TABLE OF CONTENTS Jan 2000 - 0 comments

Lead <b>CAS Number: 7439-92-1</b><i>Elemental lead</i><i>Molecular Weight + 207.19</i>

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By: Ronald Brecher, Ph.,D.
2000-01-01
Toxicity summary

Acute effects: Short-term exposure to high levels of lead can result in abdominal pain, constipation, cramps, nausea, vomiting and weight loss, reduced liver function, renal damage and neurological effects. In children, developmental defects -- including learning disabilities, lowered IQ, and behavioural abnormalities -- can occur without symptoms at blood lead levels above 10 micrograms/decilitre. At greater levels of exposure, headache, fatigue, irritability and malaise may occur. At high levels, encephalopathy, seizures and focal neurologic findings with imminent risk of death, permanent mental retardation and motor deficits may occur.

"Physical signs can be facial pallor, malnutrition, abdominal tenderness and pallor of the eye grounds."

Chronic effects: Lead is eliminated slowly from the body; its half-life in the blood is approximately one month for adults and 10 months for young children. Low level, long-term exposure can result in an increased body burden. Chronic exposure can adversely effect the kidney and the cardiovascular, immune, reproductive and central nervous systems. Symptoms often include weakness, weight loss, lassitude, insomnia, hypertension and disturbance of the gastrointestinal tract (constipation, anorexia, and abdominal discomfort or colic). Physical signs can be facial pallor, malnutrition, abdominal tenderness and pallor of the eye grounds. In children, chronic exposure can negatively impact the neurological, neurobehavioral and developmental systems and may result in decreased hearing acuity, growth retardation, decreased IQ performance and impaired mental development.

Carcinogenicity: The US EPA classifies lead as a Group B2 "probable human carcinogen" based on results of animal bioassays. The International Agency for Research on Cancer classifies lead and inorganic lead compounds as a Group 2B "possibly carcinogenic to humans."

Reproductive toxicity: Reproductive effects in men include reduced sperm count and abnormal sperm. In women, reduced fertility can occur. Lead can be transferred transplacentally and can result in reduced birth weight, reduced apparent gestational age and increased incidence of still birth and neonatal death.

Quick reference index

Description -- Lead is a naturally occurring non-ferrous element found within the earth's crust. It is a bluish-grey metal that's highly malleable and ductile. Rarely found pure in the environment, it is found in both organic and inorganic compounds (e.g., lead acetate, lead subacetate, lead dioxide, lead azide and lead chromate). Elemental lead is soluble in nitric acid and hot concentrated sulphuric acid and dissolves slowly in water that contains a weak acid. Lead salts are insoluble in water.

Use -- Lead is used to manufacture batteries, chemicals, paint, various metal products (e.g., sheet lead, solder and pipes) and ammunition. The amount of lead used in many products has been reduced due to potentially harmful health effects. The use of lead in gasoline was eliminated in North America in 1990. An estimated 70 per cent of lead used in the US is considered recyclable. Over 90 per cent of lead used to manufacture lead-acid batteries is recycled and converted to impure lead and lead alloys.

Sources -- Principle natural sources of lead are from lead-bearing rocks and volcanic emissions. Anthropogenic releases occur during the mining and smelting of lead-bearing ores, iron and steel production and the incineration of municipal waste. Lead is also released into the environment by products such as lead plumbing and solder, cigarettes, paints and ceramic glazes.

Exposure -- Exposure occurs primarily through inhalation and ingestion (drinking water and eating soil or foods that contain lead). For children, swallowing non-food items such as chips of lead-containing paint is an additional source of exposure. Minor amounts enter the body dermally. The major source of exposure to lead is variable and depends on many factors including occupation and the presence of leaded paints, plumbing and steel industries or hazardous waste sites in an environment.

Useful regulatory information

ValueAgencyParameter
WHOAcceptable Daily Intake3 mg/kg (adult)
Drinking Water Guideline Value0.01 mg/L
Health CanadaMaximum Acceptable Concentration Drinking Water (MAC)0.010 mg/L
0.015 mg/L
US EPADrinking Water Maximum Contaminant Level (MCL) (treatment technique
action level)
0.100 mg/m3
NIOSHRecommended Exposure Limit - TWA (10 hr. work shift)(for metallic lead,lead oxides)
0.050 mg/m3
(metallic lead,
OSHAPermissible Exposure Limit - TWA (PEL-TWA)inorganic lead and
organic compoundscalled soaps)
Ontario1/2 - hour Point of Impingement Criterion (POI)6 µg/m3
Ministry of24 - hour Ambient Air Quality Criterion (AAQC)6 µg/m3

EnvironmentDrinking Water MAC0.01 mg/L

ACGIHThreshold Limit Value - Time Weighted Average(for metallic lead,(TLV - TWA) (8-Hr. work shift)inorganic compounds)

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Lead  CAS Number: 7439-92-1   Elemental lead   Molecular Weight + 207.19
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Ronald Brecher, Ph.D., C. Chem., DABT is a Board-certified toxicologist and a founding partner of GlobalTox International Consultants Inc. with offices in Canada and the US. Contributing authors to this column are: Beta Montemayor and Savannah Gomes.
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