Effect of Polypropylene Microplastics on Water and Salt Movement and in Saline Soils

Abstract

【Objective】 Polypropylene microplastics are fragments of polypropylene. They exist in soil and have potential impact on soil environment. This paper investigates their influence on water flow and salt redistribution in soil under drip irrigation. 【Method】 The experiment was conducted in cuboid tanks packed by saline soil. Steady water infiltration into the soil was maintained by a Martensian flask; the infiltration rate was controlled at 0.36 L/h by a rotameter. The content of polypropylene microplastics in the soil was 2%, and the salt content was 0.5%, 4% or 7%. 【Result】 Soil water content and initial soil salt content were positively correlated. The average water content in the soil with initial salt content of 7.0% was 9.4% and 11.2% higher than that in soils with initial salt contents of 4.0% and 0.5%, respectively (P<0.05). Compared with soil without polypropylene microparticles, the presence of polypropylene microparticles increased soil water content at the depth of 16.6 cm beneath the infiltration point on the soil surface by 6.2%~9.4%, and soil water content at the location 12 cm away horizontally from the infiltration point by 6.2%~7.9% (P<0.05), with the increase depending on initial salt content. Compared to control without polypropylene microplastics, existence of polypropylene microplastics also increased soluble salt 163.2% to 326.9% (P<0.05), with the increase depending on initial salt content, in addition to the increased soil pH. 【Conclusion】 Polypropylene microplastics increased soil moisture content, salt content and soil pH. These findings demonstrated the impact of polypropylene microplastics on soil properties and the importance of considering them in soil and water management.

Keywords

• saline soil
• microplastic
• salt
• the moisture content
• ph