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Extension Toxicology Network

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


Publication Date: 9/93


Trade names include Dirimal, EL-119, Rycelan, Ryzelan, Ryzelon and Surflan.


Products containing oryzalin must bear the signal word "Caution" (1).


Oryzalin is a selective preemergence surface-applied herbicide used for control of annual grasses and broadleaf weeds in fruit trees, nut trees, vineyards, established bermudagrass turf and established ornamentals. It inhibits the growth of germinating weed seeds. It is available in aqueous suspension, dry flowable, and wettable powder formulations (1).



Oryzalin has low acute toxicity to mammals (1, 5). In dogs and cats, large oral doses caused nausea and vomiting (4). Oryzalin can cause mild irritation to the skin or eye (4). It may cause allergic skin reactions in some individuals (1, 2).

The oral LD50 for technical oryzalin in rats and mice is > 5,000 mg/kg (4), and in cats, dogs and chickens is > 1,000 mg/kg (2, 5, 7). The dermal LD50 for technical oryzalin on rabbits is > 2,000 mg/kg (2, 4). The 1-hour LC50 in rats is > 0.88 mg/l (4).


Long-term exposure to oryzalin has caused blood changes and tumors in animals (4). When oryzalin was fed to rats in doses as high as 135 mg/kg for 2 years, there was an increase in the incidence of thyroid, mammary and skin tumors. Repeated ingestion of large doses led to adverse changes in blood cell formation on dogs (2). The NOEL in a 1 year feeding study with dogs was 5 mg/kg/day (6).

Rats fed a dietary level of 45 mg/kg for 2 years exhibited blood changes, increased liver and kidney weights, inhibition of growth, and decreased survival (2). Mice given dietary doses of 1,350 ppm for 1 year exhibited decreased uterine and ovarian weight. The NOEL for this study was 500 ppm (75 mg/kg/day) (2, 6). Rats fed 45 mg/kg or 135 mg/kg, the highest dose tested, for one year showed minimal signs of toxicity (5).

Reproductive Effects

There were no adverse effects on reproduction in a 3-generation study with rats fed dietary concentrations 12.5, 37.5 or 112.5 mg/kg/day, the highest dose tested. Fetotoxic effects appeared at 12.5 mg/kg/day (2, 6).

Teratogenic Effects

There were no birth defects in the offspring of pregnant rats fed dietary concentrations as high as 112 mg/kg/day for 3 generations, nor in the offspring of pregnant rabbits given doses of 125 mg/kg/day, the highest dose tested (4, 6).

Mutagenic Effects

EPA reports that oryzalin was not mutagenic in several tests, including tests on live rats and mice and on bacterial cell cultures (6).

Carcinogenic Effects

There were no tumors in mice fed doses as high as 548 mg/kg/day for 2 years (6). Thyroid tumors and benign skin and mammary tumors occurred in rats fed a dietary level of 45 mg/kg for 2 years. The NOEL for this study was 15 mg/kg/day (2, 6). Because oryzalin did not produce tumors in more than one test species, did not produce tumors in more than one experiment, and did not produce an unusual degree of tumors, EPA has classified oryzalin as a possible human carcinogen (6).

Organ Toxicity

Poisoning by oryzalin may affect the thyroid. Rats fed a dietary level of 45 mg/kg for 2 years exhibited blood changes, increased liver and kidney weights, inhibition of growth, and decreased survival (2).

Fate in Humans and Animals

When oryzalin was administered to male rats, 40% of the dose was excreted in the urine and 40% in the feces within 3 days. Similar results were obtained from tests with rabbits, a 400 pound steer, and with Rhesus monkeys (5).


Effects on Birds

Oryzalin is not hazardous to birds (4, 5). Its oral LD50 in bobwhite quail and mallard ducks is > 500 mg/kg (7), and > 1,000 mg/kg in hens (1). The 5-day dietary LD50 for oryzalin in quail and ducks is > 5,000 mg/kg (4).

Effects on Aquatic Organisms

Oryzalin is moderately toxic to fish. Direct contamination of a body of water with oryzalin in wettable powder formulations may kill fish. Run-off from fields into open bodies of water should be avoided (4). The 96-hour LC50 for oryzalin in bluegill sunfish is 2.88 mg/l, 3.26 mg/l in rainbow trout (1, 4), and > 1.4 mg/l in goldfish fingerlings (7).

Effects on Other Animals (Nontarget species)

The nature of its use rules out any danger to bees (11).


