Chapter 2: The Physical Environment and Its Impact on Child Well-Being3
In the past few years, there has been growing international concern about the effects of the physical environment on children's health.
In 1997, the G8 Environment Ministers acknowledged that environmental hazards pose significant threats to the health of children throughout the world. They also committed to working together to address these issues. Four years later, in 2001, these same Ministers pledged to "develop policies and implement actions to provide children with a safe environment, including during prenatal and postnatal development". Canada, the United States and Mexico, through the Commission for Environmental Cooperation, have committed to working together on the trilateral Cooperative Agenda for Children's Health and the Environment in North America (2002).
This chapter summarizes how hazards in the physical environment, including chemical contaminants and biologic agents (molds, mildew, bacteria, house-dust, mites, etc.), can affect the health of young children in Canada. It draws from national data on Canadian children whenever possible. Relevant information from other countries has also been included.
The first section of the chapter outlines why it is important to understand the links between environmental hazards and children's health. Subsequent sections summarize available scientific information on children's exposures to hazards in the physical environment and potential health effects.
Why Are Children Uniquely Vulnerable to Environmental Hazards?
Recent scientific evidence indicates that children are more vulnerable to environmental hazards than adults because of their unique patterns of exposure behaviours, as well as their rapid growth and physiological development. There is also increasing evidence that child health is a determinant of adult health.
Children's exposures are often greater and/or different than those of adults. On a weight-for-weight basis, children eat more food, drink more water and breathe more air than adults because their metabolic rates are much higher. Therefore, if the food, water or air around them contains harmful substances, children will experience higher levels of exposure. Children's behaviours can also increase their exposures. Young children tend to play on the ground and often put dirty objects in their mouths. As a result, children's ingestion of soil and dust is higher than adults'. Also, a child's "breathing zone" is closer to the ground, where levels of particulate matter4 and some chemicals may be higher.5
Rapid growth is a key factor in the greater risk children face from environmental hazards. Typically, infants double their birth weight within the first 4-6 months of life, and triple it by their first birthday.6 Cells that are growing and dividing most rapidly are more likely to be affected by environmental contaminants than those that are less active.7 Children's physiology is also different. For example, children are more susceptible to the effects of some toxic chemicals because their blood-brain barrier is more permeable than adults. They have immature immune and detoxification systems, and are less able to cope with environmental exposures. They also absorb more lead and other substances through the gastrointestinal tract than adults.8
Some groups of children are especially vulnerable to the effects of environmental hazards, such as those with an underlying disease or those living in poverty. For example, several chronic diseases, including asthma and cystic fibrosis, are worsened by exposure to poor air quality.12 Children living in low-income families are more likely to grow up in neighbourhoods adjacent to polluting industries and major roads.13
Taken together, these factors highlight the need for information on hazards in the physical environment and how they affect children's health.
How Are Children Exposed to Environmental Hazards?
Young children can be exposed to environmental hazards in many different ways. The following section outlines the ways in which children are exposed to these hazards in the natural and indoor environments.
The Natural Environment
The environment plays a crucial role in the healthy growth and development of children, and enhances their quality of life. In the natural environment, children can be exposed to environmental hazards in the air they breathe, the water they drink, the food they eat, and even the soil they come into contact with.
In 2000, Canada set new emission standards for the major components of smog (particulate matter and ozone) to be achieved by 2010. Several regions of Canada require major improvements in air quality to achieve these goals. However, most areas are below the maximum acceptable guidelines for other pollutants.
Air pollution is primarily associated with everyday human activities. Pollutants are released by motor vehicles, industrial processes (pulp and paper mills, ore smelters, petroleum refineries, power generating stations and incinerators), and the burning of fossil fuels such as gas, oil, coal and wood.
The most commonly measured outdoor air pollutants in Canada include ground level ozone, particulate matter, carbon monoxide, sulphur dioxide and nitrogen oxides. These substances are the principal ingredients or precursors of smog, and some also contribute to acid rain.
