Systematic assessment of the ecotoxicological effects and mechanisms of biochar-derived dissolved organic matter (DOM) on the earthworm Eisenia fetida

The interaction between biochar and earthworms: Revealing the potential ecological risks of biochar application and the feasibility of their co-application

Biochar's interaction with soil-dwelling organisms, particularly earthworms, is crucial in ensuring the effective and secure utilization of biochar in the soil. This review introduces the application of biochar in soil, summarizes how earthworms respond to biochar-amended soil and the underlying factors that can influence their response, discusses the synergistic and antagonistic impacts of earthworm activity on the efficacy of biochar, and considers the feasibility of applying them together. A review of existing research has identified uncertainty in the effect of biochar exposure on earthworms, with biochar derived from animal wastes, produced at higher pyrolysis temperatures, and used at higher doses of biochar having more negative effects on earthworms. Habitat modification, toxicity release, particle effects, and contaminant immobilization are underlying factors in how biochar affects earthworm indicators. While biochar in contaminated soils may alleviate the stress of pollutants on earthworms by decreasing their bioaccumulation, this remedial effect is not always effective. Additionally, earthworm bioturbation can enhance the migration, fragmentation, and oxidation of biochar, while also stimulating extracellular enzymes that convert biochar into 'vermichar'. Earthworms and biochar can synergize well to improve soil fertility and remediate soil organic pollution, yet exhibit contrasting roles in soil C sequestration and immobilizing heavy metals in soil. These findings highlight both the advantages and risks of their co-application. Therefore, when considering the use of biochar alone or with earthworms, it is crucial to thoroughly assess its potential ecotoxicity on earthworms and other soil organisms, as well as the influence of bioturbation, such as that caused by earthworms, on the effectiveness of biochar.

Multilevel investigation of the ecotoxicological effects of sewage sludge biochar on the earthworm Eisenia fetida

The ecological risks of sewage sludge biochar (SSB) after land use is still not truly reflected. Herein, the ecological risks of SSB prepared at different temperature were investigated using the earthworm E. fetida as a model organism from the perspectives of organismal, tissue, cellular, and molecular level. The findings revealed that the ecological risk associated with low-temperature SSB (SSB300) was more pronounced compared to medium- and high-temperature SSB (SSB500 and SSB700), and the ecological risk intensified with increasing SSB addition rates, as revealed by an increase in the integrated biomarker response v2 (IBRv2) value by 2.59-25.41 compared to those of SSB500 and SSB700. Among them, 10% SSB300 application caused significant oxidative stress and neurotoxicity in earthworms compared to CK (p < 0.001). The weight growth rate and cocoon production rate of earthworms were observed to decrease by 25.06% and 69.29%, respectively, while the mortality rate exhibited a significant increase of 33.34% following a 10% SSB300 application, as compared to the CK. Moreover, 10% SSB300 application also resulted in extensive stratum corneum injury and significant longitudinal muscle damage in earthworms, while also inducing severe collapse of intestinal epithelial cells and disruption of intestinal integrity. In addition, 10% SSB300 caused abnormal expression of earthworm detoxification and cocoon production genes (p < 0.001). These results may improve our understanding of the ecotoxicity of biochar, especially in the long term application, and contribute to providing the guidelines for applying biochar as a soil amendment.

Effects of biochar-derived dissolved organic matter on the gut microbiomes and metabolomics in earthworm Eisenia fetida

The ecological risks of biochar-derived dissolved organic matter (DOM) to soil invertebrates at different organismal levels remains limited. This study comprehensively explored the ecological risks of biochar-derived DOM on earthworm gut through assessments of enzyme activity response, histopathology, gut microbiomes, and metabolomics. Results demonstrated that DOM disturbed the digestive enzymes in earthworm, especially for 10% DOM300 groups. The integrated biomarker response v2 (IBRv2) indicated that the perturbation of earthworm digestive enzymes induced by DOM was both time-dependent and dose-dependent. Pathological observations revealed that 10% DOM300 damaged intestinal epithelium and digestive lumen of earthworms. The significant damage and injury to earthworms caused by DOM300 due to its higher concentrations of heavy metal ions and organic substrates (e.g., toluene, hexane, butanamide, and hexanamide) compared to DOM500 and DOM700. Analysis of 16S rRNA from the gut microbiota showed a significant decrease in genera (Verminephrobacter, Bacillus, and Microbacteriaceae) associated with inflammation, disease, and detoxification processes. Furthermore, 10% DOM300 caused the abnormality of metabolites, such as glutamate, fumaric acid, pyruvate, and citric acid, which were involved in energy metabolism, These findings contributed to improve our understanding of the toxic mechanism of biochar DOM from multiple perspectives.