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FOR MEMBERS' USE ONLY COMEAP/2002/MIN/3
COMMITTEE ON THE MEDICAL EFFECTS OF AIR POLLUTANTS
Minutes of the meeting held on Friday 8th November 2002 in Room 137B, Department of Health, Skipton House, 80 London Road, London SE1 6LH.
Present:
Chairman: Professor J G Ayres
Members: Professor H R Anderson
Secretariat: Dr H Walton Assessors: Dr M Meadows (DEFRA)
In Attendance:
ITEM 1. OPENING REMARKS, APOLOGIES FOR ABSENCE AND ANNOUNCEMENTS
1.Apologies for absence were received from Professor Ken Donaldson, Professor William MacNee, Professor Peter Blain, Arthur Johnston (assessor), Nigel McMahon (assessor), Stephen Wall (assessor), Mr Martin Williams (assessor), Dr Bob Maynard (Secretariat), Mrs Emma Hellingsworth (Secretariat), Ms Julia Cumberlidge (Secretariat).
2. The Chairman announced that the resignation of Lord Toby Harris had been accepted and that he had been thanked for his contribution.
3. The Chairman welcomed Claire Townsend, who had returned from her
travels to present the paper she had written whilst working at the Secretariat,
on Long Term Exposure to Ozone, which had been deferred at the last meeting
of COMEAP (Item 4.1).
ITEM 2. MINUTES OF THE MEETING HELD ON 21st July 2002
[ACTION: Secretariat] ITEM 3. MATTERS ARISING 3.1 Statement on Unflued Gas Fires
ITEM 4.1 EFFECTS ON HEALTH OF LONG TERM EXPOSURE TO OZONE - COMEAP/2002/9B [ACTION: Secretariat] 30. It was noted that there would be a paper on the mechanisms of ozone health effects at the next meeting. [ACTION: Secretariat] ITEM 4.2 EFFECTS ON LUNG FUNCTION IN PANEL STUDIES - COMEAP/2002/12A 31. Dr Heather Walton introduced the paper and acknowledged the contribution made by Professor Anderson and his team by providing an overview of the studies from their database. 32. As part of the Committee's consideration of whether or not there is a threshold for ozone, this paper provided Members with an update on the evidence for ozone having an effect on lung function from consideration of panel studies. The annexes of COMEAP/2002/12A contained figures illustrating the shape of the dose - response functions and key studies were provided as COMEAP/2002/12B, so providing Members with the opportunity to discuss the plausibility of there being a threshold. The paper also considered whether an overview of the panel studies provided any support or otherwise to the plausibility of effects on respiratory hospital admissions at low concentrations. Members were reminded that, since there were only 2 UK studies available which had contradictory conclusions, COMEAP had previously decided that it was not appropriate to quantify the effects of ozone on lung function. 33. The Committee agreed with the conclusions from a large number of studies that ambient levels of ozone are associated with decrements in lung function for 1 hour average ozone concentrations and lung function in healthy children. They agreed that the evidence was not so clear for other averaging times and subject groups, nor was it clear from the panel studies that subjects with respiratory disease are more susceptible to the effects of ozone on lung function. Some studies examined the effect of other pollutants, although levels were generally very low or had no effect on lung function. Despite the occasional confounding by particles or acidity, the overall impression was that there was a genuine independent effect of ozone on lung function, irrespective of whether subjects displayed respiratory symptoms or not. 34. The Committee agreed that, although there was sufficient evidence to quantify an effect of ozone on lung function, the clinical significance of the quantified effects would be difficult to interpret. The Committee agreed however, that any reduction in peak flow, even the very small changes which were shown (which showed the power of the studies), demonstrated that there was an effect occurring. This could be a cause for public health concern as exposure to ozone is universal. The Committee discussed the huge variability around the mean (Fig. 3 COMEAP/2002/12a) which, it was felt, could hide individuals who were, for example genetically susceptible. Members discussed how a shift in the mean, even by a small amount, could have important implications for a small number of people at the tail end of the population distribution. This issue had been discussed elsewhere (Kunzli et al (2000) Eur. Respir.J 15: 131-136). 35. It was also noted that a health effect of ozone (e.g. lung inflammation) may occur with no effect on lung function and any changes in lung function in response to ozone could be imperceptible to the individual. 