Lead exposure can cause permanent mental impairment
Prof. Dr. NasirSulman
Department of Special Education
University of Karachi
Lead poisoning is a serious and sometimes fatal condition. It occurs when lead builds up in the body. Lead is a highly toxic metal and a very strong poison. It is found in lead-based paints; including paint on the walls of old houses and toys. It is also found in:
- art supplies
- contaminated dust
- gasoline products
Lead poisoning usually occurs over a period of months or years. The poisoning can cause severe mental and physical impairment. Young children are most vulnerable to lead poisoning. Children get lead in their bodies by putting the lead containing objects in their mouths. They may also be poisoned by touching the lead and then putting their fingers in their mouths. Lead is more harmful to children because their brains and nervous systems are still developing. Severe lead poisoning is treated with chelation therapy and EDTA. However, damage from lead poisoning cannot be reversed. Common sources of lead include:
- house paint
- toys and household items
- bullets, curtain weights, and fishing sinkers made of lead
- pipes and sink faucets, which can contaminate drinking water
- soil polluted by car exhaust or chipping house paint
- paint sets and art supplies
- jewelry, pottery, and lead figures
- other types of art hobbies and projects
- storage batteries
- Kohl or kajol eyeliners(used more in other countries)
- Some traditional ethnic medicines
Symptoms of Lead Poisoning
Symptoms of lead poisoning are varied. They may affect many parts of the body. Most of the time, lead poisoning builds up slowly. It follows repeated exposures to small quantities of lead.Lead toxicity is rare after a single exposure or ingestion of lead.Signs of repeated lead exposure include:
- abdominal pain
- abdominal cramps
- aggressive behavior
- sleep problems
- loss of developmental skills in children
- loss of appetite
- high blood pressure
- numbness or tingling in the extremities
- memory loss
- kidney dysfunction
Since a child’s brain is still developing, lead can lead to mental impairment. Signs of mental impairment may include:
- behavior problems
- low IQ
- poor grades at school
- problems with hearing
- learning difficulties(short and long term)
- growth delays
A high, toxic dose of lead poisoning may result in emergency symptoms. These include:
- severe abdominal pain and cramping
- muscle weakness
- stumbling when walking
- encephalopathy, which manifests as confusion, coma and seizures
In 1890, the first case of lead poisoning was discovered in Australia. However the source of the lead was not traced to the paint on the verandahs and railings until 1904. In the United States the first recorded case of lead poisoning occurred in 1914 when a little baby ate the paint chips from his crib; this characteristic of children to taste everything the touch is referred to as pica.
Most of the dysfunctions produced by the absorption of lead are due to lead’s ability to mimic and inhibit the actions of calcium. In humans the lead is directly absorbed, distributed, and excreted. Once in the bloodstream lead is distributed to three main compartments: blood, soft tissue (kidney, bone marrow, liver, and brain), and mineralized tissue (bones and teeth). Lead effects children and adults in different ways. Low lead levels in children can cause the following side effects:
- Nervous system and kidney damage.
- Learning disabilities, attention deficit disorder, and decreased intelligence.
- Speech, language, and behavior problems.
- Poor muscle coordination.
- Decreased muscle and bone growth.
- Hearing damage.
- Seizures, unconsciousness, and death.
In adults high levels of lead in their systems can cause the following:
- Increased chance of illness during pregnancy.
- Harm to a fetus, including brain damage or death.
- Fertility problems (in men and women).
- High blood pressure.
- Digestive problems.
- Nerve disorders.
- Memory and concentration problems.
- Muscle and joint pain.
Once lead enters the body it interferes with normal cell function and physiological processes. Some of the physiological effects of lead include harm done to the peripheral and central nervous system (PNS, CNS), blood cells, metabolism of vitamin D and calcium, and reproductive toxicity. The nervous system seems to be the most sensitive to lead poisoning.
Neurons are the functional unit of the nervous system and are specialized for the transmission of signals from one location to the next. The dendrites of the neuron receive the input signal and relay it to the rest of the neuron. The axon of the neuron relays this input signal in the direction of its tips. The tips of the axon have specialized endings known as synaptic terminals that relay the signal to other cells by using a chemical messengers, neurotransmitters. The neuron will release the neurotransmitter molecules, located in synaptic vesicles, into the synapse only when an action potential arrives and depolarizes the surface of the synaptic terminal that before the cleft. Calcium ions play an important role in the nervous system; they help convert the electrical pulse into a chemical signal. The depolarization of the presynaptic membrane causes the calcium ions to travel through voltage gated channels into the neuron. The sudden increase in the concentration of calcium triggers the synaptic vesicles to fuse with the presynaptic membrane, spilling the neurotransmitters into the synaptic cleft by means of exocytosis. The neurotransmitters then go on to diffuse through to the postsynaptic cleft, which is the plasma cell body (or dendrite) on the other side of the synapse.
