阻隔主要外源输入重金属对土壤-水稻系统中镉铅累积的影响

土壤-水稻系统中重金属输入输出调控对稻田污染防治和水稻安全生产具有重要意义。该文研究稻草移除、截断大气沉降、清洁水灌溉等调控措施对稻田土壤-水稻系统中重金属Cd和Pb的累积与运移特征的影响。结果表明,稻草移除、截断大气沉降和清洁水灌溉均能明显降低污染土壤中有效态重金属含量和水稻中重金属的累积量。与稻草还田对照处理相比,除种植早稻后的土壤有效态Pb含量外,稻草移除处理下土壤中有效态Cd、Pb含量均略有降低,且在该处理下,早稻糙米中Pb含量与晚稻糙米中Cd、Pb含量显著降低,降幅分别为3.6%、10.4%和32.4%;稻草移除+截断大气沉降处理下,土壤中有效态Cd、Pb含量均不同程度地下降,种植晚稻后的土壤有效态Pb含量显著降低,除早稻的根和糙米中Cd含量外,其余早晚稻水稻各部位Cd、Pb含量均显著降低,水稻根和茎叶Cd、Pb含量平均降幅分别为32.8%、36.8%和32.2%、24.8%,晚稻糙米Cd、Pb累积量分别显著降低66.3%和22.2%;稻草移除+清洁水灌溉处理下,种植早晚稻后的土壤有效态Cd、Pb含量平均下降幅度分别为11.7%和15.9%,早晚稻各部位Cd、Pb含量降低幅度较大,早晚稻根和茎叶Cd、Pb含量平均降幅分别为38.34%、30.35%和43.4%、13.2%,晚稻糙米中Cd、Pb累积量降幅分别为39.4%、67.2%。分析水稻地上部的Cd、Pb富集与转运系数表明,稻草移除结合截断大气沉降或清洁水灌溉等控源措施可显著降低Cd、Pb在水稻地上部位的富集系数,减少地上部位重金属的累积量。上述结果表明,采用稻草移除结合截断大气沉降或清洁水灌溉措施可进一步降低土壤中有效态Cd、Pb含量和水稻中Cd、Pb富集。因此,控制区域大气污染,净化农田灌溉水等控源措施,同时施行稻草移除等输出污染农田土壤中重金属等策略,可有效实现污染农田土壤安全利用和水稻安全生产。

Effect of impeding main exogenous heavy metal input on accumulation of Cd and Pb in paddy soil-rice system

Abstract: Regulation and control of heavy metal input and output in paddy soil-rice system are of great significance to rice pollution control and safe production. The effects of straw removal, truncation of atmospheric sedimentation and clean water irrigation on the accumulation and migration of heavy metals in the paddy soil-rice system were investigated with the arrangement of field experiments from April to October in 2016, which selected the typical rice fields contaminated by atmospheric sedimentation in the town of Leidashi, located at the downwind direction of an industrial area in Zhuzhou City, Hunan Province. The results showed that straw removal, truncation of atmospheric deposition and irrigation with clean water all could significantly reduce the available content of heavy metal in soils and heavy metal accumulation in rice. Compared with the control of rice straw returning, the content of available Cd (cadmium) and Pb (plumbum) in the soil under straw removal treatment decreased slightly except the effective Pb content of the soil after planting early rice. Under this treatment, the Pb content in the brown rice of early rice and the contents of Cd and Pb in brown rice of late rice were significantly decreased, which were reduced by 3.6%, 10.4% and 32.4%, respectively. Under the treatment of straw removal + truncating atmospheric deposition treatment, the contents of available Cd and Pb in soil decreased to different extents. The soil available Pb content decreased significantly. Except the Cd content in root and brown rice of early rice, the contents of Cd and Pb decreased significantly in the organs of early and late rice varieties. The average content of Cd and Pb decreased by 32.8% and 36.8% respectively in rice roots and by 32.2% and 24.8% respectively in rice stems, and the cumulative amount of Cd and Pb in brown rice of late rice significantly decreased by 66.3% and 22.2%, respectively. Under straw removal+clean water irrigation treatment, the available Cd and Pb content of the soil reduced by 11.7% and 15.9%, respectively. The content of Cd and Pb in different organs of rice decreased to a large extent. The content of Cd and Pb decreased by 38.34% and 30.35% in roots and 43.4% and 13.2% in stems, respectively. The cumulative amounts of Cd and Pb in brown rice of late rice decreased by 39.4% and 67.2%, respectively. Through analysis of the accumulation and transport of Cd and Pb at the aboveground part of rice, it was found that the removal of straw of rice combined with interception of atmospheric deposition or clean water irrigation could significantly reduce the accumulation of Cd and Pb in the aboveground parts of rice. The Pb contents in brown rice were lower than the National Standard of Pollutant in Food of China (GB 2762-2017) under the straw removal+clean water irrigation treatment in the late-rice paddy field. The above results indicate that the control measures such as control of regional air pollution, purification of farmland irrigation water, combined with the removal of straw or other measures outputting soil heavy metal of polluted farmland, can effectively achieve the safe use of contaminated farmland and guarantee the rice safety in production.