Lead is a significant contaminant because of its persistence and
the widespread exposure of past generations of children to lead
from a variety of sources. Lead also provides the best-documented
example of a contaminant that causes neurotoxic developmental effects
associated with low levels of exposure. The effects of low-level
lead exposure manifest as a cascade of health problems. These
are characterized by overall dysfunction of the central nervous
system including developmental deficits that can be observed as
lowered IQ, behavioural problems and poor performance
Source: Adapted from Wallace and Cooper (1986)
and USEPA (1986). United States Environmental Protection Agency,
"Air Quality Criteria for Lead," Volumes III-IV. Environmental
Criteria and Assessment Office (Research Triangle Park, North
Carolina, 1986) EPA-600/8-83/028dF.
How Are Children Exposed to Lead?
Children are exposed to lead mainly via ingestion, although
they can also inhale fine lead particles or dust. Lead exposure
can also be in utero. Lead becomes stored in bone and when
maternal calcium stores in bone are liberated for fetal skeletal
development, mothers who were exposed to high levels of lead throughout
life may give birth to infants with congenital lead poisoning.10
Health Canada suggests that Canadian children are most often exposed
to lead from food, air and drinking water.11
of exposure to lead are, however, multimedia and multi-route
as this diagram from the New South Wales EPA’s Web site suggests.
Since the removal of lead from gasoline in North America (as of
January 1, 1990, for Canada) children’s exposures and hence blood
lead levels have declined significantly. A 1994 intergovernmental
committee report cautiously estimated that, although levels have
been steadily decreasing since the 1970s when unleaded gasoline
was introduced, as many as 66,285 urban children in Canada may
have blood lead levels greater than the current level of concern
"It has been calculated by the World Health
Organization that a child’s lead exposure of 3.7 micrograms/kg/day
will result in a blood lead level of 10 micrograms/dL. The
actual exposure would be 0.06 mg13
or perhaps the amount of pure lead that could fit on the
head of a pin. It is no wonder that extreme lead poisoning
can result from childhood exposure to dust and flakes of old
lead-bearing paint which can typically contain 20% or even
as much as 50% pure lead… It is easy to see how very low levels
of lead contamination from a multiplicity of sources can approach
or exceed the amount needed to contribute to a blood lead
level of 10 micrograms/dL. "14
Despite the removal of such a significant source of lead exposure
in the environment (i.e., lead in gasoline), there are still many
potential ways by which children can be exposed to lead. Because
of lead’s persistence and binding to soil and dust particles, researchers
have recently suggested that soil around heavily trafficked areas
is a significant reservoir of lead.15
Children are also exposed to lead from industrial and household
sources. These include primary and secondary lead smelters and various
industrial activities that result in lead emissions. In the home,
there can be many sources of lead. The most common source of lead
now is from old paint and the paint chips and lead dust that can
result in significant exposures to children. Other potential sources
are from lead solder in plumbing and canned foods, and cigarette
smoke. Where homes have older plumbing there is risk of lead contamination
of drinking water and prepared foods. Currently, these household
sources are the ones that pose the greatest risk to the average
However, there seems to be a continual supply of new and unexpected
sources of exposure to lead in a variety of consumer products, including
items such as some plastic toys, plastic mini-blinds, imported crayons
Some imported items and
traditional or folk remedies used by people from South and Central
American, Asian and Middle Eastern countries have also been found
to contain high amounts of lead.
The greater exploratory behaviour of children
of different ages may bring them into more frequent contact with
contaminants in their environment. Exposure to lead via dust
(whether from outdoors or from household items that release lead
particles) may be the most important route in young children, especially
those exhibiting pica and frequent hand-to-mouth behaviour.17
Infants and small children are also particularly vulnerable to exposure
via direct ingestion of contaminated soil since they frequently
put objects (and their hands) in their mouths. This behaviour, called
pica (eating of non-food items, including soil) is common in many
toddlers and children.18
Neurodevelopmental Effects from Lead Exposure
Because of the rapid neuronal growth and extensive synapse formation
that occur in the nervous systems of very young children, exposure
to lead prior to age three is particularly hazardous.
