PNNL

Abstract

Trace organic compounds (TrOCs) enter the environment with discharge of treated wastewater to rivers. These effluents can also contain high loads of dissolved organic matter (DOM). In this 48 h field study, the attenuation of 17 polar TrOCs and turnover of seven DOM compound classes was investigated in a small lowland stream impacted by treated wastewater. Correlations between TrOCs and DOM compound classes were calculated and used to identify simultaneous attenuation patterns in surface water and the hyporheic zone. Changes in TrOC concentrations ranged between an increase of 152.2 % for the transformation product gabapentin-lactam and a decrease of 29.2 % for methylbenzotriazole in surface water and between a decrease of 4.9 % for primidone to 93.8 % for venlafaxine in the hyporheic zone. TrOC attenuation coincided with a decline of the proportion of easily biodegradable DOM compound classes while poorly biodegradable DOM compound classes correlated negatively with TrOCs. This concurrence indicates similar or linked attenuation pathways for biodegradable DOM and TrOCs. Strong correlations between TrOCs and DOM compound classes as well as high attenuation of TrOCs primarily occurred in the hyporheic zone making it the hotspot for DOM turnover and TrOC mitigation in a river.