Bioaccessibility and Toxicity Assessment of Polycyclic Aromatic Hydrocarbons in Two Contaminated Sites

Identification and health risk evaluation of soil contaminated by polycyclic aromatic hydrocarbons at shale gas extraction sites based on positive matrix factorization

The impact of shale gas extraction on surrounding environmental media remains unclear. In this study, the current state of contamination by polycyclic aromatic hydrocarbons (PAHs), which are high-frequency contaminants of shale gas, was investigated in the soil surrounding emerging shale gas development sites. The source analysis of PAHs was conducted in the soils of shale gas extraction sites using positive matrix factorization (PMF). The health risk assessment (HRA) was calculated for ingestion, dermal contact, and inhalation exposures, and the priority sources of PAHs in the soil were jointly identified by PMF and HRA to refine the contribution level of different individual PAHs to the carcinogenic risk. The results showed that both Sichuan and Chongqing mining site soils were contaminated to different degrees. Shale gas extraction has an impact on the surrounding soil, and the highest contributing source of PAHs in the mining site soil of Sichuan was anthropogenic activity, accounting for 31.6%, whereas that in the mining site soil of Chongqing was biomass combustion and mixed automobile combustion, accounting for 35.9%. At the two mining sites in Sichuan and Chongqing, none of the three exposure pathways (ingestion, dermal contact, and inhalation) posed a carcinogenic risk to children, whereas the dermal exposure pathway posed a carcinogenic risk to adults. Health risk assessments based on specific source assignments indicate that when managing soil pollution, the control of fossil fuel combustion and vehicular emissions should be prioritized.

Characteristics and Risk Assessment of PAH Pollution in Soil of a Retired Coking Wastewater Treatment Plant in Taiyuan, Northern China

We analyzed the soil at the site of a former coking wastewater treatment plant on redeveloped land in Taiyuan, northern China, in an attempt to detect the presence of 16 types of priority polycyclic aromatic hydrocarbons (PAHs) listed by the United States Environmental Protection Agency (US EPA) and evaluate the potential pollution risks. The results show that the total proportion of PAHs in the surface soil of the redeveloped land ranged from 0.3 to 1092.57 mg/kg, with an average value of 218.5 mg/kg, mainly consisting of high-ring (5-6 rings) components. Characteristic ratio analysis indicated that the pollution was mainly related to the combustion of petroleum, coal, and biomasses. The wastewater treatment units operated according to the following treatment train: advection oil separation tank, dissolved air flotation tank, aerobic tank, secondary sedimentation tank, and sludge concentration tank. Our study found that pollution resulting from low-ring PAHs mainly appeared in the advection oil separation tank during the pre-wastewater treatment stage, while medium-ring PAH contamination mainly occurred in the dissolved air floatation tank, aerobic tank, and secondary sedimentation tank during the middle stages of wastewater treatment. High-ring PAH contamination primarily appeared in the sludge concentration tank in the latter stage of wastewater treatment. Based on our assessment of the ecological risk using the Nemerow Comprehensive Pollution Index and the toxicity equivalent factor (TEF) method, we determined that individual PAHs in the study area exceeded acceptable levels and the total amount of pollution was potentially harmful to the ecological environment. In addition, the comprehensive lifetime cancer risk for different populations resulting from exposure to the soil in the study area was determined to be within acceptable limits based on the average PAH concentrations.