Identification, sources and accumulation behavior of priority odorants discharged to surface water from stormwater systems with illicit connections.

The odor nuisance of urban surface water after rainfall events has aroused public concerns and threaten the aquatic organisms. Herein, the first study to investigate 150 odorants in storm sewer discharge was performed in humid regions of China. During rainfall events, the total concentrations of odorants at storm sewer outlet increased by 1.3-2.1 fold from 1.7-9.4 μg/L to 2.1-20.0 μg/L with 37 odorants having detection frequencies above 50 % on rainy days, and the concentrations of total odorants in air also significantly increased resulting in worse odor nuisance. The accumulation of odorants in sewer sediment and the remobilization of sewer sediment were factors resulting in more intensified emission of odorants from storm sewer on rainy days. More than half of odorants discharged during rainfall were contributed by sewer sediment. Thioethers, indoles, 2-isopropyl-3‑methoxy pyrazine, acetophenone and coumarin exhibited high sediment-accumulation. Quantitative structure-property relationship models revealed that enhanced sediment-accumulation of chained aliphatic and aromatic odorants can be explained by the electrostatic attraction and topological characteristic, respectively. The multicriteria analysis was further introduced for relative odorants ranking by considering the variations in hazard criteria of environmental occurrence, ecotoxicity, persistence, odor nuisance and sediment accumulation. Among priority odorants, thioethers and indoles were attributed by their distinct sediment-accumulation and odor nuisance potential, while chlorinated anisole and pinenes prioritized due to their higher ecotoxicity. These findings provide novel insights into the odorants from storm sewer discharges and explore the environmental behaviors of odorants in sewer sediment.