Breakdown of Chemical in Soil and Groundwater

Oryzalin is soluble in water and it does not have a strong tendency to adsorb to soil particles (3). It leaches downward to a limited extent with rainfall (4) and has a moderate potential to contaminate groundwater (3).

Its soil half-life is 20 days (3). Microbial degradation may be responsible for the breakdown of oryzalin in soils. It is subject to photodecomposition, but not volatilization, at the soil surface (4).

Breakdown of Chemical in Surface Water

Oryzalin has a low solubility in water. There was no observed hydrolysis at pH 5, 7, 9 (9).

Breakdown of Chemical in Vegetation

Plant metabolism of oryzalin is minimal. Unmetabolized oryzalin is rarely detected (9). When used at the recommended level, damage to plants in the following year is not expected (11).


Technical oryzalin is a bright yellow-orange crystalline powder (1). Technical oryzalin is a flammable solid (4) and oryzalin dust may form flammable or explosive mixtures with air. Keep it away from all ignition sources and avoid dispersion of dust. Oryzalin is stable under normal temperatures and pressures, but may pose a slight fire hazard if exposed to heat or flame. It may burn, but does not ignite readily. It poses a fire and explosion hazard in the presence of strong oxidizers. Thermal decomposition of oryzalin may release highly toxic oxides of nitrogen and sulfur (2).

Exposure Guidelines:

No occupational exposure limits have been established for oryzalin by OSHA, NIOSH or ACGIH (2).

ADI: 0.0094 mg/kg/day based on a NOEL of 18.75 mg/kg/day in a 90-day dog feeding study and a 2,000 fold safety margin (8).
MPI: 0.5625 for a 60 kg person (8)

Physical Properties:

CAS #: 19044-88-3
Chemical name: 3,5-dinitro-N4, N4-dipropylsulfanilamide
Chemical Class/Use: dinitroaniline sulfonamide herbicide
Specific gravity: 1.138 - 1.239 at 25 degrees C (10)
H20 solubility: 2.5 ppm at pH 7 and 25 degrees C (1)
Solubility in other solvents:readily soluble in organic solvents such as acetone, ethanol, methanol, and acetonitrile; slightly soluble in benzene and xylene; insoluble in hexane (1).
Melting point: 286-288 degrees F (141-142 degrees C) (2)
Boiling point: 212 degrees F (100 degrees C) (10)
Decomposition temperature: NA
Flashpoint: 200 degrees F (93.3 degres C) (1)
Vapor pressure: negligible (2); 1 x 10-7 mm Hg at 25 degrees C (1).
Koc: 600 (3)


9002 Purdue Rd.
Indianapolis IN 46268-1189
Emergency: 517-636-4400

Review by Basic Manufacturer:

Comments solicited: April, 1993
Comments received: April, 1993


  1. Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister Publishing Company, Willoughby, OH.
  2. Occupational Health Services, Inc. 1992 (Nov. 17). MSDS for Oryzalin. OHS Inc., Secaucus, NJ.
  3. U. S. Department of Agriculture, Soil Conservation Service. 1990 (Nov.). SCS/ARS/CES Pesticide Properties Database: Version 2.0 (Summary). USDA - Soil Conservation Service, Syracuse, NY.
  4. WSSA Herbicide Handbook Committee. 1989. Herbicide Handbook of the Weed Science Society of America, 6th Ed. WSSA, Champaign, IL.
  5. U.S. Environmental Protection Agency. June 30, 1987. Pesticide Fact Sheet Number 211: Oryzalin. US EPA, Office of Pesticide Programs, Registration Div., Washington, DC.
  6. U.S. Environmental Protection Agency. June 20, 1990. Pesticide tolerance for oryzalin. Federal Register 55 (119): 25140-1.
  7. British Crop Protection Council. 1983. The Pesticide Manual: A World Compendium, 7th ed. Croydon, England.
  8. U.S. Environmental Protection Agency. Nov. 21, 1984. Tolerances and exemptions from tolerances for pesticide chemicals in or on raw agricultural commodities; oryzalin. Federal Register 49 (226): 45854-5.
  9. Washington State Department of Transportation. 1993. Roadside Vegetation Management: Environmental Impact Statement. WSDOT.
  10. Elanco Chemical Company. 1989. Summary of Basic Data for Oryzalin Herbicide. MSDS. Indianapolis, IN: Elanco Products Co.
  11. The Royal Society of Chemistry. 1983. The Agro-Chemicals Handbook. University of Nottingham, England.