Source identification and toxicity apportionment of polycyclic aromatic hydrocarbons in surface soils in Beijing and Tianjin using a PMF-TEQ method

Abstract

Beijing and Tianjin are two of the largest cities in northern China with high population densities and highly developed manufacturing industries. In the past decade, some authors have reported their PAH concentrations in surface soils, identified their sources and quantitatively reported their health risks. However, the contributions of different PAH sources to their toxicity have not been reported thus far. In this study, we reviewed the PAH concentrations, contributions of different sources to the toxicity, and cancer risks in soils from different land use types found within Beijing and Tianjin from data gathered by 41 studies. The total PAH concentration varied in the range of 175.7-1989.0 ng g-1 with a higher median PAH concentration detected in urban soils (789.7 ng g-1), followed by suburban soils (647.3 ng g-1) and rural soils (390.8 ng g-1). Source identification using diagnostic ratios and principal component analysis (PCA) suggested that the PAHs in all three land use types mainly originated from biomass and coal combustion, vehicular emissions, and petrogenic processes with contributions varying from 13% to 62%. Furthermore, results from a positive matrix factorization (PMF) model suggested that vehicular emissions and coal combustion in urban soils, and the vehicular emissions, coal combustion and biomass combustion in suburban and rural soils dominated the total PAH concentrations (>85%). These results were consistent with those of the PCA model. Results of the additional toxicity apportionment performed using the PMF model suggested that vehicular emissions and coal combustion contributed the most to the toxic equivalent quantity for Benzo(a)Pyrene (BaPTEQ) and, by extension, to the carcinogenic potencies. The incremental lifetime cancer risk (ILCR) values suggested a low risk level for adults exposed to PAHs in the different land use types found within Beijing and Tianjin.

Fig 1

Cross plots for PAH isomeric ratios in surface soils in urban (a, b), suburban (c, d) and rural area (e, f). The calculations of source ratios followed the methods described by Yunker et al [15].

Fig 2

Source profiles of each PMF factor for PAHs in urban soils (a), suburban soils (b) and rural soils (c).

Fig 3

Source contributions to BaP_TEQ for PAHs in urban soils (a), suburban soils (b) and rural soils (c).

Fig 4

Predicted probability density functions of incremental lifetime cancer risk (ILCR) for adults exposed to the PAHs in urban soils (a), suburban soils (b) and rural soils (c).