The types of health outcomes associated with air pollution in children (Table 1) are similar to those in adults, but children are more vulnerable. This is because children tend to play outdoors and are more active than adults. Moreover, children have a higher metabolic rate than adults, resulting in a threefold higher intake of air per unit weight per day. Because children's lungs are still developing, damage from repeated exposure to air pollutants can impede lung development and may lead to chronic lung disease later in life.14
| Air Pollutant | Health Outcomes |
| Particulate Matter | Increased mortality risk Reduced lung function and growth Worsens asthma Increased hospitalization for heart and lung disease and respiratory illness |
| Ground Level Ozone | Lung irritation and inflammation Reduced lung function Cough, chest pain, shortness of breath Reduced ability to exercise Worsens asthma and bronchitis Increased mortality risk Increased hospitalization for heart and lung disease and respiratory conditions |
| Carbon Monoxide | Reduced capacity of the blood to carry oxygen Reduced capacity to exercise Reduced time to onset of angina pain Neurobehavioural effects |
| Sulphur Dioxide | Worsens asthma Wheezing, chest tightness, shortness of breath |
| Nitrogen Oxides | Decreased lung function Cough, chest pain, shortness of breath Increased hospitalization for asthma |
Access to a safe and adequate supply of water for drinking, cooking and washing is essential for healthy child development. Safe drinking water is especially important for children's health because they drink more than two and half times more water than adults.16 Young children can be exposed to water-borne chemical and biologic pollutants through the consumption of contaminated water, or in some cases by absorbing chemical contaminants from water directly through their skin during recreational activities such as swimming or playing in water.
Today, about 87% of Canadians and their children receive treated municipal drinking water in their homes, resulting in one of the lowest rates of serious water-borne disease in the world.17 In Canada, the most common bacteria found in untreated water include Campylobacter, Escherichia coli (E. Coli), Salmonella and Shigella.18 In 1996, Campylobacter was the most common enteric disease brought to the attention of public health authorities,19 followed by Salmonella and Giardia (a parasite).20 Rates of reported Salmonella infection are higher in infants under one year of age than in any other age group and Campylobacter, Shigella, Giardia and E. coli O157 21 infections are reported more often for children 1-4 years of age than for any other group.22 Infections from these organisms can also come from food, and it is difficult to identify from sources of data on enteric infections whether they arise from water or food-borne pathogens. Children who are at greater risk of exposure include those who do not receive treated municipal water, for example, children living in rural and remote regions of the country.
Levels of chemical contaminants in treated drinking water are usually below the minimum detection levels or very low. However, water from private wells on, or close to, farms can contain high levels of nitrates, which have been linked to blood disorders in very young infants.
In Canada, food is the main route of exposure to biologic and chemical contaminants. It is especially important for children because they eat three to four times more than an average adult in relation to their body weight.23 Food-borne bacterial contamination results in over 10000 reported cases of food-related illness in Canadian adults and children every year, and it is estimated that there may be as many unreported cases.24 The leading causes of food-borne illness are Salmonella, Campylobacter, and E. coli. Most cases of illness could be prevented by proper food handling, storage and cooking.
Approximately 80%-90% of total daily exposure to persistent organic pollutants (POPs), such as PCBs, dioxins, and organochlorine pesticides, occurs through food.25 However, levels of many POPs in the environment have decreased over the past decade. The Northern Contaminants Program has found that some Inuit women from the North who eat traditional foods have levels of certain POPs and mercury in their bodies that are above Health Canada guidelines. Their infants may experience subtle neurodevelopmental effects as a result of early exposures to these toxic substances. Although the consumption of traditional foods containing contaminants may be associated with greater exposures and health risks, diets containing these foods have substantial nutritional benefits and are the foundation of the social, cultural and spiritual way of life for Canada's Aboriginal peoples.26
Research has shown the value of breastmilk for newborn's health and almost 80% of Canadian infants are breast fed at birth.27 However, it can contain very low levels of POPs accumulated in the mother's body, including PCBs and even some pesticides. Health Canada has monitored levels of these chemicals in breast milk since 1967. The results show that levels have decreased over time.
Although infants can be exposed to POPs through breast milk, Health Canada, the World Health Organization (WHO), the Canadian Pediatric Society and the American Pediatric Society all state that breast feeding provides known health benefits that far outweigh the theoretical risks associated with current levels of contaminants in breast milk.28
Infants and toddlers can ingest soil or dust by playing on the ground or by putting objects or their fingers into their mouths. It has been estimated that the average child ingests 0.1-0.2 milligrams of soil per day. However, children with "pica" (abnormal cravings for dirt or other non-food substances) can ingest from 5-10 grams of soil per day.29
The ingestion of dust and soil is widely regarded as the key pathway for childhood exposure to lead and other metals. Concentrations of many key metals and metalloids–including lead, mercury, arsenic, cadmium, copper, zinc and antimony–are commonly elevated in indoor dust compared to exterior dust and soil in ordinary urban environments. The precise causes for this enrichment in household dust are, in most cases, unknown.30 However, lead-based paint, used in older homes, contributes to lead levels in dust.
