Effect of dissolved organic matter and heavy metals ions on sorption of phenanthrene at sedimentary particle scale

Co-toxicity and co-contamination remediation of polycyclic aromatic hydrocarbons and heavy metals: Research progress and future perspectives

The combined pollution of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) has attracted wide attention due to their high toxicity, mutagenicity, carcinogenicity and teratogenicity. A thorough understanding of the progress of the relevant studies about their co-toxicity and co-contamination remediation is of great importance to prevent environmental risk and develop new efficient remediation methods. This paper summarized the factors resulting in different co-toxic effects, the interaction mechanism influencing co-toxicity and the development of remediation technologies for the co-contamination. Also, the inadequacies of the previous studies related to the co-toxic effect and the remediation methods were pointed out, while the corresponding solutions were proposed. The specific type and concentration of PAHs and HMs, the specific type of their action object and environmental factors could affect their co-toxicity by influencing each other's transmembrane process, detoxification process and increasing reactive oxygen species (ROS) and some other mechanisms that need to be further studied. The specific action mechanisms of the concentration, environmental factors and the specific type of PAHs and HMs, their effect on each other's transmembrane processes, investigations at the cellular and molecular levels, non-targeted metabolomics analysis, as well as long-term ecological effects were proposed to be further explored in order to obtain more information about the co-toxicity. The combination of two or more methods, especially combining bioremediation with other methods, is a potential development field for the remediation of co-contamination. It can make full use of the advantages of each remediation method, to achieve an increase of remediation efficiency and a decrease of both remediation cost and ecological risk. This review intends to further improve the understanding on co-toxicity and provide references for the development and innovation of remediation technologies for the co-contamination of PAHs and HMs.

The heterogenous molecular characteristics of biomass-pyrogenic smoke dissolved organic matters (BPS-DOMs) binding with PAHs: Novel insights from combined analysis of FT-ICR MS and fluorescence variation

Biomass-pyrogenic smoke dissolved organic matter (BPS-DOM) can co-deposit with polycyclic aromatic hydrocarbons (PAHs), thereby altering their environmental behavior and fate in surface environments. However, the heterogeneous molecular characteristics of BPS-DOM binding with PAHs remain unclear. This study systematically elucidates the binding characteristics of PAHs (phenanthrene and pyrene), with various molecular compositions in BPS-DOM, utilizing FT-ICR MS and fluorescence variation analysis. CHO compounds in BPS-DOM, characterized by high aromaticity and abundant CO bonds, significantly enhance PAHs binding by promoting π-π electron donor-acceptor interactions. In contrast, CHON compounds with higher aliphaticity inhibit pyrene binding by competing for binding sites on BPS-DOM. Furthermore, the binding sequence of different fluorescent molecules follows the order of CHO→CHOS→CHON for phenanthrene and CHO→CHON→CHOS for pyrene. This was primarily due to the larger conjugated aromatic structures of CHO compounds, which provide stronger π-π interaction sites for PAHs binding. The difference in binding sequences between phenanthrene and pyrene is primarily attributed to phenanthrene's reliance on π-π electron donor-acceptor interactions induced by -SO and -N = O, while pyrene binding depended on π-π interactions driven by larger conjugated aromatic structures. These results provide an important theoretical foundation for further understanding the molecular-level interactions between BPS-DOM and PAHs.

Effect of UV exposure and natural aging on the in vitro PAHs bioaccessibility associated with tire wear particles in soil

Tire wear particles (TWP), as an emerging type of microplastics, are a significant source of contaminants in roadside soils due to their high concentration of pollutants, including polycyclic aromatic hydrocarbons (PAHs). This study explored the impact of ultraviolet (UV) exposure and natural aging on the in vitro bioaccessibility of PAHs associated with TWP in soil on a China-wide scale. Our findings suggested that UV exposure amplified the negative charge of TWP by 75 % and increased the hydrophobic groups on the particle surface. The bioaccessibility of 3- and 4-ring PAHs in TWP was significantly (p < 0.05) heightened by UV exposure. After 20 types of soils containing 2 % UV-exposed TWP underwent natural aging, the bioaccessibility of PAHs saw a significant decrease (p < 0.05) to 16-48 %, compared to 28-96 % in the unaged group. Soil pH and electrical conductivity (EC) were the two primary soil properties positively influencing the reduction of in vitro PAHs concentration and PAHs bioaccessibility. According to the prediction results, soils in southern China presented the highest potential region for the release of bioaccessible PAHs from TWP, highlighting the regional specificity of environmental impact. Our study provides valuable insights into the biological impact of PAHs associated with TWP on a regional scale, and offers scientific evidence for targeted soil risk management strategies.

