Safety & Stewardship
Rejuvra's® Environmental and toxicological profile
General Description
Rejuvra® herbicide is a cellulose-biosynthesis inhibitor (CBI) and is classified as a Group 29 Herbicide by the Weed Science Society of America. Rejuvra inhibits crystalline cellulose deposition in plant cell walls, affecting cell wall formation, cell elongation and division. Actively growing meristematic root and shoot tissues (areas of cell division and elongation) of germinating weed seeds are affected. Generally, weeds are only controlled if Rejuvra is applied and sufficiently activated by rainfall before seeds start to germinate. Rejuvra is not susceptible to degradation from sunlight and is not volatile.
Mammalian Toxicity
Rejuvra exhibits low acute (short-term) toxicity via all routes of exposure (inhalation, ingestion and dermal) and is not a skin sensitizer. Longer-term toxicity testing showed no evidence of immunotoxicity, developmental or reproductive toxicity, genotoxicity, or carcinogenicity. Further, there is low dietary and occupational exposure. Based on these study results, the label carries the CAUTION signal word. CAUTION signifies that standard personal protective equipment is needed to ensure safety to anyone handling the product. All mixers, loaders, applicators and other handlers must wear a long-sleeved shirt, long pants, shoes plus socks and chemical-resistant gloves.
Groundwater and Surface Water Advisories
U.S. pesticide labels require groundwater and surface water advisories based on laboratory measurements of degradation and sorption. Some key environmental and chemical properties are provided in the nearby table. Rejuvra degrades in soil by microbial activity. Field dissipation studies determined a soil half-life of between nine and 69 days and a mean half-life of 41 days. This represents expected dissipation from operational use. This is much faster than degradation rates measured in laboratory studies where half-lives were greater than 150 days. Rejuvra is used at very low use rates of 0.7 to 1 ounce active ingredient per acre. Low use rates combined with moderate soil degradation rates, medium-to-low mobility and the fact that Rejuvra binds to soil organic matter results in low potential for movement into groundwater when used according to label directions. This is supported by low downward movement measured in field studies. There is some potential for surface runoff of Rejuvra, but this can be mitigated by following label instructions regarding rainfall and vegetative buffer strips.
Environmental Risk Assessment
To understand the risk that Rejuvra poses in the environment, the expected exposure is calculated based on label use directions and the environmental fate properties of the active ingredient in Rejuvra. The predicted exposure is compared to the toxicity endpoints (concentrations at which toxicity was observed) in laboratory studies. If exposure is predicted to be lower than the concentration at which toxicity occurs, risk to non-target organisms is considered minimal.
The risk assessment for Rejuvra indicates that nonvascular aquatic plants, fish, aquatic invertebrates, terrestrial invertebrates, marine/estuarine organisms, birds, mammals and bees are not at risk because of low predicted exposure.
The Rejuvra® herbicide label states that it is toxic to fish and aquatic invertebrates. This statement is based solely on results of laboratory toxicity tests without consideration of the potential environmental exposure from using Rejuvra according to label directions. When potential exposure from using Rejuvra according to label directions is considered, no impact to fish and aquatic invertebrates is expected.
Non-target terrestrial plants and aquatic vascular plants are potentially at risk from exposure as is expected for an herbicide compound. All label instructions should be followed to minimize the risk to non-target plants. Rejuvra has no effect on microbes at rates far above typical field rates. Rejuvra did not adversely affect the respiration of sewage sludge bacteria nor was it found to cause adverse effects in carbon mineralization or nitrogen fixation rates in bacteria.
Water solubility
.4.4 mg/L (pH 4) 2.8 mg/L (pH 7-9)
moderate solubility
Vapor pressure
2.5 x 10-8 pascal
not volatile
Absorption to soil (Koc)
496
150-500 = medium mobility; 500-2,000 low mobility; *Rejuvra is on the boder between medium and low mobility
Soil degradation (field)
9-to-69-day half-life, mean 41 days
moderate degradation
*McCall's soil mobility classification scheme
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