Lead Toxicity - Clinical Features, Diagnosis, and Treatment

Introduction

Lead is a heavy metal. It is a naturally existing material in the earth’s crust. Although the universal use of lead has been stopped in many countries, it is still used in car batteries, solders, pigments, arms, ammunition, toys, jewelry, and weights. It is even used in radiation protection. However, lead is extremely harmful due to its non-biodegradable nature. Hence, lead toxicity poses a threat to humanity.

What Is Lead Toxicity?

Lead is a toxic metal. High lead levels can induce toxicity. It can affect adults and children. It is also called lead poisoning or plumbism.

What Are the Sources of Lead Exposure?

There are various sources through which lead exposure can occur.

• Ingestion of Food or Water Contaminated with Lead: Lead toxicity can occur due to ingesting fruits and vegetables grown in lead-contaminated soil. Lead is also used in water pipes. Hence, contaminated water is one of the prominent sources of lead. The absorption rate of lead is very high through contaminated water, i.e., 20 to 70 percent.

• Accidental Ingestion of Contaminated Soil, Dust, or Lead-Based Paint: Although banned, lead-based paint is still a cause of exposure in children. Old paint easily cracks and lead particles settle into the ground. In addition, small children have a natural hand-to-mouth behavior leading to unintentional lead ingestion. As children are more sensitive to low amounts of lead, lead toxicity has more grave consequences than adults.

• Occupational Exposure: Occupational exposure to lead is also a prominent threat. Occupational workers such as welders, miners, plumbers, battery manufacturers, and construction workers are at an increased risk of lead exposure.

What Are the Clinical Features of Lead Toxicity?

The clinical features of lead toxicity depend on acute or chronic exposure. Following are the signs and symptoms.

1. Acute Toxicity: The typical signs and symptoms of acute lead toxicity are muscle pain, weakness, tingling, and numbness. Other features include abdominal pain, nausea, vomiting, diarrhea, loss of appetite, weight loss, and constipation. Also, patients surviving acute toxicity can exhibit signs and symptoms of chronic toxicity.

2. Chronic Toxicity: Chronic lead toxicity involves multiple organs. The eyes, ears, liver, skin, bones, and teeth are commonly affected. A bluish-purple line formation on the gums is called the Burtonian line. It occurs on the deposition of lead sulfide due to the reaction of lead and oral bacteria. The body systems most seriously affected are described below.

• Renal System: The long-term accumulation of lead in kidneys leads to loss of kidney function. It is also called chronic renal insufficiency. Low levels of lead exposure also accelerate the condition.

• Central Nervous System: The brain is highly prone to lead exposure. Lead is known to interfere with central nervous system (CNS) neurotransmitters (signal transmitters in the body), such as glutamate. Glutamate is involved in learning and memory functions. Hence, children with lead exposure can suffer from learning disabilities and express aggressive behavior. A blood lead level (BLL) of 50 micrograms (mcg) per deciliter (dL) (mcg/dL) can permanently impair the CNS. As a result, short-term memory loss, depression, anxiety, and loss of coordination have been reported in adults.

• Reproductive System: Sperm count is reduced when BLL exceeds 40 mcg/dL. The sperm's structure and function are also affected. In women, chronic lead exposure causes miscarriage, low birth weight, and premature birth. Increased BLL is also associated with delayed puberty in females.

How Is Lead Toxicity Detected?

In the case of lead exposure, a thorough history is important. A complete physical examination of the affected individual should follow. Several methods are used to detect lead toxicity.

Blood Investigations:

• Blood Lead Level- BLL is the tool to detect lead toxicity. However, it can only indicate the amount of circulating lead in the blood due to recent or current exposure. It does not give any idea about the accumulated dose. Therefore, the Centers for Disease Control and Prevention (CDC) of the USA have set a BLL of 5 mcg/dL and 10 mcg/dL for children and adults, respectively.

• Erythrocyte Protoporphyrin Test: Erythrocytes are red blood cells. Protoporphyrin is involved in erythrocyte function. Lead toxicity is sometimes evaluated by measuring erythrocyte protoporphyrin (EP) because the latter increases with a rise in lead levels. However, EPT is also positive in iron deficiency anemia, which might lead to false positive results

Peripheral Blood Film: Peripheral blood film is viewed under a microscope after drawing a blood sample. Red blood cells show characteristic dots, also called basophilic stripping.

Imaging: Plain skeletal radiographs are very useful in detecting lead in bone. They may show a thick band at the neck portion of a long bone. Abdominal radiographs are important to detect any accidental ingestion, such as paint chips. X-ray fluorescence is another convenient imaging method.

Urine: Urine estimation of lead is a precise tool for detecting occupational exposure. Electrothermal atomic absorption spectrometry is the technique used for urinary lead measurement.

Biopsy: As lead accumulates in the kidneys, a biopsy is useful in seeing microscopic changes. Bone marrow biopsy is another technique for lead detection.

What Is the Management for Lead Toxicity?

The first and foremost step to treating lead toxicity is eliminating any potential cause. Different treatment strategies are available.

1. Supportive Care: Adequate hydration is a must. Whole bowel irrigation uses polyethylene glycol solution (PEG) to flush out lead. The principle is to remove it before its absorption. Further, endoscopic recovery of the ingested lead can also be done.

2. Chelation Therapy: Chelation therapy is recommended under the guidance of a toxicologist for BLL above 45 mcg/dL. Dimercaprol (British Anti-Lewisite- BAL), Succimer, and Calcium Disodium Ethylenediaminetetraacetic acid (EDTA) are the frequently used chelating agents in severe lead toxicity. BAL is administered intramuscularly (in the muscle) twice daily for three days. Lead has a greater affinity to calcium. Hence, a lead chelate forms by an exchange with Calcium-EDTA. A third-line chelating agent used is D-penicillamine. However, D-penicillamine is contraindicated in pregnancy.

3. Others: Various multivitamins are known to reduce the toxic effects of lead in the body. Vitamins B1, C and E are some examples. N-acetyl cysteine (NAC) is an antioxidant chelator. Alpha-lipoic acid, methionine, and homocysteine are sulfur-containing compounds beneficial in decreasing lead-induced effects in tissues. Garlic, coriander, and green tea have also been tried for their chelating and antioxidant properties in mild to moderate lead toxicity.

Conclusion

Lead toxicity is caused due to excessive blood lead levels. Lead exposure can occur through various sources. Prevention is better than cure, and with that thought, lead toxicity is preventable. Further, the best measure is to avoid exposure to lead. Proper education of children regarding lead, hygiene maintenance, and adequate nutrition is pertinent.