Pollution Characteristics and Source Analysis of Polycyclic Aromatic Hydrocarbons in Agricultural Soils from Shandong

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants that originate mainly from anthropogenic sources. PAHs have elicited much concern because they exhibit strong toxic, carcinogenic, and mutagenic properties. Agricultural soil is at risk of PAH contamination mainly caused by atmospheric depositions, wastewater irrigation, or organic substances and biowaste applied as fertilizers. The surface agricultural soils were collected from Shandong in July 2015, and measured for 16 US EPA priority PAHs using high performance liquid chromatography with UV and fluorescence detector. The content and composition of PAHs were analyzed. The differences of PAHs between soils from the field for growing crops and from vegetable greenhouses, and between soils from point sources and from non-point sources were compared. The sources of PAHs were determined with methods of ratio between PAHs and positive matrix factorization (PMF), and the risks of PAHs were assessed. The results showed that the total content of 16 PAHs (∑16PAHs) ranged from 111.5 ng·g-1 to 2744.1 ng·g-1, with the mean of 556.3 ng·g-1. The content of 3-ring PAHs was relatively high, with the mean of 201.5 ng·g-1; while the contents of 2-ring and 6-ring PAHs were relatively low, with the mean of 39.3 ng·g-1 and 43.4 ng·g-1, respectively. According to the contamination classification in Poland, 71% of the samples in Shangdong were weakly contaminated. Compared with other areas in China, the content of PAHs in the agricultural soils in Shandong was in the middle range. Acenaphthene, fluorine, and fluoranthene were the major PAH compounds, accounting for more than 10% of the total PAHs; while the contribution of indeno (1,2,3-cd) pyrene was low. The content of ∑16PAHs and contribution of 7 carcinogenic PAHs were significantly higher in soils polluted by point sources than those in soils from non-point sources. Moreover, the contribution of PAHs with 2-3 rings was significantly higher in soils from non-point sources, while the contribution of PAHs with 4-6 rings was significantly higher in soils polluted by point sources. There was no significant difference in soils from vegetable greenhouses and from adjacent field soils, and the contribution of PAHs with 3-4 rings was high. The PAH isomer pair ratios of Ant/(Ant+Phe), Flu/(Flu+Pyr), BaA/(BaA+Chr), and InP/(InP+BP) were utilized as molecular indices to elucidate the possible PAH sources, and the results suggested that the PAHs in the soils were mainly from combustion. To quantitatively assess the contribution of various sources to PAH contamination, PMF was used to analyze the sources. The sources of PAHs were combustion of coal biomass, oil combustion from traffic, coking, and petroleum pollution, with contribution of 42.7%, 19.3%, 22.8% and 15.2%, respectively. Toxic equivalency factors were used to evaluate PAH contamination in the soils, and the carcinogenicity of other PAHs relative to BaP was quantified to estimate the BaP-equivalent concentration (TEQBaP). The TEQBaPof 16 PAHs (∑16TEQBap) in soils from non-point sources and vegetable greenhouses was 31.69 and 44.47 ng·g-1, respectively, which were below the safe value in Canadian soil quality guidelines. However, the ∑16TEQBap in some field soils from point sources exceeded the safe value, indicating that there were potential risks in the soils from point sources in Shandong.