Objective Long-term fertilization can lead to heavy metal accumulation in red soil, posing potential health hazards to humans. Accurate assessment of the ecological and health risks of heavy metals in the soil-peanut system is crucial for guiding soil fertility management in the hilly red soil regions.

Method Based on a long-term erosion plot experiment established in 2012 at the Chinese Academy of Sciences Red Soil Ecological Experimental Station, surface soil and peanut samples were collected in 2023. This study analyzed the concentrations of Cr, Cu, Zn, and Cd content in the soil-peanut system under three treatments: control (CK), chemical fertilizer (NPK), and a combination of pig manure with chemical fertilizer (NPK + PM). Soil heavy metal pollution grades and ecological risks were assessed using the single-factor pollution index, Nemerow comprehensive pollution index, and the potential ecological risk index. Additionally, a health risk assessment model was applied to analyze carcinogenic and non-carcinogenic risks posed to adults and children from the contaminated soil and peanut grains.

Result Compared to the control, total Cr content in the surface soil increased significantly by 23.8% (P < 0.05) after 12 years of chemical fertilization. In contrast, the combined application of pig manure with chemical fertilizer over 12 years significantly increased total Cu, Zn, and Cd in the surface soil by 110 - 130% (P < 0.05), while significantly reducing Cu and Cd in peanut grains by 50.6 - 83.0% (P < 0.05). Long-term application of pig manure with chemical fertilizer resulted in a mild pollution index for Cu, while the comprehensive pollution index indicated slight pollution. However, the potential ecological risk of soil heavy metals under long-term fertilization remained at a slight risk level. Under long-term fertilization, the non-carcinogenic risk index from ingesting peanuts remained within the safe threshold for both adults and children. The combined pig manure with fertilizer treatment increased the non-carcinogenic risk index for Cu, Zn, and Cd in soil by 67.5 - 174% compared to chemical fertilizer alone, but still remained within safe limits. However, Cr in soil exceeded the carcinogenic risk threshold for children. Compared to adults, children showed a significantly higher proportion of non-carcinogenic risks from ingesting soil heavy metals (4.72% - 4.83%) and a significantly lower proportion through skin contact (22.9% - 23.0%).

Conclusion The study showed that long-term application of pig manure significantly increases the accumulation and pollution risks of heavy metals in the plow layer of sloping red soil. However, it does not pose significant health hazards to humans through peanut kernels. It is recommended to treat pig manure with high-temperature composting or by adding heavy metal immobilizers before application. Additionally, adjusting the application rate and frequency, coupled with regular environmental monitoring, can effectively reduce potential risks to soil environments and human health.