title: Toxicity of the norflurazon to the aquatic macrophyte Vallisneria americana (Michx.).
abstract: Vallisneria americana (Michx.) (common name tapegrass) is a submersed, vascular aquatic plant that reproduces vegetatively and by seed. The objective of this study was to determine the no-observable-effects concentrations (NOECs) and lowest-observable-effects concentrations (LOECs) for tapegrass exposed to the herbicide norflurazon (0-0.1 mg/L) following a 14-d exposure and a postexposure period. The primary symptom of norflurazon toxicity was bleaching of newly emerged leaf blades at concentrations of 0.04 mg/L and higher after 14 d of exposure. Leaf greenness effect levels were 0.04 mg/L (NOEC) and 0.06 mg/L (LOEC). All other endpoints measured resulted in a NOEC greater than 0.1 mg/L following the exposure period. Latent effects were observed 14 d postexposure for new leaf production and fresh weight gains, with a NOEC and LOEC of 0.08 and 0.1 mg/L, respectively. Total leaf growth was the least sensitive endpoint measured. Following the exposure/postexposure periods, significant effects on vegetative reproduction were apparent, with no effects occurring at concentrations up to 0.08 mg/L, but with significant reduction at the 0.1 mg/L treatment level. Root and stolon dry weights were significantly reduced at the 0.1 and 0.08 mg/L treatments, respectively. Total soluble sugars (TSS) and hexose content in shoots was reduced at concentrations of 0.04 mg/L and higher. TSS, hexose, and sucrose contents were higher in roots of plants exposed to 0.1 mg/L. Some recovery was apparent for all treatment concentrations following the postexposure period, indicating that the effects were at least partially reversible.
authors.affiliation: University of Florida/IFAS Indian River Research and Education Center, Department of Soil and Water Science, Fort Pierce, Florida 34945, USA. pcwilson@mail.ifas.ufl.edu
authors.forename: P Chris
authors.initials: PC
authors.lastname: Wilson
authors.forename: Sandra B
authors.initials: SB
authors.lastname: Wilson
authors.forename: Daniel
authors.initials: D
authors.lastname: Haunert
mesh_terms: D006540:Herbicides / Q000633:toxicity*; D031321:Hydrocharitaceae / Q000187:drug effects*; D019055:No-Observed-Adverse-Effect Level; D010858:Pigmentation; D018515:Plant Leaves / Q000737:chemistry / Q000187:drug effects; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D011724:Pyridazines / Q000633:toxicity*
chemical_list: D006540:Herbicides; D011724:Pyridazines; C008677:norflurazone