health effects of air pollution in dublin

HEALTH EFFECTS OF AIR POLLUTION IN DUBLIN

John Kevany, Michael Rooney and John Kennedy

Departments of Social Medicine and Statistics, Trinily College, Dublin.

Summary A STUDY of the relationship between air pollution and specific health

indicators in Dublin 1970-73 was undertaken using partial correlation analysis. Deaths and hospital admissions from cardiovascular and

respiratory disease showed significant correlations with levels of sulphur dioxide and smoke in the winter months (October to March). Implications for community health and the need for further study are discussed.

Introduction The problem of air pollution in Ireland was examined by De Wytt and

Kevany in 1971 and it was concluded that serious levels of pollution existed in the city of Dublin over the preceding decade for the winter period, Oct- ober to March. During these months pollution levels frequently exceeded the standards recommended by the World Health Organization (1972a) as desirable for good health and regularly exceeded the levels known to produce sensory effects and to exacerbate pre-existing disease (W.H.O. 1972b). The same study also analysed specific trends and noted that while smoke levels were gradually declining, there was a substantial and consistent increase in SO2 levels in both summer and winter months, indicating a progressive contribution from industry and transportation as well as from space heating. Continuous monitoring carried out by the Electricity Supply Board (E.S.B.) and the Department of Local Government indicates that these trends continue undiminished (Lawlor, 1974; Local Gov., 1973).

The health effects of air pollution have been widely studied in other parts of the world (W.H.O. 1968). To date, no attempt has been made to assess these effects in Dublin city with a view to quantifying the problem in terms of health, disease, loss of productivity and the increased costs of health care. It was decided, therefore, in 1974 to examine some aspects of the present situation as a joint research project of the Departments of Social Medicine and of Statistics in Trinity College, Dublin, in order to provide a factual basis for decision making in this area. The following text describes the methodology and results of the study and presents an interpretation of the health effects on the community.

Methodology Selection of indicators (i) Air Pollution

Smoke and SOs are the two substances that are routinely monitored in Dublin by various interested bodies, specifically the E.S.B., the Depart- ment of Local Government and the Eastern Health Board. As in other urban situations, there is an extensive range of air pollutants in Dublin, with differ- ing significance in terms of health effects. Smoke and SO2 have the advan-

102

HEALTH EFFECTS OF AIR POLLUTION IN DUBLIN 103

tage of being widely accepted as indicators of general pollution conditions and can be measured with considerable precision. In selecting the data source, the E.S.B. results were chosen because of their comprehensive coverage (24 stations), consistency of recording and the quality and acces- sibility of stored data. It was decided to establish three distinct categories of indicator for each pollutant based on : a ten-station average, an eight- station average and a single station measurement. The location of stations selected for pollution indicators are shown in Figure 1.

SELECTED STATIONS for POLLUTION INDICES

~ O I0 ST. INDEX ~ 1 O 8 ST. INDEX v " ~

IS% I N D E X ~

Fig. 1

It can be observed that these stations are located in a roughly circular pattern around the centre of the city and correspond well with areas of low lichen abundance indicating high levels of pollutants (Moore, 1973). Two of the stations at the North Wall and the Pigeon House, are located near major sources of emission (a fertilizer factory and an old generating station) and consequently give readings that cannot be considered representa- tive of general ambient conditions. In consequence, the eight-station index created by excluding these two units was used as a second pollution indicator. In order to provide an alternative to mean values as indicators of pollution levels, a single station index was included in the study. The monitoring station in Schoolhouse Lane was selected for this purpose as it is centrally located, uninfluenced by heavy industry and has a recording pattern consistent with other stations in the composite indices. In summary, the three indices used were based on :

(a) Ten selected sites: smoke (10), SO,_,(10) (b) Eight selected sites: smoke (8), SO=(8) (c) One selected site: smoke( I ) , SO2(1)

104 IRISH J O U R N A L O F M E D I C A L S C I E N C E

As an illustration of current trends for air pollution in Dublin, daily levels of SO2 recorded by the Schoolhouse Lane station (SO2(1) are summarized in Figure 2.

