Lead is a multi-affinity toxicant that has adverse effects on multiple systems of the body after entering the body. 90% of lead is in the skeletal system and the rest exists in the blood. The toxicity of lead is long-lasting, with a half-life of up to 10 years, and it is not easily excreted by the body, so the amount of lead in the human body is 5 times higher than that in the environment, and there is no lower limit for lead pollution, and any level of lead pollution will have adverse effects on human health. Moreover, even if we get out of the lead pollution environment and carry out lead expulsion treatment, the blood lead level will drop, but it will not restore the damaged nerve cell development to the original normal level.
I. The metabolic process of lead in the body
(I) Absorption of lead
1. Intestinal absorption: The intestine is the main way of lead absorption in the case of non-occupational lead exposure. Lead is absorbed into the blood from the small intestine through both active transport and passive diffusion. Lead and calcium, iron and zinc enjoy the same part of transport protein in the process of intestinal absorption, so increasing the content of calcium, iron and zinc in the diet can effectively reduce the absorption of lead in the intestine.
2.Respiratory absorption: Lead in the air is inhaled into the lungs through the respiratory tract and then absorbed into the blood through the alveolar capillary units.
3.Dermal absorption: The amount of lead absorbed through the skin is very small.
(II) Distribution of lead in the body
Lead is distributed in the body in a three-chamber pattern: blood, soft tissues and bones. Blood and soft tissues are the exchange pool, and the lead in the exchange pool is transferred to the storage pool bone tissue in about 25-35 days, and the lead in the storage pool maintains the dynamic balance with the lead in the exchange pool.
1.Lead in blood: More than 99% of the lead involved in blood circulation exists in red blood cells, and only less than 1% exists in plasma, and the lead inside and outside the red blood cells also maintains a dynamic balance.
2. Lead in bone tissue: Bone tissue holds more than 90% of the total lead in the body. The accumulation of lead in bone starts from fetal period and gradually increases with age, and the accumulation of lead in bone can last for about 50 years. When the body fluid is acidic due to infection, trauma and acidic medicine, the insoluble lead orthophosphate in the bone is converted into soluble lead phosphate and moved to the blood, causing the blood lead concentration to rise sharply and causing poisoning or aggravating the symptoms of the original disease. When calcium deficiency in food or blood calcium decreases, or when calcium excretion in body increases, lead enters blood with calcium, causing blood lead to rise.
3.Lead in other tissues: a small amount of lead is distributed in liver, kidney, spleen, brain, muscle and other organs. Brain tissue is an important target organ of lead. Soft tissues contain relatively more highly active and mobile lead. This is one of the reasons for the strong reaction of the organism in children with lead poisoning.
4. Half-life of lead in the body: the half-life of lead in blood is about 25-35 days, the half-life of lead in soft tissues is about 30-40 days, and the half-life of lead in bones is about 10 years. Therefore, the blood lead level can only reflect the lead exposure condition in the last 1 month or so, while only the bone lead level can reflect the chronic lead exposure condition for a longer period of time.
(iii) Excretion of lead
Lead is excreted from the body through three ways. About 2/3 of lead is excreted via kidney in urine; about 1/3 is excreted into intestinal lumen through bile secretion and then excreted in stool; and a very small amount of lead is excreted through hair and nail shedding.
(D) Characteristics of lead metabolism in children
1. Absorption: Children absorb more lead than adults, both through respiratory tract and digestive tract. Digestive tract is the main way of lead absorption in children.
(1) The absorption rate of lead in children is as high as 42%-53%.
(2) Children have more hand-to-mouth movements.
(3) Children consume significantly more food per unit of body weight than adults, and the amount of lead absorbed through the food route is also relatively high.
(4) Children have faster gastric emptying than adults, and the absorption rate of lead increases substantially.
(5) Larger particles are inhaled from the respiratory tract and swallowed more into the digestive tract.
There are several reasons why children inhale more lead from the respiratory tract than adults.
(1) Lead mostly accumulates in the atmosphere about 1m above the ground, while 75-100cm from the ground is exactly the breathing zone of children.
(2) Children have a high demand for oxygen, so the ventilation per unit body weight is far greater than that of adults.
(3) The absorption rate of lead in children’s respiratory tract is higher than that of adults, which is 1.6-2.7 times higher than that of adults.
(2) Less excretion: The excretion rate of lead in children is only about 66%, and about 1/3 of lead still remains in the body. The maximum daily excretion of lead for adults is 500μg, while the daily excretion of lead for young children around 1 year old is only equivalent to 1/17 of adults.
3. The lead in the storage pool is more mobile: the lead in the storage pool of children is more mobile and moves more easily to the blood and soft tissues, thus the chance and degree of endogenous lead exposure are higher.
II. Manifestations of lead poisoning
The effects of lead poisoning on the body are multi-organ, multi-system and systemic, and the clinical manifestations are complex and lack of specificity. The common manifestations are as follows.
