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Journal of Soils and Sediments

, Volume 19, Issue 12, pp 3945–3953 | Cite as

Characteristics, sources, and in situ phytoremediation of polycyclic aromatic hydrocarbon in rural dumpsites

  • Junwei MaEmail author
  • Chao Gao
  • Hongxia Yan
  • Yuqian Li
  • Jiajun Chen
  • Yan Zhao
  • Xinghui Xia
Technological Innovation for Soil/Sediment Remediation

Abstract

Purpose

Without precaution to deal with gas emissions and leachate generation, dumpsites have become a severe environmental problem in many developing countries. The objectives of this study were to investigate the pollution status of polycyclic aromatic hydrocarbons (PAHs) in dumpsite soil in rural areas of China and to verify phytoremediation effectiveness with Sedum alfredii Hance and alfalfa (Medicago sativa L.) under complex pollution conditions in PAH-contaminated soil.

Materials and methods

In this study, we collected soil cores from four dumpsites in rural areas of North China (Hebei Province) for analysis, and correspondingly conducted an in situ phytoremediation experiment using Sedum alfredii Hance and alfalfa (Medicago sativa L.) at one of these sites, monitoring the total PAH concentration in soil.

Results and discussion

Results showed generally moderate pollution by PAHs in soil samples from dumpsites with pockets of heavy pollution. PAH concentrations in dumpsite soil ranged from 827 to 1101 ng/g (dry weight). High-molecular-weight PAHs were present in higher proportions at oldest dumpsite in operation. Certain molecular ratios of PAHs can be used to diagnose the source of PAHs in soil, and it indicated that the main sources were combustion of domestic coal and biomass, as well as the automobile exhaust and kitchen exhaust. A 17-month in situ phytoremediation experiment resulted in the effective removal of PAHs in the Sedum alfredii and alfalfa plots, with total PAH concentrations decreasing by 82.4% and 81.3%, respectively. Furthermore, PAH concentrations in plants correlated to plant growth conditions.

Conclusions

This study indicated that the soils of the dumpsites were generally moderately polluted by PAHs, and some parts of the area were heavily polluted. Both Sedum alfredii and alfalfa absorbed PAHs from soil, and PAH concentrations in these two plants correlated to the growth conditions of the plants. Phytoremediation can effectively be used for PAH removal in open dumpsites.

Keywords

Contaminated soil In situ phytoremediation PAH sources Polycyclic aromatic hydrocarbon Rural dumpsite 

1 Introduction

Dumpsites are open lands where solid waste is dumped without precaution to deal with gas emissions and leachate generation, which have become a serious environmental problem in many developing countries (Nagendran et al. 2006; Zarate et al. 2008; Chakraborty et al. 2018a; Padilla and Trujillo 2018; Peter et al. 2018). In China, with the ever-accelerating commercialization and the continuous improvement in the living standards of rural residents, the quantity of solid waste continues to increase in rural areas (Zeng et al. 2016; Wang et al. 2018). Solid waste generation from villages and towns in China has reached 210 million tons per year, and the annual growth rate of per capita of rural residents is 8–10% (Wang et al. 2018). However, in China’s suburban areas and rural areas, a well-defined system for the sorting, collection, and disposal of solid waste does not yet established, and only less than 30% of rural solid waste was harmlessly disposed (He et al. 2014; Zeng et al. 2015). Consequently, a large amount of waste is randomly dumped, resulting in a large number of rural dumpsites (Li’ao et al. 2009; Huang et al. 2013). Over 80% of the dumpsites were within 100 m of residential areas (Wang et al. 2016). With poor precaution and occasional open burning of waste solid, it would be a significant threat to the surrounding environment (Prechthai et al. 2008; Chakraborty et al. 2018a; Chakraborty et al. 2018b). This is not only a source of visual pollution; it could also result in severe soil contamination through the seepage of leachates into soil and the surrounding environment by means of rainfall and surface runoff.

