Influence of Fe addition on the accumulation of oxytetracycline in rice seedlings (Oryza sativa L.) growing in hydroponic and soil culture

Abstract

The accumulation of oxytetracycline (OTC) in rice plants has been found, which may directly threaten food safety. Fe(II) ions are among the most common metal ions in the aquatic and soil environment. There have been no published papers discussing the uptake of OTC in plant exposed to treated solution and soil after adding Fe(II). In this work, the effect of Fe(II) on uptake and translocation of OTC in rice plants (Oryza sativa L.) was investigated. Hydroponic and soil culture were conducted under greenhouse conditions to identify changes in rice biomass, OTC uptake, and translocation exposed to three different OTC concentrations, including 0, 10, and 50 mg·L−1/mg·kg−1 for 30 days. For same OTC exposure treatment, rice seedlings were grown in a nutrient solution or paddy soil with adding four different Fe(II) concentrations, including 0, 10, 30, 50, and 70 mg·L−1/mg·kg−1. The concentrations of OTC in iron plaque (IP) on root surface, root, and shoot were analyzed, and biological concentration factor (BCF) and transfer factor (TF) of OTC were calculated. Adding proper Fe(II) (10–50 mg·L−1 in solution and 10–30 mg·kg−1 in soil) alleviated the inhibition function of OTC on rice growth. IP was formed with high amounts after adding Fe(II) although OTC decreased IP amounts. OTC concentration in IP increased with increasing Fe(II) addition. OTC translocation from root surface to root presented a declining trend with increasing Fe(II) concentration. Fe(II) addition inhibited effectively OTC uptake by rice exposed to high OTC of 50 mg·L−1/mg·kg−1 in solution or soil. PCA and correlation analysis showed that the decrease of OTC accumulation in rice was determined more strongly by the increase of OTC accumulation in IP. IP acting as a buffer function reduced effectively OTC uptake by rice seedlings due to promoting OTC accumulation on root surface and reducing OTC translocation from root surface to root. Also, Fe(II) addition promoted OTC degradation and reduced OTC bioavailability due to the complexes of OTC and Fe(II), which then decreased OTC uptake by rice. In soil, OTC uptake was affectted more strongly by the decrease of OTC concentrations in rhizosphere than ones in non-rhizosphere.