Tài liệu THE BURDEN OF DISEASE ATTRIBUTABLE TO ENVIRONMENTAL POLLUTION pptx

THE BURDEN OF DISEASE

ATTRIBUTABLE TO ENVIRONMENTAL POLLUTION

Professor Ian Mathews and Dr Sharon Parry

Department of Epidemiology, Statistics, Public Health

University of Wales College of Medicine

Cardiff University

Heath Park

Cardiff

CF14 4XN

The views presented in this paper are those of the authors and do not necessarily

represent HPA views

July 2005

The burden of disease attributable to environmental pollution

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Summary

This paper presents a summary of the information available in the literature aimed at

estimating the fraction of mortality and/or morbidity that can be attributed to

environmental factors. It is a first step in the process of quantifying the possible burden

of disease from environmental pollution. Current estimates are based on very uncertain

data and limited datasets and therefore need to be interpreted with extreme caution.

The extent to which environmental pollutants contribute to common diseases is not

accurately resolved. However, global estimates conservatively attribute about 8-9% of

the total burden of disease to pollution. Data is presented on the evidence available for

diseases such as asthma, allergies, cancer, neuro-developmental disorders, congenital

malformations, effects of ambient air pollution on birth weight, respiratory and

cardiovascular diseases and mesothelioma. Health effects from environmental lead

exposure and disruption of the endocrine function are also presented.

1. Background

The need to estimate the burden of disease associated with pollutants is highlighted not

only by the evidence base on associations but also by the scale of use of chemicals in

our modern society. Fifteen thousand chemicals are produced in quantities in excess of

10,000 pounds annually and 2,800 are produced in annual quantities in excess of 1

million pounds. These high volume chemicals have the greatest potential to be

dispersed in environmental media and less than half of these have been tested for

human toxicity (US EPA, 1996; Goldman LR et al, 2000; NAS, 1984). There are

approximately 30,000 chemicals in common use and less than 1% of these have been

subject to assessment of toxicity and health risk (Royal Commission on Environmental

Pollution, 2003).

Environmental pollutants may be defined as chemical substances of human origin in air,

water, soil, food or the home environment. The extent to which such pollutants may

contribute to common diseases of multi-factorial aetiology is not accurately resolved.

However in recent years attempts have been made to estimate the environmentally

attributable burden of disease globally, in the USA and in regions of Europe. In the first

instance estimation has concentrated on health outcomes for which there is strong

evidence of an association with pollutants.

At a global level a summary of early estimates first appeared in the 1997 report ‘Health

and Environment in Sustainable Development’ by the World Health Organisation (WHO,

1997). In subsequent years further estimates have been made of the fraction of

mortality and morbidity that can be attributed to environmental factors (Smith KR et al,

1999; Ezzati M et al, 2002). Substantial proportions of global disease burden are

attributable to these major risks where developing countries bear the greatest burden,

unsafe water and indoor air pollution are the major sources of exposure and children

under five years of age seem to bear the largest environmental burden. Estimates vary

The burden of disease attributable to environmental pollution

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but conservatively about 8-9% of the total disease burden may be attributed to pollution

(Briggs D, 2003).

In the framework of the European Environment and Health Strategy various

Technical Working Groups on priority diseases reviewed the evidence base in

support of the development of the Children’s Environment and Health Action Plan

for the European region (CEHAPE) expressed in the Budapest declaration (WHO

2004a). It was considered that one sixth of the total burden of disease from birth

to 18 years is accounted for by exposure to contaminated air, food, soil and water

causing respiratory diseases, birth defects, neuro-developmental disorders and

gastrointestinal disorders. Waterborne gastrointestinal disorders are not a major public

health problem in the UK. The remaining priority diseases identified by CEHAPE are

considered below for children.

