health impact of asbestos health impact of asbestos all types of asbestos fibers are known to cause serious health hazards in humans. the most common diseases associated with chronic exposure to asbestos are asbestosis and mesothelioma. asbestos warning label. figure a shows the location of the lungs, airways, pleura, and diaphragm in the body. figure b shows lungs with asbestos-related diseases, including pleural plaque, lung cancer, asbestosis, plaque on the diaphragm, and mesothelioma. left-sided mesothelioma (seen on the right of the picture): chest ct amosite and crocidolite are considered the most hazardous asbestos fiber types; however, chrysotile asbestos has also produced tumors in animals and is a recognized cause of asbestosis and malignant mesothelioma in humans, and mesothelioma has been observed in people who were occupationally exposed to chrysotile, family members of the occupationally exposed, and residents who lived close to asbestos factories and mines. during the 1980s and again in the 1990s it was suggested at times that the process of making asbestos cement could "neutralize" the asbestos, either via chemical processes or by causing cement to attach to the fibers and changing their physical size; subsequent studies showed that this was untrue, and that decades-old asbestos cement, when broken, releases asbestos fibers identical to those found in nature, with no detectable alteration. risks exposure to asbestos in the form of fibers is always considered dangerous. working with, or exposure to, material that is friable, or materials or works that could cause release of loose asbestos fibers, is considered high risk. however, in general, people who become ill from inhaling asbestos have been regularly exposed in a job where they worked directly with the material. according to the national cancer institute, "a history of asbestos exposure at work is reported in about 70 percent to 80 percent of all cases. however, mesothelioma has been reported in some individuals without any known exposure to asbestos." a paper published in 1998, in the american journal of respiratory and critical care medicine, concurs, and comments that asbestosis has been reported primarily in asbestos workers, and appears to require long-term exposure, high concentration for the development of the clinical disease. there is also a long latency period (the time taken between harmful contact and emergence of the actual resulting illness) of about 12 to 20 years, and potentially up to 40 years. the most common diseases associated with chronic exposure to asbestos are asbestosis and mesothelioma. according to osha, "there is no 'safe' level of asbestos exposure for any type of asbestos fiber. asbestos exposures as short in duration as a few days have caused mesothelioma in humans. every occupational exposure to asbestos can cause injury or disease; every occupational exposure to asbestos contributes to the risk of getting an asbestos related disease." asbestos-related diseases main article: asbestos-related diseases diseases commonly associated with asbestos include: asbestosis: progressive fibrosis of the lungs of varying severity, progressing to bilateral fibrosis, honeycombing of the lungs on radiological view with symptoms including rales and wheezing. individuals who have been exposed to asbestos via home, environment, or work should notify their doctors about exposure history. asbestos warts: caused when the sharp fibers lodge in the skin and are overgrown causing benign callus-like growths. pleural plaques: discrete fibrous or partially calcified thickened area which can be seen on x-rays of individuals exposed to asbestos. although pleural plaques are themselves asymptomatic, in some patients this develops into pleural thickening. diffuse pleural thickening: similar to above and can sometimes be associated with asbestosis. usually no symptoms shown but if exposure is extensive, it can cause lung impairment. pneumothorax: some reports have also linked the condition of pneumothorax to asbestos related diseases. malignant mesothelioma: an aggressive and incurable tumour arising from mesothelial cells of the pleura (the lining of the thoracic cavity). safety and exposure prevention asbestos exposure becomes an issue if asbestos containing materials become airborne, such as due to deterioration or damage. building occupants may be exposed to asbestos, but those most at risk are persons who purposely disturb materials, such as maintenance or construction workers. housekeeping or custodial employees may be at an increased risk as they may potentially clean up damaged or deteriorated asbestos containing materials without knowing that the material contains asbestos. asbestos abatement or remediation workers and emergency personnel such as firefighters may also become exposed. asbestos-related diseases have been diagnosed in asbestos workers' family members, and in residents who live close to asbestos mines or processing plants. common building materials containing asbestos currently in the united states, several thousand products manufactured and/or imported today still contain asbestos. in many parts of the industrialized world, particularly the european union, asbestos was phased out of building products beginning in the 1970s with most of the remainder phased out by the 1980s. even with an asbestos ban in place, however, asbestos may be found in many buildings that were built and/or renovated from the late 1800s through the present day. residential building materials containing asbestos include a variety of products, such as: stipple used in textured walls and ceilings; drywall joint filler compound; asbestos contaminated vermiculite, vinyl floor tile; vinyl sheet flooring; window putty; mastic; cement board; asbestos cement pipes and flues; furnace tape; and stucco. asbestos is widely used in roofing materials, mainly corrugated asbestos cement roof sheets and asbestos shingles sometimes called transite. other sources of asbestos-containing materials include fireproofing and acoustic materials. identification and assessment a fiber cannot be identified or ruled out as asbestos, either using the naked eye or by simply looking at a fiber under a regular microscope. the most common methods of identifying asbestos fibers are by using polarized light microscopy (plm) or transmission electron microscopy (tem). plm is less expensive, but tem is more precise and can be used at lower concentrations of asbestos. if asbestos abatement is performed, completion of the abatement is verified using visual confirmation and may also involve air sampling. air samples are typically analyzed using phase contrast microscopy (pcm). pcm involves counting fibers on a filter using a microscope. airborne