Polycyclic aromatic hydrocarbons in leaves of Cinnamomum camphora along the urban-rural gradient of a megacity: Distribution varies in concentration and potential toxicity

Relationship between foliar polycyclic aromatic hydrocarbons (PAHs) concentrations and plant traits: Intracanopy variability for a broadleaf species in an urban environment

The emission of potentially harmful compounds, including polycyclic aromatic hydrocarbons (PAHs), and the resulting air pollution is a serious problem in modern cities. It is therefore important to develop mitigation strategies, such as "smart" planting of trees that act as sinks for PAHs. However, the intra-individual (within-tree) variability in leaf PAH concentrations remains unknown. In this paper, we studied 15 ornamental apple trees (Malus × moerlandsii 'Profusion') growing on a main street in a medium-sized city in Galicia (NW Spain). We determined the PAH concentrations at 12 canopy positions in each tree (2 orientations and 2 distances from the trunk at 3 heights), measured various ecological traits (specific leaf area [SLA], δ13C, stomatal density, fatty acid contents and leaf hairiness) and analyzed the variability in traits within the canopy in relation to PAH concentrations. We observed high intra-individual variability in the PAH concentrations and the leaf traits. Statistical analyses revealed that leaf height was the main source of variability both in the PAH concentrations and in the traits, mainly due to the leaf morphology, particularly to the SLA. Therefore, the ideal vegetation to remove PAHs would be high leaf biomass trees, not too tall and with a high proportion of shade leaves.

Integrated metabolomics, transcriptomics, and proteomics analyses reveal co-exposure effects of polycyclic aromatic hydrocarbons and cadmium on ryegrass (Lolium perenne L.)

Cadmium (Cd) and polycyclic aromatic hydrocarbons (PAHs) are prominent soil contaminants found in industrial sites, and their combined effects on plants are not yet fully understood. To investigate the mechanisms underlying the co-exposure of Cd and PAHs and identify key biomarkers for their co-effects, an integrated analysis of metabolomics, transcriptomics, and proteomics was conducted on ryegrass leaves cultivated in soil. In nontarget metabolomics analysis, nine differentially expressed metabolites that were specifically induced by the compound exposure were identified. When combined with the analysis of differentially expressed genes and proteins, it was determined that the major pathways involved in the response to the co-stress of Cd and PAHs were linoleic acid metabolism and phenylpropanoid biosynthesis. The upregulation of 12,13-dihydroxy-9Z-octadecenoic acid and the downregulation of sinapyl alcohol were identified as typical biomarkers, respectively. Compared to scenarios of single exposures, the compound exposure to Cd and PAHs disrupted the oxidation of linoleic acid, leading to alterations in the profiles of linoleate metabolites. Additionally, it intensified hydroxylation, carboxylation, and methylation processes, and interfered with reactions involving coenzyme A, thus inhibiting lignin production. As a result, oxidative stress was elevated, and the cell wall defense system in ryegrass was weakened. The findings of this study highlight the ecological risks associated with unique biological responses in plants co-exposed to Cd and PAHs in polluted soils.

Polycyclic aromatic hydrocarbons (PAHs) in a sediment core from Lake Taihu and their associations with sedimentary organic matter

Sediment core is the recorder of polycyclic aromatic hydrocarbon (PAH) pollutions and the associated sedimentary organic matter (SOM), acting as crucial supports for pollution control and environmental management. Here, the sedimentary records of PAHs and SOM in the past century in Lake Taihu, China, were reconstructed from a 50-cm sediment core. On the one hand, the presence of PAHs ranged from 8.99 to 199.2 ng/g. Vertically, PAHs declined with the depth increased, and the sedimentation history of PAHs was divided into two stages with a discontinuity at 20 cm depth. In composition, PAHs in the sediment core were dominated by three-ring PAHs (44.6% ± 9.1%, mean ± standard deviation), and were followed by four-ring (27.0% ± 3.3%), and five-ring (12.1% ± 4.0%) PAHs. In toxicity assessment, the sedimentary records of benzo[a]pyrene-based toxic equivalency were well described by an exponential model with R-square of 0.95, and the environmental background toxic value was identified as 1.62 ng/g. On the other hand, different components of SOM were successfully identified by n-alkane markers (p < 0.01) and the variations of SOM were well explained (84.6%). A discontinuity of SOM was recognized at 22 cm depth. Association study showed that the sedimentary PAHs were associated with both anthropogenic and biogenic SOM (p < 0.05) with explained variances for most individual PAHs of 60%. It indicated the vertical distributions of PAHs were driven by sedimentary SOM. Therefore, environmental processes such as biogenic factors should attract more attentions as well as PAH emissions to reduce the impacts of PAHs.

