Volatilization from plants

Methyl parathion may also be introduced into the air as a result of its volatilization from plant surfaces, and somewhat from soil, especially in the period just after application. Under simulated field conditions (20° C air velocity 1 meter/second relative air humidity 40-60%), an emulsifiable concentrate formulation of methyl parathion was applied to bare soil and bean plants. After 24 hours, the amounts of methyl parathion that had volatilized from bare soil and bean plants were 5 and 64% of the applied amount, respectively (Rudel 1997). 

Dicke M, van Loon JJA, Soler R (2009) Chemical complexity of volatiles from plants induced by multiple attack. Nat Chem Biol 5 317-324... 

Duckart EC, Waldron LJ, Donner HE. 1992. Selenium uptake and volatilization from plants growing in soil. Soil Science 153(2) 94-99. 

One of the main objectives of the EC project APECOP ° was to develop process descriptions for pesticide volatilization from plants and to include them in the current PEC models (predicting environmental concentrations of pesticides), PEARL, PELMO, and MACRO. As a screening-level approach for estimating the initial volatilization rate after plant application, a correlation between physicochemical pesticide properties and measured volatilization fluxes was used. For the prediction of cumulative losses from plant surfaces, a similar estimation method was developed by Smit. Despite intense research in recent years, including the development of numerous laboratory and field methods to measure volatilization rates," " knowledge of rate-determining processes is currently not sufficient for developing a reliable, physically-based model approach to predict fluxes of pesticide volatilization from plant surfaces. 

ZiEVE R and Peterson J (1984) Selenium volatilization from plants and soils. Sd Total Environ 32 197-202. 

Many of the volatiles from plants are oxygenated volatile organic compounds (OVOCs). Measurement of OVOCs is difficult (e.g., methanol easily partitions with water) and, in many cases, time-consuming (up to 1 h per sample). This is too slow to measure fast emissions/ changes (e.g., when a plant is wounded), and in this case, PTR-MS can be useful. PTR-MS can measure a wide range of compounds (including OVOCs and sulfur compounds among others) fast and on-line, which makes it a suitable method to study on-line plant emissions and uptake. 

Essentia.1 Oils. Essential oils (qv) are extracted from the flower, leaf, bark, fmit peel, or root of a plant to produce flavors such as mint, lemon, orange, clove, cinnamon, and ginger. These volatile oils are removed from plants either via steam distillation, or using the cold press method, which avoids heat degradation. Additional processing is sometimes employed to remove the unwanted elements from the oils, such as the terpenes in citms oils which are vulnerable to oxidation (49,50). 

Oleoresin. Natural oleoresins are exudates from plants, whereas prepared oleoresins are solvent extracts of botanicals, which contain oil (both volatile and, sometimes, fixed), and the resinous matter of the plant. Natural oleoresins are usually clear, viscous, and light-colored Hquids, whereas prepared oleoresins are heterogeneous masses of dark color. 

Exceptions to the simple definition of an essential oil are, for example, gadic oil, onion oil, mustard oil, or sweet birch oils, each of which requires enzymatic release of the volatile components before steam distillation. In addition, the physical process of expression, appHed mostly to citms fmits such as orange, lemon, and lime, yields oils that contain from 2—15% nonvolatile material. Some flowers or resinoids obtained by solvent extraction often contain only a small portion of volatile oil, but nevertheless are called essential oils. Several oils are dry-distiUed and also contain a limited amount of volatiles nonetheless they also are labeled essential oils, eg, labdanum oil and balsam oil Pern. The yield of essential oils from plants varies widely. Eor example, nutmegs yield 10—12 wt % of oil, whereas onions yield less than 0.1% after enzymatic development. 

Miscellaneous. Where a copper refinery is adjacent to a lead (qv) plant it is feasible to recover the selenium in slimes by smelting them in conjunction with lead-bearing materials. Utilizing the lower temperatures needed to melt lead, the selenium is volatilized from a lead bath or cupel blown with air. The selenium is recovered from flue dust and fume by scmbbing. This is the process used by Union Miniere at its Hoboken plant in Belgium. 

Metallurgical (smelter) plants and spent acid decomposition plants usually produce acid of good (low) color because the SO2 feed gases ate extensively purified prior to use. In some cases, however, and particularly at lead smelters, sufficient amounts of organic flotation agents are volatilized from sulfide ores to form brown or black acid. Such acid can be used in many applications, particularly for fertilizer production, without significant problems arising. 