Cells absorb lead through the same channels they absorb calcium from. The drugs that regulate the intake of calcium also increase the amount of lead uptake. High levels of lead decrease transport of calcium and vice versa, therefore these two metals function as competitive inhibitors. Lead can enter through the same ion channels as calcium and regulate the activity of those channels to uptake more lead into the cell.
Lead, even at low concentrations, has the ability to increase the basal release of the neurotransmitters from the presynaptic nerve endings. This can occur both in the PNS and CNS. Micromolar concentrations of lead can cause the spontaneous release of dopamine, acetylcholine (ACh), and gama-aminobutyric acid (GABA). Control movement and emotional response are some of the brain processes that are affected by dopamine. An acetylcholine receptor has the responsibility for transducting nerve impulses to muscular contraction. GABA is an amino acid classified as a neurotransmitter. GABA is thought to play a role in the secretion of growth hormones according to some studies. Lead can also block the release of neurotransmitters when the action potential is taking place. This double effect of lead can have serious consequences on a developing nervous system. It can result in a decrease of pruning, what shapes the early brain, of an infant. The early brain, which has more synapses than an adult brain, is patterned according to the stimuli received during development. If there is an increase in neural activity, brought about by lead, the development process can be inhibited and have permanent effects on synaptic anatomy and function of the brain. It is believed that this is one of the causes of learning and behavioral problems that occur in children.
In the CNS lead increases the permeability of the blood-brain barrier (BBB) which produces brain edema (an accumulation of fluid in the body tissues or cavities that causes swelling or distention). Usually the BBB seals the neural tissue from the circulating blood; this is done by linking a series of epithelial cells together. This arrangement would only let solutes pass through via specialized transport proteins. Lead exposure causes a disruption in the BBB allowing large molecules, such as albumin, to enter a developing brain. Osmotic pressure causes ions and water to follow resulting in edema of the brain and intracranial pressure. With the pressure increasing towards the systemic blood pressure, a cerebral perfusion decrease causes ischemia. It is believed that lead changes the functional state of BBB’s endothelium, which might be losing their ability to distinguish between outside tissue and the brain. Lead poisons the astrocyte, an important component of the BBB. With the BBB despecialized the neurological development of a maturing child is altered.
Lead, a metal that can be found everywhere, can cause irreversible damage to the body’s nervous system. The damage caused by lead ranges from learning disabilities to high blood pressure and to death. Lead poisoning can also have hematologic and endocrine effects in the human body. In most cases the symptoms of lead are misdiagnosed and people are unaware of the damage that can be caused by lead. It recent years more attention and research has been directed towards lead poisoning and its effect on the human body.
Lead poisoning is diagnosed with a blood lead test. This test is performed on a standard blood sample.Lead is common in the environment. Low levels in adults are not harmful. However, low levels in children are a cause for concern. Normal lead levels vary by age group. The amount of lead in the blood is measured in micrograms per deciliter (mcg/dL).
For adults, a normal result is less than 20 mcg/dL. Slightly higher levels may not be serious. Treatment is recommended if the adult has symptoms of lead poisoning. It is also recommended for a blood lead level greater than 60 mcg/dL.
For children, a normal result is less than 10 mcg/dL. Any level higher than normal should be monitored closely. The source of lead should be immediately removed. A level greater than 45 mcg/dL should always be treated. Levels of 10-25 mcg/dL have been associated with impaired neurobehavioral development in children. Levels of 25-50 mcg/dL may be associated with headache, irritability, and early nerve problems. Levels of 50-70 mcg/dL are associated with moderate toxicity, and levels greater than 70-100mcg/dL are associated with severe poisoning.
Additional tests could include blood tests to look at the amount of iron storing cells in the blood, X rays and possibly a bone marrow biopsy.
The first step of treatment is to locate and remove the source of the lead. Keep children away from the source. If it cannot be removed, it should be sealed. Call your local health department for information on how to remove lead. They can also help you reduce the likelihood of lead exposure.
In more severe cases, a procedure known as chelation therapy can be used. This treatment binds to accumulated lead. The lead is then excreted in urine. Activated charcoal can be used to bind the lead in the gastrointestinal tract and substances which encourage elimination via defecation(cathartics) may also be used. A chemical called EDTA may also be used but it can be hard to reverse the effects of chronic exposure to lead.
Simple steps can help you prevent lead poisoning. Some tips include:
- Avoid or throw away painted toys and canned goods.
- Keep your home free from dust.
- Use only cold water to prepare foods and drinks.
- Make sure everyone washes their hands before eating.
- Test your water for lead. If lead levels are high, consider using a filtering device. You can also drink bottled water.
- Clean faucets and aerators regularly.
- Wash children’s toys and bottles regularly.
- Teach your children to wash their hands after playing.
- Use lead-free paint in your homes.
- Screen young children for blood lead levels.
- Avoid areas where lead based paint may have been used
What Can Be Expected After Treatment?
Adults with moderate exposure usually recover without any complications. In children, recovery can take time. Even low lead exposure can cause permanent mental impairment.