Fumigation ozone

Methyl bromide has been identified as an ozone-depleting substance and is being gradually removed from world markets. Current legislation and plans call for the elimination of methyl bromide in most industrial countries by 2005, with possible exemptions for quarantine (UNEP, 1996). Currently there is an extensive search worldwide for products that are alternatives to methyl bromide (Kawakami, 1999). These alternatives are broadly defined and include components of management plans such as sanitation, monitoring, contact insecticides, heat treatments, and modified atmospheres, in addition to new fumigants (Batchelor, 1998). 

Kerwin et al. [41] determined methyl bromide soil fumigant by cyrotrapping and electron capture gas chromatography. Down to 0.23pM of methyl bromide could be detected by this procedure. Kerwin et al. [41] found levels of methyl bromide in the stratosphere and claimed that this contributed to ozone destruction. 

Cyanogen, a colorless gas with an almond-like odor, is used in organic syntheses, as a fumigant, as a fuel gas for welding and cutting heat-resistant metals, and as a rocket and missile propellant with ozone or... 

Due to its gaseous nature it may have an effect on the stratospheric ozone layer [281, 402, 404]. After injection into soil for fumigation, methyl bromide rapidly diffuses through the soil pore space to the soil surface and then into the atmosphere [159,162,163,405,406]. Since a plastic sheet typically covers the soil surface, the rate of emission into the atmosphere depends upon the thickness and density of the plastic, if other conditions are the same [159, 406]. Other routes of disappearance from soil include chemical hydrolysis, methylation to soil organic matter through free radical reactions, and microbial degradation [ 136,159,405,407]. Several reports appeared on the study of the microbial transformations of methyl bromide, summarized as follows ... 

Adedipe, N. O., and D. P. Ormrod. Ozone-induced growth suppression in radish plants in relation to pre- and post-fumigation temperatures. Z. Pflanzenphysiol. 71 281-287, 1974. 

Cantwell, A. M. Effect of temperature on response of plants to ozone as conducted in a specially designed plant fumigation chamber. Rant Dis. Rep. 52 957-960. 1968. 

Cathey, H. M., and H. E. Heggestad. Effects of growth retardants and fumigations with ozone and sulfur dioxide on growth and flowering of Euphorbia pulcherrima WUld. J. Amer. Soc. Hort. Sci. 98 3-7, 1973. 

Heagle, A. S. Effect of low-level ozone fumigations on crown rast of oats. Phytopathology 60 252-254, 1970. 

Hodgson, R. H., K. E. Dusbabek, and B. L. Hoffer. Diphenamid metabolism in tomato Time course of an ozone fumigation effect. Weed Sci. 22 20S-210. 1974. 

Houston, D. B. Response of selected Pinus strobus L. clones to fumigations with sulfur dioxide and ozone. Can. J. Forest Res. 4 65-68, 1974. 

Menser, H. A., and G. H. Hodges. Tolerance to ozone of flue-cured tobacco cultivars in field and fumigation chamber tests. Tobacco Sci. 13 176-179, 1%9. 

Injury to important primary-producer species constituting forest ecosystems is not limited to California. In the eastern United States, a disease called emergence tipbum of eastern white pine was related to ozone by Berry and Ripperton. Occurrence of similar symptoms on the same species in eastern Canada could not be definitely related to ozone by Linzon.- The disease is characterized by bands of necrosis initiated in the semimature tissue of elongating needles the necrosis spreads to the needle tip. In other studies with ozone fumigations at 0.07 ppm for 4 h or 0.03 ppm for 48 h, the tipbum appeared additional symptoms were silvery or chlorotic flecks and chlorotic mottling. - ... 

Significant increases have been reported in length of root tissue colonized hyp. annosus when artificially inoculated ponderosa and Jeffry pine seedlings were fumigated with ozone at 431 Mg/m (0.22 ppm) and 888 (0.45 ppm) 12 h/day for 58 and 87 days. ... 

The reflection coefficient ( a ) was estimated by allowing leaf tissue to equilibrate first in distilled water, then in a O.U M mannitol solution for two hr and finally in a distilled water solution overnight. The difference in weight between the initial distilled water equilibration and final distilled water equilibration was assumed to be an estimate of internal solute leakage and, therefore, a direct estimate of a. The data in Table V shows that loss of solute by the tissue is significant after ozone fumigation and verifies the predicted decrease in the reflection coefficient. 

Intact tobacco plants were exposed to 0.60-0.70 yl/1 ozone for 1 hr mitochondria isolated from visibly injured tissue demonstrated an inhibition of oxidative phosphorylation in conjunction with an increase in respiration (6). However, when detached tobacco leaves were fumigated with 1.0 yl/1 ozone for 1-5 hr, the mitochondria extracted from the tissue prior to s3rmptom development exhibited reduced oxygen uptake and reduced oxidative phosphorylation (7 ). In an experiment of similar design when ozone was bubbled through a solution of isolated mitochondria, both respiration and oxidative phosphorylation were reduced (7 ). 

