0 引言
城市快速发展的一个重要推动因素就是不断加快的工业化进程。在有效促进城市经济发展的同时,工业化也带来了一定的环境和生态污染[1⇓⇓⇓-5]。这其中,最广受关注的问题之一就是对城市周边土壤化学性质可能产生的影响。土壤直接或间接吸收了大量来自不同来源的污染物,其中包括重金属。土壤是重要的环境组成部分,因为它不仅是污染物的地球化学汇,还通过控制重金属向大气、水圈和生物圈的运输而成为天然缓冲区[6]。在被污染的土壤中,污染物会转移到其他环境组分中,间接威胁人类健康。重金属因其具备持久性和毒性,在研究土壤污染物方面意义重大,净化土壤重金属在世界各地都是一个重大的研究成果,通过研究土壤中影响其重金属分布的地质及环境因素,可作为研究区土壤重金属污染状况评估工作的理论支撑[7]。
1 材料与方法
1.1 研究区概况
研究区的年平均日照时间在2 400~3 100 h,年平均降水量300~800 mm,年降雨量较少,1月平均气温在3 ℃以下,7月平均气温在18~27 ℃,四季气温变化分明,属于温带大陆性季风气候。瀑河属于滦河的源头,由北至南贯穿研究区。研究区为典型资源型城市,区内有多家大型采矿企业,涉及金矿、铁矿、铜矿及石灰石矿等其他多种类型矿产。研究区位于河北北部燕山丘陵地带,全境多山,山脉蜿蜒层叠为不同形状大小的沟谷,其基本地貌格局由中生代燕山运动所奠定,而现代地貌形态则主要受控于新生代喜马拉雅造山运动。区内西北部发育有中生代侵入岩,西部地区发育有新元古代变质岩和古生代碳酸盐岩,东部及南部地区发育有古生代碎屑岩、中生代碎屑岩等(图1)。
图1
图1
研究区地质简图与采样位置
Fig.1
Geological diagram and sampling location of the study area
1.2 采样与分析方法
本次研究对象为瀑河流域典型岩石露头风化剖面,采样剖面选择远离主干道及居民区的人工开挖露头,共采集剖面71个,主要包括第四系剖面7个、中生代碎屑岩剖面12个、中生代中酸性岩剖面19个、中生代火山碎屑岩剖面3个、震旦纪—二叠纪碳酸盐岩剖面10个、震旦纪—石炭纪泥质碎屑岩剖面6个、前寒武纪基性岩剖面4个和前寒武纪变质岩剖面10个。每个剖面采取具有原生代表性的土壤(0~20 cm的腐殖质层表层土壤、50~100 cm腐殖质层以下的深层土壤)和成土母岩,共采集71个表层土壤样品、65个深层土壤样品(5个第四系、1个碳酸盐岩剖面未采集)和66个成土母岩样品(5个第四系剖面未采集)。样品采集时,土壤样由3~5处不含杂草、根系、碎石等杂质的子样等量均匀的混合成1~1.5 kg样品,成土母岩样避免外貌、颜色、结构等异常的岩块,挑选新鲜露头的岩石约500 g,所有样品按顺序编号后送往实验室。测试方法参照《区域地球化学样品分析方法》(DZ/T 0279—2016)和《岩石矿物分析》第四版,对As、Cd、Cr、Ni、Cu、Pb、Hg、Zn、CaO、MgO、K2O、Na2O、Fe2O3、Al2O3和SiO2的含量进行分析,其中As、Hg采用原子荧光光谱方法,K2O、Na2O、Fe2O3和Al2O3采用X射线荧光光谱法,Cd、Ni、Cu、Pb、Zn、Cr采用电感耦合等离子体质谱法测定,重量法测定SiO2、CaO、MgO,离子选择性电极法测定土壤pH值,激光法和筛分法测定土壤质地。
使用Excel和SPSS软件处理数据和绘制相关图件,并使用ArcGIS 10.1软件绘制研究区地质简图及采样位置图、空间分布图。
2 测试结果与数据分析
2.1 重金属元素含量特征
瀑河流域表层、深层土壤及成土母岩3个层面的重金属元素(Cr、Ni、Cu、Zn、Cd、Pb、Hg、As)含量和分布特征统计结果见表1。
表1 表层、深层土壤及成土母岩中重金属元素的含量及相应统计参数
Table 1
| 项目 | 统计参数 | Cr | Ni | Cu | Zn | Cd | Pb | Hg | As |
|---|---|---|---|---|---|---|---|---|---|
| 表层土壤 | 最大值 | 1374.0 | 369.0 | 192.0 | 172.0 | 2.070 | 57.2 | 0.221 | 33.7 |
| 最小值 | 14.6 | 11.6 | 4.9 | 11.2 | 0.050 | 9.3 | 0.011 | 2.1 | |
| 平均值 | 86.1 | 37.3 | 30.9 | 82.3 | 0.199 | 26.5 | 0.040 | 9.9 | |
| 标准差 | 159.1 | 44.1 | 26.3 | 26.1 | 0.280 | 7.4 | 0.034 | 5.5 | |
| 变异系数/% | 184.7 | 118.1 | 85.0 | 31.7 | 140.4 | 27.9 | 87.0 | 55.2 | |
| 深层土壤 | 最大值 | 1975.0 | 443.0 | 234.0 | 219.0 | 3.190 | 53.2 | 0.290 | 30.5 |
| 最小值 | 8.8 | 3.4 | 1.1 | 4.5 | 0.018 | 6.0 | 0.005 | 1.0 | |
| 平均值 | 96.5 | 39.4 | 33.1 | 84.8 | 0.207 | 25.1 | 0.033 | 9.0 | |
| 标准差 | 238.6 | 53.2 | 35.6 | 29.3 | 0.453 | 5.9 | 0.045 | 5.5 | |
| 变异系数/% | 247.4 | 134.8 | 107.6 | 34.6 | 218.8 | 23.6 | 138.2 | 61.2 | |
| 成土母岩 | 最大值 | 2542.0 | 652.0 | 307.0 | 350.0 | 3.250 | 59.7 | 4.124 | 116.7 |
| 最小值 | 6.5 | 2.2 | 1.0 | 2.9 | 0.028 | 5.2 | 0.004 | 0.4 | |
| 平均值 | 85.1 | 34.6 | 27.5 | 72.4 | 0.229 | 21.6 | 0.101 | 6.3 | |
| 标准差 | 320.7 | 84.0 | 52.3 | 64.1 | 0.530 | 10.2 | 0.528 | 17.0 | |
| 变异系数/% | 376.7 | 242.6 | 190.2 | 88.4 | 231.7 | 47.3 | 520.9 | 269.0 | |
| 背景值[16] | 河北省表层 | 68,3 | 30.8 | 21.8 | 78.4 | 0.094 | 21.5 | 0.036 | 13.6 |
| 河北省深层 | 72.6 | 34.1 | 23.0 | 78.4 | 0.097 | 25.1 | 0.022 | 14.2 |
