Health issues linked to asbestos useJanuary 16, 2013, 8:11 pm
Lecturer Rajarata University of Sri Lanka
Asbestos is the generic name for a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. Asbestos became increasingly popular among manufacturers and builders in the late 19th century because of its sound absorption, average tensile strength, its resistance to fire, heat, electrical and chemical damage, and affordability. Over 2 million metric tons of asbestos is used worldwide each year for thousands of different commercial applications.
Two-third of all asbestos produced is added to cement, giving it better resistance to weather. It was used in such applications as electrical insulation for hotplate wiring and as heat insulation in factories, schools, and other buildings. In addition, it can be found in brake pads, brake linings, hair driers, patching plasters, and a multitude of other products.
Asbestos mining began more than 4,000 years ago, but did not start large-scale until the end of the 19th century. For a long time, the world's largest asbestos mine was the Jeffrey mines in the town of Asbestos, Quebec.
Six mineral types are defined by the United States Environmental Protection Agency (US-EPA) as "asbestos", including those belonging to the serpentine class and those belonging to the amphibole class. All six asbestos mineral types are known to be human carcinogens. Serpentine class fibres are curly and Chrysotile is the only member of this class. Chrysotile is obtained from serpentinite rocks which are common throughout the world. Chrysotile is seen as a white fibre under the microscope. Chrysotile has been used more than any other type and accounts for about 95% of the asbestos found in buildings in America. It is more flexible than amphibole types of asbestos and thus it can be spun and woven into fabric.
The most common use is within corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and garages. It is also found as flat sheets used for ceilings and sometimes for walls and floors. Numerous other items are also made containing chrysotile, including brake linings, cloth behind fuses (for fire protection), pipe insulation, floor tiles, and rope seals for boilers. Amphibole class fibres are needle-like. Amosite, crocidolite, tremolite, anthophyllite and actinolite are members of this class.
In 2009, 2 million tonnes of asbestos were mined worldwide. Russia was the largest producer with about a 50% world share followed by China (14%), Brazil (12.5%), Kazakhstan (10.5%) and Canada (9%). In late 2011, Canada's remaining two asbestos mines, both located in the province of Quebec, halted operations. It was followed through by the successive government as well.
Asbestos is dangerous because its fibres are easily dislodged. Floating in the air, these fine particles may be inhaled into the lungs, where they are neither broken down nor expelled, but remain for life. Three major disorders may result due to long term exposure to asbestos. They are pulmonary (lung) fibrosis, lung cancer and mesothelioma.
Pulmonary fibrosis or asbestosis is an upsurge of scar tissues in the lungs that may occur in people who breathe in asbestos. The disease takes 10 to 20 years to develop upon chronic exposure to asbestos.
Asbestos exposure becomes a health concern when high concentrations of asbestos fibres are inhaled over a long period of time. People who become ill from inhaling asbestos are often those who are exposed on a day-to-day basis in a job where they worked directly with the material. As a person's exposure to fibres increases, because of being exposed to higher concentrations of fibres and/or by being exposed for a longer time, then that person's risk of disease also increases. Disease is very unlikely to result from a single, high-level exposure or from a short period of exposure to lower levels.
Asbestos is the only known cause of mesothelioma, a cancer that develops in the lining of the lungs (the pleura). Highly malignant, this cancer spreads rapidly and kills victims within a year from the time of diagnosis. However, mesothelioma has also been reported in some individuals without any known exposure to asbestos. The incidence of lung cancer in asbestos workers who smoke is 92 times greater than in asbestos workers who are non-smokers, providing a striking example of synergism.
Stanton and Layard hypothesised in 1977-‘78 that toxicity of fibrous materials is not initiated by chemical effects, but that physical property must presumably be triggering the development of cancer. Such properties might cause mechanical damage or result in unwanted signal channels which might disrupt normal cell activity, especially mitosis. There is experimental evidence that very slim fibres (<60 nm in length and <0.06 gm in breadth) do intertwine destructively with chromosomes. This is likely to cause the sort of mitosis disruption expected in cancer.
Unwanted Signal channels have recently been explored theoretically, but not yet experimentally. The theory argues that this effect would only be feasible for asbestos fibres >100 nm in breadth (>150 nm in the case of chrysotile), suggesting that we should be on the watch-out for a possible mixture of diverse mechanisms for the different fibre-diameter-ranges.
Discovery of toxicity
The first documented death associated with asbestos was in 1906. In the early 1900s researchers began to notice a large number of early deaths and lung problems in asbestos mining towns. Dr. H. Montague Murray in London conducted a post mortem examination on a young asbestos factory worker who died in 1899. Dr. Murray gave testimony on this death in connection with an industrial disease compensation hearing. The post-mortem confirmed the presence of asbestos in the lung tissue, prompting Dr. Murray to express as an expert opinion his belief that the inhalation of asbestos dust had at least contributed to, if not actually caused, the death of the worker.
The first diagnosis of asbestosis was made in the UK in 1924. The term mesothelioma was first used in medical literature in 1931 and its association with asbestos was first noted sometime in the 1940s.
In Australia, asbestos was widely used in construction and other industries between 1945 and 1980. From the 1970s there was escalating concern about the jeopardy of asbestos. The use of asbestos was phased out in 1989 and banned entirely in December 2003.
In 1989 the EPA issued the Asbestos Ban and Phase out Rule which was subsequently overturned in the case of Corrosion Proof Fitting. In 2010, Washington State banned asbestos in automotive brakes starting in 2014. The EPA has proposed a concentration limit of seven million fibres per litre of drinking water for long fibres (lengths greater than or equal to 5 um).
In the United Kingdom, blue and brown asbestos materials were banned outright in 1985 while the import, sale and second hand reuse of white asbestos was outlawed in 1999. The 2012 Control of Asbestos Regulations state that owners of non-domestic buildings (e.g., factories and offices) have a "duty to manage" asbestos on the premises by making themselves aware of its presence and ensuring the material does not deteriorate, removing it if necessary.
In 1984, the import of raw amphibole (blue and brown) asbestos into New Zealand was banned. In 2002 the import of chrysotile (white) asbestos was banned. A complete ban on asbestos in Turkey went into effect in 2011.
Tokyo had, in 1971, ordered companies handling asbestos to install ventilators and check health on a regular basis; however, the Japanese government did not ban crocidolite and amosite until 1995, and a full-fledged ban on asbestos was implemented in October 2004. Asbestos use was banned in Korea in 2009.
With the help of aggressive media marketing, asbestos is the number one roofing material in the island. Since the war, the local market for asbestos has increased substantially especially in the North and East.
Many asbestos manufacturers do not wish to comment on any speculation that they may be in serious danger. They claim that they have routine medical check-ups and they are alright. These companies remain safe as long as health professionals do not test for mesothelioma or asbestosis. Moreover, Sri Lanka hospitals do not have enough facilities to effectively diagnose asbestos related diseases. The government of Sri Lanka has not taken any clear cut policy on banning of asbestos yet.
Who are at risk?
Contrary to the common belief that only workers handling asbestos are at risk, studies show that asbestos is carried through the air and inhaled by unsuspecting victims. As stated above asbestos is also used to manufacture brake pads in buses and other vehicles. People do not realize that when buses are travelling at high speeds along roads in Sri Lanka, braking friction is high and consequently large amounts of asbestos fibres are discharged into the environment.
Last Updated Dec 02 2016 | 09:13 pm