Meta-analyses of the relatively enormous body of scientific data
on children’s exposure to lead have determined that in children
under age four there is about a two point decrease in IQ
with an increase in blood lead from 0.5 to 1.0 micromoles/L (10
to 20 micrograms/dL).19 The current blood
lead level of concern is 0.5 micromoles/L (10 micrograms/dL), as
established by the US Center for Disease Control in 1991. A growing
body of researchers suggests, however, that there are a number of
troubling behavioural and cognitive effects from exposure to levels
below the concern level, including attention deficit hyperactivity
disorder (ADHD) and learning disabilities in school age
children.20 It is also generally believed
that there is no real "threshold" for these neurotoxic
effects from lead, as they can be demonstrated down to blood lead
levels of 1 micrograms/dL.21
Questions to Ask
Given that there are a number of potential ways that a child may
be exposed to lead, questions must cover the fundamental areas as
outlined by the CH2OP framework.
To determine whether, and in what way, the child has been exposed
to lead, and to ensure that such exposure is eliminated, the following
questions are relevant to ask:
- Are there local sources of potential lead exposure, such
as a lead smelter operation or battery recycling plant, etc?
Since the elimination of lead in gasoline in this country in 1990,
industrial sources of lead represent a reason we still may find
some children with higher than average blood lead levels.
- What is the age of the home?
Older homes (prior to 1950) are more likely to have lead plumbing
or copper pipes with lead soldering, which can affect
the lead content of tap water. They are also more likely to have
lead painted surfaces. If the home is in disrepair and has
peeling paint, there is greater likelihood that the child will be
exposed to lead in paint chips or lead dust on surfaces.
- Was there any recent renovation work done?
Depending on the age of the home, this could signal possible exposure
to lead dust from old paint.
Hobbies of Household Members
- Is lead used in hobby materials?
Lead solder used in stained glass, certain enamels and pottery
glazes have high lead content.
Restoration of old painted furniture may involve exposure to lead
paint. If a household member works on automotive repair as a hobby,
there are a number of potential sources of exposure to lead from
- What is the occupational history of the parents?
If parents are exposed to hazardous substances such as lead through
their work, this may mean lead dust is brought home if proper clean
up is not observed. Exposure to lead may occur to someone in the
home renovation business or in auto repair.
- Does the child exhibit pica behaviour?
Children who have a penchant for eating non-food items, especially
soil or dirt, have a greater risk of exposure to lead in their environment.
- Does the child use a pacifier, suck his or her thumb or exhibit
frequent hand-to-mouth behaviour?
Such behaviour increases the risk that children will ingest any
lead dust that they come in contact with. One study demonstrated
that the use of a pacifier, in particular, was associated with increased
odds for elevated blood lead, indicating that the pacifier provided
perhaps a constant source of exposure to small amounts of lead dust.23
- What is the child’s nutritional status, dietary intake of
calcium and iron levels?
Low dietary calcium is associated with increased gastrointestinal
absorption of lead, and iron-deficient children are more likely
to eat soil which can expose them to contaminants, lead among them.24
Given that a number of unusual sources of lead have been documented
of late (e.g., imported crayons, candle wicks, toys, accessories,
etc.), the physician may have to probe further if none of the above
questions highlights an obvious exposure.
Assessing Exposure to Lead
A test of blood lead levels is the only dependable indicator of
a child’s current exposure to lead. Acute lead poisoning is associated
with children’s blood lead levels above 3.4 micromoles/L (70 micrograms/dL).
At this exposure the patient would require hospitalization as there
is likely to be damage to the peripheral nervous system, causing
severe health effects such as muscle and abdominal pain, mental
symptoms, paralysis, coma and even death. Exposure at such high
levels is quite infrequent and unusual these days in Canada.25
There is however, a continuum of neurotoxic symptoms in
children linked with blood lead levels well below 3.4 micromoles/L.
For blood lead levels between 0.48 and 1.93 micromoles/L (10 and
40 micrograms/dL, respectively), the associated neurotoxic effects,
while "clinically invisible," are significant nonetheless.
In Ontario, limited data indicate that currently the average blood
lead level for children is about 0.14 micromoles/L (3 micrograms/dL).26
Although these average levels are below the current "concern
level," the actual distribution of blood lead levels indicates
that approximately 5% of the children in this country do have blood
lead levels that are above or around the intervention level.
Who should be tested for blood lead levels?
From Wallace and Cooper, 1986. With permission.
We do not have universal screening for blood lead in Canada. Some
sources recommend that if the answer to any of the following questions
in this simple personal risk assessment is "yes"
or "not sure," the physician should consider a
screening test for blood lead levels, especially in children younger
than three years.27
- Does the child spend substantial amount of time in a home or
facility that was built before 1950?