注:Cr、Ni、Cu、Zn、Cd、Pb、Hg和As含量单位为10-6。
由表1可以看出,重金属元素在瀑河流域表层土壤中的平均含量为: Cr(86.1×10-6) > Zn(82.3×10-6)>Ni(37.3×10-6) > Cu(30.9×10-6) > Pb(26.5×10-6) > As(9.9×10-6) > Cd(0.199×10-6) > Hg(0.040×10-6);深层土壤中为:Cr(96.5×10-6) > Zn(84.8×10-6) > Ni(39.4×10-6) > Cu(33.1×10-6) > Pb(25.1×10-6) > As(9.0×10-6) > Cd(0.207×10-6) > Hg(0.033×10-6);成土母岩中为:Cr(86.1×10-6) > Zn(72.4×10-6) > Ni(34.6×10-6) > Cu(27.5×10-6) > Pb(21.6×10-6) > As(6.3×10-6) > Cd(0.229×10-6) > Hg(0.101×10-6)。总体而言,表层土壤与深层土壤重金属含量较为相近,重金属元素在成土母岩中含量最低,说明其主要富集在土壤中。Cr、Zn含量比较高,主要与其在地壳的丰度有关。研究区主要为丘陵浅山区,地形起伏较大,且岩性变化较大,可能受基岩风化过程中重金属的相对富集及地形等因素的影响,土壤重金属表现为中高空间变异。Pb和Zn的变异系数(CV)在20%~30%,为中度变异,Cr、Ni、Cu、As、Cd和Hg的变异系数大于35%,为高度变异,这说明重金属在土壤中的含量波动较大,数据的离散程度高[17]。
通过河北省表层、深层土壤背景值,得出As的平均含量比背景值要小,其余的几种重金属均超出背景值这一结论,其中表层、深层土壤中Cd分别为背景值的2.12倍、2.13倍[18],其余重金属元素仅略超背景值。
2.2 重金属元素空间分布特征
研究区内重金属元素空间分布如图2所示,从图中可以清楚地看出,研究区不同重金属元素的空间分布特征较为相似,且这些元素的空间分布极具地带性,即存在明显的高值分布区和低值分布区,这些地带性的分布规律可以概括为:①在形态上从中间到周围呈多带分布、同心圆逐渐减少的特征。②元素间高、中、低值分布区存在空间上响应,表现为高值区呈带状分布,中值区和低值区广泛分布在研究区域内,其中Ni、Zn、Cu和Pb含量空间分布基本一致,高值区分布在王土房乡与卧龙镇西北交界处、卧龙镇北部及道虎沟乡与平泉镇北部交界地带;Cd与As含量的空间分布基本相同,高值区分布与Ni和Zn分布在王土房乡—卧龙镇和道虎沟乡—平泉镇一带具有耦合性,且其在杨树岭镇北部及小寺沟镇一带分布较为广泛,其中As高值区在研究区中部呈NW向及东部呈WS—EN向条带状分布;Hg和Cr高值区在研究区内分布较集中,Hg主要分布在王土房乡西北部及在研究区东部呈ES向条带状分布,Cr分布在王土房乡与卧龙镇西北交界处及卧龙镇北部。③在区域上,8种重金属元素高值区与卧龙镇一带铁矿及道虎沟乡一带石灰石矿所在的区域基本一致,矿石选矿、尾矿渣堆放、露天矿厂和尾矿库渗透液的排放导致了重金属含量较高[19-20]。
图2
图2
表层土壤重金属元素含量空间分布
Fig.2
Spatial distribution of heavy metal content in surface soil
3 讨论
3.1 成土母岩对重金属分布的影响
统计不同岩性单元土壤及成土母岩中重金属的含量(表2),研究重金属在各个层面的垂向分布特征,发现重金属在各个层面的分布与外界条件的变化有很大关系,空间分布特征非常复杂,也和地质背景有着千丝万缕的关系,其分布既有共性又有差异性。
表2 研究区不同成土母岩单元中土壤及成土母岩重金属均值
Table 2
| 岩性单元 | 采样位置 | Cr | Ni | Cu | Zn | Cd | Pb | Hg | As |
|---|---|---|---|---|---|---|---|---|---|
| 第四系 | 表层土壤 | 77.57 | 33.73 | 33.21 | 78.87 | 0.180 | 29.80 | 0.033 | 8.15 |
| 深层土壤 | 61.90 | 27.15 | 23.45 | 74.45 | 0.145 | 27.80 | 0.022 | 6.46 | |
| 成土母岩 | 61.10 | 27.00 | 18.60 | 75.40 | 0.065 | 17.20 | 0.008 | 0.59 | |
| 中生代 碎屑岩 | 表层土壤 | 63.07 | 29.94 | 23.66 | 75.09 | 0.124 | 27.03 | 0.039 | 9.94 |
| 深层土壤 | 60.67 | 29.96 | 22.64 | 75.05 | 0.096 | 25.43 | 0.018 | 7.37 | |
| 成土母岩 | 28.85 | 16.44 | 14.97 | 54.16 | 0.144 | 20.40 | 0.001 | 3.34 | |
| 中生代中 酸性岩 | 表层土壤 | 52.53 | 23.54 | 29.33 | 82.56 | 0.156 | 28.07 | 0.032 | 6.87 |
| 深层土壤 | 57.06 | 26.34 | 27.13 | 84.80 | 0.152 | 27.90 | 0.024 | 7.72 | |
| 成土母岩 | 21.99 | 11.48 | 23.06 | 69.76 | 0.246 | 26.91 | 0.015 | 3.38 | |
| 中生代 火山碎屑岩 | 表层土壤 | 63.50 | 29.97 | 21.50 | 66.93 | 0.105 | 25.27 | 0.025 | 9.28 |
| 深层土壤 | 69.50 | 34.13 | 26.37 | 76.17 | 0.120 | 26.27 | 0.016 | 9.30 | |
| 成土母岩 | 26.97 | 19.05 | 11.42 | 51.40 | 0.054 | 25.63 | 0.034 | 1.40 | |
| 震旦纪—二叠 纪碳酸盐岩 | 表层土壤 | 56.19 | 29.28 | 23.88 | 72.44 | 0.230 | 23.74 | 0.043 | 12.11 |
| 深层土壤 | 56.30 | 29.74 | 22.78 | 71.96 | 0.112 | 22.54 | 0.020 | 9.77 | |
| 成土母岩 | 24.60 | 18.53 | 7.00 | 38.08 | 0.071 | 10.99 | 0.022 | 3.45 | |
