北京市凉凤灌区小麦重金属含量的动态变化及健康风险分析——兼论土壤重金属有效性测定指标的可靠性

Dynamic of heavy metals in wheat grains collected from the Liangfeng Irrigated Area, Beijing and a discussion of availability and human health risks

通过对北京市凉凤灌区小麦籽粒及其相对应土壤样品的调查发现,小麦籽粒中的Ni、Pb、Zn超标率分别为38·1%、28·6%、4·8%;Hg、Cd虽然未发现超标现象,但也有部分样品接近国家食品卫生标准(GB2762—1994和GB15201—1994);与1976年的调查结果相比,在过去的30年中,小麦籽粒中Hg、Pb、Cu含量呈显著增加的趋势.研究结果表明,北京凉凤灌区的小麦存在Hg、Pb、Zn等污染的潜在风险.无论是测定的土壤重金属全量,还是测定的土壤重金属的可提取态含量,都与小麦籽粒的重金属含量无显著的相关性.因此,在评价土壤重金属污染是否对农作物(小麦籽粒)影响时,采用目前通用的土壤可提取态重金属并不一定会优于土壤重金属全量.

Irrigation using wastewater containing elevated levels of heavy metals can result in steadily increasing soil concentrations which, in turn, can contribute to elevated tissue levels in crops. A field experiment was conducted in the Liangfeng Irrigated Area in Beijing to investigate the effects of wastewater irrigation on heavy metal concentrations in wheat grain. In addition, the study explored the relationship between total and extractable concentrations of heavy metals in soil and concentrations in grain. Twenty- one soil samples and earresponding wheat grain samples were collected, and the concentration of As, Cr, Cd, Cu, Hg, Ni, Pb and Zn were measured. The concentrations of Ni, Pb, and Zn in wheat grain were 38.1, 28.6 and 4.8 ok higher, respectively, than the China National Hygienic Standards for Food. The concentrations of Hg and Cd in some samples were near, although still lower than, the China National Hygienic Standards for Food. Concentrations of Hg, Pb and Cu in wheat grain were significantly higher than concentrations measured during investigations in the same area in the 1970s. These data indicate that the accumulation of some heavy metals has accelerated and there may be human health risks associated with consumption of the grain of wheat grown in the Liangfeng Irrigated Area. Despite the elevated levels of some metals in wheat, there were no significant correlations between either the total or the extractable metal concentrations in soils and metal concentrations in wheat grains. It might indicate that using the extractable heavy metal to evaluate the effect of heavy metal to the crop in soil was not more convictive than total heavy metals.