At present, the world releases about 6.5438+0.5 million tons of mercury, 3.4 million tons of copper, 5 million tons of lead, 6.5438+0.5 million tons of manganese and 6.5438+0.5 million tons of nickel every year, which has caused heavy metal pollution in soils of different countries. Heavy metal pollution in soil directly affects soil quality, water quality, crop growth, agricultural output and agricultural product quality. Because heavy metals cannot be biodegraded, on the contrary, they can be enriched thousands of times under the biomagnification of the food chain and eventually enter the human body. Heavy metals can interact strongly with protein and enzymes in human body, making them inactive, and may accumulate in some organs of human body, causing chronic poisoning, ranging from strange diseases (such as Minamata disease and osteopathy in Japan) to death. Therefore, the impact of heavy metals on food safety is very important. From this point of view, fully understanding the long-term, hidden, irreversible characteristics of soil heavy metal pollution and its inability to completely decompose or disappear, and carrying out heavy metal pollution control has become a common concern of all countries in the world.
Man-made Unsafe Factors in Food Production In 1960s and 1970s, Australia, the United States, Germany and other countries began to study heavy metal pollution in soil. The research on heavy metal pollution in China began in 1980s, and the main research direction focused on the ecological effects of heavy metals in soil, the zonal differentiation law and zoning of critical content. The deposition of heavy metals in the atmosphere, the irrigation of industrial wastewater and the pollution of acid wastewater from metal mines all aggravate the heavy metal pollution in the soil.
1. Excessive lead
Since the end of August 2006, Xi 'an Xijing Hospital has tested the blood lead of 8900 people in Shuiyang Township, Huixian County, Gansu Province, among whom 373 are children. More than 90% of these children's blood lead exceeded the standard, and the highest blood lead content was 6 19 μ g/L, which exceeded the standard several times (lead poisoning, that is, the venous blood lead level was equal to or higher than 200 μ g/L for two consecutive times). It was diagnosed as severe lead poisoning, and adult blood lead exceeded the standard. Local villagers believe that a lead ingot smelter located next to Xinsi Village in Shuiyang Township is the "culprit". On September 12, 2006, Gansu Provincial Government held a press conference. After preliminary monitoring by the investigation team, the land within 400 meters of Huixian Nonferrous Metals Smelting Co., Ltd., which caused the accident of 334 children's blood lead exceeding the standard in Shuiyang Township, Huixian County, Longnan City, Gansu Province, has all been polluted. The joint investigation team of Gansu Provincial Environmental Protection Bureau has instructed the local government to further clean up the remaining pollution sources and completely dismantle other ancillary facilities for smelting and production. The dismantled facilities shall not be transferred to avoid new pollution. Crude lead smelting waste residue belongs to dangerous waste residue, and the waste residue stored in the temporary slag yard, the slag stored in the factory area and the surrounding road paving slag should also be cleaned up.
After lead enters the human body, except a part of it is excreted through feces and sweat, the rest dissolves into the blood after several hours, which hinders the synthesis of blood, leading to anemia, headache, dizziness, fatigue, drowsiness, constipation and limb pain. Some mouths have a metallic taste, and symptoms such as arteriosclerosis, digestive tract ulcer and fundus hemorrhage are also related to lead pollution. Children with lead poisoning have developmental retardation, loss of appetite, inconvenient walking, constipation and insomnia; If you are a pupil, you will be accompanied by hyperactivity, hearing impairment, inattention and mental retardation. This is because lead enters the human body and invades the nerve tissue of the brain through blood, which makes the supply of nutrients and oxygen insufficient and causes brain tissue damage, which may lead to lifelong disability in severe cases. Adult lead poisoning often appears: fatigue, depression, heart failure, abdominal pain, kidney deficiency, hypertension, joint pain, reproductive disorders, anemia and other symptoms. After lead poisoning in pregnant women, there will be serious consequences such as abortion, low birth weight, stillbirth and infant dysplasia.
It is very important to prevent and detect lead poisoning. However, the symptoms after lead poisoning are often very hidden and difficult to find, so the most reliable method at present is blood test.
Effective prevention of lead poisoning is one of the topics that scientists are exploring and overcoming. But as an individual, it is very important to strengthen prevention and self-protection. First of all, don't use lead-containing materials to make tableware, and it is best not to use colored glazed ceramic products to hold acidic food and drinks; Wash vegetables and fruits before eating, and peel those that can be peeled; Usually eat more fruits and vegetables such as lemon, cabbage, laver, sea cucumber, grass carp, persimmon, garlic, etc., so as to facilitate detoxification and lead discharge.
2. Mercury poisoning
In the early 1950s, in a place called Minamata Town, Kumamoto Prefecture, south of Kyushu Island, Japan, some patients with slurred speech, stunned faces, trembling hands and feet and mental disorders appeared. If these patients are not cured for a long time, they will bend over and die tragically. This town has 40,000 residents. In a few years, 1000 people have suffered from this disease to varying degrees, and this disease has also been found in other places nearby. After several years of investigation and study, it was confirmed by the research report 1956 of the Medical College of Kumamoto National University in Japan in August that this was caused by the long-term consumption of mercury-containing seafood by eight generations of seawater bay residents, which was considered as a major industrial disaster.
