Remediation of di(2-ethylhexyl) phthalate (DEHP) contaminated black soil by freeze-thaw aging biochar

Effect of freeze-thaw cycle aging on biochar application in DEHP contaminated Mollisols: Insights from soil properties and microbial community

Biochar holds significant promise for remediation of organic pollutants. However, the impact of biochar on di-(2-ethylhexyl) phthalate (DEHP)-contaminated Mollisols after freeze-thaw cycles is largely unknown, according to the seasonal traits observed at high latitudes. In this study, fresh biochar (BC) was produced from corn straw, and freeze-thaw aging biochar (FBC) was prepared by simulating winter temperatures in the Mollisol region of Northeast China using BC as a precursor. Pot experiments were conducted to evaluate the effects of freeze-thaw aging on the detoxification efficiency of biochar, the improvement of soil physical and chemical properties, and the regulation of soil microbial community structure and functional genes. The results indicated that biochar after freeze-thaw cycling significantly improved the physical and chemical properties of Mollisols compared with the control, reducing DEHP content by 99.08 % after 28 days. Metagenomic sequencing further revealed the presence of microorganisms and genetic elements potentially involved in DEHP degradation in the soil. The treatment group with freeze-thaw aging biochar exhibited higher microbial diversity and abundance, particularly in Proteobacteria, Bacteroides, and Firmicutes. Analysis of the DEHP degradation pathway via benzoic acid route revealed an increase in the abundance of degraded functional genes/enzymes (benC-xylZ, pacL, catB, pcaG, mhpE, and mhpF). The up-regulation of nitrogen fixation genes and nitrification genes (amoB, hao, narG, nifD, and vnfH) along with a 49.19 % increase in soil microbial biomass nitrogen suggested that freeze-thaw aging biochar benefited nitrogen cycling. Furthermore, the feasibility of applying biochar to high-latitude agricultural settings was validated using pakchoi (Brassica rapa L. ssp. chinensis) as a test crop. These findings suggest that the freeze-thaw aging process enhances the effectiveness of biochar in remediating DEHP-contaminated Mollisols. This study offers a novel perspective on the restoration and improvement of Mollisol productivity in high-latitude regions through biochar application.

Phytotoxic impact of di-butyl phthalate (DBP) on physiological, biochemical, and oxidative stress parameters of rice (Oryza sativa)

Phthalates are synthetic compounds, well-known plasticizers, with numerous applications and reported to have adverse effects on all living organisms residing in terrestrial and aquatic environments. In this study, the rice (Oryza sativa) seedlings were exposed to di-butyl phthalate (DBP) exogenously for 7 days, with varying concentrations of 0, 200, 400, 800, and 1600 mg/L, to explore the toxicological, physiological, and biochemical consequences by measuring various parameters such as pigment, lipid, and H2O2 (hydrogen peroxide) contents. The biochemical analysis of seedlings showed that the pigments, lipids, and H2O2 concentrations were altered abnormally. After 7 days of exposure, the maximum amount of DBP was accumulated and translocated in both the shoot and root of the grown seedlings, and all morphological parameters (i.e., length and weight of both shoot and root) and pigment content (such as total carotenoid, chlorophyll a and b) were declined significantly. Superoxide dismutase (SOD), H2O2, and thiobarbituric acid reactive substance (TBARS) levels in seedlings increase as the stress increases due to the higher exposure dose of DBP. Cell viability was observed under a confocal microscope confirming the damage of the plasma membrane. Additionally, molecular docking studies indicated that DBP has a good binding affinity with key antioxidant enzymes of Oryza sativa, interacting via hydrogen bonds with specific amino acids. This suggests a potential mechanistic pathway for the observed biochemical changes in Oryza sativa.

Mechanisms of synthetic bacterial flora YJ-1 to enhance cucumber resistance under combined phthalate-disease stresses