Leachate poses a serious threat to the surrounding ecosystem, it contains a large number of hazardous compounds, such as polycyclic aromatic hydrocarbons (PAH) and heavy metals, as well as high ammonia nitrogen (NH3–N) concentrations, and it often percolates down and contaminates groundwater and soil and even runs as a stream into the surrounding water bodies (Motorykin et al. 2013; He et al. 2015; Xu et al. 2015; Yang et al. 2017). The PAHs are ubiquitous in waste and leachate originating from various household materials, such as batteries, used paints, polyvinyl chloride (PVC) products, oils, solvents, pesticides, treated wood scraps, discarded electronic equipment, and construction and demolition debris (Chrysikou et al. 2008), and they could be formed during incomplete combustion of organic material, vehicle emissions, and industrial processes (Wei et al. 2014; Wang et al. 2015). Due to their resistance to biodegradation, bioaccumulation potential, and carcinogenicity, PAHs have caused significant environmental concern.

Under conditions of dispersed rural solid waste (RSW) sources, flawed legislation, and poor infrastructure in rural areas, the aim of this study was to propose an economically viable and manageable method to remediate soil pollution caused by the accumulation of PAHs in rural dumpsites in China.

Phytoremediation is a convenient and economic operation, which could remediate the polluted soil in situ (Nagendran et al. 2006; Luo et al. 2017). It does not interfere with the ecosystem but confers to the treated land an added esthetic value through the plant cover (Cristaldi et al. 2017). It can also reduce secondary pollution, restore degraded land to its original state, and be easily scaled up to include larger areas. There have been studies on phytoremediation of soil with heavy metal and organic pollutants, such as soil in smelting, mining areas, sewage irrigation areas, and soil with petroleum, as well as soil in e-waste disassembly areas (Cook and Hesterberg 2013; Liao et al. 2016; Petrová et al. 2017). Compared with the previous studies, soil in the dumpsites contains more complex potential pollutants, such as PAHs and heavy metals, as well as high ammonia nitrogen (NH3–N) concentrations. In the process of phytoremediation, the toxic effects of various pollutants on plants could be superimposed, synergistically or antagonistically, which makes the phytoremediation process ambiguous.

In this study, we investigated PAH compounds and concentrations in rural dumpsites in North China, while also conducting an in situ phytoremediation experiment (Hebei Province, North China). This study was conducted (1) to investigate the concentration and composition of PAHs in rural dumpsites; (2) to evaluate the degree of pollution and potential local sources of PAHs; (3) to conduct a phytoremediation experiment at a local dumpsite using Sedum alfredii Hance and alfalfa (Medicago sativa L.) to verify their remediation effectiveness under complex pollution conditions in PAH contaminated soil.

2 Materials and methods

2.1 Study areas

The study area is located in Hebei Province, North China. The climate is characteristic of a temperate continental monsoon climate, and the soil type is sandy loam.

Four typical dumpsites (designated S1, S2, S3, S4) of different size, age, and position and one background site (CK) were chosen to examine and describe pollution characteristics. The surrounding villagers have been dumping household waste on these dumpsites for decades and have burned waste aperiodically and illegally. No safeguards or measures were taken to protect the soil from contaminants produced by waste or combustion. Samples collected from a poplar forest, where was less affected by vehicle emissions and had no waste there, could therefore be regarded as CK. S1 is a relatively new dumpsite that has only been in use for approximately 1 year, while S2 and S3 have been in use for approximately 3–4 years. S4 is an abandoned dry river channel that has functioned as a dumpsite for greater than 7 years, and it is covered by numerous types of waste material. S2 was chosen as the site to conduct the in situ phytoremediation experiment.

