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Article

Emerging Contaminants in Landfill Leachate and Groundwater: A Case Study of Hazardous Waste Landfill and Municipal Solid Waste Landfill in Northeastern China

by
Nan Zhang
1,2,
Zhihao Zhang
1,2,*,
Chunyang Li
3,
Jiani Yue
1,2,
Yan Su
1,2,
Weiguo Cheng
1,2,
Shoushan Sun
1,2,
Xi Chen
1,2,
Deyu Shi
1,2 and
Bo Liu
4
1
Shenyang Academy of Environmental Sciences, Shenyang 110167, China
2
Liaoning Province Urban Ecology Key Laboratory, Shenyang 110167, China
3
Coal to Methanol Branch, Ningxia Coal Industry Co., Ltd., Yinchuan 750411, China
4
Shenyang Municipal Bureau of Ecology and Environment, Shenyang 110167, China
*
Author to whom correspondence should be addressed.
Water 2024, 16(18), 2575; https://doi.org/10.3390/w16182575
Submission received: 31 July 2024 / Revised: 7 September 2024 / Accepted: 9 September 2024 / Published: 11 September 2024
(This article belongs to the Special Issue Management of Solid Waste and Landfill Leachate)
Browse Figures
Versions Notes

Abstract

:
Emerging contaminants (ECs) present a significant risk to both the ecological environment and human health. Landfill leachate (LL) often contains elevated EC levels, posing a potential risk to localized groundwater. This study aimed to characterize ECs in municipal solid waste landfills (MSWLs) and hazardous waste landfills (HWLs) in northeast (NE) China. One and three HWLs and MSWLs in NE China with varying types, operational years, and impermeable layers were selected as case studies, respectively. Statistical analysis of 62 indicators of nine ECs in leachate and the groundwater environment indicated the presence of perfluorinated compounds (PFCs), antibiotics, alkylphenols (APs), and bisphenol A (BPA). The leachates of the four landfills exhibited elevated concentrations of ECs of 21.03 μg/L, 40.04 μg/L, 14.54 μg/L, and 43.05 μg/L for PFCs, antibiotics, Aps, and BPA, respectively. There was a positive correlation between the highest concentrations of ECs in groundwater and those in leachate as well as with operational duration of the landfill; in contrast, groundwater EC was negatively correlated with the degree of impermeability. This study can guide future management of ECs in landfills and hazardous waste sites in China, particularly in NE China.

1. Introduction

Emerging contaminants (ECs) represent substances that are being newly detected in the environment and pose risks to human and environmental health. These ECs typically are not yet effectively managed or regulated under existing measures. Known ECs mainly include pharmaceuticals, industrial chemicals, pesticides, surfactants, endocrine disruptors, personal care products, antibiotics, hormones, analgesics, and a wide variety of other drug compounds [1]. ECs are typically resistant to environmental breakdown, resulting in their accumulation in ecosystems. In addition, ECs display a range of biological toxicities, with effects including toxicity to organs, the reproductive, neurological, developmental, immunological, and endocrine systems, carcinogenicity, and teratogenicity [2,3,4].
To date, the main identified sources of ECs to the environment include wastewater discharge and landfill leachate (LL) [5]. A past study has identified increasing quantities of ECs in landfills that are transported to the surrounding environment through a range of routes, with their transport to the groundwater environment of particular concern. Clearly, landfills have emerged as the main sources and sinks of ECs [6]. A range of ECs have been identified in LL and groundwater in recent years, including antibiotics and bisphenol A (BPA) [7,8,9,10], fluorinated compounds [4,11], pharmaceutical and personal care products (PPCPs) [12,13], and alkylphenols [14]. Musson et al. [15] identified as many as 22 ECs from a municipal solid waste landfill site in Florida, including ofloxacin (OFL), ibuprofen, and nicotine (with a mean average mass concentration of 8.1 mg/kg). Although a subset of ECs can possibly undergo breakdown or adsorption within the landfill matrix during disposal [16], most can be transported into the surrounding environment through leachate, thereby becoming important sources of groundwater contamination [17,18]. A summary of global studies on ECs showed ECs in landfill leachate to be relatively elevated, which was attributed to the prevalence of these ECs in landfill sites. In addition, the high age of many landfills has resulted in considerable damage to impermeable soil layers. The breakdown of impermeable soil layers can contribute to the transport of ECs to groundwater by leachate. In addition, groundwater concentrations of ECs in areas of landfills have been shown to be elevated [5,6,17,18].
Studies on ECs remain preliminary, with most being concentrated in developed countries and in the southern coastal cities of China [8,12,19,20,21] and other developed regions. Among these studies, those focusing on ECs in LL and surrounding environmental media, particularly in groundwater, remain sparse. These studies are particularly few in developing countries and northern China. The aim of the present study was to characterize ECs in landfill leachate and surrounding groundwater in NE China. One and three hazardous waste landfills (HWLs) and municipal solid waste landfills (MSWLs) in NE China were selected as study areas, respectively. The present study statistically analyzed the distributions of ECs in LL and groundwater among the different case study landfills. Differences in EC characteristics based on landfill operation years, anti-seepage conditions, and filling types were identified and reported. The results of the present study can guide increased understanding of the types and concentrations of ECs in LL and groundwater. The results can also guide the formulation of policies for managing HWLs and MSWLs.
Hazardous waste landfills and municipal solid waste landfills are the main carriers of ECs. This study innovatively reveals the pollution characteristics of ECs in municipal solid waste landfills and hazardous waste landfills in northeastern China’s harsh climate, and describes the differential impact of operation years, anti-seepage conditions, and filling types on ECs in groundwater and leachate by comparing and analyzing the differences between different sites. It provides data support for subsequent related studies.

