What Are Factors Affecting Children’s Susceptibility to Exposures?

Upon completion of this section, you will be able to

• describe factors that usually render children more susceptible to exposure to toxicants compared to adults.

Children’s caregivers have a direct effect on child safety. And health caregivers are entrusted to protect children from danger as well as consult child health care providers when appropriate. A child relies on adults for protection from such toxic exposures

• excessive sunlight,
• noise,
• pesticides,
• secondhand smoke (SHS),
• take-home exposures, and
• other environmental hazards.

Having access to an excellent caregiver is essential for a child’s optimal growth and development. Even if a child has excellent caregivers, however, he or she is often at increased risk from environmental exposures, especially when compared with adults. Among a caregiver’s responsibilities is protection of children from environmental hazards.

Exposures and vulnerabilities

Compared with adults, children’s exposures put them at greater risk for harm from exposure to environmental hazards. Their vulnerabilities to exposure include

• critical windows of susceptibility,
• diets at different stages of development,
• inherent behaviors and physical characteristics, and
• unique vulnerabilities – including rapid growth and development.

Opportunities for exposure-related change increase as a child grows from total dependence on parents or other caregivers to adolescent independence. Socioeconomic circumstances, diet, behaviors, life-stage development, and environmental regulations can restrict or augment pediatric exposure risks.

Multiple factors enhance a child’s opportunity for exposure. Children may experience exposures in a wide range of settings including home, child care, school, and play environments.

• Because children grow and develop, they have a higher metabolic rate and thus have a greater need for oxygen, water, and food. Children breathe more air, drink more water, and eat more food per kilogram of body weight than do adults. These result in greater exposures per kilogram of body weight to any contaminants in the air, water, or food, compared with adults.
• An infant’s respiratory rate is more than twice that of an adult’s.
• In the first 6 months of life, children drink seven times as much water per kilogram of weight than does an adult.
• From 1 to 5 years of age, children consume three to four times more food per kilogram of weight than do adults.
• Children eat different foods than adults eat – fruits and vegetables are a larger proportion of children’s diets.
• Breast-feeding infants may be exposed to lipophilic contaminants in breast milk.
• Limited food preferences often seen in the diets of infants and toddlers lead to greater exposures to contaminants if those contaminants are present in commonly consumed foods. For example, because children consume about 15 times more apples and apple products per unit of body weight than do adults do, they are more exposed per kilogram of body weight to any contaminants – such as pesticides – that might be present in or on apples. Thus assessments of risk to children from those pesticides, if based on a typical adult diet, may underestimate a child’s risk of exposure to pesticide residues.
• Deficiencies of dietary iron and calcium can increase lead absorption.
• Children have an increased surface area-to-body mass ratio (in infants and young children) resulting in an increased risk of dermal exposure and absorption.
• Some toxicants more readily penetrate children’s skin, especially in the newborn period when the skin is more permeable (e.g., dermal exposure to lindane or hexachlorophene, with subsequent neurotoxicity).
• Physical stature: children are short; they live and play closer to the ground where many contaminants are found.
• Immobility: young children are not mobile and must rely on adults to remove them from hazardous exposure situations such as a room containing secondhand smoke.
• Children’s long life expectancy increases their risk of adverse outcomes (e.g., cancer, renal or liver failure, senility) from exposures to those toxicants whose effects are expressed after a long latency period.

Examples of children’s increased exposure risk

In a home contaminated with mercury (e.g., caused by spillage or mercury carried home on work shoes), a toddler’s high respiratory rate, proximity to surfaces likely to be contaminated, and playful rolling around on the floor will increase the risk of mercury exposure. Other possible contaminants that settle near the floor are

• floor-cleaning products,
• formaldehyde (from new synthetic carpet),
• pesticides, and
• radon.

And children crawling on a lawn may come into contact with lawn chemicals, pesticides and herbicides.

Infants and children’s behaviors and activities often increase exposures. Oral exploratory behavior, hand-mouth behavior, poor hand washing, and curiosity in exploration all contribute to a child’s increased risk of contaminant exposure.

Children who eat nonfood items exhibit pica behavior. Soil pica may involve the recurrent ingestion of unusually high amounts of soil (i.e., on the order of 1,000 milligrams (mg)-5,000 mg per day). Groups at risk of soil-pica behavior include children age six years and younger, and children who are developmentally delayed. The Agency for Toxic Substances and Disease Registry (ATSDR) uses 5,000 mg soil per day as an estimate of soil intake for children with soil-pica behavior [ATSDR 2001a]. Other studies, including Binder et al. [1987], have demonstrated that through normal outdoor play, children have a soil intake of about 180-1800 mg/day.

Because of socioeconomic disparities, more children live in poverty than any other age group in the United States. Their families are more likely to live in public housing or in neighborhoods in close proximity to industry, with higher degrees of environmental contamination. For example, children living in poverty-ridden urban areas may be exposed to benzene, a gasoline component and a known carcinogen. Benzene levels in air correlate with heavy automobile traffic; children playing in the streets in poor neighborhoods have disproportionately high exposures [Weaver et al. 1996].

Parents of children living in poverty often have no access to healthcare services. Asthma and atopic disease are often underdiagnosed. The prevalence of physician-undiagnosed asthma among urban Detroit schoolchildren in 3rd to 5th grade was estimated as high as 14.3% [Joseph et al. 1996]. The prevalence of asthma among children living in the Bronx, NY, was found to be twice the U.S. average, with higher prevalence rates among both Hispanic and lower-income groups [Crain et al. 1994]. Childhood asthma may have racial as well as socioeconomic determinants, with black children – independent of income – generally more affected than whites [Weitzman et al. 1992; Cunningham et al. 1996].

Socioeconomic status accounts for racial and ethnic disparities in childhood lead poisoning. Lead poisoning is found disproportionately among black and Hispanic children exposed to lead-containing dust found in older, dilapidated housing. New immigrants and migrant families are more likely to live in low-cost, hazardous housing. These families are often unfamiliar with, or are unable to access the community’s health system or other services for their children [CDC – NCEH 2011].

Hazardous waste sites and landfills are frequently located in or near to poorer neighborhoods. This disparity has sparked attention to the need for environmental justice.

The U.S. Environmental Protection Agency (EPA) defines environmental justice [Executive Order 12989, EPA 1994] as

the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies [EPA 2012].

In addition to these specific obvious toxic environments, recent substantial scientific evidence has shown that aspects of the “built environment” can have profound, directly measurable effects on physical and mental health, particularly adding to the burden of illness among ethnic minority populations and low-income communities [Hood 2005]. Negative aspects of the built environment include

• lack of sidewalks and safe recreational areas,
• dilapidated housing (with increased risks of exposure to lead paint and to environmental asthma triggers such as mold and cockroaches), and
• lack of supermarkets with fresh food.

The “built environment”

. . . encompasses all buildings, spaces and products that are created, or modified, by people. It includes homes, schools, workplaces, parks/recreation areas, greenways, business areas and transportation systems. It extends overhead in the form of electric transmission lines, underground in the form of waste disposal sites and subway trains, and across the country in the form of highways. It includes land-use planning and policies that impact our communities in urban, rural and suburban areas [Health Canada 2002].

• Certain host factors such as a small child’s increased respiratory rate, and dietary factors such as an infant’s exposure to pesticides in foods, and the thinner skin of the newborn present unique opportunities for exposure.
• Behaviors such as pica often found in small children also present unique exposure opportunities for children.
• Children living in poverty may be more exposed to environmental contaminants due to older housing stock and location of schools and homes near hazardous waste sites, high volume transportation routes, and industrial zones.