Priority Soil Pollution Management of Contaminated Site Based on Human Health Risk Assessment: A Case Study in Southwest China

Abstract

The human risk assessment model can serve as a tool for regional contaminated site comprehensive management. However, site-specific risk assessment is still seldom applied in China as a basis for making decisions on risk management actions. In this study, a total of 112 soil samples were collected from ten polluted sites in Southwest China. The human health risk assessment method was used to assess the risk of Cd, As, Cu, Pb, Cr, Zn, and Hg pollution. According to the findings, the average concentrations of As, Zn, and Pb in contaminated sites are substantially higher than those of Cu, Cd, Cr, and Hg. Further studies conclusively showed the soil at contaminated site in its present condition pose risk to human health to potential future receptors. The main contribution of non-cancer and cancer risks was through incidental soil and dust ingestion. The priority control site remediation order is Region VI > Region V > Region IV > Region III > Region VII > Region X > Region IX > Region VIII > Region I > Region II. Finally, management recommendations are made, including reducing pollutant intake, implementing a stringent monitoring scheme, utilizing bioremediation, and strengthening the implementation of relevant laws. This study provides a case for the comprehensive evaluation of soil pollution at contaminated sites in China.

1. Introduction

Among all types of soil pollution, heavy metal(loid)s has become an emergent environmental concern worldwide [1]. The southwestern provinces in China (including Guizhou, Yunnan, and Guangxi) are well-known as karst areas for their richness in mineral resources which has resulted in the formation of a metal smelting industrial area [2,3]. Mining and metallurgical operations generate large amounts of wastes and derivatives, in which heavy metal(loid)s are readily dissolved under an oxidized atmosphere, causing contamination of surrounding soil [4]. Since 2017, China’s provincial capital cities have successively announced to the public the status of 174 contaminated sites in their jurisdiction [5]. In provincial capital cities alone, there are more than 144 contaminated sites are being remediated of which 109 are expected to redevelopment recently, and 25% of the contaminated sites have been sold, with a total amount of 104.96 billion RMB [6]. Therefore, the remediation and priority of heavy metal contaminated sites, which requires further study.

Contaminated site management is also a priority for China environmental policies [7,8,9]. The main Chinese regulation for the contaminated site management is represented by the regulation for contaminated site soil environmental [10], which require the environmental investigation, human health risk assessment, risk management and control, remediation, and supervision. Hechi city, located in the Southwest region of China, has been listed as the pilot area for comprehensive prevention and control of soil pollution. Following the selecting of a pilot area for contaminated sites management, the next issue that arises is the prioritizing the contaminate sites to determine which is the most urgent to be remediated [11,12]. Decision-makers must prioritize their management to maximize the benefit derived from limited funds [13]. This is a very complex task that relies on a variety of techniques and treatments, which incorporate multiple technical, social, economic, and environmental criteria required for any informed decision [14]. However, contaminated site prioritization was often founded on risk-based principles that assess the likelihood that a hazard will have an adverse im-pact on a receptor [15]. Health risk assessment (HRA) was based on a distinct assessment of the toxicity of the chemicals by exposure route (i.e., inhalation, ingestion, and dermal contact), as well as the evaluation system of pollution source-contact route-receptor-risk was constructed. Many contaminate site restoration projects may result either second pollution, and prioritization control area can provide remedies for remediation contaminated sites.

The heavy metals emitted from industrial and mining activities tend to initially accumulate in nearby soil [16] and may be transferred to environmental compartments, such as water, soil and plants, and eventually could be absorbed through ingestion, dermal contact and inhalation, increasing their risk to human health [17,18,19]. Human health risk assessment is the most rational approach for contaminated site risk management and has been the prevailing approach by international consensus [20,21,22,23]. By calculating and comparing these human health risk scores, decision-makers are able to determine which site is a priority. There are few published cases of site prioritization based on human health risk assessment in China. Moreover, frameworks that use risk assessment-based methodology to prioritize contaminated site risk management options, together with their application in two case studies in China, have recently been reported in the literature [24]. There is sufficient evidence to indicate the crucial role of human health risk assessment in the process of contaminated site redevelopment and subsequent risk management decision-making.

Therefore, it is essential to illustrate the crucial role of human health risk assessment (HHRA) in contaminated site prioritization and subsequent risk management decision-making. However, few attempts have been made to prioritize sites in industrial regions, particularly in regions with large numbers of abandoned industrial contaminated sites. We address this gap by developing a risk-based tool to prioritize contaminated sites in Southwest China. Herein, we report the following: (1) the soil contamination characteristics of contaminated sites in Southwest China; (2) the human health risk derived from contaminated sites; and (3) the priority control areas determined for contaminated sites. The findings of this study will be useful in providing decision-makers with a pragmatic solution for the determination of priority and, ultimately, regional contaminated site comprehensive management.

2. Materials and Methods

2.1. Study Area

The study area is located in the middle of Hechi city, Guangxi Province (106°34′–109°09′ E, 23°41′–25°37′ N), China (Figure 1). The study area, located in the met-allogenic belt of nonferrous metals, is a typical metalliferous industrial district with abundant mineral resources [25]. Due to lack of proper disposal and safe landfill, the waste residues caused serious pollution to the surrounding environment of the study area. Limestone soil is the major soil type in the karst area [26]. According to the China National Environmental Monitoring Center, the background value of heavy metals (loid) in limestone soil is higher than that in other soils types [27].

The study area has monsoon-influenced humid subtropical climate. The temperature difference between season is small, with the average temperature is about 16.9–21.5 °C. The frost-free period is long, the annual sunshine hours are 1447–1600 h in most areas [25]. On the whole, the terrain is high in the northwest and low in the southeast. According to monitoring data, as a result of long-term mining area, the quality of soil environment in the region declined, especially the contamination of arsenic, cadmium and lead that are in excess.

2.2. Sample Collection and Analysis

Using a regular grid, soil samples were collected from the 10 sites in Hechi city, Guangxi Province, from November 2016 to December 2016 (Figure 1). Before field work, the sampling coding system and sampling cell were created using the global positioning system on a digital map. A total of 112 samples were collected from the soil surface of the study area. An S-shaped sampling approach was adopted to sample flat locations with high soil heterogeneity. A quincunx approach was adopted to sample flat locations with homogeneous soil. Considering the identified primary pollution sources, the following contaminants were chosen for risk assessment purposes: cadmium (Cd), arsenic (As), copper (Cu), lead (Pb), chromium (Cr), zinc (Zn) and mercury (Hg). According to site characteristics and profiles length, the focus was on the surface soil layer up to the depth of 0.5 m, using a regular grid of 200 m × 200 m. Before sampling, the surface soil was levelled with a shovel to remove surface impurities. The samples were collected from the undisturbed soil and sealed in polyethylene bags with a wooden shovel. All samples were stored in a low-temperature incubator at 4 °C until all soil samples were sent to the laboratory.

During the pretreatment of soil samples, all samples were dried in a cool and ventilated place, and after natural air drying, animal residues, stones and plant roots were removed. Then, the soil samples were passed through a 100-mesh sieve and digested with HNO₃-HF-HClO₄ [1,18]. The concentrations of heavy metals (Cd, As, Cu, Pb, Cr, and Zn) were determined by inductively coupled plasma–mass spectrometry (ICP–MS, Bruker 820-MS) [28,29]. Atomic fluorescence spectrometry (AFS-9700) was used to determine the content of total mercury in the soil. Samples were analyzed using national standard soil samples (GSS-1, GSS-2, GSS-3, and GSS-4) as references, while quality assurance and quality control procedures were performed in accordance with USEPA 6020A [30]. The results indicated that the accuracy and bias of the analysis were generally less than 10%.