2. Case Study Areas, Sampling, and Analysis of Data

2.1. Study Area

The present study chose case study landfill areas in NE China (see Figure 1). NE China has a temperate, semi-humid continental climate with a mean yearly precipitation and temperature of 600 to 800 mm and 6.2 to 9.7 °C, respectively. NE China experiences rapid changes in temperature in spring and autumn and short seasons, with spring characterized by strong winds and a sunny autumn.
The single case study HWLA (Landfill A) was officially commissioned in 2003 and has a designed treatment capacity of 240,000 tons. Over its past 21 years of operation, it has been estimated to have processed 2.25 million tons of hazardous waste. Waste in the landfill is buried at a depth of 4–5 m, with a pile height of 7–8 m aboveground. The site generates around 1 ton of leachate daily. This leachate is temporarily stored before external disposal. Prior to the establishment of the landfill, most of the land in the area was agricultural, with some artificial forestry and shrubland.
The first MSWL (Landfill B) officially commenced operations in 2003. By the end of 2012, the landfill had a daily treatment capacity of 4000 tons, double its designed capacity. This landfill generates 1300 to 1400 tons of leachate daily, with an additional 100,000 tons of existing leachate disposed by an external company. The site ceased accepting wase in October, 2019 with a waste pile of 22.25 million tons. Current operations at the site focus on maintenance and landfill closure.
The second MSWL (Landfill C) commenced operations in 2012. This site can dispose of 100 tons of household waste a day and has a total capacity of 2.053 million m3, of which to date 0.75 million m3 has already been utilized. Waste in the landfill is buried to a depth of 4–5 m whereas the height of the waste mound reaches 5–7 m. The site generates around 20 tons of leachate daily. This leachate is collected in a pond before undergoing treatment. There were no major buildings or industry in the area prior to the construction of the landfill.
The third MSWL site officially started operation in 2009. This site has a designed capacity of 0.822 million m3. To date, this designed capacity has been exceeded, with total stored waste of 0.950 million m3. The depth of waste burial at the site is 7 m, whereas the waste mound extends to a height of 8 m. The site generates around 37.5 tons of leachate daily. This leachate is collected in a pond for external disposal. There were no major buildings or industry in the area prior to the construction of the landfill.
Among the four case-study landfills, all are equipped with effective anti-seepage and leachate collection systems. Landfills A and B have been in operation for 21 years, whereas C and D have operated for 12 and 15 years, respectively. Since there have to date been no examinations of the integrity of the impermeable layers at these four landfill sites, their status remains unknown.