2.2 Soil and plant sampling and preparation

Six soil samples were collected from each sampling site. For each sample, soils were collected from five different depths (0, 10, 20, 30, 40 cm) with a columnar sampler. Soil samples per site were thoroughly homogenized to produce a single sample, then stored in a brown glass bottle. Five soil samples were generated in total, which were labeled CK, S1, S2, S3, and S4, respectively. All these samples were air-dried at room temperature and sieved through a 2-mm nylon sieve to remove stone, coarse debris, and wastes. The samples were stored at 4 °C prior to analysis. Physicochemical properties of the soil samples are given in Table 1. The results indicated that the soils contained not only PAHs, but also several kinds of heavy metals and high concentrated nitrogen and phosphorus, which were much higher than the background values.
Table 1

Physicochemical properties of test soil

Property

Value of S

Value of CK

Silt (%)

9.98

7.89

Sand (%)

90.02

92.11

pH(1:5)

8.43

8.53

Total organic carbon (g/kg)

30.63 ± 4.21

4.47 ± 0.54

Total nitrogen (g/kg)

2.52 ± 0.27

0.66 ± 0.15

Total phosphorus (g/kg)

0.91 ± 0.07

0.40 ± 0.02

As (mg/kg)

17.92 ± 4.34

8.25 ± 0.37

Cr (mg/kg)

87.16 ± 22.69

41.78 ± 0.37

Cd (mg/kg)

0.74 ± 0.23

0.11 ± 0.04

Cu (mg/kg)

121.83 ± 25.39

16.56 ± 0.81

Pb (mg/kg)

198.62 ± 57.02

35.51 ± 8.82

Zn (mg/kg)

85.72 ± 16.03

26.51 ± 11.79

For the in situ phytoremediation site (S2), samples were collected once every other month or two in order to trace changes in pollutants. The soil samples were freeze-dried, grinded in a mortar, and subsequently sieved through a 2-mm mesh. Each plant sample (roots and shoots) was a composite of three plants from the same plot. Roots were washed with distilled water to remove any residual soil particles. Plant samples were separately cut into small pieces, homogenized, dried at 35 °C in an oven for 7 days, and then weighed and pulverized into fine powder using a cutting mill (Retsch SM100, Germany). Each soil and plant sample was divided into two technical replicates for PAH analysis.

2.3 Chemicals and reagents

The standard PAH solution consisted of a mixture of 16 priority PAHs at a concentration of 100 μg/ml (AccuStandard Inc., USA). This mixture was prepared in methanol/dichloromethane (v/v = 1:1). In addition, a mixture of six perdeuterated PAHs (i.e., naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12, perylene-d12, and benzo[g,h,i]perylene-d12) was used as a surrogate standard, and 2-fluorobiphenyl was used as an internal PAH standard. Silica gel (100–200 mesh, Sinopharm Chemical Reagent Co., Ltd., China) and anhydrous sodium sulfate (Xilong Chemical Co., Ltd., China) were activated at 450 °C for 4 h. Dichloromethane, n-hexane, and acetone were all of HPLC grade (J.T. Baker Inc., USA).

2.4 Polycyclic aromatic hydrocarbon sample extraction and analysis

The samples were freeze-dried, and after the removal of stones, wastes, and residual roots, they were homogenized using a mortar and pestle prior to being sieved (0.149 mm).

The PAHs in soil were extracted in duplicate using an accelerated solvent extractor (ASE 300, Dionex Corporation, USA), and a mixture of dichloromethane/n-hexane (v/v = 1:1) was used as the extracting solvent. Briefly, 10 g of soil was extracted twice under the following conditions: oven temperature, 100 °C; pressure, 1500 psi; pre-heating period, 5 min; static time, 5 min; flush volume, 60% of the extraction cell volume; nitrogen purge, 100 s.

The extracts were concentrated to 1 ml by rotary vacuum evaporation at 25 °C. Concentrated extracts were cleaned (adsorbed) using the silica gel column chromatography method (25 cm × 1 cm internal diameter). The glass chromatography column, fitted with a Teflon stopcock, was packed from the bottom with absorbent cotton, 5 g of silica gel, 6 cm of alumina, and 1 cm of anhydrous sodium sulfate. The fraction containing PAHs was eluted with 15 ml n-hexane and then 30 ml n-hexane/dichloromethane (v/v = 7:3). Following this step, the fraction was concentrated to 2 ml using a rotary evaporator and further concentrated to 1 ml under a gentle stream of nitrogen. This sample was then transferred to a GC vial. Finally, 100 μl of the internal standard was added to the extract prior to quantitative analysis.

