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 is contaminated by heavy metals. The area of ​​farmland soil contaminated by 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.

Cadmium in soil or from phosphate fertilizer

"Under the same conditions, the cadmium content in soil will increase, and the cadmium content in rice will 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 this report, this caused the related governments of Hunan Province, Zhuzhou City and Ganyu County. The department attaches great importance to it. From May 19th, Jingxian County has convened an investigation team composed of various government departments such as 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 and was investigated.

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

Tong Qianming, a professor at the Institute of Geology of Hunan Province, agrees. He believes that pollution caused by unreasonable use of phosphate fertilizer is also worthy of attention 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 ranges 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 Hunan's agricultural production, 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 a fertilizer store, and sold one bag per acre (50 The traditional habit of using kilograms instead of adjusting for 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 very high, but in the sampling of five farmland, the cadmium content of surface soil was significantly higher than that of 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 fertilizers 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.

Hybrid rice absorbs more cadmium

The results of the study by Pan Genxing, director of the Institute of Agricultural Resources and Ecological Environment of Nanjing Agricultural University, Wang Jiarong, executive director of the Hunan Soil and Fertility Society and Ecological Society, and professor of the Graduate School of the Chinese Academy of Sciences, showed that the hybrid rice has obvious differences compared to ordinary rice. Absorb cadmium trends.

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 pollution 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.

Arable land management campaign is expected to succeed

Over the past three years, the reporter’s ongoing investigations, the soil restoration work in Hunan Province, and the heavy metal control work in the Xiangjiang River Basin have all 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. However, the pollution of farmland, its potential pollution, and the extent of its coverage and impact may be heavier.

"Because it has a direct impact on the security of food and agricultural products, it directly affects people's health. For example, some rice in Hunan are sold to Guangdong and Hong Kong." Prof. Luo Lin said with concern that heavy metal pollution in farmland in Hunan Province. In the short-term and even in the mid-term, it cannot be turned into a safe state. 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 to comprehensively manage

Luo Lin introduced that at present, the state and Hunan Province attach great importance to the pollution of arable land, the heavy metal pollution in the Xiang River Basin as a major environmental issue, ready to invest in more than 100 billion over ten years to comprehensive management. 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 technology we use must not damage the original functions of farmland soils. For example, using chemicals to leach out heavy metals in 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, and the mechanism of repairing and fertilizer effect mechanisms of heavy metal-contaminated soils.

Stop using phosphate fertilizer with high cadmium content

A senior person engaged in the sales of agricultural materials said that after the phosphorous ore in 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 sold domestically and the prices were high. Most of Hunan's farmers use low-priced compound fertilizers, most of which 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 a kind of food crop exceeds the standard. It is not something to eat, such as cotton and 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. It can absorb this cadmium several dozen times, and reeds are used to make paper.

Prof. Pan Genxing said that it can be used while managing, such as planting flowers, seedlings, or planting tobacco crops; different crops have different absorptive capacity for heavy metals, 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 pollution and the intensity of pollution.