Distribution, sources, and ecological risk assessment of HCHs and DDTs in water from a typical coal mining subsidence area in Huainan, China
Coal mining subsidence areas are a special and widespread ecosystem in China and many developing countries in the world. However, limited research has focused on HCHs and DDTs in coal mining subsidence areas. Investigating the concentration, distribution, and sources of HCHs and DDTs at the Yangzhuang coal mining subsidence area in Huainan, China, is the object of this study. Water samples from different depths were collected from this region to detect and analyze HCHs and DDTs using gas chromatography–mass spectrometry. The result showed that the concentrations of HCHs and DDTs increased with increasing water depth, and the average concentrations of HCHs and DDTs in the top (T-layer), middle (M-layer), and bottom (B-layer) layers were 152, 169, and 182 ng∙L−1, respectively. Spatial distribution of HCH and DDT concentrations in the study area revealed that the concentrations gradually decreased in the direction of water flow, and the highest concentration was observed at the entrance of the Nihe River. The T-layer was easily influenced by environmental and human activities, while the M-layer and B-layer were mainly influenced by sediment. Using principal component analysis and diagnostic ratios, we found that HCHs and DDTs in the study area mainly originated due to natural and human activities (such as pesticide use). Hexachlorocyclohexanes (HCHs) were mainly derived from lindane, and dichlorodiphenyltrichloroethanes (DDTs) mainly originated due to the recent agricultural use of dicofol; both of these are directly related to agricultural activities. Based on a comparison of reported concentrations of HCHs and DDTs in the rivers and lakes throughout China, we found that the overall ecological risk of HCHs and DDTs in the study area was elevated. The results are important for further understanding the transfer characteristics of HCHs and DDTs as well as the ecological health of the water in coal mining subsidence areas.
Keywords: Coal mining subsidence; Water; Hexachlorocyclohexanes; Dichlorodiphenyltrichloroethanes; Huainan
Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s11356-022-20087-3.
Introduction
Organochlorine pesticides (OCPs) are semivolatile organic pollutants (Jones et al. 2017), characterized by chemical durability, nondegradability, and bioaccumulation (Liu et al. [18]; Wang et al. [36]). They can migrate in the environment and accumulate in organisms, causing environmental neurotoxicity (Dewan et al. [6]), carcinogenicity (Siddarth et al. [30]; VoPham et al. [33]), neurotoxicity (Parron et al. [26]), and immunotoxicity (Freire et al. [9]). OCPs include hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), aldrin, heptachlor, and endrin. Among them, HCHs (including α-HCH, β-HCH, γ-HCH, and δ-HCH) and DDTs (including o,p′-DDT, p,p′-DDT, o,p′-DDD, p,p′-DDD, o,p′-DDE, and p,p′-DDE) are usually the main components of OCPs and widely studied; they have been identified as priority pollutants by the United States Environmental Protection Agency (US EPA) and placed on China's priority control list (GB 3838–2002 2002). Previous studies have shown that HCHs and DDTs primarily originated due to natural and human activities, and human activities usually had a greater impact (Nguyen et al. [21]; Lisouza et al. [15]; Sah et al. [28]; Olisah et al. [22]). Once HCHs and DDTs are produced, they are transported through the atmosphere and/or flowing water and eventually accumulate in the water, soil, and sediment of rivers, lakes, subsidence areas, etc. (Lisouza et al. [15]). Therefore, water bodies are carriers for the transmission and accumulation of HCHs and DDTs, leading to HCHs and DDTs pollution.
