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Article

Organochlorine Pesticides in Soil–Groundwater–Plant System in a Famous Agricultural Production Area in China: Spatial Distribution, Source Identification and Migration Prediction

by
Chuansheng Li
1,
Xiaofan Qi
2,*,
Yu Wang
3,4,*,
Qingjie Meng
1,
Wenpeng Li
2,
Lanyu Liu
1,*,
Yuejun Zheng
2 and
Huqun Cui
5
1
Shandong GEO-Surveying & Mapping Institute, Ji’nan 250012, China
2
China Institute of Geo-Environment Monitoring, Beijing 100081, China
3
National Engineering Research Center of Coal Mine Water Hazard Controlling, China University of Mining and Technology, Beijing 100083, China
4
Shandong Mingjia Surveying & Mapping Co., Ltd., Zibo 255086, China
5
Center for Hydrogeology and Environmental Geology, CGS, Baoding 071051, China
*
Authors to whom correspondence should be addressed.
Water 2023, 15(23), 4147; https://doi.org/10.3390/w15234147
Submission received: 27 October 2023 / Revised: 22 November 2023 / Accepted: 25 November 2023 / Published: 29 November 2023
(This article belongs to the Section Soil and Water)
Browse Figures
Versions Notes

Abstract

:
Being a famous hometown of vegetables in China, Shouguang City has a long history of vegetable cultivation and is a comprehensive national commodity base for vegetables and fruits. In recent decades, with the expansion of agricultural production, the use of pesticides is increasing. Although organochlorine pesticides (OCPs) have been banned, there are still some residues in soil, groundwater and other media. The study on the migration of the OCPs in soil and groundwater is of great importance for the maintenance of food security. Using methods of hydrogeological survey, laboratory testing and numerical simulation, the spatial distribution characteristics, sources and pollution degree of OCPs in soil and groundwater were analyzed, and the migration and transformation of OCPs in soil–groundwater was dynamically simulated and predicted. The study showed that there were many kinds of OCPs residual in the soil environment. The hexachlorocyclohexane (HCHs) in the topsoil of the study area were mainly due to the use of lindane, and the main source of dichlorodiphenyltrichloroethane (DDTs) in soil was the use of DDTs in history. The contents of HCHs, DDTs and hexachlorobenzene in the topsoil of the study area were at a low level, while the content of endosulfan metabolite endosulfan sulfate was comparatively higher. In recent years, the content of organochlorine pesticides in soil has generally decreased. The indexes of OCPs in groundwater can meet the Standards for Drinking Water quality of China. It was predicted that the HCH pollutants would mainly be distributed in Gucheng Street, Shangkou Town, and its south area where the concentration exceeds 3 ng/L exceeds that of 240 km2. DDT pollutants would mainly be distributed in the east and north of Shouguang City, where the concentration beyond 0.6 ng/L exceeds that of 200 km2. Endosulfan sulfate pollutants would mainly be distributed in the Gucheng Street Office, Shangkou Town, and its south area where the concentration exceeds 1.5 ng/L will exceed that of 150 km2. Hexachlorobenzene (HCB) pollutants would mainly be distributed in Fengcheng in the west of Shouguang City and Nancha River in the northeast, where the concentration exceeds 0.2 ng/L will exceed that of 200 km2. The study enriched the monitoring data of OCPs in agricultural planting areas and provided reference for source analysis, migration prediction, and pollution prevention of OCPs.

1. Introduction

Organochlorine pesticides (OCPs) are the earliest organic chemical pesticides synthesized by human beings. Since the 1940s, it has been widely used all over the world because of its strong insecticidal efficacy [1]. OCPs can be divided into two categories: one is chlorobenzene and its derivatives, such as dichlorodiphenyltrichloroethane (DDTs), hexachlorocyclohexane (HCHs) and hexachlorobenzene, and the other is organochlorine pesticides based on cyclopentadiene, including chlordane, heptachlor, endosulfan and so on [2,3,4,5,6,7,8,9]. OCPs have the characteristics of low volatility, stable chemical properties, not easy to decompose, long residue period, insoluble in water, soluble in fat and organic solvents, high persistence, bioaccumulation and biotoxicity [10,11,12,13,14,15]. Organochlorine pesticides are chemically stable and persist in the environment for a long time, with high residue, high enrichment and strong toxicity to organisms. OCPs are typical chemically stable persistent organic pollutants (POPs). The first Stockholm Convention on POPs contained nine OCP monomer compounds [16].
Although OCPs were widely banned in the 1970s and 1980s, they were still common in soil and groundwater [2,3,4,5], surface water [6,7,8,9], the atmosphere [17,18], ocean [19,20,21,22,23], river sediments [24], lakes [25], lake sediments [26], marine sediments [27], wetlands [28], snow [29], agricultural areas [30] and other environments. OCPs in animals [11,12], plants [12,13] and other organisms were detected, and human health was affected [14,15]. The related study focuses on spatial distribution, source identification, ecological effect, determination methods [31,32,33], degradation and removal methods [34,35,36], monitoring [37] and transport simulation [38,39], which is a hotspot in the field of environmental study. Low-dose OCPs can still bring high risk to organisms and the human body. OCP residues in the soil can not only directly harm terrestrial organisms but also affect aquatic organisms through surface runoff. It also causes indirect harm to the human body through the biological enrichment and expansion effect of the food chain of agricultural products [14,15].
Shouguang City has a long history of vegetable cultivation. Being a famous hometown of vegetables in China, it is a comprehensive national commodity base for grain, vegetables, fruits, cotton, aquatic products and animal husbandry. In recent decades, with the expansion of agricultural production, the use of pesticides has increased. Although the OCPs have been banned, there is still some residue in soil, groundwater and other media.
At present, the studies on OCPs in China are mainly focused on the distribution, causes and ecological risks in soil, surface water and sediments, while there are relatively few studies in agricultural industrial bases, so it is urgent to supplement relevant studies to grasp the environmental background of agricultural areas and ensure the quality and safety of crops. At the same time, the migration of OCPs in soil–groundwater should be further clarified. In this paper, the distribution and causes of OCPs in soil, groundwater and crops in the famous agricultural area were analyzed, the coupling model of OCP transport in soil–groundwater was established, and the migration law and evolution trend of OCPs in multi-medium environments were studied to provide scientific background data for environmental protection and agricultural production in this area.

