儿童健康研究【英文论文】

Concurrently, research fi ndings provide a clearer understanding of the hazards children face and of the links

between environmental degradation and health. Since 19, concern for the environment and health in Europe

has united the Member States in the WHO European Region, intergovernmental organizations, civil-society

organizations and the European Commission in a common commitment to improve our environment and our

health.

In 2002, Margot Wallström,1 then European Commissioner for the Environment, stressed that children’s

health and environment needed to be high on the political agenda. Political attention to environmental and

health matters culminated in the Fourth Ministerial Conference on Environment and Health, held in Budapest,

Hungary in June 2004. Here, the Children’s Environment and Health Action Plan for Europe was agreed at the

highest political level, setting the scene for national action and implementation.

The political momentum from the still tangible enthusiasm of the Conference should not be lost. To be effective,

the Action Plan, with its commitments packed concisely into less than a dozen pages, needs to be adapted

to particular national settings. This publication provides the tools for countries effectively to do just that.

Today, collaboration between WHO and the European Commission continues to strengthen, with the support

of our Member States. We are all committed to channelling our efforts towards a common goal – that of

providing a healthier future for our children.

Children’s vulnerability to

biological and social factors in the

physical environment

Biological, economic and social factors greatly infl uence children’s vulnerability to environmental risk factors

in their different developmental stages, from conception to adolescence. Environment and health policies

aimed at protecting children (and women of reproductive age) need to account for these factors and their interactions.

Biological factors

Critical windows of susceptibility during growth and development

Developing organisms are fragile and – due to their rapid growth and development – exceptionally

susceptible

to various chemical and physical agents. Developing organs and systems typically go through periods of high

vulnerability or critical windows of susceptibility. For example, in the embryo, cell growth is particularly rapid

and primary differentiation occurs, providing more opportunity for toxicants to cause mutations and congenital

anomalies (Selevan, Kimmel & Mendola, 2000). During the prenatal and postnatal periods, structures are

developed and vital connections are established. For example, during the fi rst years of life, most of the nervous

system develops. The nervous system has a limited capacity to repair any structural damage; the destruction of

brain cells by chemicals such as lead and mercury, or failure to establish vital connections between nerve cells,

may therefore result in permanent and irreversible dysfunction (Rice & Barone, 2000).

This is why exposure to many external agents during growth and development may produce adverse effects

on health, such as birth defects and neurodevelopmental damage, that have no counterpart in adult life. The

concept of windows of susceptibility is particularly important since it emphasizes that both the dose and the

timing of the exposure may be crucial in determining the nature and amount of the effect. Immature metabolism

Children’s metabolic pathways, especially in the fi rst 6–12 months after birth, are immature and may therefore

be less capable of detoxifying and excreting chemicals than those in adults, which is why lower doses per kg of

weight and longer intervals are recommended for most drugs prescribed for infants during the fi rst weeks and

months of life (Chemtob, 1991). In some instances, however, metabolic immaturity may be benefi cial with respect

to toxicity. Children may actually be less sensitive than adults to some compounds, because the metabolic

pathways that activate their toxic metabolites are not yet developed. In many other instances, infants are more

susceptible, because they do not have the capacity to metabolize (and thus detoxify) toxic compounds (Crom

et al., 1987; Bruckner, 2000; Scheuplein, Charnley & Dourson, 2002). The whole sequence of absorption, distribution,

biotransformation and excretion of xenobiotics in children differs from that of adults, particularly in

the fi rst months of life, and the overall result of these toxicity differences is typically substance specifi c (Bearer,

1995; Faustman et al., 2000; Scheuplein, Charnley & Dourson, 2002).

Greater exposure

Children may be more heavily exposed, per unit of body weight or body surface, to environmental risk factors

than are adults. There are a number of reasons for this. First, infants and young children drink more water, eat

more food and breathe more air than adults in relation to their body weight (Table 1).

Second, the absorption of many chemicals in the intestines is also increased in children. For example, infants absorb as much as 50% of the lead present in food, while adults have an uptake of only 10% (Royce, 1992). Overview of environmental risk factors and their effects on children’s health Introduction

Some of the environmental risk factors to which children are exposed act in a very specifi c way and contribute

to specifi c effects on health. Most of the effects, however, as outlined in Chapter 2, are the combined result of

many environmental factors and their interactions with social and economic factors. Understanding the hazards

prevalent in the various settings for children’s lives is a very important foundation for setting-based interventions.

Also, understanding the role of each factor and its contribution to specifi c adverse outcomes on children’s

health would be very useful in identifying courses of protective action.