Essential Oils. Volatile oils from plants are referred to as essential oils. The oils can be obtained through steam distillation, solvent extraction, or separation of the oils from pressed fmit. They consist of oxygenated compounds, terpenes, and sesquiterpenes. The primary flavor components of essential oils are oxygenated compounds. Terpenes contain some flavors but are often removed from the essential oil because they are easily oxidized (causiag off-flavors or odors) and are iasoluble. Essential oils are prepared from fmits, herbs, roots, and spices. 

Process development on fluidized-bed pyrolysis was also carried out by the ConsoHdation Coal Co., culminating in operation of a 32 t/d pilot plant (35). The CONSOL pyrolysis process incorporated a novel stirred carbonizer as the pyrolysis reactor, which made operation of the system feasible even using strongly agglomerating eastern U.S. biturninous coals. This allowed the process to bypass the normal pre-oxidation step that is often used with caking coals, and resulted in a nearly 50% increase in tar yield. Use of a sweep gas to rapidly remove volatiles from the pyrolysis reactor gave overall tar yields of nearly 25% for a coal that had Eischer assay tar yields of only 15%. 

The volatile oils are isolated from plant sources and are terpenoid in stmcture. They are purified by a combination of physical and chemical processes. Individual components of the oils ate often isolated by crysta11i2ation or, in some cases, prepared synthetically. 

The study of biochemical natural products has also been aided through the application of two-dimensional GC. In many studies, it has been observed that volatile organic compounds from plants (for example, in fruits) show species-specific distributions in chiral abundances. Observations have shown that related species produce similar compounds, but at differing ratios, and the study of such distributions yields information on speciation and plant genetics. In particular, the determination of hydroxyl fatty acid adducts produced from bacterial processes has been a successful application. In the reported applications, enantiomeric determination of polyhydroxyl alkanoic acids extracted from intracellular regions has been enabled (45). 

Supercritical fluid extraction (SFE) has been extensively used for the extraction of volatile components such as essential oils, flavours and aromas from plant materials on an industrial as well as an analytical scale (61). The extract thus obtained is usually analysed by GC. Off-line SFE-GC is frequently employed, but on-line SEE-GC has also been used. The direct coupling of SEE with supercritical fluid chromatography (SEC) has also been successfully caried out. Coupling SEE with SEC provides several advantages for the separation and detection of organic substances low temperatures can be used for both SEE and SEC, so they are well suited for the analysis of natural materials that contain compounds which are temperature-sensitive, such as flavours and fragrances. 

Freney, J. R., Simpson, J, R, and Denmead, O. T. (1983). Volatilization of ammonia. In "Gaseous Loss of Nitrogen from Plant-Soil Systems" Q. R. Freney and J. R. Simpson, eds), Martinus Nijhoff, Dr. W. Junk Publishers, Boston. 

When pure P-endosulfan was allowed to equilibrate in the apparatus, the ratio of the P-isomer to the a-isomer in the gas phase became 8 92 at 20 , suggesting that the P-isomer converts to the a-isomer (Rice et al. 1997). Several investigators have reported rapid initial losses of endosulfan residues from treated plant surfaces due to volatilization (Archer 1973 Terranova and Ware 1963 Ware 1967). One research group (Willis et al. 1987) attributed the limited runoff losses found in soybean fields treated with endosulfan to early losses of the compound during application and to volatilization/degradation of the compound from plant surfaces. Air sampling performed in a wind tunnel under defined conditions (20 air velocity 1 m/sec relative humidity 40-60%) showed that 60% of the initial dose of endosulfan is volatilized from Trench bean surfaces after 24 hours (Rudel 1997). Influences of various pesticide application formulations were not tested. 

Fig. 4.1 Sinigrin is an aliphatic glucosinolate that occurs at significant levels in the human diet, notably in mustard and Brussels sprouts. When brought into contact with myrosinase, derived either from plant cells or from colonic bacteria, it is broken down to yield a variety of products including the acrid, volatile, biologically active compoimd...

Organic compounds released from plant roots have been categorized according to (a) their chemical properties, such as stability (e.g., hydrolysis and oxidation), volatility, molecular weight, solubility in water, etc. (Chap. 2) (b) the modality of their release (exudates, secreted, or lysates) (c) the way of utilization... 

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