Evaluation of microbial-induced calcite precipitation performance for soil surface improvement and toxicity...

Microbial-induced calcite precipitation (MICP) is an environmentally friendly process that can be used to enhance soil surface stability against wind erosion. In this study, the performance of the MICP process on soil surface improvement was investigated using Staphylococcus warneri IR-103 bacteria. The biostabilizer, containing S. warneri suspension and a cementation solution consisting of 0.5 mM CaCl₂ and 1.5 mM urea, was sprayed on fine-grain soil to induce a surface MICP reaction. Soil surface strength was measured using a penetrometer test, and wind tunnel tests were conducted to evaluate the soil surface's resistance to wind erosion. Scanning electron microscopy (SEM) analysis of the treated soils was conducted to visualize carbonate crystal formations within and on the soil particles. Additionally, X-ray diffraction (XRD) was used to confirm the presence and identify the crystal structures. The ecotoxicological assessment of the biostabilizer was carried out by performing phytotoxicity and oral/dermal/ocular in vivo acute toxicity experiments due to a few case reports of S. warneri's harmfulness and virulence of coagulase-negative staphylococci, highlighting the need for safety measures for workers and end-users. Mixing cementation solution with bacterial suspension in yeast-ammonium chloride medium increased soil strength and durability. The biostabilizer did not harm the seed germination of Agropyron desertorum, and the soil surface remained resistant to wind erosion. Rat oral/dermal acute toxicity tests revealed no adverse effects during the 14-day observation period. The LD₅₀ (median lethal dose) cut-off value of the biostabilizer in oral and dermal administrations was 5000 and 1000 mg/kg body weight, respectively. Ocular administration of a 0.1 mL drop did not induce eye irritation in rabbits. In conclusion, the use of the biostabilizer for wind erosion control appears to be technically and environmentally feasible and justifiable.