| 震旦纪—石 炭纪泥质 碎屑岩 | 表层土壤 | 66.94 | 47.72 | 44.30 | 106.6 | 0.608 | 27.00 | 0.097 | 19.23 |
| 深层土壤 | 69.07 | 43.88 | 45.30 | 93.37 | 0.473 | 26.62 | 0.119 | 19.17 | |
| 成土母岩 | 130.80 | 94.84 | 93.22 | 194.60 | 0.916 | 31.82 | 0.112 | 255.50 | |
| 前寒武纪 基性岩 | 表层土壤 | 141.7 | 73.10 | 52.18 | 110.2 | 0.380 | 22.70 | 0.026 | 14.21 |
| 深层土壤 | 95.28 | 56.98 | 85.63 | 113.9 | 0.872 | 18.12 | 0.024 | 10.41 | |
| 成土母岩 | 35.45 | 42.38 | 101.7 | 116.5 | 0.505 | 14.52 | 0.023 | 4.17 | |
| 前寒武纪 变质岩 | 表层土壤 | 80.81 | 32.89 | 37.49 | 79.80 | 0.107 | 23.67 | 0.025 | 7.71 |
| 深层土壤 | 94.36 | 38.21 | 44.51 | 91.92 | 0.142 | 22.30 | 0.032 | 6.33 | |
| 成土母岩 | 119.20 | 30.66 | 18.42 | 59.74 | 0.091 | 20.42 | 0.026 | 1.41 |
注:Cr、Ni、Cu、Zn、Cd、Pb、Hg和As含量单位为10-6。
为了更好地显示分配规律,本文把Cd含量放大100倍,Hg含量放大1 000倍绘制折线图(图3),重金属在不同岩性横向上表现出:①基性岩形成的表层土壤中Cr、Ni和Zn含量最高,泥质碎屑岩中Cd、Hg和As含量最高,Cr、Ni、Zn和As在中酸性岩中含量最低,Cu和Cd在火山碎屑岩中含量最低,其中As在表层及深层土壤中整体变化幅度均较小,且含量较低,但在泥质碎屑岩中却急剧升高,其他母岩中含量很低,表明As受控于人类活动的影响,成土母岩对其影响较弱,Pb在各成土母岩及所在的表层土壤中含量较接近,说明其含量主要是成土母岩作用的结果;②深层土壤与成土母岩中重金属元素分布趋势相似,重金属在基性岩和泥质碎屑岩中分布较多,其余岩性中重金属分布相差不大,表现出耦合性。
图3
图3
表层、深层土壤及成土母岩中重金属分布特征
Q—第四系;Mzc—中生代碎屑岩;Mzm—中生代中酸性岩;Mzp—中生代火山碎屑岩;Z-Pc—震旦纪-二叠纪碳酸盐岩;Z-Ca—震旦纪-石炭纪泥质碎屑岩;Ptn—前寒武纪基性岩;Ptr—前寒武纪变质岩
Fig.3
Distribution characteristics of heavy metals in surface soil, deep soil and forming soil matrix
Q—Quaternary system;Mzc—Mesozoic clastic rock;Mzm—Mesozoic acid rock; Mzp—Mesozoic pyroclastic rock;Z-Pc—Sinian-Permian carbonate rocks;Z-Ca—Sinian-Carboniferous argillaceous clastic rock; Ptn—Precambrian base rock; Ptr—Precambrian metamorphic rock
在不同土层垂向上表现出:①深层土壤和成土母岩中重金属元素含量呈现出一定的相似性[21],表现为重金属元素在深层土壤中:碳酸盐岩<碎屑岩<第四系沉积物<火山碎屑岩<中酸性岩<变质岩<泥质碎屑岩<基性岩,在成土母岩中:碳酸盐岩<碎屑岩<火山碎屑岩<中酸性岩<第四系沉积物<变质岩<基性岩<泥质碎屑岩,这说明成土母岩对深层土壤重金属元素含量有很大的冲击;②重金属元素含量在不同成土母岩形成的表层土壤中的排序为火山碎屑岩<中酸性岩<碎屑岩<碳酸盐岩<变质岩<第四系沉积物<泥质碎屑岩<基性岩,与其在深层土壤含量的排序不一致,8种重金属元素在碳酸盐岩和碎屑岩及其形成的表层土壤中的含量截然相反,而在其他成土母岩及其形成的土壤中的含量排序没有表现出规律性,从采样位置看出,表层土壤样主要采集腐殖质层土壤,深层土壤样主要采集腐殖层以下土壤,因此表层土壤有机质含量显著高于深层土壤,而人类活动对土壤层的改造导致了表层土壤有机质含量与成土母岩的关联不明显,土壤有机质可与重金属结合形成螯合物和络合物,对重金属进行吸附,影响重金属含量[22],从而体现出表层土壤重金属与成土母岩相关性不高。以上情况反映出不仅成土母岩类别影响重金属含量,还有其他因素也影响着表层土壤中重金属含量。正是这些因素的共同作用导致重金属含量在母岩和表层土壤的相关性为负。
由图4可知,Al2O3和Ti在碎屑岩及其形成的土壤中具有较好的线性关系,R2=0.347 1(图4a),表明碎屑岩与其形成的表层、深层土壤具有同源性,不过Al2O3和Ti在碎屑岩中的分布较分散,但在其形成的土壤中分布较集中,说明碎屑岩具有较复杂的岩石成分。Al2O3和Ti在碳酸盐岩区土壤及其原岩中具有明显的线性关系,R2=0.941 7(图4b),且所有点均在趋势线附近,这是因为碳酸盐岩原地风化才出现这一情况[23]。而岩浆岩区和变质岩区原岩与土壤中Al2O3和Ti的线性关系均较差(图4c、4d),可以得出岩浆岩区和变质岩区原岩与土壤的成分较复杂。以上实验结果为下一步聚焦碎屑岩和碳酸盐岩区的研究提供支撑。
图4
图4
研究区原岩及表、深层土壤Al2O3与Ti散点图
Fig.4
Scatter plots of Al2O3 and Ti of the original rock, surface and deep soil in the study area
3.2 成土作用对重金属分布的影响
因风化剥蚀作用的影响和淋溶作用的强烈进行,土壤脱硅、富铁铝氧化物的过程逐步增强,成土母岩中硅酸盐及含有碳酸盐的矿物会不断瓦解,体积也产生了较大变动,最终呈现重金属元素盈余或不足。根据对元素迁移系数的分析,制作柱状图(图5)。
图5
图5
表层、深层土壤重金属元素迁移系数
Mzc—中生代碎屑岩;Mzm—中生代中酸性岩;Mzp—中生代火山碎屑岩;Z-Pc—震旦纪-二叠纪碳酸盐岩;Z-Ca—震旦纪-石炭纪泥质碎屑岩;Ptn—前寒武纪基性岩;Ptr—前寒武纪变质岩
Fig.5
Migration coefficient of heavy metal elements in surface and deep soils
