Download Module 7

Occupational Diseases of the Nervous System
#outcomes
Learning Outcomes
After successfully completing this module, you will be able to:
1. describe the physiology of how workplace neurotoxins affect the central and peripheral
nervous systems.
2. list at least ten (10) workplace chemicals that are known neurotoxins.
3. describe the signs and symptoms of a mixed sensorimotor peripheral neuropathy.
4. list neurologic manifestations other than peripheral neuropathies that can occur in workers
overexposed to neurotoxins.
5. list and discuss the basic strategies in the management of occupational diseases of the nervous
system.
6. discuss the effects of elemental lead, elemental mercury, and organophosphate insecticides on
the nervous system.
7. list the persistent nervous system signs and symptoms associated with chronic overexposure to
some organic solvents.
8. list and discuss the elements that make up a complete lead exposure control program in the
workplace.
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Neurologic Disorders in the Workplace
Occupational diseases affecting the nervous system are serious matters for health and safety
professionals. Not only are the diseases a direct problem for the affected worker, but the impairment
of nervous system function can also be a critical safety issue both on and off the job.
Some basic terminology: the peripheral nervous system is all of the nervous tissue outside of the central
nervous system (brain and spinal cord).
#case
Research
Title: Impairment of neurobehavioral function and color vision loss among workers exposed to low
concentrations of styrene — a review of literatures.
Authors: R. Kishi, S. Tozaki and Y-Y. Gong. Hokkaido University School of Medicine, Japan.
Journal: Industrial Health, 38, 120–126, 2000.
Summary: Epidemiological studies on the impairment of neurobehavioral function — perceptual speed,
memory, cognition, personality, and mood — and color vision loss in workers exposed to low
concentrations of styrene were reviewed. In addition, recent work on the relationship between color
vision loss and the concentration of styrene metabolites in the urine of styrene workers was presented.
It is apparent that neurobehavioral function can be impaired in workers exposed to levels of styrene at
the current occupational exposure limits (50 ppm in Japan).
/case
#Readings
Read: Pages 428–432 in Baker, E. & Fiedler, N. (2011). Neurologic and psychiatric disorders. In B. Levy,
D. Wegman & R. Sokas (Eds.). Occupational and environmental health: Recognizing and preventing
disease and injury (6th ed.). Toronto, ON: Oxford University Press.
/Readings
#link
Canadian Environmental Health Atlas
/link
#Activity
Learning Activity #1/Perspectives
1. What are the two basic forms of damage to peripheral nerves that result in peripheral
neuropathies?
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Segmental demyelination: destruction of the myelin sheath of the nerve without damage to the nerve
axon; recovery is generally rapid.
Axonal degeneration: damage to the entire neuron; recovery is very slow and often incomplete.
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2. Describe how chemicals such as carbon monoxide and lead affect the central nervous
system.
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CO and lead affect the metabolism of neurotransmitters such as dopamine and norepinephrine.
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3. Review the manifestations of a mixed sensorimotor peripheral neuropathy (page 430 of
Levy and Wegman). How do you think these manifestations would affect the ability of a
worker to perform her job safely?
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The ability of the worker to do the job safely, even in the early stages of neuropathy, is decreased
because the worker begins to have numbness and tingling in both hands and feet, and then difficulties
with fine motor control of both hands and feet. This makes grasping and walking progressively more
difficult.
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4. What are the effects on the peripheral nervous system effects and other neurological
manifestations of the following workplace chemicals?
a. N-hexane?
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Peripheral — tingling of the fingers, toes, feet, and hands; motor function weakness in hands and feet.
Other — uncoordinated walking, impaired vision
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b. Carbon disulfide?
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Peripheral — mild tingling of the fingers and toes, mild loss of hand and foot motor function
Other — neuropathy of cranial nerves, Parkinsonism, limb tremor
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c. Carbon monoxide?
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Peripheral — none likely except in cases of severe intoxication
Other — Parkinsonism, acute intoxication
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d. Methyl n-butyl ketone?
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Peripheral — similar to n-hexane
Other — uncoordinated walking
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/activity
Behavioral Effects of Occupational Neurotoxins
Some of the more disturbing effects of overexposure to some occupational neurotoxins are related to
changes that these toxins produce in worker behavior. These effects may be relatively mild, for
example, loss of concentration and minor mood changes, or much more severe, for example, acute
psychosis.