China is one of the largest energy consumers in the world. Coal plays an important role in energy production, accounting for 76% and 66% of primary energy production and consumption in China, respectively (Yuan et al. [41]; Yuan et al. 2017). China's raw coal production reached 3.75 billion tons in 2019, an increase of 4.2% from 2018 to 2019 (Data from National Bureau of Statistics of the People's Republic of China). Thus, coal may continue to be China's main energy source in the future. The Huainan coalfield is located in the northern part of Anhui Province, which is an important coal production area in China. Huainan accounts for 70% and 32% of the coal production in Anhui Province and in eastern China, respectively. Therefore, Huainan, a famous industrial city, is known as China's energy capital and East China's industrial granary (Zhang et al. [46]). The development of the mining industry has stimulated the development of electric power and coal chemical industries. Although these developments resulted in huge economic benefits (Wang et al. [35]), they caused various environmental problems, such as surface collapse, surface water pollution, and groundwater pollution (Ouyang et al. [24]; Zhang et al. [49]). Before coal mining, most of the land surface in the Huainan region was farmland, where crops such as wheat, soybeans, corn, and rice were grown. Long-term mining activities have caused surface subsidence and formed a closed water body similar to a lake in the subsidence area, which transformed the original land environment into an aquatic environment, and the original surface soil evolved into aquatic sediments (Zhang et al. [47], [48]). Changes in the subsidence area have resulted in the formation of a specific environment contaminated by agricultural nonpoint-source and coal mine pollutants. The water in the subsidence area is often used for fish farming and agricultural irrigation, which may indirectly affect the drinking water quality and physical health of surrounding residents. Therefore, it is essential to understand the concentrations, sources, and distributions of HCHs and DDTs in the water of the coal mining subsidence area before environmental protection measures can be taken.
In the past decade, researchers have mostly focused on HCH and DDT pollution in water bodies such as rivers, lakes, and bays (Dai et al. [5]; Lisouza et al. [15]; Sah et al. [28]; Olisah et al. [22]); however, limited research has been reported on HCH and DDT pollution in mining subsidence areas. In the Huainan coalfield, studies on water pollutants in mining subsidence areas mainly focused on heavy metals (Chen et al. [3]), nitrogen (Yi et al. [39]), and phosphorus (Zhang et al. [47], [48]), but the characteristics of HCHs and DDTs in coal mining subsidence water were unclear. Water in the Huainan coal mining subsidence area is not only an important ecological resource but also an important daily and agricultural water source for local residents; thus, it is important to conduct research on HCHs and DDTs in the water of the study area.
For determining the primary distribution and sources of HCHs and DDTs at different water depths in the subsidence area, this study has the following objectives:
- To analyze concentration and distribution of HCHs and DDTs in the water
- To identify the major sources of HCHs and DDTs in the water
- To assess the ecological risk of HCHs and DDTs in the water of the coal mining subsidence area.
Materials and methods
Study area
The Huainan coalfield is located on the southeastern margin of the North China Plate, with a total coalfield area of 3200 km2 (Zhang et al. [49]). Coal mining activity in the area has resulted in the formation of several deep and large subsidence water bodies over the years. By the end of 2015, the Huainan coal mining subsidence area in the southeastern part of the coalfield had reached ~ 245 km2 (Ouyang et al. [23]). The Yangzhuang coal mining subsidence area is the most important part of the Huainan coalfield mining subsidence, with an area of 4 km2.
The Yangzhuang coal mining subsidence area is the largest subsidence area with the longest subsidence time of 20 years among the coal mining subsidence areas in Huainan coalfield (Ouyang et al. [23]). The water depth of the Yangzhuang coal mining subsidence area, which is connected to the Nihe River, ranges from 2 to 7 m, with an average of 4 m. A large amount of sewage discharged from the surrounding residences and coal mines flows into the subsidence area through the Nihe River, causing different degrees of pollution in the water body (Ouyang et al. [25]). However, the nearby residents have used the water in the subsidence area to stock fish fry and raise fish to sell to the consumer market. Around the subsidence area, a large area of farmland is planted with mainly rice and wheat. Additionally, a coal gangue hill is located near the subsidence area.
