Effects of polycyclic aromatic hydrocarbons fluoranthene on the soil aggregate stability and the possible underlying mechanism

Novel insights into PAHs accumulation and multi-method characterization of interaction between groundwater and surface water in middle Yangtze River: Hydrochemistry, isotope hydrology and fractionation effect

To meet the challenge of water quality protection and management in the middle Yangtze River and understand the accumulation mechanism of PAHs in aquatic complexity systems, caused by hydro-chemical changes, anthropogenic and geological activities, and intensive surface water-groundwater interaction, a comprehensive study is urgently needed. The study investigated the pollution levels, potential sources, accumulation mechanism, and groundwater- surface water interaction of polycyclic aromatic hydrocarbons (PAHs) in wet and dry seasons of the middle Yangtze River. There was no significant difference of PAHs accumulation between wet and dry seasons of the middle Yangtze River. PAHs occurrence in the middle Yangtze River was dominated by the input of tributary. Phenanthrene and Naphthalene were still the dominant species of PAHs. Coal combustion (CC) and biomass burning (BB) were the major contributor for the PAHs occurrence. However, the CC apportionment concentration increased by 6.18 ng·L-1 from wet to dry season, suggesting higher density of coal consumption in dry season. The potential mechanism of PAHs occurrence was demonstrated by the mantel test and structural equation model (SEM). Results revealed that the pollution of the middle Yangtze River could be mainly affected by primary emission in wet and dry seasons due to the significant positive effect between eutrophication levels and PAHs pollution sources. Meanwhile, the difference in redox conditions could directly affect the fate of pollutants (including the valence state transformation of nitrogen and phosphorus). The stronger interaction of groundwater and surface water in dry season was presented by hydrochemistry and isotope hydrology (δ18O and δ2H). The similar result was also evidenced by fractionation effect of PAHs, because more similar behaviors of characteristic pollutants were observed in dry season. Consequently, PAHs can be considered as an effective geochemical tracer and further expanded their toxic effects through the surface water-groundwater interaction.

A new strategy of using periphyton to simultaneously promote remediation of PAHs-contaminated soil and production of safer crops

Contaminated farmland leads to serious problems for human health through biomagnification in the soil-crop-human chain. In this paper, we have established a new soil remediation strategy using periphyton for the production of safer rice. Four representative polycyclic aromatic hydrocarbons (PAHs), including phenanthrene (Phe), pyrene (Pyr), benzo[b]fluoranthene (BbF), and benzo[a]pyrene (BaP), were chosen to generate artificially contaminated soil. Pot experiments demonstrated that in comparison with rice cultivation in polluted soil with ΣPAHs (50 mg kg-1) but without periphyton, adding periphyton decreased ΣPAHs contents in both rice roots and shoots by 98.98% and 99.76%, respectively, and soil ΣPAHs removal reached 94.19%. Subsequently, risk assessment of ΣPAHs based on toxic equivalent concentration (TEQ), pollution load index (PLI), hazard index (HI), toxic unit for PAHs mixture (TUm), and incremental lifetime cancer risk (ILCR) indicated that periphyton lowered the ecological and carcinogenicity risks of PAHs. Besides, the role of periphyton in enhancing the rice productivity was revealed. The results indicated that periphyton alleviated the oxidative stress of PAHs on rice by reducing malondialdehyde (MDA) content and increasing total antioxidant capacity (T-AOC). Periphyton reduced the toxic stress of PAHs on the soil by promoting soil carbon cycling and metabolic activities as well. Periphyton also improved the soil's physicochemical properties, such as the percentage of soil aggregate, the contents of humic substances (HSs) and nutrients, which increased rice biomass. These findings confirmed that periphyton could improve rice productivity by enhancing soil quality and health. This study provides a new eco-friendly strategy for soil remediation and simultaneously enables the production of safe crops on contaminated land.

Research progress and prospect of glomalin-related soil protein in the remediation of slightly contaminated soil

Soil pollution caused by organic pollutants and potentially toxic elements poses a serious threat to sustainable agricultural development, global food security and human health. Therefore, strategies for reducing soil pollution are urgently required. Arbuscular mycorrhizal fungi (AMF)-assisted phytoremediation is widely recognized for its ability to remediate slightly-contaminated soil. Glomalin-related soil protein (GRSP) production by AMF is considered a vital mechanism of AMF-assisted phytoremediation. GRSP is widespread in soils and may contribute to the remediation of slightly contaminated soils. GRSP facilitates stabilization of pollutants in soils by interacting with pollutants owing to its abundant functional groups, recalcitrance, and long turnover time. It also enhances soil bioremediation and phytoremediation by stimulating soil microbial activity, improving soil structure, and providing nutrients for plants. However, research on GRSP is still in its early stages, and studies on contaminated soil remediation are limited. The effectiveness of GRSP in situ remediation remains to be proved. This review summarizes current knowledge regarding the GRSP distribution and its contribution to the remediation of slightly contaminated soils. Additionally, we present strategies to increase the GRSP content in contaminated soils, as well as prospects for future studies on the use of GRSP in contaminated soil remediation. This study focuses on recent developments that aim to improve awareness of the role of GRSP in soil remediation and relevant future directions.