Introduction Workers around the world who encounter hazardous substances are aware of the measures needed to protect themselves from acute exposures to these chemicals. However, workers are often less aware of the potential hazards associated with chronic exposures to certain substances. Because of the unawareness of the hazards, the people that work with these toxic chemicals may be unknowingly exposing themselves to the potential to develop a lethal disease. Chronic lethal death is the long-term exposure to any substance that will eventually lead to death. This concept can be useful to many people and agencies, such as the EPA. The lethal dose for 50% of the population (LD 50 ) is a measurement used for determining acute toxicity to a population of test organisms. Because the LD 50 deals with acute exposure, this limit level is not pertinent in our research. Our group considered studying various chemicals that can cause death from chronic exposure. Research was done on chemicals such as 131 I, hexavalent chromium, asbestos, and benzene. We were able to find the most relevant data for asbestos, so this chemical was chosen to be analyzed more in depth. Asbestos has a recent prominence in society, including in College Station at the Texas A&M Memorial Student Center, which makes it beneficial to be aware of its effects. One recent case study which brought to light the risks of chronic exposure to asbestos was in Libby, Montana. This case study involved miners, their family members, and the general population of the city to be exposed to asbestos and therefore can be used to determine the effects of the chemical on 1
humans. (1) This study is still relevant today because the chronic effects of asbestos can last a lifetime. The methods used by experts for toxicity determination include animal testing as well as statistical studies. The statistical studies would include things such as the previously mentioned case study because it allows the experts to see real-world scenarios and outcomes instead of predicting results based on animal testing. Asbestos Asbestos is a generic name used to describe several silicate materials. These materials, known as carcinogens, include: amosite, chrysotile, crocidolite, tremolit, actinolite, and anthophyllite. Under certain conditions these materials crystallize into bundles of fibrils that look like organic fibers. 2
Figure 1. Asbestos Under a Microscope (2) The predominant form of asbestos that is used commercially is chrysotile or white asbestos. The average fiber length of asbestos is approximately 100 µm long and 100 nm wide. Asbestos occurs naturally in the air from rocks, mining, and manufacturing. It is also used in the brake linings of cars and in insulation and heat-proof gloves. Asbestos is also leaked into the air from insulation when it becomes aged or damaged. Part of what makes asbestos dangerous is that it does not have odor or taste nor does it dissolve in water or evaporate, often making it undetectable in an average setting. The reasons asbestos is used often in insulation is because it is resistant to heat, fire, chemicals, and biological degradation. 3
Methods There are several methods available to choose to be able to determine the concentration of asbestos in air. Evey single method should incorporate field sampling protocols, laboratory regimens, and laboratory data interpretation.(7) Among all the different methods used to test for asbestos in air there can be found; phase-contrast microscopy, polarized light microscopy, transmission electron microscopy, analytical electron microscopy,tem capabilities, include ASTM D22.02 (02-01), ISO 13012, CARB 427, Superfund Method, EPA Level II, AHERA 40CFR763, and NIOSH 7402. AHERA is the method used to clear areas that are being consider to be reoccupy. This method is also mandatory for all public schools. The method lists specific counting, recording rules, and photographic documentation for every asbestos structure found on each area that is being monitored. AHERA specifies the exact type of filter material to be employed usually 0.45 μm MCE, the configuration of each air monitoring cassette, sampling units needed for testing (cassettes) to be employed as well as sampling flow rates needed. Minimum final air volumes of approximately 1200 Liters are required to achieve certain sensitivity in the testing procedure. OSHA and MIOSH use phase-contrast microscopy for monitoring occupational exposure. The definition that these organizations use to define asbestos fibers is more specific, therefore, only a small set of fibers are regulated and used in fiber concentration reports. Since asbestos is found naturally in some rock, it is also present naturally in the air. Asbestos air concentrations vary depending on different conditions. For example, if the air sample was taken near a mine, the 4
