Influence of Cu and Ca cations on ciprofloxacin transport in saturated porous media

Emerging contaminant ciprofloxacin (CIP) has been frequently detected in soils and groundwater; however, impacts of cations on its transport in the environment remain largely unknown. We examined CIP transport in saturated sand media under the influence of Cu/Ca by either mixing CIP with Cu/Ca in solution or preloading CIP onto sand then using Cu/Ca solution to mobilize CIP. Though the amount of Fe/Al oxides on native sand surface was limited, it significantly impeded CIP transport, delaying CIP breakthrough curve from 30 to >100 PV. In clean sand where Fe/Al oxides were removed, Ca and Cu significantly promoted CIP transport by reducing the retardation factor R from 22 to <2. In native sand, due to CIP's strong complexation with Fe/Al, only Cu promoted CIP transport. When CIP was pre-sorbed onto sand, neither Cu nor Ca was effective in mobilizing CIP from native sand. However, Cu effectively mobilized 90% CIP whereas Ca mobilized 30% CIP from clean sand. A mathematical model based on advection-dispersion equation coupled with equilibrium and kinetic reactions successfully simulated CIP transport in saturated sand media. Our results suggested that cations in aqueous solution and on solid phase are important to better understand CIP transport in soils. Published by Elsevier B.V.