The PAHs were analyzed using a Varian 3800 gas chromatography-4000 ion trap mass spectrometry (GC/MS) system fitted with a DB-5 capillary column (30-m length, 0.25-mm id, and 0.25-μm film thickness) and an 8400 autosampler injector (1 μl). The injection port temperature was maintained at 280 °C (Song et al. 2015). The GC oven temperature was kept at 80 °C for 3 min, increased to 230 °C at a rate of 12 °C/min, and kept at 230 °C for 2 min. The temperature was then increased to 280 °C at 2 °C/min and kept for 5 min. PAH identification was based on the selected ions and the relative retention time between the samples and the standard solution containing the individual PAHs.

The correlation coefficients for PAH calibration curves using GC/MS were all higher than 0.99. The recovery of 2-fluorobiphenyl, which was used as the recovery standard, ranged from 72 to 94% in the real soil samples.

2.5 In situ phytoremediation

Sedum alfredii Hance and alfalfa (Medicago sativa L.) were selected as the two remediation plants according to a literature review and our previous pot experiment. Site S2 was chosen as the testing ground for the in situ phytoremediation experiment, and it was divided into two plots for plants as well as one small plot with no plant for natural degradation. Both planting plots were 50 m2 in size, and the non-planting plot was approximately 6 m2 (Fig. 1).
Fig. 1

Design of testing ground for the in situ phytoremediation experiment

The Sedum alfredii plot was denoted Plot-A, and the alfalfa plot was denoted Plot-B. The duration of the in situ phytoremediation experiment was 17 months, from November 2013 to April 2015. The plants were grown in natural agro-climatic conditions, with neither fertilization nor optimum irrigation. Soil samples surrounding plants were collected to determine PAH concentrations at the start of plot construction (November 2013) and then collected semimonthly, plant samples were collected at the beginning of plant growth (June 2014) and after harvest. Sampling and detection methods used are provided in Sections 2.2, 2.3, and 2.4.

3 Results and discussion

3.1 Pollution status of polycyclic aromatic hydrocarbons in dumpsite soil

The following sections describe PAH concentration and composition as well as identifying their sources.

3.1.1 Concentration of polycyclic aromatic hydrocarbons

Soil samples from the five plots (CK, S1, S2, S3, and S4) were collected to determine the components and concentrations of the 16 PAHs (Fig. 2). The total concentration of the 16 EPA priority pollutant polycyclic aromatic hydrocarbons (∑16PAHs, dry weight) in the CK sample was 29 ng/g, while the total concentrations in the S1–S4 samples were 827–1101 ng/g, which were greater by a factor of 28.4~37.9 compared to the CK plot. The mean PAH concentration in the S-series soil samples was 983 ng/g, greater by a factor of 33.8 compared to the CK plot. Data from ∑16PAHs samples indicated that rural dumpsite soil was contaminated with PAHs. The result was close to the concentration of PAHs in dumpsite soil from rural areas in Nanjing (1060 ng/g) (Wang et al. 2015), in North Jiangsu Province, China (1208.51 ng/g) (Han et al. 2009), and that value in India (1029 ng/g) (Chakraborty et al. 2018a). Compared to the other types of land use, it was higher than in agricultural soil, which was 619.86 ng/g in Tianjin (Lv et al. 2010), 223 ng/g in Dalian (Wang et al. 2007), and the mean value 147 ng/g in rural soil in China (Ma et al. 2015), but lower than that in soil near municipal solid waste (MSW) landfill, which was 1475 ng/g in northern Greece and 1974 ng/g in northern Poland (Chrysikou et al. 2008; Melnyk et al. 2015).
Fig. 2

Concentration and composition (ng/g dry weight) of 16 PAHs in CK and different dumpsites. a Non-contaminated: the value of PAH concentration less than 200 ng/g is considered to be not contaminated. b Heavily Contaminated: the value of PAH concentration over 1000 ng/g indicates heavy contamination

According to the classification criteria for PAH pollution of soil in the Netherlands recommended by MaliszewskaKordybach, soil PAH concentrations less than 200 ng/g are not considered to be contaminated, Ʃ16PAHs between 200 and 600 ng/g indicates weak contamination, a concentration between 600 and 1000 ng/g indicates moderate contamination, and a concentration over 1000 ng/g indicates heavy contamination (MaliszewskaKordybach 1996). According to this classification, CK is considered uncontaminated, and the S-series dumpsites are considered contaminated. In this study, soil PAHs in dumpsites generally reached moderate pollution levels (S1~S4) with some pockets of heavy pollution (S1, S2).

