不同修复方式下土壤-稻谷中重金属含量特征及其评价

为探究不同修复方式对重金属污染土壤理化性质、土壤-稻谷中总Pb、总Cd、无机As含量的影响,2016年3月—11月以水稻品种"株两优819"为材料,以长沙县黄花镇某合作社的承包田为试验对象,设计6组不同修复方式,T1不做任何处理,T2施用生石灰,T3施用生石灰并进行优化水分管理,T4施用生石灰和楚戈土壤重金属调理剂并进行优化水分管理,T5施用生石灰和喷施叶面阻控剂并进行优化水分管理,T6施用生石灰和楚戈土壤重金属调理剂及叶面阻控剂并进行优化水分管理。运用地累积指数、潜在生态风险指数和危险指数法对土壤及其上生长的稻谷进行重金属污染评价。结果表明,T1~T6修复后土壤中的阳离子交换量、有机质及pH值与修复前相比均有变化,其中土壤中pH值增幅为0.033~1.017;T1~T6修复后土壤中的无机As含量增幅为0.072~1.481 mg/kg,而总Pb和总Cd含量均下降,降幅分别为0.481~3.133、0.038~0.113 mg/kg,且T4修复后土壤中的总Pb、总Cd含量下降最明显,分别下降了0.120、3.133mg/kg;T6修复后稻谷中的总Cd含量略低于国家二级标准,T1~T5修复后稻谷中的总Cd含量均超出国家二级标准,其中T1修复后稻谷中的总Cd含量超出国家二级标准4.5倍;T1~T6修复下稻谷的危险指数(hazard index,HI)顺序为T1T2T3T5T4T6,其中T6修复危险指数最小,说明多种修复方式的联合使用比单独种植低镉水稻品种修复效果好,更有利于研究区的稻谷安全与人体健康。

Characteristics and its assessment of heavy metal content in soil and rice with different repair methods

Abstract: Soil is the basis of agricultural production. Heavy metals accumulate in the soil and enter the food chain through crops, causing serious problems to the residents'' health. In order to explore the effects of different repair methods on physicochemical properties of heavy metal contaminated soil and the contents of total Pb, total Cd and inorganic As in soil and rice, and find a new way to fix heavy metal in soils and rice, the experiment was carried out in the contract field of a cooperative in Huanghua Town, Changsha County, Hunan Province from March 2016 to November 2017, in which Zhuliangyou-819 was used as the experimental material. In this experiment, 6 different repair methods named T1-T6 were designed. In T1-T6, T1 didn''t have any treatment; quicklime was applied in T2; in T3 quicklime was applied and the optimal water management was conducted; in T4 quicklime and Chuge soil heavy metal conditioner were applied and the optimal water management was conducted; quicklime and foliar spray inhibitor were applied and the optimal water management was conducted in T5; in T6 quicklime and Chuge soil heavy metal conditioner and foliar spray inhibitor were applied and the optimal water management was conducted. Assessment of heavy metal contamination in unrepaired soil and repaired soil was carried out by using the cumulative index and potential ecological risk index, and the hazard index was used to evaluate the rice grown on the repaired soils. The results showed that the average pH value, soil organic matter and cation exchange capacity of unrepaired soil were 6.508, 52.881 g/kg and 10.598 cmol/k, and the potential ecological risk index of background content of inorganic As, total Pb and total Cd in unrepaired soil was 78.235, indicating that there are some heavy metal pollutions in the local paddy soils. Amount of cation exchange, organic matter and pH value in soil were changed after repair. Besides, an increase of 0.033-1.017 was observed for pH value of soil. The content of inorganic As in soil got an increase of 0.072-1.481 mg/kg after repair. However, a decrease of 0.481-3.133 mg/kg and a decrease of 0.038-0.113 mg/kg were observed for total Pb and total Cd, respectively. The maximum removal of total Pb and total Cd was achieved by the repair of T4, which declined by 0.120 and 3.133 mg/kg, respectively. The content of total Cd in rice with the repair of T6 was slightly below the national secondary standard. The total Cd contents in rice with the repair of T1-T5 exceeded the national secondary standard, and the content of total Cd in rice with the repair of T1 was 4.5 times beyond the national secondary standard. Through the comparison of repair specific operating procedures in T1-T6, it was found that T4 repair operating procedure, which used the Chuge soil heavy metal conditioner, was useful to reduce soil Pb and Cd content. The order of hazard index of rice under T1-T6 repair was T1 > T2 > T3 > T5 > T4 > T6. Among them, the hazard index of T6 repair was the smallest. Through the comparison of various repair methods, it was found T6 repair method was more comprehensive, which indicates that the combination of multiple repair methods is more effective and more beneficial to the rice security in study area and human health.