Development and application of oxygen production rate assessment to uptake of fluorinated organics by Lemna minor.

The effects of contaminant concentration on contaminant removal by Lemna minor were examined under elevated plant densities typical of full surface coverage. Uptake of 3-fluorophenol and 3-trifluoromethylphenol by L. minor was determined at concentrations from 10 to 1750 microM. Because standardized toxicity tests typically do not measure plant activity of L. minor at high plant densities, an oxygen production rate (OP) assessment was developed with consideration of experimental parameters that may inhibit OP by L. minor, including concentrations of carbonate and phosphate buffer in the media, time of assessment, and mass of L. minor. The OP by L. minor was inhibited by increasing media pH and mass of L. minor. The developed assessment used 0.5 g of L. minor per 60 ml of modified Standard Methods medium. A total of 30 h was needed to determine toxicity of fluorinated phenols, with an exposure period of 24 h, an incubation time of 6 h, and negligible analysis time. At concentrations from 10 to 1750 microM, 3-trifluoromethylphenol exhibited a sigmoidal toxicity response. However, 3-fluorophenol was neither toxic nor inhibitory at the experimental concentrations tested. Substantial decreases in uptake rate constants were observed for increasing concentrations of both contaminants, indicating that concentration may be a more important indicator of uptake by L. minor compared with decreasing plant activity because of toxicity.

Glycosidation of chlorophenols by Lemna minor.

Metabolic fate of xenobiotics in plant tissues has an important role in the ultimate fate of these compounds in natural and engineered systems. Chlorophenols are an important class of xenobiotics used in a variety of biocides and have been shown to be resistant to microbial degradation. Three chlorophenyl glycosides were extracted from tissues of Lemna minor exposed to 2,4-dichlorophenol (DCP). The products were identified as 2,4-dichlorophenyl-beta-D-glucopyranoside (DCPG), 2,4-dichlorophenyl-beta-D-(6-O-malonyl)-glucopyranoside (DCPMG) and 2,4-dichlorophenyl-beta-D-glucopyranosyl-(6 --> 1)-beta-D-apiofuranoside (DCPAG). Identification was based on reverse phase retention (C18), electrospray mass spectra collected in negative and positive mode (ESI-NEG and ESI-POS, respectively), and nuclear magnetic resonance (NMR) spectra comparisons to reference materials synthesized in the laboratory. Liquid chromatography-mass spectrometry (LC-MS) analysis of plants exposed to 2,4,5-trichlorophenol (TCP) formed analogous compounds: 2,4,5-trichlorophenyl-beta-D-glucopyranoside (TCPG), 2,4,5-trichlorophenyl-beta-D-(6-O-malonyl)-glucopyranoside (TCPMG) and 2,4,5-trichlorophenyl-beta-D-glucopyranosyl-(6 --> 1)-beta-D-apiofuranoside (TCPAG). Enzyme catalyzed hydrolysis with beta-glucosidase was ineffective in releasing the beta-glucosides with chemical modifications at C6. Presence of these glucoconjugates confirmed that L. minor was capable of xenobiotic uptake and transformation. Identification of these products suggested that chlorophenols were incorporated into vacuoles and cell walls of L. minor.