key findings of air pollution health effects and its...

WHO European Centre for Environment and HealthWHO European Centre for Environment and Health

Key findings of air pollution health effects and its application

Recent results from the WHO systematic review

Jürgen Schneider Jürgen Schneider Project MangerProject Manger

WHO ECEH, Bonn, GermanyWHO ECEH, Bonn, Germany

CAFE Steering GroupCAFE Steering Group(Brussels, 17(Brussels, 17--18 May 200418 May 2004))


Content

•• IntroductionIntroduction•• Findings Findings •• OutlookOutlook



Published reports: Health aspects of air pollution with particulate matter, ozone and nitrogen dioxide Health aspects of air pollution – answers to follow-up questions form CAFEMeta analysis of time-series studies and panel studies op particulate matter and ozone

In preparation:Impact of air pollution on children’s health (2nd draft internally available)Short summary report (in preparation)

Complementary are the reports on the 6th and 7th meetings of thejoint WHO/UN ECE Task Force on Health

Introduction - Products


Process:

Background document on epi evidence

Background document on tox evidence

Draft answersincl rationale

Review and revisions by

SAC

External peerreview

WHO WG meeting

Revision and additional

review

Finalisation, editing, print

WHO Review - process


A full risk assessment comprises:

Hazard identification: Review of relevant evidence (epidemiologic, toxicologic, etc. to determine wether the agent poses a hazard

Exposure response function: Quantifying the relationship betweenexposure and adverse health effects

Exposure assessment: Determination of the magnitude, duration androute of exposure

Risk characterication: An integration of the above three leads to an estimation of the health budren of the hazard. The approach, assumptions and uncertaintiesshould be highlighted

Key findings


Key findings

Hazard identification

• Short term versus long term• Hot spot versus urban background• Epi versus tox evidence (susceptibility)• Thresholds for ozone• WHO AQG for NO2• Coarse PM• (Other pollutants)


Systematic Review – key finings

Relevance of exposure to peaks versus long term

Peak versus long-term:Ozone: ‘As there are usually many more days with mildly elevated ozone

levels than days with very high peaks, the largest burden of disease might be expected with the many days with mildly elevated levels and not with the few days with very high levels’

PM: ‘…the public health significance of the long-term effects clearly outweighs the public health significance of the short term effects. This obviously does not diminish the significance of the short-term effects of PM, which consist of very large numbers of attributable deaths and cardiovascular and respiratory hospital admissions in Europe.’


Systematic Review – key findings

Relevance of exposure at hot spots; exposure to peaks - Hot-spot versus urban background

• A policy which aims at a significant reduction of the overall health burden caused by air pollution will have to aim at a reduction of the exposure of the general population. This is in particular true for pollutants/health endpoints with (a) no threshold of effects and (b) a linear relationship between exposure and response.



Relevance of exposure at hot spots; exposure to peaks - Hot-spot versus urban background

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Relevance of exposure at hot spots versus urban background

• However, some studies have documented that subjects living close to busy roads experience more short-term and long-term effects of air pollution than subjects living further away. In urban areas, up to 10% of the population may be living at such “hot spots”. The public health burden of such exposures is therefore significant. Unequal distribution of health risks over the population also raises concerns of environmental justice and equity.



Consistency of epi and tox evidence in the defining thresholds - General remark

• For a uniform population with specific exposures, thresholds for certain pairs of pollutant/health endpoints may be detectable

• At a population level, susceptibility and exposure vary over a wide range. Large differences in individual exposure-response curves may lead to a disappearance of thresholds at a population level.

Taking into account these differences, the evidence coming from the epidemiological and toxicological studies is not contradictory.



Consistency of epi and tox evidence in the defining thresholds - PM

• Most epidemiological studies on large populations have been unable to identify a threshold concentration below which ambient PM has no effect on mortality and morbidity. It is likely that within any large human population, there is a wide range in susceptibility so that some subjects are at risk even at the low end of current concentrations.



Consistency of epi and tox evidence in the defining thresholds - Ozone:

• Statistical significant associations between ozone and mortality have been demonstrated at places with low ozone levels

• Sophisticated statistical analysis applied to address the question of thresholds for PM have not been applied to the same degree for O3

• There remain uncertainties about the shape of the CR function, in particular at the lower end of the ambient range

• Although there is evidence that associations exist well below the current guideline value, the confidence in the existence of associations with health outcomes decreases as concentrations decrease.



Consistency of epi and tox evidence in the defining thresholds - Ozone:

A recent paper (Kim et al., 2004) applied a linear model, a natural spline model and a threshold model to a dataset in Seoul and found that the threshold model, with a threshold at 56 µg/m3 (28 ppb) 1 hour average for effect son mortality, gave the best fit. However, the slope above the threshold was steeper than in the linear model. The authors conclude: that models that not take thresholds into consideration, could underestimate the true risk of ozone effects on mortality.

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Contribution of different sources to PM related health effects

Epi studies: Combustion sources are particularly important for health effects. Tox studies:• Primary, combustion-derived particles have a higher toxic potency. These

are often rich in transition metals and organics, in addition to their relatively high surface area

• Other single components of the PM mix are lower in toxicity in laboratory studies e.g. ammonium salts, chlorides, sulphates, nitrates and wind-blown crustal dust such as silicate clays.

