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The information in this profile may be out-of-date.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

Oryzalin

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

Regulatory Status: Oryzalin is a slightly to practically nontoxic compound in EPA toxicity class IV. Products containing oryzalin must bear the Signal Word CAUTION. It is a General Use Pesticide (GUP).

Chemical Class: Not Available

Introduction: Oryzalin is a selective pre-emergence surface-applied herbicide used for control of annual grasses and broadleaf weeds in fruit trees, nut trees, vineyards, established bermuda grass turf, and established ornamentals. It inhibits the growth of germinating weed seeds by blocking cell division in the meristems. It is available in aqueous suspension, dry flowable, and wettable powder formulations.

Formulation: It is available in aqueous suspension, dry flowable, and wettable powder formulations.

Toxicological Effects:

• Acute toxicity: Oryzalin is practically nontoxic by ingestion, with reported oral LD50 values of greater than 5000 mg/kg in rats and mice [1,58], and greater than 1000 mg/kg in cats, dogs, and chickens [1,106]. The dermal LD50 for technical oryzalin in rabbits is greater than 2000 mg/kg, indicating slight to practically no toxicity by this route [58]. It is reported to cause slight skin and eye irritation in the rabbit, and no skin sensitization in the guinea pig [58]. It is also slightly toxic when inhaled, with a 4-hour inhalation LC50 of greater than 3 mg/L in rats [58]. The formulated products (e.g., Surflan A.S.) may show moderate toxicity by either the oral or inhalation routes, and may show skin and eye irritation and skin sensitization properties [58]. In dogs and cats, large oral doses cause nausea and vomiting [8].
• Chronic toxicity: Rats fed a dietary level of about 2.5 mg/kg/day for 2 years exhibited blood changes, increased liver and kidney weights, inhibition of growth, and decreased survival [8]. Repeated ingestion of large doses led to adverse changes in blood cell formation in dogs [8]. Mice given dietary doses of about 200 mg/kg/day for 1 year exhibited decreased uterine and ovarian weights. Those exposed to doses of 75 mg/kg/day showed no observable effects [107].
• Reproductive effects: There were no adverse effects on reproduction in a three-generation study of rats fed dietary concentrations of 12.5, 37.5, or 112.5 mg/kg/day, the highest dose tested. Fetotoxic effects appeared at 12.5 mg/kg/day [58,107]. It does not appear that oryzalin causes reproductive effects.
• Teratogenic effects: There were no birth defects in the offspring of pregnant rats fed dietary concentrations as high as 112 mg/kg/day for three generations, nor in the offspring of pregnant rabbits given doses of 125 mg/kg/day, the highest dose tested [8,107]. It appears that oryzalin is unlikely to cause teratogenic effects.
• Mutagenic effects: Oryzalin was not mutagenic in several tests, including tests on live rats and mice and on bacterial cell cultures [107]. It does not appear that oryzalin is mutagenic.
• Carcinogenic effects: When oryzalin was fed to rats in doses as high as 135 mg/kg/day for 2 years, there was an increase in the incidence of thyroid, mammary, and skin tumors [107]. Thyroid tumors and benign skin and mammary tumors occurred in rats fed a dietary level of 45 mg/kg/day for 2 years [107]. However, there were no tumors in mice fed doses as high as 548 mg/kg/day for 2 years [107]. Because of these conflicting results, it is not possible to assess the carcinogenicity of oryzalin.
• Organ toxicity: Oryzalin has shown systemic effects on the thyroid, liver, and kidneys, as well as blood chemistry, in animal tests.

• Fate in humans and animals: Oryzalin is moderately well-absorbed from the gastrointestinal tract, and rapidly metabolized and eliminated following absorption. 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 in tests with rabbits, a steer, and with Rhesus monkeys [106].

Ecological Effects:

• Effects on birds: Oryzalin is slightly toxic to practically non-toxic to birds; the reported oral LD50 values in bobwhite quail and mallard ducks are greater than 500 mg/kg, and in chickens is 1000 mg/kg [1,58]. The 5-day dietary LC50 values in quail and mallard ducks are greater than 5000 ppm [8].
• Effects on aquatic organisms: Oryzalin is highly toxic to fish, with reported 96-hour LC50 values of 2.88 mg/L in bluegill sunfish, 3.26 mg/L in rainbow trout, and greater than 1.4 mg/L in goldfish fingerlings [8].
• Effects on other organisms: The reported oral LD50 for the compound in bees is 11 ug/bee, indicating it is nontoxic to bees [1,58].

Environmental Fate:

• Breakdown in soil and groundwater: Oryzalin is of low to moderate persistence in the field, with reported field half-lives ranging from 20 to 128 days [58,11]. A representative value for soil half-life is estimated to be 20 days [11,58]. Microbial degradation is mainly responsible for the breakdown of oryzalin in soils, but it may undergo photodecomposition near the soil surface [58]. Volatilization is not appreciable [58]. Oryzalin is slightly soluble in water and it does not have a strong tendency to adsorb to soil particles [58,11]. It is bound to a greater extent with increasing soil organic matter and clay content. In soils with low proportions of these, high water tables and increased rainfall, oryzlin may be mobile, and thus present a risk of contamination to groundwater.
• Breakdown in water: No breakdown of oryzalin by hydrolysis was observed at pH 5, 7, and 9 [8]. Based on its behavior in soil, breakdown by microbial processes is probably slow in the aquatic environment due to low levels of oxygen and low microbial activity. Photodegradation may be significant in the upper portions of the water column.
• Breakdown in vegetation: Oryzalin is readily absorbed via the roots, and plant metabolism of oryzalin is minimal [58].

Physical Properties:

• Appearance: Technical oryzalin is a bright yellow-orange crystalline powder [1].
• Chemical Name: 3,5-dinitro-N4,N4-dipropylsulfanilamide [1]
• CAS Number: 19044-88-3
• Molecular Weight: 346.36
• Water Solubility: 2.5 mg/L @ pH 7 and 25 C [1]
• Solubility in Other Solvents: v.s. in organic solvents such as acetone, methanol, and acetonitrile; s.s. in benzene and xylene; i.s. in hexane [1]
• Melting Point: 141-142 C [1]
• Vapor Pressure: <0.013 mPa @ 30 C [1]
• Partition Coefficient: 3.7340 @ pH 7 [1]
• Adsorption Coefficient: 600 [11]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: 0.05 mg/kg/day [13]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

DowElanco
9330 Zionsville Road
Indianapolis, IN 46268-1054

• Phone: 317-337-7352
• Emergency: 800-258-3033
  

References:

References for the information in this PIP can be found in Reference List Number 10

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.