Comprehensive Analysis of Unsymmetrical Dimethylhydrazine: Adsorption Behavior, Environmental Fate, and Toxicity Across Contrasting Soil Matrices

Unsymmetrical dimethylhydrazine (1,1-Dimethylhydrazine, UDMH) is widely used as a high-performance liquid rocket propellant for the space industry globally. The release and leakage of UDMH into the environment, especially the soil environment, pose serious threats to ecosystems and human beings. In order to reveal the hazards of UDMH to soil and facilitate subsequent remediation, the adsorption behavior of UDMH in typical soil (yellow-brown soil, red soil, and black soil) matrices was explored, the environmental fate and toxicity of UDMH were presented by simulation calculation, and the phytotoxicity was evaluated by germination assay in the present study. The results showed that the adsorption performance of red soil, yellow-brown soil, and black soil for UDMH increased sequentially by integrating the findings from kinetic and thermodynamic studies. A highly significant correlation between the physicochemical and adsorption parameters for various soil matrices indicated a considerable impact of soil physicochemical properties on the adsorption behavior of UDMH in soils. The environmental fate simulation calculation indicated that UDMH and its transformation products were prone to being dissolved in soil water and migrating; however, once these compounds were present in the surface layer of dry soil, severe ecological and environmental pollution would occur. Based on a thorough evaluation of the toxicity parameters, formaldehyde dimethylhydrazone has been identified as demonstrating the most pronounced environmental toxicity profile, thus warranting prioritized attention. The results of a germination assay demonstrated that more than 100 mg·kg^-1 of UDMH in the soil would lead to strong phytotoxicity to plants, and more than 200 mg·kg^-1 of UDMH would significantly affect the early germination of seeds. Hence, this research provided helpful insights and theoretical support for the environmental fate and remediation of UDMH.