In Section 2 two different methodologies are outlined by which burden of disease

attributable to environment can be estimated. In the first the health loss due to

environmental risk factor(s) is calculated as a time-indexed “stream” of disease burden

due to a time-indexed “stream” of exposure. Such a time-indexed “stream” of exposure

data is only available for environmental lead and ambient urban outdoor air pollution.

Therefore in Section 9 WHO estimates of the burden of disease attributable to

environmental lead exposure are presented. Similarly in section 10 and 11 estimates

are given of the burden of disease due to exposure to air pollution published by the

Committee on the Medical Effects of Air Pollution of the Department of Health.

Since population exposure data are lacking in connection with asthma, cancer and

neurobehavioral disorders a second methodology is employed in Sections 3, 5 and 6.

This was devised in the U.S. specifically for children and is outlined in Section 2. This

method is also used to infer the burden of allergy attributable to environment in

Section 4.

Finally the primary research literature was assessed to estimate the burden of

congenital malformations attributable to environment (Section 7) as well as effects of

ambient air pollution on birth weight (Section 8) and on children’s lung function (Section

10).

2. Methodology

The Global Burden of Disease (GBD) 1990 project stimulated debate about the crucial

role of risk factor assessment as a cornerstone of the evidence base for public health

action. It was affected by a lack of conceptual and methodological comparability across

risk factors but the Comparative Risk Assessment (CRA) project co-ordinated by WHO

was planned as one of the outputs of the GBD 2000 project to strengthen these aspects.

(WHO 2004b). In particular in the CRA framework:

• The burden of disease due to the observed exposure distribution in a

population is compared with the burden from a hypothetical distribution or

The burden of disease attributable to environmental pollution

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series of distributions, rather than a single reference level such as the non￾exposed population.

• The health loss due to risk factor(s) is calculated as a time-indexed

“stream” of disease burden due to a time-indexed “stream” of exposure.

• The burden of disease and injury is converted into a summary measure of

population health, which allows comparing fatal and non-fatal outcomes,

also taking into account severity and duration.

The CRA framework has been used to investigate the burden of disease associated with

exposure to a limited number of environmental risk factors. These are: unsafe water,

sanitation and hygiene, urban air pollution and indoor air pollution from household use of

solid fuels as well as lead exposure (WHO 2004c).

To provide the knowledge base for the development of the Children’s Environment and

Health Action Plan for the European region (CEHAPE), the burden of disease

attributable to environmental factors (BODAE) was assessed in terms of deaths and

disability-adjusted life years (DALYS) among children and adolescents. The

assessment was restricted to outdoor and indoor air pollution, inadequate water and

sanitation and lead (Valent F et al, 2004). The methodology employed is outlined in

Appendix 1 and used the distribution of risk-factor exposure within the study population

and the exposure-response relation for the risk factor to calculate the impact fraction for

the particular health outcome.

To date the estimates of burden of disease attributable to environmental factors

provided by the WHO are of limited value in a UK context with the exception of lead

exposure. Inadequate water and sanitation and indoor air pollution from household use

of solid fuel for cooking and heating are not major issues in the UK. Further the

population health effects arising from outdoor ambient air pollution have been estimated

by the Committee on the Medical Effects of Air Pollution (COMEAP) of the Department

of Health (COMEAP 1998).

However, a different methodology has been developed and employed in the USA to

estimate the morbidity and mortality for asthma, cancer and developmental disabilities in

children. (Landrigan P.J. et al 2002) For each disease, expert panels were convened

from prominent physicians and scientists with extensive research publication in the field.

Each panel member was supplied with an extensive collection of reprints of published

articles that discussed linkages between the disease in question and toxic

environmental exposures. A formal decision-making process, the modified Delphi

technique (Fink A. 1984), was then enacted by which the panel developed a best

estimate from 0% to 100% of the Environmentally Attributable Fraction (EAF) for the

disease in which they were expert. Panels chose deliberately not to consider outcomes

related to tobacco or alcohol that are the consequence, at least in part, of personal or

familial choice. It is these EAF’s which are used below in estimating the BODAE for the