Mzc—Mesozoic clastic rock; Mzm—Mesozoic acid rock; Mzp—Mesozoic pyroclastic rock; Z-Pc—Sinian-Permian carbonate rocks; Z-Ca—Sinian-Carboniferous argillaceous clastic rock; Ptn—Precambrian base rock; Ptr—Precambrian metamorphic rock
在计算土壤重金属的迁移系数时,选择惰性元素作为稳定元素,土壤中Sc、Zr、Ti、Al在风化和土壤形成过程中含量变化较小且相对稳定,本文以Al为稳定元素计算重金属元素的迁移系数[24]。其表达式为:
式中:
图5反映出,重金属元素因为成土母岩的变化,其迁移系数也发生变化。同一种重金属元素在基性岩、碎屑岩、碳酸盐岩、中酸性岩这4种成土母岩中呈现以下特征:①基性岩形成的土壤中重金属元素迁移系数最大,具有明显的富集特征;碎屑岩形成的土壤中重金属元素迁移系数均小于0,在这4种成土母岩中最低,具有弱亏损特征。这一情况与图2反映出的重金属元素在基性岩及其形成的土壤中含量均相对较高的结果保持一致,并且母岩中重金属元素含量碎屑岩高于基性岩,土壤中重金属元素含量碎屑岩小于基性岩,也同样证实了基性岩形成的土壤迁移系数最大这一特征。②碎屑岩和碳酸盐岩这两种母岩形成的土壤迁移系数小于0,其他大多大于0且具有富集特征;同时重金属元素在表层土壤和深层土壤的迁移系数也不同(表层土壤>深层土壤),这反映了重金属在表层土壤中相对聚积。③图3、图5显示碳酸盐岩重金属元素含量最低,且除了As在表层土壤显著聚积外,其他重金属元素都出现了不同程度的损失,但在中酸性岩中含量较高,其形成的土壤迁移系数较大,由此推断,碳酸盐岩形成的土壤中重金属含量较低,中酸性岩形成的土壤偏高,但事实却刚好相反。综上所述,表层土壤中重金属元素的二次富集还存在其余要素影响[25]。
3.3 土壤理化性质对重金属分布的影响
3.3.1 土壤氧化物对重金属分布的影响
为探讨元素间的内部关系,采用Pearson相关系数对碳酸盐岩和碎屑岩形成的表层、深层土壤中8种重金属元素和氧化物进行相关性分析。由表3看出:①研究区表层土壤Cu、Zn和亲铁元素(Cr、Ni、Pb)间的相关系数较高,为0.614~0.928,表明这些元素在土壤形成过程中表现出相似的富集特征,这可能是重金属元素在研究区表土空间分布中具有良好耦合的原因;Cd、Hg、As亲硫元素与Cu、Zn、Cr、Ni、Pb间相关性不高,为-0.326~0.434,Cd与As相关性为0.663,Hg与其他重金属元素间相关系数为-0.326~0.061,与图1中Hg的空间分布与其他元素耦合性不高相一致。②深层土壤研究区重金属元素间的相关系数为0.370~0.949,除Hg与Zn和Pb的相关系数为0.370、0.371外,其余重金属之间的相关系数均显著(p<0.05),表明深层土壤重金属元素在成土过程中具有相似的来源,结合图3、图4研究结果,可以得出成土母岩影响着深层土壤重金属元素的分布。
表3 表层土壤样品(无底色)和深层土壤样品(底色为灰色)中8种重金属元素与氧化物的Pearson相关系数
Table 3
| 指标 | SiO2 | CaO | MgO | Al2O3 | Fe2O3 | K2O | Na2O | Cr | Ni | Cu | Zn | Cd | Pb | Hg | As |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SiO2 | 1 | -0.941** | -0.958** | 0.629** | 0.391 | 0.565** | 0.316 | 0.321 | 0.116 | 0.297 | 0.395 | 0.033 | 0.693** | 0.163 | 0.218 |
| CaO | -0.969** | 1 | 0.940** | -0.837** | -0.652** | -0.757** | -0.479* | -0.516* | -0.334 | -0.501* | -0.604** | -0.146 | -0.822** | -0.213 | -0.305 |
| MgO | -0.688** | 0.573** | 1 | -0.729** | -0.494* | -0.686** | -0.480* | -0.363 | -0.153 | -0.376 | -0.456* | -0.066 | -0.750** | -0.194 | -0.239 |
| Al2O3 | 0.879** | -0.929** | -0.581** | 1 | 0.895** | 0.931** | 0.723** | 0.707** | 0.573** | 0.702** | 0.799** | 0.270 | 0.862** | 0.234 | 0.391 |
| Fe2O3 | 0.792** | -0.856** | -0.540** | 0.962** | 1 | 0.866** | 0.652** | 0.777** | 0.710** | 0.822** | 0.869** | 0.409 | 0.767** | 0.331 | 0.474* |
| K2O | 0.692** | -0.706** | -0.480* | 0.819** | 0.827** | 1 | 0.763** | 0.564** | 0.406 | 0.573** | 0.721** | 0.105 | 0.740** | 0.100 | 0.185 |
| Na2O | 0.743** | -0.717** | -0.518* | 0.650** | 0.539** | 0.455* | 1 | 0.316 | 0.183 | 0.378 | 0.468* | 0.161 | 0.425* | 0.256 | 0.322 |
| Cr | 0.716** | -0.774** | -0.483* | 0.900** | 0.932** | 0.773** | 0.411 | 1 | 0.949** | 0.907** | 0.771** | 0.516* | 0.785** | 0.488* | 0.709** |
| Ni | 0.491* | -0.529** | -0.307 | 0.703** | 0.722** | 0.617** | 0.166 | 0.878** | 1 | 0.892** | 0.730** | 0.588** | 0.686** | 0.451* | 0.728** |
