Spatiotemporal distribution, sources apportionment and ecological risks of PAHs: a study in the Wuhan section of the Yangtze River

Geographic heterogeneity of polycyclic aromatic hydrocarbons in Yangtze River sediments: Evidence from the longest river in Asia

This work is the first comprehensive survey of the Yangtze River, covering its origin to the estuary mouth. It focuses on the geographical and industrial factors influencing the distribution of polycyclic aromatic hydrocarbons (PAHs) in sediments, along with their contamination levels, sources, and ecological risks. The total concentrations of PAHs ranged from 2.14 to 796 (mean 179 ± 179) ng/g, which falls within the low-to-middle range compared to global levels. Four-ring PAHs were observed with the highest proportion (34.0%), followed by three-rings (24.7%), five-rings (16.0%), two-rings (16.6%), and six-rings (8.62%). PAH levels were significantly higher downstream of the confluences of the Yangtze mainstream and its major tributaries, as well as in areas with frequent industrial activity. Heavy metals (Zn, Pb, and Cd) and industry output values were positively correlated with PAHs concentrations, especially three-ring PAHs. The results of source analysis, based on molecular diagnostics and principal component analysis, identified coal, biomass, and petroleum combustion as the main sources of PAHs. Among these, industrial coal combustion and vehicle emissions were dominant, contributing 39% and 64% of the PAHs pollution in top and bottom sediments, respectively. The toxicity equivalence (TEQ) evaluation results showed that the total TEQ of ∑16PAHs (mean: 14 ng/g) was below the 600 ng/g TEQBaP standard established by the Canadian Council of Ministers of the Environment. BaP had the highest TEQBaP, followed by DahA and BbF. The risk assessment indicated that Nap and Pyr were the two congeners with the highest risk, accounting for 24-33% and 21-28% of the Risk Quotient for negligible concentration values (RQNCs) and maximum Permissible Concentration values (RQMPCs) of ∑16PAHs, respectively. Despite the overall low to moderate risks of PAHs in the region, the above-mentioned major compounds (e.g., BaP, DahA, BbF, Nap, and Pyr) should be of continued concern.

High-density sampling reveals the occurrence, levels and transport flux of 15 polycyclic aromatic hydrocarbons derivatives (PAHs-d) along the Yangtze River

Polycyclic aromatic hydrocarbons derivatives (PAHs-d) have higher toxicity levels compared to its parent polycyclic aromatic hydrocarbons (PPAHs). Their partitioning in different media and large-scale transport patterns in rivers remain largely unknown. This study investigated the occurrence of 15 PAHs-d and 19 PPAHs in water and suspended particulate matter (SPM) of the Yangtze River between 2019 and 2020. The range of Σ15PAHs-d concentrations was 20.54 to 2010.03 ng·L-1 in water and 0.62 to 29.80 μg·g-1 in SPM. The primary PAHs-d components were 2,6-dimethylnaphthalene, 2-methylnaphthalene, and anthraquinone. The range of Σ19PPAHs concentrations in water and SPM was 34.89 to 739.53 ng·L-1 and 0.37 to 204.62 μg·g-1, respectively. And low-ring PAHs-d and PPAHs were more prevalent in water than SPM. Partitioning behaviors indicated that PAHs-d and PPAHs were more readily partitioned into water and SPM during normal and dry periods, respectively. The concentrations of PAHs-d saw significant changes in their spatial distribution, which rose in water and reduced in SPM in downstream of the Three Gorges Dam. This is due to the dam's blocking effect on sediment transport. Positive matrix factorization source analysis revealed biomass combustion upstream and vehicle emissions downstream as primary sources, shaped by the evolving energy consumption patterns of urban areas situated around the Yangtze River. The annual fluxes of PAHs-d in water and SPM of the Yangtze River were 90.40 t·yr-1 and 11.95 t·yr-1, representing 88.3 % and 11.7 % of the overall PAHs-d fluxes, respectively. The total fluxes of PAHs-d and PPAHs in water and SPM tended to increase spatially along the river, with growth rates exceeding 76 and 24 times, respectively. Interception within the Three Gorges Reservoir area has resulted in the differences in the concentration and transport distribution of PAHs-d and PPAHs upstream and downstream, which play important roles in reducing PAHs-d and PPAHs entry into the sea. Future studies on PAHs-d in Yangtze River basin tributaries and estuaries are essential.