2.2. Geology and Hydrogeology

Landfills A and B are situated within 3.78 km of each other and within a common hydrogeological unit. Consequently, they exhibit similar geological structures with substantial unsaturated zones, and shallow confined water and pressurized confined water groundwater types.
Landfill A has a vadose zone thickness and permeability of 9.1 m to 12.8 m and 5.3 × 10−6 cm/s to 6.2 × 10−6 cm/s, respectively. The aquifer of Landfill A mainly comprises Quaternary period unconsolidated rock pore confined water, characterized by a low water-bearing capacity. The depth and elevation of the water table at Landfill A ranges between 9.45 m and 13.10 m and 53.91 m to 55.14 m, respectively. Groundwater at Landfill A flows in an overall direction of east to west, with groundwater level decreasing from the southwest to the northeast.
Landfill B has a vadose zone thickness and permeability of 25.8 m to 48.9 m and 1.4 × 10−7 cm/s to 60 × 10−7 cm/s, respectively. Groundwater occurs in the clay layer constituting a shallow confined aquifer. The depth and elevation of the stable water table depth at Landfill B varies from 0.17 m to 5.32 m and 49.12 m to 65.96 m, respectively, with an average hydraulic gradient of 4.726‰. At this site, the coarse sand, fine sand, and clay layers interbedded with fine soil contain confined water. The stable water table depth and elevation ranges from 1.30 m to 4.50 m and 56.34 m to 63.58 m, respectively, and groundwater flows from southwest to northeast.
Landfill C has a vadose zone thickness and permeability of 0.4 m to 2.4 m and 9 × 10−6 cm/s to 0.02 cm/s, respectively. The aquifer at the site contains consists of Quaternary strata dominated by fine sand. The depth and elevation of the groundwater table at the site varies from 1.50 m to 4.26 m and 10.62 m to 14.47 m, respectively, and groundwater flows from northeast to southwest.
Landfill D has a vadose zone thickness and permeability of 5.71 m and 1.08 × 10−3 cm/s, respectively. The aquifer occurs in Quaternary strata dominated by fine sand. The depth and elevation of the groundwater table ranges from 1.50 m to 4.26 m and 37.5 m to 39.9 m, respectively, and groundwater flows from northeast to southwest.
Figure 1 shows the equivalent groundwater levels for the four landfill sites.

2.3. Sampling and Analysis of Data

The present study collected groundwater samples and leachate samples from upstream, downstream, and both sides of the four landfills in November, 2022 and June, 2023. Untreated leachate was obtained from the leachate collection ponds. Groundwater samples collected from Landfills A and B represented shallow confined aquifers, whereas those collected from Landfills C and D represented unconfined aquifers. The present study collected 4 leachate samples (1 sample per landfill) and 27 groundwater samples (6, 5, 9, and 7 samples from landfills A to D, respectively). Figure 1 shows the leachate and groundwater sampling sites.
The present study identified nine and four indicators of ECs in groundwater and leachate from the four landfills, respectively:
(1)
Perfluorinated compounds (PFCs): perfluorobutanoic acid (PFBA), perfluorovaleric acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoA), perfluorotridecanoic acid (PFTriDA), perfluorotetradecanoic acid (PFTeDA), perfluorohexadecanoic acid (PFHxDA), perfluorooctadecanoic acid (PFOdA), perfluorobutane sulfonate (PFBS), perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS), perfluorodecane sulfonate (PFDS).
(2)
Antibiotics: tetracycline (TET), oxytetracycline (OXY), chlortetracycline (CHT), penicillin (PC), doxycycline (DC), spiramycin (SPM), erythromycin (ETM), clarithromycin (CLR), azithromycin (AZM), roxithromycin (ROX), tylosin (TYL), norfloxacin (NOR), ciprofloxacin (CIP), pefloxacin (PEF), enrofloxacin (ENR), ofloxacin (OFL), difloxacin (DIF), lomefloxacin (LOM), sulfadiazine (SDZ), sulfamonomethoxine (SMM), sulfadimidine (SDM), sulfadimethoxypyrimidine (SDT), sulfamethoxazole (SMX), ulfathiazole (STZ), sulfamerazine (SMZ), sulfachloropyridazine (SCP), sulfapyridine (SPY), sulfisoxazole (SIZ), trimethoprim (TMP).
(3)
Alkylphenols (APs): 4-tert-butylphenol (4-t-BP), 4-butylphenol (4-BP), 4-pentylphenol (4-PP), 4-hexylphenol (4-HxP), 4-tertoctylphenol (4-t-OP), 4-heptylphenol (4-HpP), 4-octylphenol (4-OP), 4-nonylphenol (4-NP).
(4)
Pentachlorophenol (PCP).
(5)
Poly brominated diphenyl ethers (PBDEs).
(6)
Hexabromocyclododecane (HBCD): α-HBCD, β-HBCD, γ-HBCD.
(7)
Tetrabromobisphenol A (TBBPA).
(8)
Hexachlorobutadiene (HCBD).
(9)
Bisphenol A (BPA).
Samples for measurement of PFCs, antibiotics, APS, PCP, PBDEs, TBBPA, HCBD, and BPA were stored in pre-sterilized amber glass bottles; those for measurement of HCBD were stored in small bottles. All samples were stored and transported under refrigeration. Samples were stored at 4 °C in the laboratory prior to analysis and were processed within 24 h. Liquid chromatography–mass spectrometry was used to measure PFCs, antibiotics, HBCD, and TBBPA; high-performance liquid chromatography was used to analyze APs and BPA; gas chromatography–mass spectrometry was used to analyze PCP and PBDEs; thermal desorption/gas chromatography–mass spectrometry was used to analyze HCBD. The PFCs were analyzed using LC–MS/MS, with the detection instrument being a Waters TQ-S micro (model SEP-SH-J743). A total of 500 mL of sample was filtered through a 0.45 μm filter, and an internal standard solution was added. A solid phase extraction column with styrene-divinylbenzene copolymer as the adsorbent or an equivalent column with the same efficiency was installed on a solid phase extraction device. A total of 4 mL of 0.1% ammonia/methanol solution, 4 mL of methanol, and 4 mL of ultrapure water were added in sequence. The sample with the internal standard was passed through the solid phase extraction column at a flow rate of approximately 1 drop per second. A 4 mL solution of 25 mmol/L ammonium acetate buffer was used to elute the solid phase extraction column. At this point, the perfluorinated compounds were fixed on the solid phase extraction column, and the previous sample and elution liquid were discarded. The solid phase extraction column was dried using a vacuum freeze-dryer and successively eluted with 4 mL of methanol and 4 mL of ammonia/methanol solution. The elution liquid was collected in 15 mL polypropylene centrifuge tubes. The collected elution liquid was concentrated to near dryness using a nitrogen gas evaporator under high purity nitrogen, and 1 mL of the initial mobile phase was added to dissolve it and filter it through a 0.22 μm filter before being loaded into 1.5 mL brown sample vials and stored at 4 °C for LC–MS/MS analysis. Standard solutions were prepared as a series of 1.0, 2.0, 5.0, 10, 20, and 50 μg/L solutions, with an internal standard solution added and mixed for analysis. The standard solution chromatogram is provided in the Supplementary Materials.
Data processing and analysis were performed in Origin 2022 and SPSS 20.