concentration would be higher due to the rocks the asbestos is stored in being broken up and released into the air. In outdoor rural areas, asbestos concentrations can be up to 10 fibers/m 3. Levels of asbestos are ten-fold higher when tested in cities. To put these concentrations in perspective, an average person inhales approximately one cubic meter of air in one hour. For persons working near mines or in factories, their exposure level could reach 10,000 fibers/m 3 or higher. Buildings that contain asbestos in places like insulation can have concentrations in the air ranging from 30 to 6,000 fibers/m 3. In addition to inhaling asbestos, it can also be ingested. This happens when asbestos erodes from a natural deposit or a pile of waste, allowing the asbestos to get into a water source. Asbestos can also end up in drinking water by cement pipes used to carry the water, or filtering water through an asbestos-containing filter. The US drinking water supplies are reported to have concentrations less than 1 million fibers/liter. Long asbestos fibers are more carcinogenic than small fibers because they are more easily hung in the body. Lifetime exposure to asbestos dust containing 0.0001 fibers greater than 5µm in length per milliliter of air could result in 2-4 excess cancer deaths per 100,000 people. Inhalation of asbestos is regarded as cumulative and it is very difficult for the body to extract these fibers. Toxicity Asbestos toxicity is considered severe. OSHA permissible exposure level (PEL) is 0.1 respirable fibers/ml and OSHA short term exposure limit (STEL) is 1 respirable fiber/ml. Some symptoms of chronic exposure to asbestos are asbestosis, dyspnea, restricted pulmonary function, and lung 5
cancer. The one we are covering is asbestosis because it results from chronic exposure to asbestos. Asbestosis can be most easily described as asbestos fibers getting trapped in the lungs. This entrapment causes the buildup of scar-like tissue in the lungs and in the membrane that surrounds the lungs. This scar-like tissue does not expand and contract like normal lung tissue so breathing for the affected person becomes difficult. As a result, blood flow to the lungs may be decreased which causes the heart to enlarge. (6) The scar-like tissue on the lungs causes lung cancer, mesothelioma and also cancer of the membrane surrounding the lungs and other organs; all of which are fatal. The direct interaction between asbestos fibers and cell molecules are partly responsible for the toxicity of asbestos. Levels of asbestos in the air that lead to lung cancers depend on how long a person was exposed, how long it has been since the exposure started, whether the person smoked cigarettes or not and the type and size distribution of the fibers. To date, there is no clear method to remove asbestos from the lungs but some natural antibodies have been recorded to attempt to fight off the effects of asbestos. Many times these attempts have similar detrimental effects on the body that asbestos could have. This work of the body to heal itself can be best described when alveolar macrophages attempt to phagocytize the asbestos fiber and digest it by producing reactive oxygen species. Some of these reactive species are hydrogen peroxide and superoxide radical anion which are both relatively mild species. These species can however spontaneously react with one another to produce free radicals which are more toxic to the body. Ironically, this toxic reaction is enhanced by the presence of iron which comes from the asbestos fiber itself. Some studies have shown that the effects of asbestos can be cut down by free radical scavengers which reduce the levels of reactive 6
oxygen species. Diseases associated with asbestos Information on health effect of asbestos was studied mostly by people who were exposed in the past to level of asbestos fiber (greater than 5 μm in length) in workplaces. The asbestos fiber, like a needle, sticks to epithelial cells in the lungs and membranes. The sharp asbestos fiber is not easily removed by the lung, coughing, and excretion through blood. Then blood flow would decrease because damaged tissue cannot expand and contract like normal tissue. This disease is called asbestosis. According to Government date on asbestos mortality, 43,073 people have been killed by asbestos since 1979. As well as its direct hazard, it is one of the major causes of cancers and causes chronic fibroplasias. Workers exposed to higher level of asbestos have increased chances of getting two types of cancers, one of which is cancer in the lung tissue. Lung cancer is the leading cancer killer in both men and women in the United States. As you can see Figure 4, Lung cancer causes more death than following three other cancers (Colon, breast and pancreas). An estimated 160,000 Americans were expected to die from lung cancer in 2012. Death rate for lung cancer is 63.6 per 100,000 persons for men and 39.0 per 100,000 persons for women. 7
