Uptake and decomposition of the herbicide propanil in the plant Bidens pilosa L. dominating in the Yangtze Three Gorges Reservoir (TGR), China

Propanil (3′,4′-dichloropropionanilide) is a selective post emergence herbicide for controlling broad leaf and grass weeds in rice (Oryza sativa L.). After being taken up by plants, the fate of propanil in decomposing plant material is of particular importance to the phytoremediation of the environment. Therefore, we investigated the biotransformation of propanil in the plant Bidens pilosa under conditions close to those present in the Three Gorges Reservoir (TGR), China. Plants pre-treated with ¹⁴C-ring-labeled propanil were either (treatment a) directly submerged in TGR water for 90 days or (treatment b) pre-extracted with organic solvents, and subsequently only insoluble materials and non-extractable residues (NER) of the pesticide fractions were similarly incubated. After incubation in TGR water (treatment a), 30 % of applied radioactivity was released into water and simultaneously, amounts of NER in the plant debris appeared to increase with time finally amounting to 40 % of applied ¹⁴C. The radioactivity contained in the extractable fractions were identified as propanil, 3,4-dichloroaniline (DCA), and N-β-D-glucopyranosyl-3,4-dichloroaniline (DCA-Glu). In treatment b, significant ¹⁴C amounts were released to the water (6 % of applied ¹⁴C) and the solubilized radioactivity fractions were demonstrated to agree with those found in the extractable fractions. Therefore, if residues of the pesticide propanil are taken up by plants, it may enter again the aquatic environment after plant death and submergence. This phenomenon may have a potential impact on aquatic organisms, which to our knowledge has not been reported before. As plant uptake and degradation of xenobiotics are recognized as detoxification, we consider B. pilosa with its high uptake potential, at least for propanil, as suitable species for phytoremediation.