TOXICITY OF THE NORFLURAZON TO THE AQUATIC MACROPHYTE VALLISNERIA AMERICANA (MICHX.)

摘要

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