Sampling
In August 2019, we collected and analyzed samples from the Yangzhuang coal mining subsidence area based on our several on-site investigations of this area and its surroundings. Seven sampling points were arranged using GPS, as shown in Fig. 1. At each sampling point, we collected three water samples using a polyethylene bucket from different layers: top (T-layer), middle (M-layer), and bottom (B-layer) layers. The T-layer was 0.5 m below the water surface, the B-layer was 0.5 m above the bottom of the water, and the M-layer was located between the T-layer and B-layer. The sampling depth of each sample is shown in Table S1. We placed 4 L of each sample in a brown glass bottle and brought the samples to the laboratory as soon as possible and analyzed them within 24 h.
Graph: Fig. 1 Geographical location of the study area and distribution of the sampling points
Materials and reagents
A C18 solid-phase extraction (SPE) column (1 g/3 mL, Waters, USA), anhydrous sodium sulfate, glass fiber filters, sodium hydroxide, and a blow concentrator (DN-12 W, Shanghai Omeng Industrial Co. LTD, China) were used for the pretreatment of samples. n-Hexane, dichloromethane, and methyl alcohol were used as reagents. These reagents were chromatographically pure (TEDIA Corporation, United States). α-HCH, β-HCH, γ-HCH, δ-HCH, p,p′-DDD, p,p′-DDE, o,p′-DDT, and p,p′-DDT (O2si, USA) were included in the standard mixture used herein. Pentachloronitrobenzene (Dr. Ehrenstorfer, Germany) was used as the injection standard. 2,4,5,6-Tetrachloro-m-xylene was used as the standard recovery rate indicator (Dr. Ehrenstorfer, Germany). All standards were diluted using n-hexane.
Sample extraction
The water samples were extracted by solid-phase extraction (SPE). The solid-phase extraction columns were activated with 3 mL of dichloromethane, 3 mL of methyl alcohol, and 3 mL of ultrapure water. Ten milliliters of methyl alcohol and recovery rate indicator were added into 1000 mL of water samples. Using vacuum pumping, water samples flowed via the SPE columns at a flow velocity of 10 mL/min. When the extraction was completed, the HCHs and DDTs captured in SPE columns were eluted with 8 mL of dichloromethane/n-hexane (7:3, V/V). Then, anhydrous sodium sulfate (roasted at 300 °C) was used to dehydrate the extracts, and then the extracts were concentrated to roughly 0.5 mL with high-purity nitrogen streaming. The extracts were spiked with internal standards and redissolved to 1 mL with n-hexane. Finally, the extracts were transferred into vials and kept sealed at – 20 °C until analysis.
Instrumental analysis
This experiment used a Clarus SQ8 GC–MS (PerkinElmer, USA) instrument, comprising Clarus 680 GC and SQ 8 mass spectrometer.
The chromatographic column was a fused silica capillary Elite-5/MS (30 m × 0.25 mm inner diameter and 0.25-µm film thickness, PerkinElmer, USA). Helium was used as the carrier gas with a flow rate of 1 ml/min. Each injection volume was 1 μL, with splitless injection. The temperature of the column inlet was 250 °C. The initial oven temperature was 80 °C, which was maintained for 1 min, then raised to 160 °C at a rate of 30 °C/min, maintained for 1 min, and finally raised to 265 °C at a rate of 3 °C/min and maintained for 1 min.
The ion-source and transmission-line temperatures of the mass spectrometer were 250 °C and 280 °C, respectively. The electron bombardment energy of the mass spectrometer was 70 eV, and MS was conducted in selected ion monitoring and full-scan mode, which was 50–500 m/z.
Quality assurance (QA)/quality control (QC)
For QA/QC, the quality control methods recommended by the US EPA were used to establish blank methods, parallel samples, and standard sample recovery rates. In the early stages of the experiment, the recovery rates of the mixed reference materials were all within the range of 70–140%. The recycling rates of tetrachloro-m-xylene were between 70 and 130%. The relative standard deviation between parallel samples was < 5%. No target contaminants were detected in the blank sample.
