Pesticides, liquid actives

Surface-active substances raising the spreading and wetting capacities of pesticide liquids may at the same time reduce the adhesive qualities of the particles, particularly under the influence of atmospheric deposits. With increasing concentration of the SAS the adhesion usually diminishes. It is therefore important to introduce the optimum quantity of SAS into the spraying compositions... 

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. 

Surface-active substances (SAS) are the most widespread contaminants of sewage and natural waters. They translate in small dispertion condition liquid and firm polluting substances - chlororganic, mineral oils, pesticides. Therefore, the SAS contents determination in water solutions is now one of actual tasks of analytical chemistry. 

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. 

In summary, the development of materials for the extraction of pesticides from water samples has progressed from simple liquid-liquid extraction for the principal active compound to sophisticated SPE media capable of exclusively trapping the target pesticide and metabolites selectively. The development of alkyl bonded phase silica cartridges and extraction disks combined with on-line extraction techniques is currently the principal means used for the extraction and trace enrichment of pesticides and metabolites from water. 

Experiment 1. Effects of volatile allelochemicals on development of pollen tubes. In this experiment, volatile and liquid excretions from plants with pesticidic properties were tested (Table 3). The development of pollen tubes depend on the concentration and the distance from the object glass with microspores moistened with nutrient medium vapors of lavender oil (active matter) depress the process as well as red pepper, but garlic not. Water extracts of garlic were more effective. 

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%. 

Tu. C. H., Hsian. H. Y., Chou. Y. T., and Wang, W.-F. Vapor-liquid equilibria of methanol, ethanol, propan-2-ol, and 2-methylpropan-2-ol with a five-component hydrocarbon mixtrue at 101.3 kPa,/. Chem. Eng. Data, 46(5) 1239-1243, 2001. Tu. C.M. Influence of pesticides and some of the oxidized analogues on microbial populations, nitrification and respiration activities in soil. Bull Environ. Contam. Toxicol, 24(1) 13-19, 1980. 

TRW Systems, Inc., conducted a laboratory-scale incineration study for the U.S. Army from 1973 to 1975 (9). Eleven individual pesticide formulations and three mixed pesticide formulations containing six different active ingredients (chlordane, 2,4-D, DDT, dieldrin, lindane, and 2,4,5-T) were incinerated in a liquid injection incinerator. The experimental apparatus consisted of a fuel atomizer, combustion chamber, afterburner, quench chamber, and scrubber unit. Destruction efficiencies exceeded 99.99% for a minimum 0.4-s residence time at temperatures above 1000°C with 45 to 60% excess air. 

Pyrethrins are naturally occurring pesticides derived from chrysanthemum plants. They are active against many insects and mites. Over-the-counter liquid and gel preparations of pyrethrins with piperonyl butoxide are available for the treatment of pediculosis (piperonyl butoxide inhibits the hydrolytic enzymes that metabolize the pyrethrins in the arthropod). A synthetic pyre-throid, permethrin (Elimite), is available by prescription. A lower concentration of permethrin (Nix) is available without prescription. Pyrethrins and permethrin are quite safe. 

There are two principal types of monolithic device. If the active agent is dissolved in the polymer medium, the device is called a monolithic solution. Examples of this type of device are pesticide-containing cat and dog collars to control ticks and fleas. Such devices are often used when the active agent is a liquid some polymers [for example, poly(vinyl chloride)] can easily sorb up to 20 % or more of these liquids. However, if the solubility of the active agent in the... 

Microencapsulation can be used to provide a temporary barrier between a chemical species and its surrounding environment see also Section 14.3). This permits controlled (slow) release of the active agents following application. Depending on the product and the situation, an active ingredient such as a pesticide may need to be released slowly at low concentration, or slowly at high concentrations. Such controlled release can both reduce the number of crop applications that are required and also help prevent over use and subsequent run-off. The barrier can be provided by a polymer film, in the case of suspensions [867], or a liquid membrane, in the case of single or multiple emulsions [865], Microemulsions have also been used [234,865],... 

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