2. Study Area

The study area is located in the northwest of Weifang City, Shandong Province. Located to the north of the mountains of central Shandong, it is mainly composed of the Mihe alluvial–pluvial slightly inclined plain and the coastal plain formed by the interaction between sea and land. The geomorphological types transit from the alluvial–pluvial piedmont plain to the alluvial–pluvial piedmont inclined plain and alluvial–marine slightly inclined plain. The terrain is a plain area that descends slowly from south to north. Rivers and surface runoffs flow from southwest to northeast, forming micro-geomorphological differences. The overall topography of the city is divided into three parts and seven micro-geomorphological units (Figure 1).
Shouguang City is located in the middle latitude zone, which belongs to the continental climate of the warm temperate monsoon zone. The alternating influence of cold and warm air flow forms the main climatic characteristics of drought in spring, hot in summer, cool in autumn and cold in winter, with four distinct seasons. The annual average temperature is 12.7 °C. The average annual precipitation is 593.8 mm. The average annual evaporation is 2029.5 mm, and the annual average sunshine hours is 2548.8 h [40].
There are 18 rivers in Shouguang. The main rivers are the Mihe River, Danhe River, Guihe River, Yuelonghe River and Yishouhe New River (Figure 1).
There are four soil types in the study area, which are cinnamon soil, fluvo-aquic soil, Shajiang black soil and saline soil, and eight subtypes are cinnamon soil, which are cinnamon soil, Chao cinnamon soil, salinized fluvo-aquic soil, wet fluvo-aquic soil, Shajiang black soil and coastal tidal saline soil.

3. Materials and Methods

3.1. Groundwater Types and Water Abundance Characteristics

The main type of groundwater in the study area is loose rock pore water. According to the characteristics of the water-bearing medium and lithologic combination and the occurrence conditions of groundwater, the pore water can be divided into shallow pore water and deep pore water. The aquifers of Middle Pleistocene (Q2), late Pleistocene (Q3) and Holocene (Q4) are shallow pore water aquifers. The Piedmont alluvial–alluvial plain area reveals the water-bearing sand layers of the Middle Pleistocene (Q2), late Pleistocene (Q3) and Holocene (Q4). The pore water of the Middle Pleistocene (Q2), late Pleistocene (Q3) and Holocene (Q4) in the northern alluvial–marine plain is salt water, which is not used now, while the pore water of the early Pleistocene (Q1) is fresh water, and the deep fresh water is exploited in this area. The strong phreatic water abundance area is mainly distributed in the Piedmont alluvial fan area south of the Fengcheng-Shouguang urban-Daotian area. The lithology of the aquifer is mainly coarse sand and gravel, and the water yield from a single well is 3000–5000 m3/d. The alluvial fan is in the area of Yuesi Han-Sunjiaji, where the water yield from a single well is greater than 5000 m3/d. From the axis of the alluvial–pluvial fan to both sides, the lithologic particles of the aquifer gradually become finer, and the water abundance gradually weakens. The medium water abundance area is mainly distributed in the vast area to the north of the strong water-rich area. The lithology of the aquifer is medium sand and fine sand deposited in the edge zone of alluvium and floodplain, and the water yield from a single well is 1000–3000 m3/d. The weak water abundance area is only distributed in the local area from Xingyao to Xiazhou. The lithology of the aquifer is mainly fine sand and silty sand deposited by river flooding, and the water yield from a single well is less than 1000 m3 (Figure 2).
The material sources of the early Pleistocene water-bearing sand layer and Neogene Minghuazhen formation loose sandstone are both piedmont alluvial material, and the waterproofing layer between each aquifer is thin and discontinuous. The chemical characteristics and the dynamic characteristics of groundwater in the two layers are similar. The upper part of the aquifer roof of the early Pleistocene (Q1) is a very thick clay stratum, which makes the groundwater up and down completely different from each other. The groundwater of the early Pleistocene sand layer and the Neogene Minghuazhen formation layer are both deeply confined freshwater.

3.2. Recharge, Runoff and Discharge of Shallow Pore Water

The shallow groundwater in the study area is mainly recharged by atmospheric precipitation and lateral runoff, receives lateral recharge from rivers and receives a large amount of artificial recharge in the Piedmont alluvial plain. The direction of groundwater movement in the area is generally consistent with the direction of the topographic slope. The groundwater moves slowly from south to north. Due to the high groundwater level in the mainstream zone of the Mihe River, a groundwater watershed has been formed in the area. In recent years, with the increasing exploitation of groundwater, some small funnels have been formed due to the over-exploitation of local groundwater. In the alluvial–pluvial plain in the south, the shallow groundwater discharge mode is mainly artificial exploitation, followed by south-to-north lateral discharge. In the northern alluvial–marine plain, the main discharge is mainly natural evaporation and lateral runoff.

3.3. Vegetable Planting

Shouguang City has a long history of vegetable cultivation, and it is known as the hometown of vegetables as early as the Qing Dynasty. Large areas of vegetable cultivation began in the 1970s. The first greenhouse was built in Xiaodongguan village in 1978, and then the greenhouse developed. In 1989, a warm winter plastic greenhouse was established, which can cultivate temperature-loving vegetables all year round, ushering in a new era of Shouguang vegetable production technology. In 1990, large-scale development of greenhouses began. In 1995, Shouguang City was named ‘the Hometown of Chinese Vegetables’ and ‘the Advanced County of National Vegetable Production’. Over the past decade, Shouguang City has given full play to local advantages, paid close attention to the ‘Vegetable Garden’, enriched the ‘Vegetable Basket’, grasped production on the one hand, promoted circulation on the other and vigorously developed the development of vegetable industrialization, which has achieved remarkable results, and the vegetable area is constantly increasing. It is the largest vegetable trading center in the country. At present, the main vegetable-growing areas in Shouguang City are mainly located in the southern villages and towns (Figure 3).

3.4. General Situation of Pesticide Use

OCPs such as DDTs, BHC, Aldrin, dieldrin and others have been widely used in the study area since the 1950s. These pesticides are not easy to degrade and remain in the environment for a long time. Organophosphorus and carbamate pesticides were widely used afterward.
At present, pesticides and fungicides are used in vegetable cultivation areas, and herbicides are almost not used. Insecticides include insect growth regulators, heterocycles, carbamate vinegar, microorganisms (sources), organophosphorus, pyrethroid, methylamine and others. There are mainly ten kinds of fungicides: mixed, wow, substituted benzenes, antibiotics, organic sulfur, carbamate, phenylphthalamines, difuroformamines, inorganic and heterocyclic compounds.