36. The Committee agreed that there was a small, yet strongly statistically significant effect of ozone on lung function despite the potential confounding effect of other pollutants, which remains uncertain. Threshold 37. Studies presented to the Committee showed that the effects of ozone are not limited only to severe photochemical episodes and studies have shown significant negative effects on lung function in places with high ozone levels and others have shown significant effects on lung function in places with low ozone levels. 38. Some studies presented suggested thresholds and some studies suggested a curved dose-response relationship with lung function beginning to decline at 40ppb (8hr average) with others at around 50 or 60ppb (1hr average). The Committee noted that Higgins et al 1995 (Fig. 6) did not find any evidence for a threshold down to very low levels in a group of bronchoreactive patients. However, it was noted that this study had used patients with a mixture of diseases and had not controlled for particles. 39. The Committee noted that the evidence for a health effect of ozone on hospital admissions was stronger for COPD than for childhood asthma. Unfortunately, the panel studies did not tend to examine this group, which lessened the potential of the panel studies to provide supporting evidence for an effect on hospital admissions at low levels of ozone. 40. It was noted by Members that the panel study evidence provided some plausibility to the increase in deaths and hospital admissions at lower ozone levels found in the time-series studies. However, it was acknowledged that deaths and hospital admissions could be the result of entirely different mechanisms. 41. There was a general feeling within the Committee that there probably was not a threshold for ozone as the studies provided did not show clear evidence of a threshold. 42. The Committee agreed that for the next meeting of COMEAP, they would like to see further information on hospital admission data using 24hr and 1hr averages and also to include mortality as an end point. From the panel studies the Committee requested, papers on respiratory symptoms and ozone to be analysed and it was agreed that this paper had also highlighted the need for a paper on mechanisms and chamber studies. 43. It was suggested that further questions presented on pages 4 and 5 of the paper would be discussed between Dr Walton and the statisticians within COMEAP. [ACTION: Secretariat] ITEM 4.3 FURTHER ANALYSIS OF THE EFFECTS ON MORTALITY AND HOSPITAL ADMISSIONS - COMEAP/2002/12C, 12C Addendum, 12C Addendum 244. Dr Heather Walton introduced this paper and its addendum and drew Members' attention to the further tabled addendum to this paper. 45. This paper covered a further consideration of seasonal differences and publication bias on studies on the effects of 8 hour average ozone on mortality and hospital admissions. The addendums covered information relating coefficients for 8-hour average ozone and mortality to the ozone concentrations in the places where the study was performed. 46. The Committee were informed that there was no evidence of publication bias. 47. This paper set out to see whether seasonal differences could give clues to the possibility of there being a threshold for ozone through comparison of the coefficients in time periods with low and high ozone levels. Dr Walton explained that the difficulty in providing enough information for the Committee lay in studies rarely providing sufficient information on both the seasonal ozone coefficients and the seasonal ozone concentrations. 48. Only a small number of studies provided information on seasonal pollutant concentrations. In addition, there was considerable overlap in ozone concentrations between the two six month periods usually selected. These ranges in ozone concentrations were not sufficiently distinct to illustrate a threshold. One paper (Simpson et al 1997) showed a marked drop in the effect estimate despite little difference in ozone concentration by season which suggested that there might be other reasons for the difference. 49. Plots of coefficients against various measures of ozone concentrations in the different cities were presented. Some of the confidence intervals from the studies chosen were wide making the confidence in the size and direction of the trend weak. (Formal trend tests had not been performed). 50. The Committee agreed that conclusions from these few papers needed to be interpreted cautiously as there was considerable overlap in the ozone ranges and the coefficients themselves could have been imposing a linear shape on thresholded raw data. Plotting coefficients against ozone concentrations could not provide conclusive evidence against a threshold but the absence of a positive trend with ozone concentration did constitute absence of evidence for a threshold. It was noted that even if a positive slope had been found, this could have other explanations. 