Distribution and Health Risk Assessment of Polycyclic Aromatic Hydrocarbons in Soil from a Typical Contaminated Urban Coking Sites in Shenyang City

The rapid increase of urban contaminated sites along China's urbanization during the last 30 years

Contaminated sites pose serious threats to the soil environment and human health. However, the location and temporal changes of urban contaminated sites across China remain unknown due to data scarcity. Here, we developed a machine-learning model to identify the contaminated sites using public data. Results show that the trained model with 2,005 surveyed site samples and six variables can achieve a model performance evaluation value of 0.86. 43,676 contaminated sites were identified from 83,498 polluting enterprise plots in China. However, these contaminated sites have significant spatiotemporal heterogeneity, mainly located in economically developed provinces, urban agglomerations, and core urban areas. Moreover, the contaminated sites increased by 325% along with urban expansion from 1990 to 2018. The abandoned contaminated sites increased rapidly, but the contaminated sites in production decreased continuously. This methodological framework and our findings contribute to the precise management of contaminated sites and provide insights into urban sustainable development.

Ecological risk assessment of priority PAHs pollutants in crude oil contaminated soil and its impacts on soil biological properties

Polycyclic aromatic hydrocarbons (PAHs) are one of the major toxic constituents of crude oil and therefore, an understanding on PAHs associated risks and their relationship with soil biological parameters are necessary for adopting effective risk-based and site specific remediation strategies in the contaminated soil. Here, risks evaluation of eight detected PAHs in terms of toxic equivalent concentration (TEQ_C), benzo(a)pyrene equivalent (BaPeq), contamination factor (CF), pollution load index (PLI), hazard quotient (HQ), hazard index (HI), toxic unit for individual PAHs (TU) and PAHs mixture (TU_m) have been evaluated. Besides, the effect of PAHs contamination on soil biological properties has also been investigated and correlated with PAHs concentrations. The TEQc of eight PAHs was recorded in the range of 0.06-5.0 mg kg^-1 soil_, whereas the BaPeq value was 25.3 mg kg^-1 soil which exceed the permissible limit. Similarly, CF (85.5-1668.2), PLI (322.8), HQ (311.7-8340.9), HI (26,443.8), TU (227.9-3821.6) and TU_m(7916.2) also exceed the permissible values for non-toxic conditions indicating carcinogenic risk for humans. Besides, activities of soil dehydrogenase, urease, alkaline-phosphatase, catalase, amylase and cellulase were decreased by 1.5-2.3 folds in the contaminated soil than control. The results of Pearson's correlation matrix also established negative impact of PAHs on the soil's biological properties.

Survey and Risk Assessment of Contaminants in Soil from a Nitrogenous Fertilizer Plant Located in North China

China is the world’s largest consumer of fertilizer, with fertilizer plants widely distributed throughout the country. With the removal and closing of fertilizer factories in recent years, pollutant surveys and risk assessments (human health risks) for these sites have become increasingly necessary. However, there has been little research on contaminated fertilizer factory sites. This study aimed to characterize the distribution of pollutants, assess the health risk of the site, and calculate the remediation area and volume in a typical fertilizer plant site in North China. A total of 443 samples were collected in 2019; they indicated that the study site had high concentrations of copper (Cu), ammonia-nitrogen (NH3-N), total petroleum hydrocarbons (TPH), and fluoride at maximum ratios (the ratio of the highest value of all test data for a particular pollutant to the standard value of the pollutant) of 3.30, 2.55, 19.69, and 1.10, respectively. The health risk assessment results suggested that some hazard quotients exceeded the threshold safe level (>1 established by environmental regulations). The risk control values of soil were 2000 mg/g (Cu), 826 mg/g (TPH), and 1549 mg/g (NH3-N), and the total remediation soil volume was 72860.71 m3. The results provided basic information on soil pollution control and environmental management in a contaminated fertilizer plant site.