DAILY LEVELS of SO 2 in FREQUENCY of OCCURRENCE

/qg/m 3 btocks. S c h o o l h o u s e L a n e : SO 2 (1) 50

I I I 1970 I 19711 1972 I 1973

i I 10 t J I [ Daily M e a n

z 01 15o

2o t 7. lo

0

6Q

50.

40

~.' 30.

20-

10"

0-

40

2' 2o

10

0

I r I I I J

I : t !

B i t I g I f ~

100 - 1 5 0

50 - 100

0-50

DUBLIN AIR POLLUTION SURVEY (E,S.B.) Summarised Daily Results 1970-1973

Fig. 2

it is evident that there has been a progressive rise in the frequency of SO2 levels of 50-100/~g/m 3 with a corresponding decrease in levels of 0-50 Fg/m 3 indicating an upward shift in concentration. There does not appear to be any major increase in the frequency of higher levels during these years.

(ii) Health

The indicators of health effects used in this study were selected on the basis of universality of data for the population under study and their avail- ability for analysis. The two types of indicators that fulfilled these technical criteria were mortality and morbidity statistics. Mortality data were derived from death certificates for Dublin County Borough residents collected by the Central Statistics Office. Morbidity data, expressed as daily hospital


admissions, were derived from the Hospital In-Patient Enquiry of the Medico- Social Research Board. The use of sickness absence data was explored with the Department of Social Welfare. This was not feasible, however, as the data were not available at that time in a form suitable for analysis.

The limitations on validity and precision of mortality and morbidity indicators are clearly recognised in terms of "pure" pollution effects. Thus validity is based on the concept of the aged and chronically ill as a biologic- ally vulnerable or sensitive group. In such individuals the effects of air pollution may produce a measurable change in status that is universally recognised and recorded (i.e. death and hospital admission). To increase the specificity of the health indicators, mortality and morbidity data were limited to cardiovascular and respiratory disease categories. These were refined further by excluding influenza from the general analysis as its infectious transmission characteristics might well obscure more relevant respon- ses. Furthermore, examination of the data for upper respiratory tract disease revealed that a substantial proportion of hospital admissions were for chronic tonsillitis. As this condition is insensitive to short term environmental influences, the sub-category was excluded.

Specific categories of disease were identified according to the first two digits of the International Statistical Classification of Diseases, Injuries and Causes of Death (I.C.D.) issued by the World Health Organisation (1967), with certain exclusions as indicated previously. These two-digit categories are expressed as disease entities in Table I.

TABLE I

Selected disease categories, derived from the standard I.C.D. code : 8th Revision.

Class Category No. Disease Group

I Cardiovascular 39 Active and chronic rheumatic heart disease

40 Hypertensive disease

41 Ischaemic heart disease

42 Other forms of heart disease (including 42.8:

II Respiratory

43

44

45

46

48

49

50

51

"other myocardial insufficiency")

Cerebrovascular disease

Diseases of arteries, arterioles and capilliaries

Diseases of veins and lymphatics

Acute respiratory infections (including 46.6: "acute bronchitis and bronchiolitis")

Pneumonia (bacterial, viral and unspecified)

Bronchitis, emphysema and asthma

Other diseases of the U.R.T. (excluding 50.0: "hypertrophy of tonsils and adenoids")

Other diseases of the respiratory system (including 51.4: "pulmonary hypostasis" and 51.8 : "bronchiectasis")

106 IRISH JOURNAL OF MEDICAL SCIENCE

(iii) Meteorology The effect of temperature on morbidity and mortality has been well

documented, particularly in relation to cardiovascular and respiratory disease (Rose, 1966; Boyd, 1960). Any attempt to quantify the effects of air pollution on health must therefore allow for this variable. Data on meteor- ological conditions during the periods under study were obtained from the E.S.B. and included maximum, minimum and average daily temperature readings. In selecting a single weather indicator, the maximum 24 hour temperature appeared to provide the best indication of overall "coldness" during daylight hours, which might be expected to affect human health and su rvival.

