典型区域果园表层土壤5种重金属累积特征

Analysis on accumulation characters of 5 kinds of heavy metals in orchard topsoil in typical production zone in China

在我国典型果业生产区域的黄土高原、胶东半岛和北京郊区选择11个采样区的99个果园,利用GPS定位仪共采集0—20cm表土样品99份,测定了铅、砷、铜、锌和铬等5种主要重金属的土壤累积数量,并对土壤重金属累积数量的环境安全性、土壤累积差异性以及区域分布特点进行了分析讨论。结果表明:(1)果园表层土壤5种重金属累积浓度未超过国家土壤环境质量标准,处于环境安全状态;(2)不同重金属在果园表层土壤中累积特征不同,重金属铅累积相对明显;其次是铜;再其次是锌、铬和砷;(3)不同区域果园表层土壤的重金属累积情况不尽一样,经济发达、或城市郊区或果园发展历史长的地区,果园表层土壤重金属累积相对显著一些。

Accumulated heavy metals that can cause soil pollution are mainly derived from industrial smoke and dust, chemical species from car exhaust by dry and wet deposition, fertilizers, pesticides, organic matter, waste water and sewage effluent used in irrigation. Aiming to control soil heavy metal pollution, we carried out the field-scale study to determine the accumulation character and distribution pattern of heavy metals in orchard topsoil. With the help of GPS, totally 99 samples of 0 -- 20 centimetre topsoil were collected from 99 orchards representing 11 sampling zones located in the major fruit producing regions in China, including the Loess Plateau, Jiaodong Peninsula and suburb of Beijing city. Using these samples, we measured the accumulation of heavy metals such as As, Cu, Zn, Pb and Cr, and evaluated the environmental safety, variation of accumulation and the regional distribution of heavy metals in topsoil. The orchards were classified into 3 groups according to orchard ages ： 5 -- 10, 10 -- 15 and over 15 years, and 3 orchards were chosen from each orchard group with an area of about 0.25 --2.5hm^2/orchard. Meanwhile, the crop fields close to orchard were used as controls with the average dimension ranging from 0.1 to 0.5hm：. The sampling period was from early October to early November in 2007. The methods of measurement and analysis for heavy metals were in accordance with the Environmental Quality Standard for Soil（ GB15618--1995 ）. The testing result shown as follows are the average, minimum and maximum value of concentration, respectively, including Pb： 30.32,7. 14 and 99.59 mg/kg; Cu： 28.51,8.74 and 69.63 mg/kg; Zn： 78. 13,24.23 and 99. 16 mg/kg; Cr： 65. 24,25.91 and 79.04 mg/kg; and As： 14. 75,3. 73 and 16. 51 mg/kg. Coefficients of Variance of all heavy metals clearly indicate that orchard topsoil is polluted by various exogenous heavy metals, predominantly by Pb, and also by Cu as the second leading cause of the pollution. Pb is 7.6% higher than the average value, and such values for Cu,Zn,Cr, and As are 9.8% , 16.7% , 12.9% , and 13.6% , respectively. These results reveal the different accumulation patterns among heavy metals in orchard topsoil. Analysis based on One-Way ANOVA and Hierarchical cluster by using SPSS software demonstrate that there are significant differences in metal accumulation among different metal types as well as different regions. According to the significance of the heavy metal accumulation, Pb is the major sources of the metal pollution in topsoil. Cu has less effect than Pb, but more important than the other metals such as Zn, Cr and As. Additionally, the sampling regions were classified into 4 groups base on the extent of pollution status varying from high to low which are Qixia county, Muping county, Tongzhou county, Changping county, Luochuan county, Xunyi county, Taigu county, Wugong county, Ruicheng county, Baishui county and Baota county. In summary, the conclusions drawn from this study are： （ 1 ） the concentrations of the assayed 5 heavy metals in orchard topsoil are all at the environmentally safe level according to the Environmental Quality Standard for Soil. （2）the accumulation levels of the heavy metals are different, among which Pb is the most abundant heavy metal in orchard topsoil; whereas the other 4 metals Cu, Zn, Cr and As show the accumulation levels with a decreasing trend in turn. （3） the heavy metalaccumulations have a regional dependent variation. Orchard topsoil samples from developed areas, suburb and areas with long history of fruit industry have relative higher level of accumulation than those from remote areas or underdeveloped regions.