Some HAPs impact not only the troposphere but also the stratosphere. The most obvious example is highly toxic methyl bromide, CH3Br, used as a soil fumigant as well as for treatment of buildings for termites. As discussed in Chapter 12, this is a significant source of stratospheric bromine and hence contributes to stratospheric ozone depletion. Its continued use has been controversial and is being phased out (e.g., see Thomas, 1996 Ristaino and Thomas, 1997 and Duafala, 1996). 

Second, reaction 8.9 and other relevant reactions appear to occur preferentially on available solid surfaces, which are often ice crystals but may also be particles of sulfate hazes from volcanic eruptions or human activity. Third, volatile bromine compounds are even more effective (via Br atoms) than chlorine sources at destroying ozone methyl bromide is released into the atmosphere naturally by forest fires and the oceans, but anthropogenic sources include the use of organic bromides as soil fumigants (methyl bromide, ethylene dibromide) and bromofluorocarbons as fire extinguishers (halons such as CFsBr, CF2BrCl, and C2F4Br2). 

Masten et al. (1996) investigated the oxidation of chlorinated benzenes such as 1,2-dichlorobenzene (1,2-DCB), 1,3,5-trichlorobenzene (1,3,5-TCB), and pentanoic acid (PA). TCB is often generated as a by-product of pesticide manufacturing, while DCB is commonly manufactured as an insecticide or a fumigant for industrial odor control. Due to their resistance to biological treatments, PA is usually nonreactive with ozone but can react with hydroxyl radicals (Masten et al., 1996). 

One of the most effective fumigants is methyl bromide. It essentially sterilizes soil when applied under a ground covering, because it kills insects, nematodes, and weed seed but also is used to fumigate warehouses. Overexposure to this compound causes respiratory distress, cardiac arrest, and central nervous effects. The inhalation LC50 is 0.06 mg/L (15 min) of air (rat) and 7900 ppm (1.5 h) (human). Methyl bromide has been classified as an ozone depleter under the Clean Air Act and is due to be phased out of use by 2005. 

Many of the effects that occur as a result of these fumigations can probably be attributed to a destruction of chlorophyll. Chlorophyll loss attributed to fumigation with ozone or ozonated hexenes has been described (37, 39, 40, 41) and can be used as a quantitative measure of injury to cultured plants by certain pollutants. However, in the case of N02, growth suppression of tomato and bean occur after exposure to 0.5 ppm N02 for 10-12 days with a concomitant greening of the leaves, indicating the possibility of nitrogen accumulation and no chlorophyll destruction by the pollutant. 

At Pennsylvania State University, breeding for resistance to ozone and S02 in scotch pine is underway. Resistance seems to be genetic. Selections for resistance were made initially in a fumigation nursery and will be tested further in stands planted near pollutant sources. Crosses are being made for genetic studies as well as for selection for resistance and for favorable ornamental traits of crown form, branching habit, and needle color (15). 

Methyl bromide, CH3Br (boiling point 4.5°C)—Methyl bromide is a gaseous fumigant used both in the soil and on commodities. In the soil, it is used for preplant soil fumigation with chloropicrin to control nematodes, insects, and fungi. Its use was banned in 2005, except for "critical use" exemptions, because it is an ozone depleter. Methyl bromide has an oral LD50 in rats of 100 mg/kg. 

SAFETY PROFILE Poison by inhalation. Potentially explosive decomposition at 200°C. Flammable when exposed to heat or flame. Explosive reaction with ammonia + heat, chlorine, concentrated nitric acid, ozone. Incompatible with oxidants. The decomposition products are hydrogen and metallic antimony. When heated to decomposition it emits toxic fumes of Sb. Used as a fumigating agent. See also ANTIMONY COMPOUNDS and HYDRIDES. 

For some pesticide compounds, such as dini-troaniline herbicides (Weber, 1990), phototransformation occurs primarily in the vapor phase, rather than in the dissolved or sorbed phases. Perhaps the most environmentally significant pesticide phototransformation in the atmosphere, however, is the photolysis of the fumigant methyl bromide, since the bromine radicals created by this reaction are 50 times more efficient than chlorine radicals in destroying stratospheric ozone (Jeffers and Wolfe, 1996). Detailed summaries of the rates and pathways of phototransformation of pesticides and other organic compounds in natural systems, and discussions of the physical and chemical factors that influence these reactions, have been presented elsewhere (e.g., Zepp et al, 1984 Mill and Mabey, 1985 Harris, 1990b). 

As a soil fumigant methyl bromide leaves no toxic residue in soils. The volatile gas rises into the atmosphere. Methyl bromide is an ozone-depleting substance. Although methyl bromide is very soluble in water, its high vapor pressure in various soil types indicates a low tendency to adsorb to soils and rapid evaporation. Methyl bromide has a half-life in air estimated from 0.3 to 1.6 years. Degradation is primarily due to photolysis. In soils, the half-life is 0.2-0.5 days. In water, a half-life of 3 h was calculated. 

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