Results and discussion
Concentration and distribution of HCHs and DDTs
Concentration of HCHs and DDTs
Underground coal mining resulted in the coal mining subsidence area, where the surface gradually subsided and eventually formed a sink under the effect of rainfall. Previous studies have found that HCHs and DDTs can migrate through air, water, and sediment (Chrysikou et al. [4]; Jiao et al. [11]; Lisouza et al. [15]; Yang et al. [37]); therefore, the concentration of HCHs and DDTs in water bodies at the same location may vary greatly owing to the degree of influence of the atmosphere and sediment. In this study, each sampling point was divided into three layers, i.e., T-layer, M-layer, and B-layer, for sample collection. The concentrations of OCPs in the three layers of water were added and averaged (Table 1). The average concentrations of HCHs and DDTs in the three layers from top to bottom were 152, 169, and 182 ng∙L−1 (Table 1), respectively, showing that the concentrations of HCHs and DDTs increased as water depth increased as a whole.
Table 1 HCH and DDT statistics for different water depths in the Yangzhuang coal mining subsidence area (ng∙L−1)
Individual species | T-layer | M-layer | B-layer |
|---|
Min–Max | Mean | Min–Max | Mean | Min–Max | Mean |
|---|
α-HCH | 2.90–6.02 | 4.36 | 2.78–4.92 | 3.68 | 2.80–4.50 | 3.27 |
β-HCH | 8.78–14.9 | 11.4 | 8.3–16.0 | 11.2 | 9.79–13.3 | 10.9 |
γ-HCH | 20.8–26.1 | 22.8 | 20.7–26.5 | 23.7 | 20.5–26.1 | 21.6 |
δ-HCH | ND–43.5 | 27.2 | 33.3–41.4 | 35.8 | 33.2–38.5 | 35.9 |
o,p'-DDT | ND–45.1 | 30.6 | ND–49.9 | 36.4 | ND–52.6 | 38.9 |
p,p'-DDD | ND–15.7 | 11.2 | ND–16.5 | 13.5 | 15.5–18.0 | 16.2 |
p,p'-DDT | ND–89.6 | 44.0 | ND–81.8 | 44.6 | ND–81.5 | 54.8 |
p,p'-DDE | ND a | ND | ND | ND | ND–0.47 | 0.07 |
ΣHCHs | 38.0–83.0 | 65.9 | 67.7–81.2 | 74.3 | 67.8–75.2 | 71.6 |
ΣDDTs | ND–148 | 85.8 | 15.6–147 | 94.6 | 15.5–151 | 110 |
ΣHCHs + ΣDDTs | 38.0–218.14 | 152 | 93.6–217 | 169 | 84.7–222 | 182 |
aNot detected
To analyze the vertical change characteristics of HCHs and DDTs, in different layers (depths) of water, a box plot of the comparison of HCH and DDT concentrations at different water depths was designed, as shown in Fig. 2. The concentration of HCHs in the M-layer was slightly higher than that in the T-layer or B-layer, which might be related to the superimposed influence of the T-layer and B-layer. The concentration of HCHs in the T-layer fluctuated considerably (Fig. 2), suggesting that the T-layer was more easily influenced by the environment and human activities, while the concentration of HCHs in the B-layer was the most stable with little fluctuation (Fig. 2) owing to its depth and low external interferences. From top to bottom, the concentrations of DDTs gradually increased (Fig. 2), showing that concentrations increased from the water surface to the sediment. The concentrations of DDTs in the T-layer fluctuated more than those in the M-layer and B-layer (Fig. 2), and the concentrations of DDTs in the M-layer and B-layer showed similar fluctuation trends (Fig. 2), again indicating that the T-layer was more easily influenced by the environment and human activities, while the M-layer and B-layer were mainly influenced by sediment.
