Beginning in the mid-1980s, the University of Minnesota School of Public Health researchers were involved in identifying potential health issues among Iron Range workers. Some 70,000 individuals, all working for one year or more in the taconite industry sometime between 1952 and 1983, were identified. Researchers were able to capture general work history information for approximately 75% of the cohort being studied. No further health assessments were made by university researchers at that time due to funding constraints.
Since 1997, the Minnesota Department of Health (MDH) has observed an increase in mesothelioma cases compared to expected cases in the general population of northeastern Minnesota. As of March 2010, 63 cases of mesothelioma have been identified, using the Minnesota Cancer Surveillance System (MCSS) from within the group originally identified by the University of Minnesota.
The identified mesothelioma cases triggered concern about the potential risks from mining dust among the taconite workers and also within the community. With the increase in case numbers and the circumstances surrounding the findings, the need to conduct a thorough epidemiologic investigation into the cause(s) of the excess cases and to assess other health parameters in the Minnesota taconite mining industry became apparent. In June 2007, the University of Minnesota School of Public Health received a formal request from Iron Range legislators to investigate the matter fully.
University of Minnesota Research Approach
Since legislation was enacted to fund research into this issue, discussions with various stakeholders and the University of Minnesota researchers have raised three questions that have shaped the scientific approach of the Minnesota Taconite Workers Health Study:
Because no one study design can address all of these questions or adequately assess the issues involved, the research team developed an approach based on five interrelated study designs, which are the: Occupational Exposure Assessment, Mortality (cause of death) Study, Cancer Incidence Study, Respiratory Health Survey of Taconite Workers and Spouses, and Environmental Study of Airborne Particulates. In addition to investigating the excess cases of mesothelioma among taconite workers, these studies are looking at a variety of respiratory diseases to determine the relationship between working in the taconite industry and lung health. Each of the approaches offers unique perspectives on miner health.
Occupational Exposure Assessment
There are three main goals for the exposure assessment component of this research:
Based on analysis of historical data and current measurements, researchers have classified the workers into approximately 30 Similarly Exposed Groups (SEGs) in the eastern and western zones of the Mesabi Iron Range. An analysis of the measurements leads to the following preliminary conclusions: (a) The amphibole elongated mineral particles (EMP) concentration was much less than the total EMP concentration, a result indicating that amphibole EMP are not major components of taconite EMP; (b) The respirable dust measurements are nearly all below the regulatory limit; and (c) Silica measurements had frequent excursions over the regulatory limit. This finding is similar to Mine Safety and Health Administration (MSHA) findings. Further analysis of the silica exposures is expected to completed later this year.
Researchers also conducted a detailed study of the efficacy of existing exposure control measures, including primary engineering controls (enclosures, ventilation, and particle collectors), work practice and administrative controls, and personal protective equipment. They toured the control systems of all the mines. They also measured air velocity into selected enclosures and in selected ducts in four mines, and have compared their findings to the American Conference of Industrial Hygienist (ACGIH) ventilation guidelines. In general, the types of installed controls match ACGIH guidelines, although the velocity into some enclosures is lower than recommended. The following are preliminary conclusions: (a) Engineering controls are appropriate for normal operations; (b) Miners may be exposed to dust levels at or over the regulatory limit when making repairs or performing maintenance and respiratory protection should be used under these conditions.
Activities for the next several months will concentrate on incorporating the occupational exposure information into the human health investigations (Mortality and Incidence Studies) which are described below.
Mortality and Incidence Studies
The overall objective of this part of the study is to determine whether employment in the taconite industry, and more specifically exposure to dust from taconite mining and processing, is related to dying from specific diseases. Given the nature of the dust encountered in this industry, and the previously identified diseases, this study is focusing on mesothelioma, lung cancer, and non-malignant respiratory disease (NMRD).
Preliminary analyses of the mortality rates of taconite workers compared to the rest of Minnesota by duration of employment have been completed. As known previously, the Standardized Mortality Ratio (SMR) for mesothelioma and lung cancer is elevated. Multiple other causes of death were also evaluated and the SMR was found to be similar or the same as for those living in Minnesota and not working in the taconite industry. This finding indicates that taconite workers are not at more risk of dying from certain diseases (such as diabetes; kidney disease; neurological disorders such as Parkinson’s disease; or cancers of the breast, stomach, and esophagus) than those not working in the industry.
As the work continues additional effort will be made to validate the data, identify missing information, and determine if supplemental data are available. The concentrated effort at this time is to connect the work history data to the specific exposure information from the occupational exposure assessment study.
Respiratory Health Survey of Taconite Miners and Spouses
The Respiratory Health Survey of Taconite Workers and Spouses operated research clinics from August 2009 to October 2010 in Virginia and Silver Bay where 1188 taconite workers and 498 spouses participated in a clinical evaluation of their lung and respiratory health. The study procedures included: a questionnaire; a physical examination and blood test; a chest X-ray; and two types of lung function tests. The participants were given the results of their tests and referred back to their own health care provider if follow-up was needed. The chest X-rays were subsequently evaluated by B-readers and assessed for dust related lung diseases. The research team is in the process of combining the breathing tests results with the chest X-ray interpretations while incorporating the exposure information, which will enhance the accuracy of determining the presence of dust-related lung disease.
Environmental Study of Airborne Particulates
The goal of the environmental study of airborne particulates is to evaluate the effect of past and present emissions from taconite mining on community air quality across the Mesabi Iron Range. This research is measuring the difference between airborne particulates in communities surrounding taconite operations and those in comparable towns in Northeast Minnesota. NRRI is in the final stages of analytical work and is developing aids in which to help interpret and report the results later this year.