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The information in this profile may be out-of-date.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

Simazine

Trade and Other Names: Trade names include Aquazine, Caliber, Cekusan, Cekusima, Framed, Gesatop, Primatol S, Princep, Simadex, Simanex, Sim-Trol, Tanzine and Totazine. This compound may also be found in formulations with other herbicides such as amitrole, paraquat dichloride, metolachlor, and atrazine.

Regulatory Status: Simazine is a General Use Pesticide (GUP). It is in EPA toxicity class IV - practically nontoxic. Products containing simazine bear the Signal Word CAUTION. In November 1994, the U.S. EPA began a Special Review of simazine which could result in use restrictions or even cancellation if data warrant such action.

Chemical Class: Triazine

Introduction: Simazine is a selective triazine herbicide. It is used to control broad-leaved weeds and annual grasses in field, berry fruit, nuts, vegetable and ornamental crops, turfgrass, orchards, and vineyards. At higher rates, it is used for nonselective weed control in industrial areas. Before 1992, simazine was used to control submerged weeds and algae in large aquariums, farm ponds, fish hatcheries, swimming pools, ornamental ponds, and cooling towers. Simazine is available in wettable powder, water dispersible granule, liquid, and granular formulations. It may be soil-applied.

Formulation: Simazine is available in wettable powder, water dispersible granule, liquid and granular formulations. It may be soil-applied.

Toxicological Effects:

• Acute toxicity: Simazine is slightly to practically nontoxic. The reported oral LD50 for technical simazine in rats and mice is >5000 mg/kg [6,15]; its dermal LD50 is 3100 mg/kg in rats and > 10,000 mg/kg in rabbits [6,15]. The 4-hour inhalation LC50 in rats is greater than 2 mg/L (6). The formulated products, in most cases, are less toxic via all routes [15]. Simazine is nonirritating to the skin and eyes of rabbits except at high doses [3]. Patch tests on humans have shown that simazine is not a skin irritant, fatiguing agent, or sensitizer [3]. However, rashes and dermatitis from occupational exposure to simazine have occurred [3]. The triazine herbicides disturb energy metabolism (thiamin and riboflavin functions). Symptoms include difficulty in walking, tremor, convulsions, paralysis, cyanosis, slowed respiration, miosis (pinpoint pupils), gut pain, diarrhea, and impaired adrenal function [3]. No cases of poisoning in humans have been reported from ingestion of simazine [3]. Rats given an oral dose of 5000 mg/kg exhibited drowsiness and irregular breathing. In another study, a single oral dose of 4200 mg/kg produced anorexia, weight loss, and some deaths in rats within 4 to 10 days [26]. For unknown reasons, sheep and cattle are especially susceptible to poisoning by simazine. Doses of 500 mg/kg were fatal in sheep with death delayed for 5 to 16 days. Symptoms exhibited by poisoned sheep included lower food intake, higher water intake, incoordination, tremors, and weakness, especially in the hindquarters [3].
• Chronic toxicity: Some 90-day feeding studies showed reduced body weight at 67 to 100 mg/kg/day [10]. This same effect and kidney toxicity were seen in rats at doses of 150 mg/kg/day [10]. In 2-year chronic oral feeding studies in which rats were given daily dosages of 5 mg/kg/day of simazine in the diet, no gross or microscopic signs of toxicity were seen [3]. When rats were given repeated doses of 15 mg/kg/day, some liver cells degenerated during the first 3 days, but the condition did not progress. Instead, the liver adapted and the compound was metabolized [3]. Other effects observed in test animals include tremors, damage to the testes, kidneys, liver, and thyroid, disturbances in sperm production, and gene mutations [10].
• Reproductive effects: No adverse effects on reproductive capacity or development were observed in a three-generation study of rats fed 5 mg/kg/day simazine [10]. High rates of fetotoxicity and decreased birth weight were noted in the fetuses of pregnant rabbits fed 75 mg/kg/day [26]. Reproductive effects are not likely in humans under normal circumstances.
• Teratogenic effects: No dose-related teratogenic effects were observed when rabbits were given daily doses of 5, 75, or 200 mg/kg for days 7 through 19 of pregnancy [26]. Chronic inhalation of a cumulative dose of 0.3 mg/L for 8 days in pregnant rats resulted in no treatment-related developmental abnormalities [10]. Simazine does not appear to be teratogenic.
• Mutagenic effects: Simazine has shown negative results in a variety of mutagenicity tests on bacterial cultures [10]. Tests on human lung cell cultures have produced both positive and negative results [10]. When injected into adult male fruitflies, simazine increased the frequency of sex-linked lethal mutations, but failed to do so when fed to larvae. Other tests for mutagenicity in fruitflies were negative [3]. It is likely that simazine is either nonmutagenic or weakly mutagenic.
• Carcinogenic effects: Simazine was not tumorigenic in mice at the maximum tolerated dose of 215 mg/kg/day over an 18-month period [10]. In other studies, doses as low as 5 mg/kg/day produced excess tumors (thyroid and mammary) in female rats [3,10]. Because of inconsistencies in the data, it is not possible to determine simazine's carcinogenic status.
• Organ toxicity: Damage to the testes, kidneys, liver, and thyroid has been observed in test animals [3,10].

