四川省沐川县典型土壤剖面重金属分布特征和生态风险评价

廖碧霞; 沈文灵; 贺灵

doi:10.15898/j.ykcs.202305090062

四川省沐川县典型土壤剖面重金属分布特征和生态风险评价

1.
中国地质科学院地球物理地球化学勘查研究所，河北廊坊 065000

2.
桂林理工大学，广西桂林 541006

基金项目: 中国地质调查局地质调查项目(DD20190522-03，DD20221641-02)

详细信息

作者简介: 廖碧霞，硕士研究生，主要研究方向为环境地球化学。E-mail：1470949680@qq.com

通讯作者: 贺灵，博士，高级工程师，主要研究方向为生态地球化学调查与评价。E-mail：lingh1237@163.com。

中图分类号: S151.93；X820.4

收稿日期: 2023-05-09

修回日期: 2023-07-06

录用日期: 2023-08-06

刊出日期: 2023-12-31

Distribution Characteristics and Ecological Risk Assessment of Heavy Metals in Typical Soil Profiles of Muchuan County, Sichuan Province

1.
Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang 065000, China

2.
Guilin University of Technology, Guilin 541006, China

More Information

Corresponding author: HE Ling, lingh1237@163.com

Received Date: 09 May 2023

Revised Date: 06 July 2023

Accepted Date: 06 August 2023

Publish Date: 31 December 2023

摘要

摘要:
根据全国土壤污染状况调查显示，全国土壤的环境状况总体不容乐观，耕地土壤环境质量令人担忧，已对粮食安全构成威胁。已有的研究工作多集中于土壤重金属的空间分布特征及污染源分析、重金属污染风险评估以及评估方法，但对于不同土壤深度重金属在耕地中的积累与剖面分布的变化及其生态风险分析相对较少。为研究四川省沐川县土壤剖面重金属分布特征和生态风险，本文在研究区选择三个不同地质背景区采集了土柱剖面样品开展相关工作。结果表明：样品中As、Cd、Hg、Pb、Ni、Cu、Zn七项指标中，除了Cu外，其余重金属元素含量都高于国家和四川省土壤背景值，表明这些元素在土壤中呈现不同程度地富集。土壤中7种重金属的浓度与土壤养分(氮、磷、钾)，土壤有机碳和pH值存在相关性，如在玉米地剖面中，氮和磷与Cd呈显著正相关，相关系数分别为0.845、0.747。大量研究表明，磷肥中含有一定量的重金属。磷肥中重金属含量高低与磷矿及其来源有关，磷肥能够增加土壤 Cd 含量。土壤有机碳与Cd呈显著正相关，相关系数为0.934，其原因是土壤有机质对重金属的吸附作用，有机碳对土壤中重金属的保留起了重要作用。pH值与Cd呈显著负相关，相关系数为-0.964，随着pH值的增加，土壤对重金属离子的吸附会增加，从而导致土壤中活性重金属离子减少。土壤重金属之间存在显著的正相关关系，表明它们普遍存在同源性。采用地质积累指数($ {I}_{\mathrm{g}\mathrm{e}\mathrm{o}} $)评价土壤重金属污染程度，并选取潜在生态风险指数($ RI $)评价其潜在生态风险，结果表明土壤中主要污染元素为Cd。生态风险指数显示，玉米地的潜在生态风险较大，其中Cd、Hg的生态风险较高，潜在生态风险指数($ RI $)随着剖面深度的增加而降低。当地应采取适当措施，加强对该地区污染的防治工作，避免对人体健康造成危害。
- 土壤 /
- 重金属 /
- 含量分布 /
- 污染评价 /
- 电感耦合等离子体质谱法
Abstract: BACKGROUND
Soil is a precious resource for human survival and social development. The quality of the soil environment is impacted by a variety of issues due to the social economy’s rapid expansion, and the issue of heavy metal contamination in farmed land has garnered great attention globally. Heavy metals in soil pose a severe risk to the security of agricultural products and public health due to their persistence, latency, and ease of entry into the food chain.　　In recent years, many scholars have carried out research on soil heavy metal pollution and ecological risk assessment under different conditions such as natural conditions, industrial and mining industries and developed transportation in different regions. Zhou et al.^[11] found that Xiong’an New Area was affected by the production activities of surrounding enterprises. The contents of As, Cd, Cu, Pb and Zn in some root soil samples exceeded the screening value standard for soil pollution risk of agricultural land (GB 15618—2018), and the exceeding ratios were 23.33%, 96.67%, 33.33%, 33.33% and 10.00%, respectively. Song et al.^[12] evaluated the characteristics of heavy metal pollution in the surface soil of Fuping County, Hebei Province, and found that As and Cd exceeded the acceptable carcinogenic risk level (As is 10⁻⁵, Cd is 10⁻⁶). Kumar et al.^[10] collected data on heavy metal-contaminated soils in India from 1991 to 2018. The average Cd content of all soil types exceeded the limit values, and the potential ecological risk values of Cd were greater than 320, reflecting a higher ecological risk. For the heavily polluted soil, according to the different pollution situation in our country, the remediation measures are taken according to local conditions. However, due to the wide area of contaminated soil and the complex composition of pollution sources, the current soil remediation work still faces huge problems.
OBJECTIVES
To study the vertical distribution characteristics of heavy metals in soil, the relationship between soil heavy metals and soil nutrient elements, as well as the degree of pollution and potential ecological risks.
METHODS
The contents of Cd, Cu, Ni, Pb, Zn were measured using inductively coupled plasma-mass spectrometry (ICP-MS); As content was determined by hydride generation atomic fluorescence spectrometry (HG-AFS); P and K₂O contents were determined by X-ray fluorescence spectrometry (XRF); N content was determined by oxidation combustion gas chromatography (GC); Hg content was determined by cold vapor atomic fluorescence spectrometry (CV-AFS); Organic carbon content was determined by high-frequency combustion infrared absorption method (IR); potentiometric method (POT) was used to measure soil pH value. Statistical analysis and calculation of soil heavy metal content, pollution index, and ecological risk index were conducted using Excel 2016. Pearson correlation analysis was conducted using SPSS 26, and the degree of soil heavy metal pollution was evaluated using the geoaccumulation index (I_geo). Potential ecological risk index (RI) values were selected to evaluate potential ecological risks.
RESULTS