(i) Nervous system: The nervous system is most vulnerable to lead damage. Lead can cause impairment of figurative intelligence, visual-motor function, memory, reaction time, language and spatial abstraction, sensory and behavioral functions, and symptoms such as fatigue, insomnia, irritability, headache, and hyperactivity. Due to the late maturation of the blood-brain barrier and the relative fragility of the central nervous system, coupled with the imperfect excretory function, they are vulnerable to lead damage. When children ingest a large amount of lead compounds at one time or in a short period of time, brain tissue produces cell edema, hemorrhage, demyelination degeneration, and atrophy of hippocampal structure. Clinical symptoms of acute poisoning appear: such as dullness, anorexia, vomiting, abdominal pain, diarrhea, delirium, convulsions, coma and other symptoms of pre-encephalopathy, and in severe cases, epilepsy or death or leaving serious sequelae. When children are exposed to low levels of lead, it can cause reduced synaptic density in brain cells, reduced dendritic branching, a decrease in their range of synaptic plasticity, slowed conduction of motor nerves, and EEG changes. Due to the uneven division of lead in the brain, the symptoms of chronic lead poisoning are atypical, such as movement disorders, slow reactions and mental retardation in children. For every 10μg/dl increase in blood lead level, IQ will be reduced by 6-7 points.
(2) Hematopoietic system: lead can inhibit the synthesis of heme and antagonize iron, zinc and calcium, inducing anemia, which will be aggravated with the increase of lead poisoning. Especially for children with iron deficiency anemia.
(iii) Cardiovascular system: After statistical survey, it is found that vascular diseases in the population are related to the increased lead load of the body. Degeneration of aorta, coronary artery, renal artery and cerebral artery were found in lead poisoning patients, and myocardial degeneration was also found in children who died from lead poisoning. In addition, it has been found that lead poisoning can lead to the excessive aggregation of intracellular calcium ions, which increases the tension and tone of vascular smooth muscle and causes hypertension and cardiac arrhythmia.
(iv) Digestive system: Lead acts directly on smooth muscle, inhibiting its voluntary movement and increasing its tension to cause abdominal pain, diarrhea, constipation, indigestion and other gastrointestinal disorders. The intact liver cells have a certain protective effect on lead toxicity, but the level of liver mixed function oxidase system and cytochrome P450 decreases in acute lead poisoning, so that the liver detoxification function is impaired and lesions appear.
(v) Genitourinary system: Long-term exposure can cause chronic nephritis in children and adults. Because of the large compensatory function of the kidney, the nephrotoxic effect of lead is often underestimated, and lead reduces the clearance of the kidney, which in turn increases the retention of lead in the kidney and other tissues. It affects normal physiological functions, such as nephrogenic hypertension and central nervous system diseases, and with the prolongation of time, renal damage is aggravated, resulting in impaired renal tubular excretion and reabsorption, amino acid urine, diabetes, gout, and renal failure in the late stage. Lead has reproductive toxicity, embryotoxicity and teratogenic effects. Recently, it has been reported that blood lead up to 25-40μg/dl can affect male reproductive function and cause sperm malformation. Even at low levels, exposure can still affect the growth and development of the fetus in utero, causing malformations, premature birth and low birth weight. The metabolic pathways of lead and calcium in the body are very similar, and during pregnancy, the chance of lead transfer from mother to fetus increases in order to meet the needs of fetal development and bone calcification. Lead in pregnant women can pass through the placenta smoothly and act on the embryo. Exposure to high doses of lead during the first 3 months of pregnancy can cause stillbirth, miscarriage and fetal malformation. The first 3 months are a critical period for fetal neurological development, when the blood-brain barrier is not yet mature, and long-term low-level lead exposure can impair the early formation and later maturation of neural networks. The pattern of synapse formation is related to learning ability.
(vi) Immune system: Lead can bind antibodies, and the increase of lead in drinking water reduces circulating antibodies. Lead can act on lymphocytes and decrease the titer of complement, making the body more susceptible to endotoxin and lowering the resistance, often causing repeated infections in the respiratory and intestinal tracts.
(vii) Endocrine system: Lead can inhibit the secretion of vitamin D activating enzyme, adrenocorticotropic hormone and growth hormone, leading to physical development disorders in children. For every 100μg/L increase in blood lead level, the height of children will be 1-3cm less.
(H) Bone: Most of the lead in the body is deposited in the bone, which affects the synthesis of vitamin D3, inhibits calcium absorption, and acts on osteoblasts and osteoclasts, causing disorders of bone metabolism and osteoporosis. Epidemiological studies show that when bone loss occurs, lead is released from the bone into the blood, causing long-term and lasting toxic effects on all major systems.
These are the damages caused by lead to the major systems of human body. In addition, lead can also cause the loss of various nutrients and trace elements, resulting in the disorder of enzyme system, and then lead to the related physiological functions.
