Composition of soil organic matter drives total loss of dieldrin and dichlorodiphenyltrichloroethane in high-value pastures over thirty years

Soil properties and organochlorine compounds co-shape the microbial community structure: A case study of an obsolete site

Organochlorine compounds (OCs) such as chlorobenzenes (CB) are persistent organic pollutants that are ubiquitous in soils at organochlorine pesticides (OCP) production sites. Long-term contamination with OCs might alter the soil microbial structure and further affect soil functions. However, the effects of OCs regarding the shaping of microbial community structures in the soils of OCs-contaminated sites remain obscure, especially in the vertical soil profile where pollutants are highly concealed. Hence this paper explored the status and causes of OCs pollution (CB, hexachlorocyclohexane (HCH), and dichlorodiphenyltrichloroethane (DDT)) in an obsolete site, and its combined effects with soil properties (pH, available phosphorus (AP), dissolved organic carbon (DOC), etc) on microbial community structure. The mean total concentration of OCs in the subsoils was up to 996 times higher than that in the topsoils, with CB constituting over 90% of OCs in the subsoil. Historical causes, anthropogenic effects, soil texture, and the nature of OCs contributed to the differences in the spatial distribution of OCs. Redundancy analysis revealed that both the soil properties and OCs were important factors in shaping microbial composition and diversity. Variation partitioning analysis further indicated that soil properties had a greater impact on microbial community structure than OCs. Significant differences in microbial composition between topsoils and subsoils were observed through linear discriminant analysis effect size (LEfSe) analysis, primarily driven by different pollutant conditions. Additionally, co-occurrence network analysis indicated that heavily contaminated subsoils exhibited closer and more intricate bacterial community interactions compared to lightly contaminated topsoils. This work reveals the impact of environmental factors in co-shaping the structure of soil microbial communities. These findings advance our understanding of the intricate interplay among organochlorine pollutants, soil properties, and microbial communities, and provides valuable insights into devising effective management strategies in OCs-contaminated soils.

Design, synthesis, and biological evaluation of novel berberine derivatives against phytopathogenic fungi

BACKGROUND

The abuse of chemical fungicides not only leads to toxic residues and resistance in plant pathogenic fungi, but also causes environmental pollution and side effects on in humans and animals. Based on the antifungal activities of berberine, seven different types of berberine derivatives (A1-G1) were synthesized, and their antifungal activities against six plant pathogenic fungi were evaluated (Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, Phytophthora capsici, Sclerotinia sclerotiorum, and Magnaporthe oryzae).

RESULTS

The results for antifungal activities in vitro showed that berberine derivative E1 displayed good antifungal activity against R. solani with a median effective concentration (EC₅₀ ) of 1.77 μg ml^-1 , and berberine derivatives F1 and G1 demonstrated broad-spectrum antifungal activities with EC₅₀ values ranging from 4.43 to 42.23 μg ml^-1 against six plant pathogenic fungi. Berberine derivatives (E2-E29, F2-F18, and G2-G9) were further synthesized to investigate the structure-activity relationship (SAR), and compound E20 displayed significant antifungal activity against R. solani with an EC₅₀ value of 0.065 μg ml^-1 . Preliminary mechanism studies showed that E20 could cause mycelial shrinkage, cell membrane damage, mitochondrial abnormalities and the accumulation of harmful reactive oxygen species, resulting in cell death in R. solani. Moreover, in vivo experimental results showed that the protective effect of E20 was 97.31% at 5 μg ml^-1 , which was better than that of the positive control thifluzamide (50.13% at 5 μg ml^-1 ).

CONCLUSION

Berberine derivative E20 merits further development as a new drug candidate with selective and excellent antifungal activity against R. solani. © 2022 Society of Chemical Industry.

Thermal desorption optimization for the remediation of hydrocarbon-contaminated soils by a self-built sustainability evaluation tool

Current thermal desorption practices of hydrocarbon-contaminated soils focus on remediation efficiency and cost, with little systematic assessment of the reuse value of treated soils. This study evaluated various integrated indices of treatment cost and reuse of treated soils at three desorption temperatures. Various typical engineering and ecological characteristics closely related to soil reusability were selected to analyze the changes in various treated soils, including shear strength, Atterberg limits, particle size distribution, permeability, soil carbon, and soil biomass. A sustainability evaluation tool was developed for the greener disposal of hazardous soils considering both the treatment cost and reuse indices. Such an evaluation led to the conclusion that the contaminated soils treated at 350 °C generated the highest soil reusability with an excellent remediation efficiency. The sensitivity analysis confirmed that the tool had better stability in a common situation where the weight of the remediation cost was heavier than the soil reusability. Meanwhile, published data were input into the tool to validate its applicability under different scenarios. The results were consistent with the qualitative assessment of the literature. The tool can quantitatively select a more sustainable desorption method for the disposal and reuse of hazardous soils.

