Committee on the Medical Effects of Air Pollutants (COMEAP)

Committee on the Medical Effects of Air Pollutants (COMEAP)

On 10th April 2008 a meeting took place between COMEAP’s Bob Maynard and UKWIN’s Stephen Eades, David Levy and Andy Tubb. Some of the information below arises from that meeting.

COMEAP was set up in 1992 together with Expert Panel on Air Quality Standards (EPAQS). COMEAP’s remit is to advise the Chief Medical Officer of the Department of Health (DoH), the DoH will in turn advise Defra and other government departments. Air Quality Standards (AQS) were originally set by EPAQS but are now set by the EU, although some EPAQS standards remain in place. Air Quality Objectives and time scales for reaching them are used to set targets.

COMEAP is funded by the DoH. Bob Maynard is employed by the Health Protection Agency (HPA). Their work programme is determined by Bob Maynard (in his role as Secretary to the Committee), together with the membership of the Committee, as represented by the Chair (currently Prof Ayers of Aberdeen University, who retires form the committee at the end of 2008). This process is informed by Defra and DoH.

An individual or group who wished to get something on to the work programme (for example consideration health impacts from incineration), would have to write to their MP, who in turn would ask the Minister for Health, who would ask the DoH, who would ask the Secretary, who would put it onto the programme (agenda). Alternatively one could write to Louise Newport on the DoH directly and hope for the best.

[Note: Prof Ayers was asked by David Levy at a meeting of Environmental Protection UK (formerly National Society for Clean Air) in Bristol on 21 February 2008: Has COMEAP considered the health effects of particulate emissions from incinerators? And his answer was: No, because no one had asked the Committee to investigate this, and also because the Committee does not usually comment on emissions from a specific source.

When asked: How could the committee be invited to consider it? Prof Ayers said that those concerned should write to the Committee and ask for the issue to be put onto the agenda. Prof Ayers went on to explain that the Committee had an awful lot of work already, that they meet only three times per year and that they were not paid – so, whether or not the Committee would consider the issue a priority was uncertain.]

How does the Committee arrive at their decisions and outputs?

According to Bob Maynard, outputs can take the form of short letters to the DoH in response to specific questions, statements in response to published works or papers and full reports which may be lengthy. The Secretariat works from published research papers and the expertise of the Secretary and the membership to arrive at the content of a report. The report is written by the Secretary, and Committee members comment and add to it.

How do things like policy principles influence the reports and outputs from the Committee, for example do they take account of the proximity principle or cost-benefit analysis?

According to Bob Maynard, these do not matter to the Committee. The proximity principle is not taken into account. The Committee is not concerned with cost-benefit analysis.

What they do is say that the health effect is such and such, e.g. the Committee determined that the PM10 particulate coefficient is: 6 % mortality increase per 10 mg m-3 increase in concentration. This figure is then used by government in determining the cost-benefit analysis of a particular air quality objective. The results of cost-benefit analysis may then be used to set the AQO, or government may set it for some other reason. COMEAP have no role in setting the AQO.

How did COMEAP arrive at the 6% coefficient?

According to Bob Maynard, this was a difficult process. There were many diverse studies with results varying from 1 – 17% as the coefficient and with different error limits. There is not any universally accepted standard method for arriving at a best answer from such diverse studies as these. In fact there is no method at all. The 6% coefficient came from an American study which had an exceptionally large number of participants and had relatively small error limits. It is arguable that American particles are not exactly comparable to UK particles in composition. So we put it to the Committee members (which number 12 in total) to use their expertise to arrive at what they thought was the best value. Generally they agreed with one another that 6% was the most justifiable value.

How does COMEAP verify the validity of the data it uses, and what are it’s sources of evidence?

According to Bob Maynard, the Committee uses peer reviewed publications, relying on COMEAP members’ experience and drawing on the evidence and experience of other groups reports such as the US Environmental Protection Agency (EPA). The Committee strives to be critical of the information it has and is cautious about the value of the data it receives. However COMEAP does not gather its own data, and therefore relies on the peer review process (except in so far as Committee members are academics who conduct their own research and have some grounds to regard themselves as experts).

Given that there are error limits why do COMEAP recommend the use of the central value rather than the upper confidence limit?

According to Bob Maynard, the central value is the best estimate.

This provides only 50:50 protection, why not go for the 95 % CL and make the level of safety better?

According to Bob Maynard, this is because the central value is the best estimate of the truth.

But it is only an estimate, and the point is that the level of protection can take into account the confidence limits.

According to Bob Maynard, the confidence limits are used in the cost-effect calculations.

Statutory consultees on a planning application for an incinerator include the Environment Agency (EA) and the local Primary Care Trust (PCT). The EA will comment on the emissions compared to the Waste Incineration Directive and ground level concentrations. The PCT will ask the Health Protection Agency (HPA) what are the health effects from incinerators and the HPA will say that there is no evidence of any health effects from incineration. How does this square with the coefficient of 6%?

According to Bob Maynard, the effect is negligible on a small village.