2.3. Health Risk Assessment Model

According to the health risk assessment model recommended by the U.S. Environmental Protection Agency (US EPA), the carcinogenic and noncarcinogenic risks of soil heavy metal exposure in the study area were evaluated and predicted. The health risks of heavy metals depend on two aspects. One aspect is the level of environmental pollution, including the concentration, form and toxic effects of heavy metals [18]. The other aspect is human exposure behavior, including the behavior and characteristics of human exposure to heavy metals. After heavy metals enter the soil, the exposure of the population is estimated in three ways: skin contact, hand–oral ingestion, and inhalation of dust with attached heavy metals [31,32]. These exposure routes are represented as follows:

$${\mathrm{ADD}}_{\mathrm{ingest}}=\frac{\mathrm{c}\times \mathrm{IngR}\times \mathrm{EF}\times \mathrm{ED}\times \mathrm{EF}}{\mathrm{BW}\times \mathrm{AT}},$$

(1)

$${\mathrm{ADD}}_{\mathrm{inh}}=\frac{\mathrm{c}\times \mathrm{SA}\times \mathrm{AF}\times \mathrm{ABS}\times \mathrm{EF}\times \mathrm{ED}\times \mathrm{CF}}{\mathrm{BW}\times \mathrm{AT}},$$

(2)

$${\mathrm{ADD}}_{\mathrm{der}}=\frac{\mathrm{c}\times \mathrm{EF}\times \mathrm{ED}}{\mathrm{PEF}\times \mathrm{AT}},$$

(3)

As adults and children have different physical characteristics and behavior patterns, Table 1 provides detailed values and descriptions of parameters in health risk assessment. The human body exposure parameters were mainly selected from CRNCDSR (2015), while the toxicity parameters for the heavy metals were derived from USEPA guidelines and international research findings. Various types of heavy metals enter the human body through different exposure routes that produce different toxic effects. The hazard index (HI) was defined as the relationship between the predicted exposure and the theoretical reference (RfD) for exposure. It is generally believed that when HI < 1.0, pollutants will not pose a threat to human health, so the risk can be ignored. However, when HI > 1.0, the pollutants will have adverse effects on human health, indicating that there is a risk of cancer. Cancer risk (CR) is used to assess the risk of cancer. CR was measured by multiplying the exposure by the carcinogenic slope factor (SF). The SF consists of oral intake, skin exposure and inhalation risk. HI and CR can be calculated using the following formula [18,31]:

$$\mathrm{HI}=\sum \frac{\mathrm{ADD}}{\mathrm{RfD}},$$

(4)

$$\mathrm{CR}=\mathrm{ADD}\times \mathrm{SF},$$

(5)

Cancer risk is calculated only for some established heavy metals. When CR < 10⁻⁶, the cancer risk of a single pollutant is acceptable. When 10⁻⁶ < CR < 10⁻⁴, the combined cancer risk of contaminants is acceptable. When CR > 10⁻⁴, contaminated site cleanup is recommended [33,34].

Table 1. Calculation parameters used in human health risk assessment [18,27,35].

Parameter	Symbol	Units	Value
Body weight	BW	kg	70 (adults); 15 (children)
Average time	AT	d	ED × 365 (noncarcinogenic), 25,550 (carcinogenic)
Exposure frequency	EF	d/y	350
Exposure duration	ED	y	24 (adults), 6 (children)
Soil ingestion rate	IngR	mg/d	100 (adults), 200 (children)
Conversion factor	CF	kg/mg	1 × 10−6
Surface area	SA	cm2/d	5700 (adults), 2800 (children)
Adherence factor to skin	AFsoil	mg cm2	0.5 (trace metals), 0.2 (organic compounds)
Dermal absorption factor	ABS	Unitless	0.03 (As), 0.001 (trace metals except As)
Gastrointestinal absorption factor	ABSGI	Unitless	0.025 (Cd),1.0 (As), 1.0 (Cu), 1.0 (Pb), 0.025 (Cr), 1.0 (Zn), 0.07 (Hg)
Particle emission factor	PEF	m3/kg	1.36 × 109
Ingestion reference value	Oral RfD	mg/kg d	3.00 × 10−4 (As), 1.00 × 10−3 (Cd), 3.00 × 10−3 (Cr), 4.00 × 10−2 (Cu), 3.00 × 10−4 (Hg), 3.5 × 10−3 (Pb), 3.00 × 10−1 (Zn)
Dermal reference value	Dermal RfD	mg/kg d	3.00 × 10−4 (As), 2.50 × 10−5 (Cd), 7.50 × 10−5 (Cr), 4.00 × 10−2 (Cu), 2.10 × 10−5 (Hg), 3.50 × 10−3 (Pb), 3.00 × 10−1 (Zn)
Inhalation reference value	Inhal RfD	mg/m3	1.50 × 10−5 (As), 1.00 × 10−5 (Cd), 1.00 × 10−4 (Cr), 4.02 × 10−2 (Cu), 3.00 × 10−4 (Hg), 3.25 × 10−3 (Pb), 3.00 × 10−1 (Zn)
Oral slope factor	SFO	(mg kg−1 d−1)−1	1.5 (As), ** (Cd), 5.0 (Cr), ** (Cu), ** (Hg), 8.50 × 10−3 (Pb), ** (Zn)
Dermal contact factor	SFO×ABSGI	(mg kg−1 d−1)−1	1.5 (As), ** (Cd), 2.0 (Cr), ** (Cu), ** (Hg), 8.50 × 10−3 (Pb), ** (Zn)
Inhalation unit risk	IUR	(mg/m−3)−1	4.3 × 10−3 (As), 1.80 × 10−3 (Cd), 8.40 × 10−2 (Cr), ** (Cu), ** (Hg), 1.2 × 10−5 (Pb), ** (Zn)

**: not available.

Table 1. Calculation parameters used in human health risk assessment [18,27,35].

Parameter	Symbol	Units	Value
Body weight	BW	kg	70 (adults); 15 (children)
Average time	AT	d	ED × 365 (noncarcinogenic), 25,550 (carcinogenic)
Exposure frequency	EF	d/y	350
Exposure duration	ED	y	24 (adults), 6 (children)
Soil ingestion rate	IngR	mg/d	100 (adults), 200 (children)
Conversion factor	CF	kg/mg	1 × 10−6
Surface area	SA	cm2/d	5700 (adults), 2800 (children)
Adherence factor to skin	AFsoil	mg cm2	0.5 (trace metals), 0.2 (organic compounds)
Dermal absorption factor	ABS	Unitless	0.03 (As), 0.001 (trace metals except As)
Gastrointestinal absorption factor	ABSGI	Unitless	0.025 (Cd),1.0 (As), 1.0 (Cu), 1.0 (Pb), 0.025 (Cr), 1.0 (Zn), 0.07 (Hg)
Particle emission factor	PEF	m3/kg	1.36 × 109
Ingestion reference value	Oral RfD	mg/kg d	3.00 × 10−4 (As), 1.00 × 10−3 (Cd), 3.00 × 10−3 (Cr), 4.00 × 10−2 (Cu), 3.00 × 10−4 (Hg), 3.5 × 10−3 (Pb), 3.00 × 10−1 (Zn)
Dermal reference value	Dermal RfD	mg/kg d	3.00 × 10−4 (As), 2.50 × 10−5 (Cd), 7.50 × 10−5 (Cr), 4.00 × 10−2 (Cu), 2.10 × 10−5 (Hg), 3.50 × 10−3 (Pb), 3.00 × 10−1 (Zn)
Inhalation reference value	Inhal RfD	mg/m3	1.50 × 10−5 (As), 1.00 × 10−5 (Cd), 1.00 × 10−4 (Cr), 4.02 × 10−2 (Cu), 3.00 × 10−4 (Hg), 3.25 × 10−3 (Pb), 3.00 × 10−1 (Zn)
Oral slope factor	SFO	(mg kg−1 d−1)−1	1.5 (As), ** (Cd), 5.0 (Cr), ** (Cu), ** (Hg), 8.50 × 10−3 (Pb), ** (Zn)
Dermal contact factor	SFO×ABSGI	(mg kg−1 d−1)−1	1.5 (As), ** (Cd), 2.0 (Cr), ** (Cu), ** (Hg), 8.50 × 10−3 (Pb), ** (Zn)
Inhalation unit risk	IUR	(mg/m−3)−1	4.3 × 10−3 (As), 1.80 × 10−3 (Cd), 8.40 × 10−2 (Cr), ** (Cu), ** (Hg), 1.2 × 10−5 (Pb), ** (Zn)

