Health effects of air pollution in Canada : Expert panel findings for The Canadian Smog Advisory Program

OBJECTIVE: To review the evidence on health effects of air pollution for the Canadian Smog Advisory Program.


BACKGROUND
Although air 4uality in Canada has generally improved over the past 15 years, smog episodes still Ol'cur.These episodes.which are primarily a summer phenomenon.consist principally of elevated concentrations of ground-level ozone.although al'icl aerosol s (a type of airborne particle) may also be present (2).A different form or smog, 'winter smog ' , may also lll'l'ur, whose principal constituents are sulphur dioxide and airborne particles (inl'luding acid aerosols) (2).G round-lewl owne and airbornL• particles were the focus of the panel process.
Ground-lcwl ('tropospheric') ozone.which should be d istinguished from stratosphcriL• o;:one ('the ozone layer' ). is a gas that is formed when its precursors, oxides of nitroge n and hydrocarbons.interact in the aunosphere in the presence of high temperatures and sun light (3 ).Smog and its precursors may be transported long distances through the atmosphere (3) with the result that high concentrations of ground-level owne may be found in both rural and urban areas (4).Although long range transport contributes significantly to ob-de !'uti lisa ti on des med ic ame nt s ct des consultations ti l' urgence nu chcz le medecin pa rmi !cs individus so ufl'rant d'une affect ion pulmonairc ou cardiaquc.unc tolera nce rcduitc a r•cxcrcicc.unc augrnenlat ion des hospitalisations ct aug mentation possible de la mortalitc .On pense quc des clTcts sirn ilaircs sc produisent en assoc iation avec !cs pa rticulcs aerogcncs.f1 l'exl'cption des changemcnts inllammatoircs, ct en y ajoutanl une au gmcn tation de l'abscnrcismc scolaire.Des donnccs in suflisantcs sur !'exposition individue ll e ant etc iclcnti fiecs comme unc limi ta tion des etudcs sur lcs hosp italisations et la morta litc.RF.COMMANOATIONS : Les experts ont id cntilil' le bcsoin de rclleter correctcmcnt lcs preuvcs sans trop sou lever d'inquietudes dans la population et ont recommandc quc !cs mcssagcs-sante icl entifient lcs e !Tcts attcndus sur la sant c. pendant quc !cs po urvoy c urs des soins de santc pourraicnt plus adcqualcmcnt recommancler des comportemcnts protcctcurs aux indiviclus.Des strategies cducatives supplcmcnta ircs ct unc evaluation du Prog ramme d'avc rtisscmcnt ont aussi cte rccommandccs .
served ground-level ozone concentrations in a number or regions, its impacr is particularly apparent in Atlantic Canada.where peak concentrations may occur at night.In most other areas, peaks occur during the late afternoon and early evening in the summer months.In Canada, the current National Ambient Air Quality Object ive for ground-level ozone (I h maximum of 82 parts per bil lion ippbl -maxim um acceptable concen tration) is exceeded most often in southern Ontario.southern Quebec, Vancouver and southern New Brunsw ick (5) (Figure I) .
Airborne particles are very smal l pieces of solid or liquid matter, which vary in si ze, chemical composition and sou1n•.Smaller particles.which have the greatest health significance, tend to arise fro m man-made sources, particularly fuel combustion, and include acid aerosols such as sulphates and nitrates, as well as metal oxides (6).Larger particles consist mainly of naturally occ urri ng substances.particularly soil (6).Particles less than IO ~1111 in diameter (PM 10) are considered 'inhalable' (7).T he current National Ambient Air Quality Objective for total suspended particles (TSP -airborne particles of all sizes) is 120 µg/111 3 for 24 h concentration.
which is still exceeded at least I 0 % of the time in some cities across C anada (5).The current US standa rd fo r PM 10 is 150 µg/rn 3 for 24 h concentration.Recent data reveal 24 h concentrations that e xceed I 00 µg/m 3 in a number o f Canadian cities (8).Health Canada is currently developing a Canadian PM 10 objective.
The Smog Advi sory Progra m was introduced in the summer of l 993 under Canada 's G reen Plan as a means of info1ming the public about both environmental and health aspects of smog e pisodes.The program was fi rst implemented in Saint John, New Brunswick, in southern Ontario and in the G reater Vancouver Regional District, and began in program , ground-level ozone forecasts arc produced cooperativ ely by Environment Canada, the provincial min istries of environ ment and munic ipal air quality offices.based on meteorological and air monitoring data.Advi sories are issued when l h maximum level s are foreca stcd to exceed a specifie d level, de pend ing on the jurisdiction, but generally 82 ppb.They consist of an environmental message that describes the pollution sources that contribute to smog (chiefl y automobi le transport) and the need for the public to red uce its de pe ndency on cars, as well as a health message that advi ses the public of poss ible health risks associated with smog ex posure.T he exact content of the messages is determined by provincial environmental and health authoriti es.ln I 993 .the tirst summe r of the prog ram's exi stence, four advisories were issued -two in Saint John and one each in southern O ntario and the Greater Vancouver Regional Di strict.A si milar number of adv isories was issued in 1994.As seen in Figure I. a sign ifi cantly greater number of episodes of elevated groundlevel ozone concentrations has occurred in these areas in previous years.measurement, and hea lth care delivery.The chair and several pane l members had independe ntly conducted literature reviews before their participation in the panel s and ke y references were provided to panel members in preparation for one-clay meetings of each group.Each panel was asked to defi ne the health effects expected at level s of exposure given hy the National Ambient Air Q uality Objectives; to examine a variety of issues related to communicating with the puhlic abo ut env ironmental healt h ri sks: and to draft health me:ssages for the advisory program.Although under the Smog Advi sory Program.advisories are issued only for groundleve l ozone, e ffects of airborne particles were also L'Onsidered by the panels .While the same indiv idual chaircd bnth panels.great care was taken to allmv each group scope to produce differing conclusions and recommendations .Nonethe less.a strong concurrence was noted between the findi ngs of the two pane ls .Once the panels were completed, mi nutes of each pane l as well as a synthesis were circulated to the panel me mbers for comment and revision .

