Characteristics of fluoride adsorption in different soil types: potential factors and implications for environmental risk assessment

Abstract

The adsorption of fluoride by soils influences its mobility and bioavailability. Therefore, the fluoride adsorption process in soils has garnered widespread attention. Yet research on assessing environmental risk based on the characteristics of fluoride adsorption in soil is still limited. Here, a suite of batch experiments were conducted using three soil types with distinct properties. The results demonstrate that soil organic matter (SOM) and pH are critical factors determining fluoride adsorption in soils. Paddy soil (PS) with its higher SOM content has a higher adsorption capacity compared with loessal soil (LS) and brown soil (BS). Under acidic conditions, BS and LS whose Ca²⁺ content is higher exhibited a higher adsorption capacity. The fluoride adsorption process in soils may involve electrostatic adsorption, complexation, and precipitation. The desorption results showed stronger fluoride binding to PS and LS than BS, while the fluoride adsorbed onto BS was almost completely desorbed. This research demonstrates that a deeper understanding of regional differences in soil properties is crucial for better studying the migration and accumulation characteristics of fluoride and its bioavailability in various soils. This study provides a theoretical basis for evaluating the bioavailability, exposure risk, and groundwater pollution risk of fluoride in different soils.