Risk assessment of three fluoroquinolone antibiotics in the groundwater recharge system

•Single and mixture of OFL, ENR and NOR adsorption-desorption onto soil were investigated.•Silty clay loam has higher sorption capacity than loamy sand.•Competitive adsorption exists when the three selected FQs coexist.•The risk order in reclaimed water is OFL>ENR>NOR.•OFL and ENR pose a high risk whilst NOR poses little apparent risk in groundwater.

Three fluoroquinolone antibiotics agents (FQs) in groundwater and reclaimed water have been investigated in Changzhou and Beijing, China. The occurrence of ofloxacin (OFL), enrofloxacin (ENR) and norfloxacin (NOR) is in nanograms per liter and has 100% frequency. The concentration order of FQs in reclaimed water is NOR>OFL>ENR, whilst the order in groundwater is NOR>ENR>OFL. And then the single and mixture adsorption-desorption have been studied and showed that (i) silty clay loam has higher sorption capacity than loamy sand, (ii) competitive adsorption exists when the three selected FQs coexist, (iii) ENR has a significantly priority sorption to NOR, whilst OFL has a least sorption among the mixture, (iv) there is no significant difference between the desorption results of mixture and the indivdual compound in relatively low concentration, (v) the formed chemical bonds and the irreversible combination of adsorption point are the significant influential factors for explaining desorption hysteresis of the selected FQs. Based on the above study, transport model and risk quotient have been performed, and the calculated risk quotient reveals that: (i) the selected FQs risk order in reclaimed water is OFL>ENR>NOR, (ii) in groundwater, OFL and ENR pose a higher risk than NOR no matter whether considering the long time groundwater recharge. This study will help policy makers to decide which FQs need to be covered in the priority substance lists defined in legislative frameworks.

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