Mercury, also known as mercury, is a silvery white metal, which shows how many degrees in our common thermometer. It is a highly toxic heavy metal with strong volatility. The toxicity of mercury to organisms depends not only on its concentration, but also on its chemical form and the characteristics of organisms themselves. It is generally believed that mercury enters the body through the penetration of marine organisms (skin and gills) or the intake of mercury-containing food. The main ways of mercury entering the ocean are industrial wastewater, the loss of mercury-containing pesticides and the deposition of mercury-containing waste gas. In addition, mercury-containing slag and pulp are also one of its sources.
Scientific experiments have confirmed that the safe concentration of mercury in human blood is 1 μ g/10ml, and when it reaches 5 ~10μ g/10ml, obvious poisoning symptoms will appear. It is calculated that if a person eats 200 grams of fish containing 0.5 mg/kg of mercury every day, the amount of mercury ingested by the human body is just within this safe range. However, the mercury content of seafood in Minamata Bay is determined to be as high as several tens of milligrams per kilogram, which has greatly exceeded the standard. In addition, people have to match other foods every day, and these foods may also contain a certain amount of mercury, so the total intake of the whole day is far higher than the safe limit standard.
Mercury is easily contaminated by pollutants in the environment through various channels, which directly affects people's food safety and harms human health. Mercury is a highly accumulative element, which mainly accumulates in animals. Aquatic plants and aquatic products in lakes and swamps tend to accumulate a lot of mercury. Fish is a natural concentrate of mercury. The older the fish, the more mercury accumulated in the body. Since mercury-containing acaricide was used in agriculture in the late 1950s, the pollution of mercury to soil, natural water system and atmosphere has become increasingly serious. Mercury-containing wastewater discharged from factories is the main source of water pollution. The hygienic standard of drinking water quality in China stipulates that mercury should not exceed 0.001mg/L.
3. Cadmium pollution
At the beginning of the 20th century, it was found that rice in Toyama Prefecture in central Japan generally grew poorly. 193 1 There is another strange disease, mostly female, with symptoms of joint pain such as waist, hands and feet. After several years of illness, patients will have neuralgia and bone pain in all parts of the body, and difficulty in moving or even breathing will bring unbearable pain. In the late stage of the disease, the patient's bones soften and shrink, the limbs bend, the spine is deformed, the bones are fragile, and even coughing can cause fractures. The patient couldn't eat and was in great pain. They often shout "It hurts!" "It hurts!" Some people commit suicide because they can't stand the pain. This disease is named "Osteodynia" or "Pain Disease" (Itai? During the period of 1946- 1960, Japanese medical professionals engaged in comprehensive clinical, pathological, epidemiological, animal experiments and analytical chemistry found that "bone pain" was caused by cadmium poisoning caused by waste water from Shengang mine in the upper reaches of Shentongchuan. According to records, due to the development of industry, Shengang Mine in the upper reaches of Shentongchuan in Toyama Prefecture became the production base of aluminum-zinc mine in Japan from 65438 to 1980s. Zinc smelting started from 19 13 in Shentongchuan Valley. The "bone pain" was caused by cadmium-containing wastewater discharged from zinc smelter polluting the surrounding cultivated land and water sources.
Cadmium is a heavy metal, which is harmful to human body. Cadmium in human body is mainly ingested by polluted water, food and air through digestive tract and respiratory tract, and a large amount of savings will cause cadmium poisoning. The mineral enterprises in Kamoka have been injecting untreated wastewater into Shentongchuan for a long time, resulting in high concentration of cadmium-containing wastewater polluting the water source. Using this cadmium-containing water to irrigate farmland, rice seedlings grow poorly, and the rice produced becomes "cadmium rice" "Cadmium rice" and "cadmium water" brought people on both sides of Shentongchuan into the haze of "bone pain". 196 1 year, Toyama Prefecture established the "Toyama Prefecture Local Special Disease Countermeasures Committee" and began a nationwide survey. 1967 The research group published a joint report, which showed that "osteodynia" was mainly caused by heavy metal poisoning, especially cadmium poisoning. From 1968, the patients and their families filed a civil lawsuit against the metal mining company, and the plaintiff won in 197 1. The defendant refused to accept the appeal and the plaintiff won the case again with 1972.
