Review of Asbestos | Microorganism of the Month: Spegazzinia species
By Dr. Kamashwaran Ramanathan
The word asbestos comes from the Greek word meaning "inextinguishable" or "indestructible." Once considered a "magic mineral" due to its unique properties of fire resistance and thermal insulation, asbestos has a variety of uses in building materials such as flooring, roofing, insulation, cements, mortars, etc. It can be subdivided into two major classifications of minerals: amphiboles and serpentines. Chrysotile, the most common type of asbestos found in building material, is a serpentine mineral. Amosite, Tremolite, Crocidolite, Actinolite and Anthophyllite are amphiboles. Amphibole fibers have single solid cylindrical shapes which usually only break transversally, whereas Serpentine fibers are like ropes and are composed of many smaller fibrils which tend to unwind. Chrysotile is very flexible and less likely to be friable than the amphiboles. In composition, the amphiboles such as Amosite and Crocidolite both have molecular structures in which iron comprises 25% to 36% and magnesium comprises 6% to 25% by weight. In contrast, the serpentine Chrysotile has little iron and usually contains 1% to 5% iron and 33% magnesium by weight.
There are many methods for the identification and quantification of asbestos in bulk samples including polarized light microscopy, transmission electron microscopy (TEM), x-ray diffraction, infrared adsorption, etc. There are limitations with all the methods. For example, x-ray diffraction cannot differentiate between fibrous and non-fibrous varieties of similar minerals. Microscopic examinations such as polarized light microscopy or transmission electron microscopy provide information on the confirmation of asbestos and are the most commonly used methods. The fact that PLM analysis with dispersion staining is much more rapid and cost efficient in comparison to the TEM analysis makes it the method of choice in most cases. For all bulk samples except for liquid samples, the use of both the stereo and polarized light microscope for identifying and quantifying asbestos is considered to be the method of preference by the vast majority of people. If the sample being tested is water or another liquid, identification by TEM is mandated.
Figure 1: Chrysotile bundles in 1.550 HD liquid with central stop dispersion staining.
Figure 2: Chrysotile bundles in crossed polars and Red I compensator.
Most authorities in the United States and the rest of the world consider asbestos to be one of the major occupational health and safety problems in the world today. The Environmental Protection Agency (EPA) has no general ban on the use of asbestos. However, asbestos was one of the first hazardous air pollutants regulated under Section 112 of the Clean Air Act of 1970, and many applications of asbestos have been forbidden by the Toxic Substances Control Act (TSCA). Asbestos litigation, which has become the longest and the most expensive mass tort in U.S. history, has been estimated to have approximately 850,000 claimants suing for asbestos related injuries. It has costed approximately 70 billion dollars, leading to bankruptcies of at least 74 companies and loss of more than 50,000 jobs so far. It is estimated that in the United States, 10,000 people a year die from asbestos-caused diseases, including one out of every 125 American men who die over the age of 50. The rate at which people are diagnosed with the diseases relating to asbestos exposure is expected to likely increase through the next decade. It has been estimated that the total costs of asbestos litigation in the USA alone may eventually reach $200 billion. Even if a worldwide ban on asbestos were to be introduced forthwith, past exposures is something that we will still have to deal with for the near foreseeable future.
Since asbestos is naturally present in two thirds of the rocks in the earth's crust, we need to be prudent towards maintaining a working and living environment in which airborne asbestos is in a concentration low enough that it will not result in adverse health effects. The bio-persistence of asbestos fibers following inhalation has been a topic of much interest for researchers throughout the world. Understanding this may help in further understanding the effects of the different asbestos fibers on human health. Calidria chrysotile (California, USA), Canadian chrysotile (textile grade), and Brazilian chrysotile (Cana Brava Mine) are the three different commercial chrysotile fibers that have being studied in detail till date. Researchers at U.C. Davis have recently completed the largest study to examine the question of whether naturally occurring asbestos also poses a cancer risk. Published in the American Journal of Respiratory and Critical Care Medicine, the study found that living near asbestos-containing rock is indeed associated with an increased risk of developing mesothelioma. Reports like this underscore the need to understand asbestos and its effects in more detail.
Similarly, a recent study that was published in the Journal of Occupational and Environmental Hygiene has evaluated the efficiency of respirator filters against asbestos fibers; it has demonstrated that the respirator filters used during asbestos remediation have a surface charge that enhances their collection efficiency. Further, an increased surface charge improved their collection efficiency when compared to respirators with low surface change. The surface charge of these respirators was found to decrease in a high-temperature, high-humidity environment and was found to disappear after one week.
