长期施用猪粪稻田的重金属迁移规律与累积风险

在国家大力推进畜禽养殖废弃物资源化利用的背景下,为探究长三角地区“猪-稻”种养结合模式猪粪全量还田潜在的农田土壤重金属累积风险问题,对6类特征重金属在“饲料-粪污-土壤”系统中的迁移规律进行了为期5年的连续跟踪监测。结果显示,As、Cr、Pb、Cu、Zn和Cd等重金属在饲料中均有检出,Cu和Zn含量远高于NY/T 65—2004《猪饲养标准》中的推荐添加量。粪便中各类重金属含量总体呈现“秋冬高、春夏低”的特点,其中,冬季粪便中Cr、Cu、Zn和As的质量浓度最高,分别为115.9、1 150.1、1 630.0、2.62 mg·kg^-1。配套农田耕作层(0~20 cm)土壤中As、Cr、Cd、Cu和Zn的含量表现出明显的累积趋势,其中Cu、Zn的累积效应较明显,平均年累积率分别高达5.13、2.29 mg·kg^-1。各重金属均向深层土壤发生了迁移,Pb、Cu、Zn、Cd总体上呈现出一定的纵向递减的变化规律,但深层土壤中As、Cr的含量有所增加,表现出较为明显的淋溶下移性特点。归趋分析结果显示,稻米中的Cd含量占输入总量的9.11%,远高于其他类型重金属。因此,需要在实际生产中严格控制含Cu、Zn、Cd的饲料添加剂用量,并规范猪粪处理和还田利用方式,降低土壤重金属污染风险。

Migration regularity and accumulation risk of heavy metals after continuous application of swine manure in paddy soils

Resource utilization of livestock manure has been encouraged vigorously in China. To explore the potential risks of heavy metal accumulation in paddy fields under “swine-rice” nutrient management option, a 5-year field-scale experiment was conducted in this study. A swine farm with manure fully treated and returning to field was selected as the case-study farm to monitor and track the migration regularity of six heavy metals in the paddy soil. The results showed that the heavy metals such as As, Cr, Pb, Cu, Zn and Cd were detected in the feed, and the content of Cu and Zn was much higher than the recommended addition amount in NY/T 65-2004 “Standard for Pig Feeding”. The content of heavy metals in the manure showed the characteristics of “high in autumn and winter and low in spring and summer”. Among them, the contents of Cr, Cu, Zn and As in the manure in winter were the highest, which were 115.9, 1 150.1, 1 630.0, and 2.62 mg·kg^-1, respectively. The contents of As, Cr, Cd, Cu and Zn in the plough layer (0-20 cm) soil of the supporting farmland showed an obvious accumulation trend, while Cu and Zn was accumulated obviously, and the average accumulation rate was as high as 5.13 and 2.29 mg·kg^-1, respectively. Heavy metals all migrated to the deep soil, and Pb, Cu, Zn, Cd generally showed a certain vertical decreasing change, while the content of As and Cr in the deep soil increased, showing a leaching down characteristic. Through the analysis of fate characteristics, it was found that the content of Cd in rice accounted for 9.11% of the total input, which was much higher than the other types of heavy metals. Therefore, it is necessary to strictly control the amount of feed additives containing Cu, Zn, and Cd in livestock production and standardize the swine manure disposal and utilization management, to reduce the risk of heavy metal pollution in farmland soils.