3.1.2 Composition and source identification of polycyclic aromatic hydrocarbons in dumpsites

Six types of PAHs were detected in CK, and all were two–three rings. At least 13 types of two–six-ring PAHs were detected in the S-series samples. The composition profiles of PAHs in different dumpsites are provided in Fig. 3. The main components were two-ring PAHs (63.61%) in S1, in which naphthalene (Nap) was dominant PAH, followed by phenanthrene (Phe). Two-ring PAHs (54.66%) were also the main components in S2, Nap was the dominant PAH and followed by anthracene (Ant). Three-ring PAHs had the highest overall percentage (65.8%) in S3 sample, and the dominant PAH was Phe. This indicated that low-molecular-weight PAHs (LMW PAHs; 2–3 rings) were the dominant PAHs in S1~S3, accounting for about 71.53%~90.56% of the total 16 PAHs. The oldest dumpsite, S4, had a relatively even distribution, where the individual PAH occupation descended in the following order: five-ring PAH (34.91%) > four-ring PAH (30.04%) > three-ring PAH (17.88%) > six-ring PAH (12.79%) > two-ring PAH (4.37%). This indicated that high-molecular-weight PAHs (HMW PAHs; 4–6 rings) were the dominant PAHs, accounting for about 77.74% of the total 16 PAHs. Compared to CK, the composition of PAH in S-series dumpsites differed and was more complex, which could be attributed to the different sources.
Fig. 3

The mean concentration of individual PAHs and contribution of individual PAHs in different dumpsites. PAHs with different number of rings are shown as colors, respectively

Certain molecular ratios of PAHs can be used to diagnose the source of PAHs in soil samples (Karaca 2016; Oliva et al. 2015). Some typical values of these indices are given in Table 2 (Duan et al. 2015). Ant/(Ant + Phe), a source diagnostic index, varied in the range of 0.11~0.94, higher than 0.1, indicating that soil PAHs were originated mainly from pyrolytic origins. Fla/(Fla + Pyr) varied in the range of 0.61~0.63, higher than 0.4, further confirming the pyrolytic origins. In addition, BaA/(BaA + Chr) values were higher than 0.2, while the values of IcdP/(IcdP + BghiP) were mostly higher than 0.2, suggesting that combustions of coal, biomass, and liquid fossil fuel (such as automobile exhaust and kitchen exhaust) were the main sources of PAHs. So in this study, sources of PAHs in soil for all dumpsites are pyrolytic origins.
Table 2

Characteristic values of selected molecular ratio for pyrolytic and petrogenic origins of PAHs

 

Petrogenic originsa

Pyrolytic originsb

S1

S2

S3

S4

Ant/Ant + Phe

<0.1

>0.1

0.11

0.94

0.15

0.11

Fla/Fla + Pyr

<0.4

>0.4

0.63

0.62

0.61

0.61

BaA/BaA + Chr

<0.2

>0.2

0.49

0.44

0.84

0.30

IcdP/(IcdP + BghiP)

<0.2

>0.2

0.49

0.43

NA

0.33

NA not available

aPetrogenic origins: petroleum

bPyrolytic origins: grass, wood, and coal combustion

Nearby residents typically discard household coal ash, kitchen waste, and corn straw at these dumpsites, and the waste is frequently burned, which could make a contribution to PAHs in dumpsites. Moreover, by being close to residential areas and roads, automobile exhaust and kitchen exhaust can also be the sources of PAHs in dumpsites. Compared to LMW PAHs, HMW PAHs, which are more toxic and carcinogenic, tend to accumulate in soil through dry and wet deposition of ambient particles, and will remain in the soil under absorption, adsorption, and sequestration processes. Compared to the other plots, S4 was older and therefore experienced more cycles of incomplete combustion and vehicle emissions. Therefore, S4 had a greater proportion of HMW PAHs, and the total concentration of HMW PAHs was approximately greater by a factor of two compared to LMW PAHs.