The average contents of As, Cd, Cu, Hg, Ni, Pb, and Zn in the soil of YS plot were 20.8mg/kg, 0.35mg/kg, 26.38mg/kg, 0.121mg/kg, 33.29mg/kg, 42.37mg/kg, and 94.47mg/kg, respectively; The average contents of As, Cd, Cu, Hg, Ni, Pb, and Zn in the soil of PS plot were 7.21mg/kg, 0.32mg/kg, 28.32mg/kg, 0.028mg/kg, 47.34mg/kg, 33.29mg/kg, and 116.45mg/kg, respectively; The average contents of As, Cd, Cu, Hg, Ni, Pb, and Zn in the soil of GS plot were 5.42mg/kg, 0.16mg/kg, 22.38mg/kg, 0.08mg/kg, 31.8mg/kg, 30mg/kg, and 75.03mg/kg, respectively. The concentrations of As, Cd, Hg, Ni, Pb, and Zn were higher than the national and Sichuan soil background values, indicating that these metals were relatively enriched in the soil of Muchuan County. The relationship between seven heavy metals at different soil depths was evaluated through Pearson correlation analysis (seen in Table 4). There was a significant positive correlation between heavy metals, indicating their widespread homology. In the PS profile, the correlation between Cd, Hg and organic carbon was very high, with correlation coefficients of 0.934 and 0.955, respectively (Fig.5); As, Cd, Cu, Hg, Zn showed a highly significant negative correlation with pH, and the correlation between Cd, Hg content and soil pH was shown in Fig.5, with correlation coefficients of −0.964 and −0.944, respectively. The content of heavy metals in soil was closely related to organic carbon and pH value, which should be attributed to the adsorption of organic matter and the fact that pH not only affected the electrostatic adsorption of heavy metals by soil particles, but also damaged the inert part of the parent material. Soil organic matter and pH value are important factors affecting the migration of heavy metals in soil. The surface soil had a high content of organic matter, multiple adsorption sites, and a high soil pH value, which reduced the solubility of heavy metals and thus the metal migration rate.　　Soil pollution assessment results. The I_geo values of Cu and Zn in all soil profiles were less than 0, indicating that the soil in the study area was not contaminated by these heavy metals. The I_geo value of Cd at four depths was significantly reduced. Except that the I_geo value at GS point was less than 1, YS and PS were greater than 1, indicating that the Cd pollution degree of corn land (YS, PS) was more serious than that of tea garden land (GS). This may be due to the difference of tillage conditions, and the I_geo value of surface soil at YS point was between 2 and 3, showing moderate-strong pollution. The I_geo values of As, Hg, Ni and Pb at four depths were all less than 1 and close to 0, indicating that the soil pollution was slight, which may be caused by human input or natural changes. In general, conventional agricultural practices lead to the enrichment of heavy metals in soils due to excessive use of fertilizers and pesticides, wastewater irrigation and atmospheric deposition. Zhao et al.^[42] found that use of fertilizers and manure increased the content of heavy metals (Cd, Cu, Pb, and Zn) by approximately 3% per year. The order of heavy metal pollution degree from high to low is Cd>Hg>As>Pb>Ni.　　Potential ecological risk assessment. According to the description of risk level, the YS plot had the highest potential risk index for Cd and Hg, and there was a significant ecological risk of Cd and Hg at depths of 0-140cm (80≤E_i<160), among which the surface soil Cd had a strong ecological risk (160≤E_i<320). It indicates that Cd pollution sources in the region may be affected by past agricultural activities, including fertilizers and pesticides. The soil Cd of PS plot exhibited strong ecological hazards (160≤E_i<320) at the depth of 0-30cm while exhibiting strong ecological hazards (80≤E_i<160) at 60-110cm. The Cd and Hg in surface soil at the GS plot site had moderate ecological risks (40≤E_i<80). The value of RI showed a strong ecological risk (300≤RI<600) at 0-10cm of the YS plot, and a moderate ecological risk (150≤RI<300) at 30-140cm. Moderate ecological hazards (150≤RI<300) were present in the PS plot, while mild ecological hazards (RI<150) were present at 60-110cm. The ecological hazards of GS plot at 0-130cm were relatively weak. The E_i values of heavy metals in soil decreased with the increase of depth, which was consistent with the evaluation results of I_geo pollution. The E_i values of Cd in the three profiles were relatively high, indicating that special attention should be paid to the control of heavy metal pollution.
CONCLUSIONS
According to the results of soil vertical profile data, it can be concluded that heavy metal content tends to accumulate in the surface soil, and its content decreases with increasing depth. The I_geo value and E_i value also decrease with the increase of formation depth. The geoaccumulation index and potential ecological risk analysis indicate that Cd poses significant ecological risks to the local soil, and appropriate measures should be taken to strengthen pollution prevention and control in the area to avoid harm to human health. The content of heavy metals is closely related to soil nutrients and physicochemical properties, positively correlated with organic carbon content, and negatively correlated with pH value. According to the research results, it is suggested to carry out further research on the accumulation of heavy metals in soil, rationally assess its ecological harm, and ensure the safe use of land.
- soil /
- heavy metals /
- content distribution /
- pollution assessment /
- inductively coupled plasma-mass spectrometry

