Abuse of phosphate or excessive cadmium in rice

The cadmium exceeded the rice crisis, which has seriously endangered people's health. However, a large amount of arable land in Hunan suffers from heavy metal pollution. The area of ​​farmland soil contaminated with heavy metals is not less than 20%, and farmland cadmium pollution is developing on a large scale.

What is the relationship between cadmium-contaminated land and cadmium-exceeding rice? Professor Luo Lin, who has long been engaged in research on the treatment of cadmium-contaminated soil, has analyzed the correlation. He introduced that soil generally contains cadmium, some of which will exist in the form of compounds (known as the "effective state"), through the absorption of crops, some "effective state" will enter the rhizomes and grains of rice. If the content of the "valid state" exceeds the safety standards, it will become excessive cadmium rice.

The content of cadmium in soil or from phosphorus fertilizer "under the same conditions, the content of cadmium in soil will increase, and the cadmium content in rice will also increase accordingly. The correlation between the two is up to 99%." Tong Qianming also said so.

Yesterday afternoon, the reporter learned from the Propaganda Department of the County Committee of Hunan Province that the rice produced by the three rice processing plants in Ganxian County was found to have exceeded the cadmium standard in Guangzhou. After the disclosure of the cadmium exceeded event, it caused the related governments of Hunan Province, Zhuzhou City, and Ganyu County. The department attaches great importance to it. From May 19th, Jixian County has convened an investigation team composed of a number of government departments including agriculture and environmental protection to conduct investigations. At present, three manufacturers that have been exposed to excessive cadmium in rice have been required to stop production for investigation. The Hengdong County Party Committee Propaganda Department also responded that the Dongyang Rice Factory in Dayu County, Hengdong County also stopped production for investigation.

Chen Zhanjun, director of the Bureau of Legal Propaganda Department of the Hunan Provincial Environmental Protection Agency, said that cadmium in the environmental background does not exceed the standard, and why did cadmium and cadmium be produced in Jing County and Hengdong County? He said: "I tend to think that it was brought in by the fertilizer."

Tong Xianming, a professor at the Institute of Geology of Hunan Province, agrees that he believes that pollution caused by unreasonable use of phosphate fertilizer is also worth paying attention to compared with industrial pollution.

As one of the three most commonly used fertilizers, phosphate fertilizer is widely used in agricultural production. Its main raw material is phosphate rock, natural associated cadmium, and its content per kilogram of phosphate fertilizer varies from a few milligrams to hundreds of milligrams. Improper application of phosphate fertilizer will cause soil cadmium pollution, has been internationally recognized, in some European and American countries, the cadmium content in phosphate fertilizer is strictly limited by legislation, China also in early 2002 developed a "fertilizer arsenic, cadmium, lead, chromium, mercury limit" Draft standard.

"But in the agricultural production in Hunan, this standard has not been effectively implemented." Tong Qianming said that in most rural areas in Hunan, farmers bought a bag of compound fertilizer from the fertilizer store, and sold one bag per acre (50 The traditional habit of using kilograms is not based on the actual fertility of the soil.

In 2005, Tong Qianming had conducted a survey on a drinking water source protection site in Changsha. The local soil cadmium content was not high, but in the sampling of five farmland, the cadmium content in the surface soil was significantly higher than that in the bottom layer. Rice samples taken at the premises contain cadmium exceeding national standards. "There is no pollution in the nearby mines. The only explanation is that the application of phosphate fertilizer will increase the cadmium content in the surface soil."

"From the point of view of Hunan, the application of nitrogen and phosphate fertilizer is excessive, but potassium fertilizer is insufficient." said Xie Weiguo, the director of the Hunan Provincial Department of Agriculture Fertilizer Station.

According to Tong Qianming, Hunan now uses phosphate fertilizer in large areas in order to increase production. Phosphorus fertilizers are applied to the fields, and cadmium accumulates. After a certain degree of cadmium, the cadmium content of the soil will exceed the standard and eventually cause crop contamination.

The enrichment of cadmium in the soil has not found a way to eliminate it. It is better to remove the cadmium element in the phosphate fertilizer in advance, but the cost is high. Heavy metal treatment in the Xiangjiang River Basin has just begun.

"If the current national standard for cadmium per kilogram of rice is 0.2 milligrams, then the cadmium content of rice products in all production areas of Hunan Province will exceed the standard." Tong Qianming conducted a nine-year tracking and survey of farmland soil in Hunan Province. After researching the results of the research of agricultural and environmental protection experts from other provinces and beyond, he made an astonishing conclusion about the heavy metal pollution in Hunan's grain and farmland soil.

