Children are uniquely vulnerable to pollutant exposures

From the time of implantation, through gestation, birth, and early childhood, humans are exposed to chemicals and chemical combinations, which place their health in jeopardy. Numerous toxic agents have been detected in umbilical cord blood samples, a finding potentially significant because tissues, organs, and genetic material of the unborn and young are particularly susceptible to biologic insult. The National Research Council reported in 1993 that children are uniquely vulnerable to pollutant exposures because growing and developing organ systems may suffer permanent impairment.

A growing body of literature suggests there is an association between maternal inhalation of common ambient air pollutants and adverse birth outcomes, including an increased risk for preterm delivery, intrauterine growth retardation (IUGR), low birth weight, small head circumference, and increased rate of malformations. Potentially more worrisome are recent studies, which report a relationship between exposure to airborne particulate matter and heritable mutations in laboratory animals. The contaminants noted in these studies are ubiquitous to many urban environments.

Outdoor air pollution is not the only potential source of non-employment-related airborne contamination. The United States Environmental Protection Agency (EPA) determined that people in developed countries spend 90% of their time indoors, where the air pollutant concentration is 3 to 5 times higher than outdoors. Although research examining the effect of indoor air pollutants on pregnancy outcomes is sparse, data gleaned from environmental tobacco smoke studies suggest reason for concern. Nonsmoking pregnant women exposed to environmental tobacco smoke have an increased risk of delivering a low birth weight infant.

After birth, children continue to be vulnerable, particularly for exposure to air pollutants. The EPA found that children under the age of 1 have inhalation rates 3.4 times higher per kilogram of body weight than their adult counterparts; for children aged 3 to 5 years, the ratio is 2.8 times higher.Children very likely internalize greater doses of contamination from pollutants suspended in the air column as a function of their inhalation rates and body weight, and endure greater risk of excessive tissue damage because of their underdeveloped immune systems.

Children suffer disproportionately from exposure to environmental hazards in general and indoor air pollutants in particular. Globally, 40% of disease burden attributable to environmental factors impacts children under the age of 5, although this cohort accounts for only 10% of the world's population. An egregious environmental risk factor is exposure to indoor cooksmoke (i.e., the combustion contaminants generated from fuels during the cooking of foods and other indoor activities requiring fire).

An estimated 90% of rural households in developing countries and up to one half of homes worldwide use biomass fuels as their primary source of energy (biomass homes). These fuels are plant based in origin; examples include animal dung, crop residues, wood, and charcoal. Unfortunately, the products of incomplete combustion emanating from these burning fuels include a catalog of pollutants known to present risk to human health. A partial list includes airborne particulate matter, polynuclear aromatics, carbon monoxide, formaldehyde, and oxides of nitrogen and sulfur.

The indoor combustion of biomass fuels has been linked to acute lower respiratory infections, the single most important cause of mortality in children under the age of 5, accounting for some 2 million deaths annually. Acute lower respiratory infection is also the cause of mortality for many children reported to have measles, pertussis, and HIV/AIDS.

Poverty is a strong predictor of indoor air contamination in developing countries. Modest income earners rely on accessible, low-quality/low-cost fuels, and frequently reside in homes that tend to exacerbate poor air quality. Cooking fires are customarily contained in 3-stone stoves, open pits, or inefficient cooking appliances, all of which have a propensity to produce copious quantities of air pollutants. The dwellings often do not possess chimneys to capture and expel smoke and combustion by-products, and in many cases, are not designed to maximize dilution ventilation from doors and windows, exacerbating an already risk-prone environment. Although few empirical studies have been conducted to assess risk to mothers, women of reproductive age, and children, the few data that exist suggest substantial exposures to indoor air pollutants occur.

One representative contaminant, airborne particulate, can be relatively easily measured in the indoor environment. Small airborne particles possess an aerodynamic diameter of 10 microns or less, and are hazardous because they can be inhaled deeply into the lung and serve as a vehicle for toxins that may be adsorbed onto their surface. Particle concentrations in the range of 300 to 3000 mcg per cubic meter of air are present during cooking in biomass homes, with peak concentrations upward to 30,0000 mcg/m3. As a point of reference, the EPA has traditionally maintained 2 standards to protect human health against exposure to small airborne particulates. The first standard is a 24-hour average exposure of 150 mcg/m3, which is not to be exceeded more than once per year. The second standard is 50 mcg/m3, which represents an average annual exposure that should not be exceeded, on average, over the course of a calendar year.

Few studies have quantified the combustion contaminant exposure to women while they cook using biomass fuels. To gain insight into this issue and to bolster the public health inventory of published works on this subject, the authors conducted a preliminary study in Gimbie, Ethiopia, to assess various factors associated with exposure to cooksmoke in that environment.


http://www.medscape.com/viewarticle/507502_2