#reading
Read: Pages 433–435 in Baker, E. & Fiedler, N. (2011). Neurologic and psychiatric disorders. In B. Levy,
D. Wegman & R. Sokas (Eds.). Occupational and environmental health: Recognizing and preventing
disease and injury (6th ed.). Toronto, ON: Oxford University Press.
/reading
#case
Research
Title: Body burden of aluminum in relation to central nervous system function among metal inert-gas
welders.
Authors: V. Riihimaki, H. Hanninen, R. Akila, T. Kovola,E. Kuosma, H. Paakkulainen, S. Valkonen and
B. Engstrom.
Journal: Scandinavian Journal of Work, Environment and Health, 26(2), 118–130, 2000.
Summary: The relationship between elevated body levels of aluminum, and central nervous system
function, was studied in 65 aluminum welders and 25 mild steel welders. Body burdens of aluminum
were determined by measurement of aluminum in serum and urine. Central nervous system functions
were assessed with a neuropsychological test battery, symptom and mood questionnaires, and with
electroencephalography. Both objective neurophysiological and neuropsychological measures and
subjective symptoms indicated that a mild, but significant impairment of central nervous system
function is associated with increasing aluminum body burden. Threshold levels of aluminum level in
serum and urine above which central nervous system impairment begins to occur were found to be
4.0–6.0 μmol/L in urine and 0.25–0.35 μmol/L in serum.
/case
#activity
Learning Activity #2/Perspectives
1. Complete the following: “In general, neurotoxins particularly affect psychomotor
performance by causing …”
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… slowness in response time, impaired hand-eye coordination, and diminished concentration ability.
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2. Which chemical agents in the workplace are known to be able to cause acute
intoxication in workers?
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Many organic solvents (because they are designed to be fat solvents, they are especially harmful to the
myelin sheath) and carbon monoxide.
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3. Management of occupationally-induced neurological problems consists primarily of
what two strategies?
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identification of the neurotoxin causing the disease
removal of the worker from further exposure to the neurotoxin.
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/activity
Effects of Selected Neurotoxins
We know that certain workplace chemicals produce very predictable and characteristic effects on the
nervous system. Some of these chemicals are widely used in the workplace. The use of many of these
chemicals is strictly regulated in most provinces. Many provinces have very detailed requirements for
health and safety programs for workers that are potentially exposed to these neurotoxins. The health
and safety professional has an obligation to understand these very detailed requirements.
#reading
Read: Lead (Case 2), pages 201–205, in Gochfeld, M. & Laumbach, R. (2011). Chemical hazards. In B.
Levy, D. Wegman & R. Sokas (Eds.). Occupational and environmental health: Recognizing and
preventing disease and injury (6th ed.). Toronto, ON: Oxford University Press.
/reading
#case
Research
Title: Impairment of color vision in workers exposed to organic solvents.
Authors:S. Semple, F. Dick, A. Osborne, J.W. Cherrie,A. Soutar, A. Seaton and N. Haites.
Journal: Occupational and Environmental Medicine, 57(9). 582-587, 2000.
Summary: Color vision impairment was studied in 68 male dockyard workers occupationally exposed to
mixed organic solvents and compared to 42 controls. Genetic differences that might affect the workers’
level of risk were also assessed. Exposure to mixed organic solvents is associated with impairment of
color vision and the risk increases with increasing exposure. Genetic polymorphisms for certain
glutathione transferases and acetyltransferases did not affect the risk for color vision loss.
/case
#activity
Learning Activity #3/Perspectives
1. Refer to the occupational health and safety regulations for your province. Summarize
the regulations regarding lead exposure in the workplace.
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Answers will vary by province. All provinces set exposure levels for lead. Many others have
requirements for routine air monitoring, health surveillance (blood lead levels), environmental hygiene,
and record keeping.
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2. Baker says that the manifestations of lead neurotoxicity as currently encountered differ
significantly from those seen in reports from the earlier part of the 20th century. Why do
you think that this is so?
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It is likely because current regulations require a stricter level of exposure control now than earlier in the
20th century. The symptoms seen in workers today are likely the result of chronic low-level exposure.
The symptoms seen in the early 20th century are the result of either acute exposure to very high levels
of lead, or of chronic exposure to higher levels of lead than one would expect to find in well-run
workplaces today.
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3. Summarize the neurologic symptoms most often seen in workers overexposed to lead.
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Fatigue, irritability, difficulty in concentrating, inability to perform tasks requiring sustained
concentration, arm muscle weakness.