**: not available.

2.4. Development of Site-Specific Risk-Based Remedial Levels (RBRLs)

The second critical step in HHRA is the development of risk remediation levels at specific sites. When the total HI exceeds 1 or the total CR exceeds 1 × 10⁻⁴, the remedial level is calculated by the simplified method of the US EPA (2000) [36], and the formula is as follows:

$$\mathrm{RBRL}=\mathrm{C}\times \frac{\mathrm{TR}}{\mathrm{Calculated} \mathrm{Risk}},$$

(6)

where C is the concentration of heavy metals in the soil, TR represents the noncancer targeted risk (NTR) or cancer targeted risk (CTR) [37], the calculated risk is the value of the noncancer risk and cancer risk in the HHRA, and RBRL is the risk-based remediation level.

Based on the remediation recommendations of the US EPA (2002) [38], the site-specific RBRLs were calculated separately for carcinogenic and noncarcinogenic effects and separately for oral/dermal and inhalation exposures due to the potential for different health effects (target organs) via these routes. For noncarcinogens, an HI of 1 was established as the NTR since an HI above 1 indicates that toxic effects may appear [31]. If more than one noncarcinogen affects the same target organ system, the RBRLs should be adjusted to reflect the potential for additive risks [38]. The adjustment can be made by dividing the RBRL calculated for individual noncarcinogens by the number of chemicals with the same target organs/effects [37]. Concerning carcinogens, since multiple contaminants and multiple pathways of exposure occurred at contaminated sites, the CTR of 1 × 10⁻⁶ was initially considered sufficiently protective. Finally, the RBRLs could be modified so that the cumulative risk level would be at least at the 1 × 10⁻⁴ level corresponding to the upper end of the US EPA’s acceptable risk range of 1 × 10⁻⁶ to 1 × 10⁻⁴ [39].

The calculated soil remediation target values were compared, and the lowest of these values was suggested as a preliminary remedial level. The final repair target value needs to be compared with the local background value; if the lowest RBRL values were lower than the relevant background concentration, the background concentration could be considered the remedial level. However, this should be a site-specific decision and should not be carried out automatically.

2.5. Special Case: Lead

Inorganic lead is a special case with strong toxicity. There is no safety level of minimum allowable lead exposure, so HHRA is no longer used in the toxicity evaluation of lead pollution. For industrial and commercial land, the ALM model is usually used to assess lead exposure and formulate a RBRL [39,40,41]. Lead exposure pathways in the direct ingestion of soil and indoor dust are considered in the adult ALM health model. The blood lead concentration in women of childbearing age was calculated by using Formula (7):

$${\mathrm{PbB}}_{adult,central}={\mathrm{PbB}}_{adult,0}+\frac{\mathrm{PbS}\times \mathrm{BKSF}\times {IR}_s\times A{F}_s\times E{F}_s}{A{T}_s},$$

(7)

where ${\mathrm{PbB}}_{adult,central}$ is the blood lead concentration of adults at the center of the site exposed to lead pollution. ${\mathrm{PbB}}_{adult,0}$ is the background lead level in blood from women of childbearing age not exposed to lead, with a reference value of 4.79 μg/dL. PbS: refers to the lead content in soil (mg/kg). BKSF refers to the slope coefficient of blood lead vs. daily intake of lead content in the body, and the reference value is 0.4 d/dl. IR_s refers to the daily soil or indoor dust intake, with a reference value of 0.05 d/dL. AF_s refers to the gastrointestinal absorption efficiency of lead intake in the body, with a reference value of 0.12 (dimensionless). EF_s refers to the average number of days to lead pollution exposure every year, with a reference value of 240 d/a. At_s refers to the average time of long-term exposure, with a reference value of 365 days/y.

The risk-based criterion ensures that the probability of fetal ${\mathrm{PbB}}_{adult,central}$ being 10 μg/dL does not exceed 5%, and the risk-based target of adult blood lead concentration is calculated by Formula (8):

$${\mathrm{PbB}}_{adult,central, goal}=\frac{{\mathrm{PbB}}_{fetal,095,goal}}{GS{D}_{i, adult}^{1.645}\times R_{fetal/maternal}},$$

(8)

where ${\mathrm{PbB}}_{adult,central, goal}$ is the target value of the average blood lead content of pregnant women exposed to lead-contaminated sites. ${\mathrm{PbB}}_{fetal,0.95,goal}$ is the 95% probability target value of fetal blood lead content, with a reference value of 10 μg/dL. $GS{D}_{i, adult}^{1.645}$ is the geometric standard deviation of blood lead content of women of childbearing age, with a reference value of 1.48 (dimensionless). $R_{fetal/maternal}$ is the correlation coefficient of blood lead content between a fetus and mother, with a reference value of 0.9 (dimensionless).

The soil lead concentration for a given exposure scenario and ${\mathrm{PbB}}_{adult,central, goal}$ can be calculated by Formula (9), and ${\mathrm{PbB}}_{adult,central,goal}$ can be replaced by ${\mathrm{PbB}}_{adult,central}$.

$$\mathrm{RBPL}=\mathrm{PbS}=\frac{\left({\mathrm{PbB}}_{adult,central,goal}-{\mathrm{PbB}}_{adult,0}\right)\times A{T}_s}{\mathrm{BKSF}\times I{R}_s\times A{F}_s\times E{F}_s},$$

(9)

where RBPL represents the desired remediation value of soil lead concentration (PBs) for adult blood lead concentration (${\mathrm{PbB}}_{adult,central, goal}$) and the corresponding 95% foetal blood lead concentration (${\mathrm{PbB}}_{fetal,095,goal}$) at a specific site.

3. Results and Discussion

3.1. Descriptive Statistics of Soil Heavy Metals

The descriptive statistics of heavy metals in soil at different sites are shown in

Table 2. Descriptive statistics of soil heavy metals in different regions.

