Environmental Health Hazards: How Children Are Different from Adults

Abstract

In policymaking on environmental health, it is often assumed that the entire population is exposed to and reacts to environmental contaminants in a similar manner. However, this assumption is misguided, especially where children are concerned. This article presents the scientific basis for the impacts of the environment on children, showing how children are different from adults in the ways in which they are exposed to environmental contamination and the ways in which they react to it when exposed. Specifically, the article examines the changing physical and biological environments of children. Children at different stages of development have unique physical risk factors for certain types of exposure because of changing location, levels of mobility, oxygen consumption, eating patterns, and behavior. When children are exposed to contaminants, their developing biological makeup--the way in which they absorb, distribute, and metabolize chemicals--will also affect how their bodies deal with the foreign substance. Each of these factors, along with the customs, laws, and regulations that affect the way in which children are exposed to the contaminants, had implications for the well-being of children in the years to come.

Full text

Environmental Health
Hazards: How Children Are
Different from Adults
Cynthia F. Bearer
Abstract
In policymaking on environmental health, it is often assumed that the entire popula-
tion is exposed to and reacts to environmental contaminants in a similar manner.
However, this assumption is misguided, especially where children are concerned. This
article presents the scientific basis for the impacts of the environment on children,
showing how children are different from adults in the ways in which they are exposed
to environmental contamination and the ways in which they react to it when exposed.
Specifically, the article examines the changing physical and biological environments
of children. Children at different stages of development have unique physical risk
factors for certain types of exposure because of changing location, levels of mobility,
oxygen consumption, eating patterns, and behavior. When children are exposed to
contaminants, their developing biological makeup—the way in which they absorb, dis-
tribute, and metabolize chemicals—will also affect how their bodies deal with the for-
eign substance. Each of these factors, along with the customs, laws, and regulations
that affect the way in which children are exposed to the contaminants, has implica-
tions for the well-being of children in the years to come.
A
s the human population increases, its demands on the earth also
increase. Today, the demand for food, potable water, clean air,
energy, and manufactured goods; the need for solid and liquid
waste disposal; and the requirement for habitable land are all expanding.
With this expansion, increasing amounts of pollutants are released into
the environment, and more and more people come into contact with
polluted environments.
Interaction with polluted environments can have an adverse impact on
the health of humans and other living creatures. This impact is felt first
among the most vulnerable members of a population. Children, because of
their unique physical, biological, and social characteristics, are among the
most vulnerable members of our population.
We have become increasingly aware of the dangers posed by the
accumulation of pollutants in the environment and have looked to policy
11
The Future of Children CRITICAL ISSUES FOR CHILDREN AND YOUTHS Vol. 5
•
No. 2 – Summer/Fall 1995
Cynthia F. Bearer, M.D.,
Ph.D., is asssistant pro-
fessor of pediatrics in the
Department of Pediatrics
at Case Western Reserve
University.

THE FUTURE OF CHILDREN – SUMMER/FALL 199512
in the form of legislation, regulation, and private, voluntary action for pro-
tection. It may, however, be costly to identify and effectively deal with envi-
ronmental hazards, particularly when there are benefits to be gained from
the use of hazardous materials. Under these circumstances, effective poli-
cymaking depends on honest and accurate assessment of the risks posed
to all members of society, including children. For a variety of reasons, spe-
cial consideration should be given to protecting children in formulating
environmental policies: children are less able than adults to protect them-
selves, may be more vulnerable to particular toxins, and are not consid-
ered responsible for pollution. Crafting environmental policies responsive
to the special needs of children requires a thorough consideration of
these special needs and an understanding of how these needs may change
as children grow and develop.
This article presents the scientific basis for the impacts of the envi-
ronment on children. It describes the differences between adults and
children in physical, biological, and social environments, and highlights
why children should not be treated as “little adults” in developing envi-
ronmental policy.
Human Environments
Children exist within three broad types of
environments: physical, biological, and
social (see Figure 1). Each affects their
well-being, is at risk of degradation, and is
amenable to policy intervention. The
physical environment is anything that
comes in contact with the body. Air, for
example, is in constant contact with our
lungs and skin, and is a large part of our
physical environment. To define the phys-
ical environment precisely, it may be nec-
essary to divide a large environment into
smaller units, called microenvironments.
For example, in a room contaminated
with radon, the radon will not be evenly
dispersed; air near the floor has a higher
radon concentration while air near the
ceiling has a lower radon concentration.
Therefore, the environment of an infant
playing on the floor would be much dif-
ferent from that of an adult standing in
the room. These microenvironments can
differ enormously between adults and chil-
dren in many situations.
The biological environment consists of
the internal physiological workings of the
body as it takes up, processes, and inter-
acts with the substances it contacts. The
body has specific chemical pathways used
to digest, process, and excrete substances
found in air, food, and water. The multiple
steps by which a toxic hazard may result in
adverse health effects help illustrate the
complexity of the biological environment.
The steps are (1) absorption (how the
chemical gets into the body), (2) distribu-
tion (once inside the body, how the chem-
ical gets to each of the organs and in what
amount), (3) metabolism (how the body
processes the chemical), and (4) the toxic
action (how the chemical interacts with
the biochemistry of the body). Each of
these steps depends on the developmental
stage of the child because the child’s bio-
logical environment changes over time.
The social environment includes the
day-to-day circumstances of living in a fam-
ily or other setting as well as the laws and
regulations that affect day-to-day living.
Children, because of their continued devel-
opment and their different physical and
biological environments, are a unique
group of individuals in relation to toxic
hazards. If laws, regulations, policies, and
behavior do not reflect this fact, then chil-
Children are less able than adults to protect
themselves, may be more vulnerable to
particular toxins, and are not considered
responsible for pollution.