Graph: Fig. 2 Box plot of HCH and DDT concentration comparisons at different water depths in the Yangzhuang coal mining subsidence area
As shown in Fig. 3a, the proportion of δ-HCH is 46–54% and that of γ-HCH is 26–67%. The high concentration of γ-HCH was related to lindane input, which was proved by Yuan et al. ([42]). High concentrations of δ-HCH might be related to the conversion of α-HCH and γ-HCH pollutants (Yang et al. [38]). However, the reason for this phenomenon remains to be further studied. The residual forms of DDTs in most water samples were o,p′-DDT and p,p′-DDT. As shown in Fig. 3b, except SY02 and SY05, the proportion of o,p′-DDT is 29%–100%, and the proportion of p,p′-DDT is 53–60%, which may be related to pesticide contamination or industrial pollution (Metcalf et al. 1973). For the T-layer of SY02, the proportion of o,p′-DDT is 71% and that of p,p′-DDT is 29%. For SY05, only p,p′-DDD is detected (100%) in the M-layer and B-layer, which may be related to the surrounding environment (Qiu et al. [27]). For the M-layer of SY06, the proportion of o,p′-DDT was 100%, which may be related to the new input of the pesticide dicofol around the study area (Qiu et al. [27]); SY02 (T-layer), SY07 (M-layer), and SY03 (B-layer) were found to mainly contain o,p′-DDT and p,p′-DDD, which may be related to the low content of dissolved oxygen in the water body (Doong et al. [8]); however, the reason for this phenomenon remains to be further studied.
Graph: Fig. 3 Histograms of HCH and DDT compositions at different water depths in the Yangzhuang coal mining subsidence area
Spatial distribution of HCHs and DDTs
To compare the characteristics of HCH and DDT spatial distribution in a more direct way, the ArcGIS 10.2 software was used to analyze HCHs and DDTs at different depths (layers) of water. After the superposition of grids using the grid calculator, three interpolation diagrams were obtained (Figs.4a–c), which demonstrated that the HCH and DDT concentrations in the water samples from all three layers near the Nihe River were considerably higher than those in other samples. Our research group previously reported that a certain amount of HCHs and DDTs had accumulated in the water and sediment of the Nihe River owing to long-term agricultural activities nearby (Zhou et al. [51]). Therefore, the HCH and DDT concentrations were highest at the entrance of the Nihe River in the southwest (SY04 sampling point), and the concentrations gradually decreased along the direction of water flow. This trend was especially obvious in the M-layer (see Fig. 4b). The HCH and DDT concentrations at SY01 in Fig. 4a are higher than those of the surrounding water, which is probably related to the sampling location. SY01 is located in the stagnant area of the water body, where the water flow and circulation speed are slow and HCHs and DDTs are more prone to accumulation than to dilution and diffusion. The HCH and DDT concentrations close to sediments in the B-layer (Fig. 4c) are more stable, which indicates that the HCH and DDT concentrations in sediment are more balanced than those in water, except for local exceptions. At SY05 and SY03 sampling points, the HCH and DDT concentrations in the B-layer decrease (Fig. 4c), which may be related to the sediment background values. Therefore, the HCH and DDT concentrations were influenced by several complex factors, which require in-depth analysis and discussion to yield the significance of our work.