3. Results

3.1. ECs in Leachate

The main ECs identified in the leachate from the HWL (Landfill A) and the three MSWLs (Landfills B, C, and D) were PFCs, antibiotics, APs, BPA, and HBCD. However, four ECs were not detected at any of the sites, namely PCP, PBDEs, TBBPA, and HCBD. Figure 2 shows the concentrations of ECs in LL, in which it is clear that EC concentrations are elevated. The ranking of the different ECs in leachate in terms of concentration was: LD (43,052.87 ng/L) > LB (40,039.15 ng/L) > LA (21,029.91 ng/L) > LC (14,542.04 ng/L). The concentrations of ECs in leachate detected in the present study significantly exceeded those detected in the largest landfill in the city of Jinan, northern China [22] at which 45 ECs were identified at concentrations of 2.0 ng/L to 5080 ng/L. The EC types at the highest concentrations detected in LL in the present study were Aps, BPA, and PFCs at maximum concentrations of 32,927, 26,200, and 20,397.51 ng/L, respectively.
The rank of different types of PFCs detected in LL according to concentration was: LA (20,237.51 ng/L) > LB (2881 ng/L) > LC (839.24 ng/L) > LD (250.73 ng/L); that of antibiotics was: LB (917.27 ng/L) > LC (217.8 ng/L) > LD (92.14 ng/L) > LA (30.4 ng/L); that of APs was: LB (32,927 ng/L) > LD (16,720 ng/L) > LC (3320 ing/L) > LA (485 ng/L); that of BPA was: LD (26,200 ng/L) > LC (10,270 ng/L) > LB (3312 ng/L) > LA (117 ng/L). HBCD was detected only in Landfill B at a concentration of 1.88 ng/L.

