Simazine properties

Herbicides. An array of herbicides are registered for use in aquatic sites, but copper sulfate and diquat dibromide are of additional interest because they also have therapeutic properties (9,10). Copper sulfate has been used to control bacteria, fungi, and certain parasites, including Jchthjophthirius (ich). Diquat dibromide can control columnaris disease, but it also exhibits fungicidal properties (9,10). EPA recentiy proposed to limit the amount of diquat dibromide, endothaH, glyphosate, and simazine that can be present in drinking water therefore, the use of these compounds may be reduced if they cannot be removed from the effluent. 

In general, triazines are pre- and post-emergence selective herbicides particularly effective on annual and perennial broadleaf and grassy weeds in corn, sorghum, cotton, soybeans, sugar cane, and a host of other fruit and cereal crops. Some have anti-fungicidal properties (e.g., anilazine), and some (e.g., simazine) can be used for... 

Studies on sorption of triazines by individual soil constituents and by model sorbents have been very helpful in evaluating sorption mechanisms and in assessing the potential contribution of various constituents to triazine sorption by soils. However, intimate associations between organic substances, silicate clays, and oxyhydroxide materials modify the sorptive properties of the individual constituents. Associations between soil constituents influence soil properties - such as pH, specific surface area, and functional group availability - which in turn influence triazine sorption behavior. For instance, atrazine and simazine sorption behavior is different for synthetic mixtures of model soil... 

The structures and other properties for simazine, propazine, prometryn, prometon, and other triazine herbicides and many of their degradation products can be found in the Appendices, Tables Al, A2 and A3. As shown in Figure 30.12, atrazine and simazine degrade to DIA. 

Many chemicals are regulated by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and their properties are as diverse as the properties of ecosystems. In forestry, however, relatively few herbicides are used very much. In fiscal year 1981, for instance, the USDA Forest Service used more than 25 different herbicides in the National Forests, but 2,4-D and picloram alone and in combination accounted for 70% of the total amount of herbicide applied. Atrazine, glyphosate, dalapon, simazine, fosamine, and hexazinone accounted for an additional 18% (2). 

The symmetrical triazines, such as simazine, have a wide range of properties and are being used to cover a wide range of crops. They vary in water solubility from about 5 to 3500 p.p.m. The triazines are stable to aqueous alkali and dilute acids, but they are broken down gradually by catalysts in the soil and by microorganisms. They are not strongly fixed in soils, and some of them are relatively persistent, particularly in arid areas (8,21). 

Hydroxysimazine has also recently been reported in four soils incubated 32 weeks with radioactive simazine (16). It is conceivable that a soil constituent with strong nucleophilic properties could also cause the conversion of simazine to hydroxysimazine. 

The documented occurrence of pesticides in surface water is indicative that runoff is an important pathway for transport of pesticide away from the site of appHcation. An estimated 160 t of atrazine, 71 t of simazine, 56 t of metolachlor, and 181 of alachlor enter the Gulf of Mexico from the Mississippi River annually as the result of mnoff (47). Field appHcation of pesticides inevitably leads to pesticide contamination of surface runoff water unless runoff does not occur while pesticide residues remain on the surface of the soil. The amount of pesticides transported in a field in runoff varies from site to site. It is controlled by the timing of mnoff events, pesticide formulation, physical—chemical properties of the pesticide, and properties of the soil surface (48). Under worst-case conditions, 10% or more of the appHed pesticide can leave the edge of the field where it was appHed. 

Harris, C.I. and T.J. Sheets. Influence of Soil Properties on Adsorption and Phytotoxicity of CIPC, Diuron, and Simazine, Weeds, 13 215-219 (1965). 

---