3.5. Sample Collection and Testing

3.5.1. Soil Sample

The residue and migration of various OCPs in soil are not only related to the physical and chemical properties of the pesticide itself but also related to soil factors (composition, organic matter content, humidity, pH and Eh), biological factors (microbial community), climatic factors (temperature, humidity and light intensity, etc.) and farming conditions. For agricultural soil, the amount of OCPs in the soil is different under different utilization patterns, and different utilization patterns make the soil form different biochemical conditions, which directly affect the variation of OCPs, resulting in differences in their residues and distribution. Therefore, the influence of various factors should be fully considered in the layout of sampling points.
The soil sampling sites were determined by considering soil natural conditions (climate, topography, geology), pollution sources, soil properties (types, hierarchical characteristics, pollution history, etc.) and agricultural conditions (land use, crop types, chemical fertilizers, pesticides, etc.). The sites should fully cover the areas of different types, and a total of 30 soil samples were collected.
When sampling soil, it is necessary to remove the surface debris and collect the soil vertically from the surface to a depth of 20 cm to ensure uniform collection up and down. Plant residues, gravel, fertilizer lumps and so on should be discarded in the sample. Using the plum blossom cloth method, four more points were taken around the selected central point, and the 1 kg topsoil was collected at each point with a shovel. The soil samples of 2 kg were mixed evenly, and then the soil samples were put into the sample bag and sealed with adhesive tape (Figure 3).

3.5.2. Water Sample

Groundwater samples were collected with consideration the same as soil samples. A total of 15 groundwater samples were collected in August 2017 and November 2017 separately (Figure 3).
The washing and sterilization of the sampling container should be soaked in potassium dichromate solution for 24 h, then rinsed with tap water, washed with distilled water and baked at 180 °C in the oven for 4 h, and then washed several times with purified ethane and petroleum ether after cooling. The samples were filled with 1 L brown thin-mouthed glass bottle with polytetrafluoroethylene film in the bottle cap, removing the bubbles, and the bottle cap was wound, sealed and stored at 4 °C for analysis.

3.5.3. Plant Sample

In November 2017, 10 vegetable samples were collected from 10 representative vegetable plots in the main vegetable growing areas of the study area (Figure 3), including 7 kinds of vegetables: balsam pear, cantaloupe, white radish, cucumber, pepper, carrot and tomato. The edible part of vegetables was collected, and the sampling amount was about 0.5 kg. After being quickly brought back to the laboratory, the surface dust was washed, and the samples were dried, crushed and stored in a low-temperature refrigerator.

3.5.4. Testing

Considering the history of OCP usage in the study area, 23 test components of OCPs in soil, groundwater and plants were tested, which are BHC, α-HCH, β-HCH, γ-HCH, δ-HCH, DDT, p,p′-DDE, p,p′-DDD, p,p′-DDT, o,p-DDT, Hexachlorobenzene (HCB), heptachlor, heptachlor, α-chlordane, γ-chlordane, α-endosulfan, β-endosulfan, Ai reagent, Di reagent, Isodil reagent, endosulfan sulfate, isodide reagent aldehyde and methoxy DDT.
All the sample tests were analyzed by the laboratory of the Third Hydrogeology and Engineering Geology Brigade of Shandong Geology and Mineral Resources Exploration and Development Bureau. The test of groundwater refers to the relevant requirements of the Standard Test Method for Drinking Water (GB/T5750-2006). The test method was gas chromatography, and the main equipment used was a gas chromatograph. In this test, the recovery rate of matrix addition was more than 75%, the detection limit was 0.01 ng·L−1, and the relative standard deviation of parallel samples was about 5%, which met the requirements of gas chromatography.
Soil tests and plant samples refer to the organochlorine pesticide residue analysis method of “Gas Chromatographic Analysis of Pesticide Multi-component Residues”, and gas chromatography analyzer was used for analysis. According to the determination of BHC and DDT in soil by gas chromatography (GB/T14550-2003) and the rules for the implementation of quality assurance and quality control of agricultural environmental monitoring, the sample test satisfied that the qualified rate of repeated analysis was more than 90%, and the recovery rate was 95%.
Agilent 7890B-5977A gas chromatography-mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) was used for analysis. The water samples were extracted, purified, concentrated and analyzed by gas chromatography-mass spectrometry (HJ-2014) for the determination of organochlorine pesticides and chlorobenzenes in water quality. Liquid-liquid extraction and purification were used for extraction, the Floristic column was used for purification and parallel evaporation was used for concentration. The soil samples were extracted, purified, concentrated and analyzed by gas chromatography-mass spectrometry (HJ 835-2017). The samples were extracted by accelerated solvent extraction with Semefeld ASE350 (Waltham, MA, USA), purified by Florisil column, and concentrated by parallel evaporation. The plant samples were crushed with freeze-dried samples and then extracted with ASE350 after crushing, and the rest of the steps were the same as the soil.
Substitute recovery calculation equals quantitative measurement divided by the amount added multiplied by 100%. Matrix standard recovery calculation equals (quantitative determination of standard sample minus quantitative determination of this sample) divided by addition amount multiplied by 100%.
Chromatographic conditions: The column temperature was kept at 50 °C for 5 min, then increased to 180 °C for 2 min at the rate of 20 °C/min, and then increased to 300 °C at 5 °C/min for 4 min. The injection port temperature was 250 °C, the injection volume was 1.0 μL, and the column flow rate was 1.0 mL/min.

3.6. Numerical Simulation

3.6.1. Model Area

In order to study the groundwater pollution caused by OCPs and its migration and transformation in Shouguang City, the simulation takes the whole Shouguang area as the simulation area, which was 1238 km2.

3.6.2. Aquifer Generalization

The regional aquifers include Holocene (Q4), late Pleistocene (Q3) and Middle Pleistocene (Q2) water-bearing sand layers. The pollution and migration of OCPs in soil and groundwater mainly occurred in phreatic water and micro-confined water, so the aquifer in the simulation is phreatic water and micro-confined water aquifer (Q4, Q3).

3.6.3. Generalization of Boundary Conditions

Due to the influence of groundwater exploitation, there was no obvious boundary of the hydrogeological unit in the simulation area. Considering the flow field, the south boundary of the simulation area was set as the inflow boundary, and the north boundary was set as the outflow boundary. The western and eastern boundaries are set to zero flow boundary or inflow boundary.
The upper boundary of the phreatic water is the free water surface, through which the whole aquifer system has vertical water exchange with the outside of the system, mainly for precipitation infiltration recharge, irrigation infiltration recharge, evaporation discharge and exploitation discharge.
There was a stable and continuous impermeable layer with a thickness of more than 10 m between the phreatic and micro-confined aquifer and the confined aquifer. The simulation took the roof of the impermeable layer as the floor of the phreatic aquifer.

