Probing the occurrence, sources and cancer risk assessment of polycyclic aromatic hydrocarbons in PM2.5 in a humid metropolitan city in China.

Fifty-two consecutive PM2.5 samples from December 2021 to February 2022 (the whole winter) were collected in the center of Chongqing, a humid metropolitan city in China. These samples were analysed for the 16 USEPA priority polycyclic aromatic hydrocarbons (16 PAHs) to explore their composition and sources, and to assess their cancer risks to humans. The total concentrations of the 16 PAHs (ng m-3) ranged from 16.45 to 174.15, with an average of 59.35 ± 21.45. Positive matrix factorization (PMF) indicated that traffic emissions were the major source (42.4%), followed by coal combustion/industrial emission (31.3%) and petroleum leakage/evaporation (26.3%). The contribution from traffic emission to the 16 PAHs increased from 40.0% in the non-episode days to as high as 46.2% in the air quality episode during the sampling period. The population attributable fraction (PAF) indicates that when the unit relative risk (URR) is 4.49, the number of lung cancer cases per million individuals under PAH exposure is 27 for adults and 38 for seniors, respectively. It was 5 for adults and 7 for seniors, when the URR is 1.3. The average incremental lifetime cancer risk (ILCR) for children, adolescents, adults and seniors was 0.25 × 10-6, 0.23 × 10-6, 0.71 × 10-6, and 1.26 × 10-6, respectively. The results of these two models complemented each other well, and both implied acceptable PAH exposure levels. Individual genetic susceptibility and exposure time were identified as the most sensitive parameters. The selection and use of parameters in risk assessment should be further deepened in subsequent studies to enhance the reliability of the assessment results.

An integrated approach to identify the source apportionment of potentially toxic metals in shale gas exploitation area soil, and the associated ecological and human health risks.

Public awareness of the potential environmental risks of shale gas extraction has increased in recent years. However, the status and environmental risks of potentially toxic metals (PTMs) in shale gas field soil remain unclear. A total of 96 topsoil samples were collected from the first shale gas exploitation area in China. The sources of nine PTMs in the soils were identified using positive matrix factorization and correlation analysis, and the ecological and human health risks of toxic metals from different sources under the two land use types were calculated. The results showed that mean pollution load index (PLI) values for farmland (1.18) and woodland (1.40) indicated moderate pollution, As, Cd and Ni were the most serious contaminants among all nine PTMs. The following four sources were identified: shale gas extraction activities (43.90%), nature sources (31.90%), agricultural and traffic activities (17.55%) and industrial activities (6.55%). For ecological risk, the mean ecological risk index (RI) values for farmlands (161.95) and woodlands (185.27) reaching considerable risk. The contribution ratio of shale gas extraction activities for farmlands and woodlands were 5.70% and 8.90%, respectively. Regarding human health risk, noncarcinogenic risks for adults in farmlands and woodlands were negligible. Industrial activities, agricultural and traffic activities were estimated to be the important sources of health risks. Overall, shale gas extraction activities had little impact on the ecological and human health risk. This study provides scientific evidence regarding the soil contamination potential of shale gas development activities.

River water influenced by shale gas wastewater discharge for paddy irrigation has limited effects on soil properties and microbial communities.

The processes of hydraulic fracturing to extract shale gas generate a large amount of wastewater, and the potential impacts of wastewater discharge after treatment are concerning. In this field study, we investigated the effects of the irrigation of paddy fields for 2 consecutive years by river water that has been influenced by shale gas wastewater discharge on soil physicochemical properties, microbial community structure and function, and rice grain quality. The results showed that conductivity, chloride and sulfate ions in paddy soils downstream of the outfall showed an accumulative trend after two years of irrigation, but these changes occurred on a small scale (<500 m). Two-year irrigation did not cause the accumulation of trace metals (barium, cadmium, chromium, copper, lead, strontium, zinc, nickel, and uranium) in soil and rice grains. Among all soil parameters, the accumulation of chloride ions was the most pronounced, with concentrations in the paddy soil at the discharge site 13.3 times higher than at the upstream control site. The use of influenced river water for paddy irrigation positively increased the soil microbial diversity, but these changes occurred after two years of irrigation and did not occur after one year of irrigation. Overall, the use of river water affected by shale gas wastewater discharge for agricultural irrigation has limited effects on agroecosystems over a short period. Nevertheless, the possible negative effects of contaminant accumulation in soil and rice caused by longer-term irrigation should be seriously considered.

