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Delayed neurotoxicity in monkeys exposed developmentally to methylmercury
1Toxicology Research Division, Bureau of Chemical Safety, Health and Welfare Canada, Ottawa, Ontario.
Neurotoxicology
|January 1, 1989
Summary
Long-term methylmercury exposure in monkeys caused lasting neurological deficits, including impaired motor skills and sensory function, even years after exposure ended. This highlights the persistent neurotoxicity of methylmercury.
Area of Science:
- Neuroscience
- Toxicology
- Primatology
Background:
- Methylmercury is a potent neurotoxin with potential for long-term health effects.
- Understanding the chronic and delayed effects of methylmercury exposure is crucial for public health.
- Non-human primates serve as valuable models for studying human neurodevelopmental and neurodegenerative conditions.
Purpose of the Study:
- To investigate the long-term neurological consequences of early-life methylmercury exposure in non-human primates.
- To determine if methylmercury toxicity manifests with a delayed onset after exposure cessation.
- To assess fine motor skills and sensory-perceptual functions in methylmercury-exposed monkeys.
Main Methods:
- Five cynomolgus monkeys (Macaca fascicularis) received daily methylmercuric chloride (50 µg/kg/day) from birth to 6.5-7.0 years.
- Blood mercury levels were monitored throughout the exposure period and post-cessation.
- Neurological assessments, including fine motor task performance (raisin retrieval) and clinical evaluations (sensory testing, motor coordination), were conducted at approximately 13 years of age.
Main Results:
- Blood mercury levels ranged from 0.6-0.9 ppm during dosing and rapidly decreased below 0.01 ppm after cessation.
- At approximately 13 years of age, methylmercury-exposed monkeys exhibited impaired fine motor skills, taking longer to retrieve raisins compared to controls.
- Clinical neurological assessments revealed reduced sensitivity to touch and pin-prick, along with increased clumsiness and slower movement in the exercise cage among exposed individuals.
Conclusions:
- Early-life exposure to methylmercury can result in persistent neurological deficits that manifest years after the cessation of exposure.
- Methylmercury's neurotoxic effects can include long-term impairments in motor control and sensory perception.
- These findings underscore the importance of minimizing environmental mercury exposure due to its potential for chronic and delayed neurotoxicity.