- Does the child spend substantial amount of time in a home or
facility that was built before 1978 that has undergone renovations
or remodeling during the previous six months?
- Does the child have a sibling or playmate who has been treated
or followed up for lead poisoning?
- Has the child been seen eating paint chips?
Personal Prevention of Exposure to Lead
- Check the house for sources of lead in plumbing pipes and replace
older types (prior to 1989) that may contain or be made of lead
(e.g., lead pipes, or old lead-soldered copper pipes, old brass
pipes, faucets and fittings).
- Only cold water from taps should be consumed and patients should
practice daily "flushing" in the morning. That is, they
should run tap water vigorously for a few minutes until water
runs cold to reduce the drinking water content of lead that accumulates
in standing water.
- Before embarking on renovations where removal of old paint may
be involved, consult appropriate sources on how best to avoid
- Parents can instill frequent hand-washing behaviour in their
children to reduce their exposure.
Suggested Web Sites
From Health Canada’s "It’s Your Health" series, Home
Renovations: Removing Lead-Based Paint
The B.C. Ministry of Health’s web page,
Lead Paint in the Home
The US National Safety Council’s Environmental Health Center
Lead Program, "Home
Repairs and Renovations: What You Should Know About Lead-Based Paint"
Further Recommended Resources
in Your Home, 1997, 23 p.
This booklet, prepared by Health Canada and Canada Mortgage and
Housing Corporation, provides readers with information about the
effects of lead in and around the home, explaining the risks to
infants, young children, pregnant women and the developing fetus. Available in PDF format.
It’s Your Health: Lead and Human Health
The Learning Disabilities Association of Canada’s brief, "Watch
Out for Lead"
Mercury is a substance that occurs naturally in the environment
in low levels and in the past was emitted from various industrial
processes. Although most such industrial uses have been eliminated
or drastically reduced in Canada since the 1970s, there is still
residual evidence of mercury contamination in fish near the former
sources of mercury pollution and significant amounts entering the
aquatic environment from all sources. Elemental mercury is the form
of mercury found in thermometers, thermostat switches, fluorescent
light tubes, disc batteries and dental amalgam used in tooth fillings. Improper disposal of such mercury-containing items is a significant
means by which we have environmental contamination with mercury.
Fish ingest methylmercury (MeHg, the organic, bioavailable form
of mercury) from water and it readily accumulates in their tissues. Health Canada releases fish consumption advisories when testing
and routine monitoring determine that fish contaminant levels are
elevated and/or research demonstrates health effects from levels
previously believed to be "safe" for consumption. Mercury
contamination is responsible for 99% of the advisories issued for
fish from inland waters, whereas Great Lakes fish are more often
contaminated with a variety of other pollutants (see POPs below).
Methylmercury is one of the most hazardous developmental neurotoxicants
known and research indicates that the developing fetal brain is
most susceptible to its adverse effects. There have been a number
of populations exposed to high levels of MeHg with tragic consequences
(e.g., Minimata, Japan, and Grassy Narrows and Whitedog28
Ojibway communities in Northern Ontario). Epidemiological studies
of fish-eating populations exposed to lower levels of mercury (e.g.,
Seychelles Islands, Faroe Islands) have not come to a consensus
on the risks to the fetal brain. However, there is some suggestion
that even in low amounts, mercury can delay developmental milestones
like walking and talking and may cause learning problems.
How Are Children Exposed to Mercury?
Exposure to mercury varies depending on the form it takes. Elemental
mercury, which is a liquid at room temperature, is inhaled as a
vapour and absorbed by the lungs. In an acute exposure it can have
local effects such as bronchitis and pneumonitis. Long-term exposure
to mercury vapour affects the central nervous system primarily,
producing early non-specific symptoms such as mild tremor, excitability,
insomnia, forgetfulness and anorexia (AAP, 1999). Symptoms progress
to more pronounced tremor and a condition known as erethism, marked
by diverse behaviour and personality changes.
In 1993, a dozen Hamilton school children between the ages of 9
and 14 found liquid mercury in the laboratory facilities of an abandoned
industrial plant.29 Over 250 other children
were eventually directly exposed to the mercury during play. Most
often, such exposures to elemental mercury are due to accidents.