3.6.4. Simulated Flow Field and Sources-Sinks

The groundwater level field in the simulation area in November 2016 was used as the identification and verification flow field. The sources and sink items mainly include lateral inflow, lateral outflow, rainfall infiltration, artificial exploitation, irrigation infiltration and so on.

3.6.5. Hydrogeological Parameters

The hydrogeological parameters were firstly given by hydrogeological survey values and empirical values and then adjusted in the stage of model identification and verification.

3.6.6. Numerical Model

The model can be generalized into heterogeneous isotropy, two-dimensional spatial structure and transient groundwater flow model.
MODFLOW was selected to simulate the groundwater flow. According to the hydrogeological conditions and the characteristics of the groundwater flow field, the simulation area was divided into 72,630 effective cells, and the cells in the south of the simulation area are encrypted. The grid length of the simulation area is 100~200 m.

3.7. Solute Transport Model

3.7.1. Simulation Principle

According to the simulation results of the groundwater flow model, it was considered that the movement of pollutants in groundwater is mainly in the mode of dispersion and convection. The adsorption, volatilization and biochemical reaction of pollutants in aquifers were not considered in the process of groundwater pollution simulation.
Based on the consideration of the maximum risk, the solute transport model assumed that OCPs precipitate from the soil and enter the phreatic aquifer. The source intensity was calculated according to the soil content concentration of each pollutant, and the transport of pollutants was predicted on the basis of the groundwater flow model.

3.7.2. Groundwater Flow Field

The groundwater flow field took into account the change of the flow field caused by the sources and sinks.

3.7.3. Simulation Parameters

According to the principle of risk maximization and referring to the previous studies, the longitudinal dispersion parameter value of the simulation was firstly given 10 m, and the transverse dispersion parameter value was given 1 m.

3.7.4. Simulated Source Strength

Considering the pollution characteristics of OCPs to groundwater in the Shouguang area, the method of areal source assignment was adopted. The source intensity of different areas was calculated according to the historical OCP amount, application type, application intensity, hydrogeological conditions, soil and groundwater monitoring results and so on. After stopping the use of the OCPs, the source strength was 0. DDTs, HCHs, endosulfan sulfate and hexachlorobenzene were pollutants in the model.

3.8. Model Identification, Verification and Prediction

The solute transport model took 1997 as the base year and predicted the distribution of OCPs in groundwater in 20 years. The model parameters were reasonably verified by the testing data in 2017. On this basis, the concentration distributions of OCPs in groundwater in the next 10 years were predicted.

4. Results and Discussion

4.1. Distribution of OCPs in Soil

4.1.1. Detection and Content of Topsoil

BHC, β-HCH, γ-HCH, δ-HCH, DDTs, p,p′-DDE, p,p′-DDD, p,p′-DDT, o,p-DD, HCB and endosulfan sulfate were detected in different degrees. There were many kinds of OCPs in the soil environment of the study area (Table 1).
According to the Soil Environmental Quality Standard (GB15618-1995), the first-level standard values of DDTs and HCHs are 50 μg/kg and 50 μg/kg, respectively, while the second-level (agricultural land) standard values are 500 μg/kg and 500 μg/kg, respectively. According to this standard, the contents of HCHs in the 30 soil samples were nd~18.64 μg/kg, and the average content was 1.44 μg/kg. The contents of DDTs were nd~ 45.33 μg/kg, and the average content was 11.28 μg/kg. The contents of all samples were up to the first-class standard of the Soil Environmental Quality Standard. The OCP residues were compared with those in different regions of China, which showed that the contents of HCHs and DDTs in the study area were at a comparatively low level. The soil in the study area was relatively clean and had little harm to humans. The content of endosulfan metabolite endosulfan sulfate was nd~128.49 μg/kg, and the average content was 18.45 μg/kg. Compared with other regions, the content was comparatively high. It can be known that endosulfan had been used in the study area, and the usage quantity and frequency were high. The average content of hexachlorobenzene was 1.56 μg/kg, which was comparatively low (Table 1).

4.1.2. Changing Trend of OCPs in Topsoil

Compared with a survey of OCPs in topsoil in 2008 [40], the residues of HCHs have changed significantly. Generally speaking, both the various isomers of BHC and the overall average content of BHC showed an obvious downward trend. The detection rates of HCHs, α-HCH, β-HCH, γ-HCH and δ-HCH were 100%, 100%, 37.5%, 72.5% and 20%, respectively, in 2008, and decreased to 16.67%, 0%, 6.67%, 6.67% and 3.33% in 2017. At the same time, the average residue of HCHs decreased from 3.81 μg/kg to 1.44 μg/kg, and the average value of HCHs decreased by 62.2% (Figure 4). This was consistent with the fact that the OCPs have been suspended for nearly 30 years. The overall content of BHC also showed a downward trend, but the distribution was different. This was related to local soil features. The soil in the north belongs to sandy loam, with low content of organic matter, low viscosity, and low adsorption to OCPs. The OCPs changed quickly. The clay loam in the south was featured by high viscosity, strong adsorption to pesticides, slow loss of pesticides, and the decreasing rate of BHC content was relatively slow.
The degradation rate of isomers of HCHs in the environment is different. The degradation rate of isomers of HCHs in the environment is γ-HCH > α-HCH > β-HCH. Among them, α-HCH can undergo photochemical reactions to produce isomerization products β-HCH and γ-HCH, and γ-HCH can be degraded by microorganisms.
Compared with 2008, the residue and detection of DDTs showed a downward trend, but the downward trend was not obvious. The detection rate of DDTs changed from 100% to 96.67%, and the residue reduced from 14.3 μg/kg to 11.28 μg/kg. This was related to the chemical properties of DDT stability. The p,p′-DDT changed dramatically. The detection rate decreased from 100% to 16.67%, and the residue decreased from 7.04 μg/kg to 1.54 μg/kg. The metabolites were more stable and persistent than their parent compounds (Figure 5).
In 2008, the concentration of endosulfan in the samples in the study area reached 7.67 μg/kg, in which the concentration of α-endosulfan was 1.83 μg/kg, and the detection rate was 20%. The concentration of β-endosulfan was 2.98 μg/kg, and the detection rate was 30%. The concentration of endosulfan sulfate was 2.86 μg/kg with a detection rate of 47.5%. In 2017, α-endosulfan and β-endosulfan were not detected. The detection rate of endosulfan sulfate was 50%, and the average content was 18.45 μg/kg (Figure 6). The endosulfan can be degraded into endosulfan sulfate and endosulfan diol. Therefore, the detection rate and content of endosulfan decreased significantly while the average content of endosulfan sulfate increased.
According to the national policy, OCPs were banned in 1983 in China. This paper analyzed the changes in OCPs in the absence of new pollution sources. The migration and transformation of OCPs in soil were affected by soil structure, microorganisms, soil chemistry conditions, groundwater chemistry conditions, hydrodynamic conditions, etc.

