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Springer 2005
European Journal of Epidemiology (2005) 20: 183–199
DEVELOPMENTAL EPIDEMIOLOGY
Exposure to ambient air pollution and prenatal and early childhood health effects Marina Lacasan˜a1,2,3, Ana Esplugues1,2 & Ferran Ballester1,4 1
Epidemiology and Statistics Unit, Valencian School of Studies for Health, Valencia, Spain; 2University Hospital La Fe, Valencia, Spain; 3Center for Environmental Health, Center for Research in Populational Health, National Institute of Public Health, Cuernavaca, Mexico; 4Public Health Department, History of Science and Gynaecology, Miguel Herna´ndez University, Alicante, Spain Accepted in revised form 7 September 2004
Abstract. Over the last years, concern for the possible influence of exposure to air pollutants in children during gestation or the first years of life has grown; exposure levels which may be reached nowadays in our dwellings and in our streets. In the present study evidence over the possible impact of ambient air pollution on the foetus and the infants (i.e.: less than 1 year) published during the last decade, 1994–2003, are revised. Studies on infant mortality and exposure to particles show an outstanding consistence in the magnitude of the effects, despite the different designs used. As a whole, data show that an increase in 10 lg/m3 of particle concentration (measured as PM10) is associated with to about 5% increase in post-neonatal mortality for all causes and
around 22% for post-neonatal mortality for respiratory diseases. Regarding damage in foetal health, although results are not always consistent, most studies show associations with exposure to air pollution during pregnancy. However, the precise mechanisms of action of air pollutants on adverse reproductive results are still unknown, so is the period of exposure most relevant during pregnancy and the specific pollutant which may represent a higher risk. Follow-up studies evaluating personal exposure to different air pollutants are required, allowing for the adequate evaluation of the impact of each pollutant in different periods of pregnancy, as well as providing hypotheses on their possible mechanisms of action.
Key words: Ambient air pollution, Congenital defects, Intrauterine growth retardation, Low birth weight, Mortality, Preterm delivery Abbreviations: BW = birth weight; CI = confidence interval; CO = carbon monoxide; IQR = interquartile range; IUGR = intrauterine growth retardation; LBW = low birth weight; NOx = nitrogen oxides; O3 = ozone; PAH = polycyclic aromatic hydrocarbons; PCB = polichlorinated biphenyls; PM10 = particles £ 10 lm diameter; PM2.5 = particles £ 2.5 lm diameter; TSP = total suspended particles; SGA = small for gestational age; SIDS = sudden infant death syndrome; SMR = standardized mortality ratio; SO2 = sulphur dioxide; WP = weeks of pregnancy
Introduction Foetal growth may be altered by maternal pathologies (diabetes, hypertension, etc.), by deficient diets, by exposure to toxic substances (tobacco, alcohol, drugs), and by ambient pollutants in air [1–3], in water and in soil [4, 5]. The foetus and the infant present a special vulnerability, compared to adults, regarding ambient toxicants due to differences in exposure, physiological immaturity, and longer life expectancy after exposure. Results from epidemiological and experimental studies show that foetuses and infants are especially susceptible to the toxic effects of pollutants such as suspended particles, polycyclic aromatic hydrocarbons (PAH), and tobacco smoke [6]. In the case of
exposure to air pollutants where exposure occurs through inhalation, children inhale a relatively higher volume of air than adults. In recent years there is a growing concern about the possible influence on health of the exposure to air pollutants during pregnancy or first childhood; exposure to concentrations which may be reached nowadays in our homes or streets. Recent studies have added proofs of the impact of exposure to air pollution on the risk of intrauterine or post-neonatal death [7, 8], or congenital defects [9], prematurity [10, 11] and foetal development [1, 3, 12]. We review the original studies which have evaluated the possible impact of ambient air pollution on the foetus and the first year of life, published in the last 10 years, from January 1994 to December 2003.
184 Methods and materials
Inclusion criteria
Search strategy
The articles included follow these criteria: (a) original article; (b) observational epidemiological study; (c) exposure to outdoor air pollutants; (d) prenatal or up to first year of life exposure, and (e) languages: English, French, Spanish, Portuguese or Italian.