13
Environmental Health Hazards: How Children Are Different from Adults
dren may be unwittingly exposed to envi-
ronmental hazards. In time, children may
become bodies of evidence that environ-
mental degradation can have severe
impacts on the health of societies.
This article concentrates largely on the
physical and biological environments of
children at various developmental stages.
The social environment is discussed in
detail in the article by Landrigan and
Carlson in this journal issue.
Developmental Stages
A child’s vulnerability to environmental
exposures is closely related to his or her
developmental stage. Changes in growth,
hormonal levels, and biochemical makeup
continually occur. Developmental stages
are periods in a child’s life characterized
by the achievement of certain intellectual
and physical milestones. For organization-
al purposes, this article recognizes five
stages: the newborn (from birth to 2
months of age), the infant/toddler (2
months to 2 years of age), the preschool
child (2 to 6 years of age), the school-age
child (6 to 12 years), and the adolescent
(12 to 18 years). The fetus is considered as
a single separate stage, although there are
multiple critical stages of development
for the fetus.
1
The Physical Environment
Exposure to an environmental agent is the
first step in a sequence of environmentally
related health effects. Exposure may occur
at any point as people move through sev-
eral environments during the course of a
day. Adult environments include home,
work, and errands outside home and
work. Infants and children spend time at
home, school, day care, and play. Because
the environments of children are typically
different from those of adults and may
vary according to the age of the child, chil-
dren’s exposure to environmental agents
may be different from exposures of adults
and may vary with the developmental stage
of the child. In addition, different patterns
of exposure to a toxin may yield different
Figure 1
A Child’s Environments
CHILD
Biological
Social
Physical

14
THE FUTURE OF CHILDREN – SUMMER/FALL 1995
health effects. For example, nitrates in
well water may cause the hemoglobin in
blood to become methemoglobin. If too
many nitrates are ingested, this chemical
change can cause insufficient oxygen to
reach the body tissues.
2
However, if the
nitrates are ingested at a rate that is slow
enough for the enzymes in the blood to
convert the methemoglobin back to
hemoglobin, no health effect will occur.
3
Exposure Before Birth
Exposures that have profound health
effects on an individual may occur before
birth. Even exposures that occur to women
before the conception of a child may have
an effect on that child (see Table 1). For
example, women who conceived after eat-
ing cooking oil contaminated with poly-
chlorinated biphenyls (PCBs) gave birth to
infants with a pattern of abnormal physical
characteristics called yusho.
4,5
In another
case, a woman inadequately treated for
lead poisoning in childhood gave birth to
an infant with congenital lead poisoning.
6,7
An individual can also be affected by
exposures that had direct effects on the
ovum and sperm prior to conception. The
ovum, formed within the fetus of the
future mother, is affected by the exposures
both of the grandmother and the future
mother. Studies have measured chemicals
foreign to the human body in the fluid
that bathes the ova prior to ovulation,
showing the potential for exposure.
8
Sperm, in contrast, are created only a few
hours to a few days prior to conception.
Thus, harmful effects to the sperm are
most likely the result of the father’s expo-
sure in the period immediately before
conception.
In most instances, exposures after con-
ception are dependent on exposures to
the mother. Infants may experience the
result of exposure to many of the toxins
mothers come into contact with during
the pregnancy. For example, maternal
smoking during pregnancy is associated
with reductions in forced expiratory flow
rates for the child.
9
Exposure from Birth to
Adolescence
Exposures for newborns, infants and tod-
dlers, preschool children, school-aged
children, and adolescents depend on their
physical location, breathing zones, oxygen
consumption, food consumption, types of
foods consumed, and normal behavioral
development (see Table 2)—all of which
change as the child develops.
Physical Location
That the physical location of children
changes with development has large impli-
cations for a child’s exposure. Premature
and sick newborn infants are exposed to
noise, light, compressed gases, intravenous
solutions, and benzyl alcohol, among
other things, during their stay in neonatal
intensive care.
10
Most newborns, however,
are usually near their mothers, so expo-
sures will be similar to those experienced
by the mothers. Moreover, a newborn fre-
quently spends prolonged periods of time
in a single environment, such as a crib.
Infants and toddlers, on the other hand,
are frequently placed on the floor, carpet,
Table 1
Periconceptual Exposures of Possible Importance
Grandmother Exposures to ova developing in mother while a fetus
Father Preconception exposures to sperm
Father-mediated exposures to pregnant mother
Mother Preconception exposures to ova
Exposures during pregnancy