The Indoor Environment
Young children in Canada spend over 90% of their time indoors,31 primarily at home. The vast majority live in housing that meets or exceeds current standards for suitability, adequacy, affordability, and core need. Further work is needed to explore whether there is a causal relationship between housing and healthy child development.
Indoor air pollution is one of the primary risks to public health.32 Table 2 shows the most common indoor air pollutants of concern to children and their sources.
| Contaminant | Potential Sources |
| Asbestos | Old insulation on heating pipes and equipment Some vinyl floor tiles Pre-1977 drywall joint-finishing materials Cement-asbestos millboard and exterior wall shingles Old (pre-1970s) finishing plaster |
Combustion By-Products
|
Gas stoves and appliances Wood and coal stoves Gas and propane engines Fireplaces Back-drafting of exhaust flues Candles and incense |
Tobacco Smoke
|
Cigarettes Pipes Cigars |
| Aldehydes | Some particle board, plywood, pressed board, paneling Some carpeting and carpet backing (especially new materials) Some furniture and dyed materials Some household cleaners and deodorizers Some glues and resins Tobacco smoke Permanent press textiles |
Biologic Agents
|
Mold, mildew and other fungi Humidifiers and stagnant water Water-damaged surfaces and materials Condensing coils and drip pans in HVAC systems Drainage pans in refrigerators Some thermophilics on dirty heating coils Animals, rodents, insects Humans |
Radon
|
Soil- and water-derived radon gas Some building materials such as granite |
Volatile Organic Compounds (VOCs)
|
Solvents, fabric softeners, deodorizers and cleaning products Paints, glues, resins, stored gasoline, waxes and polishing materials Spray propellants, dry cleaning fluids Some fabrics and furnishings Pens and markers Binders and plasticizers |
Environmental tobacco smoke is the most harmful of all indoor air pollutants. Its main impacts on child health include increased risk of middle ear infections, asthma, bronchiolitis, low birth weight, sudden infant death syndrome, and burns.34
In 2001, 21% of Canadian children under 12 years of age were exposed to environmental tobacco smoke on a regular basis in their home. This figure represents just over 800000 children. It is, however, a significant improvement from 1996-1997 when smoking occurred in 33% of homes with young children.35
Biologic agents, including molds, mildew, bacteria, dust mites, pollen, pet dander, and arthropods (such as cockroaches) are a second major source of indoor air pollution. Molds and mildew thrive in moist environments such as kitchens, bathrooms and basements. They can cause allergic reactions in some children. One study of 30 Canadian communities showed that rates of asthma, bronchitis, chest illness, wheeze, and cough were significantly higher in damp and moldy homes.36 The presence of house dust mites, pet dander and cockroaches can also trigger allergic reactions, and are associated with exacerbation of asthma.37
Young children can be exposed to pesticides at home and studies indicate that pesticide products are used in over 90% of households.38 In one American study, more than 80% of the families surveyed used pesticides while someone in the house was pregnant and 70% used pesticides in the first six months of a child's life.39 Tracking of pesticide-contaminated soil and dust into homes by pets and people is a major source of pesticide residues in house dust.40 A recent article on children living in agricultural areas indicates that approximately 30% of the children had detectable concentrations of the herbicides 2,4-D or MCPA in their urine when these herbicides were used on their farm.41
Chemical Contaminants in Consumer Products
Occasionally, products intended for use by children have been found to contain chemical residues that could be harmful. For example, in the mid-1980s the use of diethylhexyl phthalate (DEHP) in soft vinyl children's products was phased out because of health concerns, and in 1998, Health Canada issued a Health Advisory regarding di-isonyl phthalate, which was used as a replacement for DEHP.42 Products affected by the Advisory included soft teethers, rattles and other soft vinyl toys that very young children may chew or suck.
Young children can be exposed to chemical hazards in other types of products, especially those used to build, decorate or furnish the home. Particle-board, carpets, draperies, solvents, paints, glues and varnishes can all release volatile organic compounds, such as aldehydes, especially when they are new or newly applied. Children can also be exposed to low levels of the chemicals used in wood preservatives if they touch treated wood or ingest contaminated soils via hand-to-mouth activity. Although the health risks are very small,43 the wood industry is phasing out–by the end of 2003–the use of copper chromated arsenate (CCA) to treat wood used for residential purposes.44
In recent years, levels of polybrominated diphenyl ethers (PBDEs) have increased significantly in the environment45 and in human breast milk.46 PBDEs are used to decrease the likelihood and intensity of fire in a wide variety of products, including vehicles, furniture, textiles, carpets, building materials, electronic circuit boards. They are suspected to disrupt thyroid metabolism and have adverse neurological effects,47 but further research is needed to confirm these findings.
