The toxicity, carcinogenicity and persistence of polycyclic aromatic hydrocarbons (PAHs) pose a great threat to the ecological system and human health. The contamination levels, translocation and source analysis of 16 PAHs in bamboo shoot and its planted soil were investigated. The average concentrations of total PAHs were 18.80 ± 1.90 µg/kg and 123.98 ± 113.36 µg/kg in bamboo shoots and soils, respectively. The most abundant PAH was Phenanthrene (PHE), with the detected average concentrations of 5.85 µg/kg in bamboo shoots and 19.28 µg/kg in soils. The highest detected types of PAHs were 3 rings and 4 rings, with the proportions of 80.69% (bamboo shoots) and 35.23% (soils). The transfer factors of PAHs were ranged from 0.011 to 0.895, in which PAHs with 3 rings showed the strongest transfer ability. The combustion of biomass and petroleum might be the main source of PAHs in the planted soils of bamboo shoots.
As a class of persistent organic pollutions in the environment, polycyclic aromatic hydrocarbons (PAHs) have attracted increasing attention for their toxicity, carcinogenicity, and persistence. Among them, 16 PAHs defined as priority pollutants by US EPA are mainly studied (Zelinkova and Wenzl 2015), especially in vegetables due to the potential risk to human health (Gonzalez et al. 2019). Among various vegetables, more attention should be paid on the root vegetables, which might accumulate PAHs via root surface adsorption, and root uptake (Xiong et al. 2017). Total PAH contents of the root vegetables such as potato (15 µg/kg) and carrot (17 µg/kg) were higher than those from the fruit vegetables (7.9 µg/kg) and leafy vegetables (8.3 µg/kg) in Saudi Arabia (Ashraf and Salam 2012). The concentration of PAHs present in root vegetables were higher than those in other vegetables, which might result from that the adsorption and translocation of PAHs through roots are easier (Paris et al. 2018).
Soil is the most important environmental reservoir of PAHs (Pulkrabová et al. 2019), which might become an important source for the corresponding pollution of PAHs in the root vegetables. For plants cultivated in soils spiked with PHE and PYR, root vegetables like green soyabean showed 3.5 times (PHE) and 27 times (PYR) than those in shoot vegetables such as three-colored amaranth (Gao and Zhu 2004). The transfer performance of PYR from soils to root vegetables were also found in pepper and radish plantation (Hans-Holger Liste and Alexander 2000). Generally, the plant concentration factor (PCF, calculated by the ratio of PAHs concentration in plant to that in soil) is often used to determine the relative uptake of PAHs by the vegetable from soil (Chen et al. 2018). Carrot and lettuce planted in polluted soils showed higher PCF values (0.62–0.64) than that of radish (0.42–0.49) planted in less polluted soils (Waqas et al. 2014). Besides PCF, many scientists also paid more attention on the source analysis for PAHs in environment and foods (Wang et al. 2015). Results indicated that coal combustion was the most important emission source for PAHs in both environmental media and plants, and the traffic-related source, biomass burning and coking industry acted as the secondary sources (Zhang et al. 2018). The ratios of FLU/(FLU + PYR) and INP/(INP + BghiP) were used to identify and quantify the possible sources of PAHs (Wang et al. 2015; Xiong et al. 2017; Zheng et al. 2019).
Bamboo shoot (Phyllostachys heterocycla (Carr.) Mitford cv. Pubescens), a young developing bud from the rhizome of bamboo, is one of the most important root vegetables in Asian countries especially China and Japan (Jiang et al. 2019). Globally, Zhejiang Province of China has the greatest abundance of bamboo shoots, and exported to Japan, EU and the USA in great deal every year (Jiang et al. 2019). We had investigated the levels of pesticides in bamboo shoots (Liu et al. 2014, 2015), and our colleagues also found some persistent organic pollutions (hexachlorocyclohexane and 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane) in bamboo shoots (Guo et al. 2016). However, there is nearly no research conducted on the pollution level of PAHs in bamboo shoot. The present study aimed to: (1) investigate the distribution pattern of PAHs in bamboo shoot; (2) calculate the translocation of PAHs from soil to bamboo shoot; and (3) identify the sources of PAHs.
Materials and Methods
The study area is located in Zhejiang province (118° 01′–123° 10′ E, 27° 02′–31° 11′ N), one of main planting areas of bamboo shoots of China. A total of 64 bamboo shoot samples were collected from 64 plots of 16 main planting areas (details could be seen in Fig. S1) during the whole harvesting period (from December 2018 to March 2019). The corresponding soil samples (0–30 cm) were also collected. The main soil types are yellow soil and red soil. Each bamboo shoot sample (1.5 kg) was separated to shoot (edible part) and hull (non-edible part). The shoot part was chopped and later mixed with an Mixer blender and stored at – 20°C in polyethylene terephthalate (PET) bottles until further analyses (maximum in one week). Soil samples (1 kg each ) were ground to pass through a 2 mm sieve after being air-dried, and stored in paper bags at – 20°C until further analyses. The concentrations of PAHs in bamboo shoot and soil samples were also analyzed in triplicates.