Biotic and abiotic stresses have emerged as major constraints to agricultural production, causing irreversible adverse impacts on agricultural production systems and thus posing a threat to food security. In this study, a new strain of Bacillus subtilis DNYB-S1 was isolated from soil contaminated with Fusarium wilt. It was found that artificially synthetic flora (YJ-1) [Enterobacter sp. DNB-S2 and Rhodococcus pyridinovorans DNHP-S2, DNYB-S1] could effectively mitigate both biotic (Fusarium wilt) and abiotic (phthalates) sources of stresses, with the inhibition rate of YJ-1 resistant to wilt being 71.25% and synergistic degradation of 500 mg/L PAEs was 91.23%. The adaptive difference of YJ-1 was 0.59 and the ecological niche overlap value was -0.05 as determined by Lotka-Volterra modeling. These results indicate that YJ-1 has good ecological stability. The major degradation intermediates included 2-ethylhexyl benzoate (EHBA), phthalic acid (PA), diisobutyl phthalate (DIBP), and butyl benzoate, suggesting that YJ-1 can provide a more efficient pathway for PAEs degradation. In addition, there was metabolic mutualism among the strains that will selectively utilize the provided carbon source (some metabolites of PAEs) for growth. The pot experiment showed that YJ-1 with cucumber reduced the incidence of cucumber wilt by 45.31%. YJ-1 could reduce the concentration of PAEs (DBP: DEHP = 1:1) in soil species from 30 mg/kg to 4.26 mg/kg within 35 d, with a degradation efficiency of 85.81%. Meanwhile, the concentration of PAEs in cucumber was reduced to 0.01 mg/kg, indicating that YJ-1 is directly involved in the degradation of soil PAEs and the enhancement of plant immunity. In conclusion, this study provides a new perspective for the development of customized microbiomes for phytoremediation under combined biotic-abiotic stresses in agricultural production processes.

Effects of aging methods on the adsorption of antibiotics in wastewater by soybean straw biochar

BACKGROUND

The environmental pollution and ecological risks caused by the widespread use of antibiotics have attracted attention in recent years. Biochar materials have a rich pore diameter and can effectively adsorb pollutants from wastewater. However, biochar will experience high temperatures, freezing and thawing in nature, affecting its physicochemical properties and adsorption capacity. Three types of aged biochar were prepared by artificial simulated aging using soybean straw as raw material. The aged biochar's elemental composition and functional group species were investigated by characterization analysis, and their adsorption kinetics and adsorption isotherms were studied.

RESULTS

The specific surface area and pore size of the three aged biochars were lower than those of fresh biochars. The increased number of oxygen-containing functional groups of the aged biochars formed a water cluster interaction with norfloxacin (NOR), which was unfavorable to the adsorption of NOR. The adsorption mechanism of biochar on NOR comprises pore filling, electrostatic interaction, ion exchange and complexation.

CONCLUSION

The adsorption of NOR on biochar before and after aging was spontaneous and was described by quasi-second kinetics and the Langmuir equation. Different aging methods influenced the physicochemical properties and adsorption performance of biochar, and the adsorption capacity of biochar was significantly reduced after aging. Therefore, the influence of climatic factors needs to be considered when using biochar to remove target pollutants. © 2023 Society of Chemical Industry.

New mechanisms of biochar-assisted vermicomposting by recognizing different active di-(2-ethylhexyl) phthalate (DEHP) degraders across pedosphere, charosphere and intestinal sphere

Biochar-assisted vermicomposting can significantly accelerate soil DEHP degradation, but little information is known about the underlying mechanisms as different microspheres exist in soil ecosystem. In this study, we identified the active DEHP degraders in biochar-assisted vermicomposting by DNA stable isotope probing (DNA-SIP) and surprisingly found their different compositions in pedosphere, charosphere and intestinal sphere. Thirteen bacterial lineages (Laceyella, Microvirga, Sphingomonas, Ensifer, Skermanella, Lysobacter, Archangium, Intrasporangiaceae, Pseudarthrobacter, Blastococcus, Streptomyces, Nocardioides and Gemmatimonadetes) were responsible for in situ DEHP degradation in pedosphere, whereas their abundance significantly changed in biochar or earthworm treatments. Instead, some other active DEHP degraders were identified in charosphere (Serratia marcescens and Micromonospora) and intestinal sphere (Clostridiaceae, Oceanobacillus, Acidobacteria, Serratia marcescens and Acinetobacter) with high abundance. In biochar-assisted vermicomposting, the majority of active DEHP degraders were found in charosphere, followed by intestinal sphere and pedosphere. Our findings for the first time unraveled the spatial distribution of active DEHP degraders in different microspheres in soil matrices, explained by DEHP dynamic adsorption on biochar and desorption in earthworm gut. Our work highlighted that charosphere and intestinal sphere exhibited more contribution to the accelerated DEHP biodegradation than pedosphere, providing novel insight into the mechanisms of biochar and earthworm in improving contaminant degradation.