Diagnosis and evaluation of the health status of sediment-water-farmland-rice system in Longtang

As one of the largest electronic waste (e-waste) disassembling sites in China, environmental quality and human health of Longtang town have always been the focus of concern and research. With the effective enforcement of relevant laws, most informal e-waste dismantling centers have been shut down, but heavy metals are non-biodegradable and easily enriched contaminants that are difficult to remove from the environment. This research investigated the heavy metal (Cd, Pb, Cu, Zn, As, and Cr) level in sediments, water, paddy soils, and the matched rice plants in Longtang, and assessed the potential ecological risk and human health risk of heavy metals. The results showed that the heavy metal content was highest in the sediment, followed by paddy soil and rice, the lowest in water, and the surface water was higher than groundwater. In the paddy soil, the heavy metal content in the topsoil was the highest, and all exceeded the soil background value of Guangdong Province, and the level of Cu (129.45 mg kg⁻¹), Cd (0.44 mg kg⁻¹), and Pb (100.63 mg kg⁻¹) exceeded the national risk screening value (GB 15618-2018). Compared with previous studies, the contents of Cd, Cu, and Zn in soil showed a downward trend. Potential ecological risk assessment showed that the risk level of Cd in the topsoil was high, and the risk levels of Cd and Cu in the sediment were very high and considerable, respectively, posing a major risk to human health. In rice plants, heavy metals mainly accumulated in the roots of rice, and their migration ability in rice tissues was poor. The heavy metal level in grain was within the threshold value set by the Codex Alimentarius Commission (CAC, CXS 193-1995) or China (GB 2762-2017), and the risk level to human health was low. Accordingly, it is imperative to continuously monitor the content of heavy metals in the sediment and soil of Longtang, especially Cu and Cd.