A study of welders exposed to Hexavalent Chromium and the relationship of smoking
SAFETY 757: Principles of Occupational Epidemiology
26 April 2014
The principal objective of this study is to see if there is a correlation between increased cancer rates of welders who smoke and exposure to hexavalent chromium CrVI. As proven in previous studies other cancer-causing agents such as asbestos have shown higher rates of cancer in those who smoke and who have been exposed to asbestos. I will conduct prospective cohort study of two different companies that encompasses 5000 welders that are exposed to hexavalent chromium. I suspect that the incident rates among those welders who smoke will have higher rates of cancer than those of the welders that do not smoke.
Chromium occurs in three different forms, Metallic chromium, Triavalent chromium, Hexavalent chromium. Metallic chromium does not occur naturally and is produced from chromium ore a steel-gray solid with a high melting point to make steel and other alloys. Trivalent chromium is in a natural state and is in rocks, soil, animals, plants and volcanic emissions. It is used in industry as a brick lining for industrial furnaces. Hexavalent chromium is produced when Triavalent chromium is heated in processes such as welding. Hexavalent Chromium is a by-product of welding. During the welding process it is possible to strip electrons. If electrons are stripped from some of the chromium atoms it becomes hexavalent chromium. It requires that six of the atoms to be stripped to create CrVI. Welder’s main exposure to CrVI comes by inhalation when the welders breathe in the welding fume containing CrVI.
Workplace exposure to hexavalent chromium may cause irritation or damage to the throat, nose, and lungs. Repeated exposure or over exposure can damage the nasal wall separating the nasal passage. Studies have shown an association with exposure to airborne hexavalent chromium and cancer. Many factors can influence the absorption of chromium to include size, oxidation state and solubility of the chromium particles. Measurement of chromium has been done by measuring chromium in the urine, serum, and hair of workers. “The consensus from various reviews and agencies is that evidence of carcinogenicity of elemental, divalent, or trivalent chromium compounds is lacking. This is in stark contrast to hexavalent chromium compounds which have been identified as known human carcinogens via the inhalation route of exposure. Therefore, chromium compounds other than hexavalent are not considered to be human carcinogens by the Texas commission on Environmental Quality, the United States Environmental Protection Agency, The Agency for Toxic Substance and Disease Registry, or the International Agency for Research on Cancer.” (TCEQ 2009)
Welding on stainless steel is normally done one of two ways. One using coated electrodes and the other using gas shielding. Metal inert gas or commonly known as (MIG) welding is a semi-automatic process that uses a process which requires a connected source of direct-current and acts as electrode that can join two pieces of metal. Normally a flow of inert gas such as argon is passed to the weld gun and acts as a shield keeping contaminants away from the weld. Tungsten inert gas or, referred to as (TIG) is a manual welding that uses non-combustible tungsten electrode and delivers a current to the welding arc. Both ways use an electric arc between the electrodes and the welded material. Manual arc welding or stick welding uses an electrode coated in flux to weld. “Stainless steel welding is associated with exposure to metals including chromium and nickel. Manual metal arc welding of stainless steel generates hexavalent chromium. Between 50% and 90% of the chromium generated is hexavalent. The welding fumes from metal inert gas MIG welding contains 20% chromium in the hexavalent state. Increased concentrations of chromium and nickel are seen in blood and urine, especially in manual metal arc stainless steel welders.” (Sjoren,Hansen,Kjuus,Persson p1 1987)
NIOSH considers all CrVI(hexavalent chromium) compounds to be occupational carcinogens. CrVI is a well-established carcinogen associated with lung, nasal, and sinus cancer. Some of the industries in which the largest numbers of workers are exposed to high concentrations of airborne CrVI compounds include electroplating, welding, and chromate plating. (Centers for Disease Control and Provention)
Both the National Institute for Occupational Safety and Health and the Occupational Safety and Health Administration have established permissible exposure limits and recommended exposure limits. OSHA’s PEL’s for hexavalent chromium and workplace air during an eight hour workday is 5 ug/m3, while the REL is much lower at only .2 ug/m3. The NIOSH exposure limit is much less than the OSHA limit at .001 ug/m3. These exposure limits were set in 2006 and were highly debated. The chromium industry pushed to have a less stringent PEL than OSHA’s proposed PEL. OSHA ultimately settled on a less stringent standard. Different studies have found results to low-level exposure of chromium. At the current OSHA promotional exposure limit it was estimated to be 255 per 1000 for lifetime risk of lung cancer from exposure to hexavalent chromium. (Park RM, Bena JF, Stayner LT, Smith RJ, Gibb HJ, Lees PS 2004)
As found in earlier studies including one conducted by (G Berry 1985;42:12-18) they found that exposure to asbestos and subjects that smoked had a higher rates of cancer. I will look at exposure to hexavalent chromium and subjects that smoke to see if smoking has affect similar to asbestos and smoking.
