Abstract
To understand the mechanism controlling cultivar differences in the accumulation of ciprofloxacin (CIP) in Chinese flowering cabbage (Brassica parachinensis L.), low-molecular-weight organic acids (LMWOAs) secreted from the roots of high- and low-CIP cultivars (Sijiu and Cutai, respectively) and their effects on the bioavailability of CIP in soil were investigated. Significant differences in the content of LMWOAs (especially maleic acid) between the two cultivars played a key role in the variation in CIP accumulation. Based on the Freundlich sorption coefficient (Kf) and distribution coefficient (Kd), the presence of LMWOAs reduced the CIP sorption onto soil particles, and higher concentrations of LMWOAs led to less CIP sorption onto soil. On the other hand, LMWOAs enhanced CIP desorption by lowering the solution pH, which changed the surface charge of soil particles and the degree of CIP ionization. LMWOAs promoted CIP desorption from soil by breaking cation bridges and dissolving metal cations, particularly Cu2+. These results implied that the LMWOAs (mainly maleic acid) secreted from Sijiu inhibited CIP sorption onto soil and improved CIP desorption from soil to a greater extent than those secreted from Cutai, resulting in higher bioavailability of CIP and more uptake and accumulation of CIP in the former.
Highlights
Antibiotics are used globally to treat disease and protect the health of humans and animals
There was a significant difference (p < 0.05) in the transfer factors (TFs) of CIP between the two cultivars when exposed to 5 mg L−1 CIP, they were very low (
Four Low-molecular-weight organic acids (LMWOAs) excreted by roots of the two cultivars under different CIP exposures were detected at the seedling stage, while five LMWOAs
Summary
Antibiotics are used globally to treat disease and protect the health of humans and animals. Some crop cultivars that accumulated low levels of antibiotics were identified, including water spinach (Ipomoea aquatic) and Chinese flowering cabbage (Brassica parachinensis L.)[17, 18]. The uptake and accumulation of organic contaminants by crops are significantly affected by root exudates in soil[19]. Wang et al.[25] reported that high-Hg cultivars of rice tended to secrete higher levels of LMWOAs in the rhizosphere compared with low-Hg cultivars, which enhances the bioavailability of Hg for root uptake. Many studies have demonstrated that the LMWOAs of plants have an effect on the sorption-desorption behavior of organic contaminants[19,20,21, 27, 28]. Few studies have examined the effects of LMWOAs secreted from different crop cultivars on the sorption-desorption behavior of antibiotics in soil. The mechanisms involved in the effects of LMWOAs on antibiotic bioavailability may be partly responsible for the variation in antibiotic accumulation among crop cultivars
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