But it is and effect, there is no threshold.

Bob Maynard responded by saying: Like benzene? Yes I suppose that’s right but it will be very small, probably less than 0.005 extra deaths or something like that.

Yes but it is an effect and on a larger population it would have more significant impact.

Bob Maynard: Yes, but it will still be small and relatively insignificant when compared with deaths from other causes, like car accidents.

But this means that there is a calculable health impact that the HPA should be mentioning when asked about health impacts and COMEAP ought to consider this in its advice to the Chief Medical Officer.

What about morbidity – for example chronic bronchitis?

According to Bob Maynard, the report on morbidity is just about to be issued.

How will the mortality and morbidity data be combined to give the total health effect?

According to Bob Maynard, probability by adding them together.

What about using DALYS (disability and life years lost)?

Bob Maynard: Maybe DALYS or QUALYS (Quality of life years lost) – not sure these will be used. There is a report on economics of air pollution that might have used DALYS but we have not yet determined the methodology for combining the mortality and morbidity effects.

We are concerned that the volumes of material emitted are not taken into account, only the concentrations are considered by the Environment Agency. Has anyone considered this sort of information.

Bob Maynard: I don’t know. Well I suppose it goes like this – Martin Williams, the head of Air and Environment Quality Division, Technical Policy Branch at Defra, considers what the concentrations and volumes of emissions are and he will do a calculation using a model taking into account the weather, because that is the major factor in dispersion. He will calculate the concentration at ground level and he will find out the existing concentration level and will tell the Minister “there will be this much of a change in air quality” and whether or not it exceeded the AQO. If it does not go above the AQO then the Minister may very well take the decision to allow an incinerator to go ahead, and if it does then he [or she] may not. The Minister has the power to take a decision that ignores the AQO if he [she] wishes.

In practice we feel there are several issues of concern associated with this process. One is that there is very little quality control. The scrutiny of the process is by an under-resourced Environment Agency who are supposed scrutinise the product from a consultancy that is employed by the proposer and profit-maker. The reliability of the input data and the modelling are often poor and the resulting error limits are high. Another issue is that the large volume is dumped on a large area so a large population is affected by a small concentration.

Bob Maynard: There is no link that shows pollution to be a cause of asthma. There is no correlation between air quality and the occurrence of asthma in a population. For example China which has terrible air quality has a low incidence of asthma whereas New Zealand which has very good air quality has a very high incidence of asthma. No one has established the cause of the disease, it may be genetic, it may be down to the immune system and Anthony Seaton believes it is down to diet. Air pollution may trigger an asthma attack. Known triggers include cold air, allergens and irritants like SO2.

COMEAP Continues to Undercount Harm from Air Pollution

by Max Wallis (26th April 2008)

COMEAP in January 2006 (interim statement, p.68) accepted the US epidemiology and the consequent 2003 WHO-EC coefficient for dose-effect coefficient between PM2.5 and specific ill-health effects. The coefficient of 6% (range 2-11%) per 10μg.m-3 PM2.5 comes from the largest most extensively analysed cohort study (American Cancer Society – Pope et al, 2002) and was agreed by the WHO.

Defra’s Air Quality Strategy (AQS) Review of 2006 focussed on low values of ill-health coefficient, viz. 1%, 3%, and 6%; saying 6% was in line with (World Health Org.) WHO recommendations when in fact their range was twice as high with 6% as the central recommendation. At the May 2005 stakeholder consultation, Defra told people asking for the WHO range that the decision was up to the economists and the Treasury.

By June 2006, US epidemiology had moved on and gave a higher coefficient 6-17% (C A Pope & D W Dockery review (Journal of the Air & Waste Management Association Volume 56 709–742).

The AQS when issued 17 July 07 adopted 6%. No range was given – apparently the UK economists refused to contemplate any coefficient higher than 6%.

Then COMEAP in its draft report of July 2007 also adopted 6% (quibbled over the range, adopting 2-12%) from 2002. They drew on the same data-base as the US authors who upped their 2002 range but made no change. I wrote in September’s BMJ [UK continues to undercount Air Pollution’s Health-harm] 23 September 2007, that their different decision relied on a belief (little effect beyond 5 yrs) and a “Delphic” poll – none of them defended these departures from science.

The invited reviewer at the Cranfield conference (April’08; Klea Katsouyanni) gave an updated assessment in front of Bob Maynard and COMEAP’s chair (Jon Ayres) saying:

1 to 1.2% for short-term deaths (1-2 day exposure)

6 to 17% for total long-term mortality

9 to 28% for cardio-pulmonary mortality

She cited the newer paper by Pope (Inhalation Toxicology, 19 (S1) 2007, p.33–38 – Abstract below).

I asked in the session whether she agreed with COMEAP’s “belief” of little effect beyond 5 yrs; she said no – and COMEAP did not respond, though Bob Maynard took umbrage afterwards – resented my blaming the Dept of Health. Jon Ayres said to me informally that COMEAP could not change their view with every new paper.

