E X T O X N E T
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
Publication Date: 9/93
TRADE OR OTHER NAMES
Trade names include Dirimal, EL-119, Rycelan, Ryzelan, Ryzelon and
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).
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).
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).
EPA reports that oryzalin was not mutagenic in several tests, including
tests on live rats and mice and on bacterial cell cultures (6).
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).
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
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).
PHYSICAL PROPERTIES AND GUIDELINES
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).
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)
|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
Review by Basic Manufacturer:
Comments solicited: April, 1993
Comments received: April, 1993
Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister
Publishing Company, Willoughby, OH.
Occupational Health Services, Inc. 1992 (Nov. 17). MSDS for
Oryzalin. OHS Inc., Secaucus, NJ.
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.
WSSA Herbicide Handbook Committee. 1989. Herbicide Handbook of the
Weed Science Society of America, 6th Ed. WSSA, Champaign, IL.
U.S. Environmental Protection Agency. June 30, 1987. Pesticide Fact
Sheet Number 211: Oryzalin. US EPA, Office of Pesticide Programs,
Registration Div., Washington, DC.
U.S. Environmental Protection Agency. June 20, 1990. Pesticide
tolerance for oryzalin. Federal Register 55 (119): 25140-1.
British Crop Protection Council. 1983. The Pesticide Manual: A
World Compendium, 7th ed. Croydon, England.
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.
Washington State Department of Transportation. 1993. Roadside
Vegetation Management: Environmental Impact Statement. WSDOT.
Elanco Chemical Company. 1989. Summary of Basic Data for Oryzalin
Herbicide. MSDS. Indianapolis, IN: Elanco Products Co.
The Royal Society of Chemistry. 1983. The Agro-Chemicals Handbook.
University of Nottingham, England.