15
Environmental Health Hazards: How Children Are Different from Adults
or grass. They therefore have more expo-
sure to chemicals associated with these sur-
faces, such as formaldehyde and volatile
organic chemicals from synthetic carpets
11
and pesticide residues from flea bombs.
12
Children who are not yet able to walk
or crawl may also experience sustained
exposure to noxious agents because they
cannot remove themselves from hazardous
environments. The infant who is badly sun-
burned because of his or her inability to
escape from the sun is a good example.
13
Many preschool children spend part of
their day in a day-care facility, which can be
located anywhere from church buildings
to private homes. In addition, preschool
children may spend a significant period of
time in outdoor environments such as
playgrounds and backyards.
School-aged children spend a signifi-
cant period of time at school, a very differ-
ent physical environment from a house or
an apartment. Schools are sometimes built
on relatively undesirable land. School sites
may be near highways (resulting in expo-
sure to auto emissions and lead), under
power lines (resulting in exposure to elec-
tromagnetic fields
14
), or on old industrial
sites (resulting in exposure to benzene
and arsenic).
Adolescents may not only have a new
school environment, but also select for
themselves other physical environments
in which they misjudge or ignore the
risks.
15
Attendance at concerts with dam-
aging sound levels is a relatively benign
example of a situation in which adoles-
cents willingly put themselves at risk.
Many adolescents also have part-time jobs
that place them in physical environments
which may be hazardous because of occu-
pational exposures.
16
Breathing Zones
Breathing zones, the places in space where
individuals breathe, are also closely related
to development. The breathing zone for
an adult is typically four to six feet above
the floor. However, for a child, it will be
closer to the floor. It is within these lower
breathing zones that heavier chemicals
such as mercury and large breathable par-
ticulates settle out
17
and radon accumu-
lates.
18
The presence of mercury in a
child’s breathing zone which came from
latex house paint accounted for a Michigan
child’s case of acrodynia, a form of toxicity
from mercury exposure.
19
(See the article
by Goldman in this journal issue.)
Oxygen Consumption
Because children are physically smaller
than adults, their metabolic rate is higher
than that of adults and they consume
more oxygen relative to their size than do
adults. As a result, a child’s exposure to an
air pollutant may be greater than an
adult’s. For example, if radon is present, a
six-month-old child with an average oxy-
gen consumption rate will, over a given
period of time, receive twice the exposure
to radon as will an adult with an average
oxygen consumption rate.
20
Quantity and Quality of Food
Consumed
Similar to their need for proportionately
more oxygen than adults, children’s high-
er metabolic rates mean that they need to
consume more calories per pound of
body weight than adults. Quite simply, the
amount of food that children consume
per pound of body weight is higher than
that of adults.
21
The reason for this differ-
ence is that children not only maintain
homeostasis, as adults do, but also grow.
Consider the amount of water that an
infant who receives formula reconstituted
in boiled tap water drinks every day. The
average infant consumes six ounces of for-
mula per kilogram of body weight. For the
average male adult, this is equivalent to
drinking 35 cans of soda pop a day. If the
water contains a contaminant, then infants
will receive more of it relative to their size
than will an adult. Because of this differ-
ence, lead in tap water is of particular con-
cern for formula-fed infants. High blood
lead levels (greater than 10 mcg/dl) have
The average infant consumes six ounces of
formula per kilogram of body weight. For the
average male adult, this is the equivalent to
drinking 35 cans of soda pop a day.

16
THE FUTURE OF CHILDREN – SUMMER/FALL 1995
Developmental Developmental Exposure Pathways Biological Vulnerabilities Appropriate Responses in
Stage Characteristics (Physical Environment) the Social Environment
Newborn
Nonambulatory Food Brain Need for newborn-sensitive programs
(0 to 2 months) Restricted environment Breast milk Cell migration and regulations regarding:
High calorie/water intake Infant formula Neuron myelination Polychlorinated biphenyls (PCBs)
High air intake Indoor air Creation of neuron synapses Lead in drinking water
Highly permeable skin Tap/well water in home Lungs Environmental tobacco smoke
Alkaline gastric secretions Developing alveoli Need to educate parents and policymak-
ers
(Low gastric acidity) Bones concerning environmental hazards
Rapid growth and hardening
Infant/Toddler Beginning to walk Food Brain Need for child-sensitive programs
(2 months to 2 years) Oral exploration Baby food Creation of synapses and regulations regarding:
Restricted environment Milk and milk products Lungs Radon in the home
Increased time away from Air Developing alveoli Residential pesticide use
parents Indoor Lead abatement
Minimal variation in diet Layering effects
a
Environmental tobacco smoke
Tap/well water in home Need to educate parents and policymak-
ers
and day care concerning environmental hazards
Surfaces
Rugs
Floors
Lawns
Table 2
Environmental Risk Factors for Children at Different Stages of Development

17
Environmental Health Hazards: How Children Are Different from Adults
Developmental Developmental Exposure Pathways Biological Vulnerabilities Appropriate Responses in
Stage Characteristics (Physical Environment) the Social Environment
Preschool Child
Language acquisition Food Brain Need for child-sensitive programs
(2 to 6 years) Group and individual play Fruits, vegetables Dendritic trimming and regulations regarding:
Growing independence Milk and milk products Lungs Food pesticides
Increased intake of fruits Air Developing alveoli Environmental tobacco smoke
and vegetables Day care/preschool Increasing lung volume at home and at preschool
Outdoor Need to educate parents and policymakers
Water concerning environmental hazards
Tap/well
Water fountains
School-Aged Child Beginning of school Food Brain Need for child-sensitive programs
(6 to 12 years) Playground activities At home and school Specific synapse formation and regulations regarding:
Increased involvement in Air Dendritic trimming Asbestos abatement
group activities School air Lung Lead in school drinking water
Outdoor air Volume expansion Hazards in arts and crafts materials
Water Need to educate parents and policymakers
School water fountains concerning environmental hazards
Tap/well
Other
Arts and crafts supplies
Adolescent Development of abstract Food Brain Need for adolescent-sensitive programs
(12 to 18 years) thinking Air Continued synapse formation and regulations on child labor
Puberty Water Lung and other issues
Growth spurt Other Volume expansion Need to educate parents and policymakers
Occupation Gonad maturation concerning environmental hazards
Self-determination Ova and sperm maturation
Breast development
a
Layering effects occur when a particle in the air is distributed in layers in a room. Radon, for example, is more concentrated closer to the floor, where infants and toddlers are likely to be.

