipitated as lead hydroxide and transferred from the water to the sludge. The mechanical clarification can accelerate the clarification, the purification effect is 80% to 96%, and the lead concentration of the treated water is 0.37 to 0.40 mg / L. The sludge is then further harmlessly treated. For lead-contaminated soil, lime, phosphate fertilizer and other modifiers can be added to reduce the activity of lead in the soil and reduce the absorption of lead by crops.