Study On Safety Control Technologiesy Of Soil Cadmium At Typical Pollution Area In Southen China

Cadmium?Cd?in rice has become a potential threat to food security,and is becoming more and more serious with the development of industry and agriculture.An effective way to ensure food security is to investigate the status of cadmium-contaminated soil in the main rice producing areas,evaluate the characteristics of cadmium accumulation in rice,and explore reasonable cadmium pollution control measures.In order to explore the characteristics of rice Cd enrichment in rice and to screen out the optimal stable remediation measures,which can support the decision-making of urgently needed restoration of fields such as major grain-producing areas and ultimately achieve food security,this study investigated and evaluated the concentration of heavy metal Cd in soil-rice paired samples from typical contaminated areas in the south,and used the collected contaminated paddy soil for pot experiment.The results are as follows:?1?The survey results of heavy metals in farmland soils in polluted areas indicate that soil Cd concentration of five sampling areas Xiangtan?XT,Xiangjiang River Basin pollution?,Zhuzhou?ZZ,Xiangjiang River Basin pollution?,Hengyang?HY,industrial park pollution?,Changzhou?CZ,mining area pollution?and Shaoguan?SG,mine pollution?range of 0.34⁰.79,0.89³.01,respectively 0.47²7.6,0.38⁰.91,and 0.38¹8.1 mg·kg 1,respectively,and the over-standard rates are 100,100,100,11.8,and 91.4%.The coefficient of variation was HY>SG>ZZ>CZ>XT from the largest to the least,among which SG and HY were the coefficient of variation greater than 0.3.The high rate of variation and excess reflected that Cd pollution in these two areas was greatly affected by human factors.The results of single factor index of soil Cd pollution in five historical polluted areas showed that the soil of CZ 11.8%was slightly polluted by Cd,and the rest of the soil was not polluted by Cd.XT 5.00%soil was moderately contaminated with Cd and 95%soil was mildly contaminated with Cd.ZZ 3.18%soil was moderately polluted with Cd,and 96.8%soil was severely polluted with Cd.SG8.57%is clean soil,28.5%is slightly polluted by Cd,22.9%is moderately polluted by Cd,and 40.0%is severely polluted by Cd.HY 16.7%,25.0%and 58.3%were moderately and severely contaminated with Cd.In the five sampling areas,the degree of potential ecological risk is very high.The average values of soil E of XT,CZ,ZZ and HY are 71.1,85.8,248 and 430respectively,and the degree of potential risk is medium,strong,strong and strong respectively.The average value of SG soil E is 1700,and the degree of potential risk is extremely strong.Due to the low background value of Cd in the soil,the extremely strong potential ecological risk has reached the full coverage.The above research shows that the soil Cd pollution in the mining area,industrial park and the rice producing area around Xiangjiang River basin should be paid attention to.?2?The survey results of heavy metals in contaminated rice showed that there were over-standard Cd concentrations in the five sampling areas,and the over-standard rates were XT?90.0%?,ZZ?95.2%?,HY?79.2%?,CZ?2.94%?and SG?77.1%?,respectively.CZ average value was less than national safety standard value only,and can be safely produced.The results of health risk index?HQ?analysis showed that in addition to CZ adult and the child HQ of Cd in rice grain value was less than 1.0,the other four area HQ value was greater than 1.0,indicating that the area was not suitable for rice,particularly political origin of the highest concentration of Cd in rice,which was the most harmful to the potential health of the human body.The health risks of children's Cd intake through rice in five regions were higher than those in adults,and attention should be paid to and alert to the health risks posed by Cd.?3?The results of the potted rice experiment on the soil contaminated with Cd in the rice growing areas showed that the Cd concentration of the rice in the contaminated soil exceeded the food safety standard,and only the rice on the soil did not exceed the standard;Cd concentration in rice increased with soil pollution.By analyzing the influence of contaminated soil texture on rice enrichment coefficient,it was concluded that the sandy loam has the highest accumulation?1.24?and the lowest is clay?0.49?.,in sandy loam.The ability of rice to enrich soil Cd was stronger than that of soil clay and clay.The higher the soil sand content,the stronger the ability of rice to enrich soil Cd.?4?The effect of soil available?CaCl₂ extraction?concentration on the enrichment ability of high and low Cd accumulation rice showed that the Cd accumulation ability of high-accumulation rice variety“soil hybridization”was significantly greater than that of"heliangyou 1"of rice varieties with low accumulation of Cd.When the effective Cd concentration was 0.45,0.29 and 0.15 mg·kg-1,the enrichment coefficient of the high-accumulation variety was 2.32,1.24and 1.20 times of the low-accumulation variety.The enrichment coefficients of Cd of the same rice variety in different soils were significantly different.The enrichment coefficients of high and low accumulation rice varieties in different soil textures were shown as follows:>in sandy loam and>in sandy loam.?5?The results of pot experiment on passivated and stabilized paddy soil contaminated by acid Cd in south China showed that lime,sepiolite,biochar,humic acid and calcium magnesium phosphate fertilizer were applied to the soil,and the pH of the soil,the concentration of available Cd,the yield of rice and the concentration of Cd were all affected to varying degrees.When 0.5%lime was applied,the soil pH increased the most?by 1.54 units?,and the effective Cd concentration decreased the most?by 96.3%?.Followed by 0.1%lime,the pH increased by 0.44,the effective cadmium concentration decreased by 63.9%.The application of 0.5%sepiolite increased the yield significantly,with an increase of 37.9%.Followed by calcium magnesium phosphate 0.1%,an increase of 27.9%.After applying 0.1%calcium magnesium phosphate,the cadmium decreased most obviously,with a decrease of 58.2%.Followed by 1%sepiolite with a decrease of 51.7%.To sum up,lime application can effectively reduce the concentration of Cd in rice and is suitable for the rapid restoration of high wastewater paddy fields,while sepiolite and calcium magnesium phosphate application can give consideration to both yield preservation and soil remediation.