Adsorption and pH values determine the distribution of cadmium in terrestrial and marine soils in the Nansha area, Pearl River Delta

Cadmium is a toxic element with a half-life of several decades, which can accumulate in the human body by entering the food chain and seriously harm health. Coastal zones are located in the transitional zone between land and sea, and large amounts of terrigenous material input have important environmental effects on this ecosystem. The pH, Eh, hydrodynamic conditions, soil organic matter(SOM) and other factors defining the sea-land interaction within the sedimentary environment are significantly different from those defining land facies. It was found that the adsorption constant KF and the Cd2+adsorption capacity of marine soils were higher than those of terrestrial soils. However, the saturation adsorption of cadmium in terrestrial sediments was higher than in marine sediments. In order to study the key factors affecting cadmium adsorption in soils at the sea-land interface in the Nansha area of the Pearl River Delta, a test was conducted on a column of undisturbed soil. The results showed that soil pH was an important factor affecting cadmium adsorption capacity in both terrestrial and marine sediments. Neutral and alkaline topsoil conditions inhibited the vertical migration of cadmium, while the acidic environment favored it. The higher the clay and SOM were, the stronger the Cd2+ adsorption capacity of the soil was. These findings suggest that the distribution of cadmium in marine and continental sedimentary soils is not only related to adsorption, but also to the physical and chemical processes occurring in different sedimentary environments.