Lead in the Environment, and Health

Chemistry

Sources 

Health effects 

Risk reduction 

Chemistry, Pb

Lead occurs naturally in the earth's crust, usually as lead sulphide PbS (galena) -see image (right). However, as a result of human activity, in the atmosphere nowadays lead is found mainly as PbSO₄ and PbCO₃. 

Lead is malleable, and relatively low melting point, and therefore it has been used since ancient times to transport water, and found with copper Cu in metal alloys e.g. in small quantities within brass (with zinc Zn) and bronze (with tin Sn). 

Indeed lead poisoning is probably the oldest recorded industrial (occupational) disease. 

The image (right) shows a lead organ in Oxford, England. 

Lead has been used, as an organic alkyl compound - tetraethyl lead - to prevent 'knocking' in petrol (gasoline) engines by increasing the 'octane value' of the fuel. 

Lead is generally resistant to corrosion - but it will dissolve weakly in acid (low pH) water, or even in water of a very high pH. 
 
 

Sources of, and exposure to, lead

Occupational exposures may arise in:

• Plumbers, pipe fitters (exposed to solder) 
• Non-ferrous foundry workers 
• Glass manufacturers 
• Printers/ typesetters (less common nowadays)
• Lead miners, smelters and refiners (e.g. in the form of Pb, PbO, PbSO₄, and PbS) 
• Construction/ demolition workers 
• Petrol station attendants, Police officers, Traffic wardens 
• Battery manufacturers 
• Firing range instructors 
• Bridge reconstruction workers
• Other paint strippers. 

Workers  involved in high exposure jobs undergo regular health surveillance.)

Environmental exposures may arise from 

• Lead-containing paint, especially if burnt 
• Soil/dust near lead industries, roadways, lead-painted homes 
• Plumbing leachate 
• Ceramic ware (lead used to be present in some glazes) 
• 'Leaded' petrol (lead particles emitted from vehicles as alkyl compounds or as halides e.g. Bromide) 

Hobbies and Related Activities 

• Glazed pottery, and stained-glass making 
• Target shooting at firing ranges 
• Lead soldering (e.g., electronics) 
• Paint stripping and other Home "DIY" 
• Preparing lead shot, fishing sinkers etc

Substance Use/Abuse might arise from:

• Folk remedies or certain "Health foods" 
• Cosmetics 
• Petrol abuse: "sniffing" 

Environmental pathways - air

• lead particles emitted from vehicles as halides (e.g. PbBrCl, 2PbBrCl NH4Cl). 
• Lead particles are emitted from mines and smelters primarily in the form of PbSO4, PbO.PbSO4, and PbS 
• In the atmosphere, lead exists primarily in the form of PbSO4 and PbCO3. 

Environmental pathways - water

• Lead has a tendency to form compounds of low solubility with the major anions found in natural water although a significant fraction may be present in an undissolved form- colloidal particles or larger undissolved particles of lead carbonate, lead oxide, lead hydroxide

 

Environmental pathways - soil 

• Paint. 
• Dry and wet deposition of atmospheric lead
• Industrial contamination.

Absorption, distribution, and Health Effects

• Lead can be absorbed through ingestion into the gut (usually inorganic e.g. Ingestion of paint - pica in infants/children , or drinking of lead containing water), through inhalation - occupationally or environmentally of either inorganic or organic forms, or through the skin (especially for organic lead compounds) 

 
• Lead is bound to red cells (erythrocytes) in the bloodstream. Then, especially inorganic lead is distributed in blood, soft tissue and bones and teeth. Organic forms of lead are fat soluble, and therefore have a particular tendency to distribute into (and harm) the brain. 
• The half lives for lead in blood, soft tissue and bone are approx. 25 days, 40 days and 25 years respectively. It accumulates over a lifetime, being released very slowly 

 
• In blood lead is mostly associated with erythrocytes (red blood cells) - The image above shows basophilic stippling in red blood cells, resulting from the interference of lead with the sulphydryl groups responsible for the proper function of the enzymes responsible for synthesising haemoglobin. Thus abnormal haemoglobin is produced - hence the basophil stippling, and anaemia.

• Chronic effects on the nervous system - paralysis of motor nerves, poor aptitude (especially in children) and other effects on cognitive functions. 

• Lead has many other effects e.g. acute abdominal pain, kidney damage, high blood pressure and adverse reproductive consequences etc 

Risk reduction - prevention

 
• Plumbosolvency problem in UK -especially Scotland 
• Soil contamination is persistent even though original atmospheric sources reduced. 
• Large reservoir of lead in old paint - potential for high exposure rates. 

Examples of Preventive Measures - avoiding hazards, and reducing risks

• substituting, voluntarily or by legal prohibition, the use of lead in domestic paints, plumbing, toys, earthenware glazes, petrol etc. 
• raising the pH of the domestic water supply (i.e. rendering it more alkaline) by adding  lime (calcium hydroxide), or adding calcium phosphate 
• reduction of the risks of adverse effects of occupational exposure on health is achieved by substitution, enclosure, segregation, local exhaust ventilation, personal protection, and appropriate work practices i.e. by control

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