For each sample, 10 g bamboo shoot was extracted with 25 mL of acetonitrile for homogenization 1 min by a high-speed homogenizer (T18, IKA, Germany). 5 mL of final extract was cleaned-up by QuEChERS after centrifugation (5000×g, 20°C, 5 min). 2.5 mL supernatant was evaporated to near dryness under mild nitrogen and dissolved with 1 mL of hexane into injection vial with 0.2 µm PTFE filter and finally analyzed by G–MS/MS. A 10 g of soil was extracted with 25 mL of acetone: hexane (1: 1/v: v) in ultrasonic bath for 10 min. The follow-up steps were the same with bamboo shoot above. All solvents with HPLC grade (Fisher Technologies, USA), 16 USEPA priority PAHs and internal standards 5 deuterated-PAHs (including naphthalene-d8, acenaphthene-d10, phenantrene-d10, chrysene-d12, and perylene-d12) (O2si Smart Solutions, USA) were used.
PAHs were measured by gas chromatograph–tandem mass spectrometry (GC–MS/MS) system equipped with a flame ionization detector (7000B, Agilent Inc., USA) in multiple reaction monitoring mode (MRM) after being separated by a HP-5MS capillary column (30 m × 0.25 mm i.d. × 0.25 µm film thickness, Agilent, USA). Helium (99.999 %) was used as a carrier gas, and set at a constant flow of 2.4 mL/min. The GC oven programmed temperature: initially held at 70°C for 2 min, and increased to 150°C at the rate of 25°C/min. Then, increased to 200°C at the rate of 3°C/min, and finally increased to 280°C at the rate of 8°C/min and held for 5 min. The details of the analysis parameters were summarized in Table 1. Chromatograms of mixed standard PAHs and samples could be seen in Fig. S2.
The procedural blanks, spiked blanks and sample duplicates were analyzed for quality control. The linear regression coefficients (R2) from the calibration curves of 16 PAHs were ranged from 0.9960 to 0.9998. The average recoveries were 95.3 ± 6.5 % and 90.4 ± 4.7 % for bamboo shoots and soils, respectively.
Data were expressed as the mean ± standard deviation. One-way analysis of variance (ANOVA) was carried out to compare the means under Tukey’s honestly significant difference at a significant level of 0.05 using SPSS Statistics 19 (IBM, New York, NY, USA).
Results and Discussion
The concentrations of PAHs in bamboo shoots and soils are illustrated by the boxplots of Fig. 1. The mean concentrations of total PAHs were 18.79 ± 3.36 µg/kg in bamboo shoots, which were higher than those reported in cabbage (8.34 µg/kg), turnip (9.26 µg/kg), potato and carrot (11 µg/kg) from Saudi Arabia (Ashraf and Salam 2012). However, our results were lower than vegetables produced from regions close to an electronic-waste burning site in South China, in which the concentrations of PAHs in peas and shallot were 65.5 µg/kg and 48.8 µg/kg (Paris et al. 2018). The results showed that PAHs level in the planting areas had significant influence on the contamination levels of planted vegetables. For individual PAH, PHE showed the highest contribution (31%) to ΣPAH, followed by ACY (17%), FLU (14%), ACP (11%) and ANT (9%). While other 11 PAHs showed a low ratio of 18% among all PAHs. The concentrations of PHE and ANT in bamboo shoots (5.85 and 1.62 µg/kg, respectively) were almost twice as much as those in the roots of lettuce (2.58 and 1.08 µg/kg, respectively) (Mohammed et al. 2019). FLU contamination in bamboo shoot (2.68 ± 0.21 µg/kg) was three times that of potato (0.89 ± 0.07 µg/kg) (Paris et al. 2018). However, the dietary risk was assessed by incremental lifetime cancer risk (ILCR) (details could be seen in Table S1) (Inam et al. 2016). The results showed that the carcinogenic risk for children and adults (male and female) were all lower than the baseline value (10− 6), which indicated the dietary risk from bamboo shoots consumption was negligible.
The total concentrations of 16 PAHs in soils varied from 23.46 to 612.93 µg/kg (dry wt), with an average of 123.98 ± 113.36 µg/kg. The average concentration was equivalent to those in Nabeul (120.01 µg/kg), an agricultural products planting distribution center of Tunisia (Haddaoui et al. 2016). Nevertheless, our results were lower than those vegetable soils from industrial regions of Northwest China (210.31–379.43 µg/kg), Northeast China (508.9–589.9 µg/kg), and Pakistan (223–929 µg/kg) (Waqas et al. 2014; Wang et al. 2015; Chen et al. 2018). This result further confirmed our previous view that the soil had a key impact on PAHs in plants. The most abundant PAH was PHE (19.27 ± 1.63 µg/kg), followed by FLT, PYR, BbF, and CHR (ranged from 10.19 to 14.69 µg/kg), accounting for 55.1% of total PAHs. The similar trend was observed in lettuce, cabbage, Chinese cabbage and carrot soils, in which the above PAHs were accounted for 56.4% of total PAHs (Chen et al. 2018). Likewise, the five PAHs made up 63.5% of ∑16PAHs in soil of Taizhou, Zhejiang Province (Lu et al. 2019). PHE, FLU and HMW-PAHs (4–6 rings PAHs) were dominant in the soil, accounting for 67.7% of total PAHs. Similarly, HMW-PAHs dominated in the spinach, Chinese cabbage, Shanghai green cabbage, and romaine soils located in Shanghai, Eastern China, accounting for 62.0% of total PAHs (Jia et al. 2019). HMW-PAHs showed dominant contribution in soil due to their stability in environment.