| Cu | 0.476* | -0.533** | -0.187 | 0.700** | 0.713** | 0.659** | 0.147 | 0.787** | 0.871** | 1 | 0.765** | 0.698** | 0.772** | 0.558** | 0.704** |
| Zn | 0.561** | -0.582** | -0.329 | 0.670** | 0.676** | 0.611** | 0.170 | 0.817** | 0.928** | 0.856** | 1 | 0.516* | 0.843** | 0.370 | 0.468* |
| Cd | -0.178 | 0.171 | 0.320 | -0.159 | -0.227 | -0.049 | -0.352 | -0.066 | 0.311 | 0.394 | 0.434* | 1 | 0.470* | 0.790** | 0.565** |
| Pb | 0.662** | -0.672** | -0.462* | 0.681** | 0.691** | 0.578** | 0.303 | 0.698** | 0.626** | 0.614** | 0.750** | 0.070 | 1 | 0.371 | 0.486* |
| Hg | -0.402 | 0.402 | 0.152 | -0.356 | -0.366 | -0.326 | -0.180 | -0.326 | -0.263 | -0.230 | -0.303 | 0.061 | -0.254 | 1 | 0.598** |
| As | -0.291 | 0.305 | 0.100 | -0.213 | -0.219 | -0.208 | -0.271 | -0.047 | 0.290 | 0.234 | 0.323 | 0.663** | 0.115 | 0.332 | 1 |
注:“**”表示在 0.01 级别(双尾)相关性显著;“*”表示在 0.05 级别(双尾)相关性显著。
主量元素是土壤中矿物的重要组分。因此,在一定程度上重金属与土壤矿物间的关系可以由主量元素与重金属元素的相关性反映[26]。
表层土壤中CaO、K2O与重金属元素Cr、Ni、Cu、Zn、Pb的相关系数为-0.774~0.773,其中CaO与这5种重金属成负相关,Na2O与Cr、Ni、Cu、Zn、Cd、Pb、Hg和As间的相关系数为-0.352~0.411,相关性不明显,由此可以得出,K2O具有较强的重金属吸附能力,CaO对重金属的迁移起克制作用,Na2O对重金属的影响不明显,K2O、Na2O、CaO在土壤中主要以长石类矿物形式存在,Huang[27]认为Cu和Pb可以在长石中富集,而本次研究发现不同的长石矿物对重金属的吸附能力差异较明显,可能是由于强风化作用导致碳酸盐岩和碎屑岩中Ca、Na和K发生较强的淋滤。陈静生等[28]认为重金属的含量受铝铁氧化物的制约较明显,本次研究中Al2O3、Fe2O3与Cr、Ni、Cu、Zn和Pb的相关系数较高,处于0.676~0.932之间,可以得出含铝和铁的矿物对重金属的吸附能力较强,Fe有4种价态,重金属可以在其氧化物的氧化还原作用中产生迁移[29-30],Al主要在长石及黏土矿物中存在,上述得出,长石矿物对重金属迁移和富集的作用差别较大,因此黏土矿物对重金属的富集起较大影响,黏土矿物由于具有高比表面积、高阳离子交换容量和高膨胀能力,能够有效吸附土壤中的重金属[31]。MgO与重金属元素间相关系数为-0.483~0.320,说明黑云母等暗色含Mg矿物对重金属的响应能力一般[32]。SiO2与Cr、Zn和Pb的相关系数为0.561~0.716,与Ni和Cu的相关系数为0.476和0.491,与Pb、Hg和As的相关系数为-0.402~-0.178,可以认为,二氧化硅等稳定矿物对不同重金属的分布影响程度不同。氧化物与Cd、Hg和As间的相关性较弱,表明Cd、Hg和As的含量受氧化物的影响较弱。
深层土壤中重金属元素与氧化物间的相关系数与表层土壤呈现出相似性,但也有不同之处,主要表现在:Pb与氧化物间的相关性均较明显,为-0.822~0.862,表明深层土壤中Pb比较容易受氧化物的控制;SiO2与剩余7种重金属相关系数为0.033~0.321,可以认为深层土壤中SiO2含量对重金属无响应,这与Dixon等[33]的研究一致,同时也可以看出表层土壤中重金属的来源与深层土壤的来源不同。
3.3.2 土壤pH和质地对重金属分布的影响
研究区土壤pH和质地与重金属元素的迁移系数的Spearman相关性分析结果见表4。
表4 土壤pH和质地与重金属元素迁移系数的相关性
Table 4
| 项目 | TCr | TNi | TCu | TZn | TCd | TPb | THg | TAs |
|---|---|---|---|---|---|---|---|---|
| 粉粒 | 0.224 | 0.262* | 0.199 | 0.215 | 0.030 | 0.094 | 0.330* | 0.136 |
| 细砂 | 0.328* | 0.324* | 0.140 | 0.291* | 0.084 | 0.076 | 0.219 | 0.115 |
| 中砂 | -0.036 | -0.094 | -0.110 | -0.097 | -0.128 | -0.093 | -0.256 | -0.192 |
| 粗砂 | -0.319* | -0.290* | -0.118 | -0.254 | -0.100 | -0.098 | -0.241 | -0.071 |
| pH | -0.314* | -0.248 | -0.246 | -0.269* | -0.025 | 0.156 | 0.099 | 0.096 |
表5 各土壤质地占比及pH值统计
Table 5
| 参数 | 粉粒 (0.002~ 0.05mm) | 细砂 (0.05~ 0.25mm) | 中砂 (0.25~ 0.5mm) | 粗砂 (0.5~ 1mm) | pH |
|---|---|---|---|---|---|
| 最小值 | 4.87 | 14.35 | 6.96 | 5.92 | 5.96 |
| 最大值 | 36.08 | 52.79 | 34.46 | 43.08 | 8.87 |
| 平均值 | 14.66 | 38.59 | 22.70 | 21.06 | 7.71 |
| 标准差 | 4.93 | 6.93 | 5.22 | 7.29 | 0.73 |
| 变异系数 | 33.61 | 17.95 | 23.00 | 34.64 | 9.46 |
注:pH无量纲。
