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The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

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E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Linuron

Trade and Other Names: Trade names include Afalon, Garnitan, Linex, Linorox, Linurex, Lorox, Premalin, Sarclex, and Sinuron. Linuron is often used in formulations with herbicides, insecticides, and fungicides.

Regulatory Status: Linuron is a slightly toxic compound in EPA toxicity class III. It is a General Use Pesticide (GUP). Labels for products containing linuron must bear the Signal Word CAUTION.

Chemical Class: substituted urea

Introduction: Linuron is a substituted urea pre- and post-emergence herbicide used to control annual and perennial broadleaf and grassy weeds on both crop and non-crop sites. It works by inhibiting photosynthesis in target weed plants. It is labeled for field and storehouse use in such crops as soybean, cotton, potato, corn, celery, parsnips, sorghum, asparagus, and carrots.

Formulation: Not Available

Toxicological Effects:

• Acute toxicity: Linuron is of slight toxicity by ingestion, with reported oral LD50 values of 1200 to 1500 mg/kg in rats, and 2250 mg/kg in rabbits [4,8]. The reported dermal LD50 in rabbits is greater than 5000 mg/kg [4,8]. It has been reported to be a skin sensitizer in guinea pigs, and an eye irritant in rabbits, but not a skin irritant in rabbits [4,8]. The 4-hour inhalation LC50 is 6.15 mg/L, which indicates slight toxicity by this route [4].
• Chronic toxicity: Skin sensitization was seen in guinea pigs repeatedly exposed [4]. Alterations in red blood cells were seen in rats given 2.75 mg/kg/day over 2 years [4]. Anemia was seen in dogs at doses above 6.25 mg/kg/day [4].
• Reproductive effects: In a three-generation study, no reproductive effects were observed at doses of 12.5 mg/kg/day [4]. These data suggest that reproductive effects are unlikely in humans at expected exposure levels.
• Teratogenic effects: Pregnant rabbits fed high doses of linuron during the sensitive period of pregnancy had normal offspring at doses of up to 25 mg/kg/day, even though maternal weight gain was reduced [4,14]. In rats, doses of 6.25 mg/kg/day did not produce teratogenic effects. These data suggest that linuron is not likely to cause birth defects.
• Mutagenic effects: Linuron caused mutations in one microbial assay [18]. But in several other mutagencity and genotoxicity assays, including the Ames assay, E. coli culture assay, Chinese hamster ovary cell culture assay, and whole animal studies, linuron showed no mutagenic or genotoxic activity [4,8,21]. Thus, it appears that linuron is either nonmutagenic or slightly mutagenic.
• Carcinogenic effects: Several animal studies of mice, rats, and dogs have shown that it produces nonmalignant liver and testicular tumors. In these studies, doses of 72.5 mg/kg/day in rats caused testicular adenomas and 180 mg/kg/day in mice caused hepatocellular adenoma [4,11,14,18]. These data are not sufficient to determine linuron's carcinogenicity to humans.
• Organ toxicity: Rats and dogs fed linuron for 2 years had detectable residues of linuron in their blood, fat, kidney, and spleen, but these did not seem to be associated with adverse effects [4,18].

• Fate in humans and animals: In rats, linuron breaks down completely after passing through the liver [4,8]. It is thus unlikely to bioaccumulate in mammalian systems.

Ecological Effects:

• Effects on birds: Linuron is slightly toxic to birds; the reported 5- to 8-day dietary LC50 valus are greater than 5000 ppm in Japanese quail, 3000 ppm in mallard ducks, and 3500 ppm in pheasants [4,8].
• Effects on aquatic organisms: Linuron is slightly toxic to fish and aquatic invertebrate species. The reported LC50 for linuron in trout and bluegill is 16 mg/L [8,11]. The median threshold levels, i.e. levels at which adverse, sublethal effects were apparent in 50% of the test animals, are greater than 40 mg/L in crawfish and tadpoles exposed over a 48-hour period [4].
• Effects on other organisms: Linuron is nontoxic to bees [7].

Environmental Fate:

• Breakdown in soil and groundwater: Linuron is moderately persistent in soils, with a field half-life of 30 to 150 days in various soils and under various conditions [19,34]. A representative field half-life is estimated to be approximately 60 days [12]. Microbial degradation is the major process by which linuron is lost from soils; photodegradation and volatilization are not important contributors to its breakdown [4]. The metabolites of linuron (3,4-dichloroaniline and carbon dioxide) are less toxic than linuron [35]. Linuron is moderately bound to soil, and is soluble in water [19]. Losses may occur through transport of linuron in runoff water and on suspended colloidal matter. Linuron has been found at very low concentrations in well and groundwater samples in Georgia, Missouri, Virginia, and Wisconsin [8].
• Breakdown in water: Linuron is slightly to moderately soluble in water, and is not readily broken down in water [8].
• Breakdown in vegetation: Linuron is more readily absorbed by roots from soil application, than by leaves from foliar application [4]. The rate at which it is absorbed, translocated, and subsequently broken down (or metabolized) differs with various plant species [4].

Physical Properties:

• Appearance: Linuron is an odorless, white crystalline solid [7].
• Chemical Name: 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea [7]
• CAS Number: 330-55-2
• Molecular Weight: 249.11
• Water Solubility: 81 mg/L @ 25 C, slightly soluble [7]
• Solubility in Other Solvents: s.s in aliphatic hydrocarbons, m.s. in ethanol, s. in acetone [7]
• Melting Point: 93-94 C [7]
• Vapor Pressure: 2 mPa @ 24 C [7]
• Partition Coefficient: 3.0043 [4]
• Adsorption Coefficient: 400 [19]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: 0.002 mg/kg/day [31]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

DuPont Agricultural Products
Walker's Mill, Barley Mill Plaza
P.O.Box 80038
Wilmington, DE 19880-0038

• Phone: 800-441-7515
• Emergency: 800-441-3637
  

References:

References for the information in this PIP can be found in Reference List Number 9

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.