Environmental DNA-based assessment of multitrophic biodiversity in a typical river located in the Loess Plateau, China: Influence of PAHs and suspended sediments

Polycyclic aromatic hydrocarbon (PAH) pollution and high suspended sediment (SS) contents are significant anthropogenic and natural stressors that threaten aquatic biodiversity. However, the characteristics of multitrophic biological communities and their co-occurrence patterns in response to PAHs in sediment-laden rivers remain unclear. This study investigated the spatial distribution of species across three trophic levels, including algae, metazoan, and fish, in the Beiluo River on the Loess Plateau, China, using environmental DNA metabarcoding. Biodiversity was assessed in relation to 16 PAHs, SS, and environmental variables. The PAH in the dissolved phase ranged from 19.70 to 1613.30 ng/L dominated by low molecular weight (LMW) PAHs. Partial least squares path modeling (PLS-PM) revealed a negative correlation between PAH distribution and SS in the river. In terms of biodiversity, the richness and Shannon index of algae (Chlorophyta and Dinophyceae) were positively associated with acenaphthene (ACE) levels. Conversely, the Shannon index and richness of metazoans (Rotifera and Arthropoda) appeared to decline in response to Benzo[a]anthracene (BaA) and pyrene (PYR). Fishes (Cypriniformes and Clupeiformes) demonstrated greater tolerance to PAH contamination than algae and metazoans, and their reduced richness and Shannon index were linked to the high SS loads (> 0.45 μm). The co-occurrence patterns highlighted a stronger association connection between algae and metazoan communities than fish. This study provides valuable insights into how PAHs could reshape the structure of riverine multitrophic communities under conditions of elevated SS loads.

Unpuzzling spatio-vertical and multi-media patterns of aniline accelerators/antioxidants in an urban estuary

Aniline accelerators and antioxidants (AAs) are high-production-volume industrial additives that have recently attracted emerging concern given their ubiquity in environmental compartments and the associated (eco)toxic effects. Nonetheless, available information on the multi-media behavior of AAs and their transformation products (TPs) remains scarce. Therefore, we determined the residues of twenty-four AA(TP)s in paired dissolved phases (i.e., filtered water), suspended particulate matter (SPM), and sediment samples collected from the Yangtze River Estuary (YRE), a highly urbanized estuary in the East China. The median total concentrations of targeted compounds were 0.73 ng/g dw, 34.4 ng/L, and 39.6 ng/L in sediments, surface and bottom water, respectively. Diphenylamine (DPA) was the most abundant congener in SPM, while 1,3-diphenylguanidine (DPG) and dicyclohexylamine (DChA) dominated in the dissolved phases and sediments. Various anthropogenic emissions and (a)biotic degradation may collectively shape the matrix-specific accumulation patterns and spatial trends of these compounds across the YRE. However, the vertical patterns of AA(TP)s were obscure, probably due to the estuarine hydrodynamics and/or the modest sample size. The SPM fractions of AA(TP)s in water (Ф: 7.9-100%) and the sediment sorption coefficients (KOC: 0.01-6.56) both positively correlated with their hydrophobicity as indicated by the octanol-water partition coefficient (KOW). Moreover, risk quotients implied moderate to high aquatic toxicity posed by several AA(TP)s at certain YRE sites. The estimated total annual fluxes of our analytes transported via water and sediments towards the East China Sea were 5.90-365.5 tons and 4.23-1,100 kg, respectively. This work provides a systematic investigation of multi-media processes and ecological risks of AA(TP)s in a highly-urbanized estuary, contributing to holistic comprehension of these emerging contaminants in estuarine environments.

Prioritization of the ecotoxicological hazard of PAHs towards aquatic species spanning three trophic levels using 2D-QSTR, read-across and machine learning-driven modelling approaches

Polycyclic aromatic hydrocarbons (PAHs) represent a common group of environmental pollutants that endanger various aquatic organisms via various pathways. To better prioritize the ecotoxicological hazard of PAHs to aquatic environment, we used 2D descriptors-based quantitative structure-toxicity relationship (QSTR) to assess the toxicity of PAHs toward six aquatic model organisms spanning three trophic levels. According to strict OECD guideline, six easily interpretable, transferable and reproducible 2D-QSTR models were constructed with high robustness and reliability. A mechanistic interpretation unveiled the key structural factors primarily responsible for controlling the aquatic ecotoxicity of PAHs. Furthermore, quantitative read-across and different machine learning approaches were employed to validate and optimize the modelling approach. Importantly, the optimum QSTR models were further applied for predicting the ecotoxicity of hundreds of untested/unknown PAHs gathered from Pesticide Properties Database (PPDB). Especially, we provided a priority list in terms of the toxicity of unknown PAHs to six aquatic species, along with the corresponding mechanistic interpretation. In summary, the models can serve as valuable tools for aquatic risk assessment and prioritization of untested or completely new PAHs chemicals, providing essential guidance for formulating regulatory policies.