Region	n	Concentration	Cd	As	Cu	Pb	Cr	Zn	Hg
I	11	Max	0.78	25.20	8.78	68.90	0.10	62.20	2.30 × 10−4
		Min	0.02	0.25	0.01	0.05	0.01	0.09	5.00 × 10−5
		Median	0.14	2.80	1.02	0.05	0.02	8.73	5.00 × 10−5
33II	2	Max	0.01	1.05	0.61	0.05	0.03	0.64	3.00 × 10−3
		Min	3.00 × 10−3	0.04	0.02	0.05	0.01	0.36	2.50 × 10−3
		Median	0.01	0.54	0.32	0.05	0.02	0.50	3.00 × 10−3
3III	11	Max	10.80	5810.00	-	74.40	-	653.00	6.46
		Min	0.10	12.50	-	10.80	-	49.50	0.39
		Median	1.17	151.00	-	22.90	-	131.00	0.71
IV	8	Max	17.30	3915.00	-	165.00	-	1554.00	5.02
		Min	4.49	52.50	-	73.30	-	682.00	0.73
		Median	13.40	1290.00	-	114.00	-	985.00	1.67
V	6	Max	14.60	530.00	-	116.00	-	882.00	1.19
		Min	0.90	527.00	32.40	23.80	-	113.00	-
		Median	4.86	1526.00	63.90	79.60	-	445.00	-
VI	8	Max	22.50	164,000.00	-	429.00	-	833.00	15.50
		Min	3.66	377.00	-	24.30	-	129.00	0.43
		Median	12.40	3895.00	-	53.90	-	368.00	3.29
VII	15	Max	1.98	1350.00	-	43.60	-	192.00	12.70
		Min	0.08	11.50	-	8.81	-	22.90	0.14
		Median	0.38	184.00	-	14.30	-	49.50	1.02
VIII	3	Max	0.09	32.40	-	49.50	-	70.20	0.33
		Min	0.01	4.39	-	42.80	-	27.80	0.12
		Median	0.05	8.28	-	45.70	-	62.10	0.25
IX	20	Max	9.10	78.00	269.00	2030.00	212.00	611.00	1.40
		Min	0.10	14.70	3.10	2.70	50.30	43.80	0.10
		Median	0.65	25.40	18.10	18.40	85.00	121.50	0.30
X	28	Max	56.00	463.00	484.00	7600.00	151.00	978.00	6.27
		Min	0.17	10.50	4.00	2.80	20.00	18.80	0.10
		Median	1.67	38.00	76.50	30.20	39.00	105.50	0.29
Total	112	Max	56.00	164,000.00	776.00	7600.00	212.00	5078.00	15.50
		Min	3.00 × 10−3	0.04	0.01	0.05	0.01	0.09	5.00 × 10−5

Note: The units of heavy metals are mg/kg, n: the sample size.

. The elemental contents determined for each polluted site were compared with their mean background levels in Guangxi Province and China (

Table A1. A summary of soil heavy metals in different regions.

Region	Concentration	Cd	As	Cu	Pb	Cr	Zn	Hg
I	CV	1.07	1.23	1.14	3.13	0.88	1.27	0.746
	Over Cg	13.2	0.617	0.131	0.336	0.0005	0.348	0.0008
	Over Cc	2.11	0.567	0.120	0.243	0.0005	0.492	0.0010
II	CV	0.527	0.935	0.929	0	0.538	0.277	0
	Over Cg	0.409	0.053	0.015	0.003	0.0003	0.011	0.029
	Over Cc	0.066	0.048	0.014	0.002	0.0003	0.015	0.036
III	CV	1.11	1.81	-	0.641	-	0.952	1.12
	Over Cg	179	86.9	-	1.62	-	4.11	18.8
	Over Cc	28.7	79.9	-	1.17	-	5.81	23.4
IV	CV	2.12	1.11	-	0.452	-	0.468	16.3
	Over Cg	840	125	-	6.06	-	21.2	19.2
	Over Cc	134	115	-	4.38	-	30.1	23.9
V	CV	1.27	1.29	1.18	1.66	-	1.20	-
	Over Cg	922	925	11.6	22.6	-	34.8	-
	Over Cc	148	850	10.7	16.4	-	49.2	-
VI	CV	0.525	2.14	-	1.25	-	0.514	1.03
	Over Cg	757	2402	-	5.33	-	8.43	51.4
	Over Cc	121	2209	-	3.86	-	11.9	63.9
VII	CV	0.839	1.17	-	0.603	-	0.633	1.52
	Over Cg	34.9	29.5	-	1.06	-	1.36	29.4
	Over Cc	5.58	27.1	-	0.764	-	1.92	36.5
VIII	CV	0.596	0.825	-	0.060	-	0.344	0.373
	Over Cg	3.17	1.46	-	2.45	-	1.15	2.71
	Over Cc	0.507	1.34	-	1.77	-	1.63	3.36
IX	CV	1.59	0.502	1.53	2.21	0.385	0.788	0.710
	Over Cg	75	3.32	1.74	11.5	1.58	3.54	4.25
	Over Cc	12	3.05	1.599	8.32	1.52	5.01	5.29
X	CV	2.22	1.35	1.16	3.32	0.606	1.32	1.97
	Over Cg	356	7.26	4.06	24.0	0.807	3.78	6.62
	Over Cc	56.9	6.67	3.73	17.3	0.778	5.35	8.22

Note: CV/%, coefficient of variation; Cg, background value of metals in soils of Guangxi Province. Cc, background value of metals in soils of China.

). The mean background levels of all elements were higher in Guangxi Province than in China [26,42,43]. There were differences in the degrees of heavy metal pollution at the different polluted sites. The contents of Cu, Pb, Cr, Zn and Hg in region I are the lowest, and the contents of Cd and As in region II are the lowest. The contents of Cu and Pb in region V are the highest. The contents of As and Hg in region VI are the highest. The contents of Cu and Pb in area V are the highest. However, the contents of As and Hg in region VI are the highest. The content of Cr in region IX is the highest (Table 2). The contents of Cd and Pb in region X are the highest.

The coefficient of variation (CV) can reflect the data dispersion degree. According to relevant research on the degree of variation, the CV can be divided into 0 < CV < 0.16 (weak variation), 0.16 ≤ CV< 0.36 (medium variation), and CV ≥ 0.36 (high variation) [44,45]. Overall, from the CVs of heavy metals in regions I~X, Pb and Hg in region II show weak variation, Pb and Zn in region VIII show medium variation, and heavy metals in other regions show high variation (Table A1), indicating that the content of heavy metals in each region changes significantly in space and is subject to discrete inputs of certain natural or external factors.

3.2. Human Health Risk Assessment

3.2.1. Noncarcinogenic Risk

The noncarcinogenic risks of heavy metals by various exposure routes are shown in

Table A2. Summary of the mean values of noncancer and cancer risk.