Impacts of atmospheric copper and cadmium deposition on the metal accumulation of camphor leaves and rings around a large smelter

The atmospheric deposition of copper (Cu) and cadmium (Cd) was monitored in eight sites around a Cu smelter with similar distance to verify whether tree leaf and ring can be used as bio-indicators to track spatial pollution record. Results showed that total atmospheric deposition of Cu (103-1215 mg/m²/year) and Cd (3.57-11.2 mg/m²/year) were 4.73-66.6 and 3.15-12.2 times higher than those in background site (164 mg/m²/year and 0.93 mg/m²/year). The frequencies of wind directions significantly influenced the atmospheric deposition of Cu and Cd, and the highest atmospheric deposition of Cu and Cd were at the prevalent northeastern wind (JN), and low frequency south (WJ) and north (SW) winds for the lowest deposition fluxes. Since the bioavailability of Cd was higher than that of Cu, the atmospheric deposition of Cd was more easily adsorbed by tree leaf and ring, resulting in only significant relation between atmospheric Cd deposition and Cinnamomum camphora leaves and tree ring Cd. Although tree rings cannot correctly record the atmospheric Cu and Cd deposition, higher concentrations in the indigenous tree rings than the transplanted tree rings suggested that tree rings can reflect to some extent the variations of atmospheric deposition. Generally, spatial pollution of atmospheric deposition of heavy metals cannot reflect the distribution of soil total and available metals around the smelter, and only camphor leaf and tree ring can bio-indicate Cd deposition. A major implication of these findings is that leaf and tree ring can serve for biomonitoring purposes to assess the spatial distribution of atmospheric deposition metal with high bioavailability around a pollution source with similar distance.

Biomonitoring of atmospheric PAHs using fir and spruce needles in forests in the vicinity of mountain villages

The aim of the study was to use chemical analyses of spruce and fir needles to determine environmental exposure to polycyclic aromatic hydrocarbons (PAHs) in forests surrounding small mountain towns, including popular tourist destinations. The Beskid Mountains in Poland were chosen as the study area because they are very popular with tourists. The 6- and 12 month old needles were collected in two consecutive years from permanent study plots. Two vintages of needles were used to determine the differences between seasons in the profile of deposited pollutants. Some of plots were located away from roads and buildings, while others were located near tourist destinations. The comparison plots were located in the centre of a tourist resort, near a highway, and in a forest localised in the industrial city characterised by a high degree of urbanization. The analyses of 15 PAHs content showed that the amount and type of compounds retained by the needles were influenced not only by the proximity and amount of the surface emitters, but also by the location of the research sites above sea level. The results obtained can be explained, among other things, by the phenomenon of smog, which is not uncommon in the study region in autumn and winter.

Coagulation effect of atmospheric submicron particles on plant leaves: Key functional characteristics and a comparison with dry deposition

Submicron particles have become a new focus in research on air pollution control. The abilities of urban tree species to retain particles can be used to alleviate urban haze pollution. However, research has focused mostly on plants and environmental conditions rather than on particle itself. Particle migration and transformation at the leaf-air interface are the key to dust retention. Submicron particles coagulate when they are retained by leaves. In this study, NaCl was used to simulate submicron particles. The average sizes of the particles on the leaves of 10 greening tree species in Shanghai in different seasons were measured using the sweep-resuspension method to characterize the coagulation effect. Thereafter, the effects of leaf characteristics were investigated and analyzed in relation to dry deposition velocity. The results indicated that the particles on the leaves of Ginkgo biloba, Osmanthus fragrans, Sabina chinensis (L.) Ant. "Kaizuca," Cinnamomum camphora, and Metasequoia glyptostroboides were large. The seasonal variability of the sizes of the particles on the leaves of different tree species varied. The average particle size was positively correlated with wax content and negatively correlated with single leaf area; however, the other factors correlated with particle size varied by season. For example, in April, the average particle size was positively correlated with tensile strength, wind resistance, adaxial epidermal roughness, and water potential, whereas the effects of stomatal conductance were more complex. Non-significant correlation was identified between coagulation and dry deposition although both were positively correlated with roughness and wax content. This study explored the effects of leaf characteristics on coagulation. The results may serve as a theoretical foundation for explaining the microscopic process underlying dust retention in plants and may provide a clearer scientific basis for the prevention and control of submicron particle pollution and the selection of urban greening tree species.

