Effects of different order spiking on bioavailability and ecological risk of phenanthrene in mangrove sediment-biochar system

Innovative solutions for coastal wetlands pollution: Application of Spartina alterniflora Loisel. - biochar for cadmium removal and carbon sequestration

Coastal wetland ecosystems are extremely fragile, with heavy metal contamination and uncontrolled growth of invasive plants (e.g. Spartina alterniflora Loisel.) could result in threaten the ecological security and resource wastage. In this study, Spartina alterniflora-biochars at two different temperatures (400 and 600 °C), as well as phosphorus-modified biochars (400BC, 600BC, 400PBC, and 600PBC) were produced, and evaluated for their removal capacity in cadmium (Cd)-contaminated sediments. The maximum sorption capacity, as determined by the Langmuir equation, was in the order of 600BC (838.81 mg/g) > 400BC (707.25 mg/g) > 600PBC (581.69 mg/g) > 400PBC (455.82 mg/g) for Cd, with adsorption occurred through single-layer chemical processes. In the Cd removal tests, increasing incubation times led to a significant reduction in bioavailable Cd (from 84.74 mg/kg at 1 h to 34.79 mg/kg at 7 day). There were significantly negative correlation (p < 0.01) and highly linear regression correlation (R2 > 0.81) between bioavailable Cd and three enzymes' activities (urease, sucrase, and acid phosphatase). Moreover, 63.52%-98.75% of the desorbed Cd can be reabsorbed and fixed in the presence of biochar after 56 d, which effectively reducing the potential for secondary release of heavy metals into the environment. Notably, a comprehensive evaluation through cost-benefit analysis (CBA) and life cycle assessment (LCA) revealed that the biochar system can generate an overall profit of $302.8/tonne and result in a net reduction of CO2 emissions by 1455.479 kg/tonne. The application of biochar could reduce carbon footprints and promote carbon neutrality, and be an effective in-situ remediation strategy for Cd-contaminated coastal wetland.

Laccase as a useful assistant for maize to accelerate the phenanthrene degradation in soil

Polycyclic aromatic hydrocarbon (PAH) pollution has attracted much attention due to their wide distribution in soil environment and serious harm to human health. In order to establish an efficient and eco-friendly technology for remediation of PAH-contaminated soil, phytoremediation utilizing maize assisted with enzyme remediation was explored in this study. The results showed that the participation of laccase could promote the degradation of phenanthrene (PHE) from soil and significantly reduce the accumulation of PHE in maize. The degradation efficiency of PHE in soil could reach 77.19% under laccase-assisted maize remediation treatment, while the accumulation of PHE in maize roots and leaves decreased by 41.23% and 74.63%, respectively, compared to that without laccase treatment, after 24 days of maize cultivation. Moreover, it was found that laccase addition shifted the soil microbial community structure and promoted the relative abundance of some PAH degrading bacteria, such as Pseudomonas and Sphingomonas. In addition, the activities of some enzymes that were involved in PAH degradation process and soil nutrient cycle increased with the treatment of laccase enzyme. Above all, the addition of laccase could not only improve the removal efficiency of PHE in soil, but also alter the soil environment and reduce the accumulation of PHE in maize. This study provided new perspective for exploring the efficiency of the laccase-assisted maize in the remediation of contaminated soil, evaluating the way for reducing the risk of secondary pollution of plants in the phytoremediation process.

A 50-year systemic review of bioavailability application in Soil environmental criteria and risk assessment

Bioavailability has become a critical factor in improving ecological risk assessment and environmental remediation efficiency in contaminated soil research. However, the soil environmental quality standards and risk assessment procedures used in most countries are still based on the total amount of pollutants for lacking sufficient understanding of the exposure pathways and action mechanisms of pollutants. we collected relevant literature from the Web of Science database, spanning the period from 1950 to 2021 by using Citespace to analyze the scientific development of bioavailability. As of January 09, 2022, the database contained 118,813 publications on bioavailability. The review summarizes the progress in bioavailability research and emerging trends, including exploring advanced analytical techniques, advancing modeling approaches, and integrating interdisciplinary approaches to better understand the fate and behavior of pollutants in complex environmental matrices. In particular, the review emphasizes the need for better integration of bioavailability concepts into soil environmental reference, risk assessment procedures, and environmental remediation strategies. Overall, this review emphasized the necessity of incorporating the concept of bioavailability into soil environmental reference, risk assessment procedures, and environmental remediation strategies.

Evaluation and characterization of biochar on the biogeochemical behavior of polycyclic aromatic hydrocarbons in mangrove wetlands

As the inter-tidal regions between land and ocean, mangrove ecosystems have high polycyclic aromatic hydrocarbons (PAHs) content, and the over accumulation of PAHs in mangrove wetland poses a serious ecological risk to the health of plant and living creatures. Comparison to the agricultural sources -biochar, biochar produced from wetland plant has lower O/C (molar ratio), larger N contents, higher stability and more benefits. However, whether the rhizosphere action occurs in biochar- amended sediment and how to influence the biogeochemical behavior of PAH have rarely been reported. In this context, a leaching procedure and pot experiment (60-d) were performed on migration and transformation of PAH at the sediment, and toxicity and their bioavailability in plant affected by the presence of Kandelia obovate-derived biochar in Southeast China. Root exudates amendments significantly increased the cumulative leaching-loss of pyrene by 36-51 % with or without biochar amendment via continuous diffusion and partition process, and biochar amendments decreased the bioavailability of pyrene (16.8-25.8 %) probably due to a faster pyrene sorption on inter-phase transport against desorption. The regression analysis indicated a significant relationship (p < 0.05) between leachate pH and pyrene concentrations. Notably, the bioaccumulation of pyrene on K. obovate parts had significant negative correlation (p < 0.05) to biochar. The activities of four key antioxidizes (phenylalanine ammonia-lyase, dismutases, peroxidases and catalases) were significantly decreased with the application of biochar. Moreover, biochar plays a positive role in cytochrome C release and phosphatidylserine secretion, and a combined biochar-rhizosphere approach can improve the stress tolerance and resistance of K. obovate with an enhanced synergetic effect, which could be a feasible remediation strategy for alleviating the mangrove sediment contaminated by PAH.

Remediation of phenanthrene phytotoxicity by the interaction of rice and endophytic fungus P. liquidambaris in practice

Phenanthrene cannot be effectively degraded in the agricultural production systems and it is greatly hazardous for food safety and human health. In our study, the remediation ability and mechanism of rice and endophytic fungus Phomopsis liquidambaris interaction on phenanthrene in the rice-growing environment were explored using laboratory and pot experiments. The results showed that plant-endophyte interaction had the potential to enhance remediation on phenanthrene contamination in the rice-growing environment. The content of phenanthrene in soil and rice (including leaves, roots, and grains) of the plant-endophyte interaction system was about 42% and 27% lower than of the non-inoculated treatment under 100 mg kg^-1 treatment. The mechanism may be related to the improvement of plant growth, root activity, chlorophyll content, ATP energy supply, and antagonistic ability of rice to promote the absorption of phenanthrene in the rice-growing environment, and then the phenanthrene absorbed into the rice was degraded by improving the phenanthrene degrading enzyme activities and gene relative expression levels of P. liquidambaris during plant-endophyte interaction. Moreover, the plant-endophyte interaction system could also promote rice growth and increase rice yield by over 20% more than the control under 50 mg kg^-1 treatment. This study indicated a promising potential of the plant-endophyte interaction system for pollution remediation in agriculture.