18 THE FUTURE OF CHILDREN – SUMMER/FALL 1995
been found in infants with heavy expo-
sure to tap water from reconstituted for-
mula.
6
Adults consuming the same tap
water would suffer no adverse health
effects because they would ingest much
less lead relative to their body weight.
In addition, the types of food children
consume differ from those consumed by
adults.
22
The diet of many newborns is lim-
ited to breast milk, which may contain
environmental pollutants including lead,
PCBs, and dioxins.
23–25
The diet of chil-
dren also contains more milk products,
fruits, and vegetables than the typical adult
diet, and as a result, children may be
exposed to more dangerous levels of pesti-
cides and other chemical residues than
adults.
26
Normal Behavioral Development
The normal behavioral development of a
child will also influence environmental
exposures. Infants and young children may
not be able to remove themselves from
noxious environments. Normal children
pass through a developmental stage of
intense oral exploratory behavior from
about age six months to two years, when
most objects grasped will be placed in the
mouth. This behavior is one common
cause of lead poisoning in environments
with high levels of lead dust, such as hous-
es painted with lead-based paint.
27
It also
places the child at risk in environments
that have not taken the oral orientation of
young children into account. For exam-
ple, some wood used in playground equip-
ment is treated with arsenic and creosote.
In the course of normal play, children will
frequently place their mouths on play-
ground equipment, inadvertently expos-
ing themselves to these toxic chemicals.
28
The ability to walk often places chil-
dren in play situations that have the poten-
tial for dangerous exposures, such as near
empty lots, mud puddles, and used con-
tainers holding oil or other liquid sub-
stances. As children become adolescents,
they gain more and more freedom from
the parental supervision that might other-
wise protect them from some exposures.
Their physical strength and stamina are
well developed, but they are still acquiring
abstract thinking.
29
They do not consider
cause and effect, particularly delayed
effects, in the same way that adults do.
Because of this lack of perception, they
often place themselves in situations with
greater risk than an adult would willingly
face. An example is the higher incidence
of farm injuries among adolescents than
among adults.
30
The Biological Environment
The biological environment—the internal
physiological workings of the body as it
takes up, processes, and interacts with the
chemicals it contacts—is another impor-
tant part of a child’s overall environment.
The body has specific chemical pathways
used to digest, process, and excrete sub-
stances found in air, food, and water,
which vary at different stages of develop-
ment. A chemical that comes into contact
with the biological systems of a child’s
body can produce adverse health effects or
be processed into nonharmful substances.
Absorption
Absorption is the way a chemical enters
the body. Absorption generally occurs in
one of four ways: through the placenta,
the skin, the respiratory tract, or the diges-
tive tract. Each of these portals of entry is
dependent on the developmental stage of
the child.
Through the Placenta
During the fetal stage, the placenta is a
major pathway of absorption.
31
Several
classes of compounds readily cross the pla-
centa, including compounds with low mo-
lecular weight, those that are fat-soluble,
and other specific compounds such as cal-
cium and lead. Carbon monoxide, a poi-
sonous compound of low molecular
weight, crosses the placenta readily. When
carbon monoxide enters the blood, it
binds to hemoglobin, creating carboxyhe-
moglobin. This bond prevents hemoglo-
bin from binding to oxygen and delivering
The diet of children also contains more
milk products, fruits, and vegetables than
the typical adult diet.

19Environmental Health Hazards: How Children Are Different from Adults
it to the cells. Because carbon monoxide
has a higher affinity for fetal hemoglobin
than it does for adult hemoglobin, the
concentration of carboxyhemoglobin is
higher in the fetus than in the mother.
32
Therefore, the infant may have reduced
oxygen delivered to tissues, with subse-
quent organ damage.
Fat-soluble, or lipophilic, compounds,
such as polycyclic aromatic hydrocarbons
(found in cigarette smoke) and ethanol
(found in alcoholic beverages), readily
gain access to the fetal circulation and
thereby may cause toxic effects in the
fetus. Also, mechanisms in the placenta
actively transport specific nutrients and
toxins to the fetus. Lead, for example, is
found in equal concentrations in the
mother and the fetus.
33
Through the Skin
The skin undergoes enormous changes
with development which affect its absorp-
tive properties. Pathways of absorption
through the skin are particularly impor-
tant for fat-soluble compounds. Because
the skin is mainly composed of fatty chem-
icals, fat-soluble chemicals generally cross
it more readily than other chemicals.
The outside skin layer of a fetus lacks
the rough exterior dead skin layer called
keratin
34
and thus is without one of the
major barriers of the skin.
35
The acquisi-
tion of keratin occurs over the initial three
to five days following birth. Therefore, the
skin of a newborn is a particularly absorp-
tive surface, and absorption of chemicals
through the skin has caused many cases of
illness in newborns. For example, hypothy-
roidism has resulted from iodine in beta-
dine scrub solutions used for sterilization
of the skin prior to birth or other skin pen-
etrating procedures, such as obtaining
blood or starting intravenous fluids.
36
Neurotoxicity has occurred from hexa-
chlorophene solutions which were used to
bathe infants following birth,
37
and hyper-
bilirubinemia has resulted from a pheno-
lic disinfectant used to clean equipment
between use for different patients.
38
An additional factor in the absorption
of these chemicals through the skin is the
larger surface-to-volume ratio of newborns
compared with older children and adults.
This means that for the same amount of
skin covered with a chemical, the younger
child may receive up to three times the
dose received by an adult.
Through the Respiratory Tract
During prenatal life, the fetus makes
breathing motions. Although the net flow
of fluid is from the lungs out of the tra-
© Courtesy of California Department of Health Services

