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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.
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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).
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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.
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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.
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Table 1.
The six common asbestos minerals.
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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).
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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.
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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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