51. The NMMAPS study had found a significant positive association for ozone in summer but a significant negative effect in winter. This could be due to confounding by other pollutants which are higher in winter. It was noted that adjustment for other pollutants was important for assessing causality of the ozone effect. The Committee also questioned whether it might be possible that ozone had a protective effect. This was a theoretical possibility if ozone induced antioxidant defences. Other possible explanations for seasonal difference included the model for adjustment for temperature (Thurston and Ito (2001) J. Exp. Anal. Env. Epidemiol. 11: 286-294) and changes in personal exposure as a result of spending more time outdoors and leaving windows open in the summer. 52. The Committee agreed that the studies available on seasonal differences were not informative about a possible threshold for an effect of ozone and evidence for a threshold (lower slopes at lower ozone levels) was not found in the plots of ozone coefficients for all cause mortality against ozone concentrations in the different cities. 53. The Committee agreed that it would be worth testing the statistical significance of the trend and performing a similar analysis for the other health outcomes. [ACTION: Secretariat] [At this point Mr Fintan Hurley left the meeting]
2) Availability of Minutes - Members agreed that since meeting minutes from 1999 onwards were posted on the COMEAP website, it therefore fulfilled the need for the availability of minutes retrospectively. It was agreed that should minutes prior to this date be required, they could be requested. The Secretariat would then check the relevant minutes and send them out subject to omission of certain parts if justified by the Environmental Information Regulations. 3) References - It was suggested that a stand alone list of references for an issue considered by the Committee be made available on the website, rather than just as a reference list attached to COMEAP papers. This was agreed to. [ACTION: Secretariat] 4) Open register of stakeholders - The Chairman informed the Committee that this was not legislative, but purely recommended by the Code of Practice. The Committee agreed that to have a stand alone list of stakeholders would be impossible as different issues discussed by the Committee involved different stakeholders. It was decided that a list of stakeholders consulted for each issue would be included in Committee reports.[ACTION: Secretariat] 5) Dealing with the media - The Committee agreed that they were happy with current arrangements for dealing with the media, whereby information on a final COMEAP view may be discussed, but not issues currently 'under discussion'. Members were reminded that on all issues, they could refer the caller to either the Chairman or Secretariat and that it was helpful to make clear whether they were speaking to the media as a member of COMEAP or in their personal capacity.6) Information exchange - Members agreed that it was important to have opportunities to exchange information between relevant government Committees. It was agreed that the Chairman would write to the Chairmen of COC, and COT, to indicate that they would be consulted as and when matters of mutual concern arose. It was also noted that, in the case of EPAQS, the Secretariat was shared and many of the Members were cross-represented. ITEM 5B WORKSHOP - CODE OF PRACTICE FOR SCIENTIFIC ADVISORY COMMITTEES
(NOTE FOR INFORMATION) - COMEAP/2002/14
2) greater use is to be made of horizon scanning. This in theory was a good idea, but it was agreed that problems occur when resources to do this decrease, as workload increases. 3) confidentiality was discussed and it was agreed that not being open was counter-productive, unless items were held as commercial-in-confidence. 4) conflicts of interest were discussed, although it was realised that if too wide a definition of a conflict of interest was used, there would be no experts left to serve on expert Committees. 5) it was suggested that serving on an expert Committee should be given more importance in the Research Assessment Exercise (RAE) of Universities, although this would in fact conflict with the main objectives of the RAE. No questions arose out of this summary. ITEM 6. SUB-GROUP ON ASTHMA AND AIR POLLUTION [ACTION: Secretariat]
64. Professor Anderson updated the Committee on the potential difficulties
emanating from the still unresolved problem with the GAMs. 69. Professor Roy Richards gave a talk on the application of modern analytical
methods to stored samples of 1950s particles. Secretariat 2003
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