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Ozone

Properties of Ozone

Ozone (O₃) is the triatomic, allotropic form of oxygen (O₂). It is an unstable gas with a pungent odor. Since ozone is unstable, it must be generated at the point of application.

The ozone molecule, having a molecular weight of 48, is made up of three oxygen atoms bound by equal oxygen-oxygen bonds at an obtuse angle of 116°49’. This structure is inherently unstable and is the reason for ozone’s powerful oxidizing ability. Ozone has approximately 150% the oxidizing potential of chlorine. The physical properties of ozone and comparative oxidizing potentials for other chemical oxidants are presented in Table 1 and Table 2, respectively.

Ozone has a half-life of 12 hours or less in the atmosphere and degrades simple diatomic oxygen as its decomposition product. The technology can be easily incorporated into existing application practices and requires no onsite transportation, storage, handling, or discharge of toxic chemicals. The following narrative summarizes the potential environmental and human health and safety benefits of using ozone as a soil fumigant:

• On-site Manufacture – No transportation, Storage, or Discharge of Hazardous or Toxic Chemicals. Ozone is manufactured on site and at low pressures. It is not stored and is immediately consumed in the soil treatment process. A widespread sudden release of ozone into the atmosphere that would be harmful to humans cannot occur as it can with compressed methyl bromide or other persistent, toxic gases or chemicals.

• No Environmentally Persistent Chemicals Left in Soil. Ozone has a very short half-life of minutes or less in soil with simple diatomic oxygen as its decomposition or reaction product. Use of ozone in soil treatment does not result in the buildup of any environmentally persistent and toxic compounds.

• No Reentry, Permitting, or Use Restrictions. Ozone is regulated by the U.S. Environmental Protection Agency (EPA) as a “biocidal device” and is thus exempt from further restriction requirements by the EPA for state regulatory agencies. The California Department of Pesticides Regulation has confirmed this interpretation in writing. In addition to the associated lack of permitting requirements, the short half-life of ozone allows virtual immediate reentry after application without any risk of adverse exposure to workers.

• Minimum Human Acute and Chronic Toxicity- No Human Carcinogenicity or Teratogenicity. Except in extremely rare cases of extended, severe overexposure to high concentration to ozone (several hours at greater than 2 to 3 parts per million), the physical symptoms of ozone exposure are transitory in nature. Indeed, ozone has been used commercially in water treatment for over 100 years in tens of thousands of installations without a single recorded fatality.

Although ozone is considered an airborne pollutant when formed in the atmosphere by photosynthic reactions of nitrogen compounds, the use of ozone in aqueous applications is actually exempted from regulation by many regional air pollution control districts. For instance, the South Coast Air Quality Management District, the country’s largest air pollution control district covering most of Southern California, has exempted ozone from all permitting requirements for aqueous applications.

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