Polycyclic aromatic hydrocarbon (PAH) accumulation in Quercus palustris and Pinus nigra in the urban landscape of Gothenburg, Sweden

Trees have the potential to improve urban air quality as leaves and needles capture air pollutants from the air, but further empirical data has been requested to quantify these effects. We measured the concentration of 32 polycyclic aromatic hydrocarbons (PAHs) in leaves of pin oak (Quercus palustris) and needles of black pine (Pinus nigra) in the City of Gothenburg, Sweden, during the summer of 2018. Oak leaves were collected twice (June, September), while one-year-old (C + 1) and three-year-old (C + 3) pine needles were sampled in June to study the temporal development of leaf/needle PAH concentrations. Specific leaf area (SLA) was estimated, which permitted calculation of leaf/needle area-based PAH content that were compared with the mass-based concentration. In addition, the air concentration of PAHs and NO₂ was measured using passive samplers. There was a strong correlation between air concentrations of PAH and NO₂, indicating that the pollutants to a large degree originate from the same sources. In the oak leaves there was a significant decrease in low molecular mass PAHs (L-PAH, mainly gaseous) between June and September, but a significant increase in high molecular mass PAHs (H-PAH, mainly particle-bound). There was a strong correlation between L-PAH concentration in leaves and in air indicating an influence of equilibrium processes between ambient air and leaf. In the pine needles, there was a significant increase of both L-PAH and H-PAH in three-year-old needles compared to one-year-old needles. Pine was superior to oak in accumulating PAHs from the air, especially for L-PAHs when comparing area-based content. However, H-PAH concentrations were higher in oak leaves compared to pine needles on a leaf mass basis, emphasizing the importance of how concentrations are expressed. The results from this study can contribute to the development of urban planning strategies regarding the effect of vegetation on air quality.

The potential risks and exposure of Qinling giant pandas to polycyclic aromatic hydrocarbon (PAH) pollution

Rapid industrialization and urbanization have created a substantial urban-rural gradient for various pollutants. The Qinling Mountains are highly important in terms of biodiversity, providing habitat for giant pandas, which are endemic to China and are a widely recognized symbol for conservation. Whether polycyclic aromatic hydrocarbon (PAH) exposure risks regarding in situ animal conservation zones are affected by environmental pollution or even enhanced by the mountain-trapping effect requires further research. Our group carried out a large-scale investigation on the area ranging from Xi'an to Hanzhong across the giant panda habitat in the Qinling Mountains by collecting atmosphere, soil, bamboo, and fecal samples from different sites over a two-year period. The total toxicity of atmospheric PAHs and the frequencies of soil PAHs above effect range low (ERL) values showed a decreasing trend from urban areas to the central mountains, suggesting a distance effect from the city. The proportions of total 5- and 6-ring PAHs in the atmosphere were higher in the central mountainous areas than in the urban areas, while this difference was reversed in the soil. Health risk assessments showed that the incremental lifetime carcinogenic risks (ILCR) of PAH exposure by bamboo ingestion ranged from 2.16 × 10^-4 to 3.11 × 10^-4, above the critical level of 10^-4. Bamboo ingestion was the main driver of the PAH exposure risks. The concentration difference between bamboo and fecal samples provided a reference for the level of PAHs absorbed by the panda digestive system. Since the Qinling Mountains possess the highest density of giant pandas and provide habitats to many other endangered animal and plant species, we should not ignore the probability of health risks posed by PAHs. Monitoring the pollution level and reducing the atmospheric emissions of toxic pollutants are recommended actions. Further detailed research should also be implemented on pandas' health effects of contaminant exposure.