Combining eDNA and morphological approaches to reveal the impacts of long-term discharges of shale gas wastewaters on receiving waters.

The potential threats of shale gas wastewater discharges to receiving waters is of great concern. In this study, chemical analyses and biomonitoring were performed three times in a small river that received treated wastewater over a two-year period. The results of chemical analyses showed that the concentrations of chloride, conductivity, barium, and strontium increased at the discharge site, but their concentrations decreased considerably farther downstream (≥500 m). The concentrations of toxic organic compounds (16 US EPA priority polycyclic aromatic hydrocarbons and 6 priority phthalates), trace metals (strontium, arsenic, zinc, copper, chromium, lead, cadmium, nickel, and neodymium), and natural radionuclides (40K, 238U, 226Ra, and 232Th) were comparable to the corresponding background values or did not exhibit obvious accumulation in sediments with continued discharge. Morphological and environmental DNA approaches were used to reveal the potential effects of wastewater discharges on aquatic ecosystems. The results showed that the community structure of benthic invertebrates was not altered by the long-term discharges of shale gas wastewaters. However, the biodiversity indices (richness and Shannon) from the two approaches showed inconsistencies, which were caused by multiple reasons, and that substrates had a strong influence on the morphological biodiversity indices. A multimetric index was proposed to further analyze morphological and environmental DNA data, and the results showed no significant difference between the upstream and downstream sites. Generally, the chemical and biological results both demonstrated that the discharges of shale gas wastewaters had limited impacts on river ecosystems within two years.

Characterization of microbial communities and functions in shale gas wastewaters and sludge: Implications for pretreatment.

As hydraulic fracturing (HF) practices keep expanding in China, a comparative understanding of biological characteristics of flowback and produced waters (FPW) and sludge in impoundments for FPW reserve will help propose appropriate treatment strategies. Therefore, in this study, the microbial communities and functions in impoundments that collected wastewaters from dozens of wells were characterized. The results showed that microbial richness and diversity were significantly increased in sludge compared with those in FPW. The vast majority of microorganisms found in FPW and sludge are organic degraders, providing the possibility of using these indigenous microorganisms to biodegrade organic compounds. Our laboratory findings first show that wastewater pretreatment using these microorganisms was effective, and organic compounds in FPW from different shale formations were removed by 35-68% within 72 h in a wide temperature range (8 - 30 â„ƒ). Meanwhile, highly toxic compounds such as phthalate esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), and petroleum hydrocarbons were effectively eliminated in reactors. The main microorganisms, key functional genes, and putative pathways for alkanes, PAHs, and PAEs degradation were also identified.

Storage strategy for shale gas flowback water based on non-bactericide microorganism control.

Shale gas is a promising unconventional natural gas in the world, however the produced flowback water have severe challenges to surrounding water resource. Conventional reuse technology uses bactericide to control corrosive microorganism, which might bring uncontrolled drug resistance and other secondary pollution. In this study, storage strategy of flowback water was designed as a pre-control stage to decline corrosive microorganism. Dissolved oxygen and temperature were chosen as two key parameters based on microbial physiological and biochemical characteristics. Results showed that under the cross effect of temperature and dissolved oxygen, 15 °C and anaerobic condition had the optimal microorganism control effectiveness. Microorganism amount and live/dead cell ratio decreased by 63.7% and 68.74% respectively compared raw water. COD removal efficiency reduced to only 20%, indicating that the microorganism activity was extremely inhibited. However, microorganism in flowback water was more sensitive to dissolved oxygen compared to temperature. Redundancy analysis confirmed that dissolved oxygen contribution was as high as 91.5% while temperature was not significant (p > 0.05), the contribution rate was only 8.5%. Thermococcus, Archaeoglobus, Thermovirga, Thermotoga and Moorella were the dominated thermophilic, anaerobic and sulfate reduction or metal corrosion microorganism in flowback water, so all these identified microorganisms were control targets. Importantly, all the target microorganisms detected in flowback water were declined after different storage strategies. This study provides an effective storage strategy for flowback water to inhibit the microbial amount and activity without biocides addition, which could help promote the green exploitation of shale gas.

