There are nearly 1000 substances which have been identified as having, or possibly having, neurotoxic effects. Exposure to sufficient amounts of these chemicals, either in the work place or elsewhere, can cause neurological and brain problems. Likewise chronic exposure (long term, lower level exposure) can also have damaging effects.
For purposes of this website I will focus on four major categories of exposures that can have adverse effects on the brain:
Lead is the major culprit here. The most serious effects of lead exposure are on developing children. Exposure to lead through paint chips, or other sources, is suspected, blood test can be done to determine if there is ongoing exposure. Based upon the level found in the blood, the seriousness of the exposure can be estimated. It can also create neurological deficits such as wrist or foot drop and can result in decreased motor speed and strength. Federal standards regarding the minimum safe blood level have recently been lowered.
Mercury can cause brain damage involving the cerebellum, the basal ganglia and the visual centers of the occipital lobe (Feldman, 1982). Upon a mercury exposure which does not result in death we find breathing problems, motor slowing, clumsiness, tremor and mental dulling. Mercury levels can be detected in the urine and have been associated with short term memory deficits (P. Smith 1983).
Manganese is another metal which has been linked with brain damage. This type of exposure generally occurs with workers over a long period of time. Initial complaints may include drowsiness, dizziness, sleep disturbance with nightmares, clumsiness, trembling and difficulty learning.
Solvents and Fuels
Many of the complex organic compounds found in glues, paints and thinners have been found to cause neurological problems. Upon exposure, people complain of headache, dizziness, fatigue and mental confusion. Toluene particularly has been linked to long term neurological impairments including dementia, balance and coordination problems, visual problems and brain atrophy (Lazar 1983). Chronic exposure to solvents has been studied for many years and is well documented as resulting in abnormal EEG's, altered sense of smell, numbness or weakness in the extremities and cognitive deficits including problems with attention and memory and overall dulling. Emotional problems include depressive tendencies, anxiety and social withdrawal. Long term solvent exposure may result in an Alzheimer's type of syndrome.
There are many types of pesticides which have neurotoxic effects on humans. Upon immediate exposure, patients can experience headaches, blurred visions, slurred speech, and difficulty walking. Also, lung and organ failure can occur. Exposure can occur through breathing in of gases or the absorption of the chemical through the skin. Exposure can be acute or chronic.
Carbon Monoxide poisoning occurs frequently in the United States. It can occur when carbon monoxide, usually through the combustion of fossil fuels, takes the place of oxygen in the atmosphere. Unfortunately, carbon monoxide is not able to be detected in the atmosphere by the human senses. Therefore, many times persons exposed to threshold levels and above will loose consciousness because of lack of oxygen to the brain and death can commonly occur. Blood tests done at the emergency room or shortly thereafter can sometimes detect abnormal levels of carbon monoxide in the blood stream. Survivors of carbon monoxide poisoning show decrease in mental abilities, difficulty learning, and other neurological damage due to hypoxic injury (how the brain can be damaged because of lack of oxygen). Changes including depression, headaches, irritability, dementia and incontinence.
The safe level threshold in 10 ppm. Abnormalities in the globus pallidus or white matter can be seen on MRI in some cases.
A recent study at Duke University showed that frequent and prolonged application of the insecticide DEET in rats caused the neurons to die in regions of the brain that cause muscle movement, learning, memory and concentration. The author of the study Dr. Abou-Domia cautioned that the effects should cause concern in humans and further studies are needed.