3.2 In situ phytoremediation effects of Sedum alfredii and alfalfa

The following sections describe the in situ phytoremediation effects of Sedum alfredii and alfalfa relative to changes in total PAH concentrations and plant absorption. Figure 4 showed the growth of two plants during the in situ phytoremediation process.
Fig. 4

Plants growth process of in situ phytoremediation

3.2.1 Changes in the total concentration of the 16 PAHs in dumpsite soil

Soil samples in the in situ phytoremediation area were collected once every other month or two to determine PAH content. Results in Fig. 5 indicated that Σ16PAHs exhibited an overall decreasing trend in both the Sedum alfredii (Plot-A) and alfalfa (Plot-B) plots. Compared to data taken from polluted soil prior to the phytoremediation experiment (i.e., November 2013), Σ16PAHs decreased by 82.4% in Plot-A and 81.3% in Plot-B. Compared to Plot-A and Plot-B, Σ16PAHs decreased by 49.2% in the plot where plants were removed, which indicated that the natural degradation rate of PAHs was low. Figure 5 a shows concentration and composition changes of the 16 PAHs in the soil of Plot-A. From November 2013 to April 2015, the total concentration of the 16 PAHs decreased from 1037 to 182 ng/g. Plot-B exhibited a similar trend with a decrease from 1023 to 191 ng/g (Fig. 5b). From June to July 2014, during vigorous plant growth (producing high biomass), corresponding PAH concentrations in soil decreased at a higher degree. Accordingly, high biomass production can effectively remove PAHs in soil. After plants reached maturity, they were harvested and removed. After a 17-month phytoremediation experiment, the soil of both Plots-A and Plot-B reached a level of less than 200 ng/g (signifying no contamination). This indicated that in situ phytoremediation using both Sedum alfredii and alfalfa in PAH-polluted soil exhibited good remediation effects. At same time, beautifying the environment, it would therefore be feasible to extend this method to other rural dumpsites worldwide.
Fig. 5

Changes in the 16 PAH concentration and composition in the planting area a and b indicate the changes of concentrations for each kind of PAHs from Nov. 2013 to Apr. 2015 in situ phytoremediation experiment grounds with Sedum alfredii and alfalfa, respectively. a Non-contaminated: the value of PAH concentration less than 200 ng/g is considered to be not contaminated. b Heavily contaminated: the value of PAH concentration over 1000 ng/g indicates heavy contamination

Figure 6 shows variation trends in PAH concentrations comprised of different rings, where concentrations of two–three-ring PAHs mainly exhibited a decreasing trend, but where an evident rebound was observed for four–six-ring PAHs.
Fig. 6

Concentration of PAHs with different rings in the planting area (lines in this figure are the tendency of PAHs concentration with different rings (lines for 2–3-ring PAHs mainly present decline trend, but there is an evident rebound for 4–6-ring PAHs)

Concentrations of two–three-ring PAHs generally exhibited a decreasing trend, but an increase was observed in initial concentrations throughout remediation. This was because HMW PAHs during the initial stage of the phytoremediation process degraded to LMW aromatic hydrocarbons, after which monocyclic benzene rings degraded into other substances. During the latter stage of remediation, LMW PAH concentrations decreased, and their proportion decreased in the total PAH concentration, indicating that the degradation of HMW PAHs in phytoremediation was more difficult.

In November, four–six-ring PAH concentrations significantly increased in both Plot-A and Plot-B. Taking into account that residents near the testing sites burn coal and other fuels in winter, these pyrolytic sources released a certain amount of PAHs. After migration and atmospheric sedimentation, PAHs were deposited back into the soil. However, lower temperatures in winter would make it more difficult for PAHs to evaporate.