Data Processing Information was obtained from each of the services mentioned above by

submitting specific requests and receiving the corresponding data in suit- ably edited form to guarantee confidentiality. The data sets necessary for the analysis were then set up on an IBM 2314 disk in the Computer Science Laboratory in Trinity College, Dublin. The purpose of the project was to investigate a possible association between air pollution and ill-health rather than to construct a comprehensive model of factors producing death and disease. Consequently, it was considered that the use of multiple re- gression was unnecessary and partial correlation was selected as the method of analysis. On this basis partial correlations of pollution indices with mortality and morbidity indices were calculated while controlling for weather. Maximum daily temperature was chosen as the controlled weather variable. Associated with every partial correlation obtained, a two-tailed significance level was also computed. The Statistical Package for the Social Sciences (S.P.S.S.) on the Trinity College computer was used ex- clusively in the analysis since the package was available for both batch and remote terminal programmes.

It is recognised that the selected health indicators do not necessarily provide an immediate response to high pollution due to a variety of factors. For this reason, different lag times ranging from 0-3 days were applied to the mortality and morbidity data in order to allow for these effects. Another aspect of importance in assessing overall effect in aged and diseased population subgroups is the phenomenon of "cropping". Individuals of advanced age or with serious disease conditions have at any given time a probability of dying much greater than average. Air pollution may therefore act by precipitating death or hospital admission in such individuals, only to produce an " inert" or compensatory phase of low frequency due to absence of borderline cases. By using moving averages for varying time spans, it is possible to reduce this dichrotic effect and to show the magnitude of real change in the frequency of death or hospital admission.

Results for Cardiovascular Disease

(i) Mortality Mortality for cardiovascular disease for the winters 1970-73 was found

to be significantly correlated with SOs levels within the same 24 hours (lag = 0 ) , controlling for ambient temperature. Ischaemic heart disease (I.C.D.


41) was the major component of this correlation and the results are expressed in Table II and Fig. 3 below.

TABLE II

Partial correlations for cardiovascular disease, mortality with SO2(8) 1970-73, as thresholds increase, when controlling for temperature,. Lag=0.

Disease Threshold : /~g/m ~

0 50 75 100 125 150

ICD39 r 0.001 0.060 0.179 0.156 --0.087 0.305 P 0,490 0.122 0.013" 0 123 0.361 0.279

ICD40 r 0.029 --0.021 --0.010 --0,033 --0,155 --0.439 P 0.249 0.345 0.449 0.403 0.263 0 192

ICD41 r 0.116 0.112 0,138 0.229 0,368 0.878 P 0.003* 0.015" 0.043* 0.043* 0.061 0.011 *

ICD42 r --0.038 --0.049 --0,042 --0.051 0.107 0.0,75 P 0.187 0.170 0.302 0.354 0.331 0.444

ICD43 r 0.010 --0.043 --0,075 --0.127 --0.117 0.524 P 0,411 0.200 0.176 0.174 0.316 0.143

ICD44 r --0,064 --0.086 --0.018 0.031 --0.141 0.851 P 0.068 0.048* 0.411 0.409 0.282 0.016*

ICD45 r 0.018 --0,0021 --0,014 --0.140 --0.322 --0.529 P 0,335 0,484 0.433 0,150 0.090 0.140

C.V. Total r 0.076 0.032 0.076 0.126 0.154 0.821 P 0.038* 0.269 0.174 0.174 0.265 0.022*

* Positive correlations significant at the 5 per cent level.

It can be observed that there is a consistent and progressive positive correlation between total cardiovascular mortality and SO= at increasing threshold levels, with r=0.821; P=0.02 at 150 Fg/m 3. It is evident that the major contribution to this correlation is ischaemic heart disease (I.C.D. 41) which shows a progressive increase in correlation at rising thresholds, with r=0.878; P=0.01 at 150 /~g/m 3 (Fig. 3). The overall correlation for ischaemic heart disease and SO= at all levels (threshold 0) is significant at the 0.003 level. The fact that this trend is not followed by chronic myocardial insufficiency (IC.D. 42) suggests that these are sudden and unpredicted coronary deaths, possibly in younger age groups. Extending the analysis to cardiovascular deaths occurring in the 24 hours succeeding a stated pollution level (lag = 1, day), the correlation became insignificant (r=0.0239; P=0.289), except in the case of valvular heart disease (I.C,D, 39) which showed highly significant correlations indicated below in Table Ill.

These correlations were not sustained with a lag period of two days nor in relation to smoke indicators at any lag period or threshold level.