4.1.3. Characteristics of BHCs and DDTs in Soil

HCHs and DDTs with low water solubility and high fat solubility were the main varieties of OCPs used in China. They can affect organisms and even human beings through the enrichment of the food chain. DDTs have potential genotoxicity, endocrine disrupting effect and carcinogenicity; DDE is easy to accumulate in animal fat and cause long-term toxicity. The use of HCHs and DDTs was banned in China in 1983, but there was still a large number of residues in agricultural soil because of their stable chemical properties.
Among all the soil samples, the detection rate of p,p′-DDE was the highest, which was as high as 96.67%. The detection rate of δ-HCH was the lowest, which was 3.33%. The highest residual concentration in soil was p,p′-DDE, followed by p,p′-DDT. The residue levels of DDTs in the soil of the study area were significantly higher than that of HCHs, which is mainly attributed to the fact that the property of DDTs was more stable than that of HCHs and that the historical usage of DDTs was significantly higher than that of HCHs. Although they were both hydrophobic organic matter, HCHs had higher vapor pressure and solubility and were easier to migrate with the atmosphere and water flow.
The detection rates of HCHs (the sum of α, β, γ, δ-HCH) were 16.67%. The content range was nd~18.64 μg/kg, with an average of 1.44 μg/kg. The detected area accounted for 23.71% of the study area, which was mainly distributed to the west of Gaojiazhuang-Hanjiazhuang-Xiajiadianzi, and the center was located in the north of Chengnan Village, Shouguang City. The undetected area of HCHs in soil accounted for 76.29% of the study area, which was mainly distributed in the central and eastern part of the study area (Figure 7).
The order of HCHs isomer contents was β-HCH > γ-HCH > δ-HCH > α-HCH. α-HCH was not detected. The content of β-HCH is nd~18.64 ng/g, and the difference between δ and γ-HCH content was not obvious. In the environment, α-HCH and γ-HCH can be converted into β-HCH, resulting in the gradual accumulation of β-HCH and the decrease of α-HCH.
The content of DDTs was nd~45.33 μg/g, with an average of 11.28 μg/kg. The highest content of DDTs was 45.33 μg/kg, which was located in the west of Lijiazhuang village in the south of Shouguang City.
The places with the highest DDTs content were mainly concentrated in the Wenjia Street, Sunjiaji Street, Tianma-Luocheng area and Hanjiazhuang-Fujiamaotuo-Majiazhuang-Zhangjiatun area. These areas were mainly vegetable-growing areas. The total OCP contents in these areas were high, too. The vegetables planted in these areas had used a lot of pesticides. Among DDTs and their metabolites, p,p′-DDE and o,p′-DDT were the main products (Figure 8).
The content of DDT isomers were in the following order: p,p′-DDE > o,p′-DDT > p,p′-DDT > p,p′-DDD. Among them, the detection rate of p,p′-DDD was only 10%. The detection rate of p,p’-DDE was 96.67%, and the content was nd~31.75 μg/kg, with an average of 8.33 μg/g (Figure 9). The distribution of p,p′-DDE contents was similar to that of DDTs, and the high-value areas were mainly concentrated in the Wenjiajie-Sunjiaji-Tianma-Luocheng area and Hanjiazhuang-Fujiamaotuo-Majiazhuang-Zhangjiatun area (Figure 10). Where the content was high, the historical DDT usage was high. After the degradation of DDTs, the p,p′-DDE came into being, which indicated that DDTs were degraded. The detection rate of o,p’-DDT was 66.67%, and the content was nd~10.47 μg/kg. The high content areas were mainly in Wenjia Street, Sunjiaji Street, Tianma-Luocheng area and Fujiamaotuo-Qianzhaobu (Figure 11). It can be known that the distribution of DDTs, p,p′-DDT and o,p′-DDT in the soil of the study area were similar. The high content of p,p′-DDE in the soil of the study area and the low content of p,p′-DDT in the soil of the study area was mainly due to the fact that the p,p′-DDT was degraded by microorganisms and transformed into p,p′-DDD and p,p′-DDE, which were difficult to degrade in the natural environment.
The transformations and sources of HCHs and DDTs were analyzed. HCHs and DDTs have been banned in China for nearly three decades. According to the ratio of their isomers to metabolites, their degradation, transformation and sources can be analyzed.
The transformations and sources of HCHs were analyzed. The ratio of α/γ-HCH can be used as an index to track the release source of HCHs and HCHs migration. Because α-HCH has a longer air life (about 25% longer than γ-HCH), γ-HCH can be converted into α-HCH during diffusion. Therefore, after long-distance transportation, the ratio of α-HCH to γ-HCH will change. The ratio of α/γ-HCH in industrial BHCs is stable between 4.64 and 5.83, while that in lindane is almost zero. According to this ratio, we can judge whether HCHs come from industrial BHC or from the use of lindane. The detection rate of α-HCH in the study area was 0, and the detection rate and content of γ-HCH were higher than that of α-HCH. Therefore, the regional α/γ-HCH ratios were much less than 4.64. This showed that the pollution of HCHs in this area was mainly due to the use of lindane.
The transformation and source of DDTs were analyzed. The main degradation products of p,p′-DDT were p,p′-DDE and p,p′-DDD. The ratio of p,p′-DDE, p,p′-DDD and p,p′-DDT can reveal whether the pollution of DDTs was caused by the recent use of pesticides or the historical use of DDT. When the p,p′-DDT/(p,p′-DDD+p,p′-DDE) ratio is less than 1.0, it can be considered that the source of DDTs in the soil is mainly pollution caused by the historical use of DDT pesticides. If the ratio is greater than 1.0, it is considered that DDT pesticides have also been used recently. In 2017, the detection rate and content of p,p′-DDT was lower than that of p,p′-DDE. The ratio of p,p′-DDT/(p,p′-DDD+p,p′-DDE) in soil was less than 1.0. It can be concluded that the DDTs in the soil were mainly caused by the use of DDT pesticides in history.