3.2. Groundwater ECs

The ECs in groundwater data from the HWL (Landfill A) were statistically compared with those from the three MSWLs (Landfills B, C, and D). As shown in Figure 3, Landfill B showed both the highest concentrations and frequencies of ECs, whereas those in Landfill D were the lowest; the highest frequency and concentration of PFCs were detected in Landfill B (100%) and Landfill A (143 ng/L), respectively; the highest antibiotics frequency (67%) and concentration (8.39 ng/L) were identified in Landfill C; the highest frequency (100%) and maximum concentration (2062 ng/L) of APs were detected in Landfill B; the highest frequency (40%) and maximum concentration (18.74 ng/L) of HBCD were found in Landfill B; the highest frequency and max concentration of BPA were detected in Landfill A (50%) and Landfill C (160 ng/L), respectively.
The rank of ECs according to frequency of detection in groundwater at Landfill A was: PFCs (67%) > BPA (50%) > antibiotics (33%); the remaining ECs were not detected. PFCs were the most abundant ECs in groundwater (ND–143 ng/L), followed by BPA at a maximum concentration of 100 ng/L.
The rank of ECs detected in groundwater of Landfill B according to frequency was: APs (100%) > HBCD > and BPA (40%); the remaining ECs were not detected; according to concentration the rank was APs (1462–2062 ng/L) > BPA (maximum of 65.6 ng/L) > PFCs (maximum of 20.27 ng/L)> HBCD (maximum of 18.74 ng/L).
The rank of ECs detected at Landfill C according to frequency was: antibiotics (67%) > PFCs (44%) > BPA (22%) > APs (11%); the remaining ECs were not detected; that according to concentration was BPA (ND–160 ng/L) > Aps (maximum of 108 ng/L).
The rank of ECs detected in groundwater of Landfill D according to frequency was: PFCs (43%) > BPA (14%); the remaining ECs were not detected; that according to concentration was BPA (ND–47 ng/L) > PFCs (maximum of 2.57 ng/L).

3.3. Comparison of Groundwater and Leachate ECs

Figure 4, Figure 5, Figure 6 and Figure 7 show the concentrations of detected ECs in leachate and adjacent groundwater at the four landfill sites.
The present study detected 14 ECs in leachate of Landfill A with concentrations of 1.6 ng/L to 19,783 ng/L and with PFBS showing the highest concentration. Six ECs were detected in groundwater, with concentrations of 1.1 to 143 ng/L and PFBS showing the highest concentration. Groundwater PFBS was positively correlated with that in leachate, with the slightly higher concentration in the former indicating the effect of the landfill on the surrounding groundwater.
The present study detected 18 ECs in the leachate of landfill B at concentrations of 0.25–30,414 ng/L and 4-BP showing the highest concentration; 6 ECs were detected in groundwater at concentrations of 1.25–1471 ng/L, with 4-BP showing the highest concentration. These results show a positive correlation between 4-BP in groundwater and that in leachate. The elevated concentrations of 4-BP in all monitoring wells indicated the effect of the landfill on surrounding groundwater.
The present study identified 21 ECs in the leachate of Landfill C at concentrations of 1.69–10,269 ng/L and with BPA at the highest concentration. Eight ECs were detected in groundwater at concentrations of 1.10–160 ng/L and with BPA showing the highest concentration. These results showed a positive correlation between groundwater BPA and that in leachate, with the slightly higher concentration in the former indicative of the effect of the landfill on surrounding groundwater.
The present study detected 17 ECs in the leachate of Landfill D at concentrations of 1.96–26,200 ng/L and with BPA showing the highest concentration. Three ECs were detected in groundwater at concentrations of 2.00–47 ng/L and with BPA showing the highest concentration. The above results show a positive correlation between groundwater BPA and that in leachate. However, the overall concentration of groundwater BPA was relatively low, as were the concentrations of other detected groundwater ECs, indicating the limited effect of this landfill site on groundwater.

