Herbicidal formulations

In 1976, Ross al. first reported that the powerful carcinogens, N-nitrosodimethylamine (NOMA) and N-nitrosodi-n-propyl-amine (NDPA) were found at parts per million (ppm) concentrations in certain commercial herbicide formulations (1., ). Since then, scientists have learned that carcinogenic N-nitroso compounds can be formed in a wide variety of media of interest to those who manufacture, use, or study pesticide products. Some of these nitrosation-supporting media are listed in Table I. 

Slimicide and biocide toxic pollutants containing pentachlorophenol are used at mills in the pulp, paper, and paperboard industry. Initially, pentachlorophenol was used as a replacement for heavy metal salts, particularly mercuric types. Trichlorophenols are also used because of their availability as a byproduct from the manufacture of certain herbicides. Formulations containing organo-bromides and organo-sulfur compounds are also being used. Substitution of alternative slimicide and biocide formulations can lead to the virtual elimination of pentachlorophenol and trichlorophenol from these sources. 

Herbicide fates, environmental, 13 307—313 Herbicide formulations, encapsulated, 16 458-459... 

Following the earlier work of Kirkland [125] on phenylurea herbicides, Sidwell and Ruzicka [126] applied liquid chromatography to the identification and determination of active ingredient contents of phenylurea herbicide formulations. Smith and Lord [118] have used liquid chromatography for the determination of Chlorotoluron residues in soil, but Diuron and Monuron interfered in their chromatographic system. 

Releases of thiocyanate to soil result from anthropogenic and natural sources. Anthropogenic releases occur primarily from direct application in herbicidal formulations (e.g., amitrol-T, a mixture of ammonium thiocyanate and amino-1,2,4-triazole) and from disposal as byproducts from industrial processes. Nonanthropogenic sources include damaged or decaying tissues of plants from the family Brassica (e.g., mustard, rape) (Brown and Morra 1993). Thiocyanate has been detected in soil samples collected at 2 of the 8 hazardous waste sites, and in sediment samples at 3 of the 8 hazardous waste sites where thiocyanate has been detected in some medium (HazDat 1996). The HazDat information used includes data from both NPL and other Superfund sites. 

Table VI shows the concentration of herbicide in two of the three sets of field plots established in Utah in 1972. It was only after the plots were established and the first soil samples analyzed that it became apparent that the herbicide formulation...

Arsenic trioxide is used as a starting material to prepare metallic arsenic and a number of arsenic compounds. It is also used as a decolorizer for bottle glass in pigments and ceramic enamels for preserving hides as a wood preservative as an analytical standard in oxidimetry titrations and in many rodenticide and herbicide formulations. 

Borax pentahydrate occurs in nature as mineral tincalconite, formed by dehydration of borax. It has several industrial applications, mostly the same as its decahydrate. The pentahydrate is used in the manufacture of borosili-cate glass. It also is used in cleaning agents ceramic glaze adhesives cosmetics antifreeze and herbicide formulations. It is added to fertihzers to provide boron as a nutrient to the plants. 

Fine, D. H. N-Nitroso compound impurities in herbicide formulations. J. Agric. Food Chem., 1977, 25 (6), 1416-1418. 

Table 5 is a more comprehensive compilation of the DMN content of some herbicides formulated as the dimethylamine salts (53). Five out of six formulations of 2,4-D contained DMN at levels of between 60 and 370 Pg/l. All four formulations of MCPA contained DMN at levels of between 250 and 650 yg/1. DMN levels of between 187,000 and 640,00 yg/1 were found in formulations of 2,3, 6-trichlorobenzoic acid which had been stored in metal cans to which sodium nitrite had been added. Table 5 represents a comparative study between an EPA laboratory and Thermo Electron. The decrease of the DMN level for any one compound reflects the success of the manufacturers in decreasing the DMN contamination (60). 

N-nitrosodimethylamine Content of Herbicides Formulated as Dimethylamine Salts (53)... 

The initial federal approval of an atrazine formulation in the United States occurred December 1, 1958, when the USDA registered Geigy Atrazine 50W for preemergence and postemergence control of several broadleaf weeds on corn and for nonselective weed control in noncrop areas. A wettable powder was the most popular choice for herbicide formulations at that time and could easily be sprayed uniformly across a field. 

Up to the late 1960s, only dry formulations of atrazine were available. Ciba-Geigy Corporation later developed the first water-based, flowable concentrate formulation of an herbicide, AAtrex 4L, which was approved on January 15, 1970. This development launched a new era in herbicide formulation technology. The water-based formulation improved the manufacturing process, minimized dust, was easier to package and to load into application equipment, and easier to mix. Gradually, more and more farmers who used atrazine switched to the liquid formulation, which is now the preferred formulation. 

While each of these milestones brought forth a renewed interest in chemical weed control and led to more research in the field, the use of chemicals for selective weed control in crops was very limited and not very successful until the discovery and development of 2,4-D, MCPA, and other phenoxyacetic acid herbicides in the 1940s. These compounds were the first truly selective herbicides that could reliably kill broadleaf weeds in cereal crops, including com, and they quickly developed widespread popularity and use after World War II. With this major milestone, new application technology emerged, including the low-volume sprayer, and new herbicide formulations were developed. 

Qrt, M.P., J.F. Fairchild, and S.E. Finger (1994). Acute and chronic effects of four commercial herbicide formulations on Ceriodaphnia dubia. Arch. Environ. Contam. Toxicol., 27 103-106. 

The distribution of body weights was assumed to be a normal distribution with mean 70 kg and a 20% coefficient of variation (i.e., a standard deviation equal to 14kg). The amount of exposure for a body part was a PHED-based distribution, depending on the body part and the type of user, as well as the type of herbicide formulation used. The herbicide formulations were granule (G) formulated with fertilizer and used by homeowners for residential lawn care flowable formulation (FF), which is among the formulations classified as emulsifiable concentrate (EC) in PHED and water-dispersible granule (WDG). 

Baker, J.L. and L.E. Shiers (1989). Effects of herbicide formulation and application method on washoff from corn residue. Trans. Am. Soc. Agr. Eng., 32 830-833. 

They are widely used in several hundred commercial herbicide formulations (Morgan, ref. 20, Chap. 6). 

Having achieved the first step the further ethoxylation is catalysed with base, sodium or potassium hydroxide, to give the degree of ethoxylation required. The reaction temperature is about 150°C. The two main materials produced commercially are the diethanolamines, which are used in plastics as antistatic or anti-fog agents and the 15-mol ethoxylate, which is used as an adjuvant in herbicide formulations. 

Policello, G. and Stevens, P. (1998) Nonionic siloxane blends with surfactants, as adjuvants in herbicide formulations, Eur. Pat. Appl. 862857. (OSI Specialties, Inc., USA Crompton Corporation). 

Fundamental relationships can be used to solve present and future problems of herbicide formulation. Careful consideration of some of these relationships will point the way to new experiments to obtain information that will permit solution of even more general relationships. 

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