Fact Pack

Children’s Special Vulnerability to Environmental Risks

Information for this section provided by the Child Proofing Our Communities Campaign: Creating Safe Learning Zones.

The central theme of a pivotal report by the National Academy of Sciences in 1993 was that children are not “little adults” – a fact already known to legions of parents, teachers, and others worldwide.(1) Infants and children are different from adults because they are growing and developing.

Environmental Hazards Affect Children Differently Than Adults

Their bodies are not fully mature, and therefore may not be capable of detoxifying certain harmful compounds. The very nature of children’s behavior – highly curious and physical – can also put them at increased risk. That children are uniquely vulnerable to environmental hazards is well established in scientific literature. In fact, the World Health Organization recommended more than a decade ago that, “when health risks from chemicals are evaluated, the special characteristics of infants and children must be recognized.”(2)

Greater Exposure

Pound for pound, children breathe more air, drink more water, and consume more food than adults. This higher rate of intake means that children will receive higher doses of whatever contaminants are present in the air, water, or food. In addition, infants have a relatively greater surface area of skin than adults, thereby increasing their potential dermal absorption of certain compounds.

Differential Intake

Infants and children drink more than 2.5 times as much water daily as adults do as a percentage of body weight.(4) (An infant living solely on formula consumes about one-seventh of his/her own weight of water each day, which corresponds to approximately three gallons, or thirty-five cans of soda, for a 155-pound adult man.(2))

The air intake of a resting infant is twice that of an adult under the same conditions. A typical newborn weighs one-twentieth of the weight of an adult male, but the infant’s surface area is one-eighth as great.(2) Therefore, the total area of skin that could be exposed to a chemical (by swimming or bathing in polluted water or rolling in dirt) is 2.5 times as great per unit of body weight in the infant as in the adult.(2)

Childhood Behavior

The typical nature of children’s behavior also increases their exposure to environmental
toxicants. An infant frequently explores objects by placing them in his or her mouth. This
common hand-to-mouth behavior increases an infant’s ingestion of substances in soil,
household dust, floors and carpets, and on the objects themselves. In recognition of this,
the U.S. Environmental Protection Agency (EPA) recently proposed assuming that children, aged three to five years old, put their hands to their mouths an average of 1.5 times per hour.(5)

As children grow, their endless curiosity and lack of fear can further increase their exposure to environmental hazards. With considerable physical energy, children can explore locations without regard for the consequences of their actions.

At rest, children’s breathing rates are faster than those of adults, and children’s greater levels of physical activity can increase their breathing rates even further.

Children often play at ground level. In contrast, an adult’s common breathing zone is four to six feet above the floor. Children will receive greater inhalation and dermal exposure to chemicals present on floors, carpet, grass, or dirt. Also, heavier chemicals such as lead and particulates will settle and accumulate in the air at ground level.(2)

Increased Susceptibility

Human infants and children differ from adults not only in their size but also in the relative immaturity of their biochemical and physiological functions. Childhood is characterized by rapid physical and mental growth. Accordingly, certain organs may not be fully developed and may be more vulnerable to injury. Children absorb, metabolize, and excrete compounds differently than adults.

Rapid Growth and Development

An infant gains weight more rapidly during the first 4 - 6 months after birth than at any other time during his or her life.(2) Typical newborns double their weight during the first 5 - 6 months and, by their first birthday, will weigh 3 times their birth-weight.(3) The growth of integral parts of the central nervous system (brain) and the immune system (thymus) proceeds most rapidly in the first six years of life. At age six, a child’s weight is only about 30 percent of an adult’s, but the child’s thymus is approximately the size of the adult’s, and the brain is about 80 percent of adult size.(9)

Many organs are not fully developed at birth and continue developing for years. The nervous system, lungs, immune system, and reproductive organs undergo extensive growth and development in utero and throughout infancy and early childhood. For example, sex organ development is not complete until puberty; myelination, the insulating of the nerve fibers of the brain, is not complete until adolescence; and the alveoli, or terminal air sacs in the lung where oxygen from the air enters the blood, continue to increase in number until adolescence.(10)

Differential Absorption, Metabolism, and Excretion

Infants’ and children’s pathways of absorption, metabolism, and excretion of compounds are different from those of adults.(1) In some instances, children may be more susceptible than adults, due to their increased rates of absorption or decreased rates of elimination of foreign compounds; in other cases, the opposite may be true. Children will absorb about 50 percent of lead ingested, whereas adults will absorb only about 10 to 15 percent.(11) Kidneys are the principal pathway for elimination of most chemicals from the body. At birth an infant’s kidney’s filtration rate is a fraction of adult values, and by age one the rate is at adult levels.(10)

Recent molecular epidemiological data indicate that infants and children retain greater amounts of certain environmental toxicants. In a study of Polish newborns and their mothers, biomarkers, levels of polycyclic aromatic hydrocarbon (PAH)-induced DNA damage, were measured. Among newborns exposed to PAHs in utero, the level of DNA damage was comparable to the level in their mothers, even though the estimated dose to the fetus was one-tenth of that to the mother. Similarly, in young children (under two years of age), levels of an indicator of exposures to PAHs (1-hydroxypyrene glucuronide) in urine were higher than in their mothers.(12) Another study investigated PCB levels in individuals residing on a Mohawk reservation downstream from pollution sources on the St. Lawrence River. PCBs were found in the breast milk and urine of women who ate fish caught in the river. The PCB concentrations in the urine of breast-fed infants were 10 times higher than in the urine of their mothers.(12)

Longer Lifetimes

Children have more years of future life than most adults. Therefore, they have more time to develop any chronic diseases that might be triggered by early environmental exposures. Many diseases initiated by chemical hazards require decades to develop. Early childhood exposure to certain carcinogens or toxicants may be more likely to lead to disease than the same exposures experienced later in life.(13)