PANEL FINDINGS
The pane ls considered a variety of evidence on the relati onship between air pollution and health .This included lahorato ry studies, which have examined the pathophysiolog ic:al mechani sms through which pollutants exert their effects: chamber stud ies.which ha ve been used to measure various hu man heal th effects at contro lled exposure• levels: panel studies, in which (for example) children attending summer The panels conceptual ized the potential health effects or air pollution as occurring in a logica l \:ascade' or •pyramid ' .ranging from severe.uncommon events (cg.death) to mild.common effects (eg.eye.nose and throat irritation) and asymrtomatic changes of unclear clinical significance (cg.small pulmonary function decreme nts and pulmonary inflammation) (9.10).Thus.while according lo this 11H1dcl SL:vcre health events prec ipitated by air pollution would Ill' rare.there is a potentially large overall impact on he,lllh and well -be ing (Figure 2).
Wit h respect lo ground-level 01,one.the panels kit that cu rre nt palhophysiological evidence suggested that ozone is associated with an inflammatory response manife sted by increased airway membrane pe rmeability and bronchial hype1Teactivity ( 11.12).Some or the nxenl epidemiulogic:11 I ilerature reviewed by the panels indicated that pulmonary runction measures in children attend ing summer camp in southern Ontario were reduced on average by 3.5 to 7<1< wlll'Il I h av erage coneentrations of ground-level 01011L'.reached 140 ppb ( 13) .that approximately 5% of On tario hospital admissions ror respiratory disease may be attributable lo elevated conccnlralion.s of ground-level O/\lllC (4.14) (up to \ 5';{ in those umicr two years of age I in combination with sulphate particles 1141).and that in Los Angeles the combination of ground-level ozone.nitrogen dioxide and lemperalltre accounted for 4% of the day lo day variability in mortality (excluding accidents and suicides) ( 15).Whether the effects observed in epidemiological studies can be directly allributccl to inflammatory responses seen in laboratory studies is unclear.The e vidence for chronic effects is also unclear.The panels concluded that there was some evidence that certain groups arc more susceptible 10 the acute clTccts or groundlevel ornne.either on the basis of increased sensitivity (lhe very young, the elde rly.those with chronic cardiac or resp iratory di sease) or increased expos ure during outdoor activity (school chi ldren.joggers, cycl ists and other athle tes, and outdoor workers such as fann and con struction workers ).However.this was recogni zed as a controversia l area .The panels differed in their interpretat ion of the evide nce on the occurrence of hann ful effects in the general popu lation at levels below 80 ppb./\ synthesis of the effects ide ntified by the pane ls at concentration s g iven by the Nat ional Ambient Air Q uality O bject ives is presen ted in Table I.Th is table summarizes the curre nt sc ienti fic ev idence.weigh ing what the panels saw as the relati ve st rength of the evidence for various effects al various levels.T he contents of the table do not translate the ev idence into appropriate messages fo r comm unicating with the gene ral public .
Although the pane ls were not spec ificall y asked to address the issue or whether there was a threshold concentration for ground-leve l ozone below which effects wo ul d not be expected, they were requi red to frame their findi ngs accord ing to the Nati onal Ambient Air Q uali ty Objectives.which inevitably rai sed the threshold issue.T here was little support among panel members for the concept of a threshold concentration fo r effec ts of ground-level ozone, which is re fl ected by their concl usion that the probability and severi ty of e xpected healt h e ffect s increases with increasi ng ex posure (Table I).Howe ver. it was recognized that this was a separate issue fro m choos ing an adm in istrative th resho ld concentration ( 16) for the purposes of issuing adv isories.The latter issue was fe lt to be more appropriately addressed by authorities in the individual regions where advisories are issued (as described earlier).
W ith respect to airborne parti cles.the panel s felt that the pat hophysiolog ical mechanism through whi ch they exert the ir effects on respiratory health was not wel l understood.Some of the recent epidemiological li terature reviewed by the pane ls (much of which ori gi nates in the Uni ted S tates ) indicated that e levat ions of PM to concentrations of approximately I 00 to 150 ~tg/mJ are associated with reductions in peak expiratory !low of up to 6% ( 17.18).approx imately si xfold increases in medication use :nnong asthmatics ( 18 ).1. 5to twofo ld increases in resp iratory symptom reporting ( 17.18), 40% increa •es in school absentee ism (19).statistically significant increases in respiratory hospital admissions (20) and up to 16% increases in mortality (excluding accidents and suicide) (21 ).The panels concluded that groups with greatest susceptibility appear to be those with chronic cardiac and resp iratory disease, although thi s was recogni zed as a controversial area.As was the case for grou nd-leve l ozone, although the panels were not specificall y asked to address the 4uest ion of the e xi stence or level of a threshold concentration fo r the effects of airborne p;.irtic les. the question again arose beca use the pane l was re4uired to fra me its fin di ngs accord ing to various leve ls of exposure as was done for ground-leve l ozone.T here was little support among panel members for the concept of a threshold for the effects or airborne particle~.
Can Respir J Vol 2 No 3 Fall 1995 Health effects of air pollution in Canada "Ground-level ozone, the major compon ent of smog. is of primary co ncern because it is a powerful irritant and can have potentially harmful effects on the respiratory system .Symptoms are most likely to occur in individuals who are physically active outdoors .People with heart or lung disease.especially asthma, may experience a worsening of thei r condition ." •• commonly reported symptom s include irritation of the nose and throat, cough , and chest tightness .Minimize your exposure by avoiding outdoor exercise particularly in the afternoon and early evening when ground-level ozone concentrations tend to be at their highest." "Children tend to be more sensitive tt1 an adults because they breathe faster and in the summ er spend more time outdoors being physically active.Reduce your child's exposure by encouraging outdoor activities early in the day when pollutant levels are lower."