Region I	Adults								Children
	Noncancer Risk (Unitless)				Cancer Risk (Unitless)				Noncancer Risk (Unitless)				Cancer Risk (Unitless)
Element	HIoral	HIdermal	HIinhalation	THI	CRoral	CRdermal	CRinhalation	TCR	HIoral	HIdermal	HIinhalation	THI	CRoral	CRdermal	CRinhalation	TCR
Cd	3.29 × 10−4	2.88 × 10−4	1.48 × 10−5	6.32 × 10−4	NA	NA	9.16 × 10−14	9.16 × 10−14	7.53 × 10−3	2.69 × 10−3	1.48 × 10−5	1.02 × 10−2	NA	NA	2.29 × 10−14	2.29 × 10−14
As	2.90 × 10−2	2.48 × 10−2	2.99 × 10−4	5.41 × 10−2	4.48 × 10−6	3.83 × 10−6	6.61 × 10−12	8.31 × 10−6	9.48 × 10−1	2.71 × 10−1	2.99 × 10−4	1.22 × 10	1.04 × 10−5	7.31 × 10−8	1.65 × 10−12	1.05 × 10−5
Cu	9.28 × 10−5	2.65 × 10−6	4.75 × 10−8	9.55 × 10−5	NA	NA	NA	NA	8.66× 10−4	6.07 × 10−5	4.75 × 10−8	9.27 × 10−4	NA	NA	NA	NA
Pb	2.47 × 10−3	7.05 × 10−5	1.37 × 10−6	2.55 × 10−3	2.52 × 10−8	NA	1.83 × 10−14	2.52 × 10−8	2.31 × 10−2	1.62 × 10−3	1.37 × 10−6	2.47 × 10−2	5.89 × 10−8	4.12 × 10−10	4.58 × 10−15	5.93 × 10−8
Cr	1.45 × 10−5	1.27 × 10−5	1.96 × 10−7	2.74 × 10−5	6.54 × 10−9	NA	5.66 × 10−13	6.54 × 10−9	3.32 × 10−4	1.19 × 10−4	1.96 × 10−7	4.51 × 10−4	1.53 × 10−8	4.27 × 10−9	1.41 × 10−13	1.95 × 10−8
Zn	7.37 × 10−5	2.10 × 10−6	3.79 × 10−8	7.58 × 10−5	NA	NA	NA	NA	6.88 × 10−4	4.82 × 10−5	3.79 × 10−8	7.36 × 10−4	NA	NA	NA	NA
Hg	3.15 × 10−7	1.28 × 10−7	1.62 × 10−10	4.44 × 10−7	NA	NA	NA	NA	2.94 × 10−6	2.94 × 10−6	1.62 × 10−10	5.89 × 10−6	NA	NA	NA	NA
Total	3.20 × 10−2	2.52 × 10−2	3.15 × 10−4	5.75 × 10−2	4.51 × 10−6	3.83 × 10−6	7.28 × 10−12	8.34 × 10−6	9.80 × 10−1	2.75 × 10−1	3.15 × 10−4	1.26 × 10	1.05 × 10−5	7.78 × 10−8	1.82 × 10−12	1.06 × 10−5
Region II
Cd	1.02 × 10−5	8.97 × 10−6	4.62 × 10−7	1.97 × 10−5	NA	NA	2.85 × 10−15	2.85 × 10−15	2.34 × 10−4	8.37 × 10−5	4.62 × 10−7	3.19 × 10−4	NA	NA	7.13 × 10−16	7.13 × 10−16
As	2.48 × 10−3	2.12 × 10−3	2.55 × 10−5	4.62 × 10−3	3.82 × 10−7	3.27 × 10−7	5.64 × 10−13	7.09 × 10−7	8.09 × 10−2	2.31 × 10−2	2.55 × 10−5	1.04 × 10−1	8.92 × 10−7	6.24 × 10−9	1.41 × 10−13	8.98 × 10−7
Cu	1.08 × 10−5	3.08 × 10−7	5.54 × 10−9	1.11 × 10−5	NA	NA	NA	NA	1.01 × 10−4	7.06 × 10−6	5.54 × 10−9	1.08 × 10−4	NA	NA	NA	NA
Pb	1.92 × 10−5	5.47 × 10−7	1.06 × 10−8	1.97 × 10−5	1.96 × 10−10	NA	1.42 × 10−16	1.96 × 10−10	1.79 × 10−4	1.25 × 10−5	1.06 × 10−8	1.92 × 10−4	4.56 × 10−10	3.20 × 10−12	3.55 × 10−17	4.60 × 10−10
Cr	1.02 × 10−5	8.90 × 10−6	1.37 × 10−7	1.92 × 10−5	4.58 × 10−9	NA	3.96 × 10−13	4.58 × 10−9	2.33 × 10−4	8.31 × 10−5	1.37 × 10−7	3.16 × 10−4	1.07 × 10−8	2.99 × 10−9	9.90 × 10−14	1.37 × 10−8
Zn	2.28 × 10−6	6.50 × 10−8	1.17 × 10−9	2.35 × 10−6	NA	NA	NA	NA	2.13 × 10−5	1.49 × 10−6	1.17 × 10−9	2.28 × 10−5	NA	NA	NA	NA
Hg	1.14 × 10−5	4.65 × 10−6	5.88 × 10−9	1.61 × 10−5	NA	NA	NA	NA	1.07 × 10−4	1.07 × 10−4	5.88 × 10−9	2.13 × 10−4	NA	NA	NA	NA
Total	2.54 × 10−3	2.14 × 10−3	2.61 × 10−5	4.71 × 10−3	3.87 × 10−7	3.27 × 10−7	9.63 × 10−13	7.14 × 10−7	8.18 × 10−2	2.34 × 10−2	2.61 × 10−5	1.05 × 10−1	9.03 × 10−7	9.24 × 10−9	2.41 × 10−13	9.12 × 10−7
Region III
Cd	4.48 × 10−3	3.93 × 10−3	2.02 × 10−4	8.60 × 10−3	NA	NA	1.25 × 10−12	1.25 × 10−12	1.03 × 10−1	3.66 × 10−2	2.02 × 10−4	1.39 × 10−1	NA	NA	3.12 × 10−13	3.12 × 10−13
As	4.09E × 10	3.50E × 10	4.21 × 10−2	7.63E × 10	6.31 × 10−4	5.40 × 10−4	9.31 × 10−10	1.17 × 10−3	1.34E × 102	3.82E × 101	4.21 × 10−2	1.72E × 102	1.47 × 10−3	1.03 × 10−5	2.33 × 10−10	1.48 × 10−3
Cu	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Pb	1.19 × 10−2	3.39 × 10−4	6.60 × 10−6	1.22 × 10−2	1.21 × 10−7	NA	8.82 × 10−14	1.21 × 10−7	1.11E× 10−1	7.78 × 10−3	6.60 × 10−6	1.19 × 10−1	2.83 × 10−7	1.98 × 10−9	2.21 × 10−14	2.85 × 10−7
Cr	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Zn	8.70 × 10−4	2.48 × 10−5	4.48 × 10−7	8.95 × 10−4	NA	NA	NA	NA	8.12 × 10−3	5.68 × 10−4	4.48 × 10−7	8.69 × 10−3	NA	NA	NA	NA
Hg	7.49 × 10−3	3.05 × 10−3	3.85 × 10−6	1.05 × 10−2	NA	NA	NA	NA	6.99 × 10−2	6.99 × 10−2	3.85 × 10−6	1.40 × 10−1	NA	NA	NA	NA
Total	4.12E × 10	3.51× 10	4.23 × 10−2	7.66 × 10	6.31 × 10−4	5.40 × 10−4	9.33 × 10−10	1.17 × 10−3	1.34 × 102	3.83 × 101	4.23 × 10−2	1.72 × 102	1.47 × 10−3	1.03 × 10−5	2.33 × 10−10	1.48 × 10−3
Region VI