The absorption of cadmium in hybrid rice includes more Pan Xingxing, director of the Institute of Agricultural Resources and Ecological Environment of Nanjing Agricultural University, Wang Kairong, executive director of Hunan Institute of Soil and Fertility and Ecological Society, professor of the Graduate School of the Chinese Academy of Sciences, and other experts. The results show that hybrid rice and common rice In comparison, there is a clear tendency to absorb cadmium.

Pan Gen-hsing suggested that super rice should be planted as far as possible in areas where acid and cadmium have been contaminated. This means that in the promotion of hybrid rice, the contamination of specific cultivated land must be considered. Why is there such a risk for hybrid rice? Pan Genxing believes that this may be related to the genes of hybrid rice.

The arable land remediation campaign is expected to be successful. The reporter continued to investigate for more than three years. The soil remediation work in Hunan Province and the heavy metal remediation work in the Xiangjiang River Basin have progressed rapidly.

Professor Luo Lin of Hunan Agricultural University introduced that the pollution of farmland with heavy metals is not as concerned with the pollution of industrial land. Because the concentration of pollution caused by industrial land and some industrial enterprises is relatively high, the occurrence of acute accidents is more prominent, but the pollution of farmland, its potential pollution, the coverage and impact degree may be heavier.

"Because it has a direct impact on the security of food and agricultural products, it also directly affects people's health. For example, some rice in Hunan is sold to Guangdong and Hong Kong." Prof. Luo Lin has expressed concern about the heavy metal pollution in farmland in Hunan Province. In the short-term and even mid-term, it cannot be turned into a safe state, and the province’s food products will also continue to be in a state of “cadmium exceeded” for a long time.

Ten years invested more than 10 billion yuan to comprehensively manage Rowling. At present, the state and Hunan Province attach great importance to the pollution of cultivated land. Taking heavy metal pollution in the Xiangjiang River Basin as a major environmental protection issue, it is planned to invest more than 100 billion in a decade to comprehensively manage it. First of all, we must block the pollution sources in the Xiangjiang River Basin. The enterprises that have suffered serious pollution should be stopped. Even if they can't stop, they must reform and become a new type of industry. The row of waste water should reach the standard before being discharged into the Xiang River.

He believes that farmland pollution is a piece of pollution, unlike the point of industrial and mining companies may be around the source of pollution, but now is through irrigation. There are several characteristics of heavy metal pollution in farmland management: "The technologies we use must not destroy the original functions of farmland soils. For example, using chemicals to leach out heavy metals from the soil will destroy the original functions of the soil and it will not be able to grow land. Due to the large area of ​​pollution, the cost of restoration is greater than the industrial pollution," said Rowling. Therefore, an ecological remedy must be adopted and repaired in situ.

At present, they have achieved remarkable results in the remediation of heavy metals. This method is red mud treatment. Red mud is a kind of waste from the aluminum plant. Although it also contains heavy metals, it is rare. The most important thing is that it can inhibit cadmium and keep it from becoming active. If it is not active, rice root will not absorb it. It also has many beneficial elements for the growth of crops, such as silicon, aluminum, calcium, and phosphorus in the inside, as well as rare metals needed for more than a dozen crops, the mechanism of restoration of heavy metal-contaminated soil, and the mechanism of fertilizer efficiency.

Stopping the use of high-cadmium phosphate fertilizers A senior person engaged in the sale of agricultural products said that after the phosphorite from Yunguichuan and other places were made into fertilizers, most of them were exported to foreign countries due to the low content of cadmium, and only a small part was in China. Sales, and high prices, so most of Hunan's farmers use low-cost compound fertilizer, most of them are high-cadmium phosphate fertilizers.

Tong Qianming, a professor at the Institute of Geology of Hunan Province, pointed out that it is now necessary to stop popularizing phosphorus fertilizers with high cadmium content. In addition, there are several ways to repair, one approach is to repair the project, and the easiest way to repair the project is to change the soil. This method is very easy to do but it is difficult, it is not very realistic and not economic. The second method is phytoremediation. For example, in this soil, its cadmium content is very high, and the cadmium content of the food crop exceeds the standard. It is not something to eat, such as cotton or mulberry.

Tong Qianming introduced that some plants have a strong ability to absorb cadmium. For example, Dongting Lake is the kidney of the earth. Why is it the kidney of the earth? Because it can take drugs and detoxify it. In Dongting Lake, there is a plant called Lusheng, which is a highly negative plant that can absorb this cadmium several dozen times. Reeds are used to make paper.

Professor Pan Genxing said that he can use one side while he is governing, such as planting flowers, seedlings, or planting crops; the absorption capacity of different crops on heavy metals is very different, and some dry crops, such as corn, have a significantly weaker ability to absorb Cd than rice. Therefore, crops can be selected based on the type of pollutants and the intensity of pollution.