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

Abstract

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.

Environmental Background Values and Ecological Risk Assessment of Heavy Metals in Watershed Sediments: A Comparison of Assessment Methods

“…These results indicate that I geo values are only related to the total concentration of heavy metals based on selected background values and did not be affected by sediment properties [42]. However, sediment properties and composition can influence the availability of heavy metals in sediments and thus affect the risk assessment [43]. In addition, the risk values of heavy metals with the same content may differ due to the different background values for each type [44].…”

“…The reason may be that Cu, Zn, As, Cd, and Pb mainly come from anthropogenic sources, such as the discharge of industrial wastewater and domestic sewage, which leads to serious heavy metal pollution with extremely high toxicity to local organisms [2,50]. On the contrary, Cr, Ni, and Hg mainly come from natural sources, and the influence of sediment characteristics cannot be ignored [43,51]. Meanwhile, the results also indicated that the three indicators have similar effects.…”