表4显示出,粗砂与TCr、TNi的相关系数为-0.319、-0.290(p<0.01),呈弱负相关性,细砂与TCr、TNi和TZn的相关系数为0.291~0.328(p<0.01),呈弱正相关性,粉粒与TNi、THg的相关系数为0.262、0.330(p<0.01),呈弱正相关性,其余元素的迁移系数与土壤质地相关性不高。由此得出,随着土壤颗粒的变大,重金属元素的迁移系数逐渐变小,重金属元素的富集受到阻碍,当土壤颗粒变小时,重金属元素在土壤中得到富集,其中Cr、Ni、Zn主要富集在细砂中,Hg主要富集在粉粒中。研究区土壤质地主要以细砂(0.05~0.25 mm)为主(表5),占比平均值为38.59%,其次为中砂(0.25~0.5 mm),平均值为22.70%,表层土壤与深层土壤质地相似,由此可知,研究区土壤质地利于重金属元素在土壤中迁移富集。
3.4 土壤重金属来源分析
通过Pearson相关性分析可以看出,不同重金属元素间及与氧化物间的相关系数具有相似性也有差异性,为了进一步研究土壤中重金属的来源,采用主成分分析来判别碳酸盐岩和碎屑岩形成的表层和深层土壤中重金属的主要来源[35]。
由表6可以得出:主成分1(F1)显示重金属在表层土壤中的方差贡献率为55.018%,Cr、Ni、Cu、Zn和Pb的因子载荷为0.778~0.977,通过Pearson相关系数,可以发现Cr、Ni、Cu、Zn、Pb这5种重金属元素与代表土壤性质的氧化物间具有较高的共变关系,且其在土壤中的含量与母岩中含量较接近,同时重金属元素间相互系数也较高,表明其主要来源于成土母岩,Boruvka等[36]通过主成分分析,把Cr、Ni、Cu、Zn的来源看作同一类,主要起源于地质背景,Nanos等[37]利用因子克里金法和主成分分析法得出人类活动尚未改变Cr、Ni、Cu、Zn和Pb的自然含量,自然因素对其的影响更大,因此F1主要为自然来源,受控于地质背景的影响。主成分2(F2)代表的方差贡献率为23.108%,Cd、Hg和As的因子载荷为0.555~0.785,与河北省背景值接近的有Hg和As这两个元素,而Cd的平均值则是河北省背景值的两倍以上,Cd、Hg和As常形成硫化物,与氧化物间相关系数均较小,最大值分布于泥质碎屑岩中,但在其所形成的土壤中含量却较小[38],表明成土母岩对该元素的影响不高,人类活动对其的影响效果增强,曾咏梅等[39]认为Cd的人为来源主要来源于工业“三废”,Han等[40]和Abedin等[41]认为采矿、冶炼等则是导致土壤As和Hg污染的重要原因,从重金属的空间分布上来看,Cd、Hg和As主要分布于铁矿和石灰石矿所在区域附近,可以得出是人类活动影响了表层土壤中Cd、Hg和As的含量这一结论,因此F2主要为人为来源,受控于矿业开采的影响。
表6 研究区土壤重金属元素因子载荷
Table 6
| 指标 | 表层土壤 | 深层土壤 | ||
|---|---|---|---|---|
| F1 | F2 | F1 | F2 | |
| Cr | 0.873 | -0.367 | 0.931 | -0.222 |
| Ni | 0.954 | 0.008 | 0.916 | -0.156 |
| Cu | 0.917 | 0.046 | 0.952 | -0.068 |
| Zn | 0.977 | 0.064 | 0.828 | -0.352 |
| Cd | 0.368 | 0.785 | 0.754 | 0.510 |
| Pb | 0.778 | -0.191 | 0.820 | -0.369 |
| Hg | -0.330 | 0.555 | 0.668 | 0.661 |
| As | 0.291 | 0.864 | 0.784 | 0.233 |
| 特征值 | 4.401 | 1.849 | 5.602 | 1.089 |
| 方差/% | 55.018 | 23.108 | 70.019 | 13.611 |
注:旋转法采用凯撒正态化最大方差法;旋转在 3 次迭代后已收敛。
深层土壤重金属F1的方差贡献率为70.019%,Cu、Zn、Cr、Ni、Hg、Cd、Pb和As这8种重金属元素的因子载荷都很高,为0.668~0.952,由图3、图4得知,重金属元素在深层土壤和成土母岩中的相关性较高,Pearson相关系数表明深层土壤重金属在成土过程中具有相似的来源,可以解释为深层土壤中8种重金属来源一致,成土母岩对其掌控力较强,因而F1为天然来源。F2代表的方差贡献率为13.611%,Hg和Cd的因子载荷分别为0.611和0.510,由表层土壤主成分分析可以得知Hg和Cd主要来源于矿业开采,因此F2为人为来源。此外,Hg和Cd在两个主成分上都有较高载荷这一现象也值得关注,可认为其具有两种主成分的来源[42],在地质背景和人类活动因素的共同影响下,深层土壤中的Hg和Cd分布会发生变化。
4 结论
1)研究区重金属元素含量在表层土壤和深层土壤中较为类似,呈现出Cr>Zn>Ni>Cu>Pb>As>Cd>Hg,除As平均含量比背景值要小外,其余重金属元素含量均低于河北省背景值。各元素空间分布极具耦合性和地带性,铁矿和石灰石矿区附近重金属元素含量相对较高。
2)重金属元素含量在深层土壤与成土母岩中表现出一定的相似性,在表层土壤中与其在深层土壤中的含量排序不一致,碳酸盐岩和碎屑岩与其形成的表层土壤中重金属含量呈负相关性,其他成土母岩与其形成的表层土壤中重金属含量规律性不明显;Al2O3与Ti的线性关系得出碳酸盐岩和碎屑岩与其形成的表层、深层土壤具有同源性,以上表明表层土壤重金属元素与成土母岩响应较弱,深层土壤重金属元素与成土母岩有较好的呼应。
3)基性岩形成的土壤迁移系数较高,具有明显的富集特征,碎屑岩和碳酸盐岩则较小,且呈弱亏损现象;碳酸盐岩中重金属含量最低,其形成的土壤迁移系数也较小,但在表层土壤中重金属含量却相对较高,表明表层土壤重金属元素的二次富集较复杂。
4)相关性分析表明Cr、Ni、Cu、Zn和Pb间相关系数较高,CaO、K2O、Al2O3、Fe2O3与Cr、Ni、Cu、Zn、Pb的相关性较好,MgO、SiO2、Na2O与重金属元素的相关性较低,研究区pH值阻碍了土壤中Cr、Zn的迁移富集,而土壤质地促进了重金属元素在土壤中的迁移富集。主成分分析表明重金属元素在表层与深层土壤中具有不同的来源,成土母岩控制着表层土壤Cr、Ni、Cu、Zn和Pb的分布,人类活动影响着Cd、Hg和As的分布;深层土壤中成土母岩对8种重金属的分布均有较强的控制力,且地质背景和人类活动共同影响着Cd和As的分布。
参考文献
Soil metal concentrations and toxicity:Associations with distances to industrial facilities and implications for human health
[J].
