Variation in soil aggregate-size distribution affects the dissipation of polycyclic aromatic hydrocarbons in long-term field-contaminated soils

The regulating mechanisms of Triton X-100 affected oxidation of PAHs in site soil aggregates using sodium citrate assisted Fe2+-persulfate

Here, we present a first investigation of the inhibition mechanism of surfactant Triton X-100 (TX-100) on the oxidation degradation of polycyclic aromatic hydrocarbons (PAHs) in site soil aggregates using sodium citrate assisted Fe2+-activated persulfate (SC/Fe2+/PS). First, TX-100 was not only competed the adsorption sites of soil aggregates with PS, but also consumed PS, which inhibit the PAHs remediation rate in the TX-100 elution followed by the SC/Fe2+/PS oxidation system from 55.6 % in the oxidation system to 50.3 %. Furthermore, in the oxidation followed by elution system, PAHs was adsorbed on the iron minerals produced during the oxidation, which would be form a bound PAHs that was difficult to react with PS, and then re-eluted to the soil by the TX-100. Additionally, it was found that the oxidative and the elution efficiency of PAHs exhibited negative correlations with aggregate particle sizes. Finally, soil microorganism communities were more strongly changed by SC/Fe2+/PS oxidation and PAHs concentration than that of TX-100 elution, with obvious alterations bacteria than fungi, the effects of SC/Fe2+/PS and PAHs concentration on microorganism communities were opposite. This study provided a proof of regulating mechanisms for the site soil remediation using surfactants combined with the iron-PS system.

Features of the polycyclic aromatic hydrocarbon's spatial distribution in the soils of the Don River delta

PAHs are one of the most toxic organic compounds classes which is obligatory controlled all over the world. There is a luck of studies devoted to the PAHs levels and sources identification in the south of Russia. The features of the PAHs accumulation and spatial distribution in hydromorphic soils (Fluvisol) were studied on the example of the soils of the Don River delta floodplain landscapes. It has been shown that changes in the PAHs content in soils depended on the type and intensity of the emission source. A factor analysis and multivariate linear regression analysis were carried out to determine the features of the spatial distribution for individual PAH compounds, considering the properties of soils and typical differences in the emission source. The most polluted areas in the studied area located along the transit line of the long-distance tankers, where the content of the most toxic high molecular PAHs compounds reached 8862 ng g-1. As a result of regression analysis, a relationship was established between the PAHs accumulation rate with the content of silt (particles less than 0.001 mm in size) and Ca2+ and Mg2+ exchangeable cations in the soil (at p-level < 0.0001). Differences in individual PAH content for medium and heavy loamy Fluvisol and depend on the influence of different types of pollution sources.

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.

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

Soil contamination by polycyclic aromatic hydrocarbons (PAHs) is an increasing problem in many countries, impacting the ecological environment's sustainable development. This study investigated the effects of fluoranthene (Fla) on soil aggregate stability. A possible mechanism for the interaction of Fla with soil aggregates was proposed by characterizing the aggregate structure. The results showed that Fla significantly improved the aggregate stability in the concentration range of 0-30.0 mg/kg. The content of macro-aggregates reached the maximum value at 10 mg/kg of Fla, which increased by 24.25% compared with the control group, while the content of large-aggregates decreased by 12.11%. Meanwhile, the mean weight diameter (MWD) and geometric mean diameter (GMD) increased by 56.63% and 37.66%, respectively. However, the macro-aggregates zeta potential value and specific surface area (SSA) decreased by 12.68% and 13.61%, respectively. The cracks of macro-aggregates were also significantly reduced. In addition, Fla-based free radicals were detected on the macro-aggregates. The absorption peak of the C-O group significantly increased, indicating that Fla may be covalently bound to the aggregates by aromatic ether bonds, which is a possible mechanism for the interaction between Fla and aggregates. This study provides theoretical support for revealing the effects of PAHs on soil.

Rhizoremediation as a green technology for the remediation of petroleum hydrocarbon-contaminated soils

Rhizoremediation is increasingly becoming a green and sustainable alternative to physico-chemical methods for remediation of contaminated environments through the utilization of symbiotic relationship between plants and their associated soil microorganisms in the root zone. The overall efficiency can be enhanced by identifying suitable plant-microbe combinations for specific contaminants and supporting the process with the application of appropriate soil amendments. This approach not only involves promoting the existing activity of plants and soil microbes, but also introduces an adequate number of microorganisms with specific catabolic activity. Here, we reviewed recent literature on the main mechanisms and key factors in the rhizoremediation process with a particular focus on soils contaminated with total petroleum hydrocarbon (TPH). We then discuss the potential of different soil amendments to accelerate the remediation efficiency based on biostimulation and bioaugmentation processes. Notwithstanding some successes in well-controlled environments, rhizoremediation of TPH under field conditions is still not widespread and considered less attractive than physico-chemical methods. We catalogued the major pitfalls of this remediation approach at the field scale in TPH-contaminated sites and, provide some applicable situations for the future successful use of in situ rhizoremediation of TPH-contaminated soils.

Soil aggregate-associated distribution of DDTs and HCHs in farmland and bareland soils in the Danjiangkou Reservoir Area of China

Soil organic matter (SOM) is the principal aggregating agent for soil aggregation and also the main adsorbent for organochlorine pesticides (OCPs) such as dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH), which may thereby affect OCP distribution in soils subjected to different land use types. However, the potential effects of land use on SOM and OCP distribution patterns in soil aggregates are not well understood. In this study, soils from farmlands and barelands in the Danjiangkou Reservoir area were analyzed to determine the influence of land use on OCP distribution and composition in different aggregate fractions (>3, 1-3, 0.25-1, and <0.25 mm). The results showed that the levels of ∑DDTs ranged from 9.01 to 27.48 with a mean of 14.40 ng g^-1, and ∑HCHs ranged from 2.06 to 4.66 with a mean of 3.19 ng g^-1 in farmland soils. In comparison, bareland soils were less contaminated, with total DDTs and HCHs fell in the range of 0.75-5.01 ng g^-1 and not detected (n.d.)-1.40 ng g^-1 respectively. In regard to the distribution patterns in soil aggregates, the residual levels of ∑DDTs and ∑HCHs tended to a certain degree to enrich in microaggregates (<0.25 mm) relative to bulk soils. A further analysis revealed that the enrichment of ∑DDTs and ∑HCHs in microaggregates were mainly attributed to the accumulation of p,p'-DDE and β-HCH. Moreover, SOM was found also enriched in microaggregates. The enrichment of SOM was significantly and positively correlated with these of ∑DDTs, ∑HCHs, and the dominant metabolites (i.e., DDE and β-HCH) in both land use types. Such results indicated that the variations in behavior of OCPs could be linked to the processes of soil aggregate turnover. These findings may help to enrich the theory of soil OCPs sequestration and establish targeted strategies to mitigate their health risks in the environment.