Graph: Fig. 4 Spatial distribution of HCHs and DDTs at different water depths in the Yangzhuang coal mining subsidence area: a T-layer, b M-layer, and c B-layer
Possible sources of HCHs and DDTs
Based on the dimensionality reduction idea of the principal component analysis (PCA) (Shen et al. [29]), the eight indicators of HCHs and DDTs in the seven water sampling sites were integrated into eight factors to analyze HCHs and DDTs pollution in the study area and identify the sources of the main residual HCH and DDT components. PCA obtained four valid PCs (PC1, PC2, PC3, and PC4) with eigenvalues of > 1.0 and a total cumulative variance of > 80% using the Kaiser criterion and scree-plot methods (Voutsis et al. [34]), as shown in Table 2. PC1 explained 34.380% of the total variance and was characterized by high positive loading for δ-HCH, o,p′-DDT, p,p′-DDD, and p,p′-DDT (Table 3), which represent DDT pesticide residues. PC2 explained 21.91% of the total variance and was characterized by high positive loading for γ-HCH and p,p′-DDT (Table 3), which may represent the use of lindane. PC3 explained 12.79% of the total variance and was characterized by high positive loading for α-HCH and p,p′-DDT (Table 3), which may represent natural factors or atmospheric deposition (Sun et al. [31]). PC4 explained 11.043% of the total variance and was characterized by high positive loading for α-HCH (Table 3), which may represent the pesticides from agricultural activities (Liu et al. [17]).
Table 2 Explanation of the variables obtained by principal component analysis
Component | Initial Eigenvalues | Extraction Sums of Squared Loadings |
|---|
Total | % of Variance | Cumulative % | Total | % of Variance | Cumulative % |
|---|
PC1 | 2.75 | 34.38 | 34.38 | 2.75 | 34.38 | 34.38 |
PC2 | 1.75 | 21.91 | 56.29 | 1.75 | 21.91 | 56.29 |
PC3 | 1.02 | 12.79 | 69.08 | 1.02 | 12.79 | 69.076 |
PC4 | 0.8 | 11.04 | 80.12 | 0.88 | 11.04 | 80.119 |
PC5 | 0.52 | 6.52 | 86.64 | | | |
PC6 | 0.49 | 6.11 | 92.75 | | | |
PC7 | 0.33 | 4.12 | 96.87 | | | |
PC8 | 0.25 | 3.13 | 100.00 | | | |
Table 3 Component matrix of HCHs and DDTs in the water of the Yangzhuang coal mining subsidence area
Individual species | Principal Component |
|---|
PC1 | PC2 | PC3 | PC4 |
|---|
α-HCH | − 0.512 | 0.206 | 0.546 | 0.501 |
β-HCH | 0.287 | − 0.742 | 0.171 | 0.383 |
γ-HCH | − 0.636 | 0.493 | − 0.170 | 0.174 |
δ-HCH | 0.601 | − 0.531 | 0.084 | 0.103 |
o,p'-DDT | 0.765 | 0.370 | 0.073 | 0.255 |
p,p'-DDD | 0.763 | 0.300 | − 0.300 | − 0.087 |
p,p'-DDT | 0.625 | 0.593 | 0.046 | 0.341 |
p,p'-DDE | 0.288 | 0.239 | 0.749 | − 0.506 |
Generally, HCH and DDT originate due to natural and human activities, and human activities have more influence. The ratio method was adopted to further analyze the source of HCHs and DDTs in the Yangzhuang coal mining subsidence area. In general, if β-HCH/(α-HCH + γ-HCH) < 0.5, there are new HCH inputs in this area, mainly from lindane or atmospheric sources (Liu et al. [17]). α-HCH and γ-HCH are the most volatile and persistent substances among the various isomers, and the characteristic ratio of α-HCH/γ-HCH is often used to identify the source of HCHs. If α-HCH/γ-HCH ≤ 1.0, then HCHs mainly originate from lindane; while if α-HCH/γ-HCH > 1.0, then HCHs mainly originate due to industrial activities (Kalantzi et al. [13]). As shown in Fig. 5a, the ratio of α-HCH/γ-HCH for each sampling point is < 1.0, indicating that the HCHs in the study area are mainly derived from lindane.