chea into the amniotic fluid, some chemi-
cals in amniotic fluid may come in contact
with the lining of the respiratory tract.
Studies on this pathway of exposure to for-
eign chemicals are limited.
The surface absorptive properties of
the lung do not change during develop-
ment; the lungs continuously absorb air-
borne chemicals in the same manner.
However, from birth to adolescence, the
lung continues to develop more alveoli,
the terminal air sacs through which
humans breathe.
39
The increase in the
number of alveoli increases the size of the
absorptive area in the lungs. Thus, some
airborne chemicals may gain greater
access to the body through the lungs as the
child ages.
Through the Gastrointestinal Tract
The gastrointestinal (digestive) tract, at all
stages of development, provides many
opportunities for exposure to environ-
mental toxins. The fetus actively swallows
amniotic fluid.
40
Chemicals, including cer-
tain pesticides as well as chemicals from
tobacco smoke, can be present in amniot-
ic fluid, but it is not known if the fetus
absorbs those chemicals by swallowing the
fluid. Following birth, stomach acid secre-
tion is relatively low, but it will achieve
adult levels by several months of age.
41
As
the infant grows, the difference in acidity
will markedly affect absorption of chemi-
cals from the stomach.
42
The small intestine in the newborn can
respond to increased nutritional needs by
increasing absorption of a particularly
needed nutrient. For example, because
children’s bones are still growing, they
require more calcium than adults. Thus,
children absorb more calcium than adults
do from the same food sources. However,
this enhanced absorption can create prob-
lems. Lead, because it is absorbed in place
of calcium when it is present, is absorbed
to a greater extent in children than in
adults. An adult will absorb 10% of ingest-
ed lead, whereas a one- to two-year-old
child will absorb 50% of ingested lead.
43
Distribution
The distribution of chemicals, the process
by which chemicals get to body organs,
varies with the developmental stage of the
child. For example, many drugs become
more diluted in newborns than they do in
adults, spreading out so that more of the
body has contact with them at lower lev-
els.
44
In animal models, it has been shown
that lead is retained to a larger degree in
the infant animal brain than in the
adult.
45
Lead also accumulates more
rapidly in children’s bones than in adult
bones, doubling between infancy and the
late teen years.
46
Metabolism
Metabolism is the way the body processes
chemicals using a series of steps, or path-
ways, to alter chemicals for use as fuel or
for waste. It may result in activation or
deactivation of the chemical by the body.
The metabolism of chemicals depends on
the child’s developmental stage, and the
end result may either protect or harm the
child, depending on the chemical in
question.
The activity in each step of a metabolic
pathway is determined by developmental
stage and the genetic background of each
individual. Therefore, some people are
more susceptible to adverse effects from
certain exposures. There are also large dif-
ferences in the ways enzymes work in
metabolic pathways between developmen-
tal stages.
47
The same enzyme may work
more or less depending on the age of the
individual.
48
In some instances, the lack of certain
pathways can be a protective factor. In the
adult, high levels of acetaminophen may
cause fatal liver poisoning, because adult
metabolism breaks down the drug into
subcomponents that are harmful to the
liver. However, infants are not as easily hurt
by acetaminophen. Infants born to moth-
ers with high acetaminophen levels will
also have high acetaminophen levels in the
blood, but they will not have liver damage.
20 THE FUTURE OF CHILDREN – SUMMER/FALL 1995
An adult will absorb 10% of ingested lead,
whereas a one- to two-year-old child will
absorb 50% of ingested lead.