Status of Dieldrin in vegetable growing soils across a peri-urban agricultural area according to an adapted sampling strategy

Since the fifties, organochlorine pesticides (OCPs) had been used in agriculture to protect vegetables. Two decades after their ban by the Stockholm convention in 2001, OCPs are still present in agricultural soils inducing vegetable contamination with concentrations above Maximum Residue Level (MRL). This is a major concern for a 5 km² peri-urban vegetable growing valley located in the south west of France. In the present work, the sampling method was developed to clarify the spatial distribution of one OCP, Dieldrin, and its relationship with soil properties at the scale of study area. A total of 99 soil samples was collected for physicochemical analyses and Dieldrin concentrations. Results show Dieldrin concentrations in soils up to 204 μg kg^-1. The horizontal distribution of this pesticide is heterogeneous at the study area scale but homogeneous in each reference plot studied. About 85% of the contamination was located in the top soil layers (0-40 cm depth), but Dieldrin may still be quantified at a depth of 80 cm. Among all soil physicochemical parameters analysed, SOM was the most significantly related (P < 10^-4) with Dieldrin concentrations, once different grain size fractions were considered. Moreover, results indicate a 33 times higher Dieldrin concentration and/or extractability for coarse sand than for other grain size fractions. These results show that the developed sampling method is adapted for the study area scale as it helps understanding the factors influencing the spatial distribution of Dieldrin. Historical amendments are the predominant factor for the horizontal contamination and deep ploughing for the vertical contamination. Also, the variations of coarse sand repartition in soils prevents identification of relationships between SOM and Dieldrin contamination in bulk soil. Further investigation is required to explain these relationships but these results highlight why no clear relationship between OCPs and SOM was previously identified.

Biochar reduced extractable dieldrin concentrations and promoted oligotrophic growth including microbial degraders of chlorinated pollutants

The role of organic amendments for natural degradation of aged persistent organic pollutants (POPs) in agricultural soils remains controversial. We hypothesised that organic amendments enhance bacterial activity and function at the community level, facilitating the degradation of aged POPs. An incubation study was conducted in a closed chamber over 12 months to assess the effects of selected organic amendments on extractable residues of aged dieldrin. The role of bacterial diversity and changes in community function was explored through sequenced marker genes. Linear mixed effect models indicated that, independent of amendment type, cumulative CO₂ release was negatively associated with decreases in dieldrin concentration, by up to 7% per µmol CO₂-C respired by microorganisms. The addition of poultry litter led to the highest daily carbon mineralisation, which was associated with low dieldrin dissipation after 9 months. In comparison, biochar resulted in significant decreases in extractable dieldrin residues over time, which coincided with shifts towards aerobic, oligotrophic, gram-negative bacteria, some with dehalogenation metabolism, and with increased potentials for biosynthesis of membrane components such as fatty acids and high redox quinones. The results supported an alternative theory that labile carbon promoted blooms of copiotrophic growth, which suppressed the required community-level traits and oligotrophic diversity to degrade chlorinated pollutants.

Highly decomposed organic carbon mediates the assembly of soil communities with traits for the biodegradation of chlorinated pollutants

To improve biodegradation strategies for chlorinated pollutants, the roles of soil organic matter and microbial function need to be clarified. It was hypothesised that microbial degradation of specific organic fractions in soils enhance community metabolic capability to degrade chlorinated pollutants. This field study used historic records of dieldrin concentrations since 1988 and established relationships between dieldrin dissipation and soil carbon fractions together with bacterial and fungal diversity in surface soils of Kurosol and Chromosol. Sparse partial least squares analysis linked dieldrin dissipation to metabolic activities associated with the highly decomposed carbon fraction. Dieldrin dissipation, after three decades of natural attenuation, was associated with increased bacterial species fitness for the decomposition of recalcitrant carbon substrates including synthetic chlorinated pollutants. These metabolic capabilities were linked to the decomposed carbon fraction, an important driver for the microbial community and function. Common bacterial traits among taxonomic groups enriched in samples with high dieldrin dissipation included their slow growth, large genome and complex metabolism which supported the notion that metabolic strategies for dieldrin degradation evolved in an energy-low soil environment. The findings provide new perspectives for bioremediation strategies and suggest that soil management should aim at stimulating metabolism at the decomposed, fine carbon fraction.

Integrated proteomics and metabolomics analysis reveals the antifungal mechanism of the C-coordinated O-carboxymethyl chitosan Cu(II) complex

With wide application in agriculture, copper fungicides have undergone three stages of development: inorganic copper, synthetic organic copper, and natural organic copper. Using chitin/chitosan (CS) as a substrate, the natural organic copper fungicide C-coordinated O-carboxymethyl chitosan Cu(II) complex (O-CSLn-Cu) was developed in the laboratory. Taking Phytophthora capsici Leonian as an example, we explored the antifungal mechanism of O-CSLn-Cu by combining tandem mass tag (TMT)-based proteomics with non-targeted liquid chromatography-mass spectrometry (LC-MS)-based metabolomics. A total of 1172 differentially expressed proteins were identified by proteomics analysis. According to the metabolomics analysis, 93 differentially metabolites were identified. Acetyl-CoA-related and membrane localized proteins showed significant differences in the proteomics analysis. Most of the differential expressed metabolites were distributed in the cytoplasm, followed by mitochondria. The integrated analysis revealed that O-CSLn-Cu could induce the "Warburg effect", with increased glycolysis in the cytoplasm and decreased metabolism in the mitochondria. Therefore, P. capsici Leonian had to compensate for ATP loss in the TCA cycle by increasing the glycolysis rate. However, this metabolic shift could not prevent the death of P. capsici Leonian. To verify this hypothesis, a series of biological experiments, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and enzyme activity measurements were carried out. The results suggest that O-CSLn-Cu causes mitochondrial injury, which consequently leads to excessive ROS levels and insufficient ATP levels, thereby killing P. capsici Leonian.