The NIOSH Current
Intelligence Bulletin (“Occupational Exposure to Carbon Nanotubes and
Nanofibers”) provides some initial guidance to the potential health
risks for workers who may be exposed to these nano-substances. The
concern for potential adverse health effects is solely based on animal
studies as there has been no report in the literature of human health
effects in workers or others exposed to carbon nanotubes or carbon
nanofibers.
When animals (mostly rodents) have been exposed to
these materials, the findings have ranged from acute inflammatory
changes in the lungs to interstitial fibrosis to mesothelial tumors.
Because some of the nano-materials may have durability/persistence and
aspect ratios similar to asbestos fibers, there have been findings
similar to “asbestos-type pathology”. However, there have also been
acute inflammatory changes. As is stated in this report, “differences in
results from animal studies have been attributed to differences in
physicochemical properties, surface area, the degree of agglomeration of
the test material, and differences in the observation period following
termination of exposure”. The differences in biological effect may also
depend upon the presence or absence of residual metal catalysts used in
the preparation of these substances.
Comments regarding medical surveillance (As listed in Sections 1.1, 6.6, and in Appendix B):
- General Comment: The recommended medical screening and surveillance
recommendations are not specific for possible pulmonary injuries that
may occur from inhalation of carbon nanotubes or nanofibers. The
recommendations appear to be generic. - Radiographic screening and surveillance: At this time, it is
uncertain which specific patterns of pulmonary injury may occur and when
they may appear. As a result, it is prudent to recommend that some form
of radiologic medical screening and surveillance be performed. However,
there is no justification that a NIOSH-certified B-reader must
interpret or review the chest radiographs. The presence of acute
inflammatory changes (as noted in the aforementioned animal studies) may
be seen as different radiographic patterns such as consolidation,
ground-glass opacifications, interstitial edema, etc. These are not
patterns that would be best reviewed by comparison to the standard ILO
films. Instead, the finding of any unexplained abnormality on a chest
radiograph as interpreted by a radiologist or pulmonologist should
prompt further evaluation that might include the use of a
high-resolution CT scan of the thorax. - Respiratory Symptom Questionnaires: The presence or development of
respiratory symptoms may also be critical to the identification of
possible pulmonary injury from exposure to nano-materials. We recommend
that a standardized respiratory symptom questionnaire should be used as
part of the initial screening and follow-up surveillance examinations;
e.g., ATS-DLD-78 or Medical Research Council Questionnaire, etc. - Spirometry testing: It is recommended that spirometry testing be
administered by an individual who has completed a NIOSH-approved
training course in spirometry or other equivalent training. It should
also be mentioned that the qualified health professional who is
overseeing the screening and surveillance program should be expert in
the interpretation of spirometry testing results, enabling them to
recommend further medical evaluation if abnormal test results occur;
e.g., more complete pulmonary function testing including lung volumes
and diffusing capacity measurements. - Research needs; we urge NIOSH to initiate at least one prospective
cohort study with close follow-up of exposed individuals in order to
determine as soon as possible whether occupational exposures are
associated with adverse health effects and if so, what effects occur. If
such a study is also undertaken in order to detect or characterize
exposures, in addition to determining adverse health effects, then it is
critical that the validity of monitoring methods be separately
demonstrated.