Spatial distribution and source analysis of heavy metals in soils influenced by industrial enterprise distribution:Case study in Jiangsu Province
[J].
珠江三角洲冲积平原土壤重金属元素含量和来源解析
[J].
Occurrence and source identification of heavy metals in the alluvial soils of Pearl River Delta region,South China
[J].
Heavy metals in urban soils:A case study from the city of Palermo (Sicily),Italy
[J].
辽阳市土壤重金属含量特征及潜在风险评价
[J].
Characteristics and potential risk assessment of heavy metal contents in urban soil,Liaoyang City
[J].
Distribution,source identification and health risk assessment of soil heavy metals in urban areas of Isfahan Province,Iran
[J].
承德市滦河流域土壤重金属地球化学基线厘定及其累积特征
[J].
Determination of heavy metal geochemical baseline values and its accumulation in soils of the Luanhe River Basin,Chengde
[J].
典型水源涵养区废弃矿山生态修复效益评价指标体系研究
[J].
Study on benefit evaluation index system of abandoned mine ecological restoration in typical water conservation area
[J].
青藏高原典型金属矿山河流重金属污染对比
[J].
A comparative study of the content of heavy metals in typical metallic mine rivers of the Tibetan Plateau
[J].
Heavy metals contamination characteristics in soil of different mining activity zones
[J].
滦河流域沉积物中重金属分布特征及风险评价
[J].
Distribution characteristic and potential ecological risk assessment of heavy metals in sediments of the Luanhe River
[J].
山东省土壤中元素含量与母质的关系
[J].
On the relationship between the concentrations of elements in soil and the types of soil-forming parent material in Shandong Province,China
[J].
1987-2015年京津冀西北水源涵养区生态格局时空变化
[J].
Analysis of spatial and temporal changes of regional ecological pattern in the northwest of Jingjinji as water conservation area during the past 30 years
[J].
三江平原耕地土壤重金属元素分布特征及影响因素的多元统计分析
[J].
A multivariate statistical analysis of the distribution and influencing factors of heavy metal elements in the cultivated land of the Sanjiang Plain
[J].
江西赣州地区土壤—水稻系统重金属含量特征及健康风险评价
[J].
Characteristics and health risk assessment of heavy metals in soil-rice system in the Ganzhou area,Jiangxi Province
[J].
广西典型碳酸盐岩区农田土壤—作物系统重金属生物有效性及迁移富集特征
[J].
Bioavailability,translocation,and accumulation characteristic of heavy metals in a soil-crop system from a typical carbonate rock area in Guangxi,China
[J].
贫Cd碳酸盐岩发育土壤Cd的富集与超常富集现象——以贵州岩溶区为例
[J].
Enrichment and supernormal enrichment phenomenon of Cd in soils developed on Cd-poor carbonate rocks:A case study of Karst areas in Guizhou,China
[J].
Factors influencing heavy metal availability and risk assessment of soils at typical metal mines in Eastern China
[J].
秦岭某钼矿区开发对东川河流域Cd的影响
[J].
Evaluation of Cd pollution of a molybdenum ore area in Dongchuan River Basin of the Qinling Mountain
[J].
The influence of pH and organic matter content in paddy soil on heavy metal availability and their uptake by rice plants
[J].
DOI:S0269-7491(10)00424-0
PMID:20952112
[本文引用: 1]
The experiments were done to investigate the effect of soil pH and organic matter content on EDTA-extractable heavy metal contents in soils and heavy metal concentrations in rice straw and grains. EDTA-extractable Cr contents in soils and concentrations in rice tissues were negatively correlated with soil pH, but positively correlated with organic matter content. The combination of soil pH and organic matter content would produce the more precise regression models for estimation of EDTA-Cu, Pb and Zn contents in soils, demonstrating the distinct effect of the two factors on the availability of these heavy metals in soils. Soil pH greatly affected heavy metal concentrations in rice plants. Furthermore, inclusion of other soil properties in the stepwise regression analysis improved the regression models for predicting straw Fe and grain Zn concentrations, indicating that other soil properties should be taken into consideration for precise predicting of heavy metal concentrations in rice plants.Copyright © 2010 Elsevier Ltd. All rights reserved.
Processes controlling the distribution of Ti and Al in weathering profiles,siliciclastic sediments and sedimentary rocks
[J].
黔西南喀斯特地区红色风化壳的物源及元素迁移特征
[J].
Material sources and element migration characteristics of red weathering crusts in southwestern Guizhou
[J].
碳酸盐岩风化和成土过程的重金属迁移富集机理初探及环境风险评价
[J].
Heavy metal migration and enrichment mechanism and the environmental risks during the weathering and soil formation of carbonate rocks
[J].
Feldspars,olivines,pyroxenes,and amphiboles
[G]//SSSA book series.Madison,WI,
中国东部河流沉积物中重金属含量与沉积物主要性质的关系
[J].
Relation of geochemical and surface properties to heavy metal concentrations of sediments from eastern Chinese Rivers
[J].
土壤铁锰结核中锰矿物类型鉴定的探讨
[J].
Methodological study of identifying mangnese minerals in fe-mn nodules of soils
[J].
Effect of iron oxide coatings on zinc sorption mechanisms at the clay-mineral/water interface
[J].Oxide surface coatings are ubiquitous in the environment, but their effect on the intrinsic metal uptake mechanism by the underlying mineral surface is poorly understood. In this study, the zinc (Zn) sorption complexes formed at the kaolinite, goethite, and goethite-coated kaolinite surfaces, were systematically studied as a function of pH, aging time, surface loading, and the extent of goethite coating, using extended X-ray absorption fine structure (EXAFS) spectroscopy. At pH 5.0, Zn partitioned to all sorbents by specific chemical binding to hydroxyl surface sites. At pH 7.0, the dominant sorption mechanism changed with reaction time. At the kaolinite surface, Zn was incorporated into a mixed metal Zn-Al layered double hydroxide (LDH). At the goethite surface, Zn initially formed a monodentate inner-sphere adsorption complex, with typical Zn-Fe distances of 3.18 A. However, with increasing reaction time, the major Zn sorption mechanism shifted to the formation of a zinc hydroxide surface precipitate, with characteristic Zn-Zn bond distances of 3.07 A. At the goethite-coated kaolinite surface, Zn initially bonded to FeOH groups of the goethite coating. With increasing aging time however, the inclusion of Zn into a mixed Zn-Al LDH took over as the dominant sorption mechanism. These results suggest that the formation of a precipitate phase at the kaolinite surface is thermodynamically favored over adsorption to the goethite coating. These findings show that the formation of Zn precipitates, similar in structure to brucite, at the pristine kaolinite, goethite, and goethite-coated kaolinite surfaces at near neutral pH and over extended reaction times is an important attenuation mechanism of metal contaminants in the environment.