.7 PARTIAL

.6 CORRELATION

"5 COEFFIOIENT

,4-

. 3

.2.

. !

PARTIAL CORRELATION COEFFICIENTS

for ICD 41 (MORTALITY),

using thresholds with SO 2 (8),

and controlling for temperature.

Significance in ( ) . Lag = O

t

i 2

#

t

. . ~ I'

, * * " (0 -061 )

boeoeee.ooooeOeeeeeeeeeee~eeeeoeeo~eeeeeeoeeO~ .043)

',0.003) (0.004) t0"015) (0-043)

25 + 50 + "/5 "+ 100 -I- 1 -4-

THRESHOLD /J.g/m 3

Fig. 3

§

To allow for the dichrotic effect on the mortality curve, moving averages for three and seven day periods were examined. Significant partial correlations were sustained for ischaemic heart disease (r=0.16; P=0.001) for three day averages. Moving averages for seven days showed no significant correlation for total cardiovascular disease (r=0.01; P=0.40) but ischaemic heart disease remained identifiable (r=0.08; P=0.07). This suggests that the gross effect of SOs pollution on cardiovascular and ischaemic heart disease may to some extent be compensated for at a week's interval. Smoke pollution at higher levels (threshold: 100 /~g/m 3) did show significant correlations with seven day moving averages for ischaemic heart disease (r=0.74; P--0.004) and valvular heart disease (r--0.90; P=0.001) suggesting a substantial and permanent effect on community health.

TABLE III

Partial corre lat ions between rheumatic and valvular heart disease (I.C.D. 39) and SO~(10) ( L a g = l ) .

SO,.,(10) 0 /~g/m 3 100 p~g/m ~ 125 /~g/m s 150 p.g/m 3

I.C.D. 39. r

P

0.051 0.294 0.765 0.981

0.118 0.002* 0.001 * 0.001 *

�9 Posit ive correlat ions signi f icant at the 1 per cent level.


This pattern indicates that SO2 has immediate effects on cardiovascular mortality that are compensated for by lower death rates in succeeding days. Smoke appears to have a more gradual effect producing a sustained increase in mortality over a longer time span. This finding is supported by a small but significant correlation for smoke and ischaemic heart disease deaths after a lag period of 24 hours (r=0.09; P=0.017) which was not evident with a lag period of zero (r=0.02; P=0.313).

The number of hospitals participating in the In-patient Enquiry increased over the period of study; therefore, morbidity was examined separately for specific hospitals each winter. During the first winter, 1970-71, data for hospital admissions were limited due to the small number of participating institutions. The only findings of importance were correlations between admissions for males with valvular heart disease (ICD 39) and smoke (r= 0.25; P--0.001) and SO._, ( r= 0.17; P=0.01) with a lag time of zero. In the second winter, 1971-72, there was no consistent correlation between hospital admissions and pollution levels with the exception of ischaemic heart disease and SO=(1) where r=0.22; P=0.001. As this finding was not supported by other pollution indicators, it is unlikely to be meaningful.

During winter 3, 1972-73, when the total of patients admitted to participating hospitals for cardiovascular disease was 2,364, divided approxim- ately equally between males and females, several correlations of significance emerged for each sex. The findings are expressed in Table IV for specific disease categories and for a composite cardiovascular indicator consisting of valvular heart disease (I.C.D. 39), hypertension (I.C.D. 40), ischaemic heart disease (I.C.D. 41) and myocardial insufficiency (I.C.D. 42).

TABLE IV

Admissions for cardiovascular disease: correlations with smoke and SO2 (1972-73).

Admission category Males Females Smoke(8) SO2(8) Smoke(8) SO2(8)

Ischaemic heart disease (I.C.D. 41)

Myocardial insufficiency ( I.C.D. 42)

Composite indicator (I.C.D. 39, 40, 41, 42)

0.24 (0.001) * 0.23 (0.001) *

0.17 (0.01)* 0.22 (0.001)*

0.25 (0.001) * 0.29 (0.001) *

0.04 (0.28) 0.11 (0.07)

0.10 (0.09) 0.15 (0.02)*

0.13 (0.05)* 0.18 (0.007) ~


It can be observed that hospital admissions for males for all categories of cardiovascular disease are highly significant at the 0.001 level with the exception of I.C.D. 42 and smoke, where P=0.01. Admissions for females are of much lower levels of significance with the exception of the values for the selected cardiovascular disease.