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4. Manitoba Labour has a very specific set of rules for controlling exposure to lead in the
workplace.
#link
Web Resources
Read: Lead from Manitoba Health
/link
List and briefly describe the seven elements of an occupational health service that should be
maintained for those workplaces in which lead overexposure is possible.
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Adequate engineering, ventilation, and other control measures
to limit the exposure to lead.
Implementing monitoring of airborne lead concentrations, with detailed record keeping.
Making available appropriate hygiene facilities. Providing respiratory and other protective
equipment. Supervision of workers.
Providing biological monitoring.
Implementing a training program on the prevention of lead exposure.
5. According to Manitoba Labour, what actions must be taken when a worker is found to
have a blood lead level of greater than 2.4 μmol/L? (See Part VI — Biological Monitoring
and Treatment.)
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Remove from exposure. Medical assessment required. A physician shall be consulted.
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6. Review the occupational health and safety regulations for your province. Summarize the
regulations regarding elemental mercury exposure in the workplace.
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Answers will vary by province. Mercury exposure programs are often not included in regulations in as
much detail as lead exposure programs, but provincial guidelines frequently recommend a program as
detailed as that for lead exposure.
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Prepare a table which summarizes the symptoms associated with the various persistent health effects
of organic solvent overexposure (WHO classification).
Organic Affective
Syndrome
Mild Chronic Toxic
Encephalopathy
Severe Chronic Toxic
Encephalopathy
Drag
here
Descriptors
Irritability, fatigability,
difficulty in concentrating, loss of interest in daily events
As above, plus sustained personality or mood changes and
impaired intellectual function
Dementia with significant memory and cognitive function
deterioration
Irritability, fatigability, difficulty in concentrating, loss of interest in daily events
As above, plus sustained personality or mood changes and impaired intellectual function
Dementia with significant memory and cognitive function deterioration
/activity
#Readings
Read: Effects of neurotoxins, pages 436–439, in Baker, E. & Fiedler, N. (2011). Neurologic and
psychiatric disorders. In B. Levy, D. Wegman & R. Sokas (Eds.). Occupational and environmental health:
Recognizing and preventing disease and injury (6th ed.). Toronto, ON: Oxford University Press.
/Readings
#case
Research
Title: Beyond the workplace: An exploratory study of the impact of neurotoxic workplace exposure on
marital relations.
Authors: D. Julien, D. Mergler, M. Baldwin, M-P. Sassine,N. Cormier, E. Chartrand and S. Belanger.
University of Quebec at Montreal.
Journal: American Journal of Industrial Medicine, 37(3), 316-323, 2000.
Summary: The impact on family life and social relations that may result from symptoms associated
with exposure to neurotoxic substances in the workplace has never been addressed. In this study, 55
male workers and their spouses completed standardized measures of mental health and marital
difficulties. Workers’ exposure to neurotoxic substances was evaluated by questionnaire and interview.
A positive relation was observed between exposure level and measures of workers’ psychological
symptoms and marital stress.
/case
#Activity
Learning Activity #4/Perspectives
1. Briefly describe the basic mode of action of organophosphate insecticides on the nerves
of workers.
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Inhibit acetylcholinesterase resulting in overactivity of parts of the autonomic nervous system,
inhibition of skeletal muscles, and inhibition of other central nervous system functions.
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2. Workplace neurotoxins can produce neurologic effects other than those associated with
peripheral nervous system damage. List any three of these other effects.
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Any three of those listed in Tables 2-6 on page 572 and 26-2 on page 574.
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3. Management of occupationally-induced neurological problems consists of what two
basic strategies?
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Identification of the neurotoxin causing the disease. Removal of the worker from further exposure.
/reveal
4. What are the basic signs and symptoms you would expect to see in a worker suffering
from a mixed sensorimotor peripheral neuropathy?
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 Numbness and tingling of the hands and feet
 Motor function weakness in the fingers, toes, hands, and feet Muscle atrophy.
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5. Workers may suffer persistent neurologic health effects as a result of chronic exposure
to some organic solvents. Briefly describe the signs and symptoms associated with these
effects.
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Type 1: irritability, fatigue, difficulty in concentrating; loss of interest in daily events.
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Type 2: more severe Type 1 effects; sustained personality and mood changes, and impairment
of intellectual function.
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Type 3: dementia with severe impairment of all cognitive functions.
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/activity