Cd	2.10 × 10−2	1.84 × 10−2	9.47 × 10−4	4.03 × 10−2	NA	NA	5.85 × 10−12	5.85 × 10−12	4.81 × 10−1	1.72 × 10−1	9.47 × 10−4	6.54 × 10−1	NA	NA	1.46 × 10−12	1.46 × 10−12
As	5.89 × 10	5.03 × 10	6.06 × 10−2	1.10E × 101	9.09 × 10−4	7.77 × 10−4	1.34 × 10−9	1.69 × 10−3	1.92 × 102	5.50 × 101	6.06 × 10−2	2.47 × 102	2.12 × 10−3	1.48 × 10−5	3.35 × 10−10	2.13 × 10−3
Cu	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Pb	4.46 × 10−2	1.27 × 10−3	2.47 × 10−5	4.59 × 10−2	4.55 × 10−7	NA	3.31 × 10−13	4.55 × 10−7	4.16 × 10−1	2.91 × 10−2	2.47 × 10−5	4.46 × 10−1	1.06 × 10−6	7.43 × 10−9	8.27 × 10−14	1.07 × 10−6
Cr	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Zn	4.50 × 10−3	1.28 × 10−4	2.31 × 10−6	4.63 × 10−3	NA	NA	NA	NA	4.20 × 10−2	2.94 × 10−3	2.31 × 10−6	4.49 × 10−2	NA	NA	NA	NA
Hg	7.62 × 10−3	3.10 × 10−3	3.92 × 10−6	1.07 × 10−2	NA	NA	NA	NA	7.12 × 10−2	7.12 × 10−2	3.92 × 10−6	1.42 × 10−1	NA	NA	NA	NA
Total	5.97 × 10	5.06 × 10	6.16 × 10−2	1.11 × 101	9.09 × 10−4	7.77 × 10−4	1.35 × 10−9	1.69 × 10−3	1.93E × 102	5.52 × 101	6.16 × 10−2	2.49 × 102	2.12 × 10−3	1.48 × 10−5	3.37 × 10−10	2.14 × 10−3
Region V
Cd	2.30 × 10−2	2.02 × 10−2	1.04 × 10−3	4.43 × 10−2	NA	NA	6.42 × 10−12	6.42 × 10−12	5.28 × 10−1	1.89 × 10−1	1.04 × 10−3	7.18 × 10−1	NA	NA	1.61 × 10−12	1.61 × 10−12
As	4.35 × 101	3.72 × 101	4.48 × 10−1	8.11 × 101	6.71 × 10−3	5.74 × 10−3	9.90 × 10−9	1.24 × 10−2	1.42 × 103	4.06 × 102	4.48 × 10−1	1.83 × 103	1.57 × 10−2	1.10 × 10−4	2.48 × 10−9	1.58 × 10−2
Cu	8.26 × 10−3	2.35 × 10−4	4.23 × 10−6	8.50 × 10−3	NA	NA	NA	NA	7.71 × 10−2	5.40 × 10−3	4.23 × 10−6	8.25 × 10−2	NA	NA	NA	NA
Pb	1.67 × 10−1	4.75 × 10−3	9.23 × 10−5	1.71 × 10−1	1.70 × 10−6	NA	1.23 × 10−12	1.70 × 10−6	1.55 × 10	1.09 × 10−1	9.23 × 10−5	1.66 × 10	3.96 × 10−6	2.77 × 10−8	3.09 × 10−13	3.99 × 10−6
Cr	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Zn	7.38 × 10−3	2.10 × 10−4	3.80 × 10−6	7.59 × 10−3	NA	NA	NA	NA	6.88 × 10−2	4.82 × 10−3	3.80 × 10−6	7.37 × 10−2	NA	NA	NA	NA
Hg	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Total	4.37 × 101	3.72 × 101	4.49 × 10−1	8.14 × 101	6.71 × 10−3	5.74 × 10−3	9.91 × 10−9	1.24 × 10−2	1.42 × 103	4.06 × 102	4.49 × 10−1	1.83 × 103	1.57 × 10−6	1.10 × 10−4	2.48 × 10−9	1.58 × 10−2
Region VI
Cd	1.89 × 10−2	1.66 × 10−2	8.54 × 10−4	3.64 × 10−2	NA	NA	5.27 × 10−12	5.27 × 10−12	4.34 × 10−1	1.55 × 10−1	8.54 × 10−4	5.89 × 10−1	NA	NA	1.32 × 10−12	1.32 × 10−12
As	1.13 × 102	9.66 × 101	1.16E × 10	2.11 × 102	1.74 × 10−2	1.49 × 10−2	2.57 × 10−8	3.23 × 10−2	3.69 × 103	1.05 × 103	1.16 × 10	4.74 × 103	4.07 × 10−2	2.85 × 10−4	6.43 × 10−9	4.09 × 10−2
Cu	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Pb	3.92 × 10−2	1.12 × 10−3	2.17 × 10−5	4.04 × 10−2	4.00 × 10−7	NA	2.91 × 10−13	4.00 × 10−7	3.66 × 10−1	2.56 × 10−2	2.17 × 10−5	3.92 × 10−1	9.34 × 10−7	6.54 × 10−9	7.27 × 10−14	9.40 × 10−7
Cr	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Zn	1.79 × 10−3	5.09 × 10−5	9.19 × 10−7	1.84 × 10−3	NA	NA	NA	NA	1.67 × 10−2	1.17 × 10−3	9.19 × 10−7	1.78 × 10−2	NA	NA	NA	NA
Hg	2.04 × 10−2	8.32 × 10−3	1.05 × 10−5	2.88 × 10−2	NA	NA	NA	NA	1.91 × 10−1	1.91 × 10−1	1.05 × 10−5	3.82 × 10−1	NA	NA	NA	NA
Total	1.13 × 102	9.66 × 101	1.16 × 10	2.11× 102	1.74 × 10−2	1.49 × 10−2	2.57 × 10−8	3.23 × 10−2	3.69 × 103	1.05 × 103	1.16 × 10	4.75 × 103	4.07 × 10−2	2.85 × 10−4	6.43 × 10−9	4.09 × 10−2
Region VII
Cd	7.75 × 10−4	7.64 × 10−4	3.93 × 10−5	1.58 × 10−3	NA	NA	2.43 × 10−13	2.43 × 10−13	1.78 × 10−2	7.13 × 10−3	3.93 × 10−5	2.49 × 10−2	NA	NA	6.07 × 10−14	6.07 × 10−14
As	1.39 × 10	4.40 × 10−1	1.43 × 10−2	1.84E × 10	2.14 × 10−4	6.79 × 10−5	3.15 × 10−10	2.82 × 10−4	1.68 × 101	1.29 × 101	1.43 × 10−2	2.98 × 101	4.99 × 10−4	1.30 × 10−6	7.88 × 10−11	5.00 × 10−4
Cu	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Pb	3.63 × 10−3	8.56 × 10−5	2.01 × 10−6	3.71 × 10−3	3.70 × 10−8	NA	2.69 × 10−14	3.70 × 10−8	3.38 × 10−2	1.96 × 10−3	2.01 × 10−6	3.58 × 10−2	8.63 × 10−8	5.01 × 10−10	6.72 × 10−15	8.68 × 10−8
Cr	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Zn	2.87 × 10−4	8.03 × 10−6	1.48 × 10−7	2.95 × 10−4	NA	NA	NA	NA	2.68 × 10−3	1.84 × 10−4	1.48 × 10−7	2.87 × 10−3	NA	NA	NA	NA