A bibliographical search was carried out in the online database MEDLINE (http://www.ncbi.nlm.nih.gov/ entrez/query.fcgi). With the MESH Thesaurus, the following search syntax was used (‘Air Pollution’[MeSH] AND (‘Pregnancy’ OR ‘reprod*’ OR ‘infant’ OR ‘foetal’) AND ‘Exposure’ Limits: 10 Years, Human). As a time frame, 10 years previous to the search date (December 2003) were selected. Additional to the search in MEDLINE, a search in the bibliographical database of the authors was carried out and in the references of the selected articles, The study by Bobak and Leon, 1992 [13] was included for its relevance, despite having been published before the period considered in this revision.
(a)
1,8
RR/OR
1,6
Exclusion criteria Articles which only dealt with (a) passive exposure to tobacco smoke; (b) exposure to indoor air pollutants, or (c) working place exposure, were excluded. Comparison of individual estimates In order to facilitate comparison between studies, the odds ratios or risks ratios showed in Figures 1a and b
1,4 1,2 1 0,8 0,6 SO2 TSP Exposure Study
SO2 TSP NOx
3rd trimester
Annual
Wang et al, 1997 Bobak & Leon 1999
Design
Prospective cohort
(b)
4,5
OR
4
SO2 TSP NOx
SO2 PM10 CO
NO2
PM10 CO
3rd trimester
Annual Annual Maroziene & Bobak, 2000 Maisonet et al, 2001 Whilhelm et al, 2003 Grazuleviciene, 2002 Case-control Geographical nested in a cohort 3rd trimester
3,5 3 2,5 2 1,5 1 0,5 SO2
Exposure Study Design
HC
NOx
Annual
CO
3rd trimester
TSPSO2
Petrochemical area
Annual
Annual Lin et al ,2001
Landgren, 1996
Ritz & Yu,1999
Rogers et al, 2000
Geographical
Retrospective Cohort
Population based Case-control
Geographical
Figure 1. (a) Risk of low birth weight in studies evaluating its association with exposure to different ambient air pollutants (measured as an increase of 10 lg/m3 of TSP, PM10, SO2 or NOx and as an increase of 1 mg/m3 de CO) during pregnancy. (b) Risk of low birth weight in studies evaluating its association with exposure to ambient air pollution (exposed vs. control area) during pregnancy.
185 RR/OR
1,6 1,5 1,4 1,3 1,2 1,1 1
Pollutant
PM10
SO2
combined
Wilhelm M et al, 2003
Maisonet M et al, 2001
combined
Wang X et al, 1997
Maisonet M et al, 2001
Bobak M, 2000
Bobak and León, 1999
combined
Wang X et al, 1997
Wilhelm M et al, 2003
Maisonet M et al, 2001
Study
Bobak M, 2000
0,8
Bobak and León, 1999
0,9
CO
Figure 2. Relative risk (and 95% CI) of low birth weight in studies evaluating its association with exposure to PM10 and SO2 (measured as an increase of 10 lg/m3) and CO (measured as an increase of 1 mg/m3) during pregnancy.
and 2 were recalculated to obtain the estimated effect of each outcome for every increase in the levels of TSP, PM10, SO2 and NOx of 10 lg/m3, and of 1 mg/ m3 in the levels of CO.
detected, the ‘random effect model’ was applied. For the purposes of this analysis, heterogeneity was assumed to be present if p < 0.20, however, in all meta-analyses carried out, the value of p for heterogeneity test was always above 0.20.
Meta-analysis In general, for most of the outcomes at study a very scarce number of studies met with similar criteria for: outcome, exposure or design. So a formal metaanalysis could not be attempted. However, for the case of infant mortality, especially for post-neonatal mortality, and for low birth weight some studies included quite likely measures of exposure and, therefore, an approximation to some overall estimates was done. Most of these studies included an indicator of particulates but not always the same, so, in order to have comparable measures, we approximate different levels of exposure to 10 lg/m3 of PM10 by using the following correction factors:
Results and discussion Using the above strategy, a total of 31 articles was obtained. The adverse reproductive effects evaluated in the selected articles were: intrauterine mortality, child mortality within the first year of life, birth weight, premature delivery, intrauterine growth retardation, congenital defects, (Table 1) Low birth weight, intrauterine growth retardation and premature delivery Low birth weight (
