Concentration and Potential Ecological Risk of PAHs in Different Layers of Soil in the Petroleum-Contaminated Areas of the Loess Plateau, China

Abstract

The three most representative areas of petroleum pollution on the Loess Plateau are the research subjects of this study. In this study, 16 priority polycyclic aromatic hydrocarbons (PAHs) were determined by the QuEChERS method combined with gas chromatography-tandem mass spectrometry (GC-MS/MS). The total concentrations of ∑16PAHs in top layer soils (0–10 cm), middle layer soils (10–30 cm), and bottom layer soils (30–50 cm) ranged from 1010.67 to 18,068.80, 495.85 to 9868.56 and 213.16 to 12,552.53 μg/kg, with an average of 5502.44, 2296.94 and 2203.88 μg/kg, respectively. The 3-ring and 4-ring PAHs were the most prominent components in all soil samples. Meanwhile, the average value of ∑16PAHs decreased with the depth, from 5502.44 μg/kg (0–10 cm) to 2203.88 μg/kg (30–50 cm). The PAHs levels in the studied soils were heavily polluted (over 1000 μg/kg) according to the Soils Quality Guidelines and 95% of PAHs come from petroleum sources. Moreover, the total of PAHs in petroleum-contaminated soils was assigned a high ecological risk level. Toxic equivalency quantities (TEQs) indicated that PAHs in petroleum-contaminated soils presented relatively high toxicity.

Evaluation of Sources and Ecological Risk of PAHs in Different Layers of Soil and Groundwater

“…Jiao et al, 2017 [44] came up with a similar result of decreasing concentration of ∑16PAHs by increasing the depth in the study (Shanxi, China) and explained that PAHs come from pyrolysis inputs due to industrial emissions in the industrial activities and also shows the migrate trend of PAHs in the vertical section of the soils [44]. Comparing the concentrations of ∑PAHs in soils in the Loess Plateau, China, similar values were obtained in the surface layer of soil [3], in an urban location in China [6], 6 times higher than values in the Hunpu region, a wastewater-irrigated area, Shenyang City, China [43]. Values of PAHs in locations are higher than values along the Govan to Clydebank corridor, the area with a history of heavy industry (concentrations range from 86.9-653 mg/kg) [45], similar as in examined locality.…”

“…The maximum permissible concentrations (MPCs) (concentrations of PAHs above which the risk of adverse effects is considered unacceptable) and negligible concentrations (NCs) (MPC/100) of PAHs in soils and groundwater were used, according to the research of Kalf et al [40], Wang et al [3] and Lan et al [41]. RQ(NCs) and RQ(MPCs) were defined as follows [3,41]: RQNCs = CPAHs / CQV(NCs) RQMPCs = CPAHs / CQV(MPCs) where RQNCs and RQMPCs were risk quotient values (RQ(NCs) and RQ(MPCs)), CPAHs was the PAHs measured concentration in the soil and groundwater and values CQV (C(NCs) and C(MPCs))) were the corresponding quality values of PAHs in the soil and groundwater. High-risk High-risk ≥800 ≥1 Table 4 shows the descriptive statistics of the 16 priority PAHs compounds in contaminated soils (at a depth of up to 30 cm (surface layer), 100 cm, 200 cm, 300 cm, and 400 cm) and groundwater environmental samples in four locations of the examined area.…”

“…The PAHs sources can be summarized into groups by origin: pyrogenic, petrogenic, and phytogenic [4]. Diagnostic PAHs molecular ratio methods were used for the identification of PAHs sources of the contamination: Fluo/(Fluo+Pyr), low molecular weight (LMW) (2-3 rings)/high molecular weight (HMW) (≥4 rings), IcdP/(IcdP+BghiP), BaA/(BaA+Chr), ΣCOMB/TPAH and PAH4/ PAH(5+6) [61][62][63][3][4][5], by comparing the concentrations of individual PAHs (Fluo, Pyr, BaA, Chr, IcdP, BghiP, Ant, Phe, BaP, etc.) and qualitatively distinguishing pyrolytic and petrogenic sources [63].…”

“…PAHs in soils may enter water bodies, which poses a potential environmental risk [3]. The ecological risk of PAHs was assessed by a risk quotient method based on toxic equivalency factors [39].…”

“…A risk quotient (RQ) was used to assess the ecological risk of PAHs [40] and shown in Table 9. according to risk quotient (RQ(NCs) and RQ(MPCs) in research Kalf et al [40], Wang et al [3] and Lan et al [41].…”