Hg	1.17 × 10−2	3.88 × 10−3	6.01 × 10−6	1.55 × 10−2	NA	NA	NA	NA	1.09 × 10−1	8.88 × 10−2	6.01 × 10−6	1.98 × 10−1	NA	NA	NA	NA
Total	1.40 × 10	4.45 × 10−1	1.43 × 10−2	1.86 × 10	2.14 × 10−4	6.79 × 10−5	3.16 × 10−10	2.82 × 10−4	1.70 × 101	1.30 × 101	1.43 × 10−2	3.00 × 101	4.99 × 10−4	1.30 × 10−6	7.89 × 10−11	5.00 × 10−4
Region VIII
Cd	3.78 × 10−4	6.94 × 10−5	3.57 × 10−6	4.51 × 10−4	NA	NA	2.20 × 10−14	2.20 × 10−14	6.48 × 10−4	8.67 × 10−3	3.57 × 10−6	9.32 × 10−3	NA	NA	5.51 × 10−15	5.51 × 10−15
As	2.89 × 10−1	6.87 × 10−2	7.07 × 10−4	3.58 × 10−1	1.06 × 10−5	4.46 × 10−5	1.56 × 10−11	5.52 × 10−5	6.41 × 10−1	1.10 × 101	7.07 × 10−4	1.17 × 101	2.47 × 10−5	8.52 × 10−7	3.91 × 10−12	2.56 × 10−5
Cu	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Pb	1.80 × 10−2	2.89 × 10−4	9.98 × 10−6	1.83 × 10−2	1.84 × 10−7	NA	1.33 × 10−13	1.84 × 10−7	1.68 × 10−1	6.62 × 10−3	9.98 × 10−6	1.75 × 10−1	4.28 × 10−7	1.69 × 10−9	3.34 × 10−14	4.30 × 10−7
Cr	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Zn	2.44 × 10−4	6.69 × 10−6	1.25 × 10−7	2.50 × 10−4	NA	NA	NA	NA	2.27 × 10−3	1.53 × 10−4	1.25 × 10−7	2.43 × 10−3	NA	NA	NA	NA
Hg	1.07 × 10−3	1.06 × 10−3	5.52 × 10−7	2.13 × 10−3	NA	NA	NA	NA	1.00 × 10−2	2.42 × 10−2	5.52 × 10−7	3.42 × 10−2	NA	NA	NA	NA
Total	3.09 × 10−1	7.01 × 10−2	7.21 × 10−4	3.80 × 10−1	1.08 × 10−5	4.46 × 10−5	1.58 × 10−11	5.54 × 10−5	8.22 × 10−1	1.11 × 101	7.21 × 10−4	1.19 × 101	2.51 × 10−5	8.54 × 10−7	3.95 × 10−12	2.60 × 10−5
Region IX
Cd	1.87 × 10−3	1.64 × 10−3	8.46 × 10−5	3.60 × 10−3	NA	NA	5.22 × 10−13	5.22 × 10−13	4.30 × 10−2	1.53 × 10−2	8.46 × 10−5	5.84 × 10−2	NA	NA	1.31 × 10−13	1.31 × 10−13
As	1.56 × 10−1	1.33 × 10−1	1.61 × 10−3	2.91 × 10−1	2.41 × 10−5	2.06 × 10−5	3.55 × 10−11	4.47 × 10−5	5.10 × 10	1.46 × 10	1.61 × 10−3	6.56 × 10	5.62 × 10−5	3.93 × 10−7	8.88 × 10−12	5.66 × 10−5
Cu	1.24 × 10−3	3.53 × 10−5	6.34 × 10−7	1.27 × 10−3	NA	NA	NA	NA	1.16 × 10−2	8.09 × 10−4	6.34 × 10−7	1.24 × 10−2	NA	NA	NA	NA
Pb	8.47 × 10−2	2.41 × 10−3	4.70 × 10−5	8.72 × 10−2	8.64 × 10−7	NA	6.28 × 10−13	8.64 × 10−7	7.91 × 10−1	5.53 × 10−2	4.70 × 10−5	8.46 × 10−1	2.02 × 10−6	1.41 × 10−8	1.57 × 10−13	2.03 × 10−6
Cr	4.23 × 10−2	4.83 × 10−2	6.54 × 10−4	9.13 × 10−2	2.18 × 10−5	NA	1.88 × 10−9	2.18 × 10−5	1.11 × 10	3.95 × 10−1	6.54 × 10−4	1.50 × 10	5.08 × 10−5	1.42 × 10−5	4.71 × 10−10	6.50 × 10−5
Zn	7.50 × 10−4	2.14 × 10−5	3.86 × 10−7	7.72 × 10−4	NA	NA	NA	NA	7.00 × 10−3	4.90 × 10−4	3.86 × 10−7	7.49 × 10−3	NA	NA	NA	NA
Hg	1.69 × 10−3	6.88 × 10−4	8.70 × 10−7	2.38 × 10−3	NA	NA	NA	NA	1.58 × 10−2	1.58 × 10−2	8.70 × 10−7	3.15 × 10−2	NA	NA	NA	NA
Total	2.89 × 10−1	1.86 × 10−1	2.39 × 10−3	4.78 × 10−1	4.67 × 10−5	2.06 × 10−5	1.92 × 10−9	6.73 × 10−5	7.07 × 10	1.94 × 10	2.39 × 10−3	9.01 × 10	1.09 × 10−4	1.46 × 10−5	4.80 × 10−10	1.24 × 10−4
Region X
Cd	8.88 × 10−3	7.79 × 10−3	4.01 × 10−4	1.71 × 10−2	NA	NA	2.48 × 10−12	2.48 × 10−12	2.04 × 10−1	7.27 × 10−2	4.01 × 10−4	2.77 × 10−1	NA	NA	6.19 × 10−13	6.19 × 10−13
As	3.41 × 10−1	2.92 × 10−1	3.51 × 10−3	6.37 × 10−1	5.26 × 10−5	4.50 × 10−5	7.77 × 10−11	9.77 × 10−5	1.11 × 101	3.18 × 10	3.51 × 10−3	1.43 × 101	1.23 × 10−4	8.60 × 10−7	1.94 × 10−11	1.24 × 10−4
Cu	2.89 × 10−3	8.24 × 10−5	1.48 × 10−6	2.97 × 10−3	NA	NA	NA	NA	2.70 × 10−2	1.89 × 10−3	1.48 × 10−6	2.89 × 10−2	NA	NA	NA	NA
Pb	1.76 × 10−1	5.03 × 10−3	9.78 × 10−5	1.82 × 10−1	1.80 × 10−6	NA	1.31 × 10−12	1.80 × 10−6	1.65 × 10	1.15 × 10−1	9.78 × 10−5	1.76 × 10	4.20 × 10−6	2.94 × 10−8	3.27 × 10−13	4.23 × 10−6
Cr	2.47 × 10−2	2.17 × 10−2	3.35 × 10−4	4.67 × 10−2	1.11 × 10−5	NA	9.64 × 10−10	1.11 × 10−5	2.02 × 10−1	5.66 × 10−1	3.35 × 10−4	7.69 × 10−1	2.60 × 10−5	7.28 × 10−6	2.41 × 10−10	3.33 × 10−5
Zn	8.02 × 10−4	2.29 × 10−5	4.13 × 10−7	8.25 × 10−4	NA	NA	NA	NA	7.48 × 10−3	5.24 × 10−4	4.13 × 10−7	8.01 × 10−3	NA	NA	NA	NA
Hg	2.63 × 10−3	1.07 × 10−3	1.35 × 10−6	3.70 × 10−3	NA	NA	NA	NA	2.45 × 10−2	2.45 × 10−2	1.35 × 10−6	4.91 × 10−2	NA	NA	NA	NA
Total	5.58 × 10−1	3.27 × 10−1	4.35 × 10−3	8.89 × 10−1	6.56 × 10−5	4.50 × 10−5	1.05 × 10−9	1.11 × 10−4	1.33 × 101	3.97 × 10	4.35 × 10−3	1.72 × 101	1.53 × 10−4	8.17 × 10−6	2.61 × 10−10	1.61 × 10−4