Recently EPA's National Risk Management Research Laboratory (NRMRL) has tested a new method for asbestos removal that may drastically change the way asbestos is currently removed. Comparing this new method to the conventional method in use today shows that this method not only saves time but also the money involved in such work. When employed, this new method was able complete the project within a day as compared to the conventional method that took 9 days to complete similar work. The new method was also able to save as much as 40 to 60 percent of the conventional costs. Further information on this new experimental method can also be obtained from the U.S. EPA's NRMRL website.
To conclude, let's recollect the fact that we have heard and read a lot of debates on how asbestos may have prevented the collapse of the twin towers on the tragic 9/11. An article which appeared in the New York Times on September 18, 2001, reported that anticipating a ban on the use of asbestos in construction in New York, the builders stopped using the materials by the time they reached the 40th floor of the north tower and this may have played an important role in the fall of the towers. Now with all the clean up and rebuilding efforts on way, another concern that has been in the news is how much of asbestos were the emergency workers exposed to. Although research is needed to help understand these issues, this type of news and discussion emphasizes how asbestos has influenced our society. Continuing research about asbestos and asbestos containing products will definitely help our society deal with this "miracle mineral," or shall we say "silent killer" which now seems to be the term more often associated with asbestos for its dreadful toll on human health.
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By Gregorio Delgado
One of the most distinctive-shaped spores we usually recover from outdoor spore trap samples are those of Spegazzinia, a genus of anamorphic fungi or asexual fungal states traditionally included in the form-class Hyphomycetes as dematiaceous or pigmented-wall anamorphs. According to the U.S. Department of Agriculture Fungal Database, eight species have been currently described within the genus, most of them producing two types of conidia in the same mycelium (Figure 1). This condition is called pleomorphism and refers to the capacity of some fungi to produce more than one independent form or spore state in their life cycle (Kirk et al, 2001). In the case of Spegazzinia, we can distinguish a type "a" conidia or asexual spore, morphologically very similar in almost every species and composed of 4 to 8 nearly globose or inversed egg-shaped dark brown cells, 12 to 30 µm in size, with very long spines up to 12 µm long, and a type "b" conidia, subspherical or broadly ellipsoidal in shape, with vertical and horizontal septa or resembling a clover or cross, sometimes lobed or lobulate, pale to dark brown, usually flattened in one plane and smooth or with short spines (Ellis, 1971). Conidiophores or spore-bearing hyphae arise singly from subspherical, cup-like or flask-shaped mother cells and are of two types also, a long and a short one. They bear the two different kinds of spores as "a" type conidia borne on the long ones and "b" type conidia on the shorter ones. A few species only produce the type "b" conidia. Spegazzinia is only known from their anamorphic states since no teleomorph genus or sexual phase have been correlated with them.
Figure 1: Spegazzinia spores.
A: Type "a" conidia with spines.
B: Type "b" conidia of two different species.
Spegazzinia is widely distributed from warm temperate to tropical regions. They are saprophytes occurring on dead leaves or herbaceous dead stems of many different plants, and are also isolated from soil, even from estuarine sediments (Borut & Johnson, 1962). On natural substrates, colonies are discrete, orbicular, or effuse and dark blackish brown to black. In culture, growth is relatively slow and colonies can be detected only if a long enough incubation period is provided so that sporulation can occur. Usually identified on spore traps from outdoor air, Spegazzinia is rarely detected indoors, when carried away by the wind after released from any outdoor source. EMLab™ has never found Spegazzinia growing on indoor environmental surfaces (EMLab™ 2006 IAQ Pocket Guide).
The recovery rate and spore levels of Spegazzinia detected outdoors during the year in the United States are shown on the EMLab™ MoldRANGE™ data chart (Figure 2). According to the graph, Spegazzinia spores are present outdoors at a very low frequency, with a recovery rate of less than 3% throughout the whole year. When recovered, spore density is relatively low, with a median value of about 13 spores per cubic meter, although higher counts can reach 1700 spores/m3 during the spring season (April).
Figure 2: Spegazzinia frequency of detection and spore density by month.
The gray bars represent the frequency of detection, from 0 to 1 (1=100%), graphed against the left axis. The red, green, and purple lines represent the 2.5, 50, and 97.5 percentile airborne spore densities, when recovered, graphed against the right hand axis. (Source: EMLab™ MoldRANGE™ data. Total sample size for this graph: 39,878.).
No mycotoxin production or pathogenicity in humans is reported. Allergenicity effects have not been studied, although fungal spores can be considered potential allergens, and exposure to them may provoke immune responses in susceptible individuals.
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2. Ellis, M. B. (1971): Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew.
3. EMLab 2006 IAQ Pocket Reference Guide.
4. Kirk, P. M., P. F. Cannon, J. C. David & J. A. Stalpers (2001): Ainsworth & Bisby's Dictionary of the Fungi. 9th Ed. Wallingford.
5. Fungal Databases, Systematic Botany and Mycology Laboratory
This article was originally published on November 2006.