The earthworm -based vermiremediation facilitated with benign chemicals such as nano zero-valent iron (nZVI) is a promising approach for the remediation of a variety of soil contaminants including cyanotoxins. As the most toxic cyanotoxin, microcystin-LR (MC-LR) enter soil via runoff, irrigated surface water and sewage, and the application of cyanobacterial biofertilizers as part of the sustainable agricultural practice. Earthworms in such remediation systems must sustain the potential risk from both nZVI and MC-LR. In the present study, earthworms (Eisenia fetida) were exposed up to 14 days to MC-LR and nZVI (individually and in mixture), and the toxicity was investigated at both the organismal and metabolic levels, including growth, tissue damage, oxidative stress, metabolic response and gut microbiota. Results showed that co -exposure of MC-LR and nZVI is less potent to earthworms than that of separate exposure. Histological observations in the co -exposure group revealed only minor epidermal brokenness, and KEGG enrichment analysis showed that co -exposure induced earthworms to regulate glutathione biosynthesis for detoxification and reduced adverse effects from MC-LR. The combined use of nZVI promoted the growth and reproduction of soil and earthworm gut bacteria (e.g., Sphingobacterium and Acinetobacter) responsible for the degradation of MC-LR, which might explain the observed antagonism between nZVI and MC-LR in earthworm microcosm. Our study suggests the beneficial use of nZVI to detoxify pollutants in earthworm -based vermiremediation systems where freshwater containing cyanobacterial blooms is frequently used to irrigate soil and supply water for the growth and metabolism of earthworms. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Due to high reactivity and relatively low cost, nano zero-valent iron (nZVI) has become an alternative material for in-situ remediation of contaminated sites. However, factors such as short transport distance and easy deposition in porous media also seriously restrict its injection remediation effect. The optimum ratio of bentonite and kaolin supported nano zero-valent iron (K-nZVI) in the remediation agent was determined by sedimentation and rheological tests. The transport characteristics of deionized water and bentonite suspensions carrying K-nZVI in porous media under different injection pressures were investigated using simulating column tests. The results show that bentonite suspensions could significantly improve the stability and dispersibility of K-nZVI. The proportion of bentonite and K-nZVI are 5% and 0.4%, respectively, which is the best ratio of the remediation agent. The transport capability of K-nZVI carried by deionized water increases with the increase of injection pressure, while there is a critical injection pressure for bentonite suspensions carrying K-nZVI remediation agent. The numerical simulation results show that the diffusion radius of K-nZVI is positively correlated with the injection pressure and negatively correlated with the viscosity of the remediation agent. The results provide theoretical guidance for the remediation project of heavy metal pollution in non-ferrous smelting sites.