Understanding Metal Fumes and Lead Toxicity in Industry

Metal Fumes and Vapors

Molten metal, due to its higher vapor pressure at the surface (proportional to temperature), releases fumes into the atmosphere. Oxidized metal fumes typically react with oxygen in the air and condense into solid particles smaller than one micron (µm), which remain airborne. These are termed metal fumes.

Smoke and metal fumes, along with inorganic metal powders such as lead and mercury, can cause toxic effects, irritation, or lead to pneumoconiosis. They are absorbed through inhalation or ingestion. Industrial hygiene experience indicates that poisoning via inhalation is more likely than ingestion.

Toxic smoke reaching the lungs can pass directly into the bloodstream, reaching various organs and tissues quickly. In contrast, most dust that reaches the stomach is subjected to detoxifying and filtering action before it can enter circulation.

Chronic poisoning, which manifests over weeks, months, or years, presents more intractable problems in industry than acute poisoning caused by a single exposure.

The severity of the risk posed by metal fumes depends on their solubility in organic fluids, which increases with the fineness of the particles.

Lead and Its Compounds

Diseases Associated with Lead: Lead poisoning, Plumbism, Saturnism.

Common Lead Compounds:

• Lead metal: Pb
• Lead monoxide: PbO
• Peroxide or lead dioxide: PbO₂
• Lead chloride, lead bromide, lead nitrate, and others.

Sources of Occupational Lead Exposure

Mining: Extraction, concentration, smelting, and refining of the metal.

Manufacturing: Alloys, plastics, ceramics, ammunition, and automobiles.

Chemical Industry: Manufacture of lead compounds, dyes, antioxidants, and pesticides.

Oil Industry: Handling mixtures of tetraethyl or tetramethyl lead with gasoline or cleaning tanks.

Construction Industry: Welding pipes and plates.

Other Industries: Handling ICEM vessels, printing, and metal foundries.

Routes of Entry for Lead

Respiratory: This is the most common route for fine particles and vapors. Vapors are produced when melting metal above 500 ºC. Material removed by bronchial mucus can subsequently be swallowed.

Digestive: Ingestion of larger particles due to unclean hands, or through contaminated cigarettes, food, and drink in the workplace.

Lead Metabolism

Inhaled lead has a retention rate of 40% to 60% in the lungs before entering circulation. Ingested Pb is absorbed through the intestinal tract at only about 10% efficiency.

Lead is found in the blood, liver, kidneys, brain, and especially the bone. Besides natural elimination via the respiratory tract, gastrointestinal tract (bile and feces), and urine, generalized discharges (colic) can occur.