Figure 2. Estimated Cancer Death by Site, 2012 (3) Figure 3. Attributions for Lung Cancer (3) As Figure 3 shows, active smoking is a significant contributor for lung cancer. Lung cancer can also be caused by occupational exposure, including asbestos, uranium, and coke. The combination of asbestos exposure and smoking greatly increase the risk of developing lung cancer. Mesothelioma (Malignant mesothelioma) is the second type of cancer caused by exposing high level of asbestos. Mesothelioma is the most serious of all asbestos-related diseases. According to the Centers for Disease Control and Prevention (CDC), the malignant mesothelioma death rate in the United States from 1999 through 2005 totaled 18,068 people. The death rate increased from 2,482 deaths in 1999 to 2,704 in 2005. Also, age influenced the mortality rate, as those 75 years old and older comprised the majority of patients who died from mesothelioma. (5) There are three recognized types of mesothelioma. The pleural mesothelioma is the most common and accounting 70% of mesothelioma cases. Anatomically, the pleura (outer lining of the lungs and internal chest wall) is the most common site for the growing of mesothelioma. Peritoneal mesothelioma occurs in the lining of the abdominal cavity. Pericardial mesothelioma is originated in the pericardium which lines the heart. It is important to detect mesothelioma in its early stages, but a person who has the diseases shows insignificant symptoms such as cough and fever. 8
Figure 4. Pleural Mesothelioma (4) Case Study: Libby, Montana In Libby, Montana, there was a vermiculite mine that had traces of asbestos. There were a total of 28 different sites of the mine that had asbestos detected from the 1920s to 1990. These facilities were known to be exfoliating facilities that processed more than 100,000 tons of vermiculite. All but one of the exfoliating facilities processed the vermiculite by heating it until it expanded and popped. This case was developed from noticing a high mortality rate from asbestos related diseases and lung cancer than it was expected to be. Asbestosis and mesothelioma were the other related asbestos diseases. Most of the asbestosis cases involved former miners, facility workers, and household contacts of these employees. The method that the Agency for Toxic Substances and Disease Registry (ATSDR) used to evaluate the sites was by measuring the inhalation route of exposure, the frequency 9
the workers were exposed, the duration the workers were in the mine, and the intensity of the exposure. Some of the pathways the workers and community were exposed was by being in direct contact, the plume that was created from the processing of the vermiculite, the worker s did not have any personal protection equipment, the worker s clothing not being washed at the facility, and bringing it back home. Of the 73,000 people that participated in the medical screen program, 18% had pleura abnormalities consistent with asbestos exposure. The pleural abnormalities found from the workers were 51% of the 365 participants. After a mortality review for the Libby community, the standardized mortality rates for asbestosis was 40 to 80 times higher than expected. Lung cancer was 20 to 30% higher than expected and the mesothelioma mortality rate was also higher. The ATSDR, Environmental Protection Agency (EPA), and state health departments came to multiple conclusions. The first conclusion they came to was raising more awareness to the public and explaining the potential dangers. This meant that the people who have been already exposed, to get medical check ups, and to help keep future exposure down. The next conclusion was for the facilities, and other agencies to clean up leftover vermiculite, and actions to take to prevent further exposure and lower the risk of exposure to the workers and public. The last conclusion was referring to the lack of inspections for the non-exfoliation sites, but could require further review on a case-by-case basis. 10
Figure 5: Mine in Libby, Montana (1) Conclusions Formatting 11
Work Cited 1. "Colorado Asbestos Removal Reliance Environmental Services." Colorado Asbestos Removal Reliance Environmental Services. N.p., n.d. Web. 15 Nov. 2012. <http://www.relianceabatement.com/asbestos.html>. 2. "What Is Asbestos?" ATSDR. N.p., n.d. Web. 15 Nov. 2012. <http://www.atsdr.cdc.gov/asbestos/more_about_asbestos/what_is_asbestos/>. 3. "Lung Cancer Fact Sheet American Lung Association." Homepage American Lung Association. N.p., n.d. Web. 16 Nov. 2012. <http://www.lung.org/lung disease/lung cancer/resources/facts figures/lung cancer fact sheet.ht ml>. 4. "Mesothelioma Cancer Types, Causes, Symptoms and Diagnosis." Mesothelioma Cancer Alliance The Authority on Asbestos Cancer. N.p., n.d. Web. 16 Nov. 2012. <http://www.mesothelioma.com/mesothelioma/>. 5. "Mesothelioma Death Rate Mortality Rate." Mesothelioma Center Fight Back Against Mesothelioma. N.p., n.d. Web. 17 Nov. 2012. <http://www.asbestos.com/mesothelioma/death rate.php/>. 6. Toxicological Profile for Asbestos. U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES: Public Health Service Agency for Toxic Substances and Disease Registry. 12
September 2001. 9 Nov. 2012. 7. Ehrenfeld, Frank. "ASBESTOS IN AIR BY TEM / AHERA VERSUS NIOSH 7402: A BRIEF REVIEW." (n.d.): n. pag. Iatl.com. Web. 13