COMEAP have not yet issued their final report (or said how they’ll respond to critics) but it’s clear from body language etc. that the 6% is fixed. A leading member said this to the spring conference of Environmental Protection UK (formerly NSCA) according to the April 2008 issue of the Air Quality Bulletin.

Mortality Effects of Longer Term Exposures to Fine Particulate Air Pollution: Review of Recent Epidemiological Evidence

C. Arden Pope III Inhalation Toxicology, 19 (S1) 2007, p.33–38


This article evaluates the dynamic exposure-response relationship between particulate matter air pollution (PM) and mortality risk by integrating epidemiological evidence from studies that use different time scales of exposure. The evidence suggests that short-term exposure studies are observing more than just harvesting or mortality displacement. There is little evidence of short-term compensatory reduction in deaths, and estimated PM effects are generally larger for intermediate and longer term time scales of exposure. Although proximity in time matters, with most recent exposure having the largest health impact, there is evidence that the short-term exposure studies capture only a small amount of the overall health effects of long-term repeated exposure to PM. The overall epidemiological evidence suggests that adverse health effects are dependent on both exposure concentrations and length of exposure, and that long-term exposures have larger, more persistent cumulative effects than short-term exposures.

MVEG sub-group on Euro 5 and Euro 6 1st meeting on 4 September 2003

Health Effects of Airborne Particles

Jon Ayres, Dept. of Environmental & Occupational Medicine, University of Aberdeen, Scotland, UK


Particles in the ultrafine range seem to be mainly responsible for these health effects

Particle numbers, their surface area and chemical constituents may prove to be important – transition metals, free radical activity, acidity

The mechanisms are likely to be multiple

Air pollution research has developed the new field of nano-toxicology, challenging conventional toxicological approaches to lung injury.

•Ultrafine particles contain the active fraction in terms of health effects

•The effectors are likely to be a mix of particle size range/proportion and content (e.g. free radical activity, metals, acidity etc)

•But there are different mixes of effectors which cause different health effects

•Effects can be both local and systemic in an individual

•Some are more susceptible than others…but who?

•Interactive effects of gases may also have a role to play

•Individual effect sizes are small but because population exposed is large, public health effects are large

•Chronic effects are larger than short term effects

•Control benefits can be fairly quick in onset

•But interventions need to be widespread

Bottom line……control sub-micronic particles from traffic


Ayres, J.G., Borm, P. et al. (January 2008). Evaluating the Toxicity of Airborne Particulate Matter and Nanoparticles by Measuring Oxidative Stress Potential – A Workshop Report and Consensus Statement. Inhalation Toxicology, 20(1): 75-99. Abstract.

There is a strong need for laboratory in vitro test systems for the toxicity of airborne particulate matter and nanoparticles. The measurement of oxidative stress potential offers a promising way forward. A workshop was convened involving leading workers from the field in order to review the available test methods and to generate a Consensus Statement. Workshop participants summarised their own research activities as well as discussion the relative merits of different test methods.

In vitro test methods have an important role to play in the screening of toxicity in airborne particulate matter and nanoparticles. In vitro cell challenges were preferable to in vitro acellular systems but both have a potential major role to play and offer large cost advantages relative to human or animal inhalation studies and animal in vivo installation experiments. There remains a need to compare tests one with another on standardised samples and also to establish a correlation with the results of population-based epidemiology.

COMEAP’s record on Particulate Pollution epidemiology

In the draft Long-Term Exposure to Air Pollution: Effect on Mortality consulted on by COMEAP last summer (still not finalised) why did COMEAP select a lower coefficient (6% for increase in all-cause mortality per increment of PM2.5) than did the leading US epidemiologists Pope and Dockery (6%-17%), on essentially the same set of studies?

COMEAP’s draft does mention one reason: faced with wide disagreement, the Committee resorted to a Delphi survey of members opinions that resulted in a distribution centred on 6%. Such a survey includes personal and institutional biases. Yet COMEAP’s past record shows they have erred badly toward under-estimates (while some of the individuals participating in those under-estimates are still on COMEAP).

In 1998 COMEAP decided chronic effects were too uncertain, accepting only acute effects (health-compromised people dieing in pollution episodes). In 2001 COMEAP accepted that PM probably caused chronic mortality, but decided the coefficient value of 1% was “most likely”.

The main reason argued by Pope & Dockery in 2006 for choosing the higher coefficient range of 6%-17% is that long term chronic effects are revealed only by longer term studies. Their comparison of studies reveals a “duration effect”, i.e. that longer term studies reveal stronger effects.

Over PM-pollution COMEAP appears to serve as a mechanism for delay and weakening standards. Is COMEAP self-critical over its past exercising precaution towards permitting particulate pollution rather than towards protecting health?

Secondly, scientific opinion for years has emphasised that ultra-fine particles are likely to be the major cause of harm to health. Prof. Seaton and others determined clear mechanisms two or more years ago. Why has COMEAP failed to give this clear message to government and allowed them to ignore ultrafine particles in the 2007 review of the Air Quality Strategy?

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