4.1.4. Characteristics of Endosulfan Sulfate and Hexachlorobenzene in Soil

Endosulfan sulfate is the metabolite of endosulfan. No α-endosulfan and β-endosulfan were detected in this study area, but the detection rate of endosulfan sulfate was as high as 50%, which was higher than that of endosulfan, indicating that endosulfan was used in the study area and endosulfan was degraded in the soil.
The content of endosulfan sulfate was nd~128.49 μg/kg, with an average of 18.45 μg/kg. The highest content of endosulfan sulfate was located in the west of Beichahe Village, Shouguang City, with a content of 128.49 μg/kg. The lowest content is 0 μg/kg. The places with high endosulfan sulfate content were mainly concentrated in the north of Guangling and near Jitai town. The undetected areas were mainly distributed in Fengcheng, Wenjia Street, Luocheng Street and Liulu, indicating that there is no input source of endosulfan in the region (Figure 12).
The detection rate of hexachlorobenzene in the study area was 36.67%, and the content was nd~11.54 μg/kg. The highest content of hexachlorobenzene in the study area was located in the south of Liujiabu Village, with a content of 11.54 μg/kg. The places with high hexachlorobenzene content were mainly concentrated in the southeast of Daotian town. The contents in other areas were small. The undetected area accounts for 57.68% of the study area, indicating that the usage of hexachlorobenzene in the study area was relatively low (Figure 13).
The contents of the endosulfan sulfate and the hexachlorobenzene in the soil were all lower than the national standards and had little impact on human health.

4.2. OCPs in Groundwater

4.2.1. Distribution Characteristics of HCHs in Shallow Groundwater

According to the testing data, the concentrations of HCH isomers in shallow groundwater samples were generally low. The concentrations of α-HCH were 0.07~4.29 ng/L, and the average value was 0.52 ng/L. The concentrations of β-HCH were 0.07~2.21 ng/L, and the average value was 0.50 ng/L. The average concentration of γ-HCH is 0.25~2.62 ng/L, and the average value was 0.70 ng/L. The concentrations of δ-HCH were 0.25~1.12 ng/L, and the average value was 0.53 ng/L. The contents of all OCPs were lower than the corresponding drinking water standards. The concentrations of ρ (HCHs) (∑HCHs = α-HCH + β-HCH + δ-HCH + γ-HCH) were 0.95–9.85 ng/L in the dry season, with an average of 2.26 ng/L.
The distribution of HCHs in shallow groundwater is shown in Figure 14. It can be seen that the HCH content concentration lower than 1 ng/L accounts for 14.31% of the study area, which is mainly distributed to the east of Tianma Town and the west of Jitai Town in the north of the study area. The concentration within the range of 1.0–3.0 ng/L accounted for 75.4% of the study area, and the concentration larger than 3 ng/L accounted for only 10.29% of the study area.
The average composition of HCHs isomers in groundwater samples were that α-HCH was 23.24%, β-HCH was 22.33%, γ-HCH was 31.07%, and δ-HCH was 23.33%.
The order of mass concentration of the four isomers of HCHs in the study area was γ-HCH > δ-HCH > α-HCH > β-HCH (Figure 15).

4.2.2. Distribution Characteristics of DDTs in Shallow Groundwater

The concentration of DDTs and isomers in shallow groundwater samples was generally low, which was lower than that of HCHs, which were related to the poor water solubility of DDTs. The content of p,p′-DDE was 0.04~0.87 ng/L with an average of 0.16 ng/L. The content of p,p′-DDD was 0.002~1.28 ng/L with an average of 0.30 ng/L. The content of p,p′-DDT was 0.07~1.31 ng/L with an average of 0.59 ng/L, and the content of o,p’-DDT was 0.07 to 0.66 ng/L averaged by 0.15 ng/L. The contents of all OCPs are less than the drinking water standards. The content of DDTs in the dry season was 0.72–2.88 ng/L, with an average of 1.20 ng/L.
Figure 16 shows the distribution of DDT in shallow groundwater in the study area. It can be seen that the concentration of DDTs greater than 2 ng/L accounted for only 2.79% of the study area, which is distributed in Gaojiazhuang, Wangjiadazhuang and Liujiaguanzhuang of Shouguang City. The concentrations of DDTs in other 97.21% regions were less than that of 2 ngl. Generally speaking, the content of DDT in shallow groundwater is lower than that of HCHs, which were opposite to that in soil, mainly because HCHs were higher in water solubility than DDTs.

4.2.3. Distribution Characteristics of Endosulfate in Shallow Groundwater

The concentration of endosulfan sulfate in shallow groundwater samples is generally low; the highest concentration of endosulfan sulfate was only 5.77 ng/L, and the contents of all endosulfan sulfate were less than the drinking water standards. The contents of endosulfan sulfate in the dry season were 0.32–5.77 ng/L, with an average of 1.08 ng/L.
Figure 17 shows the distribution of the endosulfan sulfate in shallow groundwater in the study area. It can be seen that the endosulfan sulfate content concentration lower than 0.9 ng/L accounted for 70.92% of the study area, which was mainly distributed in the south of the study area. The concentration within the range of 0.9~5.77 ng/L accounted for 29.08% of the study area, distributed in the northeast of the study area, mainly Shangkou, Guangling and Chakou. The concentrations of endosulfan sulfate in shallow groundwater in these areas were higher than those in other areas.

4.2.4. Distribution Characteristics of Hexachlorobenzene in Shallow Groundwater

The concentration of hexachlorobenzene in shallow groundwater samples was low; the highest concentration of hexachlorobenzene was only 0.87 ng/L, and the contents of all hexachlorobenzene were less than the corresponding drinking water standards. The content of hexachlorobenzene in the dry season was 0.01~0.87 ng/L, with an average of 0.13 ng/L.
Figure 18 shows the distribution of hexachlorobenzene concentration in shallow groundwater in the study area. It can be seen that the concentration of hexachlorobenzene in the whole study area was less than 1 ng/L.

4.3. Distribution Characteristics of Organochlorine Pesticides in Vegetables

4.3.1. Detection of Organochlorine Pesticides in Vegetables

Through the analysis of 23 kinds of OCPs, the residues in vegetables in the study area were very small. In general, OCPs in vegetables were obtained through the reabsorption of residual organochlorine pesticides in the environment, but less due to the direct use of OCPs. In response to this phenomenon of OCP residues, the International Codex Alimentarius Commission has established a series of maximum acceptable concentrations. Taking OCPs ≤ 100 ng/g as the maximum acceptable mass concentration, OCPs in vegetables in the study area were lower than the limit. The accumulated content was 0.39–5.72 ng/g. The DDTs were up to the standard of the Safety Requirements of Pollution-free Vegetables (GB18406.1-2001) and the Maximum Residue Limits of Pesticides in Food Safety National Standard (GB2763-2012).