4. Discussion

4.1. Differences in ECs among the Case-Study Landfills

Leachate is the main route for contamination of the environment from waste sites. As shown in Section 3.1. ECs in leachate from the HWLA (landfill A) MSWLs (Landfills B, C and D) were detected at high frequencies, with high concentrations and frequencies of APs, BPA, and PFCs. Further analysis of the types and concentrations of ECs identified variations among the four landfill sites which could be related to differences in types of waste deposited at each site. Specifically, Landfill A showed the highest concentration of leachate PFCs; Landfill B showed the highest concentrations of leachate Aps and HBCD; Landfill C showed elevated concentrations of leachate BPA; Landfill D had elevated levels of leachate BPA and APs. These results can be related to the status of Landfill B as an urban MSWL, with a distinct EC profile when compared to those of landfills C and D, which are rural landfills, reflecting differences in waste disposal practices between urban and rural areas. As a hazardous waste disposal site, the leachate EC profile of Landfill A is distinct from those of Landfills B, and D, with higher concentrations of PFCs and lower concentrations of antibiotics, APs, and BPA in Landfill A.
PFCs have been extensively applied as surfactants and polymers in various industries since the 1950s [23,24]. PFCs have been commonly applied as surface coatings for cookware and textiles, as aqueous film-forming foams, and for food packaging [25]. Past related global studies have shown that PFAS in untreated and treated LL range between 1378–292,000 ng/L [5,11]; Eschauzier et al. reported a combined concentration of PFCAs and PFSA (collectively known as perfluoroalkyl acids) in groundwater affected by LL of as much as 4400 ng/L [26]. The results of the present study showed leachate PFC concentrations among the four landfills ranging from 250.73 to 20,397.51 ng/L, representing a moderate concentration range when compared to those detected in past studies internationally. The high leachate PFBS concentrations of landfills A and B of 19,783 ng/L and 2106 ng/L, respectively, suggest that both sites receive considerable quantities of PFBS-containing waste, consistent with previous findings of leachate PFBS from municipal landfills in China of 890–60,000 ng/L [19].
Antibiotics are widely used globally in the medical, livestock, and aquaculture industries. A small proportion of ingested antibiotics undergoes several processes, including hydroxylation, cleavage, and glucuronidation, which generate inactive products. However, the larger proportion of ingested antibiotics is excreted from the body in an unchanged chemical form via feces and urine [27]. In addition, a considerable proportion of household products containing antibiotics is carelessly disposed of upon product expiration. These antibiotics are ultimately disposed of in landfills. A past study estimated that 20% to 40% of antibiotics used in Germany annually are disposed of as waste [28]. A survey and analysis of drug residues in leachate from four representative landfills in Taiwan by Lu et al. [29] identified 26 drug types, with 15 of these detected in leachate and with differences in drug residues between urban and rural landfills and with significant variations in levels of some drugs. An investigation of PPCPs in LL by Yu et al. [13] identified non-antibiotic concentrations to significantly exceed those of antibiotics, with some antibiotics showing even lower concentrations in LL compared to those in urban and livestock wastewater. The highest concentrations of tetracycline and trimethoprim found in urban wastewater were 48,000 ng/L [30] and 162,000 ng/L [31], respectively; those found in LL globally were 19,000 ng/L [32] and 8080 ng/L [17], respectively. In addition, the concentrations of antibiotics in the four LLs were far below those of PFCs, APs, and BPA.
APs are a class of synthetic chemicals mainly applied as surfactants for the pulp, paper, textile, paint, agricultural pesticides, lube oils, fuels, metals, and plastics industries [33]. BPA is utilized in a range of consumer products, including dental sealants, food/beverage containers and linings, medical equipment, and thermal receipts [34]. Since BPA is commonly used in daily life, deposition of BPA as landfill waste is common.
The highest leachate concentration of PFCs was found in Landfill A. This result could be attributed to the composition of waste deposited at the landfill, consisting of hazardous materials including medical waste, pesticide waste, organic solvents, mineral oil, dye and paint waste, surface treatment waste, waste containing heavy metals, and waste containing inorganic fluoride. Among these materials, the annual inputs of dye and paint waste as well as surface treatment waste to the landfill were 2556 tons and 3800 tons, respectively. The high concentrations of PFCs in the two above types of waste were reflected in their leachate concentrations at Landfill A. However, the leachate concentration of antibiotics at this landfill site remained low due to the relatively small quantity of medical waste disposed (only 200 tons/a).
Waste disposed of at landfills B, C, and D were mainly municipal solid waste, including organic kitchen waste, paper, plastics, textiles, wood and bamboo, bricks and tiles, glass, and metals. The main ECs in these municipal solid waste types are APs and BPA, which was reflected in their relatively high concentrations in leachate. In addition, concentrations of leachate antibiotics at these landfill sites exceeded that of Landfill A. Given that landfills C and D were designed for disposal of rural municipal solid waste, the leachate from these sites contained levels of BPA that significantly exceeded that of Landfill B, which was designed to receive urban municipal solid waste.

4.2. The Effect of Landfill Operational Years on ECs in Groundwater

Among the four case-study landfills, LA and LB were established the earliest in 2003, having been operational for 21 years to date. Landfills C and D commenced operations in 2012 and 2009, respectively, with both having been operational for no more than 15 years, and with very similar leachate EC profiles. While all four landfills showed high concentrations and frequencies of major ECs, those at landfills A and B generally exceeded those at landfills C and D. This result suggests that duration of landfill operation has a clear influence on the accumulation of ECs in groundwater. Furthermore, among the three MSWLs, Landfill B has experienced the largest quantity of waste deposited at 22.25 M tons. Consequently, as shown in Figure 3, Landfill B produces 1300 to 1400 tons of leachate daily, which can be resalted to its most significant impact on the groundwater environment among the three MSWLs. Landfill A is classed as a HWL and contains waste with high corrosivity and toxicity. While Landfill A received the smallest quantity of waste among the four landfill sites, groundwater at the site showed higher concentrations and frequencies of some ECs such as PFCs and BPA. This result suggests that levels of ECs in a landfill directly impact their levels in groundwater, despite extensive efforts to solidify and stabilize hazardous waste during the landfilling process.