PANEL RECOMMENDATIONS
W hile the panels made a nu mber of wide -ranging recomme ndations, onl y those relating to the content of health messages and their implementation are summarized here.
W ith respect to the content o f health messages, pa,1icul ar issues identified by the pane ls included the followi ng: appropriate emphasis fo r ' diagnostic' versus ' prescriptive ' messages (those that ident ify expected health e ffects versus those that recommend protective ac tions): identification of target groups: ensu ring that messages accurate ly re flect the scienti fi c evidence and do not unduly raise public concern: and selection of an appropriate threshold for the ground-level ozone ad visory.In consultation with provinc ial public health authorities.it was strongly recommended that the health messages be diagnostic only, wi th the recommendation that more spec ific prescriptiw adv ice be obtai ned from local public health autho rities and/or personal health care providers fam iliar with the individua l' s clinical history.
W ith respect to implen11:•ntation aspects of the advisory program.the panels recommended suppl ementary education strategies di rected towards indiv iduals at risk as we ll as pare nts , teachers.athletes, coaches, health professionals and public health officials, and identified the need for evaluation of the impact of the advisory program.
In response to these recommendations Health Canada has deve loped a series of supplementary public informat ion messages, which have been made available to the public in both official languages through the media.physicians ' offices, hospi tals and parenting magazines (sec Figure 3 for sample messages ).In addition, Health Canada is col laborat ing with Environment Canada in conducting public surveys to evaluate vario u • aspects of the adv isory program.includ ing awareness of advisories and advisory-related changes in behaviour.

CONCLUSIONS
The expert pane l process se rved as a rapid means of ide nti fying and interpreti ng the e vidence on health e ffects or ground-le ve l ozone and a irbo rne partic les .Mounting evidence was identified linking e le va ted concentrat ions of these pollutants with a spectrum of harmful effects on health, and recomme ndations were made regarding e ffectiv e communication with the public about these risks.

Note:
The original report of the pane ls (refe rence I).including a de tailed refere nce list, as we ll as public information materia ls on various air pollutants, arc available t'rom the corres pond ing author.

Figure I )
Figure I) Numhcr of days per year H'ith o:011e /cre/. 1 in excess of the f hair quality ohicctirc of 82 pun.1 f>N /Jil/i,m.,11 •cmgc of 1/1/"l'c /1ig/ws1 rears !':)83-/ 990 (Source : Cm'iro11111e11t Canada.1994) aspects of the advisory program were addressed for Health Canada and Environment Canada hy two ex pert panels convened by the Institute of Environment and Health of McMaster University and the Un ive rsity of Toron to.T he pane ls compri sed individuals with experience in air po llution health research .public hcalth, air pollution meteorology and Can Respir J Vol 2 No 3 Fall 1995