By Wade Rawlins
A draft report, prepared by the federal agency responsible for conducting research and making recommendations to protect worker health, summarizes the current state of scientific understanding of asbestos and other mineral fibers and offers a roadmap to explore unresolved questions.
The reappraisal of asbestos and other mineral fibers, written by the National Institute for Occupational Safety and Health, is intended to guide the development of specific research to reduce scientific uncertainties and provide a firm foundation for future policies.
Asbestos has been a prominent public health issue for more than three decades. During the mid- to late-20th century, scientists made advances in the understanding of the serious health effects of inhaling microscopic asbestos fibers.
Yet, questions remain, the report says. For example, due the complexity of asbestos minerals, the scientific literature contains inconsistencies about the definition of the term asbestos for health protection guidelines. And debate continues about whether to include certain non-asbestos mineral fibers under federal asbestos policies.
The results of new research can inform development of new exposure limits and policies for asbestos and other mineral fibers that are based on well-established risk estimates, NIOSH researchers say.
The report sets three goals:
- Develop better sampling and analytical methods for asbestos fibers
- Develop a clearer understanding of what determines the toxicity of elongated mineral particles
- Develop information on workplace exposures to various elongated mineral particles and health risks associated with them.
In the 1970s, federal agencies developed regulatory standards for exposure to airborne asbestos fibers based on evidence of respiratory disease in workers. Since the standards took effect, the use of asbestos has declined substantially and mining of asbestos in the U.S. stopped in 2002. Still, many asbestos products remain in use and new products continue to be manufactured and imported.
Deaths from asbestosis, a chronic disease, increased almost 20-fold from the late 1960s, when NIOSH began tracking them, to the late 1990s, the report says. Since then, they have leveled off at about 1,500 per year in the U.S. and are expected to continue for several more decades.
Meanwhile, annual deaths from malignant mesothelioma, an aggressive cancer caused by exposure to asbestos and other mineral fibers, increased 7 percent between 1999, when the disease began being categorized separately on death certificates, and 2004, the most recent year of complete data. In 2004, 2,657 people died of mesothelioma. The disease usually appears 20 to 30 years after exposure to asbestos.
The report says that scientific studies of workers exposed to asbestos have clearly documented increased risk of respiratory diseases, including lung cancer, mesothelioma and non-malignant abnormalities involving the lining of the lung. In addition, researchers have determined that laryngeal cancer can be caused by asbestos exposure and there is evidence asbestos exposure may cause other diseases including stomach and colorectal cancers and immune disorders.
Despite the decline in use, an estimated 1.3 million employees in construction and general industry still face significant asbestos exposure on the job, the U.S. Occupational Safety and Health Administration estimates.
Over time, the nature of workplace exposures has changed. In earlier decades, workers were exposed to asbestos that was used in manufacturing processes such as in textile mills and cement pipe fabrication. Today, the primary exposure is during maintenance activities and de-contamination of buildings containing asbestos. Researchers and policymakers need better projections of the number of workers exposed to asbestos fibers now and in the future, the report says.
Initially, researchers concern and workplace safety standards focused on six commercially used forms of asbestos mineral: chrysotile asbestos; and five amphibole varieties: amosite, crocidolite, actinolite asbestos, anthophyllite asbestos and tremolite asbestos.
As researchers learned more about the link between the dimensions of asbestos fibers and their ability to cause respiratory disease and cancer, they became more interested in other elongated mineral fibers that could be inhaled.
In 1990, NIOSH broadened its definition of airborne asbestos fibers to encompass other elongated mineral fibers, in part because the common method to test for microscopic airborne fibers could not distinguish between the various fibers.
Still, much less is known about other mineral fibers in terms of health effects. More research is needed to determine the toxicity of the elongated mineral fibers, the draft report says.
Populations of special interest include the workers at taconite mines in Minnesota and the talc mines in upstate New York who are exposed to mineral fibers that are non-asbestos.
An ideal outcome of the draft roadmap, the researchers write, would be scientific studies that supported recommendations for exposure limits to elongated mineral fibers to protect workers’ health.
The report currently is being reviewed by The Institute of Medicine of the National Academies, the nation’s advisors on science, medicine and engineering. That is scheduled to be completed by the fall of 2009.