All six pollution indicators showed correlations with male admissions for ischaemic heart disease significant at the 0.001 level providing strong


evidence for a causal relationship. The disparity between the sexes can be explained not only by known vulnerabi l i ty of males to ischaemic heart disease but also in terms of exposure. The work force in the central city area for the relevant age groups (35 + years) is predominantly male and frequently engaged in outdoor activities involving prolonged and direct exposure to ambient pollution.

In order to assess the effect of age on morbidity associated with air pollution, hospital admissions were subdivided into the fol lowing age and sex subsets: 35-64 years, male and female; 65 and over, male and female. Due to the smaller numbers of admissions in the Enquiry in winters 1 and 2, this analysis was confined to winter 3, 1972-73, with temperature controlled and a lag time of 0. Admissions for ischaemic heart disease in males 35-64 were signif icantly correlated with air pollution (smoke(8) and SO2(8) at the 5 per cent level, while I.C.D. 42, "other forms of heart disease" (including 42.8: myocardial insufficiency) was also correlated with all indicators at the 5 per cent level and part icularly with SO= (P=0.002). For females 35-64 years, admissions for hypertensive disease (I.C.D. 40) and cerebrovascular disease (I.C.D. 43) were highly correlated with both pollution indicators (smoke and SO~), as indicated in Table V below.

TABLE V

Females 35-64 years : correlations for hospital admission and air pollution (Lag=0) (1972-73).

Category Smoke (8) SOt (8) r P r P

LC.D. 40 : Hyperte~s',os 0.2",40 0.,?,02* 0.113 ~, 0.065

I.C.D. 43: Cerebrovascular Dis. 0.1657 0.006* 0.2024 0.003*


It can be seen that there is a highly signif icant correlation between admissions for cerebrovascular disease and both pollution indicators while hypertension is also signif icantly correlated with smoke levels. These results have considerable importance as they refer to a younger and productive sector of the population and thus imply considerable social and economic losses to the community. The fact that these analyses are based on a zero lag time indicates that many of these cases were probably of an acute nature.

At age 65 years and over, consistent significant correlations were found for males admitted for ischaemic heart disease (smoke(8): P=0.006; SO2(8): P=0.024) and myocardial insufficiency (smoke(8): P=0.011; SO2 (8): P=0.008). Myocardial insufficiency was also signif icantly correlated in females (smoke(8): P=0.043; SO_~(8): P=0.003).


Results for Respiratory Disease (i) Mortality

Mortal i ty for respiratory disease for the winters 1970-73 was less con- sistently associated with air pollut ion than cardiovascular disease. Of importance, however, was the strong correlat ion between higher levels of SOs and acute respiratory infections (I.C.D. 46), pr incipal ly acute bronchit is and bronchiol i t is, as shown in Table VI and Fig. 4. below:

TABLE VI

Partial correlations for respiratory disease mortality with SO2(8), 1970-73, as thresholds increase, when controlling for temperature. Lag=0.

Disease Thresholds : /~g/m 3

0 50 75 100 125 150

ICD46 r 0.071 0.027 0.050 0.438 0.797 0.874 P 0.049* 0.304 0.270 0.001 * 0.001 * 0.011 *

ICD48 r --0.018 --0.009 0.058 0.026 0.046 --0.379 P 0.342 0.428 0.237 0.423 0.426 0.230

ICD49 r 0.052 0.078 0.083 0.027 --0.186 0.897 P 0.114 0.064 O.152 0.422 0.223 0.008*

ICD50 r --0.064 --0.094 P 0.069 0.034* w

D

m

m

ICD51 r --0.021 --0.039 --0.120 0.043 --0.225 - - P 0.310 0.226 0.068 0.376 0.177 - -

Respiratory 0.025 0.036 0.071 0.092 --0.033 0.336 Total 0.282 0.242 0.190 0.247 0.447 0.258