4.3. The Effects of Various Impermeable Conditions on the Groundwater Environment

Modern HWLs and MSWLs are equipped with impermeable polymer liners to minimize the impact of leachate from various landfills on the surrounding groundwater [35]. As illustrated in Table 1, the rank of the four case-study landfills in terms of their strengths of their artificial barriers was: Landfill C > Landfill D > Landfill A > Landfill B. This ranking closely aligns with the overall concentrations of groundwater ECs among the four landfill sites and suggests that supplementing natural barriers with artificial barriers is crucial for preventing contamination of the groundwater environment by LL. A comprehensive artificial barrier of a high standard can effectively mitigate risks of groundwater pollution from a landfill site. While Landfill B had the thickest unsaturated zone among the four case-study landfills, groundwater at the site was the most contaminated. This contradiction can be attributed mainly to: (1) Landfill B having been operational for the longest duration, during which it had accumulated the largest volume of domestic waste, including excess leachate of 700,000 tons in 2019; (2) A relatively weaker artificial impermeable layer at Landfill B, which may have experienced damage over time due to prolonged operation.
Section 3.3. suggests a positive relationship between EC types and concentrations in groundwater and those in leachate, particularly evident for PFCs. However, these correlations were not evident for APs and BPA, attributable to their relatively lower permeability when compared to PFCs. These results highlight the important role of the vadose zone in intercepting ECs before reaching the groundwater, evident in two aspects: (1) The notable reduction in the concentration of groundwater ECs; (2) The decrease in the variety of EC species. These findings indicate that both natural and engineered barriers at landfills are crucial for mitigating the risk of groundwater pollution.

5. Conclusions

Given that China remains a developing country, studies on ECs are at a relatively lower maturity compared to those in the developed world, with this contrast highest in NE China with an absence of such studies. This study adopted one HWL and three MSWLs to characterize ECs in landfill leachate and surrounding groundwater in NE China. First, the results showed that leachate ECs mainly fell into four categories: PFCs (250.73–20,397.51 ng/L), antibiotics (30.40–917.27 ng/L), Aps (485–32,927 ng/L), BPA(117–26,200 ng/L). The main groundwater ECs were PFCs (0–143 ng/L), antibiotics (0–8.39 ng/L), APs (0–2062 ng/L), and BPA (0–160 ng/L). Second, the main factor influencing ECs in leachate was the type of waste disposed. The highest concentration of leachate PFCs was found in the HWLA (20,397.51 ng/L), whereas urban MSWL Landfill B exhibits the highest concentration of leachate APs (32,927 ng/L). The rural MSWLs (landfills C and D) showed the highest leachate concentrations of BPA (10,270 ng/L and 26,200 ng/L, respectively). Third, maximum groundwater EC concentration was positively correlated with maximum leachate EC concentration, although this relationship did not apply to all EC types. Groundwater EC concentration was positively correlated with landfill operational duration, with the longer operational durations of landfills A and B translating to higher average concentrations of four ECs. Fourth, groundwater EC concentration was negatively correlated with landfill impermeability; the rank of the four landfills in terms of effectiveness of artificial impermeable layers of: Landfill C > Landfill D > Landfill A > Landfill B, was closely aligned with differences in groundwater EC concentrations among the four sites. Fifth, concentrations of ECs in groundwater and leachate in the four case-study sites are in an intermediate range when compared to those identified in similar studies globally. The findings of this study showed that both HWLs and MSWLs have an impact on the surrounding groundwater environment, with the extent of the impact mediated by the volume of waste disposed, operational duration, and impermeability conditions. This study offers pertinent scientific evidence for tracking, managing, and treating ECs.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w16182575/s1, Figure S1: Standard solution chromatogram.

