be suspended in the air, and may determine the depth to which the particles
penetrate into the lung, and so the amounts that may be deposited and retained.
In addition to widely recognized occupational health effects of PM,
numerous epidemiological studies have confirmed that total suspended
particles (TSP) present in urban areas, especially those <2.5 mm in diameter,
were associated with increased risk of mortality in pneumonia and cardiovascular disease. The risk is particularly elevated in the elderly.
6
The limited information available on the rainforest fire episode in Indonesia
in the summer of 1997 indicates widespread acute impacts on the health of a
large number of the population. According to the Singapore Ministry of
Health, there was a 13% increase in visits to government clinics for acute
respiratory infections and a 19% increase in asthma visits during the last week
of September when PM levels peaked.
9
China has achieved high rates of economic growth during the past two
decades or so. The growth is associated with rapid industrialization,
accelerated urbanization, and greatly increased energy consumption.
10 The
accelerated urbanization is evidenced by the steady increase in the proportion
of urban population to total population, from 18% in 1978 to 31% in 1999, a
rate three times the world average during this period. The explosive economic
growth also made China the world’s second largest energy consumer, after the
U.S. Between 1978 and 1999, China’s energy consumption more than doubled,
and is the main source of anthropogenic air pollution emissions in Chinese
cities. Coal accounted for about 74% of the total energy consumption during
this period. The increased use of coal is considered the origin of many air
pollution problems, including SO 2 pollution, PM, and acid rain.
10
Studies by Xu et al.
11 show that the air-pollution levels in Beijing are
associated with adverse health outcomes. The scientists studied the data on the
average number of daily hospital outpatient visits at a community-based
hospital in Beijing, and compared the data with the levels of SO 2 and TSP in
the atmosphere. They found that increases in the levels of the two types of
pollutants were significantly correlated with the increases in the numbers of
hospital visits.
A similar observation was made in Seoul, South Korea, where several
scientists investigated the impact of air pollution on human health. For
example, Ha et al.
12 studied the effect of air pollution on mortality among
postneonates, those aged 2 to 64 years, and those over 65 years of age. The
study included daily counts of total deaths and respiratory-related deaths,
along with analyses of daily levels of PM 10 . The results showed that in terms of
mortality, infants were most susceptible to PM 10 , particularly where deaths
were related to the respiratory system.
12
9.5 SILICA
Silica (Silicon dioxide, SiO 2 ) and silicates constitute the major portion of all
rocks and their products, such as soils, sands, and clays. Silicon (Si) itself is the
138
Environmental Toxicology
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-009.3d]
Ref: 4365 MING-HO YU Chap-009 Page: 138 135-148
penetrate into the lung, and so the amounts that may be deposited and retained.
In addition to widely recognized occupational health effects of PM,
numerous epidemiological studies have confirmed that total suspended
particles (TSP) present in urban areas, especially those <2.5 mm in diameter,
were associated with increased risk of mortality in pneumonia and cardiovascular disease. The risk is particularly elevated in the elderly.
6
The limited information available on the rainforest fire episode in Indonesia
in the summer of 1997 indicates widespread acute impacts on the health of a
large number of the population. According to the Singapore Ministry of
Health, there was a 13% increase in visits to government clinics for acute
respiratory infections and a 19% increase in asthma visits during the last week
of September when PM levels peaked.
9
China has achieved high rates of economic growth during the past two
decades or so. The growth is associated with rapid industrialization,
accelerated urbanization, and greatly increased energy consumption.
10 The
accelerated urbanization is evidenced by the steady increase in the proportion
of urban population to total population, from 18% in 1978 to 31% in 1999, a
rate three times the world average during this period. The explosive economic
growth also made China the world’s second largest energy consumer, after the
U.S. Between 1978 and 1999, China’s energy consumption more than doubled,
and is the main source of anthropogenic air pollution emissions in Chinese
cities. Coal accounted for about 74% of the total energy consumption during
this period. The increased use of coal is considered the origin of many air
pollution problems, including SO 2 pollution, PM, and acid rain.
10
Studies by Xu et al.
11 show that the air-pollution levels in Beijing are
associated with adverse health outcomes. The scientists studied the data on the
average number of daily hospital outpatient visits at a community-based
hospital in Beijing, and compared the data with the levels of SO 2 and TSP in
the atmosphere. They found that increases in the levels of the two types of
pollutants were significantly correlated with the increases in the numbers of
hospital visits.
A similar observation was made in Seoul, South Korea, where several
scientists investigated the impact of air pollution on human health. For
example, Ha et al.
12 studied the effect of air pollution on mortality among
postneonates, those aged 2 to 64 years, and those over 65 years of age. The
study included daily counts of total deaths and respiratory-related deaths,
along with analyses of daily levels of PM 10 . The results showed that in terms of
mortality, infants were most susceptible to PM 10 , particularly where deaths
were related to the respiratory system.
12
9.5 SILICA
Silica (Silicon dioxide, SiO 2 ) and silicates constitute the major portion of all
rocks and their products, such as soils, sands, and clays. Silicon (Si) itself is the
138
Environmental Toxicology
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-009.3d]
Ref: 4365 MING-HO YU Chap-009 Page: 138 135-148