Simazine persistence

Until recently, the NRA has not participated during the approval process in assessing the potential environmental impact of pesticides. However, the NRA does supply monitoring data to MAFF and HSE for pesticide reviews. These occur once a pesticide has been approved for use for a certain length of time, or when further information is needed on an approved pesticide. In supplying these data, the NRA comments on any areas of concern. This contributed to the 1993 ban on the use of atrazine and simazine on non-cropped land. In January 1995 the NRA s National Centre for Toxic and Persistent Substances (TAPS) was made advisor to the DoF, on the potential impact on the aquatic environment of... 

Ureides (e.g., diuron, linuron) and triazines (e.g., atrazine, simazine, ametryne) all act as inhibitors of photosynthesis and are applied to soil (see Figure 14.1 for structures). They are toxic to seedling weeds, which they can absorb from the soil. Some of them (e.g., simazine) have very low water solubility and, consequently, are persistent and relatively immobile in soil (see Chapter 4, Section 4.3, which also mentions the question of depth selection when these soil-acting herbicides are used for selective weed control). 

Clay, D.V. The persistence and penetration of large doses of simazine in uncropped soil. Weed Res., 13 42-50, 1973. Clayton, G.D. and Clayton, F.E., Eds. Patty s Industrial Hygiene and Toxicology, 3rd ed. (New York John Wiley Sons, 1981), 2,878 p. 

Walker, A. Simulation of herbicide persistence in soil. I. simazine and prometryne, Pestic. Scl, 7(l) 41-49, 1976. 

Nearpass, D.C. (1965). Effects of soil acidity on the adsorption, penetration and persistence of simazine. Weeds, 13 341-346. 

Soil persistence of triazines is important in forest usages. Much literature confirms that significant gains are made by reducing herbaceous plant cover for more than 1 year following planting. The triazines (e.g., simazine, atrazine,... 

Scudder, W.T. (1963). Persistence of simazine in Florida mineral and organic soils. Fla. Expt. Sta. Tech. Bull., 657. 

Fernandez, M.D., R.A. Perez, C. Sanchez-Brunete, and J.L. Tadeo (2001). Persistence of simazine and hexazinone in soil. Fresen. Environ. Bull., 10 490-494. 

Smith, A.E., R. Grover, G.S. Emmond, and H.C. Korven (1975). Persistence and movement of atrazine, bromacil, monuron, and simazine in intermittently-filled irrigation ditches. Can. J. Plant Sci., 55 809-816. 

Herbicides are used to get rid of unwanted plants like weeds, brush, unproductive trees, and other vegetation that may deprive crops and other useful plants of nutrients. Numerous immunological techniques for the analysis of triazines, such as atrazine, propazine, simazine, ametryn, and cyanazine, have been developed recently (Table 8.8).185,235-237 Owing to their environmental persistence and their... 

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). 

The two closely related urea herbicides take the form of stable crystalline compounds slightly soluble in water. Owing to their high chemical stability, their strong adsorption to the soil and their poor water solubility, they remain in the upper few centimeters of the soil and are very persistent. Diuron is the most persistent herbicide apart from simazine. 

Their solubility in water is higher than that of simazine but lower than that of atrazine. Their activity and selectivity are lower than those of the compounds of the preceeding group. For these reasons they have not come into general use. As their persistence is lower than that of bis(alkylamino)-j-triazines, it is possible that they will be introduced in the future, their action lasting one growing season. 

In 2002, for the first time since 1999, the cereal herbicide isoproturon is not the most frequendy occurring pesticide. The noiu icultural herbicide diuron occurs most frequendy, with herbicide mecoprop second and isopromron third. Diuron is a persistent herbicide used on noncrop areas, particularly railways lines, recreational areas and other hard surfiice. Use of diuron as an antifoulant has been ceased in November 2002. Simazine shows an increasing level that can be explained as much targeted monitoring as by variation in agricultural practice. 

The persistence of terbuthylazine, simazine, atrazine, and prometryn (r-triazine herbicides) was studied in sea, river, and groundwaters during long-term laboratory incubation (127 days) under different laboratory conditions (light-darkness at 20 °C). Analysis of herbicides was performed by GC-NPD and their identity was confirmed by GC-MSD(NPD = nitrogen phosphorus detector MSD = mass selective detector) <2004SCT87>. 

The triazines, such as simazine (4.62), are the most used of all soil-applied herbicides small changes in the substituents give excellent control over selectivity and persistence. These substances [and the phenylureas, such as diuron (4.63), which are also soil-types] act by interfering with the Hill reaction in photosynthesis (see Section 4.6). Both of these parent substances, simazine and diuron, have undergone extensive modification for particular purposes, but each is still extensively used. A newcomer, chlorsulfuron (6.73), combines molecular features from both parents, but is notable for the greater dilution at which it acts, and also for the speed (all cell division is halted within 1 hour). This substance, l-(2-chlorophenylsulfonyl)-3-(4-methoxy-6-methyl-l, 3,5-tri-azin-2-yl)urea, is taken up by wheat, oats, and barley plants which rapidly inactivate it. It is harmless to Man (Campion and Tichon, 1981). 

Clay, D.V The Persistence and Penetration of Large Doses of Simazine in Uncropped Soil, Weed Res., 13 42-50 (1973). 

Walker, A. Simulation of Herbicide Persistence in Soil. 1. Simazine and Prometryne, Pestic. Sci., 7 41-49 (1976). 

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