Features of the physical environment represent only one dimension of the risk factors that influence a child’s exposure to environmental contaminants.

There is growing awareness of how poverty plays a role in compounding the adverse effects on children’s health from environmental exposures.

Additional Factors Influencing Environmental Health

Features of the physical environment represent only one dimension of the risk factors that influence a child’s exposure to environmental contaminants.

Genetic Differences

We presume that genetic differences between children play a considerable role in determining variability in response to environmental agents. Genes are involved in regulating functions as diverse as growth, development, metabolism, replication and repair. We are learning that the degree of individual genetic variability within the human species is immense. This variability is not well characterized and therefore represents a huge "unknown" in determining who will or will not be susceptible to adverse effects from environmental exposures.

There are a few well-documented examples of chemical sensitivities due to specific genetic differences such as deficiency of the enzyme G6PD (an X-linked disorder), which increases the individual’s susceptibility to the toxic effects of certain oxidant chemicals. Canadian researchers have shown that children who carry certain genetic mutations in the P450 cytochrome enzyme system that is involved in carcinogen metabolism had higher odds of developing acute lymphoblastic leukemia (ALL) with exposure to certain insecticides used indoors.15 We suspect that asthma likely occurs in those with a particular genetic predisposition who have an environmental exposure of some type that causes their physical symptoms to be expressed. As yet, there is no way to accurately predict who is at greatest risk of developing asthma because of such a genetic predisposition.

The Social Environment: Poverty as a Risk Factor

Childhood poverty is on the rise among Canadian children. The National Longitudinal Survey of Children and Youth determined that 1.2% of Canadian children experience hunger.16 Physicians need to be aware of the potential for children’s social and economic circumstances to affect their health. There is growing awareness of how poverty plays a role in compounding the adverse effects on children’s health from environmental exposures. This has been shown convincingly with respect to exposures to substances such as lead and pesticides.

Poorer, older housing is more likely to be unclean and in a deteriorated state. These facts increase the chances that pests such as cockroaches or hazards such as peeling lead-based paint exist, thereby increasing the risk of exposed to bioallergens (such as cockroach feces) that induce asthma,17 to pesticides used against insects, or to lead-tainted dust in the home. Studies have shown that socioeconomic status is strongly linked to the severity of asthma experienced and that poor children are more likely to suffer from disabling asthma (i.e., that has to be treated in hospital).

Poor nutrition of children from low-income homes is a risk factor because it compromises immune functioning and influences the absorption of contaminants. For example, low dietary calcium is associated with increased gastrointestinal absorption of lead, and iron-deficient children are more likely to eat soil, which can expose them to contaminants, lead among them.10 The JAMA editorial by Thomas D. Matte, MD, MPH, entitled "Reducing Blood Lead Levels: Benefits and Strategies" outlines some recent research on the characteristics of children most vulnerable to lead exposure and discusses the implications for prevention.

Among the most vulnerable subgroups of Canadian children, aboriginal children potentially suffer the worst of all possible worlds. They are much more likely to live in lower socioeconomic conditions than non-aboriginal children. Also, there is often a greater load of contaminants in their environment due to a number of factors.19,20,21 Because of the phenomena of long-range transport and biomagnification of persistent contaminants, their traditional dietary food items are increasing their exposure. In some cases, the operative factor is the proximity of reserves to sources of environmental exposures such as industrial emissions or waste storage sites.

Other influences indirectly impact the health of children of lower socioeconomic status. Women may have little choice in the jobs they work at and their occupational exposures may put their children (both unborn and living) at risk of exposure. Researchers from Toronto’s Hospital for Sick Children conclude that those who were occupationally exposed to organic solvents during pregnancy had a 13-fold risk of fetuses developing major malformations compared to controls.3

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