Graph: Fig. 5 Source analysis of HCHs and DDTs in the water of the Yangzhuang coal mining subsidence area: a HCHs and b DDTs
In general, when DDT continues to flow into the natural environment, the ratio of degradation products DDD and DDE in DDTs is relatively low (Li et al. [14]). Thus, the ratio of DDTs/(DDD + DDE) is often used to show the degradation degree and source of DDTs. If the ratio of DDTs/(DDD + DDE) is ≤ 1.0, then the DDTs in the environment mainly originate due to historical uses; while if the ratio of DDTs/(DDD + DDE) is > 1.0, then the DDTs in the environment mainly originate due to recent input (Bosch et al. [2]). The ratios of DDTs/(DDD + DDE) for all sampling points are all > 1.0 (Fig. 5b), indicating that DDTs in most water bodies in the study area were from recent input. In addition to the input of DDT from industrial activities in the study area, there may be inputs from agricultural activities using dicofol. As the most important impurity of dicofol, o,p′-DDT was detected in large quantities in the study area (Table 1). Therefore, the ratio of o,p′-DDT/p,p′-DDT is used as the basis for further identifying the source of DDTs. In general, if the ratio of o,p′-DDT/p,p′-DDT is ≥ 0.3, then DDTs are mainly derived from dicofol; while if the ratio of o,p′-DDT/p,p′-DDT is < 0.3, then DDTs are mainly derived from industrial inputs (Aigner et al. [1]). As shown in Fig. 5b, the concentrations of o,p′-DDT and p,p′-DDT in all the water samples are very high, indicating that the majority of DDTs in this area originate due to recent agricultural use of dicofol. This is consistent with the actual situation of spraying agricultural pesticides on the surrounding farmland during rice production.
Furthermore, the HCHs and DDTs have been used as pesticides for decades in agricultural activities in the study area, although the Chinese government called for the cessation of using these chemicals in 2000 (Liu et al. [18]). Therefore, it is possible that the measured HCHs and DDTs in this study enter the environment directly from agricultural activities.
Ecological risk assessment
Water quality standards are the key criteria for ecological risk assessment and water resources management. Compared with China's standard for surface water (GB 3838–2002, 2001; γ-HCH < 2000 ng·L−1 and DDTs < 1000 ng·L−1), the HCHs and DDTs concentrations in the water of Yangzhuang coal mining subsidence area were considerably lower. The World Health Organization specifies that the γ-HCH, δ-HCH, p,p′-DDT, and p,p′-DDE concentrations cannot exceed 2 μg·L−1. The concentrations of HCHs and DDTs in the water samples analyzed in this study did not exceed this limit. According to the standards established by the US EPA ([32]), the maximum criteria concentration of γ-HCH is 0.95 μg·L−1 and the continuous criteria concentration of p,p′-DDT is 0.001 μg·L−1. In this study, the γ-HCH concentration in all the water samples is lower than this limit, indicating that the γ-HCH concentration is at a safe level. However, for some points where γ-HCH was not detected, the p,p′-DDT concentration in all the water samples is > 0.001 μg·L−1, indicating that p,p′-DDT may harm the water ecosystem and human health in the coal mining subsidence area.
Based on a comparison (Table 4) of reported concentration values of HCHs and DDTs in the river, lake, and bay water bodies throughout China (Dai et al. [5];Yang et al. [38]; Yuan et al. [42]; Yang et al. [37]; Zhang et al. [45]; Zhang et al. [43]; Zhang et al. [44]; Liu et al. [18]; Zhou et al. [50]), we found that the concentration of HCHs in the water from Yangzhuang coal mining subsidence area was higher than those in the Jiuxi Valley, Baiyangdian Lake, Honghu Lake, Quanzhou Bay, Nansi Lake, and East Lake and lower than the concentrations in the water bodies of the Minjiang River Estuary, Jiulong River Estuary, and Daya Bay. Overall, the ecological risk of HCHs and DDTs in coal mining subsidence water bodies is moderate and the observed HCH and DDT concentrations have certain ecotoxicological impacts, such as carcinogenicity, neurotoxicity, and immunotoxicity, on aquatic organisms and human health.
