Geotechnical Implications of Microplastics: A Review of Their Effects on Soil Mechanical Parameters

The increase in plastic production and consumption in recent decades has led to the widespread introduction of microplastics into the environment, particularly into soils. These persistent particles, as emerging contaminants, can alter the physical, chemical, and mechanical properties of soil and consequently change its geotechnical behavior.This study is a review paper that compiles and analyzes the findings of previous research to examine the effects of microplastic presence on soil mechanical parameters, including compressibility, permeability, shear strength, settlement, and slope stability. A review of existing data indicates that the polymer type, shape, size, and weight percentage of microplastics play a decisive role in the magnitude and direction of soil behavior changes.In most cases the presence of microplastics has resulted in a decrease in bulk density and shear strength, while increasing soil porosity and settlement. However, the findings of different studies show limited consistency due to variations in laboratory methods and soil conditions.In the final section, research challenges and opportunities in Iran are discussed, emphasizing the necessity of conducting field studies, developing identification methods, and proposing geotechnical strategies to reduce the entry and impacts of microplastics. The findings of this paper can serve as a foundation for developing environmental geotechnical approaches and sustainable design practices for structures built on microplastic-contaminated soils.