Biodegradation of Trichloroethene by Methane Oxidizers Naturally Associated with Wetland Plant Roots

Abstract

Trichloroethene (TCE) can undergo natural attenuation within wetland environments, particularly by oxidative processes that occur in the vegetated subsurface. The goal of this study was to evaluate TCE degradation potential through aerobic cometabolism by methane-oxidizing microorganisms associated with the roots of wetland plant species, Carex comosa and Scirpus atrovirens. The degradation experiments were conducted in 2.4 L Teflon microcosms with 15 g of washed, soil-free roots and amended with methane (2.1 mg/L), oxygen (8 mg/L), and TCE (three enrichment cycles without TCE and four cycles at 150 μg/L, one cycle at 600 μg/L, and one cycle at 900 μg/L of TCE). Our results indicated that methane-oxidizing activity and TCE degradation potential were comparable for the plant species investigated. The initial rates of methane degradation with TCE amendments varied between 0.21 and 0.30 mg L^–1 d^–1 for Carex comosa, and between 0.14 and 0.25 mg L^–1 d^–1 for Scirpus atrovirens. The average TCE mass removal per cycle varied between 24 and 32%, and the overall transformation yield was 0.0004 mmol TCE/mmol CH₄ for both plant species. This study suggests that wetland plants can play an important role in the natural attenuation of TCE in contaminated aquatic environments.