There has been much controversy regarding the possibility of health
effects from exposure to elemental mercury in dental amalgam. The
evidence for effects from amalgam fillings suggests that although
there is some level of mercury exposure through this route, it is
insufficient to cause clinical toxicity except in isolated cases
of allergic reactions. Health Canada’s Position
Statement on Dental Amalgam and letter "Dear
Doctor" outline some key recommendations regarding the
use or replacement of dental amalgam fillings in children and pregnant
Because it is lipid soluble, organic mercury (e.g., methylmercury)
is ingested and absorbed by the gastrointestinal tract. Therefore,
mercury contaminated foods, especially fish, are primary sources
of organic mercury. Methylmercury can cross the placenta and is
released in breast milk, so children can be exposed prenatally and
also during infancy when they are breastfed.
In both inhalation and ingestion routes of exposure, there is a
high degree (over 80 to 90%) of absorption of mercury by the body.30
Questions to Ask
- Has the child come in contact with possible sources of mercury?
Depending upon the degree of symptoms, an accidental exposure may
be suspected. Most mercury-containing devices and equipment have
been replaced and this is a rarer avenue of exposure. The amount
of mercury in sources, such as an old-style thermometer, is typically
too small to produce a clinically significant exposure.31
The physician may also want to ascertain if an adverse reaction
to a mercury amalgam tooth filling is likely.
- Does/did the patient consume sport fish or wild game? Did
the mother consume sport fish before or during her pregnancy?
Exposure to methylmercury is most commonly from food sources, especially
fish that are caught in local waters.
Assessing Exposure to Mercury
- Because methylmercury collects in red blood cells, whole
blood concentrations are a possible clue to excess mercury
exposure. In the general population blood mercury levels are typically
about 1.5 micrograms/dL or less. Five micrograms/dL blood mercury
represents an apparent threshold for symptoms of toxicity.
- Mercury levels in hair are also a biomarker of exposure
with a level of 1 ppm being a measure typical for the unexposed.
Preventing Exposure to Mercury
Physicians can counsel patients on a number of different choices
in their diet and regarding personal activities, particularly if
they are considering having children or are pregnant.
- Women of childbearing age and children under age 15, should
avoid or limit meals of sport fish and wild game
as these may be potential sources of exposure to bioaccumulating,
biomagnifying contaminants such as POPs and heavy metals.
- Clearly, patients should not be advised to avoid fish consumption
altogether as eating fish provides an important nutritional benefit
and fish oils are an unique source of certain essential fatty
acids that are important in brain functioning and otherwise beneficial
to health. Commercially available, store-bought fish are indeed
considered safe sources since they are monitored by government
agencies so patients should be reassured that not all fish
are considered harmful.
- If they routinely eat fish caught for sport, they should be
aware of the species and waterways that have the highest contaminant
levels. Generally larger species, which are higher up on
the aquatic food chain, and older fish, will have the highest
levels stored in their fatty tissues. For example, certain species
such as walleye and northern pike, which feed on
other fish, have higher contaminant levels than species such as
whitefish, which feed on non-fish organisms.
- Also, there are recommended cleaning and cooking methods that
will reduce the amount of contaminants ingested. In particular,
skin and fat of fish should be avoided as prime depots
of stored contaminants.
- In Ontario, the Guide
to Eating Ontario Sport Fish is published annually in print
(distributed free in beer stores and at fishing licence agencies)
and online. The guide gives detailed recommendations for reducing
exposure to contaminants in sport fish.
- Other provinces have similar resources. For example, in Quebec,
Fleuve, the online newsletter for the St. Lawrence Vision
2000 Web site, presents reports on risks from eating St. Lawrence
marine life. See. for example, "Monitoring
poisonings linked to the consumption of shellfish from the St.
- People who eat sport fish must also make themselves aware of
special advisories. For example, in order to synchronize
with more rigorous Health Canada guidelines for consumption of
mercury, the Ontario Ministry of the Environment issued an advisory
in July 1998 that women of childbearing age and children
under 15 should eat only the least contaminated fish (as outlined
in the Guide).
- These two groups should also consume no more than 1 or 2
meals per month of certain types of fish - shark, swordfish
and fresh (but not canned) tuna - as these are known to be generally
higher in mercury contamination.
- Primary prevention requires that we all be aware of sources
of mercury and reduce input to the environment. Therefore as individuals
we can dispose of mercury-containing items (such as disc batteries
and fluorescent tubes, etc.) at appropriate hazardous waste
Further Recommended Resources
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