Unfortunately, the epidemiological and toxicological studies intended to unravel associations between environmental

risk factors and specifi c conditions have several limitations. These are both external (such as insuffi

cient resources and available information for potentially important studies) and internal (such as inherent or

unavoidable limitations in design). An awareness of these limitations might help in understanding the varying

strength of the evidence on specifi c associations. Given these limitations, this chapter provides an overview of

the current knowledge of the main environmental risk factors and the main effects on health that result from

exposure in childhood, from before conception to adolescence. Current estimates of the burden of disease in

children, expressed in deaths and DALYs associated with some of the main environmental factors in the European

Region, are also provided. Valent et al. (2004a) describe WHO’s methods in estimating the burden of

disease attributable to each factor.

Poor indoor air quality

Burning coal or biomass at home for cooking and heating creates smoke emissions. Such smoke contains carbon

monoxide, nitrogen oxides, sulfur oxides, benzene, formaldehyde, polyaromatic compounds, and suspended

particulate matter (PM). Indoor sources of air pollution are likely to produce very high levels of exposure

(Bruce, Perez-Padilla & Albalak, 2000; Ezzati & Kammen, 2001), and the highest levels of indoor air pollution

(up to 2000 μg/m3 PM10 – PM with an aerodynamic diameter smaller than or equal to 10 μm) are produced

by use of biomass solid fuel. Since children spend most of their time indoors, they are likely to receive high

levels of exposure, even for pollutants with relatively low concentrations in air. Exposure levels are higher in

conditions of poor ventilation.

On a global basis, solid fuel use represents the largest source of indoor air pollution. It is still widespread in

many countries in the European Region. In eastern Europe and central Asia, an estimated 22.8–41.5% of households

still rely on biomass fuel (wood and coal) combustion for heating and cooking (World Bank, 2003).

High levels of indoor air pollution lead to an increased risk of lower respiratory infection in children, resulting

in increased morbidity and mortality (Bruce, Perez-Padilla & Albalak, 2000; Ezzati & Kammen, 2001;

Black, Morris & Bryce, 2003). In Eur-B and -C, it has been estimated that 1.1–6.6% of deaths and 0.7–5.0%

of DALYs in children aged 0–4 years, as well as 3.7–11.5% of the total asthma burden in children aged

5–14 years, are attributable to indoor air pollution due to solid fuel use (Valent et al., 2004b).

Morbidity linked to poor indoor air is observed even in the most developed areas, owing to exposure to ETS,

chemicals in furnishing and construction materials, and such biological agents as moulds. Maternal smoking is associated with adverse outcomes of pregnancy, such as miscarriage premature

birth, low birth weight and some congenital anomalies, and with increased risk of respiratory diseases and developmental delay in the early years of life (DiFranza & Lew, 1995, 1996). Also, exposure to ETS after birth

is associated with increased incidence of respiratory infections and wheezing and is likely to cause an increase

in chronic respiratory disease and cancer later in life (DiFranza & Lew, 1996; Ji et al., 1997; Strachan & Cook,

1998; Courage, 2002). Environmental health indicators

In recent years, the WHO Regional Offi ce for Europe, working with several Member States, EEA and the

EC Directorate-General for Health and Consumer Protection, has made substantial progress towards creating

a harmonized environment and health information system based on common indicators. The environmental

health indicators that have been developed and pilot tested use solid scientifi c evidence about the links between

health effects and environmental exposures to foster policy development. The work resulted in: • methodological guidance for generating and analysing key environmental health indicators and using them

in policy-oriented reporting;

• after a check of the indicators for compatibility with EU legislation, the proposal of a core set of 17 to become

part of the EC health indicators (WHO Regional Offi ce for Europe, 2003a, 2004b); and

• World-Wide-Web-based tools bringing together the data necessary to construct selected indicators from

different information sources and to facilitate access to information.

Demonstration products applying the environmental health indicator methodology were prepared for the Budapest

Conference: a pilot report (WHO Regional Offi ce for Europe, 2004c) and a prototype Web portal (WHO

European Centre for Environment and Health, 2004).

Along with the CEHAPE, the Budapest Conference participants

References

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Atlanta, GA, Agency for Toxic Substances and Disease Registry.

ATSDR (1995). Study of effect of residential proximity to waste incinerators on lower respiratory illness in

children. Atlanta, GA, US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry.

Autier P, Doré JF (1998). Infl uence of sun exposures during childhood and during adulthood on melanoma risk.

EPIMEL and EORTC Melanoma Cooperative Group. European Organisation for Research and Treatment

of Cancer. International Journal of Cancer, 77(4):533–537.

Barker DJP (1998). Mothers, babies, and health in later life. Edinburgh, Churchill Livingstone. Bearer CF (1995). How are children different from adults? Environmental Health Perspectives, 103(Suppl. 6):7–12.