A review on the application of clay minerals as heavy metal adsorbents for remediation purposes
[J].
Location of natural trace elements in silty soils using particle-size fractionation
[J].
Soil mineralogy with environmental applications
[R].
Effect of soil pH and organic matter content on heavy metals availability in maize (Zea mays L.) rhizospheric soil of non-ferrous metals smelting area
[J].
DOI:10.1007/s10661-019-7793-5
PMID:31522295
[本文引用: 1]
Maize plant tissues and rhizosphere soil were collected from an agricultural area around the Huludao Zinc Plant in Liaoning Province, China, to investigate the effects of soil pH and organic matter content on heavy metal concentration and accumulation in different types of maize tissues. The mean pH of the soil samples was 7.02 (range 5.74-7.86), and the mean organic matter content was 31.03 g kg (range 18.80-52.20 g kg). The average Cu, Zn, Pb, and Cd contents in soil were 2.92, 6.72, 7.95, and 16.28 times greater than the corresponding background values, respectively. The geo-accumulation index indicated that the soils were uncontaminated to moderately contaminated by Cu, moderately to strongly contaminated by Pb and Zn, and strongly contaminated by Cd. The average available Cu, Pb, Zn, and Cd contents in the soil samples were 16.34, 6.997, 69.77, and 0.190 mg kg, respectively, while their bioavailability coefficients were 28.53%, 1.65%, 40.44%, and 10.83%, respectively. The respective mean Pb and Cd concentrations in grain samples were 0.341 and 0.342 mg kg, which exceeded the maximum concentrations permitted by the Chinese National Standard. Thus, the maize grain is not safe for consumption and poses potential risks to human health. With the exception of Cu, the combined effect of pH and organic matter content had a stronger influence on the availability of heavy metals in soil compared with either factor alone. Cd uptake in maize plant tissues was affected by the combination of soil pH, organic matter content, and bioavailable Cd content in soil; however, the combination of these three factors had only slight effects on Cu, Zn, and Pb absorption in maize tissues.
结合主成分分析法(PCA)和正定矩阵因子分解法(PMF)的鄱阳湖丰水期表层沉积物重金属源解析
[J].
Combination of PCA and PMF to apportion the sources of heavy metals in surface sediments from Lake Poyang during the wet season
[J].
Principal component analysis as a tool to indicate the origin of potentially toxic elements in soils
[J].
Multiscale analysis of heavy metal contents in soils:Spatial variability in the Duero River Basin (Spain)
[J].
Distributions and contamination assessment of heavy metals in the surface sediments of western Laizhou Bay:Implications for the sources and influencing factors
[J].
DOI:S0025-326X(17)30266-7
PMID:28365020
[本文引用: 1]
Heavy metals (Cu, Pb, Cr, Cd and As) contents in surface sediments from western Laizhou Bay were analysed to evaluate the spatial distribution pattern and their contamination level. As was mainly concentrated in the coastal area near the estuaries and the other metals were mainly concentrated in the central part of the study area. The heavy metals were present at unpolluted levels overall evaluated by the sediment quality guidelines and geoaccumulation index. Principal component analysis suggest that Cu, Pb and Cd were mainly sourced from natural processes and As was mainly derived from anthropogenic inputs. Meanwhile, Cr originated from both natural processes and anthropogenic contributions. Tidal currents, sediments and human activities were important factors affecting the distribution of heavy metals. The heavy metal environment was divided into four subareas to provide a reference for understanding the distribution and pollution of heavy metals in the estuary-bay system.Copyright © 2017 Elsevier Ltd. All rights reserved.
土壤中镉污染的危害及其防治对策
[J].
Damage of the cadmium(Cd) pollution in soil and its control
[J].
Industrial age anthropogenic inputs of heavy metals into the pedosphere
[J].
Arsenic uptake and accumulation in rice (Oryza sativa L.) irrigated with contaminated water
[J].
日照市土壤重金属来源解析及环境风险评价
[J].
Sources identification and hazardous risk delineation of heavy metals contamination in Rizhao city
[J].
DOI:10.11821/xb201207010
[本文引用: 1]
A total of 445 surface soils samples were collected at the nodes of a 2×2 km grid from Rizhao City and analyzed for 10 heavy metals (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb and Zn). Sources of heavy metals pollutant and the differences of contents among various land use types and parent material were revealed by multivariate analysis; meanwhile, spatial distribution of hazardous risk from heavy metals contamination was given by geostatistics based on GIS. The results are shown as follows. (1) The mean concentrations of As, Co, Cr and Cu were lower than the background values (BV) in eastern Shandong Province, respectively; but those of Cd, Hg, Mn, Ni, Pb and Zn exceeded the BV, especially for Cd and Hg (1.85 and 1.38 times of BV, respectively), indicating distinct accumulations of some heavy metals in soils of Rizhao City. (2) A total of 10 heavy metals could be classified as 4 Principal Components (PCs), including PC1 (Co, Cr, Mn, Ni and Zn), PC2 (Cd, Pb), PC3 (As, Cu), and PC4 (Hg). PC1 and PC3 were the factors dominated by natural sources, PC2 represented the factors from industrial, agricultural and traffic sources, and PC4 was contributed by industrial sources. Pb and Zn with a high load in different PCs might originate from the mixed sources including anthropogenic and natural sources. (3) There were significant differences in Cd and Hg contents among various land cover types with the highest level in urban areas. The concentrations of Co, Cr, Cu, Mn and Ni in the soils from weathered granite and metamorphic rock were all higher than those in the soils from alluvial and marine deposits. (4) The single element, elements integration and the corresponding PC presented similar spatial patterns of hazardous risk. The high risk regions with comprehensive assessment on all elements were located in densely-populated urban areas and western study area, which was attributed to the higher geological background in the western part and strong human interference in the eastern part.