21Environmental Health Hazards: How Children Are Different from Adults
The reason for this lack of damage is that
the metabolic pathways of the fetus have
not yet developed enough to break down
the drug into harmful subparts.
49
Target Organ Susceptibility
Children are also different from adults
because their organs are undergoing
growth and maturation, a process that may
be adversely affected by exposure to harm-
ful chemicals. Responses of children’s
bodies to harmful exposures may differ
from responses of adults’ bodies to these
exposures in both the nature and the
severity of the effect. Examples of such
outcomes are poor fetal growth, poor
growth in childhood, diminished intelli-
gence quotient (IQ), precocious puberty,
small head size, and diminished lung
capacity.
The body experiences three types of
growth: multiplicative, where cells divide;
auxelic, where existing cells become larg-
er; and accretionary, where ground sub-
stance and nonliving structural compo-
nents accumulate.
50
Multiplicative growth
is complete around six months after con-
ception for tissues that do not undergo
continual turnover throughout life, such
as skin cells. After that point, all growth is
accretionary or auxelic.
Cells undergo two further processes to
become the adult organism: differentia-
tion and migration. Differentiation occurs
when cells take on their individual tasks
within the body and lose the ability to
divide. The trigger for differentiation may
be hormones, so when chemicals mimic
hormones they can alter the differentia-
tion of some tissues. Because the organ
systems in children, including the repro-
ductive system, are continuing to differ-
entiate, a chemical that mimics a hor-
mone can have drastic effects on the
development of those organ systems.
Chlorinated insecticides are an example
of this mechanism. Studies have shown
effects on the adult rat reproductive sys-
tem from neonatal exposure to chlorde-
cone,
51
including abnormal growth of the
vagina and sterility.
52
Cell migration is necessary for certain
cells to reach their destination for func-
tion. Neurons, for example, originate in a
structure near the center of the brain,
then migrate out to a predestined location
in one of the many layers of the brain.
53
Chemicals such as the ethanol in alcoholic
beverages may have a profound effect on
this process, as shown in children with
fetal alcohol syndrome. Prenatal exposure
to ethanol may result in interruption in
this process severe enough to cause obvi-
ous malformations of the brain.
54,55
Some organs continue to develop for
several years. The brain and the lungs
both have prolonged periods of postnatal
development which are not complete until
adolescence.
39,56
This protracted period of
growth and development increases the vul-
nerability of these organs. For example,
brain tumors are frequently treated by
radiation therapy in adults, with uncom-
fortable but reversible side effects. However,
in infants, radiation therapy needs to be
minimized when possible because of pro-
found and permanent effects on the devel-
oping central nervous system.
57
Another example of the unique vulner-
ability of children is the toxic effects of
lead on the brain and nervous system. The
current blood lead concentration of con-
cern for children is 10 mcg/dl,
58
based on
studies
59
which found that children with
blood lead concentrations above that level
may have measurable decreases in intelli-
gence quotient. Because of differences in
developmental stage, the occupational
limit for exposure to lead for adults is six
times higher than the limit for children.
60
The Social Environment
For every developmental stage, there are
unique combinations of developmental
characteristics, physical environment, and
biological environment that place children
at special risk of harm. To protect children
from the harms caused by exposure to
Responses of children’s bodies to harmful
exposures may differ from responses of adults’
bodies to these exposures in both the nature
and the severity of the effect.

environmental toxins, it is necessary also to
consider the customs, laws, and regulations
that help define children’s environments.
In many ways, regulatory policies have
not taken the characteristics of children
into account. For example, for infants who
are formula-fed, the amount of water con-
sumed is enormous, and yet our water
safety policies do not always take the
increased consumption and special vul-
nerabilities of newborns into account
when they are determined. Standards for
radon testing and reentry times listed on
the label of home pesticides should allow
adequate protection for infants who spend
so much of their time on the floor, but
such considerations may not be reflected
in recommended practice. Similarly, pesti-
cide regulations should be made with the
special diet of children in mind. Adequate
laws to prevent exposure to environmental
tobacco smoke for children attending day-
care facilities could prevent the exposure
of many children to environmental tobac-
co smoke.
61
For the school-aged child, regulation
of the school environment is of particular
concern. The drinking water at the tap in
schools should be judged safe for a child’s
consumption. Arts and crafts supplies
should be designed and purchased keep-
ing in mind a child’s unique way of han-
dling these materials. For adolescents who
are beginning to work, child labor laws
should be adequate not only to protect
them from occupational risks, but also to
ensure that their ability to learn in school
is not adversely affected.
These are only a few examples of the
potential effects of laws and regulations on
the environments of children. These social
environment effects are discussed more
thoroughly in the article by Landrigan and
Carlson in this journal issue.
Conclusion
There are many reasons children cannot
be considered little adults in the area of
environmental health. Important differ-
ences exist between children and adults in
exposures, absorption pathways, tissue dis-
tribution, ability to transform and elimi-
nate chemicals, and body response to envi-
ronmental chemicals and radiation. Each
of these differences is dependent on the
developmental stage of the child, and all
children are not the same during each
stage (see Table 2). When considering the
health impacts of a particular exposure on
the population and potential policies to
alleviate those impacts, each of these dif-
ferences must be heeded.
What can be done to alleviate the
harm—both potential and actual—done
to children by environmental pollution?
Health care providers, policymakers,
teachers, community leaders, parents, and
children all have roles to play in prevent-
ing children’s exposure to harmful agents
in their environment and in addressing
the consequences for children who are
exposed.
Education about the unique vulnera-
bility of children to environmental pollu-
tion is one powerful tool for change.
Teaching parents and children how to
avoid harmful exposures and therefore
prevent environmental illnesses is an
important piece of prevention, which can
occur at many levels and in different set-
tings. However, education can and should
go beyond parents and children. Clinicians
can be especially helpful when serving as
educators, investigators, and advocates for
children. Most environmentally caused
diseases have been diagnosed by alert,
environmentally aware clinicians, and
publication of case studies has allowed fur-
ther education of other clinicians about
environmentally mediated diseases.
Increased awareness of the effects of envi-
ronmental hazards on children can influ-
ence both exposure and treatment for
children.
Community leaders and policymakers
can use information presented by par-
ents, clinicians, scientists, and other advo-
22 THE FUTURE OF CHILDREN – SUMMER/FALL 1995
Health care providers, policymakers,
teachers, community leaders, parents, and
children all have roles to play in preventing
children’s exposure to harmful agents in
their environment.

