Role of Carex aquatilis and Typha latifolia in the Dissipation and Detoxification of Naphthenic Acid Fraction Compounds in Constructed Wetland Mesocosms

Abstract

Constructed wetland treatment systems (CWTS) were evaluated for their ability to attenuate naphthenic acid fraction compounds (NAFCs) in oil sands process-affected water (OSPW) using mesocosms containing OSPW-only, unplanted, and planted treatments with Carex aquatilis, Typha latifolia, or a mixed planting. High-resolution molecular profiling, stable carbon isotope analysis, and fathead minnow embryo bioassays were used to assess NAFC dissipation and detoxification. Negligible NAFC removal occurred in OSPW-only treatments, while removal increased from 19% in unplanted mesocosms to 46–48% in planted systems, indicating that substrate-mediated processes and plant-associated mechanisms enhanced attenuation. Preferential loss of higher molecular weight O2 and O2S compounds and an increase in oxygenated transformation products suggested microbial transformation and selective removal of more toxic fractions. Targeted NAFCs also accumulated in plant roots (≈10–2300 ng/g), supporting plant uptake as a contributing mechanism. These chemical changes corresponded with reduced fathead minnow embryo toxicity, with all treatment systems reaching control-level responses by Day 87. The results demonstrate that CWTS can substantially reduce NAFC concentrations and associated toxicity in OSPW and highlight the importance of congener-specific monitoring and long-term evaluation of transformed and root-associated compounds.