Watershed-scale assessment of surface water-related risks from shale gas development in mountainous areas, China.

Water risks are one of the key issues dominating environmental debates on shale gas development. Water withdrawals and wastewater discharges in shale gas fields of mountainous areas are more complicated than in plain areas due to different climatic, topographical and hydrological conditions, which would impact water resources. This research identifies the surface water-related risks from shale gas development in mountainous areas as water shortage and water pollution. Conceptions of accessibility for both water supply and water pollution are proposed to describe the vulnerability of water resources and the exposure to water pollution. Based on a risk probability model, a water risk assessment method for mountainous areas is constructed from the perspectives of dangers, exposures and vulnerabilities. Finally, the assessment method is applied in Chongqing, China. The results show that, from 2010 to 2020, the water consumption of shale gas development has a little impact on regional water resources in total, but more significant impacts are seen in a few areas, including the seasonal water-deficient areas in Western Chongqing, the urban and suburban areas with high pollutant loadings in Midwest Chongqing, and other areas with high pollutant accessibility and vulnerable water environments. The surface water-related risks of the shale gas development in Chongqing are principally composed of low and relatively low levels of risks, which cover 60% of the total area of Chongqing and display a spatial difference of west > northeast > southeast areas. Based on Monte Carlo method, the results of uncertainty analyses show the model is reliable. This research provides a reference for water comprehensive risk assessment of shale gas development in mountainous areas.

The Co-occurrence of DNRA and Anammox during the anaerobic degradation of benzene under denitrification.

It was revealed that Anammox process promotes the anaerobic degradation of benzene under denitrification. This study investigates the effect of dissimilatory nitrate reduction to ammonium (DNRA) and exogenous ammonium on anaerobic ammonium oxidation bacteria (AnAOB) during the anaerobic degradation of benzene under denitrification. The results indicate that anammox occurs synergistically with organisms using the DNRA pathway, such as Draconibacterium and Ignavibacterium. Phylogenetic analysis showed 64% (16/25) and 36% (5/25) hzsB gene sequences, a specific biomarker of AnAOB, belonged to Candidatus 'Brocadia fuldiga' and Candidatus 'Kuenenia', respectively. Exogenous ammonium addition enhanced the anammox process and accelerated benzene degradation at a 1.89-fold higher average rate compared to that in the absence of exogenous ammonium and AnAOB belonged to Ca. 'Kuenenia' (84%) and Ca. 'Brocadia fuldiga' (16%). These results indicate that Ca. 'Brocadia fuldiga' could also play a role in DNRA. However, the diversity of abcA and bamA, the key anaerobic benzene metabolism biomarkers, remained unchanged. These findings suggest that anammox occurrence may be coupled with DNRA or exogenous ammonium and that anammox promotes anaerobic benzene degradation under denitrifying conditions. The results of this study contribute to understanding the co-occurrence of DNRA and Anammox and help explore their involvement in degradation of benzene, which will be crucial for directing remediation strategies of benzene-contaminated anoxic environment.

Simultaneous removal of organic matter and iron from hydraulic fracturing flowback water through sulfur cycling in a microbial fuel cell.