Despite these differences among constituents studied under laboratory conditions, it is currently not possible to quantify the contributions from different sources and different PM components to health effects from exposure to ambient PM.



Coarse particles and health

• There is limited evidence that coarse particles are associated independently of PM2.5 with mortality in time series studies.

• One study has investigated the effect of long-term exposure to coarse particles on life expectancy without producing evidence of altered survival.

• There is evidence that coarse particles are independently associated with morbidity endpoints such as respiratory hospitalizations in time-series studies.

There is sufficient concern about the health effects of coarse particles to justify their control.



Basis for maintaining the WHO AQG for NO2

• New toxicological studies show that LT exposure to NO2 at concentrations higher than current ambient concentrations have adverseeffects.

• Uncertainty remains over the significance of NO2 as a pollutant with a direct impact on human health at current ambient air concentrations

• NO2 has been associated with adverse health effects even when theannual average NO2 concentration is within a range that includes 40 µg/m3

It is recommend that the WHO annual specific guideline value of 40 µg/m3

should be retained or lowered.



Effects of air pollution on children’s health

• There are several factors which potentially increase children’s susceptibility to adverse effects of air pollution

• There is solid evidence for effects of air pollution (PM) on infant mortality

• Poor air quality effects lung development of children • Air pollution is associated with increased upper and lower respiratory

symptoms in children• Air pollution may increase bronchitis, cough and aggravates asthma

symptoms• There are uncertainties whether ambient air pollution at current levels

causes cancer in children


The evidence is sufficient to recommend strongly furtherpolicy action to reduce levels of air pollutants includingPM, NO2 and ozone; it is reasonable to assume that a reduction of air pollution will lead to considerable healthbenefits.




Meta-analysis of time-series studies

• Set-up of a Task Group upon recommendation of a WHO WG• Development of a strict protocol• Bibliographic database of time-series studies at St. George’s

Hospital/London• Summary estimates for different health outcomes related to PM and

ozone• Outcome in RR per 10 µg/m3 increase in pollution level• Analysis of possible publication bias



European studies on ozone and and all-cause mortality

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RR for all-cause mortality – PM and ozone

Relative risks (RR) for mortality endpoints related to a 10 µg/m3 increase in pollution including 95 % confidence intervals; left part: PM10, black smoke (BS) and ozone from European studies; right part:

PM2.5 from North American studies

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RR for all-cause mortality – publication bias

Relative Risk for all-cause mortaility, 10 µg/m3 increase inpollution level, without and with correction for publication bias

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Develop recommendations on the approach to model health impacts within RAINS

Health impact assessment: Science-basedNo cookbook approach yetSeveral assumptions and choices – transparency is needed‚Conservative approach‘CBA complementory

7th Meeting of the TF Health


Ozone effects:

Health endpoint: attributable mortalityCausal relationship between ozone exposure and mortalityIndependent of PMRR from WHO meta-analysis of European studies:The relative risk for all-cause mortality is 1.003 (C.I. 1.001, 1.004) for a 10 µg/m3 increase in the daily maximum 8-hour mean.

7th Meeting of the TF Health - Ozone


Ozone effects:

A linear concentration response function is assumed. The principle metric for assessing effects of ozone on mortality should be the daily maximum eight-hour mean. Current evidence is insufficient to derive a level below which ozone has no effect on mortality. The use of a cut-off for IAM at 35 ppb is recommeded

7th Meeting of the TF Health - Ozone


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Why use a cut-off?

There remain uncertainties about the shape of the CR function, in particular at the lower end of the ambient range

20 to 40 ppb is the hemispheric background – main purpose is to analyseEuropean abatement optionsThere are difficulties of state-of-the-art dispersion models to simulate low ozone situations in urban areas. Titration becomes important at low levels

Ozone


This recommendation is based on the application of a very conservative approach for integrated assessment modelling and takes account of uncertainties in relation to the evidence in health studies and lowerconfidence in model performace at low ozone levels. It is recommended to make a sensitivity analysis applying no cut-off. This estimate would outline an upper estimate of the attributable effects of ozone on mortality.

The Task Force also stressed that the approach did not yield an overall quantification of all effects related to exposure to ozone. Important effects which were currently not covered, but should be taken into account in CBA, including morbidity outcomes.

Ozone


Ozone

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Particulate matter

PM effects:Use annual mean of PM2.5 as indicator for PM related mortality (this also implies the use of one factor for different PM constituents)RR from cohort studyLinear CR function Health outcome: Reduction of life expectancyEffect for explained anthropogenic contribution only

‘Most epidemiological studies on large populations have been unable to identify a threshold concentration below which ambient PM has no effect on mortality and morbidity. It is likely that within any large human population, there is a wide range in susceptibility so that some subjects are at risk even at the low end of current concentrations.’


Systematic Review – outlook

Follow-up actions

• Finalisation of the reports• Dissemination of main results• Keep contact with CAFE• Revision of WHO Air Quality Guidelines (PM, ozone)


For further information see:

http://www.euro.who.int/air


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