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Asbestos Risk Assessment

Author: Christe Marbbn

November 2, 2009

Key words: Asbestos; Exposure Assessment; Toxicity Assessment; Risk Communication; Exposure-response; Mesothelioma; Lung Cancer

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J. Ugrad. Biol. S.
   
 

Abstract     The aim of this paper is to investigate the hazard, exposure, and toxicity associated with asbestos fibres as a model to assess the risks it poses on human health and public safety. For this purpose, information acquired from research that has explored aspects of asbestos were collectively integrated and analyzed in an unbiased, scientific approach. It was discovered that people who are constantly exposed to asbestos dust from work, are family members of the occupationally exposed, or are residents living near factories that utilize asbestos are most susceptible to asbestos exposure. Toxicity assessments revealed that prolonged exposure to asbestos ultimately causes lung tissue scarring, leading to various lung diseases such as asbestosis, mesothelioma, and lung cancer. The degree of asbestos potency is highly dependent on chemical composition, size, shape, durability, and clearance. However, a lack of consistent information provided in literature that indicate these factors, along with information based on sampling size, duration and amount of exposure, air sampling techniques, and appropriate controls, continue to plague stakeholders from reaching appropriate conclusions based on the risks identified. Finally, despite the success of asbestos monitoring methods and risk communication via the mass media in reducing the use and production of asbestos, asbestos is still a major public health concern. Consequently, more involvement from the academic community is still needed to precisely quantify the probability and characterize the risks of exposure in order to fill in the knowledge gaps that remain uncertain for both the hazard and exposure aspect of the risk equation.

 
 

Introduction

Risk perception is a subjective judgment that assessors make to characterize the severity of a risk before deciding its priority (Bebbington et al., 2001). When a certain hazard is imminent in the environment and is expected to spread beyond a particular safety boundary, it can quickly modify a stakeholder’s perception of risk, especially if it threatens to decrease the quality of life and human health of those exposed to the substance. There are many contributing factors that lead people to associate certain substances as being harmful. For many, mass media, as well as the influence of culture on society, collectively play a role in providing information about certain issues to the public, which help stakeholders decipher whether it is relevant to their lives. Unfortunately, the media has a tendency to distort facts or to report them with a slant to make headlines; consequently, most people fail to integrate, analyze, and reach a conclusion based on the assumed problem (Gunter, 1994). The word Asbestos means different things to different people, ranging from an excellent all-in-one sound absorbing wall insulator from an engineer’s perspective, to a nightmare for a bedridden lung cancer patient surrounded by asbestos-insulated walls. In order to accurately address and evaluate the health risks associated with the exposure to asbestos fibres and its related compounds, a thorough investigation involving unbiased, factual information is required. The purpose of this document is to provide an unbiased, detailed overview of the research that has explored aspects of asbestos in Canada and internationally and to evaluate the risks it poses to human health and public safety addressed from a diverse field of disciplines.

What is Asbestos?

Depending on the audience, the answer to this question can be given in numerous ways. To a scientist, asbestos is a generic term for a number of geologically similar, but not necessarily chemically related minerals (Milano, 2009). To a physician, it is a carcinogen capable of damaging the lungs. To a civil engineer, it is an inexpensive, thermal insulator. A lawyer may answer with a possible lawsuit in mind, while a stakeholder may perceive it as a health concern.

The term asbestos comes from the Greek word asbesta, meaning indestructible, imperishable, or non-combustible (Cugell & Kamp, 2004). It is a naturally occurring silicate mineral with long, thin fibrous crystals. Many minerals possess asbestiform characteristics, but only six specific minerals from two distinct groups are used industrially: Amphibole and serpentine. The amphibole fibres are straight and are arranged in long linearly organized chains (Finley et al., 2008); it encompasses amosite, crocidolite, anthophyllite, actinolite, and tremolite. The serpentine group, which represents 95 percent of manufactured asbestos, is composed of chrysotile – a softer, more fibrous form of asbestos arranged in large parallel sheets (Finley et al., 2008). A list of properties for each type of asbestos mineral is presented in Table 1. These minerals form in metamorphic terrain where amphibole and serpentine rocks are subjected to uniaxial tensile strain (Gunter, 1994). This causes the fibre to grow parallel to its principal strain axis during geological formation (Figure 1).

Crocidolite rock (left) and chrysotile rock (right). Both samples show the fibre axes indicated by the red arrow are parallel to the direction of greatest strain

Figure 1. Crocidolite rock (left) and chrysotile rock (right). Both samples show the fibre axes indicated by the red arrow are parallel to the direction of greatest strain.

Due to its wide range of desirable physical properties, asbestos has been used in many industrial applications. It is highly resistant to mechanical traction, possesses low electrical conductivity, flame-retardant and high-temperature resistant, able to absorb and retain micro-organisms in the interweaving of the fibres (Kivman et al., 1978), tensile, and able to withstand wear and abrasion. Finally, asbestos fibres have no detectable flavour or odour; this property makes detecting its presence expensive.

Table 1. The six common asbestos minerals.

The six common asbestos minerals

Problems Associated with Asbestos

After 20 years from the beginning of the industrial use of asbestos in Europe, as described in Normandy, France, in 1906, the first cases of pulmonary fibrosis – deep tissue scarring of lungs – were documented in the textile industry that used asbestos (Greenberg, 1994). The first case of asbestosis was observed in Britain in 1900, where all ten individuals working at the facility died of lung disease around the age of 30 (Greenberg, 1994). To date, three major diseases are associated with asbestos exposure: Asbestosis, mesothelioma, and lung cancer.

 

Asbestosis: This term defines a particular pneumoconiosis, a progressive, irreversible parenchyma lung disease caused by the inhalation of fine silica dust, as a result of long-term exposure to asbestos. Its diagnosis is based on clinical history, occupational history, and chest x-rays, in accordance to the guidelines outlined in the International Classification of Radiographs of Pneumoconiosis. X-rays in category zero are considered normal, while categories one (a), two, and three, represent abnormal results (ILO, 1980) (Figure 2).

Examples of normal and abnormal radiographs according to the International Classification of Radiographs of Pneumoconiosis

Figure 2. Examples of normal and abnormal radiographs according to the International Classification of Radiographs of Pneumoconiosis. Left: Normal Radiograph; Middle: Small parenchymal opacities in coal worker’s pneumoconiosis; Right: Large parenchymal opacities (progressive massive fibrosis) in coal worker’s pneumoconiosis.

Mesothelioma: Epidemiological studies suggest that 75 to 80 percent of cases related to malignant mesothelioma of the pleura are associated with exposure to asbestos. About 80 percent of cases occur among workers exposed to asbestos in the workplace (Gee & Morgan, 1989). In this disease, malignant tumour cells develop from mesothelial cells of peritoneum, pleura or pericardium – protective lining that covers most internal organs. Mesothelioma usually results in death within one to two years of its diagnosis and has a latency period of 35 to 40 years (Ross, 1984).

Lung Cancer: The risk of lung cancer depends on a number of factors, such as the dose, fibre type, type of work and duration of exposure, smoking history, and the presence of pulmonary fibrosis (Gee & Morgan, 1995). There is no clinical, radiological or pathological test that can distinguish lung cancer caused by smoking or other carcinogenic potential, since the histological distribution of asbestos-related cancers is similar to lung cancers that affect smokers without asbestos exposure (Gefter et al., 1992). In Canada, asbestos accounted for 219 documented cases of lung cancer deaths from 2000 to 2005 (Statistics Canada, 2009).

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