The causes of lead poisoning in children vary from country to country, especially influenced by the level of economic development and social and cultural background. The US Environmental Protection Agency reported in 1986 that the main ways for 2-year-old children to take lead are: food 47%, dust 45%, drinking water 6%, air and soil 1%. Davies reported that 97% of the daily lead absorbed by 2-year-old children in Britain passes through the digestive tract, and only 3% passes through the respiratory tract. Song's research found that 90% ~ 98.5% of the daily lead intake of Beijing children passes through the gastrointestinal tract, and 1.5% ~ 10.0% passes through the respiratory tract.
Lead poisoning in children is both common and serious in China. There are many reasons for the grim situation. Based on some existing research results, there are roughly the following aspects.
1, industrial pollution
Lead is widely used in industry, agriculture, transportation, national defense and many other fields, so all these fields and related manufacturing industries will produce lead pollution to varying degrees. The main industries that cause environmental lead pollution are battery manufacturing, metal smelting, printing, shipbuilding and dismantling, and machinery manufacturing. In China, due to the limitation of traditional industrial layout, almost all the above industries are concentrated in densely populated large and medium-sized cities, and the environmental protection measures of factories need to be strengthened, which makes the industrial lead pollution in China far more serious than that in industrialized countries, which is one of the main reasons leading to lead poisoning in children.
Of course, industrial lead pollution is by no means limited to these industries. Many studies have proved that the blood lead level of children and the prevalence of lead poisoning in children near lead-exposed factories and even in ordinary industrial areas are much higher than those in control children, which shows the harm of industrial lead pollution. It is worth emphasizing that in recent years, due to the development of township industries, the prevalence of lead poisoning among children has spread from cities to rural areas. In fact, the blood lead level and lead poisoning prevalence rate of children in Beijing suburbs have greatly exceeded that of children in urban areas. Several indicators of lead poisoning among children in Shanghai suburbs are also close to and exceed those in urban areas. It can be seen that the influence of environmental lead pollution on children not only occurs in cities, but also in rural areas, especially in rural children in the suburbs of large and medium-sized cities and concentrated in township enterprises.
2. Exhaust pollution of leaded gasoline
Tetraethyl lead is used as an explosion-proof agent in the traditional gasoline production process. After this gasoline is burned, lead-containing particles are discharged from the tail gas and converted into lead compounds in the atmosphere. One-third of the lead dust quickly settled on the ground (soil and crops) within a few kilometers on both sides of the road, and the other two-thirds were suspended in the atmosphere as aerosols and entered the human body with breathing. Many studies have proved that the blood lead level of children living in areas polluted by automobile exhaust is significantly higher than that of the reference population. Lead dust in the atmosphere not only directly increases the intake through children's respiratory tract, but also increases the intake through digestive tract by depositing on food and even grains and vegetables growing on both sides of the road.
At present, the relationship between leaded gasoline and lead poisoning in children is quite clear. The United States, Japan, Australia and many European countries have implemented unleaded gasoline, and many developing countries are actively following the research in China and Shanghai. It shows that with the popularization of unleaded gasoline, the blood lead level of urban children in China is also decreasing year by year.
3. Environmental pollution leads to lead content in water, soil and crops.
The study on the lead content of urban trees and soil in Guangzhou shows that the lead content of urban trees and soil is obviously higher than that of surrounding areas. Generally speaking, the lead content of plant food is higher than that of animal food, the former has the highest lead content in roots, and the latter has higher lead content in bones and viscera than in muscles and fats. Lead in food is directly related to the lead content in soil and water in this area. The lead content of rice produced in paddy fields near a smelter in Shaoguan City, Guangdong Province is 18 times higher than that in non-polluted areas. In some heavily polluted areas, almost all crops contain lead.
Oral food is the main way for children to take lead. In Poland, the consumption of local vegetables is positively correlated with the blood lead level of children, which is the result of the increase of lead content in vegetables caused by lead pollution in soil. Children's bioavailability of lead in water is higher than that of food, and the high lead content in drinking water in some areas can lead to an increase in infants' daily lead intake.
In addition, lead pollution in infant food processing is also an important factor, such as canned food, drinks, candy and so on, which are all children's favorite foods. Children's daily intake of lead from food is positively correlated with age, which is caused by the increase of intake and the widening of diet with age. Children's lead intake is related to food types, consumption and lead content. For example, canned food such as vegetables, fruits, fruit juice, etc., due to the lead weld in canned food, the lead content in food increases, and the daily lead intake also increases.
4, lead to the pollution of workers to the family environment.
The study in Jiangyin City, Jiangsu Province found that the blood lead level of children of lead exposed workers was significantly higher than that of children of the same age living in the same area and attending the same school. The study in Shanghai further found that the blood lead level of children of lead-exposed workers is higher than that of children of non-lead-exposed workers, and the blood lead level of children whose parents are bronze workers is significantly higher than that of children whose parents are lead-exposed workers. A questionnaire survey of workers in a large lead-exposed enterprise in Shanghai shows that 83% of the workers go home illegally after work, and 80% of the workers don't have the habit of taking a bath immediately after work. Therefore, it is easy to bring lead dust from the workplace to home through work clothes, hair, hands, etc. And pollute the family environment.