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图 1 研究区位置和地质简图

Figure 1.

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图 2 三个采样点土壤剖面重金属平均含量对比

Figure 2.

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图 3 三个采样点土壤剖面重金属垂向分布特征

Figure 3.

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图 4 三个采样点土壤剖面有机碳(C_org)、氮(N)、磷(P)、氧化钾(K₂O)含量和pH的垂向分布特征

Figure 4.

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图 5 紫色黏质土(PS剖面) Cd与C_org (a)、Hg与C_org(b)、Cd与pH值(c)、Hg与pH值(d)相关关系

Figure 5.

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图 6 三个采样点剖面土壤0～10cm深度(a)、30～40cm深度(b)、70～80cm深度(c)和100～110cm深度(d)的重金属地质累积指数($ {\mathit{I}}_{\mathbf{g}\mathbf{e}\mathbf{o}} $)

Figure 6.

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表 1 研究区不同类型土柱剖面取样点概况

Table 1. Sampling points of different types of soil column profiles in the study area.

采样地点	采样深度(cm)	土地利用类型	土壤类型	地质背景	可见特征描述
剖面YS	140	山坡旱地，种植玉米	黄色黏质土	三叠系雷口坡组(T₂l)，岩性为粉砂岩与白云岩、泥质灰岩互层，夹黑色碳质页岩	0～50cm灰黄色黏质土，50～140cm黄色黏质土
剖面PS	110	山坡旱地，种植玉米	紫色黏质土	侏罗系蓬莱镇组(J₃p)岩性以泥岩、砂岩和粉砂岩为主	0～80cm紫色黏质土，80～110cm紫色黏质土，土壤水分降低
剖面GS	130	茶园地	灰色黏质土	三叠系须家河组(T₃x) ，岩性主要为砂岩、粉砂岩、泥岩及煤层组成的沉积旋回	0～40cm，灰色黏质土，有机质较丰富；40～70cm，土壤颜色变黄，细砂成分增多；80～90cm，青灰色淤泥，水分增多；90～100cm，土壤变灰黑色，水分变少；100～120cm，青灰色黏质土；120～130cm，灰绿色，底部为页岩、泥岩

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表 2 各指标分析测试检出限

Table 2. Detection limit of each index analysis.

