Lead: Exposure and Hazards
Lead has been used by man
since about 4000 B.C. It is a very malleable metal and was one of the first
metals that man began to use for industrial purposes. Records of its adverse
effects date from ancient times. However, little attention was given to the
adverse effects of lead until the beginning of the 19th century. In recent
times, research has uncovered many of the mysteries concerning the toxicity of
lead. New and more subtle adverse effects of lead continue to be discovered. It
appears that the acceptable levels of lead exposure will continue to be lowered
as new findings are made. A striking fact regarding lead is that it is not an
essential nutrient and serves no useful function in the body.
Human lead exposure occurs
when dust and fumes are inhaled and when lead is ingested via lead-contaminated
hands, food, water, cigarettes, and clothing. Lead entering the respiratory and
digestive systems is released to the blood and distributed throughout the body.
More than 90 percent of total body burden of lead is accumulated in the bones,
where it is stored for decades. Lead in bones may be released into the blood
and re-exposes organ systems long after the original environmental exposure.
This process can also expose the fetus to lead in pregnant women.
Lead is commonly added to
industrial paints because of its characteristic to resist corrosion. Industries
with particularly high potential exposures include: construction work involving
welding, cutting, brazing, blasting, etc., on lead paint surfaces; most smelter
operations either as a trace contaminant or as a major product; secondary lead
smelters where lead is recovered from batteries; radiator repair shops; and
firing ranges. Oral ingestion may represent a major route of exposure in
contaminated workplaces. Lead soldering usually does not represent an
inhalation risk since controlling temperature of lead below 900°F (melting
temperature = 621°F) is effective in controlling lead fuming. Most exposures
occur with inorganic lead. Organic (tetraethyl and tetramethyl)
lead, which was added to gasoline up until the late 1970s, is not commonly
encountered. Organic forms may be absorbed through the skin, while inorganic
forms cannot.
The toxic nature of lead
is well documented. The most important aspects of lead toxicity are its effects
on the central nervous system, which may be irreversible; however, lead affects
all organs and functions of the body to varying degrees. The frequency and
severity of symptoms among exposed workers depend upon the level of exposure.
Pathways of Exposure
to Lead:
Air
Food
Soil
Water
Dust
Air: Leaded gasoline emissions are the
main contributor to airborne lead levels.
Food: Food made and sold in the
Changing from lead based can soldering technologies to welded can technology for sealing food containers may reduce the risk of lead exposure significantly. Some imported cans are lead soldered and if storing acidic foods (such as tomatoes or pineapple), may contain high levels of lead. Once opened, food should never be stored in lead soldered cans as this may further increase lead leaching from the seams.
Lead is present in some
food preparation and serving utensils such as cooking pots, pewter vessels,
china and others, from which it can leach over a period of time. This is
particularly true of older ceramics and pottery from
Soil: Apart from several unique
geological areas where natural lead levels in soil may be elevated, the natural
background level of lead in soil is usually 10 to 70 mg/kg. Soil may become
contaminated through historical industries, historical or contemporary uses of
lead or current unsafe lead management practices. Since lead does not
dissipate, biodegrade or decay, lead pollution deposited into soil and dust
remains a potential source of lead exposure.
Water: The major source of lead in
domestic drinking water is the corrosion of leaded plumbing materials in the
water supply and household distribution systems. Although in many parts of the
world leaded drinking water piping is very rare, contamination of drinking
water is more likely to arise from lead connectors (eg
goosenecks), lead-soldered joints in copper and lead-containing brass faucets
and other fixtures.
Several factors affect the
extent of lead contamination from a particular water delivery system including:
- corrosiveness of the water (pH, alkalinity and mineral
content),
- age of lead-soldered joints and other lead components
(the newer ones pose a higher risk),
- quantity and surface areas of lead materials
- standing time and temperature of water in contact with
leaded surfaces.
‘First draw’ water taken
from the pipes, particularly hot water, after standing unused (e.g. first thing
in morning) may pose a hazard in homes with lead piping or solder, brass
fixtures or fittings, PVC piping or where home-repair with lead solder
occurred.
Studies indicate that
domestic rainwater tanks pose particular problems, due to solder on the tanks
as well as fugitive dusts and emissions from nearby mining and smelter sites.
This may be an exposure pathways of particular concern to communities living
near major lead industry sites.
Lead is used in plastic
piping as a stabilizer and a pigment, but at levels less than 2% in the final
product. Lead in plastic piping appears to leach out significantly on initial
use followed by reductions in leaching.
Dust: Lead dust is perhaps the least
understood and most insidious factor in young children’s total lead exposures.
As interior or exterior lead paint ages, it ‘chalks’ into a fine dust of very
small particles. Households contain this fine dust as well as lead particles
from previous renovation activities, oil and industrial emissions accumulated
in soil and street dust tracked in by residents and pets. Ceilings, wall voids
and floor spaces as well as other housing cavities may contain lead dust.
Lead-bearing household dust can contaminate soft furnishings (e.g. carpets, lounges,
curtains), particularly if not removed or well-covered with plastic and taped
up during renovation activities.
Lead from these many lead
sources follows many pollution pathways to contaminate interior home
environments, residential yards and the rest of the natural environment. This
is particularly true of lead particles deposited on rigid surfaces (such as
footpaths, paved backyards, floors, etc) which do not bind to soil particles
somewhat diluting the lead exposure compared to lead in soils. Most pre-school
children are exposed to lead pollution through the ingestion of lead dust which
sticks to their hands or toys when playing on the ground (either inside or
outside).
Particles between 10-70 m m diameter are commonly generated by mechanical or
hand sanding and particles smaller than 40 m
m are invisible to the naked eye. Fine lead dust particles smaller than 100 m m are of particular hazard to children because:
- they adhere more strongly to the skin
- they are more soluble in the gastrointestinal tract
than coarser particles
- particles smaller than 10 m m diameter can be readily
absorbed through the respiratory tract.
Lead-safe housekeeping
techniques that minimize the quantity of lead
in dust and reduce the overall amount of dust are very important in reducing
lead exposures. Lead safe housekeeping techniques are also helpful in fighting
asthma.
LINKS:
Sources and Pathways of Lead in Our Environment
Lead Poisoning and Your Children
Health Effects of Lead Exposure and Occupational Exposure Criteria (NIOSH Site)
Characterization of Lead Exposure Among Bridge Repair Workers
Lead Exposure in Construction Industry (OSHA Site)
Last Update: January 9, 2007
By: Serdar Z. Elgun