Interactive aging of cadmium and emerging contaminant mixtures in facility agricultural soils: predictive models for...

The aging of pollutants determines their bioavailability and the corresponding toxicity thresholds in soil environments. However, existing ecotoxicological assessments of heavy metals, antibiotics, and pesticides in facility agricultural soils rarely incorporate the confounding influences of contaminant aging and soil physicochemical properties. This study selected six facility agricultural soils with differing properties and assessed their toxic effects on Chinese cabbage (Brassica rapa subsp. chinensis) biomass following exogenous addition of cadmium (Cd), tetracycline (TC), and imidacloprid (IM), administered both individually and in combination. Under single Cd contamination, the EC₅₀ for biomass inhibition increased from the 14-day value to 30.0 mg kg^-1 after 360 days of aging. For combined contamination, the EC₅₀ reached 18.3 mg kg^-1 for Cd-TC and 24.5 mg kg^-1 for Cd-IM over the same aging period. In the acidic soils, a low-dose tetracycline inducing hormetic response was observed, with biomass stimulation exceeding 110% of the control. As aging progressed from 14 to 360 days, pollutant toxicity declined. During early aging, no significant difference in aging factors was observed between composite and single pollutants. However, in the later stages, the aging factors for composite pollutants were significantly higher than those of single pollutants. Among these, the Cd-TC aging factor was lowest in Guangxi red soil (AF_360d = 3.21), and highest in Henan alluvial soil (AF_360d = 3.82). Furthermore, the aging factor increment was more pronounced for Cd-TC mixtures than for Cd-IM. In different types of facility agricultural soils, soil organic matter and clay content can effectively predict the soil aging process as the aging period increases. All predictive models for aging factors were derived, for single Cd contamination as: (AF_180d) = -0.256 + 0.455 lg pH + 0.511 lg CEC + 0.593 lg OM (R² = 0.884, p < 0.01). These findings provide data and theoretical support for the development of aging factor prediction models and the establishment of environmental quality standards for combined contamination involving heavy metals and emerging pollutants in facility agricultural soils.