Effect of Microplastics on Soil Water Infiltration and Evaporation

Abstract

In order to explore the influences of microplastics with different abundances (0.5%, 1%, and 2% of the dry weight of the soil) and different types (PP, PVC, and PE) on the moisture infiltration and evaporation of the soil, we adopted the method of indoor soil column simulation to elaborate the influences of the microplastics with different abundances and different types on the moisture accumulated infiltration time, moisture containing rate, wetting front, and evaporation characteristics, among which the A1, A2, and A3; Q1, Q2, and Q3; and Z1, Z2, and Z3 respectively represented the experimental number of PE, PVC, and PP under the abundances of 0.5%, 1%, and 2%. The influences of the microplastics with different types and different abundances on the moisture infiltration and evaporation of the soil showed obvious differentiation. Under the same types of conditions, when the abundances of the microplastics increased, the accumulated infiltration time also increased significantly. However, under the occurrence condition of the microplastics of different types but the same abundances, the accumulated infiltration time of the PP experiment group>that of the PVC experiment group>that of the PE experiment group>that of the blank experiment group. Under the occurrence condition of microplastics, the maximum moisture rate of the soil basically appeared at the depth from 10 to 25 cm, and the CK of the blank group appeared at the depth from 20-25 cm. Within the same infiltration time, when the abundances of the microplastics increased, the moving distance and the moving rate of wetting front of the soil decreased accordingly. When the infiltration time was 60 minutes, the wetting moving distances of A1, A2, and A3; Q1, Q2, and Q3; and Z1, Z2, and Z3, respectively, decreased 4.38%, 8.76%, and 10.58%; 7.30%, 10.22%, and 14.60%; and 10.95%, 13.14%, and 15.33% compared to those of the CK groups, among which the influence of PP microplastics was the most significant. The occurrence of the microplastics had a prohibition function to the moisture evaporation of the soil; when the microplastics had the same types, the accumulated amount of the soil decreased with the increase in abundance. When evaporating for 27 hours, the accumulated evaporation amount of the experiment soil column of PP, PVC, and PE microplastics with the added abundances of 2% respectively decreased 22.9%, 19.4%, and 13.3% compared to that in the CK. The Rose evaporation model relatively truly reflected the changing situation of the soil accumulated evaporation amount with time under the occurrence situation of the microplastics. This research can provide a theoretical basis for the changing study of the soil moisture movement under the occurrence condition of microplastics.