It can be seen that levels of SOs up to 75/.~g/m" do not produce any signif icant response in terms of mortality. From 100/~g/m ~ upwards there is a strong correlat ion with deaths from acute respiratory disease (I.C.D. 46), pr incipal ly acute bronchit is. At 150/~g/m 3 threshold there is also a strong correlat ion with deaths from chronic bronchit is, emphysema and asthma (I.C.D. 49). These correlat ions were sustained with moving averages for 3 days (r=0.12; P=0.003) and seven days (r=0.11; P=0.02), indicat ing a persistent and real effect on mortality for these causes. This was most evident at SOs thresholds of 100 ~g/m 3 where a highly signif icant correlat ion ( r=0.65; P = 0.006) existed for seven day moving averages for chronic bronchit is, emphysema and asthma. No signif icant correlat ions existed for smoke at any threshold or lag period. This evidence would indicate that SOs is the important pol lutant in terms of respiratory disease, correlat ions for which are sustained at seven days, suggesting real and permanent effects on community health.


"7

PARTIAL

"6

CORRELATION

.5

COEFFICIENT

-4

" 9 -

'8

'3

'2

.1

0

PARTIAL CORRELATION COEFFICIENTS for

'CD 46 f MORTALITY) with SO 2 (8) .

using thresholds, and controlling for temperature

Significance in ( ~ Lag = O

�9 'P . . . . . . . . . . . *'*(o.o11)

�9 (o.ool)

/ /

#

'(o, oot )

/ 7 /

/ 7

0"049) (0-049) noeeQeeeoeeeOee , . , o ~0.394)

~ ~ ! i i J 1

0 25 + 50 + 75 + 100 "P 12,5 -t- 150+

THRESHOLD ) 4 g / m 3

Fig. 4

(ii) Morbidity Hospital admissions for respiratory disease were examined for the three

winters under study. During winter 2, 1971-72, significant correlations existed for smoke pollution and acute bronchitis (I.C.D. 46), with r=0.1776; P=0.008, and chronic bronchitis (I.C.D. 49), with r=0.1284; P=0.042. Analy- sis of respiratory disease admissions by age was confined, as with cardiovascular disease, to winter 3, 1972-73. In the 35-64 year age group there were highly significant correlations for female admissions for pneumonia with smoke (r=0.22; P--0.001) and SO= (r=0.22; P=0.002) using 8-station indicators. This suggests a causal relationship and is an important finding in view of the social and economic significance of this age group. In the 65 year and over groups, significant correlations existed for male hospital admission for acute respiratory disease (I.C.D. 46) and SOs (r=0.1959; P=0.005). In females of this age group, admissions for chronic bronchitis, emphysema and asthma (I.C.D. 49) correlated very significantly with smoke levels (r=0.1904; P=0.005).

On the whole, the relationship between hospital admissions for respiratory disease and pollutant levels is less consistent than for mortality. This may, in part, be due to a lower priority for hospital admission for this group of diseases, with the exception of pneumonia.

Influenza Morbidity data for influenza (I.C.D. 47) were analysed separately due to

the highly infectious nature of the condition, where transmission might be expected to dominate any environmental influences. Furthermore, the vari- ation in clinical severity for influenza is considerable and hospital admission


is an infrequent outcome. The results of this analysis failed to demonstrate any significant contribution of air pollution to the incidence pattern of this condition.

Discussion The evaluation of the effects of air pollution on mortality and morbidity

indicators presents problems in interpretation which must be clearly recognised. The use of mortality and morbidity in aged and chronically ill individuals reduces specificity of effect but offers a high degree of sen- sitivity and provides clear end-points such as death and hospital admission. The measurement of pollution effects in specific subgroups as opposed to total populations permits greater precision of measurement, but the cost of such investigations represents a serious obstacle. The question of exposure is also complicated by widespread smoking, especially in adults. Nevertheles.s, air pollution can be regarded validly as an additional, and measurable, burden of pollution on the assumption that cigarette smoking patterns remain relatively constant for the total population over short time periods. The use of lag times and moving averages in the analysis serve to clarify the nature of the effect and to estimate the overall loss to the community. With these caveats in mind, the outcome of this study can be usefully interpreted in health terms.

