ArticlesCardiorespiratory and all-cause mortality after restrictions on sulphur content of fuel in Hong Kong: an intervention study
Introduction
The association between air pollution and health effects including death has been established from reports on high-pollution incidents,1 time-series analyses,2 and cohort studies.3, 4 The strongest evidence is for respirable particulates (PM10),5 but many researchers have reported associations with gaseous pollutants, especially sulphur dioxide (SO2).6 Questions remain about the public-health effect of air pollution, particularly about death rates and life expectancy.7, 8 Very few opportunities have arisen to do epidemiological studies of the effects of interventions or of individual components of pollution.
Absence of data from intervention studies means that inconsistencies between studies on the importance of particulates or gases in pollutant mixtures, as causes of health problems and premature deaths, have not been resolved. One difficulty relevant to assessment of the public-health and economic analyses is the issue of mortality displacement or so-called harvesting.9, 10 Do deaths associated with fluctuations in pollutant concentrations arise mainly in sick or highly vulnerable groups of people, who would have died anyway in the short term, or are there longer-term effects from exposures? Time-series and cohort studies have both investigated the relation between pollution and years of life lost, but each has inherent limitations.
SO2 has been described as a pollutant of public-health concern. The US Clean Air Act Amendments of 1990 proposed a reduction of 10 million tonnes of SO2 emissions by 2010, with the aim to reduce SO2, sulphate particulates, and acid precipitation.11 In the first half of 1990, ambient monthly SO2 concentrations monitored in Hong Kong ranged from 3 μg/m3 to 145 μg/m3 between the least and most polluted districts, with a regional mean of 37 μg/m3. On July 1, 1990, all power plants and road vehicles in Hong Kong were restricted to use of fuel oil with a sulphur content of not more than 0·5% by weight.12 This intervention led to an immediate improvement in air quality, which was associated with a fall in SO2 and sulphate in respirable particulates by up to 80% and 41%, respectively, in the most polluted areas. No great change in any of the other main pollutants was recorded.
In the 2 years after the intervention we showed a reduction of chronic bronchitic symptoms13 and bronchial hyper-responsiveness14 in young children. We aimed to assess the immediate and longer-term effect of the air-quality intervention on deaths in the Hong Kong population.
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Procedures
From July, 1985, to June, 1995, we obtained data for deaths per month from all causes, respiratory disease (international classification of diseases 9th revision [ICD9] 460–519), cardiovascular disease (ICD9 390–459), and neoplasms (ICD9 140–239), and other causes (ICD9 001–009; 140–161; 163–246; 280–294; 320–326; 520–629; 710–719) from the Census and Statistics Department databases.15 We stratified these data into three groups by age: 15–64 years; 65 and older; and all ages.
Air-pollutant
Results
In the first year after introduction of the intervention, mean fall in SO2 concentration at five stations was 53% (table 1). Reduction in SO2 concentration was sustained between 35% and 53% (mean 45%) of the mean value before the intervention, over 5 years. At eight stations for which complete data were available for up to 2·5 years, the average reduction in SO2 concentration over this period was 50%.
Mean concentration of sulphate in respirable particulates at five stations for 2 years before
Discussion
After introduction of the air-quality intervention in Hong Kong, in addition to the 45% average reduction in SO2 over 5 years, we noted that sulphate in respirable particulates had sustained reduction up to 2 years, but concentrations rose again and stabilised as part of a regional pattern of sulphate pollution in southern China. No comparable reductions or downward trends in the other main pollutants, PM10, NO2 and O3, were recorded. These immediate changes in concentration of sulphur-derived
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