Effects of the Removal of Soil Extractable Oxytetracycline Fractions on Its Bioaccumulation in Earthworm and Horsebean

This study provides the evidence for oxytetracycline (OTC) uptake by earthworm and horsebean after removing extractable OTC in cinnamon soil using water (T₁), 0.1 mol/L CaCl₂ (T₂), and 0.1 mol/L Na₂EDTA-McIlvaine (T₃), respectively. The control was the soil without removing any extractable OTC. During horsebean exposure, the transformation from non-extractable to extractable fractions in soils depended mainly on the alternation of wetting and drying. Two organisms increased significantly OTC concentrations of McIlvaine-fraction in soils in comparison to the absence of organisms. The removal promoted the accumulation concentration and the bioaccumulation factor (BAF) of OTC in two organisms as the order: T₃ > T₂/T₁ > the control. And the promotion was stronger for horsebean than ones for earthworm. OTC accumulation in earthworm was mainly from the digestion absorption due to limited soil extractable OTC (0–0.976 mg/kg). OTC uptake by horsebean was directly through root uptake; therefore, the removal of soil extractable fractions decreased significantly OTC accumulation in root. However, the removal promoted OTC accumulation in shoot and OTC translocation from root to shoot, especially with the highest transfer factor (TF) in T₃ reaching up to 31.7. Maybe, in T₃, this was caused by the combined effect of root as the effective transport passageway of OTC and less loss of soil extractable OTC released during 28-day exposure. These present results demonstrated the high ecological risk of remained OTC in cinnamon soil after removing all extractable fractions due to its high accumulation in soil organisms and the strong transformation from soil non-extractable to extractable fraction under certain cultivation conditions such as alternation of wetting and drying.