occupational exposure limits for asbestos are based on using the pcm method. the american conference of governmental industrial hygienists has a recommended threshold limit value (tlv) for asbestos of 0.1 fibers/ml over an 8-hour shift. osha in the united states and occupational health and safety regulatory jurisdictions in canada use 0.1 fibers/ml over an 8-hour shift as their exposure limits. environmental asbestos asbestos can be found naturally in the air outdoors and in some drinkable water, including water from natural sources. even nonoccupationally exposed members of the human population have tens to hundreds of thousands of asbestos fibers per gram of dry lung tissue, equivalent to millions of fibers in each lung. asbestos from natural geologic deposits is known as "naturally occurring asbestos" (noa). health risks associated with exposure to noa are not yet fully understood, and current us federal regulations do not address exposure from noa. many populated areas are in proximity to shallow, natural deposits which occur in 50 of 58 california counties and in 19 other us states. in one study, data was collected from 3,000 mesothelioma patients in california and 890 men with prostate cancer, a malignancy not known to be related to asbestos. the study found a correlation between the incidence of mesotheliomas and the distance a patient lived from known deposits of rock likely to include asbestos; the correlation was not present when the incidence of prostate cancer was compared with the same distances. the risk of mesothelioma declined by 6% for every 10 km (6.2 mi) that an individual had lived away from a likely asbestos source. portions of el dorado county, california are known to contain natural amphibole asbestos formations at the surface. the usgs studied amphiboles in rock and soil in the area in response to an epa sampling study and subsequent criticism of the epa study. the epa study was refuted by its own peer reviewers and never completed or published. the study found that many amphibole particles in the area meet the counting rule criteria used by the epa for chemical and morphological limits, but do not meet morphological requirements for commercial-grade-asbestos. the executive summary pointed out that even particles that do not meet requirements for commercial-grade-asbestos may be a health threat and suggested a collaborative research effort to assess health risks associated with "naturally occurring asbestos." however, the main criticism pointed at epa was that their testing was conducted in small isolated areas of el dorado where there were no amphibole asbestos deposits, thus the language regarding amphibole, nonfibrous "particles". actual surface amphibole deposits in residential areas were ignored for testing purposes. because of this, no final findings were published by atsdr. a great deal of fairfax county, virginia was also found to be underlaid with tremolite. the county monitored air quality at construction sites, controlled soil taken from affected areas, and required freshly developed sites to lay 6 inches (150 mm) of clean, stable material over the ground. globally, samples collected from antarctic ice indicate chrysotile asbestos has been a ubiquitous contaminant of the environment for at least 10,000 years. snow samples in japan have shown ambient background levels are one to two orders of magnitude higher in urban than in rural areas. higher concentrations of airborne asbestos fibers are reported in urban areas where there is more acm (asbestos containing materials) and mechanisms of release (vehicles braking and weathering of asbestos cement materials); concentrations in the range of 1–20 ng/m3 have been reported. fibers longer than 5μm are rarely found in rural areas. ambient concentrations using tem analysis have been based on mass measurements. biological interactions mechanisms of carcinogenicity stanton and layard hypothesized in 1977–78 that toxicity of fibrous materials is not initiated by chemical effects; that is, any trigger-effects of asbestos must presumably be physical, such as mechanical damage which might disrupt normal cell activity—especially mitosis. there is experimental evidence that very slim fibers (<60 nm, <0.06 μm in breadth) tangle destructively with chromosomes (being of comparable size). this is likely to cause the sort of mitosis disruption expected in cancer. chemistry asbestos fibers (sem micrograph) individual asbestos fibers are invisible to the unaided human eye because their size is about 3–20 μm wide and can be as slim as 0.01 μm. fibers ultimately form because when these minerals originally cooled and crystallized, they formed by the polymeric molecules lining up parallel with each other and forming oriented crystal lattices. these crystals thus have three cleavage planes, and in this case, there are two cleavage planes which are much weaker than the third. when sufficient force is applied, they tend to break along their weakest directions, resulting in a linear fragmentation pattern and hence a fibrous form. this fracture process can keep occurring and one larger asbestos fiber can ultimately become the source of hundreds of much thinner and smaller fibers. when fibers or asbestos structures from asbestos containing materials (acm) become airborne, the process is called primary release. primary release mechanisms include abrasion, impaction, fallout, air erosion, vibration, and fire damage. secondary release occurs when settled asbestos fibers and structures are resuspended as a result of human activities. in unoccupied buildings or during unoccupied periods, fiber release typically occurs by fallout or is induced by vibration or air erosion. friability of a product containing asbestos means that it is so soft and weak in structure that it can be broken with simple finger crushing pressure. friable materials are of the most initial concern because of their ease of damage. the forces or conditions of usage that come into intimate contact with most non-friable materials containing asbestos are substantially higher than finger pressure. smoking and asbestos smoking has a supra-additive effect in increasing the risk of lung cancer in those exposed to asbestos. studies have shown an increased risk of lung cancer among smokers who are exposed to asbestos compared to nonsmokers. history of health concerns and regulation for additional chronological citations, see also, list of asbestos disease medical articles until 1900 early concern in the modern era on the health effects of asbestos exposure can be found in several sources. among the earliest were reports in britain. the annual reports of the chief inspector of factories in 1898 included a report from lucy deane which stated that