Environmental risk due to the accumulation of metals in Sedum alfredii under different intercropping patterns during phytoremediation

A field experiment was conducted to evaluate the environmental risk of phytoextraction of Cd, Cu, and Pb using Sedum alfredii Hance. with different intercropping patterns. Three receptors representing invertebrates (earthworms), avians (yellow-feathered chickens), and small mammalian omnivores (Rattus losea) were selected as the potentially impacted environmental receptors. Soil deglutition and food ingestion are considered dominant pathways of metal exposure. Different planting patterns, including S. alfredii monoculture and S. alfredii intercropped (coordinate and malposed) with Cicer arietinum L., were used to evaluate the mobilization, absorption, and migration of Cd during phytoextraction. This study revealed that the intercropping systems, particularly the malposed intercropping patterns, significantly increased the Cd decontamination efficiency by 31.3% and enhanced the content of Cu and Pb in the aboveground tissues of the intercropped C. arietinum. Correspondingly, different planting patterns resulted in varying environmental risks. For the omnivores, which primarily consume earthworms and plant tissues, the hazard index was 0.096 for the S. alfredii monoculture, and the index decreased to 0.074 and 0.090 in the coordinate and malposed intercropping patterns, respectively. The environmental risk might be induced by the increased Cd concentrations in the roots and shoots of S. alfredii. When extrapolating the results of this treatment to the entire region, all the environmental hazard index values of the receptors were higher than 1.0. This study suggests that if a phytoextraction method is used for metal decontamination, corresponding prevention strategies should be established to prevent the diffusion of concentrated metals to higher trophic levels via the food chain.