Occupational Lead Poisoning and Carbon Monoxide Toxicity: Hygiene & Toxicology 11

Hygiene & Toxicology 11
Hygiene & Toxicology 1
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LEAD
Occupational Lead Poisoning
Several jobs are associated with lead poisoning as shown below:
i. Smelting or casting lead.
This entails the production of lead fume through secondary or primary smelting, in addition
to lead foundries, and other operation such as recycling of scrap metal. Other synonym for
this task is lead production which comprises of melting, pouring or refining lead. Smelting of
lead produces lead fumes and dust that are inhaled directly through the respiratory system
thus exposing the worker to lead related complications Balali-Mood et al. (1).
ii. Removing of lead coatings
This includes thermal stripping or sanding of old paints through scraping, abrasive blasting,
welding or torch burning. Lead exposure risk can also be encountered in occupations such as
destruction of old structures, maintenance of steel bridge, painting of petroleum tanks,
destruction of highway and railroad bridges and underground storage tanks, and commercial
and institutional remodelling. The removal of lead coatings exposes the worker to lead
poisoning through contact of the paint chips with the skin, exposure of lead dust to the skin,
hair and respiratory system Lin et al. (2).
iii. Heating, spraying lead products or machining
This poses risk of exposure to lead poisoning through the production of lead fume or dust
generated by heating, machining or spraying lead products. The specific tasks in this category
include repairing of the radiator or battery, welding, grinding lead alloys. Repair and
extraction of water lines or cast iron soil pipes. Splicing and resplicing of electrical cables,
molten lead spraying, firing ammunition, and removal and renovation of stained glass
window Grover et al. (3).
iv. Production of lead products
The manufacture of lead products include tasks such as the manufacture of lead-acid battery
and glaze; making of lead-glazed pottery, manufacture of crystal glass, production of lead
joints, cables, pewter, stained or leaded glass, paint and ink, leaded plastics. Mixing and

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weighing of lead powders, manufacture of ammunition and electric appliances such as
ceramic coated capacitors and resistors Meyer et al. (4).
Occupational Exposure Limits applicable in Singapore
The Singapore Statutes Online (5) Permissible exposure level of lead under the first schedule
is as follows:
Long-term PEL
Lead, inorganic dusts and fumes, as Pb – 0.15 mg/m3b
Lead arsenate - 0.15 mg/m3b
Lead chromate as Pb -0.05 mg/m3b
and as Cr – 0.012 mg/m3b
Toxico-Kinetics of Lead
Lead enters into the body from the environment in different forms through inhalation, eating
and drinking, and through the skin. The absorption of lead is reliant on a number of factors
such as the physical form of lead, absorbed particle size, the transit time of the GI, and the
well-being status of the person. More importantly, there is an inverse proportion between the
particle size of lead and its absorption. Smaller particles are easily ingested.
 Lead absorption through inhalation
Most of the lead used today enters the body through inhalation (breathing). When lead is
scattered in the air in the form of dust or mist, it is easily inhaled and absorbed through the
lungs and the upper respiratory tract. The leading source of occupational lead absorption is
through inhalation of airborne lead Meyer et al. (6). The amount of lead absorption through
inhalation is dependent on the size of the lead particle, the volume of the patients respiratory,
the amount of deposition, and the mucociliary clearance of the inhaled lead.
 Lead absorption through eating and drinking
Lead absorption through ingestion occurs when one handles lead containing items such as
make-ups and then goes ahead and consumes food without proper hand washing. Once it gets
through the mouth and swallowed, lead is absorbed through the digestive system causing
various gastrointestinal tract complications Laidlaw et al. (7).

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 Lead absorption through the skin
Lead absorption through the skin is limited with less than one percent cases being reported.
Lead dust or particles can enter via the skin if it is broken. An example of lead that can go
through the skin is inorganic lead Ritchey et al. (8).
Distribution of lead
Most of the lead that is absorbed through inhalation or ingestion gets directly into the blood
stream. Once lead is in the blood stream, it is circulated throughout the body and stored in
different body tissues and organs Jones et al. (9). Some of the lead that is not stored is rapidly
sieved and out of the body and excreted. The absorbed lead which is not eliminated from the
body is exchanged mainly through three elements: blood, mineralizing tissues (bone and
teeth), and soft tissue (brain, spleen, muscles, heart, liver and kidneys).
 Blood
Lead enters the blood compartment immediately after absorption. Lead in the blood is mainly
located within the red blood cells (RBCs). Only a little portion of the total lead burden is
carried by the blood, nevertheless, it serves as the first recipient of absorbed lead and spreads
it throughout the body, making it reach other body tissues or for elimination as waster
products Khan et al. (10).
 Soft tissue
The movement of lead in and out of the tissues is rapid, and it is distributed to various organs
and tissues through the blood. Studies conducted on animals show that the liver, lungs and
kidneys have the highest concentrations of soft-tissue lead straightaway after severe
exposure. The brain is also a compartment of distribution. The study by Ragan et al. (11)
prevention of lead poisoning in children indicated that adults retain less amounts of lead in
soft tissue that children. The approximate half-life of lead in soft tissues is 40 days, and
selective brain build-up may take place in the hippocampus.
 Mineralizing tissue
A greater amount of lead absorbed and retained in the human body ends up being deposited
in the bones. Over 90% of the total lead body burden is contained in the bones and teeth of
adults, whereas, 75% is contained in children. There is also irregular distribution of lead in