Cadmium in the environment can enter food through aquaculture of aquatic organisms. The roots of crops can absorb cadmium in the soil, and the cadmium content in vegetables, grains and other foods in cadmium-polluted areas is much higher than that in pollution-free areas. The incubation period of cadmium accumulation in human body can be as long as 10 ~ 30 years. After cadmium is absorbed by the human body, it forms cadmium sulfur protein in the body and accumulates selectively in the kidney and liver. Among them, the kidney can absorb nearly 1/3 of cadmium into the body, which is the "target organ" of cadmium poisoning. Other organs such as spleen, pancreas, thyroid, hair, etc. also have a certain amount of accumulation. Cadmium can bind with protein molecules containing hydroxyl, amino and sulfur groups in vivo, and inhibit various enzyme systems, thus affecting the normal function of enzyme systems in liver and kidney organs. Because cadmium damages renal tubules, the patient has diabetes, proteinuria and amino acid urine. In particular, bone metabolism is blocked, resulting in a series of symptoms such as osteoporosis, atrophy and deformation.
Drinking more water, drinking more light salt water and eating more seaweed and kelp are good for preventing cadmium poisoning. According to the recommendation of the World Health Organization, each person's weekly exposure to cadmium should not exceed 7 micrograms per kilogram of body weight. The state has made very strict regulations on cadmium in industrial "three wastes" discharge. Attention should be paid to the clinical manifestations of respiratory system or kidney damage and the determination of urinary cadmium, as well as the early diagnosis and elimination of cadmium poisoning, and active treatment should be given.
4. Harmful arsenic
Arsenic pollution poisoning incidents or public hazards (chronic arsenic poisoning) are not uncommon. For example, in Manchester, England, 6,000 people were poisoned and 7 1 person died because arsenic-containing sugar was added to beer. Morinaga Milk Powder Company in Japan, due to the use of arsenic-containing neutralizer, more than 12 100 people were poisoned, and 130 people died of cerebral palsy. Typical chronic arsenic poisoning occurs near Lujiu arsenic mine in Miyazaki Prefecture, Japan. Because the arsenic content in soil is as high as 300 ~ 838 mg/kg, pupils in this area are chronically poisoned. Residents of Gutong Mine in Shimane Prefecture, Japan also have chronic poisoning patients. China stipulates that the daily average concentration of arsenic in the air of residential areas is 3 μ g/m3, the maximum allowable concentration of arsenic in drinking water is 0.04 mg/L, and the surface water including fishery water is 0.04 mg/L..
As a member of the nitrogen family, arsenic is an odorless and tasteless semimetal, which naturally exists in rocks and soil. It can synthesize organic and inorganic arsenic with other elements, the latter is more toxic and more common in water. Arsenic-containing wastewater, pesticides and smoke will pollute the soil. Arsenic accumulates in soil and enters crop tissues. The lowest concentration of arsenic toxicity to crops is 3 mg/L, and it is also very toxic to aquatic organisms. Arsenic and arsenic compounds can generally enter the human body through water, atmosphere and food, causing harm.
After arsenic enters the human body and is absorbed, it destroys the redox ability of cells, affects the normal metabolism of cells, causes tissue damage and organism disorder, and can directly cause poisoning death. If arsenic is applied to human body, there will be irritation symptoms at first, and tissue necrosis will occur after a long time. Arsenic can stimulate mucosa and directly damage capillaries. Arsenic and its compounds absorbed through mucosa (including vagina) or skin are mainly deposited in hair, nails, bones, liver and kidneys. Ordinary people can be poisoned by taking arsenic trioxide 0.0 1 ~ 0.05g, and symptoms of poisoning appear. Taking 0.06 ~ 0.2g can cause death; Breathing in the air containing hydrogen arsenide 1mg/L for 5 ~ 10 minutes can lead to fatal poisoning. According to WHO, drinking water with arsenic content exceeding 10 mg/L for a long time can lead to arsenic poisoning, which is a chronic disease leading to skin disorder, gangrene, kidney cancer and bladder cancer.
Because arsenic has affinity with keratinized tissues of hair and nail skin, whether it is chronic arsenic poisoning or acute arsenic poisoning, as long as it survives for more than a week after poisoning, more arsenic can be found in hair. Trace elements in hair are similar to those in human blood, which can accurately reflect the internal metabolism of human body. All the components of blood come from the surrounding environment and the food produced in this environment.
For arsenic poisoning, sodium dimercaptopropane or sodium dimercaptosuccinate can be used for symptomatic treatment. To control arsenic pollution, first, do not use high arsenic water for irrigation, and second, do not let plants planted on arsenic-contaminated soil enter the food chain. For polluted soil, plants can be used to repair the environment.
Generally speaking, to control the pollution of heavy metals to food, we must first check the source and strictly control the pollution of industrial "three wastes" and urban solid waste to the agricultural environment. Secondly, speed up the implementation of standardized production, strengthen the research and promotion of key control technologies for the quality and safety of agricultural products, and increase the implementation of technical standards and norms for pollution-free agricultural products. Third, strengthen food safety supervision and inspection, strengthen quality management and improve the food safety inspection and testing system. In addition, it is necessary to strengthen food safety education, raise public awareness of environmental protection, strengthen mass supervision, protect the natural ecological environment and safeguard human health.