4.3.2. Distribution Characteristics of Organochlorine Pesticides in Vegetables

The detection rates of OCPs were in the following order: HCHs > Endidrin > heptachlor > aldehydes > Aldrin > DDTs > endosulfan sulfate > heptachlor epoxy > hexachlorobenzene > endosulfan 2 > endosulfan 1 > methoxy DDT > dieldrin > pentachloronitrobenzene > α-chlordane > γ-chlordane. The data of HCHs were much higher than that of other OCPs, which showed that HCHs were once the most commonly used OCPs in this region. Although it had been banned in China for many years, its refractory and strong retention still made it a relatively high content. Aldrin and dieldrin were also detected in high quantities; considering that Aldrin and dieldrin were not used in agricultural production in China, the two OCPs mainly come from the migration and deposition of low latitude atmosphere.
The order of OCPs in different kinds of vegetables was carrot > balsam pear > pepper > cucumber > tomato > white radish > cantaloupe. The content of OCPs in rhizome vegetables (radish) was significantly higher than that in eggplant and fruit vegetables (cucumber, pepper, tomato, and cantaloupe). This was mainly because the water contents of eggplant fruit vegetables were higher than other vegetables, and the concentration of OCPs was lower.
The types of OCPs detected in different types of vegetables were basically the same, mainly HCHs, Endidrin, heptachlor, endosulfan sulfate, Aldrin, DDTs, endosulfan sulfate and so on, and the contents of each component were different. The average content of pesticide residues was relatively high in HCHs. Aldrin and dieldrin also had high amounts, which were mainly due to the fact that Aldrin and dieldrin were mainly from the migration and deposition of the atmosphere at low latitudes, while vegetables had relatively larger leaves and they were easier to absorb pollutants carried by atmospheric particles.
According to the detected components of OCPs in soil, this study focused on analyzing the contents of HCHs, DDTs and endosulfate in different vegetables.
HCHs’ contents were ordered as follows: carrot > balsam pear > cucumber > pepper > tomato > white radish > cantaloupe. The content of carrots was significantly higher than that of other vegetables, which was mainly due to the fact that carrots were beneficial to absorbing OCP residues from soil. γ-HCH also has a large Henry coefficient and water solubility, which was easy to be absorbed by vegetables. The enrichment ability of δ-HCH in carrots was higher than other isomers.
DDT contents were ordered as follows: carrot > balsam pear > pepper > cucumber > cantaloupe > white radish > tomato. The content of carrots was significantly higher than that of other vegetables, which was mainly due to the fact that carrots were beneficial to absorbing OCP residues from soil. The main contents of DDT isomers were p,p′-DDT and p,p′-DDE. Carrots and balsam pear mainly contain p,p′-DDT, which was significantly higher than other kinds of vegetables. Cucumbers, peppers, white radishes and tomatoes mainly contained p,p′-DDE and p,p′-DDD, which showed that the residues were from the original DDT. p,p′-DDE and p,p′-DDD were the original DDT degradation products.

4.4. Migration of OCPs in Soil-Groundwater

4.4.1. Prediction of Groundwater Migration in HCHs

The area of HCHs will gradually expand, and the concentration will gradually increase. The pollutants will mainly be distributed in Gucheng Street, Shangkou Town and their southern area. In 2027, the areas with concentrations exceeding 3 ng/L will exceed 240 km2, and the range of concentrations exceeding 6 ng/L will exceed 26 km2 (Figure 19).

4.4.2. DDTs Prediction Result

The area of DDTs will gradually expand, and the concentration will gradually increase. The pollutants will mainly be distributed in the east and north of Shouguang City. In 2027, the areas with concentrations exceeding 0.6 ng/L will exceed 200 km2, and the range of concentrations exceeding 0.9 ng/L will exceed 18 km2 (Figure 20).

4.4.3. Prediction Results of Endosulfan Sulfate

The area of endosulfan sulfate will gradually expand, and the concentration will gradually increase. The pollutants will mainly be distributed in Gucheng Street, Shangkou Town and their southern area. In 2027, the areas with concentrations exceeding 1.5 ng/L will exceed 150 km2, and the range of concentrations exceeding 3 ng/L will exceed 67 km2 (Figure 21).

4.4.4. Prediction Results of Hexachlorobenzene

The area of hexachlorobenzene will gradually expand, and the concentration will gradually increase. The pollutants will mainly be distributed in Fengcheng in western Shouguang City and Nanchahe River in the northeast. In 2027, the areas with concentrations exceeding 0.2 ng/L will exceed 200 km2, and the range of concentrations exceeding 0.8 ng/L will exceed 40 km2 (Figure 22).

5. Conclusions

The space distributions, sources and migrations of OCPs in soil, groundwater and vegetables were studied in the agricultural land in Shouguang City. Through the analysis of 23 kinds of OCPs in 30 soil samples, the results showed that there were many kinds of OCPs in the soil. The transformations and sources of HCHs and DDTs analysis showed that the HCHs in the topsoil of the study area were mainly due to the use of lindane. The main source of DDTs in soil was the DDT pesticide usage in history. The contents of HCHs, DDTs and hexachlorobenzene in the topsoil of the study area were at a low level. The content of endosulfan metabolite endosulfan sulfate is comparatively higher than that in China and abroad.
The analysis of 23 OCPs in 30 shallow groundwater samples in the study area showed that all the OCPs in the study area met the hygienic Standard for drinking Water (GB 5749-2006).
The analysis of OCPs in 23 of 10 vegetable samples in the study area showed that all the OCPs met the requirements for the Safety of Agricultural Products and Pollution-free Vegetables (GB18406.1-2001) and the National Standard for Food Safety Maximum Residue Limits for Pesticides in Food (GB2763-2012). The content of OCPs in root vegetables (radish) was significantly higher than that in eggplant and fruit vegetables (cucumber, pepper, tomato, and cantaloupe).
A numerical model was established to dynamically simulate and predict the migration of OCPs in soil and groundwater. Through the prediction, it was known that HCH pollutants would mainly be distributed in Gucheng Jieban, Shangkou Town and its south area. In 2027, the area where the concentration larger than 3 ng/L will exceed 240 km2, and the concentration larger than 6 ng/L will exceed 26 km2. DDT pollutants will mainly be distributed in the east and north of Shouguang City. In 2027, the concentration larger than 0.6 ng/L will exceed 200 km2, and the concentration larger than 0.9 ng/L will exceed 18 km2. Endosulfan sulfate pollutants will mainly be distributed in the Gucheng Street Office, Shangkou Town and their south area. In 2027, the area where the concentration is larger than 1.5 ng/L will exceed 150 km2, and the concentration larger than 3 ng/L will exceed 67 km2. HCB pollutants will mainly be distributed in Fengcheng in the west of Shouguang City and Nancha River in the northeast. In 2017, the area where the concentration is larger than 0.2 ng/L will exceed 200 km2, and the concentration larger than 0.8 ng/L will exceed 40 km2.

