Investigation of the mechanism of uptake and accumulation of zwitterionic tetracyclines by rice (Oryza sativa L.).

The uptake and accumulation of organic contaminants by plants can be detrimental to the plant itself as well as consumers. Tetracycline antibiotics are present at trace levels in soil and water. Under typical environmental conditions, they exist as zwitterions. Comparatively little is known of their uptake and accumulation by plants, or the mechanism by which this occurs. To examine this, rice (Oryza sativa L.) was employed, together with a static diffusion cell equipped with a cellulose membrane as a model for the uptake process. For rice, kinetic results suggested that the zwitterions were behaving similarly to neutral organic compounds, with a passive uptake process. The diffusion cell provided qualitatively similar results. When exposed to aqueous concentrations of zwitterionic tetracyclines of 50 mg L(-1) over 15 days, no translocation to shoots or detrimental effects on plants was observed. Despite relatively low root lipid contents, concentrations in root tissue of greater than 1000 mg kg(-1) (d.w.) were determined with maximum Root Concentration Factors of the order of 2000 L kg(-1) (d.w.). Overall, for the tetracyclines investigated, kinetic and accumulation behavior in plants together with permeation in the diffusion cell were all governed by compound hydrophobicity.