Children are more vulnerable to damage due to their physiological characteristics and living habits, and the effects are lifelong and far more than we can imagine. Lead poisoning produces multi-organ, multi-system, systemic and lifelong irreversible damage to children, especially damage to the nervous system leading to mental retardation in children. The accumulation of lead in children’s bodies can lead to pediatric ADHD, emotional irritability, aggressive behavior, learning difficulties, constipation, and anorexia. In addition, in the blood, lead will “rob” the carrier protein, so that the iron, calcium and especially zinc in the blood can’t be kept in the body properly, which will lead to low intelligence, lower immunity, and impaired height development due to anemia and calcium deficiency. Finally, because lead is stored in the bones, it hinders the growth of height and makes the heart and lung function decrease, and the oxygen carrying capacity decrease, so that the memory decreases and affects the academic performance.
III. Lead pollution sources
1.Industrial pollution With the progress of urbanization and industrialization in China, environmental pollution is becoming more and more serious, among which lead is the main source of pollution.
2.The exhaust gas pollution of leaded gasoline is used as an explosion-proof agent in the production process of traditional gasoline. One third of the large particles of lead quickly settle on the ground (in soil and crops) in the area of several kilometers on both sides of the road, and the remaining two thirds are suspended in the atmosphere as aerosols, and then enter the human body with breathing. The relationship between leaded gasoline and lead poisoning in children is quite clear.
3.School supplies and toys It is known that each page of colorful picture of newspapers and magazines contains up to 2000 micrograms of lead, 60% of the surface paint in domestic toys contain soluble lead has exceeded the international maximum allowable amount, the highest lead content is more than 6 times, 36.7% exceeds the limit by 37 times: the colorful cover on textbooks exceeds the limit by 14 times, and there is more than 10 times of lead pollution in children’s colored pens.
4, food: popcorn, for example, is a favorite food of children. As the body of the popcorn machine is made of lead-containing alloy, so that the popcorn contains a high amount of lead. The traditional production process of eggs (puffed eggs) to lead oxide as a food additive, so the eggs also contain high levels of lead. Therefore, necessary education should be given to children and their parents so that children do not eat these foods as much as possible, while improving the traditional processing to reduce the lead content.
5.Other: In our life, lead pollution is everywhere, besides the lead pollution in the air and water, there are lead pollution in ceramics, paints, cosmetics, hair dyes, batteries, etc.
With the improvement of living environment, it is now necessary to pay attention to diet and adopt dietary therapy for lead detoxification. For some people who are engaged in lead work or have high lead content, they should use some health food for lead detoxification. In the Canon of Medicine, there is a saying that “food therapy is better than medicine”. Lead-removing drugs can not only remove lead but also expel some beneficial elements from the body, which has certain side effects on the body, so it is recommended to use food therapy and buy some regular health products to drive away lead.
Fourth, food therapy to drain lead
1.Milk: The protein it contains can combine with the lead in the body into a soluble compound, thus preventing the absorption of lead in the body. We suggest you to drink 1-2 cups of milk every day.
2.Shrimp: Shrimp contains up to 2 grams of calcium per 100 grams. The latest research shows that increasing dietary calcium intake is beneficial to children’s bone development in addition to reducing the absorption of lead in the gastrointestinal tract and the accumulation of lead in bone, which can effectively reduce the absorption of lead in children and reduce the toxicity of lead. For children who are exposed to low concentration of lead, the increase of calcium intake in the diet can effectively reduce the absorption of lead.
3.Kelp: Kelp has detoxification and lead detoxification effect, which can promote the excretion of lead in the body.
4.Garlic: Some organic components in garlic can combine with lead and have the effect of detoxifying lead poison.
5.Vegetables: Vitamin C in vegetables such as rape, cabbage and bitter gourd will combine with lead to produce insoluble and non-toxic salts, which will be excreted with feces. In general, the lead content of plant foods is higher than that of animal ones, and the highest lead content is found in roots and tubers.
6.Fruit: The pectin substance contained in kiwi, date and citrus can precipitate the lead in the intestine, thus reducing the absorption of lead by the organism.
7.Yogurt: It can stimulate intestinal peristalsis to reduce lead absorption and increase excretion.
Lead excretion recipes.
1.Carrot milk: 50 grams of carrot, cooked and pressed, then blend into 200 ml of milk and take.
2.Golden mushroom and shrimp dumpling: 100 grams of golden mushroom (cooked to remove soup), 50 grams of shrimp skin (slightly washed in warm water), 200 grams of lean pork, chop the above three things into a puree, add seasoning to make filling, wrap into dumplings (or wontons) and cook, can be divided into several times to eat.
3, garlic and kelp porridge: 50 grams of rice, 15 grams of kelp, chopped, two cloves of garlic pounded, rice, kelp with an appropriate amount of water first boiled, to become a porridge and then add garlic and seasonings, cooked for a few moments that is, can be divided into several times to eat.
4.Golden plum drink: 10 grams of money grass, 10 grams of plum, 10 grams of licorice, decoction of soup to remove the dregs, about 300 ml in 3 times to drink.
5, licorice mung bean soup: 10 grams of licorice, 50 grams of mung beans, boil soup, make mung beans crisp, no sugar, drink soup and eat mung beans.
The above recipes can be taken alternately and need to last for a long time to be effective, usually 1-2 months or longer, people with lead poisoning symptoms may want to try to regulate, and at the same time can be treated with drug lead repellent.