T11 AM Aquatic Plants: Methods, Mechanisms and Markers
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 343-344

(TRO-1117-827266) Uptake of Ionizable Organic Contaminants by the Aquatic Plant L. minor.

Tront, J¹, Reinhold, D¹, Saunders, F, ¹ School of Civil and Environmental Engineering, Georgia Tech, Atlanta, GA, USA

ABSTRACT- Previous research demonstrated that plants take up, metabolize and sequester organic pollutants. However, limited studies have investigated uptake of ionizable contaminants or factors which affect uptake by aquatic plants. This study examined key factors affecting uptake of a class of ionizable organic contaminants (halogenated phenols) by Lemna minor. Factors such as initial plant activity and contaminant speciation were examined in batch systems using 2,4,5-trichlorophenol (pK_a = 7.0) as the model contaminant. Initial plant activity, measured as the oxygen production rate, was found to positively correlate with contaminant uptake rate. Experimentation at a range of pH values (6 − 9) and uptake rates were linearly correlated to percent of contaminant in protonated form. The impact of halogen number, type, and positioning on uptake was investigated using a suite of halogenated phenols in batch reactors with media buffered so that aqueous-phase speciation was not a variable. Halogenated phenol uptake was quantified with pseudo-first-order rate coefficients. Data gathered for mono-, di-, and trihalogenated phenols revealed that uptake rates: (i) were not affected by halogen substituent type, (ii) were significantly affected by substituent position, and (iii) did not vary with increasing number of halogen substituents. Relationships between uptake rates and physiochemical properties (e.g., log K_ow: 1.77 − 4.13; pK_a: 5.96 − 9.54) were investigated. Data analysis comparing hydrophobicity with uptake rate indicated that hydrophobicity was not a critical variable in uptake rate of ionizable contaminants. Furthermore, uptake data did not follow Gaussian relationships previously defined for uptake by terrestrial plants (Briggs et al., 1982; Burken and Schnoor, 1998). The relationship between uptake by L. minor and fraction protonated at cytosolic pH was also examined. Therefore, results demonstrated that factors such as plant metabolic activity, percent protonated (in aqueous phase and in the cytosol) play a critical role in determining rate of ionizable organic contaminant uptake by plants.

Key words: organic pollutant, ionizable, plant uptake, duckweed