Metal toxicity – Lead poisoning
Introduction
Metal toxicity occurs when the accumulation of metals (usually heavy ones) or metal ions in a body causes detrimental effects on one’s health. This can result from exposure to metals through various sources, such as contamination via food or water, medications or industrial processes. For its abundance in the world, lead poisoning is one of the most pervasive forms of metallic poisoning all over the globe, having severe adverse effects on both juveniles and adults.
Lead poisoning
Lead poisoning, or sometimes called plumbism or saturnism, is a form of metallic poisoning caused by the accumulation of lead in the body overtime. Lead is a naturally occuring heavy metal that occupies approximately 0,0013% of the Earth’s crust. It is also a neurotoxin and its presence in soft tissues can lead to neurological disorder as well as general health detriments like cardiovascular and renal system.
Mechanism of action
After exposure, lead is distributed throughout the body, especially in bones and soft tissues. Lead can interfere with several enzyme actions, all of which are vital for the functioning of our bodies. For instance, lead disrupts the biological process of synthesizing haem, a prosthetic group in the protein Hemoglobin in red blood cells, potentially causing anemia and other hematological issues. Moreover, lead ions are known to have the ability to mimic calcium ions, which can affect the calcium-dependent process severely (those include neurotransmitter release and cellular signaling). Lead accumulation adversely affects both the central nervous system (CNS) and peripheral nervous system (PNS), later leading to symptoms such as cognitive deficits, behavioral problems, and motor dysfunction. It also stimulates the formation of reactive oxygen species (ROS), which is the main cause of oxidative stress and neuronal damage, and further contributes to cellular injury and inflammation. In addition, lead can also affect immune cells, and this makes the body more susceptible to infections.
Symptoms
Symptoms of lead poisoning can vary depending on the duration of exposure. Symptoms usually develop over a long period of time as the metal builds up in the body from a chronic exposure but in some cases, acute exposure can also be observed if the dosage and intensity are high. Due to the solubility of organic lead compounds, they are usually considered to be more toxic than those inorganic ones, and therefore, the symptoms occur more rapidly. The metal ions predominantly attack the central nervous system, causing insomnia, delirium, cognitive deficits, tremor, hallucinations, and convulsions.
In adults
In adults, early symptoms are quite nonspecific, such as depression, loss of appetite, intermittent abdominal pain, nausea, diarrhea, constipation, and muscle pain, which can be mistaken for other health conditions. Other notable changes during early stages of lead poisoning include tasting unusual flavor in the mouth or having difficulties falling asleep.
In children
Pregnant women with elevated levels of lead in their blood are at great risk of a premature birth. Due to the small size of the body and the continuous state of growth and development, children are more susceptible to lead poisoning. Typical observations of those with lead exposure include loss of appetite, abdominal pain, vomiting, weight loss, constipation, kidney failure, learning disabilities, and behavioral problems.
Acute poisoning
Absorption of a large amount of lead over a short time period can result in shock (insufficient fluid in the circulatory system) due to the loss of water from the gastrointestinal tract. Immediate neurological signs are pain, muscle weakness, numbness and tingling. The patients also experience abdominal pain, nausea, vomiting and diarrhea. Lead poisoning also contributes to renal damage as well as hemolysis (rupture of red blood cells).
Chronic exposure
Chronic exposure is primarily associated with 3 main types: gastrointestinal, neuromuscular, and neurological. The nervous system usually undergoes intense exposure. Consequently, patients may develop loss of short-term memory, depression and loss of coordination. The muscles feel numb and tingling, and abdominal pain is reported in most cases.
Source of exposure
Lead is a ubiquitous environmental pollutant, most commonly found in deteriorating lead-based paint, renovation and repair or painting activities. In industrial areas, waste containing lead can be disposed directly into soil, accumulate overtime and become lethal. Old paints and cosmetics, especially white ones, contain a large amount of lead and can be absorbed through direct contact with skin or breathing.
Real-life case
A boy in Bangladesh suffered from lead poisoning after a battery recycling factory was built near his house. The factory produced thick, dark smoke which later covered all the leaves in the surrounding with soot. After the chronic exposure via breathing, he experienced extreme symptoms and although treated, he still suffered from concentration and memory problems.
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