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Should Ozone Be Used In Mold Remediation? | Fungi of the Month: Alternaria species

Should Ozone Be Used In Mold Remediation?

By Dr. Harriet Burge

Ozone (O3) is a gaseous oxidized form of atmospheric oxygen. It is an essential part of the earth's atmosphere, forming a stratospheric layer that absorbs some of the ultraviolet light from the sun. Human activities have created holes in this layer that are allowing abnormal amounts of UV to penetrate to the earth's surface. The result of this damage to the ozone layer is the release of highly reactive chemicals (especially chlorine-containing compounds) into the atmosphere. A website for those interested in stratospheric ozone is: https://ozoneaq.gsfc.nasa.gov/.

Ozone is also produced at ground level by the photochemical oxidation of 'smog' chemicals (especially nitrogen oxides). Ozone levels can become especially high in cities that generate large quantities of chemical pollutants on hot sunny days. The following USEPA website is instructive: http://www.epa.gov/oar/oaqps/gooduphigh/ozone.html#6.

Most ozone that is detected in indoor environments has penetrated from outdoors. Because it is so highly reactive, most of the ozone that enters interiors reacts with or is adsorbed to surfaces, so that indoor levels of ozone are almost always below those of outdoor levels. If ozone levels are higher indoors than out, then some source of ozone is present in the indoor environment. Indoor sources often include copy machines and ozone generators (used to 'clean' the air).

Ozone is a toxic gas that affects organisms of all kinds. Human health effects (at levels that occur, for example, during smog episodes) include mucous membrane irritation, chest pain, exacerbation of asthma, and potentially irreversible scarring of lung tissue. Ozone exposure also damages crops and kills microorganisms that are essential to the normal functioning of the earth's ecosystem. It also oxidizes both volatile and non-volatile organic compounds and changes these compounds into others that may or may not be less hazardous than the original ones.

Because it does kill microorganisms, ozone is used to maintain water purity. When utilized for this purpose, ozone does not enter the breathing zone of humans, but does kill pathogenic (as well as other) microorganisms in the treated water. Ozone used in this way presents less risk than is posed by the microorganisms it is used to kill. This approach to the use of toxic chemicals is called risk tradeoff, and is an important concept for environmental investigators.

Using ozone to purify the air or to kill microorganisms (including fungi) on environmental surfaces presents a much more complicated risk tradeoff situation. On one hand, ozone will kill microorganisms, including fungi, if the concentrations applied to the organisms are sufficiently high. Ozone in levels that are not damaging to the human respiratory tract will not kill significant numbers of fungal spores, especially those on surfaces. Levels that are high enough to kill fungi are extremely hazardous to humans, animals and plants, and can only be used where exposure to these organisms will not occur. Ozone at levels high enough to kill fungi will also oxidize materials in the treated environment, changing them in ways that may not be desired. Thus, the risk tradeoff is the damage caused by the living organism (i.e. fungi) vs. the possible damage to the environment and the risk of human, animal or plant exposure. This comparison should be made in consideration of the fact that dead fungi may still be hazardous and must still be physically removed, and that there are other approaches to killing fungi (e.g., drying).

So, the bottom line answer to the question of whether ozone will kill fungi is yes, ozone will kill fungi. Should it be used as part of a remediation protocol? My answer would be no. I think the risk tradeoff is too high. You run the risk of dangerous exposures and damage to materials, and you will still have to go in and remove all of the 'dead' fungal growth.


Fungi of the Month: Alternaria species

By Dr. Payam Fallah

Alternaria spores are perhaps among the most recognizable (and beautiful!) fungal spores seen on spore trap samples. Microscopically, spores (conidia) are golden brown, generally club-shaped, often appearing in chains and, occasionally, have an apical beak (long extension of the spore) which does not exceed one third of the spore length. Their spore size can vary from about 15μm to about 90μm with some species having even a wider range of spore size. The spores (see Fig. A) have both transverse and longitudinal septations. When young, spores or spore fragments may be confused with spores of genera such as Ulocladium, Pithomyces, Stemphylium, or Epicoccum.

There is a striking similarity between the conidial chains of Alternaria and the chains of chlamydospores (resting/over-wintering spores) of certain species of the genus Phoma. Occasionally, Phoma grows on same substrate as Alternaria. To the untrained eye, these chains of chlamydospores may appear to develop from well-organized structures when, in reality, they are produced directly from simple hyphae. The actual conidia of Phoma are borne in an enclosed fruiting structure called a pycnidium.

In culture on malt extract agar media, colonies of Alternaria appear as light brown to olive green, and are cottony in texture. They may be different colors on other media. The colonies can reach a diameter of 6 cm in about 7 days at 25°C. Under the dissecting microscope, one can easily see the chains of conidia formed from hyphal branches.

The genus Alternaria contains about fifty species, many of which are pathogens on plants. Some species are capable of being saprophytic (living on dead organic matter) on a variety of building materials such as gypsum board, wallpaper and acrylic latex, just to name a few. All species within the genus are disseminated by wind and can travel very long distances and withstand harsh environmental conditions.

Among the species in this genus, A. alternata is perhaps one of the most widely occurring species in indoor environments. This particular species is cultivated for production of biomass used as a source material for allergen extracts. Because of its abundance in both indoor and outdoor environments, this fungus has become one of the most important sources of fungal allergens. Very little is known about mycotoxins from Alternaria however, A. alternata produces alternariol which has antifungal effects.

Figure A.
A typical Alternaria spores on spore trap.

Alternaria Microphoto


This article was originally published on December 2004.