Phytoremediation of Fluorinated Agrochemicals by Duckweed
In natural and engineered systems, aquatic plants actively remediate agricultural wastes and chemicals. Characterization of agrochemical removal by aquatic plants is essential for improved design of phytoremediation systems for polluted surface waters. To measure removal of fluorinated agrochemicals by duckweed, duckweed was exposed to fluorinated phenols in batch reactors. Aqueous fluorinated phenol concentration was regularly sampled and analyzed (HPLC/DAD/MS). After a 50 h exposure, duckweed activity was quantified using oxygen production assessment to determine whether duckweed was inhibited. Removal of fluorinated phenols by duckweed was rapid, with pseudo-first-order uptake rates of 0.21 to 0.85 L d-1 for fluoro- and trifluoromethylphenols. Uptake rates of fluorinated phenols were compound-specific and appeared to depend on factors affecting rates of enzymatic processing. However, attempts to correlate removal rates with chemical parameters were unsuccessful. The positioning and type of fluoro-substituents on the phenol ring were the most indicative parameters of uptake rates. TFM, a lampricide used in the Great Lakes, was the only fluorinated phenol that was not uptaken by duckweed. Negligible uptake of TFM by duckweed was not attributed to presence of the nitro- or trifluoromethyl- groups, as 2,4,6-trinitrotoluene and 3-trifluoromethylphenol were uptaken. Although uptake rates were not easily predicted by known chemical parameters, uptake rates indicated that duckweed plays an important role in phytoremediation of fluorinated agrochemicals in surface waters.