Exposure to Lead and Carbon monoxide in the workplace

Hygiene and toxicology
Lead and Carbon monoxide
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Introduction
While in the workplace, contaminants are inevitable. There exists a wide variety of contaminants
that could either be in liquid, solid or solid form. Exposure to substances may occur either
through skin absorption, ingestion into the food stream or through inhalation1. In most cases,
however, exposures occur by inhalation of specks of dust, gases vapors or fumes. Contaminants
can emanate from tracking in contaminants from other areas, cleaning processes and/or work
processes. Areas that are considered to possess a high risk of contamination in the workplace
include eating sections, places with dry waste and dust, construction and manufacturing areas,
chemical packaging areas and plant & equipment operation areas.2
Sources of exposure
i. Lead
Lead is a soft metal present in the environment in small quantities. Numerous lead compounds
can be formed when lead combines with other substances. While in the workplace, a person
could get exposed to lead in several ways. First, people working in places painted with lead-
based paints are at risk. When such paint chips off, it turns to dust which is then inhaled by
individuals posing a major threat when exposed for long periods of time.3 Casting or smelting
lead is another occupation that could cause lead poisoning. Both primary and secondary smelting
produces lead fume which is lethal when inhaled. Workers involved in removing coatings of lead
are also considered to be at high risk of exposure.4 Here, processes entailed includes sanding or
thermal stripping of old paints, maintenance of steel bridges, repainting petroleum tanks and
demolition of underground storage tanks. In these processes lead fumes and/or dust is produced
and acts as the contaminant.
ii. Carbon monoxide
Carbon monoxide is a tasteless, odorless, colorless and highly poisonous gas. The gas is slightly
soluble in water, non-irritant and lighter than air. Due to these properties and the fact its
production can occur accidentally when incomplete combustion occurs gives it the nickname
‘silent killer.’ It is a main industrial gas with a wide variety of applications in the manufacture of
bulk chemicals such as acetic acid.5 Employees in such areas of high production are highly
vulnerable to carbon monoxide exposure. Workers at major risks are those working in areas with

equipment with insufficient fuel burning or are faulty. These include engines, generators,
furnaces, and leaking vents or chimneys. When these types of equipment are unable to complete
combustion of fuel or are leaking, a worker is exposed to the carbon monoxide produced.6
Workers also working in the vicinity of gadgets and appliances with poorly maintained, sealed,
blocked or damaged flues are also at risk. Such flues are likely to cause leakages and subsequent
exposure of workers around them.
Applicable occupational exposure limits
i. Lead
In Singapore, the applicable or permissible exposure limits for lead in form of inorganic fumes
and dust are 0.15 milligrams per meter cubic (0.15 mg/m3). The limits for lead arsenate are also
0.15mg/m3. The limits for lead chromate are 0.05mg/m37. All these permissible limits are long
term. There is no provision for short-term occupational exposure limits, however. It is advised
that when skin rash or irritation occur upon exposure, the affected individual should seek
immediate medical attention.
ii. Carbon monoxide
The permissible exposure levels carbon monoxide are 25ppm2 and 29mg/m3. Booth the
provisions are for long-term exposure limits7. There are no set short-term permissible exposure
limits for carbon monoxide, however. Skin notations are also not applicable due to the fact that
carbon monoxide is a gaseous contaminant.
Toxicokinetics
i. Lead
Surfaces and air are the two primary media through which exposure to lead occurs. Absorption
subsequently occurs through for main routes which are percutaneous, ingestion, inhalation, and
transdermal. Size of the lead particles is an important aspect in the determination of the quantity
to be absorbed into the body.8 Generally, smaller particles are absorbed better than large particles
through both ingestion and inhalation routes. Following pulmonary or gastrointestinal
absorption, lead gains access into the bloodstream. More than 95% of the lead circulating in the
bloodstream is bound to the erythrocyte proteins. The remaining amount associates itself with the