The results of this study are highly indicative of an important role of air pollution in death and hospital admission for cardiovascular and respiratory disease in Dublin during recent years. The group of diseases identified as being significantly associated with air pollution levels are consistent with clinical evidence for a causal relationship. In particular, the strong association of pollution with deaths and hospital admissions for ischaemic heart disease in males is of considerable importance. The strengthening of this association for mortality with increasing threshold levels of pollution provides strong evidence of a dose-response effect. For hospital admissions the association is characterized by short lag times (less than one day) and by younger age groups, both of which indicate a precipitate and severe response. -This evidence is strengthened by the correlation for admissions with myocardial insufficiency. The association of pollution with admissions for hypertensive and cerebrovascular disease in younger females is also of interest, though no immediate explanation for a sex differentiation in this age group is apparent.

The significant associations of acute and chronic bronchitic disease with higher SOs levels are consistent with evidence obtained from studies in other parts of the world (Dean, 1966; Hodgson, 1970; Lave and Seskin, 1973; Lawther et al., 1962; Chapman et al., 1974). It is of interest to note that this response begins for acute respiratory conditions at the 75 /~g/m 3 level: a concentration found frequently in Dublin in recent years (c.f. Fig. 2). The difference in time lag between the response of acute ( lag=0) and chronic conditions ( l ag= l ) strengthens the evidence in favour of a causal relationship. The strong association between both pollution indicators and hospital admissions for pneumonia in younger (35-64 years) women s of interest and may represent the combined effects of smoke and SO.~ produced by ad- sorption of the gas onto solid particles, a situation where particulate levels (smoke) become critical in the presence of excess gaseous pollutant (SOs).


It is concluded that there is substantial statistical evidence to indicate that current levels of air pollution in Dublin exercise an unfavourable effect on human health and welfare and contribute to increased demands for medical care with its associated costs to the community. This situation is of particular relevance as, among 26 European countries, Ireland has the highest mortality rate from respiratory disease over the age of 15 years (W.H.O., 1974). The concentrations of SO~ in the city environment already exceed recommended levels established as desirable for human health and welfare by the World Health Organization and trends indicate that this situation will deteriorate further. The current high price of fuel oil will probably only have a minor effect in reducing the rate of increase for SO=, while any resulting increase in coal consumption will modify or reverse the downward trend in smoke levels. The combination of smoke and SO~ has a more serious effect on health than either pollutant alone and the city may be faced with crit ical pollutant interactions in the near future. The presence of marine aerosols in the Dublin area presents additional hazards, as animal studies indicate that sodium chloride particles exacerbate the irritant properties of sulphur dioxide (Frank, et al., 1974).

The formulation of adequate standards for ambient pollution levels by the appropriate government agency is an urgent requirement upon which the necessary legislation and regulation can be based. Adequate resour- ces for effective enforcement through control of emission sources is an essential corollary of such action. There is also a need for ongoing research in this area to determine more precisely the chemical and physical properties of pollutants in Dublin, with particular reference to suspended sulphates which possess far greater toxicological properties than SOs (French, 1973). Each city has its own particular distr ibution and spectrum of pollutants depending on the nature and mix of emission sources; thus results from one situation cannot necessarily be applied to another. Pre- cise dose-response relationships need to be established under controlled condit ions using more sensitive health indicators such as respiratory func- tion in specific population groups.

Finally, in the interests of efficient health planning, cost-benefit studies based on predictive models should be carried out as a priority to determine the extent of economic loss to the community in terms of premature death, loss of productivity and additional health care. Many statements have been made by the government and the medical profession regarding the need to transfer investment in health from curative to preventive services; this situation provides an excellent opportunity to put this concept into practice.

The authors gratefully acknowledge the assistance of Mr. G. Lawlor, E.S.B., Miss G. Nugent, C.S.O. and Mr. J. O'Gorman, M.S.R.B. in making available the required data for this study, and of Professor F. G. Foster and Dr. R. Johnston, Department of Statistics, T.C.D. for their advice on study design and data analysis. Our thanks also go to Teresa Farrell for her generous assistance in preparing this article for publication.

Reprints from J. Kevany, Department of Social Medicine, T.C.D.


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healthy adults. Int. J. Air Water Polrution. 8, 125. French, J. G. 1973. The effect of sulphur dioxide and suspended sulphates on acute respira-

tory disease. Arch. Environ. Health. 27, 129. Hodgson, T. A. 1970. Short term effects of air pollution on mortality in New York City.

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