Epidemiological studies have shown a significant increased risk of cancer associated with occupational exposure of inhaled asbestos. A prospective cohort study (Elmes and Simpson, 1971), of 170 asbestos insulation workers in North Ireland, followed for 26 years; showed an increase in incidence of death due to all cancer with a SMR of 390 and SMR of 1760 for cancer of pleural mesothelioma and lower respiratory tract. A retrospective cohort mortality study (Selikoff et al. 1979) showed an increased incidence of lung cancer (105.6 expected vs. 995 observed) with an SMR of 460. The study also reported an increase in mortality due to mesothelioma (175 deaths) and gastrointestinal cancers.
Multiple factors have to be taken into affect when evaluating occupational risk assessment for asbestos exposure. The impact of the exposure is based on the fiber characteristics, length of exposure, dose of exposure and confounding factors such as smoking history. Cigarette smoking increases the asbestosis mortality and the risk of lung cancer. Asbestos exposure and cigarette smoking have a synergistic effect.
The risk of mesothelioma or lung cancer in the general population primarily due to asbestosis is minimal. It is difficult to directly quantify the true risk of asbestosis exposure to the general population, based on epidemiological studies from known occupational hazardous risks. Further prospective studies need to be conducted to evaluate the true risk of asbestos exposures in the general environment. (http://www.inchem.org/documents/ehc/ehc/ehc53.htm)
Asbestos is considered to be a Type A1: Confirmed Human Carcinogen. Observation of increased mortality and incidence of lung cancer, mesotheliomas, and gastrointestinal cancer in occupationally exposed workers are consistent across investigators and study populations. The mutagenicity shows the increase in chromosome numbers and chromosome breaks in eukaryotic cells. (For more information on asbestos as a carcinogen, see www.NIOSH/NIOSHDBS/npg/npgd0041.htm).
Asbestos exposure may cause a scarring of the lung tissue leading to asbestosis. Exposure to asbestos in addition to smoking cigarettes causes a synergistic effect that may lead to lung cancer or other cancers. Most fatal of the consequences of asbestos exposure is mesothelioma. It is a nodular cancer of the plural lining of the lung. It has a long latency period, 25-40 years, and always is fatal. (For more information on the health effects of asbestos exposure, see www.labsafety.com/commerce/techhelpctr/theezfacts/ezf151.htm)