The translocation of PAHs from soil to bamboo shoots (PCFs) are shown in Fig. 2. ACY was found at a relatively high PCF (0.895), followed by ACP, ANT, FLU, PHE and NAP among the individual PAHs. The PCF of ACY was much greater than that of PHE, which was the dominant PAH both in bamboo shoot and soil. The performance might be related to the low log Kow of ACY, which made ACY easier to transfer from soil to bamboo shoots. The similar result was also observed in the PCFs from cabbage root, in which the PAHs of lower log Kow had higher PCFs (Zhang et al. 2018). However, the highest PCF found in cauliflower, carrot and lettuce were PHE (0.96), FLU (0.93) and ANT (0.83) (Waqas et al. 2014). The various performance might be plant type-dependent. In addition, an interesting observation was found that PCFs of PAHs with 3 rings were substantially higher than those with more rings in this study. The transfer factor showed a declining trend of 3 rings (0.306–0.895) > 2 rings (0.164) > 4–6 rings (0.011–0.076). Nevertheless, the efficiency and absorption of PAHs decreases with increasing the number of benzene rings in leafy vegetables (Chen et al. 2018). Due to the abundance of NAP in air, the leafy vegetables could absorb more NAP from air, which could lead to the high PCF of NAP in the plant. However, for root vegetables, the main source of NAP is the existence of NAP in soil. The small molecular weight, weak fat solubility and strong water solubility of NAP, which make NAP easy to be lost and degraded in the transfer process from soil to bamboo shoot. Correspondingly, PCFs of 3 rings PAHs from soil to bamboo shoot were higher than that of 2 rings (NAP). In general, uptake of PAHs from soil via root would be the major uptake pathway of bamboo shoot like other rootstalk vegetables (Mohammed et al. 2019).
Unsurprisingly, the PAHs level in soils had a link with those in the environment. Natural sources of PAHs include geological biodegradations, volcanic eruptions, and wildfires of forest or grassland. And yet anthropogenic sources contain automobile exhaust, oil spills, incomplete combustion of fossil flue or biomass such as wood, coal, and grass (Singh et al. 2016). The identification of any source of pollution is considered necessary to control its emissions or releases. Thus, several identification ratios were used to identify the possible sources of pollution (Wang et al. 2015; Zheng et al. 2019). Representations and results of the PAH diagnosis ratios are shown in Fig. 3. 40.6% of the ratios of FLU/(FLU + PYR) were greater than 0.5 in the bamboo shoot soils, which meant that biomass and coal combustion close to half the emission sources. Meanwhile, the values of INP / (INP + BghiP) in 57.8% of the samples were greater than 0.5, indicating that more than half of PAHs source originated from coal/biomass combustion. The values of FLU / (FLU + PYR) fell between 0.2 and 0.5, indicating a 25.0% contribution from petroleum combustion. The INP / (INP + BghiP) ratios were less than 0.2 in 7.8% samples, suggesting that the PAHs were derived from petrogenic or pyrogenic sources. The results indicated that the contribution of biomass combustion was close to that of petroleum combustion, which showed that biomass combustion and petroleum combustion were the dominant sources of bamboo shoot soils. In addition, petroleum might be an additional source. The result was consistent with several reports from other regions, a mixture of coal and petroleum combustion were the PAHs emission sources in cabbage soils of Shanxi, northern China (Xiong et al. 2017), and coal/biomass combustion were the main sources of PAHs in agricultural soils of Fujian, southeast China. (Zheng et al. 2019).
In conclusion, PHE is the dominant PAH in bamboo shoot and soil. The transfer factors of PAHs of 3 rings were substantially higher than those from PAHs of other rings. Biomass and petroleum combustion were the major potential source of PAHs accumulated in bamboo shoot soils. The decreasing straw and hay burning near bamboo forest might be helpful to reduce PAHs pollution in bamboo shoot and its planted soil.
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This work was supported by the Applied Research Project in the Public Interest of Zhejiang Province (2017C32062), and the Fundamental Research Funds for the Central Nonprofit Research Institution of CAF (CAFYBB2017SZ002).
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Shen, D., Yuan, X., Han, Y. et al. Evaluation of Polycyclic Aromatic Hydrocarbons (PAHs) in Bamboo Shoots from Soil. Bull Environ Contam Toxicol (2021). https://doi.org/10.1007/s00128-021-03124-8
- Root uptake
- Polycyclic aromatic hydrocarbons
- Bamboo shoot
- Source analysis