. The total noncarcinogenic risk was higher in children than in adults at 10 contaminated sites. The reason for this may be related to children’s lifestyle and physical characteristics (playing places and unhealthy eating habits), leading to children having more opportunities to contact soil particles polluted with heavy metals than adults [46]. In terms of individual elements, the THI values of adults for As in regions III, IV, V, VI, and VII exceeded the safety threshold (1.0). Except for regions II and X, the THI values of children for As exceeded the safety threshold (1.0). The potential mixture effect values of adults in regions III, IV, V, VI, and VII exceeded the safety threshold (1.0) and were 7.66, 11.09, 81.36, 210.79, and 1.86, respectively (Figure 2). Except for region II, the potential mixture effects value of children exceeded the safety threshold (1.0) (Figure 2). This is due to the high concentration of As in the soil, high noncarcinogenic risk to humans, and the low standard value of RfD.

Heavy metals in soil can enter the human body via three pathways: oral soil intake, skin contact and respiratory inhalation. Table A2 shows that for both adults and children, oral soil intake is the main exposure route in the study area, followed by dermal soil intake and soil intake by inhalation. Therefore, local residents and the government should consider protecting the health of people, limit people entering the vicinity of contaminated sites and encourage relevant protection research.

3.2.2. Cancer Risk

The total CRs basically exceeded the cancer risk value of 1 × 10⁻⁴, except for regions I, II and VIII (Figure 2). The total cancer risk resulted mainly from arsenic and comprised mostly oral and dermal risks, while the inhalation cancer risks were insignificantly similar to noncarcinogenic risks. Except for regions I, II and VII, the minimum total cancer risk value of As is one order of magnitude higher than the target value. Other research has found that arsenic is the primary contributor to total cancer and noncancer hazards in contaminated locations [47,48]. A previous study showed that health risks are mainly caused by direct oral intake of contaminated soils rather than dermal contact and inhalation. The inhalation cancer risks were insignificant and could be overlooked similarly to noncarcinogenic risks.

3.3. Remedial Analysis of Site-Specific Risks

When the health risk assessment value exceeds the baseline for the accepted risk level (noncancer target risk value and cancer target risk value), the remedial level repair target value is calculated (

Table 3. Summary of soil risk-based remedial levels (RBRLs: mg/kg) for regions I–X.

Regions I–X	Adults						Children
	RBRLs for Noncancer Risk			RBRLs for Cancer Risk			RBRLs for Noncancer Risk			RBRLs for Cancer Risk
Element	Oral	Dermal	Inhalation	Oral	Dermal	Inhalation	Oral	Dermal	Inhalation	Oral	Dermal	Inhalation
Cd	1.75 × 104	1.60 × 103	1.42 × 104	3.38 × 101	NA	6.57 × 104	7.82 × 101	3.43 × 10	1.42 × 104	1.45 × 101	NA	2.63 × 105
As	5.26 × 103	6.40 × 102	2.13 × 104	1.42 × 102	1.70 × 102	2.74 × 104	2.35 × 101	3.65 × 101~8.61 × 101	2.13 × 104	6.08 × 101	5.10 × 103	1.10 × 105
Cu	7.01 × 105	7.68 × 105	5.70 × 107	NA	NA	NA	3.13 × 103	4.12 × 103	5.70 × 107	NA	NA	NA
Cr	5.26 × 104	3.84 × 103	4.06 × 104	5.07 × 10	NA	9.85 × 103	2.35 × 102	2.06 × 101	4.06 × 104	2.17 × 10	NA	3.94 × 104
Zn	5.26 × 106	1.92 × 107	4.25 × 108	NA	NA	NA	2.35 × 104	2.06 × 104	4.25 × 108	NA	NA	NA
Hg	5.26 × 103	1.34 × 103	4.25 × 105	NA	NA	NA	2.35E × 101	7.20 × 10	4.25 × 105	NA	NA	NA

Note: The background values of arsenic in regions I~X are 36.5 mg/kg, 39.1 mg/kg, 58.1 mg/kg, 86.1 mg/kg, 62.3 mg/kg, 43.2 mg/kg, 76.1 mg/kg, 66.4 mg/kg, 70.1 mg/kg, 61.2 mg/kg, respectively. The background values of lead in regions I~X are 65.1 mg/kg, 79.1 mg/kg, 67.1 mg/kg, 68.1 mg/kg, 76.3 mg/kg, 54.2 mg/kg, 81.1 mg/kg, 46.4 mg/kg, 80.1 mg/kg, and 81.2 mg/kg, respectively.

). The RBRLs_lowest for noncarcinogenic effects is equal to the NTR (HI) of 1. In terms of cancer risk, only heavy metals (arsenic) were the major carcinogenic risk substances in different study areas. Therefore, the TCR risk value of 1 × 10⁻⁶ was adjusted to 1 × 10⁻⁵ [35,49].

The results of Table 3 show that the RBRLs_lowest for children were significantly lower than that for adults in all regions. Since children are more susceptible to the health impacts of heavy metals, even at extremely low levels, they must be protected. For adults, the RBRLs_lowest values of Cu, Zn and Hg were based on noncarcinogenic risks and were higher than those of all analysed samples. The RBRLs_lowest values of Cd, As and Cr were based on carcinogenic risks and were lower than the maximum values. For children, the RBRLs_lowest values of Cd, As, Cu and Hg were lower than the maximum value for all analysed samples based on noncarcinogenic risk, while that of Zn was higher than the maximum value. The RBRLs_lowest of Cr was lower than that of all analysed samples based on carcinogenic risk. As shown in Table 3, the RBRLs_lowest is determined mainly by exposure by oral and respiratory routes.

This study took Pb as an example. The RBRLs_lowest values were assessed individually as a special case with a PbB of 10 μg/dL as the goal and a maximum value that was lower than the applicable maximum value. The industrial Pb RBRLs amounted to 331 mg/kg and were higher than the region I~X background levels for lead (Table 3).

3.4. Priority Control Regions and Recommendations

The health risk assessment results of different sites are shown in Table A2, and the urgency of the remediation of contaminated sites is analyzed according to the risk values. The results show that the total risk value of each region is ranked as follows: Region VI > Region V > Region IV > Region III > Region VII > Region X > Region IX > Region VIII > Region I > Region II.

Arsenic contributes the most to the total risk of each region and is the main metal causing the health risk of all regions, followed by the heavy metals Pb, Cr and Cd, and the contributions of the heavy metals Cu, Zn and Hg are almost negligible. Further analysis found that the order of total risk for As (adult or child, noncarcinogenic or cancer) was basically consistent with the order of total risk values for each region. Therefore, the urgency of remediation at each site is mainly related to the heavy metal arsenic. Reasonable management techniques should concentrate on how to regulate pollution cleanup as effectively as possible, some of which are detailed below.

(1) Given the enormous impact of mining operations in priority control regions, comprehensive environmental protection legislation enforcement is essential, particularly with regard to large emission sources such as mining smelting and other metal consuming sectors. Although all mining firms in China are obligated by law to engage in environmental restoration efforts, mining enterprises continue to cause substantial harm to the environment via pollution owing to the use of antiquated technology and inefficiency of mining operations.

(2) It is critical to establish strict monitoring in these areas, since this will allow for a realistic assessment of the existing contamination state and forecasting of future trends. Note that to acquire precise contamination characteristics of soil arsenic, more frequent routine sampling is needed. Only by obtaining real and exact concentrations and geographical dispersion findings will policy-makers be able to provide better guidelines for precision control.

(3) Physical, chemical, and biological cleanup of arsenic-contaminated soils are the most often used methods. For the remediation of polluted soil, bioremediation has been seen as a low-cost, ecologically benign method [50]. Plant-microbial joint remediation technology has been used to carry out research. The sizes and costs determine which methods may be employed in polluted site cleanup.

4. Conclusions

This study provides valuable information for health risk assessment and risk remediation at different contaminated sites. The results of health risk assessment shown that arsenic and chromium have higher non-carcinogenic and carcinogenic risks than other trace elements. The risk assessment results and the developed RBRLs could also be used to identify the priority area for remediation. Management recommendations such as minimizing pollutant input, creating tight monitoring systems, and implementing biological remediation were made in order to safeguard Chinese inhabitants from heavy metal contamination. Implementing these techniques necessitates not only technology advancement, but also socioeconomic evaluation and efficient implementation of environmental protection regulations by local governments.

The risk assessment employed in this study includes several potential uncertainties, such as model selection and localized parameter values. It should also be noted that when planning the remediation strategy of the site, apart from human health risk, several other aspects must be taken into account, such as economic cost, implementation, and environmental impact. Further studies are required to focus on areas with a high health risk from As combined with local specific conditions and application of more accurate spatial distribution expression approaches to make remediation actions conducive to implementation.