Immune-mediated disease associated microbial community responded to PAH stress in phyllosphere of roadside greenspaces in Shanghai

Microorganisms in urban greenspaces play key roles in ecosystem service provision and potentially influence human health. Increasing evidence suggests that anthropogenic disturbance poses constant stress on urban microbial communities, yet, as previous studies have focused on non-contaminated greenspaces, it has remained largely unknown how microorganisms respond to anthropogenic stress in roadside greenspaces with contamination. Our previous effort determined phyllosphere PAHs of camphor trees in 84 sites of roadside greenspaces along the urban-rural gradient in Shanghai. Here, we further investigated the phyllosphere microbial communities (PMCs) of the same sites across the same urban categories, including urban, suburban, and rural areas using high-throughput DNA sequencing. We aimed to explore how PMCs, especially those associated with immune-mediated diseases (IMDs), were affected by PAHs and the surrounding land-use types. We found that several microorganisms associated with increasing IMD risk were stimulated by PAHs. The composition of PMCs differed between the three urban categories which can be largely explained by the variation of phyllosphere PAH concentration and the surrounding land-use types. Similar to our previous study, suburban areas were linked with the most potential adverse health effects, where we observed the lowest bacterial diversity, the highest relative abundance of IMD-associated bacteria, and the highest relative abundance of Pathotroph. Urban green-blue infrastructure (GBI) was positively correlated with the diversity of PMCs, whereas urban grey infrastructure tended to homogenize PMCs. Notably, GBI also reduced the relative abundance of IMD-associated and pathogenic microbes, indicating the potential health benefits of GBI in land-use planning. Taken together, our study emphasizes the need to further investigate environmental communities in contaminated traffic environments, as human microbiomes are directly exposed to risky microorganisms.

Assessing the ecological balance between supply and demand of blue-green infrastructure

Given that improving urban ecological environment requires a clear recognition of the urban ecological elements, investigating the ecosystem service capabilities of urban green-blue infrastructures (UGBIs) becomes ever important. This study aims to reveal and compare the synergistic ecosystem service ability of UGBIs with different characteristics and the relationship with human demand in Wuhan city. It was found that the climate regulation service and water regulation service value of lake-type parks both reached the highest over the other UGBIs. Nature-type parks revealed the most capable cultural service, and green-type parks demonstrated the greatest exercise cultural service value. The analysis showed that the ecosystem services delivered by the UGBIs were influenced by the park area, the total value of the normalized difference vegetation index and normalized water body index, and the distance from the city centre. Furthermore, a significant spatial phenomenon was found that the ecological capacity of lake-type parks in the city centre was higher than that of the other UGBIs at the same location. Regarding the relationship with the human activity intensity, the high-demand and high-supply regions were mainly concentrated in highly developed areas in terms of regulating services. Nevertheless, a severe environmental inequality occurred in small urban centres, which requires urgent attention from the government. This work answered the question of where and how to optimize the green-blue infrastructures in Wuhan, and it contributes to the construction of the existing blue-green space.

Suspended particulate matter (SPM)-bound polycyclic aromatic hydrocarbons (PAHs) in lakes and reservoirs across a large geographical scale

Suspended particulate matter (SPM) plays a key role in the environmental fate of polycyclic aromatic hydrocarbons (PAHs) in lake environment. However, less is known about the occurrence, compositions and sources of SPM-bound PAHs as well as the correlations between SPM-bound PAHs and different suspended particulate organic matter (SPOM) on large geographical scale. In this study, we focused on the SPM-bound PAHs in 46 lakes and reservoirs across China to fill this gap. Our results showed that the concentrations of Σ₂₀ PAHs ranged from 334 to 38427 ng·g^-1 with a geometric mean (GM) of 3915 ng·g^-1. The occurrence of SPM-bound PAHs in this study was at a moderate level with large variations, which was associated with location and water depth according to linear discriminant analysis (LDA). Phenanthrene (Phe) was investigated as the overwhelming species with a GM of 1777 ng·g^-1, and was followed by fluoranthene (Fla), fluorene (Flu) and pyrene (Pyr) with GMs of 499 ng·g^-1, 276 ng·g^-1 and 184 ng·g^-1, respectively. The profiles of SPM-bound PAHs were primarily dominated by low-ring PAHs ranging from 56.0% to 97.1% (85.5% ± 7.7%, mean ± standard deviation). Four diagnostic ratios were applied for preliminary diagnoses, but inconsistent results were obtained in most samples. Ridge regression was applied to ascertain the potential influences of different SPOM on SPM-bound PAHs. The results revealed that the presence of SPM-bound PAHs was not only influenced by anthropogenic emissions, but also associated with biogenic organic matter. Our results provided a higher explanation than those just preliminarily estimated by total organic carbon (TOC). Nevertheless, there still exist over 50% of variance unexplained for most PAHs, and further study could focus more on the information of SPOM structures and potential local effects.