Pesticides, solid actives

The active ingredients in pesticides are generally too potent to be used or marketed in pure form. To formulate pesticides, the active ingredients are sometimes diluted with water or a solvent in other cases they may be mixed with a solid such as sand or clay. One product at a large pesticide... 

Solid Active Ingredients - Some pesticide applications require a particular physical form, generally to conform with application equipment available to the grower. Granules, for example, are commonly used as the means to apply insecticides to com. A solid active ingredient can be dissolved in a solvent and then absorbed by a carrier. This is, however, often not economical. The alternative used by the pesticide industry is to use a mineral as a substrate onto which the solid pesticide is adhered. High absorbency here is not required, and in fact can be detrimental. 

Flowables utilize solid active ingredients, or liquid actives absorbed onto a solid carrier, but are presented to the end user as a liquid. Micronized particles of active ingredient are suspended in a liquid carrier. Water is almost invariably the carrier of choice, since it is much less expensive than any organic liquid. As noted above the problem to be overcome with this formulation is the density difference between suspended solids and the fluid medimn. The specific gravity of pesticide solids is typically on the order of 1.2, resulting in rapid settling of solids in water. 

A solvent free, fast and environmentally friendly near infrared-based methodology was developed for the determination and quality control of 11 pesticides in commercially available formulations. This methodology was based on the direct measurement of the diffuse reflectance spectra of solid samples inside glass vials and a multivariate calibration model to determine the active principle concentration in agrochemicals. The proposed PLS model was made using 11 known commercial and 22 doped samples (11 under and 11 over dosed) for calibration and 22 different formulations as the validation set. For Buprofezin, Chlorsulfuron, Cyromazine, Daminozide, Diuron and Iprodione determination, the information in the spectral range between 1618 and 2630 nm of the reflectance spectra was employed. On the other hand, for Bensulfuron, Fenoxycarb, Metalaxyl, Procymidone and Tricyclazole determination, the first order derivative spectra in the range between 1618 and 2630 nm was used. In both cases, a linear remove correction was applied. Mean accuracy errors between 0.5 and 3.1% were obtained for the validation set. 

The main purpose of pesticide formulation is to manufacture a product that has optimum biological efficiency, is convenient to use, and minimizes environmental impacts. The active ingredients are mixed with solvents, adjuvants (boosters), and fillers as necessary to achieve the desired formulation. The types of formulations include wettable powders, soluble concentrates, emulsion concentrates, oil-in-water emulsions, suspension concentrates, suspoemulsions, water-dispersible granules, dry granules, and controlled release, in which the active ingredient is released into the environment from a polymeric carrier, binder, absorbent, or encapsulant at a slow and effective rate. The formulation steps may generate air emissions, liquid effluents, and solid wastes. 

The water is then pumped through series operated sand filters, which provide the final stage of suspended solids removal and protect the garnualr activated carbon (GAC) filters from particulate contamination. Series operated GAC filters are then used to remove the dissolved creosote and pesticides from the water. To achieve compliance with specifications levels, water should be sampled and analyzed after leaving the first GAC filter. The second GAC filter normally serves as a guard bed. 

The Agency s mission is to control and abate pollution in the areas of air, water, solid waste, pesticides, radiation, and toxic substances. The EPA coordinates and supports research and anti-pollution activities by state and local governments, private and public groups, individuals, and educational institutions. 

J. Slobodnik, O. Ostezkizan, H. Lingeman and U. A. Th Brinkman, Solid-phase extraction of polar pesticides from environmental water samples on grapliitised carbon and Empore-activated carbon disks and on-line coupling to octadecyl-bonded silica analytical columns , J. Chromatogr. 750 227-238 (1996). 

It is now clear that the fate of chemicals in the environment is controlled by a combination of three groups of factors. First are the prevailing environmental conditions such as temperatures, flows and accumulations of air, water and solid matter and the composition of these media. Second are the properties of the chemicals which influence partitioning and reaction tendencies, i.e., the extent to which the chemical evaporates or associates with sediments, and how fast the chemical is eventually destroyed by conversion to other chemical species. Third are the patterns of use, into which compartments the substance is introduced, whether introduction is episodic or continuous and in the case of pesticides how and with which additives the active ingredient is applied. 

Leoni [366] observed that in the extraction preconcentration of organochlo-rine insecticides and PCB s from surface and coastal waters in the presence of other pollutants such as oil, surface active substances, etc., the results obtained with an absorption column of Tenax-Celite are equivalent to those obtained with the continuous liquid-liquid extraction technique. For non-saline waters that contain solids in suspension that absorb pesticides, it may be necessary to filter the water before extraction with Tenax and then to extract the suspended solids separately. Analyses of river and estuarine sea waters, filtered before extraction, showed the effectiveness of Tenax, and the extracts obtained for pesticide analysis prove to be much less contaminated by interfering substances than corresponding extracts obtained by the liquid-liquid technique. Leoni et al. [365] showed that for the extraction of organic micro pollutants such as pesticides and aromatic polycyclic hydrocarbons from waters, the recoveries of these substances from unpolluted waters (mineral and potable waters) when added at the level of 1 xg/l averaged 90%. 

Several studies have shown that sorption of various organic compounds on solid phases could be depicted as an accumulation at hydrophobic sites at the OM/water interface in a way similar to surface active agents. In addition Hansch s constants [19,199-201], derived from the partition distribution between 1-octanol and water, expressed this behavior better than other parameters. Excellent linear correlations between Koc and Kow were found for a variety of nonpolar organic compounds, including various pesticides, phenols, PCBs, PAHs, and halogenated alkenes and benzenes, and various soils and sediments that were investigated for sorption [19,76,80,199-201]. 

Many activations involve compounds which are used as pesticides. In the case of N-nitrosation, the precursors are secondary amines and nitrate. The former are common synthetic compounds and the latter is an anion found in nearly all solid and aqueous phases. The N-nitrosation of a secondary amine [R-NH-R ] occurs in the presence of nitrite formed microbiologically from nitrate. The product is an N-nitroso compound (i.e., a nitrosamine [RR -N-N=0]). The reason for concern with nitrosamines is their potency, at low concentrations, as carcinogens, teratogens, and mutagens. 

Encapsulation is a process in which tiny particles or droplets are covered by a coating [36-43]. Its role is either to isolate the active ingredient or to control the rate by which it leaves the capsule. As examples for the first case, one can mention the isolation of vitamins from oxygen or of a reactive core from chemical attack, and for the second case, the control of the rate of release of drugs or pesticides. Numerous encapsulation techniques have been suggested. Most of the encapsulations of the active solid materials have been carried out for solids larger than 1 pm. 

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