Table 4 Concentration comparison of dissolved HCHs and DDTs in this research area and in other waters (ng·L−1)
Research area | Year | HCHs | DDTs | References |
|---|
Jiuxi Valley, China | 2019 | 9.94–23.5 | 1.90–6.23 | Liu et al. 2020 |
Baiyangdian Lake, China | 2011 | 3.13–10.60 | 4.05–20.59 | Dai et al. 2011 |
Honghu Lake, China | 2005 | 0.95–7.04 | 0.06–0.49 | Yuan et al. 2013 |
Quanzhou Bay, China | 2020 | 10.92–17.28 | 2.56–4.97 | Yang et al. 2013 |
Nansi Lake, China | 2011 | 19.60–26.30 | 14.70–24.60 | Zhang et al. 2014 |
East Lake, China | 2012 | N.D. a–28.65 | N.D.–57.92 | Yang et al. 2014 |
Minjiang River Estuary, China | 1999 | 52.09–515 | 40.61–233.5 | Zhang et al. 2003 |
Jiulong River Estuary, China | 2000 | 31.95–129.80 | 19.24–96.64 | Zhang et al. 2002 |
Daya Bay, China | 1999 | 35.5–1228.6 | 26.8–975.9 | Zhou et al. 2001 |
Yangzhuang coal mining subsidence area, China | 2016 | 37.98–83.01 | ND–151.02 | This study |
aNot detected
Conclusions
Through a comprehensive analysis using measured datasets, the following conclusions can be drawn from this study.
- In the water of the Yangzhuang coal mining subsidence area, the average concentrations of HCHs and DDTs in the T-layer, M-layer, and B-layer were 152, 169, and 182 ng∙L−1, respectively. As the depth of the water increased, the concentrations of HCHs and DDTs increased.
- The spatial distribution of HCH and DDT concentrations in the study area gradually reduced along the direction of water flow, and the highest concentrations were observed at the entrance of the Nihe River. The concentrations of HCHs and DDTs in the T-layer were easily influenced by environmental and human activities, while those in the M-layer and B-layer were mainly influenced by sediment.
- Through the analysis of diagnostic ratios and PCA, it was found that HCHs in the water of the Yangzhuang coal mining subsidence area were mainly derived from lindane and DDTs mainly originated due to the recent agricultural use of dicofol, both of which were directly formed via agricultural activities. Pesticide pollution due to human activities had a greater influence on HCHs and DDTs in the subsidence area than that caused by nature.
Furthermore, coal mining subsidence areas play an important role in substance circulation and can affect the ecological environment and human health directly. Therefore, more attention should be paid and precautions still need to be taken for preventing pollution in the future. Meanwhile, more research should be conducted on such special and important ecosystems.
Acknowledgements
We express our gratitude to Dr. Haitao Zhang at Anhui University of Science and Technology for his guidance.
Author contribution
Xiaoqing Chen: conceptualization, methodology, visualization, writing. Liangmin Gao: conceptualization, methodology, visualization. Youbiao Hu: methodology, visualization. Leilei Luan: methodology, data collection. Rongrong Tong: methodology, data collection. Jinxin Zhang: methodology, data collection. Hui Wang: methodology, data collection. Xiaofang Zhou: methodology, data collection.
Funding
This study was financially supported by the Youth Science Research Fund of Anhui University of Science and Technology (NO. QN201520) and the Research and Development Projects of Anhui (NO. 006223303009).
Data availability
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval
Not applicable.
Consent to participate
Not applicable.
Consent to publish
Not applicable.
Competing interests
The authors declare no competing interests.
Supplementary Information
Below is the link to the electronic supplementary material.
Graph: Supplementary file1 (DOCX 49.0 KB)
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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By Xiaoqing Chen; Liangmin Gao; Youbiao Hu; Leilei Luan; Rongrong Tong; Jinxin Zhang; Hui Wang and Xiaofang Zhou
Reported by Author; Author; Author; Author; Author; Author; Author; Author
