Environmental Exposure Assessment of Fluoroquinolone Antibacterial Agents from Sewage to Soil

TLDR

The study investigated the fate of fluoroquinolone residues in agricultural soils following sludge application. Mass‑flow analysis and solid‑phase extraction coupled with liquid chromatography were used to quantify fluoroquinolones in wastewater, sludge, and treated soils during mechanical‑biological treatment and sludge application. Wastewater treatment removed 88–92% of fluoroquinolones mainly by sorption to sludge, which remains the primary reservoir; methanogenic sludge digesters showed little removal, and field trials revealed persistent, low‑mobility residues in treated soils.

Abstract

The behavior of fluoroquinolone antibacterial agents (FQs) during mechanical−biological wastewater treatment was studied by mass flow analysis. In addition, the fate of FQs in agricultural soils after sludge application was investigated. Concentrations of FQs in filtered wastewater (raw sewage, primary, secondary, and tertiary effluents) were determined using solid-phase extraction with mixed phase cation exchange disk cartridges and reversed-phase liquid chromatography with fluorescence detection. FQs in suspended solids, sewage sludge (raw, excess, and anaerobically digested sludge), and sludge-treated soils were determined as described for the aqueous samples but preceded by accelerated solvent extraction. Wastewater treatment resulted in a reduction of the FQ mass flow of 88−92%, mainly due to sorption on sewage sludge. A sludge-wastewater partition coefficient (log Kd ∼ 4) was calculated in the activated sludge reactors with a hydraulic residence time of about 8 h. No significant removal of FQs occurred under methanogenic conditions of the sludge digesters. These results suggest sewage sludge as the main reservoir of FQ residues and outline the importance of sludge management strategies to determine whether most of the human-excreted FQs enter the environment. Field experiments of sludge-application to agricultural land confirmed the long-term persistence of trace amounts of FQs in sludge-treated soils and indicated a limited mobility of FQs into the subsoil.