Influence of soil evolution on the heavy metal risk in three kinds of intertidal zone of the Pearl River Estuary

Human activities and the increasing emphasis on coastal protection contribute to the diversity and evolution of intertidal soil. But, less is known about the influence of soil evolution on the heavy metal risk in intertidal zones. In this study, soil samples were collected from three kinds of intertidal zone in the Pearl River Estuary, including bare beach (BB), a spartina growing area (SGA), and a mangrove growing area (MGA), to reveal the influence of key factors on the heavy metal risk. The results showed that the highest concentrations of Cd, Zn, Pb, Cu, Ni, and Cr mainly existed in the surface layer of SGA and MGA and decreased with depth, reaching 3.57, 365.26, 91.24 95.12, 58.47, and 111.35 mg kg(-1), respectively. Residual fractions were the main geochemical fractions and increased with depth, while exchangeable fractions showed the opposite trend. Based on the geoaccumulation index, soils were moderately to extremely polluted by Cd and partially to moderately polluted by Zn, Cu, and Ni. Cd had high potential adverse effects (ranging from 25.29 to 45) in MGA according to the risk assessment code. Correlation and principal component analyses indicated that soil organic carbon (SOC), clay, pH, Fe, and Mg were the key factors that affected the heavy metal risk. Linear regression revealed that SOC and clay were positively correlated with the pollution level of heavy metals, while clay and Fe were positively correlated with the ecological risk. Consequently, the variation in properties due to intertidal soil evolution may modulate the risk of heavy metals.

Automated summary

This study investigated the influence of key factors on heavy metal risk in intertidal soil from the Pearl River Estuary, revealing that soil organic carbon, clay, pH, Fe, and Mg were the key factors affecting the heavy metal risk. Soil evolution due to human activities and coastal protection may modulate the risk of heavy metal pollution in intertidal zones.