Spatial heterogeneity and compositional profiles of dissolved organic matter in farmland soils across mainland China

Dissolved organic matter (DOM) plays an essential role in many geochemical processes, however its complexity, chemical diversity, and molecular composition are poorly understood. Soil samples were collected from 500 vegetable fields in administrative regions of mainland China, of which 122 were selected for further investigation. DOM properties were characterized by three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) (field intensity is 15 Tesla). Our results indicated that the main constituents were UVA humic-like substances, humic-like substances, fulvic acid-like substances, and tyrosine-like substances. A total of 10,989 molecular formulae with a mass range of 100.04 to 799.59 Da were detected, covering the mass spectrometric information of the soil samples from 27 different regions. CHO and CHON molecules were dominant in DOM, whereas lignin, tannins, and aromatic substances served as the main components. The results of cluster analysis revealed that the soil properties in Jiangxi Province were considerably different from those in other regions. The key backgrounds of the DOM molecular characteristics in the vegetable-field soil samples across mainland China were provided at the molecular level, with large abundance and great variability.

Spatial distribution and source identification of potentially toxic elements in Yellow River Delta soils, China: An interpretable machine-learning approach

Identifying the driving factors and quantifying the sources of potentially toxic elements (PTEs) are essential for protecting the ecological environment of the Yellow River Delta. In this study, data from 201 surface soil samples and 16 environmental variables were collected, and the random forest (RF) and Shapley additive explanations (SHAP) methods were then combined to explore the key factors affecting soil PTEs. An innovative t-distributed random neighbor embedding-RF-SHAP model was then constructed, based on the absolute principal component score and multivariate linear regression model, to quantitatively determine PTE sources. Although average PTE concentrations did not exceed the risk control values, PTE distributions exhibited significant differences. It was found that sodium, soil organic matter, and phosphorus contents were the three most important factors affecting PTEs, and human activities and natural environmental factors both influence PTE contents by altering the soil properties. The proposed model successfully determined PTE sources in the soil, outperforming the original linear regression model with a significantly lower RMSE. Source analysis revealed that the parent material was the main contributor to soil PTEs, accounting for more than half of the total PTE content. Industrial and agricultural activities also contributed to an increase in soil PTEs, with average contributions of 19.91 % and 17.44 %, respectively. Unknown sources accounted for 10.83 % of the total PTE content. Thus, the proposed model provides innovative perspectives on source parsing. These findings provide valuable scientific insights for policymakers seeking to develop effective environmental protection measures and improve the quality of saline-alkali land in the Yellow River Delta.

Particle-scale understanding sorption of phenanthrene on sediment fractions amended with black carbon and humic acid

Black carbon (BC) and humic acid (HA) have been proposed to dominate the sorption behavior of phenanthrene in sediment. Nevertheless, little is known about the sorption mechanism that related to particle-scale by spiking of BC and HA in sediment particle size fractions. In this study, sorption isotherms for phenanthrene were determined in four particle-size sediment fractions (<2 μm, 2-31 μm, 31-63 μm and >63 μm) that amended with BC and HA, or not. The fitting results by Freundlich model indicated that the sediment particle size fractions amended with BC increased the sorption capacity and affinity for phenanthrene. Sediment coarser size fractions (31-63 μm and >63 μm) by spiking of BC contributed higher to sorption capacity factor (K_F) and nonlinearity factor (n) than the finer size fractions (2-31 μm and <2 μm). By contrast, the sediment particle size fractions amended with HA enhanced the sorption distribution coefficient (K_d), but reduced the sorption affinity for phenanthrene. All these phenomena are obviously affected by the distribution of heterogeneous organic matter that related to sediment particle-scale. Results of this work could help us better understand the impact of increased BC and HA content in sediments on the sorption of hydrophobic organic pollutants (HOCs) and predict the fate of HOCs in offshore sediments due to tidal action.