Health risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the soil around thermal power plants in southwest China

This study aimed to evaluate the PAH contamination levels and to assess the health risk of PAH in soils of two typical thermal power plants. The PAH content was detected using gas chromatography-mass spectrometry (GC-MS). The carcinogenic risk and the hazard quotient were assessed for health risk using the "Chinese Technical Guidelines for Risk Assessment of Contaminated Sites HJ 25.3-2014." The results showed that the average concentration of Σ₁₆PAHs in the soils around thermal power plants A and B are 7436 μg/kg and 8975 μg/kg, respectively indicating heavily pollution. The comprehensive carcinogenic risk of PAHs in thermal power plants A and B ranged from 0.26 × 10^-6 to 4.16 × 10^-6. Forty percent of the sampling sites exceeded the acceptable risk level (10^-6), which is a potential carcinogenic risk to the workers. Among the seven kinds of carcinogens, Bap (39.91%) and DBA (36.10%) had the highest carcinogenic risk. Oral ingestion (57.22%) and skin contact (42.49%) were the major exposure pathways that could be blocked by wearing masks, gloves, and protective clothing. The control values for oral ingestion (0.32717 mg/kg) of DBA and Bap with the highest contribution rate of the carcinogenic risk and the lowest control value were selected as reference safety thresholds for PAHs in thermal power plants.

Polycyclic aromatic hydrocarbon (PAHs) geographical distribution in China and their source, risk assessment analysis

In China, the huge amounts of energy consumption caused severe carcinogenic polycyclic aromatic hydrocarbon (PAHs) concentration in the soil and ambient air. This paper summarized that the references published in 2008-2018 and suggested that biomass, coal and vehicular emissions were categorized as major sources of PAHs in China. In 2016, the emitted PAHs in China due to the incomplete combustion of fuel was about 32720 tonnes, and the contribution of the emission sources was the sequence: biomass combustion > residential coal combustion > vehicle > coke production > refine oil > power plant > natural gas combustion. The total amount of PAHs emission in China at 2016 was significantly decreased due to the decrease of the proportion of crop resides burning (indoor and open burning). The geographical distribution of PAHs concentration demonstrated that PAHs concentration in the urban soil is 0.092-4.733 μg/g. At 2008-2012, the serious PAHs concentration in the urban soil occurred in the eastern China, which was shifted to western China after 2012. The concentration of particulate and gaseous PAHs in China is 1-151 ng/m3 and 1.08-217 ng/m3, respectively. The concentration of particle-bound PAHs in the southwest and eastern region are lower than that in north and central region of China. The incremental lifetime cancer risk (ILCR) analysis demonstrates that ILCR in the soil and ambient air in China is below the acceptable cancer risk level of 10-6 recommended by US Environmental Protection Agency (EPA), which mean that there is a low potential PAHs carcinogenic risk for the soil and ambient air in China.

Levels, sources and probabilistic health risks of polycyclic aromatic hydrocarbons in the agricultural soils from sites neighboring suburban industries in Shanghai

The levels, sources and quantitative probabilistic health risks for polycyclic aromatic hydrocarbons (PAHs) in agricultural soils in the vicinity of power, steel and petrochemical plants in the suburbs of Shanghai are discussed. The total concentration of 16 PAHs in the soils ranges from 223 to 8214ng g^-1. The sources of PAHs were analyzed by both isomeric ratios and a principal component analysis-multiple linear regression method. The results indicate that PAHs mainly originated from the incomplete combustion of coal and oil. The probabilistic risk assessments for both carcinogenic and non-carcinogenic risks posed by PAHs in soils with adult farmers as concerned receptors were quantitatively calculated by Monte Carlo simulation. The estimated total carcinogenic risks (TCR) for the agricultural soils has a 45% possibility of exceeding the acceptable threshold value (10^-6), indicating potential adverse health effects. However, all non-carcinogenic risks are below the threshold value. Oral intake is the dominant exposure pathway, accounting for 77.7% of TCR, while inhalation intake is negligible. The three PAHs with the highest contribution for TCR are BaP (64.35%), DBA (17.56%) and InP (9.06%). Sensitivity analyses indicate that exposure frequency has the greatest impact on the total risk uncertainty, followed by the exposure dose through oral intake and exposure duration. These results indicate that it is essential to manage the health risks of PAH-contaminated agricultural soils in the vicinity of typical industries in megacities.

Health risk assessment of an abandoned herbicide factory site for transportation use in Dalian, China