Lead-containing dust in living environment is a factor that can not be ignored in children's lead poisoning, and hand-mouth route is an important way for children to contact lead. Thornton and others found that the lead content in household dust is an important indicator of children's blood lead concentration, which is much higher than that in park soil. It is reported that every natural logarithm of lead content in dust in children's living environment increases by one unit, and children's blood lead will increase by 0.23 μg/dl. Therefore, it is of great benefit to strengthen the health education of lead workers and enhance their self-protection awareness to prevent lead poisoning in children.
5. Long-term exposure to lead-containing school supplies and toys
Paint on the surface of children's toys and school tools contains lead, which children will directly ingest when touching and chewing. It is reported that the soluble lead content of some paint toys is between110.3 ~ 5150.6 mg/kg. Children spend quite a lot of time touching toys and school supplies every day. Young children often suck their fingers and non-food items, and older children also bite their fingers and school supplies when they are nervous or emotional. Therefore, if the lead content of these electrical appliances is too high, it may become the cause of lead poisoning in children.
At present, most of the children's school supplies and appliances supplied in the domestic market are painted, and the paint contains a certain amount of lead. The lead content of children's toys and school supplies in the market is generally high because the relevant administrative departments of the state have not yet formulated the lead standards. Someone tested the content of soluble lead in domestic toys. According to foreign toys and school supplies, soluble lead
A few years ago, several cities on the west coast of the United States reported cases of lead poisoning among children after using crayons made in China. 1In March, 1994, the US Consumer Product Safety Commission randomly checked the lead content of 1 1 kinds of colored crayons imported from China in the US market, among which three brands exceeded the standard seriously enough to cause lead poisoning in children, and the lead content of the other eight brands also exceeded the US standard. After the major news media in the United States reported this result, they began a nationwide campaign to boycott China crayons. Therefore, we must never underestimate the toxic effects of lead in toys and school supplies on children.
In addition, a survey in Beijing shows that the lead content in indoor dust in kindergartens is 73.3μg/g, which is also higher than that outside.
6. Others
(1) Food Although the research so far has not found that the lead content in the main food of China residents exceeds the international standard, the second study on the total diet of China residents conducted in 1992 showed that the lead pollution in the diet was serious. The total dietary intake of 2-7 years old exceeds the ADI value 18.9% specified by FAO, and it is close to the ADI value in other age groups, and the intake in autumn is higher than that in spring.
Some traditional foods are high in lead. Popcorn is children's favorite food. Because the body of popcorn machine is made of lead-containing alloy, popcorn contains a lot of lead. According to the sampling survey of 66 samples, the lead content ranged from 0.25 to 21mg/kg, of which 28 samples (42.4%) exceeded the national hygienic standard for cakes (0.5mg/kg), and the highest one exceeded the standard by 4 1 times.
The traditional production process of preserved eggs (preserved eggs) uses lead oxide as food additive, so preserved eggs also contain high lead. According to the lead content of 42 preserved eggs in the market, 15 (3 1.3%) exceeded the allowable amount (3mg/kg). The over-standard rate of some brands is 100%. Therefore, it is necessary to educate children and parents, so that children should try not to eat these foods, and at the same time improve traditional processing technology to reduce lead content.
(2) Burning coal: Coal will release lead during combustion. The study in Shanghai found that the average lead content in indoor air was 18 times higher than that in outdoor air in families with coal products (such as briquettes), and the average blood lead content of children in coal-fired families was significantly higher than that in non-coal-fired families. In addition, there are similar reports in Nanjing, Beijing and Jinan.
At present, most families in China still use coal and coal products as the main fuel, especially in the cold north and coal-producing areas. Therefore, accelerating the process of household fuel gasification has certain practical significance for controlling indoor lead pollution caused by coal burning.
Third, the social factors that affect children's exposure to lead.
Although children's personal eating behavior and bad hygiene habits will affect their lead exposure, socio-economic, cultural and demographic factors are also important factors that cannot be ignored. A study in the United States shows that the blood lead level of children with high family income is lower than that of children with low income families; The blood lead level of black children with the same income is higher than that of white children. The degree of industrialization of living environment and the size of the city are the main factors affecting children's lead exposure, living in a big city (population >; The blood lead level of children is higher than that of small cities (population
Before 1970s, the lead content of paints used in the United States exceeded 50%. Many old houses are painted with this kind of paint, which leads to high lead content in the room. Children living in it are the biggest victims of lead. According to statistics, there are 10% children living in these old houses, especially blacks. These children are at the greatest risk of lead poisoning, so the centers for disease control in the United States suggested that these children should be specially examined. In China, the situation is just the opposite. After 1980s, with the rise of house decoration, the risk and prevalence of lead damage in children are increasing.
Parents' smoking and their education level are also one of the reasons that affect children's blood lead. The lead content in each cigarette is about 3 ~ 12μ g, of which 2% can be released into the smoke, which causes the lead content in the air in local small environment to increase. The higher the educational level of parents, the more attention they pay to food choices and dietary hygiene habits, so the chances of children's exposure to lead are relatively reduced.