23
Environmental Health Hazards: How Children Are Different from Adults
cates for children and the environment to take the unique vulnerability of children
into account when establishing regulatory policy. To bring about change, policymak-
ers must understand the basis for this unique vulnerability—that children are not lit-
tle adults.
1. The fetus represents a unique period of time in life when many critical chemical reactions
are occurring, the disruption of which can have far-reaching consequences. In addition, the
environment of the fetus is unique.
2. Luykens, J.N. The legacy of well-water methemoglobinemia. Journal of the American Medical
Association (1987) 257:2793–95.
3. This is an example of a threshold effect, where the health effects will not occur until the
toxin reaches a particular level in the body.
4. Tilson, H.A., Jacobson, J.L., and Rogan, W.J. Polychlorinated biphenyls and the developing
nervous system: Cross-species comparisons. Neurotoxicology and Teratology (1990)12:239–48.
5. The reason for the linkage of PCBs with birth defects is not completely clear. The most like-
ly explanation is that, when the women were exposed to high levels of the PCBs, their bod-
ies stored them in their fat tissues, where they slowly were released into the bloodstream.
When these women became pregnant, the PCBs in the bloodstream crossed the placenta
and affected the fetus. Taylor, P.R., Lawrence, C.E., Hwang, H.L., and Paulson, A.S.
Polychlorinated biphenyls: Influence on birthweight and gestation. American Journal of
Public Health (1984) 74:1153–54; Yu, M-L., Chen-Chin, H., Gladen, B.C., and Rogan, W.J. In
utero PCB/PCDF exposure: Relation of developmental delay to dysmorphology and dose.
Neurotoxicology and Teratology (1991) 13:195–202.
6. Shannon, M.W., and Graef, J.W. Lead intoxication in infancy. Pediatrics (1992) 89:87–90.
7. Storage in the woman’s bones of lead that became mobilized during pregnancy is the most
logical explanation for this result, although definitive proof is awaiting further technologi-
cal advances. Silbergeld, E.K. Lead in bone: Implications for toxicology during pregnancy
and lactation. Environmental Health Perspectives (1991) 91:63–70.
8. Trapp, M., Baukloh, V., Bohnet, H.G., and Heeschen, W. Pollutants in human follicular
fluid. Fertility and Sterility (1984) 42:146–48.
9. Hanrahan, J.P., Tager, I.B., Segal, M.R., et al. The effect of maternal smoking during preg-
nancy on early infant lung function. American Review of Respiratory Disease (1992)
145:1129–35.
10. Brown, A.K., and Glass, L. Environmental hazards in the newborn nursery. Pediatric Annuals
(1979) 8:698–700.
11. Bernstein, R.S., Stayner, L.T., Elliot, L.J., et al. Inhalation exposure to formaldehyde: An
overview of its toxicology, epidemiology, monitoring, and control. American Industrial
Hygiene Association Journal (1984) 261:1183–87.
12. Fenske, R.A., Black, K.G., Elkner, K.P., et al. Potential exposure and health risks of infants
following indoor residential pesticide applications. American Journal of Public Health (1990)
80:689–93.
13. In addition, because the risk of skin cancer is most closely related to the amount of sun
damage the skin sustains during the first 18 years of life, an infant’s caregiver determines
part of an infant’s personal risk for this disease later in life. Jackson, R.J. Testimony to the
U.S. House of Representatives, Select Committee on Children, Youth and Families, 1990.
14. The evidence that exposure to electromagnetic fields is hazardous to children is inconclu-
sive. Several studies have found an association between children’s cancer and exposure to
electromagnetic fields, but a causal relationship between exposure and disease has not
been established. For further information, see Savitz D. Overview of epidemiologic research
on electric and magnetic fields and cancer. American Industrial Hygiene Association Journal
(April 1993) 54,4:197-204; Hendee, W.R., and Boteler, J.C. The question of health effects
from exposure to electromagnetic fields. Health Physics (February 1994) 66,2:127–36.
15. Perry, C.L., and Silvis, G.L. Smoking prevention: Behavioral prescriptions for the pediatri-
cian. Pediatrics (1987) 79:790–99.

