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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. /outcomes 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? #reveal button: Answer 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. /reveal 2. Describe how chemicals such as carbon monoxide and lead affect the central nervous system. #reveal button: Answer CO and lead affect the metabolism of neurotransmitters such as dopamine and norepinephrine. /reveal 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? #reveal button: Answer 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. /reveal 4. What are the effects on the peripheral nervous system effects and other neurological manifestations of the following workplace chemicals? a. N-hexane? #reveal button: Answer Peripheral — tingling of the fingers, toes, feet, and hands; motor function weakness in hands and feet. Other — uncoordinated walking, impaired vision /reveal b. Carbon disulfide? #reveal button: Answer Peripheral — mild tingling of the fingers and toes, mild loss of hand and foot motor function Other — neuropathy of cranial nerves, Parkinsonism, limb tremor /reveal c. Carbon monoxide? #reveal button: Answer Peripheral — none likely except in cases of severe intoxication Other — Parkinsonism, acute intoxication /reveal d. Methyl n-butyl ketone? #reveal button: Answer Peripheral — similar to n-hexane Other — uncoordinated walking /reveal /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 …” #reveal button: Answer … slowness in response time, impaired hand-eye coordination, and diminished concentration ability. /reveal 2. Which chemical agents in the workplace are known to be able to cause acute intoxication in workers? #reveal button: Answer Many organic solvents (because they are designed to be fat solvents, they are especially harmful to the myelin sheath) and carbon monoxide. /reveal 3. Management of occupationally-induced neurological problems consists primarily of what two strategies? #reveal button: Answer identification of the neurotoxin causing the disease removal of the worker from further exposure to the neurotoxin. /reveal /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. #reveal button: Answer 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. /reveal 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? #reveal button: Answer 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. /reveal 3. Summarize the neurologic symptoms most often seen in workers overexposed to lead. #reveal button: Answer Fatigue, irritability, difficulty in concentrating, inability to perform tasks requiring sustained concentration, arm muscle weakness. /reveal 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. #reveal button: Answer /reveal 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.) #reveal button: Answer Remove from exposure. Medical assessment required. A physician shall be consulted. /reveal 6. Review the occupational health and safety regulations for your province. Summarize the regulations regarding elemental mercury exposure in the workplace. #reveal button: Answer 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. /reveal 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. #reveal button: Answer Inhibit acetylcholinesterase resulting in overactivity of parts of the autonomic nervous system, inhibition of skeletal muscles, and inhibition of other central nervous system functions. /reveal 2. Workplace neurotoxins can produce neurologic effects other than those associated with peripheral nervous system damage. List any three of these other effects. #reveal button: Answer Any three of those listed in Tables 2-6 on page 572 and 26-2 on page 574. /reveal 3. Management of occupationally-induced neurological problems consists of what two basic strategies? #reveal button: Answer 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? #reveal button: Answer Numbness and tingling of the hands and feet Motor function weakness in the fingers, toes, hands, and feet Muscle atrophy. /reveal 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. #reveal button: Answer Type 1: irritability, fatigue, difficulty in concentrating; loss of interest in daily events. Type 2: more severe Type 1 effects; sustained personality and mood changes, and impairment of intellectual function. Type 3: dementia with severe impairment of all cognitive functions. /reveal /activity