An abandoned herbicide factory site was used as an example of how planning should be considered for development of the site for transportation use in Dalian, China. Exposure pathways and parameters for three types of transportation use (land for a traffic hub, land for an urban road, and land for a subway) were developed. Twenty-five sampling sites were selected and 38 soil samples were collected in March 2015. Hexachlorobenzene and benzo(a)pyrene which were extracted by Soxhlet extraction and detected by gas chromatography mass spectrometry were the most significant pollutants detected. The maximum concentration of the two pollutants in the surface layer (0-0.5 m) were 0.57 and 3.10 mg/kg, and in the bottom layer (1.0 m) were 2.57 and 3.72 mg/kg, respectively. In this study, risk assessment results based on the established exposure scenario and parameters showed that there was a significant difference in traffic hub land use under specific exposure pathway and common insensitive land use exposure pathways (direct ingestion of soil, dermal contact with soil, and inhalation of soil-derived dust). Commonly considered hexachlorobenzene and benzo(a)pyrene carcinogenic risk values exceeded the maximum acceptable level (10^-6) and were found to be 23.9-fold and 189-fold higher than the carcinogenic risk values, respectively. Parameter sensitivity analysis data showed that for transportation use, the two parameters "EFOa" and "OSIRa" were the most significant factors associated with variation of the carcinogenic risk value. For traffic hub land use, urban road land use, and subway land use, the main exposure pathways were through "inhalation of soil vapors outdoors (from surface soil)," "direct ingestion of soil," and "inhalation of soil vapors indoors (from bottom soil)," which contributed 84.75, 73.00, and 100.00% to the total risk value, respectively.

Two-liquid-phase system: A promising technique for predicting bioavailability of polycyclic aromatic hydrocarbons in long-term contaminated soils

A two-liquid-phase system (TLPS), which consisted of soil slurry and silicone oil, was employed to extract polycyclic aromatic hydrocarbons (PAHs) in four long-term contaminated soils in order to assess the bioavailability of PAHs. Extraction kinetics of six PAHs viz. phenanthrene, fluoranthene, pyrene, benzo(a)anthracene, benzo(a)pyrene, dibenzo(a,h)anthrancene were selected to investigate as they covered the susceptible and recalcitrant PAHs in soil. A parallel experiments were also carried out on the microbial degradation of these PAHs in soil with and without biostimulation (by adding (NH₄)₂HPO₄). The rapidly desorbed fraction of fluoranthene, as indicated by the two-fraction model, was found the highest, ranging from 21.4% to 37.4%, whereas dibenzo(a,h)anthrancene was the lowest, ranging from 8.9% to 20.5%. The rapid desorption of selected PAHs was found to be finished within 24 h. The rapidly desorbed fraction of PAHs investigated using TLPS, was significantly correlated (R² = 0.95) with that degraded by microorganisms in biostimulation treatment. This suggested that the TLPS-assisted extraction could be a promising technique in determining the bioavailability of aged PAHs in contaminated soils. It also suggested that applying sufficient nutrients in bioremediation of field contaminated soils is crucial. Further work is required to test its application to more hydrophobic organic pollutants in long-term contaminated soils.

Performance and microbial community composition in a long-term sequential anaerobic-aerobic bioreactor operation treating coking wastewater

The combined anaerobic-aerobic biosystem is assumed to consume less energy for the treatment of high strength industrial wastewater. In this study, pollutant removal performance and microbial diversity were assessed in a long-term (over 300 days) bench-scale sequential anaerobic-aerobic bioreactor treating coking wastewater. Anaerobic treatment removed one third of the chemical oxygen demand (COD) and more than half of the phenols with hydraulic retention time (HRT) of 42 h, while the combined system with total HRT of 114 h removed 81.8, 85.6, 99.9, 98.2, and 85.4 % of COD, total organic carbon (TOC), total phenols, thiocyanate, and cyanide, respectively. Two-dimensional gas chromatography with time-of-flight mass spectrometry showed complete removal of phenol derivatives and nitrogenous heterocyclic compounds (NHCs) via the combined system, with the anaerobic process alone contributing 58.4 and 58.6 % removal on average, respectively. Microbial activity in the bioreactors was examined by 454 pyrosequencing of the bacterial, archaeal, and fungal communities. Proteobacteria (61.2-93.4 %), particularly Betaproteobacteria (34.4-70.1 %), was the dominant bacterial group. Ottowia (14.1-46.7 %), Soehngenia (3.0-8.2 %), and Corynebacterium (0.9-12.0 %), which are comprised of phenol-degrading and hydrolytic bacteria, were the most abundant genera in the anaerobic sludge, whereas Thiobacillus (6.6-43.6 %), Diaphorobacter (5.1-13.0 %), and Comamonas (0.2-11.1 %) were the major degraders of phenol, thiocyanate, and NHCs in the aerobic sludge. Despite the low density of fungi, phenol degrading oleaginous yeast Trichosporon was abundant in the aerobic sludge. This study demonstrated the feasibility and optimization of less energy intensive treatment and the potential association between abundant bacterial groups and biodegradation of key pollutants in coking wastewater.