Contamination Status and Ecological Security Thresholds of Fluoride in Farmland around a Phosphorus Chemical Plant in a Karst Area of Southwestern China

The phosphorus chemical plant (PCP) production process leads to the substantial discharge of fluoride into the surrounding environment. However, there is limited research data regarding the pollution levels and ecological safety thresholds of farmland fluoride around PCPs in karst areas. This study evaluates the local contamination status and health risks by determining the fluoride content in farmland and vegetables in vicinity of a PCP in a karst area of Southwestern China. Farmland ecological security threshold was derived based on the species sensitivity distribution (SSD) model. Results showed that the fluoride contents in the soil ranged from 529.36 to 1496.02 mg kg(−1), with the median value of 823.93 mg kg(−1), which was higher than the national background value in China (478 mg kg(−1)) by 172.37%. Fluoride contents in vegetables ranged from 0.01 to 25.21 mg kg(−1), with the median value of 1.29 mg kg(−1), which was higher than the limits of contaminants in food (1 mg kg(−1)) by 129.00%, and 53.85% of vegetable samples were contaminated. Leafy vegetables showed a higher tendency of fluoride enrichment compared to non-leafy vegetables. Despite there being no significant health risk to the residents via the intake of vegetables overall, there may be potential health risks from the intake of sweet potato leaves. Based on the SSD model, the ecological safety thresholds of fluoride in local farmland was classified into the suitable for planting category (≤174.13 mg kg(−1)), safe plant utilization category (174.13–4005.42 mg kg(−1)), and strict control of planting category (≥4005.42 mg kg(−1)). These findings will provide valuable insights to facilitate the safe cultivation of local agricultural products and optimize the utilization of soil resources.