Measures of Health and Disease
It is often very difficult to establish that environmental hazards cause specific health problems in children. This is because most health problems can be caused by a variety of factors–not just exposures to environmental hazards. However, epidemiological and toxicological studies can provide information suggesting or indicating that environmental exposures play a role in causing disease. For example, a recent American study has estimated that 30% of all childhood asthma, 10% of neurobehavioural disorders, 5% of cancer and 100% of all childhood lead poisoning are related to environmental pollutants.48
This report considers three measures of child health and disease that have been associated with environmental hazards: asthma, birth outcomes, and neurodevelopmental disorders.
Asthma
Air pollution and other environmental hazards are associated with several respiratory conditions, including exacerbation of asthma. Asthma can cause wheezing, difficulty in breathing, and chest pain. It is the most common chronic disease among children.49
Susceptibility to asthma among children appears to be determined during fetal development and in the first 3-5 years of life. Air pollution is not likely to cause asthma on its own, but can make it worse. Other possible environmental risk factors include exposure to environmental tobacco smoke and airborne allergens such as molds, pet dander, house dust mites, and cockroaches.
Ten percent of young Canadian children from birth to 5 years of age were diagnosed with asthma in 2000-2001.50 Asthma is a major cause of hospitalization for children in Canada, contributing to 12% of all admissions in the birth to 4 years age group. In 1998, children less than 5 years of age had the highest hospitalization rates resulting from symptoms of asthma of any age group, and boys of this age are more likely to be hospitalized than girls.51 However, hospitalization rates are now decreasing for both boys and girls (see Figure 1).
Figure 1: Asthma Hospitalization Rates (per 100000) by Sex for Children from Birth to 4 Years of Age, 1987/88-1998/99 (standardized to 1991 Canadian population)52
Source: Centre for Chronic Disease Prevention and Control, Health Canada using data from Hospital Morbidity File, Canadian Institute for Health Information.
Birth Outcomes
A healthy birth weight is a key determinant of child health. Low birth weight (less than 2500 grams or about 5.5 pounds) can result in serious health problems and developmental delays. In 2000, 5.6% of all babies born in Canada had a low birth weight. More than half of all low birth weight babies are premature,53 meaning they were born before 37 weeks of gestation.
An environmental factor that influences birth weight is maternal smoking. In 2000–2001, 18.5% of mothers of young children indicated that they had smoked during their pregnancy.54 Other environmental factors that may be important include maternal exposure to PCBs, lead, some pesticides and outdoor air pollution.55 One recent study in Canada's North found that prenatal exposure to PCBs decreased birth weight and length as well as duration of pregnancy.56 These findings are consistent with previous studies conducted with other populations.57
Neurodevelopmental Disorders
Studies suggest that between 3% and 8% of babies born each year in the United States will be affected by neurodevelopmental disorders.58
Neurodevelopmental disorders are disabilities in the functioning of the brain and/or nervous system that affect behaviour, memory and/or the ability to learn. The causes of these problems are largely unknown. However, some studies have indicated that exposure to some environmental contaminants may play a role.
Exposure to lead, in pregnancy or early childhood, is associated with several neurodevelopmental effects, including learning problems, reduced intelligence and impaired cognitive development. It has also been linked with attention deficit/hyperactivity disorder, increased likelihood of dropping out of school, having a reading disability, lower vocabulary, lower class standing in school, and increases the risk of antisocial and delinquent behaviour.59 Fortunately, average blood lead levels in most Canadian children have been dropping since the early 1970s, primarily because of the phase-out of leaded gasoline.
Neurodevelopmental effects have been reported in three major studies on children from New Zealand, the Seychelles, and the Faeroe Islands who were born to women who ate sea fish or mammals containing methylmercury during and before pregnancy.60 The effects included reduced intelligence, inattentiveness and poor memory and the extent of the effects correlated with the mothers' exposures. The effects on children in New Zealand and the Faeroe Islands were still present at 7 years of age, while they had faded in the Seychelles children whose mothers had lower mercury levels at the start of the study. Canadian studies of remote fishing communities in Northern Quebec have shown a correlation between immune system development and exposure in utero to methylmercury, PCBs, and lead.61
While studies have linked maternal consumption of foods contaminated with PCBs and measures of cognitive functioning in infancy or childhood, the mechanism of action is not clear.62 It may be that PCBs disrupt normal endocrine hormone metabolism, which may have an impact on neurodevelopment.
Conclusion
Studies are increasingly indicating that the physical environment significantly affects the health and development of children. Ongoing research will help to further our understanding of the linkages between environmental hazards and specific health problems in children.