PRINCIPLES OF TOXICOLOGY

treatment, or medical removal from the workplace. The results may be scrutinized for the occurrence
of sentinel health events, “red flags” such as asbestosis or mercury poisoning that indicate the presence
of a preventable exposure. Systematic epidemiologic analysis is extremely useful. For example, two
groups of workers, one with potential exposure to a toxin and one without exposure, might be compared
to determine whether the exposed group has any excess of disease. Similarly, the disease rates of one
group over time might be followed, to verify that a preventive intervention has been successful. The
necessary skills in data collection, management, and analysis are an increasingly important part of the
occupational health toolbox.
An example of a medical surveillance program is the Cadmium Medical Surveillance Program,
mandated by the United States Occupational Safety and Health Administration in the Cadmium
Standard, 29 CFR 1910.1027. Studies of human populations have suggested that excessive cadmium
exposure is associated with an increased risk of lung cancer, kidney damage, and prostate cancer.
Therefore, the Cadmium Medical Surveillance Program focuses on evaluating the respiratory, renal,
and genitourinary systems of exposed workers. For example, elements of the mandatory medical
surveillance program for cadmium are presented in Table 20.4. One limitation of most medical
surveillance programs, including the cadmium program, is that tests and methods traditionally used in
clinical medicine to detect and diagnose disease among individuals with symptoms who come forward
for medical care cannot always be relied on for detection and diagnosis of the health effects of
occupational exposures among those who are free of symptoms but may be in an early stage of disease.
Evaluations for Attribution
20.5 ACTIVITIES OF THE OCCUPATIONAL HEALTH PROVIDER 505
The occupational and environmental medicine specialist is frequently asked to make a determination
of attribution. The specific question is whether an exposure at work caused or contributed to an illness
in an individual. The results of this evaluation may be used to help diagnose and treat the disease, to
compensate the employee monetarily for lost wages due to the injury or illness, and to implement
prevention programs. This often difficult and sometimes controversial task must be based upon the
similarity of the exposure–disease relationship in the individual to those reported in the medical
literature in systematic studies of large groups. Several main characteristics of occupational illness, as
described above, can make the occupational origins of illness obscure to all except the most committed
observers. Critical issues include the fact that occupational disease is often clinically indistinguishable
from nonoccupational disease, that occupational disease can occur a long time after the end of exposure,
and that occupational exposures often have synergy with nonoccupational exposure.
An example of a case involving attribution is a 25-year-old male who experienced shortness of
breath and wheezing of three months duration. Although he had a history of seasonal allergies that
caused nasal congestion, he had no problems with wheezing prior to the past 3 months. The
occupational history revealed that 6 months prior to the onset of his respiratory symptoms, he began
to work on the production line of a company that repackages bulk quantities of isocyanate-based paint
into smaller containers. He stated that hoses leading from the bulk tanks to the filling machine would
periodically leak. He did not use personal protective equipment. Examination of the worker was
positive for wheezing and objective lung function testing revealed a pattern diagnostic of asthma.
Because exposure to isocyanates has been associated with asthma in large studies, the physician
determined that there was a causal link between the workplace exposure and the new onset of disease.
TABLE 20.4 Specific Elements of the Mandatory Medical Surveillance Program for Workers Exposed
to Cadmium
Questionnaire, completed by the employee, pertaining to health effects associated with cadmium exposure
Directed physical examination, with emphasis on the respiratory, genitourinary, and renal systems
Chest X ray and pulmonary function tests
Physiologic monitoring of kidney function (blood urea nitrogen, creatinine, B2-microglobulin, and urinalysis)
Biologic monitoring (blood and urine cadmium levels)