The high volume of flowback water (FW) generated during shale gas exploitation is highly saline, and contains complex organics, iron, heavy metals, and sulfate, thereby posing a significant challenge for the environmental management of the unconventional natural gas industry. Herein, the treatment of FW in a sulfur-cycle-mediated microbial fuel cell (MFC) is reported. Simultaneous removal efficiency for chemical oxygen demand (COD) and total iron from a synthetic FW was achieved, at 72 ±â€¯7% and 90.6 ±â€¯8.7%, respectively, with power generation of 2667 ±â€¯529 mW/m3 in a closed-circuit MFC (CC-MFC). However, much lower iron removal (38.5 ±â€¯4.5%) occurred in the open-circuit MFC (OC-MFC), where the generated FeS fine did not precipitate because of sulfide supersaturation. Enrichment of both sulfur-oxidizing bacteria (SOB), namely Helicobacteraceae in the anolyte and the electricity-producing bacteria, namely Desulfuromonadales on the anode likely accelerated the sulfur cycle through the biological and bioelectrochemical oxidation of sulfide in the anodic chamber, and effectively increased the molar ratio of total iron to sulfide, thus alleviating sulfide supersaturation in the closed circuitry. Enrichment of SOB in the anolyte might be attributed to the formation of FeS electricity wire and likely contributed to the stable high power generation. Bacteroidetes, Firmicutes, Proteobacteria, and Chloroflexi enriched in the anodic chamber were responsible for degrading complex organics in the FW. The treatment of real FW in the sulfur-cycle-mediated MFC also achieved high efficiency. This research provides a promising approach for the treatment of wastewater containing organic matters, heavy metals, and sulfate by using a sulfur-cycle-mediated MFC.

Inhibition of benzene, toluene, phenol and benzoate in single and combination on Anammox activity: implication to the denitrification-Anammox synergy.

A previous study demonstrated that denitrification synergized with Anammox could accelerate the anaerobic degradation of benzene. The inhibitory effects of benzene, toluene, phenol and benzoate in single and combination on Anammox activity were investigated by short-term batch tests. The results indicated that the inhibition of single compounds on Anammox could be well fitted with the extended non-competitive and Luong inhibition kinetic models. The inhibitions of the individual compound were in order as follows: benzene > toluene > phenol > benzoate. The joint inhibitions of bi-component mixtures of benzene with toluene, benzene with phenol and benzene with benzoate on Anammox activity were additive; the joint inhibition of a tri-component mixture (benzene, toluene and phenol) was partly additive; and the joint inhibition of a multicomponent mixture (benzene, toluene, phenol and benzoate) was synergistic. The effect of benzoate on the denitrification-Anammox synergy for benzene degradation was evaluated using a long-term test. Although the average rate of benzene degradation decreased by 13% with the addition of 10 mg L-1 benzoate, the average rate of NO3- and NH4+ increased by approximately 1- and 0.56-fold, respectively, suggesting that benzoate favors the stability of the denitrification-Anammox synergy. The carboxylation of benzene would be a more favorable pathway for the anaerobic degradation of benzene under denitrification synergized with Anammox.

Denitrification synergized with ANAMMOX for the anaerobic degradation of benzene: performance and microbial community structure.

To evaluate the effect of anaerobic ammonium oxidation (ANAMMOX) on benzene degradation under denitrification, a sequencing batch reactor (SBR) under denitrification synergized with ANAMMOX (SBR-DenAna) for benzene degradation was established by inoculating anaerobic ammonium-oxidizing bacteria (AnAOB) into a SBR under denitrification reactor (SBR-Den) for benzene degradation. The average rate of benzene degradation and the maximum first-order kinetic constant in SBR-DenAna were 2.34- and 1.41-fold those in SBR-Den, respectively, indicating that ANAMMOX improved the degradation of benzene under denitrification synergized with ANAMMOX. However, the average rate of benzene degradation decreased by 35% in the denitrification-ANAMMOX synergistic reactor when 10 mg N L-1 NO2- was added; the rate recovered once NO2- was depleted, indicating that ANAMMOX might detoxify NO2-. Results from high-throughput sequencing analysis revealed that Azoarcus within the family Rhodocyclaceae might be associated with benzene degradation in the two SBRs. AnAOB affiliated with the family Candidatus Brocadiaceae were just detected in SBR-DenAna.