Box 1.5 Children's special vulnerability

Worldwide, as much as two thirds of all preventable ill health due to environmental conditions occurs among children (1). Children most affected belong to impoverished populations living in rural and peri- urban areas in developing countries. Currently, many of these children are exposed not only to biological hazards associated with lack of access to a clean environment, but also to toxic chemicals and other pollutants that stem from uncontrolled development. These pollutants include agrochemicals, industrial chemicals such as polychlorinated biphenyls (PCBs), heavy metals such as lead and arsenic, and a variety of air pollutants. These substances have been linked with birth defects, cancer, and weakening of the immune system.

The risk for contracting environmentally related illness is altered by several factors including a person’s genetic background, nutritional status, age, lifestyle, and income level. Age is a major determinant of risk because the processes that determine exposure, absorption, metabolism, excretion, and tissue vulnerability are all age-related. The metabolism of infants and children differs from those of adults, as do their physiological and biochemical processes (2).

Susceptibility – the capacity to be affected – is a key factor in determining environmental risks to children. It also varies among different populations, ethnic groups, and genetic backgrounds, as well as by age, experience, and development. The combination of increased susceptibility and increased opportunity for exposure to a particular set of environmental threats – such as some pesticides and air pollutants – can increase health hazards for children (3).

Exposure to environmental agents is the first step in the sequence of environmentally related health effects. Exposures to these agents can occur even before conception, if the mother is exposed to certain pollutants that cross the placenta, such as lead or mercury. Exposures vary depending on one’s physical location, breathing zones , oxygen consumption, and behavioral and eating patterns, all of which can change several times before an individual reaches adulthood.

The sources and routes of exposure to toxic substances for children are multiple. Some exposures are occupationally related – when children work in fields sprayed with pesticides, for instance, or when parents carry home chemical residues on clothing, or when chemicals to which the mother is exposed at work are transferred via breast milk to the child. Still other exposures can come from discharges to the air and water, certain waste sites, and on occasion, industrial accidents (4).

Because they have higher metabolic rates than adults, children breathe more air – twice as much per pound of body weight – than adults. In addition, children breathe air that is closer to the ground, where concentrations of contaminated dust can be higher. When children are more active, they inhale more deeply and may deposit pollutants deeper into their lungs than adults. These particles are more readily retained in the lungs and absorbed (5).

The maximum concentration of air pollutants recommended by the World Health Organization (WHO) is routinely exceeded in many Latin American cities including S