3.2.2 Effects of plant absorption

Figure 7 showed changes of total PAH concentrations in plants from June 2014 to April 2015. In June 2014, plant growth rapidly increased, and PAH concentrations in plants were very high (4730.18 ng/g and 1262.63 ng/g, respectively). Total PAH concentrations of soils in both plots decreased during plant growth, and the PAH concentrations of plants were higher than that of soil, which confirmed that plant could obtain PAHs from the soil. Among the main subsets of phytoremediation, phytoextraction, (i.e., the use of plants to remove inorganic or organic compounds from soil by accumulating them in the biomass of plants) and phytodegradation (i.e., the use of plants to uptake, store and degrade organic compounds) have made a great contribution to remove PAHs from soil (Marchand et al. 2018).
Fig. 7

PAH concentrations of plants and corresponding soil in different plots from June 2014 to April 2015(As perennial herbs, Sedum alfredii and alfalfa gradually withered down after November in North China, but began to rally in the following March)

PAH concentrations in Sedum alfredii and alfalfa decreased gradually from June 2014 to November 2014 (Fig. 7), while a same tendency occurred in soil, suggesting that concentration of pollutants in plants had positive correlation on concentration in soil (Sun et al. 2011). In April 2015, with warmer temperatures and sufficient and stable hydrothermal conditions, biomass of plants increased quickly. Meanwhile, there were sharp increases in both plans, suggesting that PAH concentrations in plants were correlated to the biomass.

Comparing the two remediation plants, removal effects of PAHs were high and very close. Meanwhile, the variation trend of PAHs concentration in two plants was similar. The close values and similar trends indicated that both Sedum alfredii and alfalfa could effectively be used for PAH removal in open dumpsites.

4 Conclusions

This study measured PAHs in four typical rural dumpsites in North China to determine characteristics of PAH pollution in dumpsite soil. An in situ phytoremediation experiment using two plant species (Sedum alfredii Hance and alfalfa (Medicago sativa L.)) was simultaneously conducted in Hebei Province, to determine their remediation effectiveness under complex pollution conditions. The results are as follows:
  1. (1).

    The initial content of the 16 PAHs in rural dumpsite soil was 827–1101 ng/g, the soil of rural dumpsites in North China were generally moderately polluted by PAHs, while pockets of soil were heavily polluted. The average PAH concentration in contaminated soil was greater by a factor of 33.8 compared to the background site.

     
  2. (2).

    The PAHs in dumpsite soil are mainly derived from pyrolytic sources. The main sources of PAHs are residential coal combustion, biomass burning (especially corn straw), automobile exhaust, and kitchen exhaust. There was a higher proportion of HMW PAHs in the oldest dumpsite in operation.

     
  3. (3).

    The 17-month in situ phytoremediation experiment effectively removed PAHs in both the Sedum alfredii and alfalfa plots (Plot-A and Plot-B), and total PAH concentrations decreased by 82.4% and 81.3%, respectively, which is much higher than natural degradation processes. Both Sedum alfredii and alfalfa absorbed PAHs from soil, and PAH concentrations in these two plants correlated to the growth conditions of the plants.

     

In conclusion, Sedum alfredii and alfalfa proved to be both effective in removing PAHs from soil of rural dumpsites in North China and cost effective, as well as easily deployable and convenient to manage; therefore, phytoremediation should be promoted as a means to improve the worldwide problem of PAHs pollution over vast rural areas.

Notes

Funding

This work was supported by the National Key R&D Program of China (2017YFA0605003), the Key Laboratory for Solid Waste Management and Environment Safety (Tsinghua University, SWMES2015-12), and the National Science and Technology Support Program (2012BAJ21B03-01).

Supplementary material

11368_2019_2326_MOESM1_ESM.docx (252 kb)
ESM 1 (DOCX 252 kb)

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.State Key Laboratory of Water Environment Simulation, School of EnvironmentBeijing Normal UniversityBeijingChina

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