分析项目	检出限	分析项目	检出限
As	0.5$ \mathrm{m} $g/kg	Zn	4$ \mathrm{m} $g/kg
Cd	0.03$ \mathrm{m} $g/kg	P	10$ \mathrm{m} $g/kg
Cu	1.$ 0\mathrm{ } $mg/kg	C_org	0.10%
Hg	0.0005$ \mathrm{m} $g/kg	K₂O	0.05%
Pb	2$ \mathrm{m} $g/kg	pH	0.1
Ni	2$ \mathrm{m} $g/kg	N	20$ \mathrm{m} $g/kg

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表 3 三个采样点土壤剖面重金属与土壤养分指标的Pearson相关性

Table 3. Pearson correlation between heavy metals in soil profiles and soil nutrient indicators at three sampling points.

采样地点	养分元素	As	Cd	Cu	Hg	Ni	Pb	Zn
剖面YS	N	0.186	0.813^**	0.706^**	−0.419	−0.147	0.724^**	0.135
	P	0.401	0.947^**	0.758^**	−0.188	−0.120	0.828^**	0.307
	K₂O	0.155	−0.399	−0.486	0.795^**	0.526	−0.669^**	0.638^*
	C_org	0.003	0.759^**	0.764^**	−0.721^**	−0.340	0.861^**	−0.150
	pH	−0.492	−0.455	−0.120	−0.627^*	−0.088	−0.265	−0.836^**
剖面PS	N	0.814^**	0.845^**	0.828^**	0.924^**	−0.160	−0.072	0.724^*
	P	0.458	0.747^**	0.504	0.632^*	−0.209	0.481	0.695^*
	K₂O	−0.113	−0.266	0.047	−0.295	0.924^**	−0.121	0.424
	C_org	0.865^**	0.934^**	0.865^**	0.955^**	−0.283	0.065	0.717^*
	pH	−0.897^**	−0.964^**	−0.884^**	−0.944^**	0.287	−0.223	−0.735^**
剖面GS	N	0.934^**	0.448	−0.262	0.899^**	−0.765^**	0.897^**	−0.612^*
	P	0.186	0.144	0.661^*	0.084	0.265	0.485	0.425
	K₂O	−0.713^**	−0.237	0.801^**	−0.721^**	0.937^**	−0.366	0.863^**
	C_org	0.947^**	0.552	−0.303	0.953^**	−0.824^**	0.893^**	−0.673^*
	pH	−0.451	−0.039	−0.054	−0.358	0.227	−0.649^*	0.110
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。

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表 4 土壤剖面重金属之间的Pearson相关性

Table 4. Pearson correlation between heavy metals in soil profiles.

元素	As	Cd	Cu	Hg	Ni	Pb	Zn
As	1
Cd	0.546^**	1
Cu	0.187	0.644^**	1
Hg	0.772^**	0.141	−0.288	1
Ni	−0.369^*	0.141	0.683^**	−0.769^**	1
Pb	0.822^**	0.672^**	0.310	0.566^**	−0.311	1
Zn	0.029	0.500^**	0.783^**	−0.484^**	0.864^**	0.065	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。

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表 5 三个采样点土壤剖面重金属潜在生态风险指数

Table 5. Potential ecological risk index of heavy metals in soil profiles of three sampling points.

采样地点	采样深度 (cm)	$ {E}_{i} $							RI
采样地点	采样深度 (cm)	As	Cd	Cu	Hg	Ni	Pb	Zn	RI
剖面YS	10	21.9	278.4	5.0	83.3	5.0	8.7	1.2	403.5
	30	21.1	141.6	4.3	72.9	4.9	7.8	1.0	253.6
	60	20.0	125.3	4.5	66.7	5.1	6.9	1.0	229.6
	90	18.0	95.7	3.7	88.6	4.7	6.4	1.1	218.1
	110	20.6	96.5	3.8	96.9	5.1	6.2	1.1	230.1
	140	20.7	146.6	4.3	90.5	5.6	6.0	1.2	274.9
剖面PS	10	7.7	177.3	4.8	27.8	6.9	5.5	1.4	231.4
	30	8.0	171.6	5.0	22.5	7.2	6.0	1.4	221.7
	60	7.0	103.3	4.7	16.8	7.4	5.0	1.3	145.5
	90	6.3	80.5	4.1	15.2	7.0	4.8	1.3	147.6
	110	6.3	80.1	4.3	13.7	8.0	5.4	1.4	119.2
剖面GS	10	9.6	56.6	3.4	74.2	3.4	6.3	0.7	154.3
	30	9.7	101.8	3.8	78.6	3.9	6.2	0.8	204.8
	60	6.9	33.8	3.5	64.8	4.2	5.0	0.8	119.1
	90	2.3	64.2	3.0	31.6	5.2	3.9	0.9	111.0
	110	0.9	21.6	3.9	30.4	6.0	3.6	0.9	67.5
	130	1.5	85.1	5.0	25.7	7.4	3.8	1.2	129.7

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