Many environmental health hazards are neurotoxins. Indeed, most pesticides
kill insects and other pests by disrupting the nervous system, and the warning
labels that accompany most petroleum-based solvents and solvent-based products
(turpentine, Stoddard solvent, gasoline, laquer thinner, etc)
warn specifically about confusion and other
neurologic symptoms, including
death, that can result from prolonged exposure. "Glue sniffing" is popular
because of the confused euphoria that it produces.
Although the effects of some neurotoxicants appear to be reversible, at least in the short-term, chronic
exposure may lead to irreversible destruction of neurons and neural pathways. In
many instances, the clinical manifestations of this damage may not become
apparent until later life as neurons naturally die. For example, the symptoms of
Parkinson's disease do not become apparent until approximately 75% of the
dopaminergic neurons implicated in Parkinson's disease have died. Mercury and lead are other known neurotoxicants.
Although neurological problems caused by environmental health
hazards can occur at any age, there is a tendency to talk about several general
mechanisms by which neurotoxicants damage the nervous system:
- reversible (?) neurotoxicity; and
- neurodegenerative damage.
to environmental health hazards, such as cigarette smoke or mercury, during
pregnancy may cause neurological problems and/or may lead to underweight
premature births. Premature babies are at special risk for brain damage.
Children with a learning disability may have verbal and mathematical difficulties, or may lack self-control and attention span. Attention deficit hyperactivity disorder (ADHD), dyslexia, and autism are all types of learning disorders.†
According to the National Academy of Sciences in 2000, exposure to known
toxic substances such as drugs, cigarette smoke, lead, PCBs and mercury cause
three percent of developmental and neurological defects in children.
mercury are discussed elsewhere in this website.
Reversible (?) Neurotoxicity
Short-term low-level exposure to solvents, alcoholic beverages or
mood-altering drugs such as Valium and cocaine, neurotoxic pesticides such as
the organophosphate (OP) pesticides (Dursban and Diazinon are familiar OP
pesticides in the Houston area), and oxygen-depleting chemicals such as carbon
monoxide and methylene chloride generally cause transient euphoria, sleepiness
or other neurologic symptoms. Whether or not there is subtle long-lasting but asymptomatic damage to neurons or their pathways from low-level exposure is
uncertain but unlikely except in susceptible individuals.
use or a single high-level exposure generally causes permanent damage, the
clinical manifestations of which often intensify with age. Exposure to
neurotoxic heavy metals such as lead and mercury in adulthood is less damaging
than during brain development, but it is unclear whether reducing exposure and
body loads completely reverses the symptoms. "Painter's Encephalopathy" and
"Mad Hatter's Syndrome" (from mercury exposure) reflect occupational exposure
to neurotoxic substances.
Alzheimer's Disease, Parkinson's Disease, and Lou Gehrig's Disease
are the more well-known neurodegenerative diseases, but more subtle
forms of neuronal damage that lead to mild tremor in one's hands,
difficulty with balance, memory loss or confusion are much more
common. These changes indicate dead or dying neurons and/or
disruptions in the pathways through which neurons communicate.
Among the environmental factors that
have been implicated in neurodegenerative diseases are occupational
exposure to strong electrical fields, lead,
solvents and herbicides. Occupational exposure to lead has been
associated with an approximately 3x greater risk of developing Alzheimerís disease.
Exposure to industrial chemicals may
lead to an earlier onset of Parkinsonís Disease, as well as an increase the severity of
Parkinsonian symptoms. Parkinsonís disease may also be linked to
pesticide exposure, and farmers who regularly use pesticides have a
higher incidence of Parkinson's disease than those who use few