Considering the increase in demand for rare earth elements (REEs) and their accumulation in soil ecosystems, it is crucial to understand their toxicity. However, the impact of lanthanum, yttrium and cerium oxides (La2O3, Y2O3 and CeO2, respectively) on soil organisms remains insufficiently studied. This study aims to unravel the effects of La2O3, Y2O3 and CeO2 nanoparticles (NPs) and their corresponding bulk forms (0, 156, 313, 625, 1250 and 2500 mg/kg) on the terrestrial species Enchytraeus crypticus. The effects on survival, reproduction (21 days (d)), avoidance behavior (2 d) and DNA integrity (2 and 7 d) of E. crypticus were evaluated. No significant effects on survival were observed. For La2O3, the bulk form affected more endpoints than the NPs, inducing avoidance behavior (1250 mg/kg) and DNA damage (1250 mg/kg- 2 d; 2500 mg/kg- 7 d). The Y2O3 NPs demonstrated higher toxicity than the bulk form: decreased reproduction (>= 1250 mg/kg); induced avoidance behavior (>= 625 mg/kg) and DNA damage (>= 156 mg/kg- 2 d; 2500 mg/kg- 7 d). For CeO2, both forms exhibited similar toxicity, decreasing reproduction (625 mg/kg for bulk and 2500 mg/kg for NPs) and inducing DNA damage at all tested concentrations for both forms. REEs oxides toxicity was influenced by the REEs type and concentration, exposure time and material form, suggesting different modes of action. This study highlights the distinct responses of E. crypticus after exposure to REEs oxides and shows that REEs exposure may differently affect soil organisms, emphasizing the importance of risk assessment.

This study aims to evaluate the possibility of reusing treated marine clayey soils by stabilization/solidification (S/S) technology as geomaterial in reclamation projects from the aspects of engineering strength, chemical modification and environmental risk assessment. The lime-activated incinerated sewage sludge ash (ISSA) together with ground granulated blast furnace slag (GGBS) was employed as the binder. The multi-controlling factors including water content, curing time, salinity, and chemical compositions of mixing solution were taken into account to identify the S/S treated Hong Kong marine deposit (HKMD) slurry based on the strength tests, pH measurement, thermo-gravimetric (TG) analysis, X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS) and toxicity characteristic leaching procedure (TCLP) tests, etc. The results show that the S/S treatment using lime-activated ISSA-GGBS can effectively enhance the strength of marine soil at the initial water content of 110% and 200%. The water content and curing time have a significant impact on the S/S treated HKMD. The pH of treated soils is higher than 11.1, which proves an alkaline environment for the reactions in the treated soil. A special case is the treated HKMD at 200% water content hydrated by MgCl2 solution, which has a low pH of 10.23 and maintains a slurry state. Based on the TCLP results, the leaching concentration of heavy metals from S/S treated HKMD is environmentally safe and meets Hong Kong standard for reusing treated soil with a low level of <0.2 mg/L. The content of main products such as calcium/magnesium silicate hydrate, ettringite or Friedel's salt depends on the chemical additions (e.g. distilled water, seawater, NaCl and Na2SO4). The products in the specimens mixed with MgCl2 solutions are mainly composed of Mg(OH)(2), M-S-H and MgCO3, which is distinct with the neoformations in the other cases. Therefore, this study proves that the S/S treated soil slurry could be reused as geomaterials in reclamation projects, and the S/S process is greatly affected by water content, curing time and solution compositions, etc. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Mining activities are among the main sources of heavy metal contamination in the environment. The damage caused to land by mining has become an increasingly important problem in some countries. A pot experiment was conducted to evaluate the effects of two application rates (1% and 5% w/w) of rice straw biochars, as prepared at 420 degree celsius and 640 degree celsius(B1420 and B640), and several inorganic amendments (pumice, leca, zeolite and bentonite) on Cd and Pb bioavailability and speciation in soil and their accumulation in maize (Zea mays L.) as an indicator plant. Furthermore, the amelioration effects of the applied amendments on the potential environmental risk of the heavy metals were assessed. The amendments resulted in a considerable reduction of the Cd and Pb contents in the shoots, which was by 28.83-70.72% and 21.78-64.02%, respectively, as compared to the control. Amendments also decreased the DTPA-extractable Pb and Cd in the soil, particularly at the 5% application rate, as compared to those in the un-amended soil. Furthermore, in comparison to the control, the transfer factors of heavy metals were reduced when the amendments were applied. Amendments also decreased the exchangeable portion of Cd and Pb by 10.43-52.11% and by 6.43-55.43%, respectively; most of these were converted into oxides and more stable forms exhibiting the lower risk assessment code (RAC) and the potential ecological risk index (PERI). These results indicate that zeolite and BI420 have a high potential to decrease the uptake of Cd and Pb in the shoots and roots of maize, respectively. Biochar and zeolite, as cost-effective and safe adsorbents, performed the best in immobilizing Pb and Cd in the studied calcareous soil.