Evaluation of plant species for air pollution tolerance and phytoremediation potential in proximity to a coal thermal power station: implications for smart green cities

In metropolitan areas, air pollution poses a significant threat, and it is crucial to carefully select plant species that can tolerate such conditions. This requires a scientific approach based on systematic evaluation before recommending them to executive bodies. This study aimed to determine the air pollution tolerance index (APTI), dust retention capacity, and phytoremediation ability of 10 plant species growing in and around a lignite-based coal thermal power station. The results showed that Ficus benghalensis L. had the highest APTI, followed by Mimusops elengi L., Ficus religiosa L., Azadirachta indica A. Juss., and Annona reticulata L. F. benghalensis also showed the highest pH of leaf extract, relative water content, total chlorophyll, and ascorbic acid content, as well as the highest dust capturing capacity. Among the ten plant species, F. benghalensis, M. elengi, F. religiosa, A. indica and F. racemosa were identified as a tolerant group that can be used for particulate matter suppression and heavy metal stabilization in and around thermal power plants. These findings can inform the selection of plants for effective green infrastructure in smart green cities, promoting the health and well-being of urban populations. This research is relevant to urban planners, policymakers, and environmentalists interested in sustainable urban development and air pollution mitigation.

An investigation into the disturbance effects of coal mining on groundwater and surface ecosystems

Coal mining disturbs surface ecosystems in coal mining subsidence areas. Based on the groundwater-surface composite ecosystem analysis, we constructed an ecological disturbance evaluation index system (18 indices) in a coal mining subsidence area using the analytic hierarchy process (AHP). Taking the Nalinhe mining area in Wushen Banner, China, in 2018-2020 as an example, the weight, ecological disturbance grade and correlation of different indicators were determined by implementing fuzzy mathematics, weighting method, and correlation analysis method. The major conclusions of this review were: (i) After two years of mining, ecological disturbance was the highest in the study area (Grade III) and the lowest in the non-mining area (Grade I). (ii) Coal mining not only directly interfered with the environment, but also strengthened the connection of different ecological indicators, forming multiple ecological disturbance chains such as "mining intensity-mining thickness-buried depth/Mining thickness", "coal mining-surface subsidence-soil chemical factors", and "natural environment-soil physical factors". The disturbance chain that controls the ecological response factors in the region remains to be determined. However, the ecological response factors are the most important factor that hinders the restoration of the ecology in a coal mining subsidence area. (iii) The ecological disturbance in the coal mining subsidence area continued increasing over two years due to coal mining. The ecological disturbance by coal mining cannot be completely mitigated by relying on the self-repair capability of the environment. This study is of great significance for ecological restoration and governance of coal mining subsidence areas.

Combining hydrochemistry and 13C analysis to reveal the sources and contributions of dissolved inorganic carbon in the groundwater of coal mining areas, in East China

East China is a highly aggregated coal-grain composite area where coal mining and agricultural production activities are both flourishing. At present, the geochemical characteristics of dissolved inorganic carbon (DIC) in groundwater in coal mining areas are still unclear. This study combined hydrochemical and carbon isotope methods to explore the sources and factors influencing DIC in the groundwater of different active areas in coal mining areas. Moreover, the 13C isotope method was used to calculate the contribution rates of various sources to DIC in groundwater. The results showed that the hydrochemical types of groundwater were HCO3-Ca·Na and HCO3-Na. The main water‒rock interactions were silicate and carbonate rock weathering. Agricultural areas were mainly affected by the participation of HNO3 produced by chemical fertilizer in the weathering of carbonate rocks. Soil CO2 and carbonate rock weathering were the major sources of DIC in the groundwater. Groundwater in residential areas was primarily affected by CO2 from the degradation of organic matter from anthropogenic inputs. Sulfate produced by gypsum dissolution, coal gangue accumulation leaching and mine drainage participated in carbonate weathering under acidic conditions, which was an important factor controlling the DIC and isotopic composition of groundwater in coal production areas. The contribution rates of groundwater carbonate weathering to groundwater DIC in agricultural areas and coal production areas ranged from 57.46 to 66.18% and from 54.29 to 62.16%, respectively. In residential areas, the contribution rates of soil CO2 to groundwater DIC ranged from 51.48 to 61.84%. The results will help clarify the sources and circulation of DIC in groundwater under the influence of anthropogenic activities and provide a theoretical reference for water resource management.