• Fate in humans and animals: Studies in rats, goats, and sheep reveal that 60 to 70% of the ingested dose may be absorbed into the system [10], with approximately 5 to 10% distributed systemically to tissues. The remainder is eliminated via urine within 24 hours [6]. Distribution led to detectable levels in red blood cells (highest), liver, kidney, fat, bone, and plasma [10]. When a cow was fed 5 ppm for 3 days, no simazine was found in the cow's milk during the next 3 days. It has been reported that simazine residues were present in the urine of sheep for up to 12 days after administration of a single oral dose. The maximum concentration in the urine occurred from 2 to 6 days after administration [16].

Ecological Effects:

• Effects on birds: Simazine is practically nontoxic to birds [6,16]. The reported LD50 values in mallard and Japanese quail are >4600 mg/kg and 1785 mg/kg, respectively [6]. The acute dietary LD50 values in hens and pigeons are both greater than 5000 ppm [2]. The 8-day dietary LC50 in bobwhite quail is >5260 ppm and in mallard ducks is >10,000 ppm [6,15].
• Effects on aquatic organisms: Simazine is slightly to practically nontoxic to aquatic species [6,15]. The 96-hour LC50 for simazine is >100 mg/L [46] in rainbow trout, 100 mg/L (wettable powder) in bluegill sunfish, 0.100 mg/L in fathead minnows [46], as well as carp [2]. It may be more toxic to Daphia and stoneflies [46]. A 96-hour LC50 of >3.7 mg/L is reported in oysters [15].
• Effects on other organisms: While many mammals may be insensitive to simazine [16], sheep and cattle are especially sensitive [3]. Simazine is nontoxic to bees [6,16]. A soil LC50 in earthworms of >1000 mg/kg has been reported [16].

Environmental Fate:

• Breakdown in soil and groundwater: Simazine is moderately persistent with an average field half-life of 60 days [20]. Soil half-lives of 28-149 days have been reported [20]. Residual activity may remain for a year after application (2 to 4 kg/ha) in high pH soils. Simazine is moderately to poorly bound to soils [20]. It does, however, adsorb to clays and mucks. Its low water solubility, however, makes it less mobile, limiting its leaching potential [15]. Simazine has little, if any, lateral movement in soil, but can be washed along with soil particles in runoff. Simazine is subject to decomposition by ultraviolet radiation, but this effect is small under normal field conditions. Loss from volatilization is also insignificant. In soils, microbial activity probably accounts for decomposition of a significant amount of simazine in high pH soils. In lower pH soils, hydrolysis will occur [15]. Simazine residues have been detected in groundwater in at least 16 states. The range was from 0.00002 mg/L to 0.0034 mg/L [23].
• Breakdown in water: The average half-life of simazine in ponds where it has been applied is 30 days, with the actual half-life dependent on the level of algae present, the degree of weed infestation, and other factors [15]. Simazine may undergo hydrolysis at lower pH. It does not readily undergo hydrolysis in water at pH = 7 [15].
• Breakdown in vegetation: Plants absorb simazine mainly through the roots, with little or no foliar penetration. From the roots, it is translocated upward to the stems, leaves, and growing shoots of the plant [6,15]. It acts to inhibit photosynthesis [6,15]. Resistant plants readily metabolize simazine. Plants that are sensitive to simazine accumulate it unchanged [6]. It is possible that livestock or wildlife grazing on these plants could be poisoned.

Physical Properties:

• Appearance: Simazine is a white or colorless crystalline solid [6].
• Chemical Name: 6-chloro-N2,N4-diethyl-1,3,5-triazine-2,4-diamine [6]
• CAS Number: 122-34-9
• Molecular Weight: 201.70
• Water Solubility: 5 mg/L @ 20 C [6]
• Solubility in Other Solvents: s. in methanol, chloroform, and diethyl ether [6]; s.s. in pentane [6]
• Melting Point: 225-227 C [6]
• Vapor Pressure: 0.000810 mPa @ 20 C [6]
• Partition Coefficient: 1.9600 [6]
• Adsorption Coefficient: 130 [20]

Exposure Guidelines:

• ADI: Not Available
• MCL: 0.004 mg/L [25]
• RfD: 0.005 mg/kg/day [26]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Ciba-Geigy Corporation
P.O. Box 18300
Greensboro, NC 27419-8300

• Phone: 800-334-9481
• Emergency: 800-888-8372
  

References:

References for the information in this PIP can be found in Reference List Number 8

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.