How backfill soil type influencing on Cd and Pb migration in artificial soil on railway rock-cut slopes

Highlights: • A study on mitigating cadmium and lead pollution via backfill soil was conducted. • Pollutant concentration, soil quality, erosion durability, and rainfall impacts were considered. • Adding agricultural soil in backfill soil was best at containing both heavy metals. • The soil quality index (SQI) can serve as an indicator of Cd and Pb transformation. -- Abstract: Cadmium (Cd) and lead (Pb) that accumulates in the surface soil of railway rock-cut slopes may migrate to nearby croplands. It is important to determine whether backfill soil type influences the transportation of Cd and Pb in the surface soil. Representative rock-cut slopes, backfill soil of 100% rock fragments, 100% agricultural soil, and 50% agricultural soil and 50% rock fragments (n = 2 for each type) were selected. The pollution and migration levels of Cd and Pb and the soil quality and erodibility were investigated. The soil concentrations of Cd and Pb on the rock-cut slopes were much higher than those of China soil quality standard. Soil erosion was the most important factor that influences the migration of Cd and Pb in the slopes. Increasing the percentage of agricultural soil in the backfill soil resulted in decreasing the diffusion of Cd and Pb by reducing soil erosion. The backfill soil affected the soil quality and erosion durability, which, in turn, affected the transportation of Cd and Pb in the runoff. The soil quality index (SQI) accurately reflects the soil quality and can serve as an indicator of the migration of Cd and Pb on the surface soil of the slopes. Therefore, agricultural soil was more appropriate to use as a backfill soil in slope revegetation practice than was the rock fragment, which was helpful for decreasing the environmental risk of Cd and Pb on the slopes.