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| Toxic
Air Pollutants (TAPs)
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| 5.4.1.18 |
Toxic
air pollutants differ considerably from
CAPs due to their health effect at substantially
lower concentrations in the ambient environment
and because their health effects are typically
carcinogenic in nature. Relevant health
standards for the TAPs presented in this
section are shown in Table 5.4d.
| Table
5.4d Health Guidelines for Toxic Air
Pollutants |
| TAP |
Health
Guidelines (ugm-3) |
Average
Time |
| Cadmium |
0.005
(i) |
annual
|
| Lead |
0.5
(i) |
annual |
|
1.5
(ii) |
3
months |
| Benzene |
6x10-6
per ugm-3 (i) |
lifetime
risk |
| Benzo[a]pyrene |
0.387
(iii) |
1
hour |
| 1,3-Butadiene |
19
(iii) |
1
hour |
|
220
(iv) |
annual |
| Formaldehyde |
100
(i) |
30
minutes |
(i)
WHO Air Quality Guidelines for Europe
(ii) Air Quality Objective(AQO)
(iii) Health Protection Concentration Levels,
Technical Memorandums for Issuing Air Pollution
Abatement Notices
(iv) A Reference Note on Occupational Exposure
Limits for Chemical Substances in the Work
Environment, 1995, Labour Department HK.
A safety factor of 100 has been applied
for conversion of Time-weight-average value
to long term exposure limit and to allow
for variability in human reponse to chemicals.
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| 5.4.1.19 |
In
addition to their carcinogenic health effects,
TAPs also have a number of other potential
health effects (WHO 1987). For example,
cadmium is associated with acute respiratory
effects in humans at fume concentrations
in air above 1 mg m-3 and chronic respiratory
effects may occur from occupational exposure
to 20 ug-3 for 20 years. Long term and low
level exposure to lead in air is known to
affect inter alia, the nervous and immune
system and kidneys as well as having cardiovascular
and hepatic effects. Persistent exposure
to toxic levels of benzene may cause injury
to the human bone marrow and acute exposure
to formaldehyde may cause irritation of
eyes, nose and throat, coughing and nausea
at concentrations of between 0.1 and 3.7
mg-3.
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| 5.4.1.20 |
Data
on concentrations of TAPs have been obtained
from EPD's recent ambient monitoring programme,
supplemented with a baseline survey commissioned
as part of the SUSDEV 21 study to measure
ten TAPs at a roadside site for a one year
period. A summary of selected monitoring
results to date is provided in Table 5.4e
below, though it should be noted the data
from the two surveys are not directly comparable
due to differences in survey times and averaging
periods.
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| Table 5.4e Levels of Toxic Air Pollutants in Hong Kong |
Table 5.4e Levels of Toxic Air Pollutants in Hong Kong
| Pollutant |
1997-1998 Average Concentrations
(EPD)
Tsuen Wan
1997 |
1997-1998 Average Concentrations
(EPD)
Tsuen Wan
1998 |
1997-1998 Average Concentrations
(EPD)
Central/ Western
1997 |
1997-1998 Average Concentrations
(EPD)
Central/ Western
1998 |
1999 Average Concentration(1) (ERM)
Roadside Site |
| Cadmium (ng m-3) |
1.21 |
1.48 |
1.63 |
1.56 |
- |
| Lead (ng m-3) |
59 |
68 |
60 |
61 |
- |
| Benzene (ug m-3) |
2.9 |
2.6 |
2.4 |
2.1 |
5.12 |
| Benzo [a] pyrene (ng m-3) |
0.35 |
0.41 |
0.21 |
0.29 |
0.5 |
| 1,3-Butadiene (ug m-3) |
0.52 |
0.2 |
0.53 |
0.2 |
0.58 |
| Formaldehyde (ug m-3) |
18.4 |
4.47 |
21.0 |
5.28 |
0.82 |
Note(1) Averaging period from mid April to mid July 1999.
Source: EPD (1998d), ERM (2000e).
| 5.4.1.21 |
Comparison
between EPD monitoring data in the table and
data for 1997 show that levels of cadmium
at Tsuen Wan monitoring station have risen
whilst lead concentrations at both stations
have also increased when compared with the
previous year. Cadmium levels at Central/Western
appear to have fallen over the same period.
Among the organic substances monitored, levels
of Benzene, 1,3 Butadiene and Formaldehyde
have all fallen significantly., while Benzo[a]pyrene
levels have risen at both monitoring stations.
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| 5.4.1.22 |
A
risk assessment of the health effects of TAPs
is required under the EIAO using standards
or criteria adopted by recognised international
organisations such as WHO and USEPA (see TM
s4.4.3(a) (i) and Annex 4, 1.1d). Therefore
evaluation of concentrations is usually undertaken
using Unit Risk Factors (URFs) which have
been derived in other countries, particularly
the USA. URFs relate to the risk of contracting
cancer from long-term exposure to TAPs and
are in turn based upon Cancer Potency or Slope
Factors and a set of exposure assumptions.
When pollutant concentrations are multiplied
by the relevant URF, a risk value is derived
which can then be compared with an accepted
definition of 'acceptable risk'. |
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