Fate of fluorinated organic pollutants in aquatic plant systems: studies with lemnaceae and lemnaceae tissue cultures

Abstract

Aquatic plants of the family Lemnaceae (e.g., duckweed) actively uptake, metabolize, and sequester pollutants in natural and engineered wetland systems. Numerous interrelated processes contribute to pollutant removal in wetlands; of these processes, interactions between organic pollutants and aquatic plants may be least understood. Research focused on (1) understanding parameters that affected uptake of fluorinated organic pollutants by Lemnaceae, (2) identifying plant processes involved in removal of wastewater-associated organic pollutants by Lemnaceae, and (3) assessing use of Lemnaceae callus cultures in understanding toxicity and metabolism of fluorinated organic pollutants by Lemnaceae. Through active plant uptake, Lemna minor rapidly removed 13 fluorinated phenols, with pseudo-first order rate constants of 0.20±0.04 d-1 to 0.84±0.07 d-1. Uptake rates depended on substituent type (i.e., trifluoromethyl- vs. fluoro-) and position, with slowest removal rates for di-ortho-substituted fluorophenols. Uptake rates decreased with increasing concentrations of fluorinated phenols; assessments of inhibition of plant oxygen production in conjugation with concentration studies indicated that concentration affected uptake rates even when Lemnaceae was not inhibited. Additionally, temperature dependencies of fluorinated phenol uptake by Lemnaceae were well represented by Arrhenius relationships; however, effects of temperature on plant activity were also observed in trends of uptake rates with temperature. Increasing uptake with decreasing concentration and increasing temperature, in addition to effects of plant inhibition, plant activity, and sorption on uptake, strongly emphasized the importance of plant metabolism in uptake of fluorinated phenols by Lemnaceae. Active plant uptake of wastewater-associated organic pollutants affected fate of fluoxetine, triclosan, and 2,4-dichlorophenoxyacetic acid, while passive plant removal processes contributed to fate of four of six wastewater derived organic pollutants. Consequently, plant-associated processes were important components of fate for over 50% of experimental wastewater-associated organic pollutants. Furthermore, assessments with Lemnaceae callus cultures indicated that callus cultures were generally more susceptible to inhibitory responses to fluorinated phenols than were Lemnaceae plants; however, metabolism of 3-trifluormethylphenol in Lemnaceae callus cultures and plants was similar, indicating that callus cultures may be valuable in plant metabolism studies. Research advances understanding of fate of organic pollutants in wetland systems, and thus has important implications for water quality, ecosystem health, and human health.