Author Contributions

Conceptualization, N.Z.; Data curation, C.L.; Formal analysis, N.Z.; Investigation, S.S. and X.C.; Methodology, W.C.; Project administration, B.L.; Software, D.S.; Validation, J.Y. and Y.S.; Visualization, Z.Z.; Writing—original draft, N.Z.; Writing—review and editing, Z.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Liaoning Science and Technology Plan Project (Youth Special Fund for Basic Research) (2023JH2/101600011); Shenyang City Program for Supporting Mid-to-Young Innovative Talents in Science and Technology (RC220168); The 2024 Annual Environmental Protection Research Plan Project of Liaoning Province’s Ecological Environment Department (Liaoning Ecological Environment Department Office No. 25, 2024); Shenyang City Pollution Prevention and Control and Ecological Environment Service Support Technology Research and Application Project (Shenyang Environmental Protection Bureau Notice No. 4, 2023).

Data Availability Statement

Data were obtained from Shenyang Municipal Bureau of Ecology and Environment and are available from the authors with the permission of Shenyang Municipal Bureau of Ecology and Environment.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Maps showing the locations and sampling points at the four case-study landfill sites.
Figure 1. Maps showing the locations and sampling points at the four case-study landfill sites.
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Figure 2. A comparative analysis of the concentrations of emerging contaminants (ECs) in leachate from four landfills in northeast China.
Figure 2. A comparative analysis of the concentrations of emerging contaminants (ECs) in leachate from four landfills in northeast China.
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Figure 3. Concentrations and detection frequencies of emerging contaminants (ECs) in groundwater at four landfill sites in northeast China.
Figure 3. Concentrations and detection frequencies of emerging contaminants (ECs) in groundwater at four landfill sites in northeast China.
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Figure 4. Emerging contaminants (ECs) in leachate and groundwater at Landfill A.
Figure 4. Emerging contaminants (ECs) in leachate and groundwater at Landfill A.
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Figure 5. Comparison of concentrations of emerging contaminants (ECs) in leachate and groundwater of Landfill B.
Figure 5. Comparison of concentrations of emerging contaminants (ECs) in leachate and groundwater of Landfill B.
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Figure 6. Comparison of concentrations of emerging contaminants (ECs) in leachate and groundwater of Landfill C.
Figure 6. Comparison of concentrations of emerging contaminants (ECs) in leachate and groundwater of Landfill C.
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Figure 7. Comparison of concentrations of emerging contaminants (ECs) in leachate and groundwater of Landfill D.
Figure 7. Comparison of concentrations of emerging contaminants (ECs) in leachate and groundwater of Landfill D.
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Table 1. Impermeable layers at landfill sites for preventing groundwater contamination.
Table 1. Impermeable layers at landfill sites for preventing groundwater contamination.
LandfillThe Setting of Artificial Impermeable LayerVadose Zone Thickness (m)Groundwater Depth (m)
A1 mm thick HDPE membrane (2 layers) + 400 g/m2 geotextile (2 layers) + 100 g/m2 geotextile (2 layers)9.1–12.89.45–13.10
B1.5 mm thick HDPE membrane (1 layer) + 400 g/m2 geotextile (2 layers)25.8–48.90.17–5.32
C2.5 mm thick HDPE membrane (1 layer) + 600 g/m2 geotextile (3 layers)0.4–2.41.50–4.26
D2 mm thick HDPE membrane (1 layer) + 600 g/m2 geotextile (1 layer) + 300 g/m2 geotextile (1 layer) + sodium bentonite waterproofing mat 4800 g/m2 (1 layer)5–61.50–4.26
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Zhang, N.; Zhang, Z.; Li, C.; Yue, J.; Su, Y.; Cheng, W.; Sun, S.; Chen, X.; Shi, D.; Liu, B. Emerging Contaminants in Landfill Leachate and Groundwater: A Case Study of Hazardous Waste Landfill and Municipal Solid Waste Landfill in Northeastern China. Water 2024, 16, 2575. https://doi.org/10.3390/w16182575

AMA Style

Zhang N, Zhang Z, Li C, Yue J, Su Y, Cheng W, Sun S, Chen X, Shi D, Liu B. Emerging Contaminants in Landfill Leachate and Groundwater: A Case Study of Hazardous Waste Landfill and Municipal Solid Waste Landfill in Northeastern China. Water. 2024; 16(18):2575. https://doi.org/10.3390/w16182575

Chicago/Turabian Style

Zhang, Nan, Zhihao Zhang, Chunyang Li, Jiani Yue, Yan Su, Weiguo Cheng, Shoushan Sun, Xi Chen, Deyu Shi, and Bo Liu. 2024. "Emerging Contaminants in Landfill Leachate and Groundwater: A Case Study of Hazardous Waste Landfill and Municipal Solid Waste Landfill in Northeastern China" Water 16, no. 18: 2575. https://doi.org/10.3390/w16182575

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