Research hypothesis and methods
Welders who smoke that are exposed to hexavalent chromium have a higher risk of developing cancer than people who had similar exposures that didn’t smoke. The null hypothesis is if the risk of cancer is the same for smokers who are exposed to hexavalent chromium as smokers not exposed to hexavalent chromium.
I will conduct a prospective cohort study. The reason why a cohort study was chosen is that disease onset from hexavalent chromium usually forms after a long period of time. Cohort studies are commonly used in epidemiology to examine the effects of environmental and workplace exposures of potentially toxic agents.
The advantage’s of conducting a cohort study is that it will be able to provide incident rates of disease and health outcomes and provided direct inception of risk. Additionally, the exposure factor is well defined and there is a direct observation of risk. A further advantage of a cohort study is that it can study the exposures that are not all too common in the general population.
The disadvantage of conducting a cohort study is that it will be expensive and time consuming. This method will require several years before full results are obtained and some subjects may become lost during this extensive time frame. Furthermore, cohort studies can becomes complicated and difficult to carry out, at times.
ABC Company and DEF Company who both have welding facilities whose prime exposure is to hexavalent chromium. They both have 500 welders at each of their 5 locations totaling 5000 welders exposed to hexavalent chromium. The subjects will be broken into two groups: smokers and non-smokers. During the study, I will look for lung, nasal, and sinus cancer among the study group. Sampling would be done for Hexavalent Chromium with a 37-mm diameter polyvinyl chloride filter using a calibrated personal sampling pump. Each facility would be monitored for Hexavalent Chromium exposures.
To collect the needed data I will send out yearly surveys that ask about their exposure to hexavalent, health status, if they smoke. I will also contact the human resource department to see if they had anyone who died to help gather the required information.
To measure the association of relative risk I will take incident rate of smokers divided by the incident rate of non-smokers.
From the fourfold table I will calculate incidence of disease among the smoker group A/(A+B). Incidence of disease in the non-smoker group C/(C+D). From there we will calculate the relative risk (RR) = [A/(A+B)] / [C/(C+D)]. I will also compare the smoker rate against other studies that show the rate of cancer due smoking to see if it is higher with those exposed to hexavalent chromium and smoke.
In conclusion if the research plan went as expected I believe that the incident rates among smokers who are exposed to hexavalent chromium would have higher rate of cancer than those who do not smoke and had the same exposure to hexavalent chromium.
- Texas Commission on Environmental Quality (October 2009) Fact Sheet Chromium
From the Texas Commission on Environmental Qualitywebsite:http://www.tceq.texas.gov/assets/public/implementation/tox/dsd/facts/chromium3.pdf
- Berry G, Newhouse ML, Antonis P Combined effects of asbestos and smoking on mortality from lung cancer and mesothelioma in factory workers. 1985;42:12-18 British Journal of Industrial Medicine.
- Sjogern B, Gustavsson A, Hendstrom L Mortality in two cohorts of welders exposed to high-and low- levels of hexavalent chromium. 1987 Scand J Work Environ Health .
- Park RM, Bena JF, Stayner LT, Smith RJ, Gibb HJ, Lee PS Hexavalent chromium and lung cancer and chromate industry: a quantitive risk assessment. 2004 Risk Analysis
- Centers for Disease Control and Provention
From the Centers for Disease Control and Provention website: http://www.cdc.gov/niosh/topics/hexchrom/