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Keywords:

  • Antimicrobials;
  • Triclosan;
  • Seed germination;
  • Plant morphology;
  • Methyl-triclosan

Abstract

Three wetland macrophytes, Sesbania herbacea, Bidens frondosa, and Eclipta prostrata, were exposed (0.4–1,000-ppb nominal concentrations) to the antimicrobial triclosan for 28 d in a flow-through system. Sesbania herbacea had decreased seed germination at the 100-ppb exposure level at days 7, 14, and 21, and B. frondosa germination was reduced at the 1,000-ppb exposure level at day 7. Eclipta prostrata germination was unaffected. Seedling effects monitored were total fresh weight, shoot and root fresh weights, root length, and root surface area. Root metrics were most affected by exposure. Total root length was diminished at all exposure levels in S. herbacea and B. frondosa and at the 10-ppb and higher concentrations for E. prostrata. Root surface area decreased at all exposure levels in B. frondosa and at the 10-ppb level and above in S. herbacea and E. prostrata. Root and shoot bioconcentration factors (BCFs) were estimated for S. herbacea and B. frondosa. While BCFs were low in shoots of both species and roots of S. herbacea (<10), they were elevated in B. frondosa roots (53–101). Methyl-triclosan was formed in the system and accumulated in shoot and root tissues of S. herbacea to concentrations that exceeded those of the parent compound. However, methyl-triclosan was nontoxic in an Arabidopsis thaliana enoyl-acyl carrier protein reductase (the putative enzymatic target of triclosan) assay and did not appear to contribute to the effects of exposure. Two of the three plant species assessed exhibited reduced root systems at environmentally relevant concentrations, raising the concern that wetland plant performance could be compromised in constructed wetlands receiving wastewater treatment plant discharges.