24
THE FUTURE OF CHILDREN – SUMMER/FALL 1995
16. Pollack, S.H., Landrigan, P.H., and Mallino, D.L. Child labor in 1990: Prevalence and
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17. Leaderer, B.P. Assessing exposures to environmental tobacco smoke. Risk Analysis (1990)
10:19–26.
18. Blot, W.J., Xu, Z.Y., Boice, J.D., Jr., et al. Indoor radon and lung cancer in China. Journal of
the National Cancer Institute (1990) 82:1025–30.
19. Centers for Disease Control. Mercury exposure from interior latex paint—Michigan.
Morbidity and Mortality Weekly Report (1990) 39:125–26.
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risks from chemicals during infancy and early childhood: The need for a special approach. Geneva:
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21. Biller, J.A., and Yeager, A.M., ed. The Harriet Lane Handbook. 9th ed. Chicago: Year Book
Medical Publishers, 1981, p. 202.
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intakes by individuals, women 19–50 years and their children 1–5 years. Washington, DC: Human
Nutrition Information Service, CSFII, 1985.
23. Hayward, D.G., Ward, C., Lance, L.L., et al. PCDD and PCDF in breast milk as correlated
with fish consumption in California. Chemosphere (1989) 18:455.
24. Ong, C.N., Phoon, W.O., Law, H.Y., et al. Concentrations of lead in maternal blood, cord
blood, and breast milk. Archives of Disease in Childhood (1985) 60:756–59.
25. Rogan, W.J., Gladen, B.C., McKinney, J.D., et al. Polychlorinated biphenyls (PCBs) and
dichlorodiphenyl dichlorethene (DDE) in human milk: Effects of maternal factors and pre-
vious lactation. American Journal of Public Health (1986) 76:172–77.
26. Zeise, L., Painter, P., Berteau, P.E., et al. Alar in fruit: Limited regulatory action in the face
of uncertain risks. In The analysis, communication, and perception of risk. B.J. Garrick and W.C.
Gekler, eds. New York: Plenum Press, 1991, pp. 275–84.
27. Chao, J., and Kikano, G.E. Lead poisoning in children. American Family Physician (1993)
47:113–20.
28. Kosnett, M., ed. Case studies in environmental medicine: Arsenic toxicity. U.S. Department of
Health and Human Services, Agency for Toxic Substances and Disease Registry, 1990.
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25Environmental Health Hazards: How Children Are Different from Adults
38. Wysowski, D.K., Flynt, J.W., Jr., Goldfield, M., et al. Epidemic neonatal hyperbilirubinemia
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40. Miller, A.J. Deglutition. Physiological Reviews (1982) 62:129.
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47. Warholm, M., Guthenberg, C., Mannevik, B., et al. Glutathione S-transferases in human
fetal liver. Acta Chemica Scandinavica (1981) B35:225–27.
48. For example, theophylline, a drug commonly prescribed for all age groups by physicians, is
metabolized by several different chemical pathways. During the newborn period, these
pathways operate at low levels, so theophylline remains in the body unchanged for a long
period of time. However, the pathways become increasingly present over the next several
months, breaking theophylline down so it is not in the body as long in the same chemical
form. To keep the same level in the body, the prescribing physician has to increase the pre-
scribed dose. In adolescence, the metabolic breakdown of theophylline slows again, possibly
because steroid hormones are competing for the same pathways. (Levi, P.E. Toxic action. In
A textbook of modern toxicology. E. Hodgson and P.E. Levi, eds. New York: Elsevier, 1987, p. 152.)
To accommodate this change, the dose of the drug must be reduced to avoid overdosing
the patient.
49. Riggs, B.S., Bronstein, A.C., Kulig, K., et al. Acute acetaminophen overdose during preg-
nancy. Obstetrics and Gynecology (1989) 74:247–53.
50. Sinclair, D. Human growth after birth. 5th ed. Oxford: Oxford University Press, 1989, p. 3.
51. Gellert, R.J. Kepone, mirex dieldrin, and aldrin: Estrogenic activity and the induction of
persistent vaginal estrus and anovulation in rats following neonatal treatment. Environmental
Research (1978) 16:131–38.
52. Tissues undergoing multiplicative growth (by cells dividing) and the final stages of growth
and change (differentiation) are particularly susceptible to cancer. (Levi, P.E. Toxic action.
In A textbook of modern toxicology. E. Hodgson and P.E. Levi, eds. New York: Elsevier, 1987,
p. 152.) This increased susceptibility is due to the shortened time period for DNA repair
and the multiple changes that are occurring within the DNA as the cell grows. The epidem-
ic of scrotal cancer among the chimney sweeps of Victorian England shows how exposure
to chemicals can interfere with these stages of development. (Nethercott, J.R. Occupational
skin disorders. In Occupational medicine. J. LaDou, ed. San Mateo, CA: Appleton & Lange,
1990, p. 218.) Chimney sweeps were usually adolescent boys with developing secondary sex-
ual characteristics who would climb naked inside chimneys to clean them, exposing their
entire bodies to soot. Occupational exposure to cancer-causing chemicals such as soot was
common for many occupations at the time, but scrotal tumors were uncommon in groups
other than young male chimney sweeps. Thus, it is likely that the scrotum at this stage of
development had increased susceptibility to the chemicals in soot.

26
THE FUTURE OF CHILDREN – SUMMER/FALL 1995
53. Miller, M.W. Effects of prenatal exposure to ethanol on cell proliferation and neuronal
migration. In Development of the central nervous system: Effects of alcohol and opiates. M.W. Miller,
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54. Clarren, S.K., Alvord, E.C., Jr., Sumi, S.M., et al. Brain malformations related to prenatal
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55. In the brain, two other processes deserve mention: the making of synapses (synaptogenesis)
and dendritic trimming. Nerve cells communicate through cellular structures called synap-
ses, which are the basis for the circuitry of the brain. Up to two years of age, the brain
makes synapses rapidly. After age two, while specific synapses are formed as learning occurs,
formation is much slower. In fact, after age two, the brain begins actively to remove synaps-
es, so that a two-year-old’s brain contains more synapses than it will at any other age. This
process, called dendritic trimming, occurs so that the resulting network of neurons will be
more specific.
56. Hoar, R.M., and Monie, I.W. Comparative development of specific organ systems. In
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57. Duffner, P.K., Horowitz, M.E., Krischer, J.P., et al. Postoperative chemotherapy and delayed
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58. Centers for Disease Control. Preventing lead poisoning in young children: A statement by the
Centers for Disease Control. Atlanta: Centers for Disease Control, 1991.
59. Needleman, H.L., and Bellinger, D. Low-level lead exposure and the IQ of children: A
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60. At that level, adults do not have brain problems but may have impaired kidney function,
decreased fertility, and problems with the peripheral nerves. Royce, S.E., ed. Case studies in
environmental medicine: Lead toxicity. U.S. Department of Health and Human Services,
Agency for Substances and Disease Registry, Washington, DC, 1990, p. 5.
61. Samet, J.M., Lewit, E.M., and Warner, K.E. Involuntary smoking and children’s health. The
Future of Children (Winter 1994) 4,3:94–114.