Changes of heavy metal in fresh and litter leaves of Neolamarckia cadamba and Schefflera arboricola under sewage sludge application

Abstract

This study conducted a large root box experiment with Schefflera arboricola monoculture, Neolamarckia cadamba monoculture, and co-planting of Schefflera arboricola and Neolamarckia cadamba. The dynamic changes in Cu, Zn, Cd, and Hg contents in fresh and litter leaves of Schefflera arboricola and Neolamarckia cadamba and their litter leaves yield were analyzed for three months (September, October, and November 2020) after the surface application of 2% (W/W) sewage sludge (SS). The relationship between the heavy metal contents of fresh and litter leaves and the changes in the heavy metal return amount in litter leaves were further analyzed. The results were as follows: (1) N. cadamba had significantly higher Cu contents in fresh and litter leaves than those of S. arboricola, while had significantly lower Zn and Cd contents than those of S. arboricola. (2) The fresh leaves of S. arboricola had the lowest Zn content and the highest Hg content in November. (3) The fresh leaves of monoculture and co-planting Neolamarckia cadamba had the highest Zn, Cd, and Hg contents in November. (4) The Hg content in the litter leaves of co-planting of N. cadamba increased significantly with the time of SS application, while those of Cu, Zn, and Cd contents showed no significance. (5) The Cd content in fresh leaves was significantly and positively correlated with the Hg and Cd contents of litter leaves in Schefflera arboricola in both September and November. (6) The highest yield of litter leaves and the highest return amount of Cu, Zn, Cd, and Hg in S. arboricola occurred one month after SS application (September), while those in Neolamarckia cadamba occurred two months after SS application (October). In summary, the application time of SS showed a greater effect on the heavy metal contents in fresh leaves of N. cadamba and Schefflera arboricola than those in litter leaves; there was a positive correlation between the Cd content in the fresh leaves and the Cd and Hg contents in the litter leaves of S. arboricola; the heavy metal pollution risk of the litter leaves of S. arboricola and Neolamarckia cadamba was easy to occur in one month (September) and two months (October) after SS application, respectively. This study provides a reference for safe SS utilization and reasonable litter disposal in the landscape.

Keywords

• sewage sludge utilization
• heavy metal
• landscape plant
• litter leaf
• co-planting