Major controlling factors and predictions for cadmium transfer from the soil into spinach plants

• Phytoavailability of added Cd was higher than total Cd in soils.
• Cd soil–plant transfer could be described by an extended Freundlich-type function.
• Soil Cd, pH and organic carbon were controlling factors for Cd soil–plant transfer.
• A slight protection effect of organic carbon on Cd plant uptake was observed.

Predicting the mobility, bioavailability and transfer of cadmium (Cd) in the soil–plant system is of great importance with regards to food safety and environmental management. In this study, the transfer characteristics of Cd (exogenous salts) from a wide range of Chinese soils to spinach (Spinacia oleracea L.) were investigated. The major controlling factors and prediction equations for Cd transfer in the soil–plant system were also investigated. The results showed that plant Cd concentration was positively correlated with soil Cd concentration. The maximum transfer factor (ratio of the Cd concentration in the plant to that in the soil) was found in acid soils. The extended Freundlich-type function was able to describe the Cd transfer from soil to spinach plants. Combining soil total Cd, pH and organic carbon (OC) content in the prediction equation greatly improved the correlation performance compared with predictions based on total Cd only. A slight protection effect of OC on Cd uptake was observed at low soil Cd concentrations. The results are a useful tool that can be used to predict Cd transfer from soil to plant.