Author Contributions

Conceptualization, C.L. and X.Q.; methodology, C.L., Y.W. and Q.M.; software, Y.W. and Q.M.; validation, L.L. and H.C.; formal analysis, C.L., Y.W. and X.Q.; investigation, C.L., Q.M. and L.L.; resources, C.L. and L.L.; data curation, C.L., X.Q., Y.W. and Q.M.; writing—original draft preparation, C.L., X.Q., Y.W. and Q.M.; writing—review and editing, X.Q., W.L. and Y.Z.; visualization, Q.M., Y.W. and H.C.; supervision, W.L., Y.Z. and L.L.; project administration, C.L., X.Q. and Y.Z.; funding acquisition, C.L., X.Q. and Y.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Shandong Geological Survey Project (Ludizi[2016]93), the China Geological Survey Administration Project (102202220180000009060), and the China Geological Survey Project (DD20230075).

Data Availability Statement

The data presented in this study are available within the article.

Acknowledgments

The authors are very grateful to all anonymous reviewers, chief editors, and associate editors for their valuable comments and suggestions, which improved the quality of this paper.

Conflicts of Interest

Author Yu Wang was employed by the company Shandong Mingjia Surveying & Mapping Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Geomorphological map of the study area.
Figure 1. Geomorphological map of the study area.
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Figure 2. Hydrogeological map of the study area.
Figure 2. Hydrogeological map of the study area.
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Figure 3. Distribution map of crop types and sampling points.
Figure 3. Distribution map of crop types and sampling points.
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Figure 4. Change of HCHs in soil.
Figure 4. Change of HCHs in soil.
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Figure 5. Change of DDTs in soil.
Figure 5. Change of DDTs in soil.
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Figure 6. Change of endosulfans in soil.
Figure 6. Change of endosulfans in soil.
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Figure 7. Total HCHs content in soil.
Figure 7. Total HCHs content in soil.
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Figure 8. Isoline map of total DDT content in soil.
Figure 8. Isoline map of total DDT content in soil.
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Figure 9. Composition of DDT isomers at each sampling site.
Figure 9. Composition of DDT isomers at each sampling site.
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Figure 10. Isoline map of DDE content in soil.
Figure 10. Isoline map of DDE content in soil.
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Figure 11. Isoline map of DDT content in soil.
Figure 11. Isoline map of DDT content in soil.
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Figure 12. Isoline map of endosulfan sulfate content.
Figure 12. Isoline map of endosulfan sulfate content.
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Figure 13. Contour map of hexachlorobenzene.
Figure 13. Contour map of hexachlorobenzene.
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Figure 14. Isoline map of HCHs content in shallow groundwater.
Figure 14. Isoline map of HCHs content in shallow groundwater.
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Figure 15. Distribution map of HCHs isomer content at each sampling site.
Figure 15. Distribution map of HCHs isomer content at each sampling site.
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Figure 16. Isoline map of DDT content in shallow groundwater.
Figure 16. Isoline map of DDT content in shallow groundwater.
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Figure 17. Isoline map of endosulfate content in shallow groundwater.
Figure 17. Isoline map of endosulfate content in shallow groundwater.
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Figure 18. Isoline map of hexachlorobenzene in shallow groundwater.
Figure 18. Isoline map of hexachlorobenzene in shallow groundwater.
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Figure 19. Map of groundwater influence area of HCHs in 2027.
Figure 19. Map of groundwater influence area of HCHs in 2027.
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Figure 20. Map of groundwater influence area of DDTs in 2027.
Figure 20. Map of groundwater influence area of DDTs in 2027.
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Figure 21. Map of the influence range of endosulfan sulfate on groundwater in 2027.
Figure 21. Map of the influence range of endosulfan sulfate on groundwater in 2027.
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Figure 22. Map of the influence range of hexachlorobenzene on groundwater in 2027.
Figure 22. Map of the influence range of hexachlorobenzene on groundwater in 2027.
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Table 1. The contents of OCPs in topsoil in different regions of China [40].
Table 1. The contents of OCPs in topsoil in different regions of China [40].
AreaMean Content/(μg/kg)
HCHsDDTsEndosulfan SulfateHexachlorobenzene
Huanghe River Basin1.23~8.29 (6.23)2.56~42.41 (16.78) 0.78~8.15 (5.12)
Jianghan Plain0.85~7.0612.28~415.800.16~3.78 (0.90)0.10~15.38 (1.15)
Suburb of Shengyang0.67–224.51 (14.51)0.99~218.56 (25.28) 0.54~41.65 (8.35)
Leizhou Peninsuland~65.93 (3.43)nd~52.00 (3.83)nd~7.66 (1.48)
Zaozhuang City (Agricultural soil)21.9~26.9 (25.1)43.9~64.8 (54.8)
Liaocheng (cultivated land soil)nd~52.25 (11.16)nd~4451.06 (127.75) nd~13.72 (2.48)
Yantai city26~561 (165)10~2660 (160)
Dongying (Yellow River Estuary)0.28–1.32 (0.345)0.17~10.46 (0.634) nd~0.58 (0.19)
Qingdao city0.41~9.67 (4.01)3.88~79.55 (26.51)
The study areand~18.64 (1.44)nd~45.33 (11.28)nd~128.49 (18.45)nd~11.54 (1.56)
Note: nd—not detected.
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Li, C.; Qi, X.; Wang, Y.; Meng, Q.; Li, W.; Liu, L.; Zheng, Y.; Cui, H. Organochlorine Pesticides in Soil–Groundwater–Plant System in a Famous Agricultural Production Area in China: Spatial Distribution, Source Identification and Migration Prediction. Water 2023, 15, 4147. https://doi.org/10.3390/w15234147

AMA Style

Li C, Qi X, Wang Y, Meng Q, Li W, Liu L, Zheng Y, Cui H. Organochlorine Pesticides in Soil–Groundwater–Plant System in a Famous Agricultural Production Area in China: Spatial Distribution, Source Identification and Migration Prediction. Water. 2023; 15(23):4147. https://doi.org/10.3390/w15234147

Chicago/Turabian Style

Li, Chuansheng, Xiaofan Qi, Yu Wang, Qingjie Meng, Wenpeng Li, Lanyu Liu, Yuejun Zheng, and Huqun Cui. 2023. "Organochlorine Pesticides in Soil–Groundwater–Plant System in a Famous Agricultural Production Area in China: Spatial Distribution, Source Identification and Migration Prediction" Water 15, no. 23: 4147. https://doi.org/10.3390/w15234147

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