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Toxic
air pollutants are typically carcinogenic in nature. 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 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'. Some
URFs of the TAPs investigated in this Study are shown
in Table 1.3a.
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Table
1.3a Unit Risk Factor of Toxic Air Pollutants
|
| TAP |
URF
(ugm-3)(i) |
| Acetaldehyde |
9.00
x 10-7 (ii) |
| Anthracene |
2.8
x 10-2 (ii) |
| Benzene |
7.50
x x10-6 (ii) |
| Benzo(a)anthracene |
1.30
x 10-3 (ii) |
| Benzo(a)pyrene |
8.70
x 10-2 (ii) |
| 1,3-Butadiene |
2.80
x 10-4 (iii) |
| Chrysene |
8.70
x 10-3 (ii) |
| Formaldehyde |
1.30
x 10-5 (iii) |
| Methylene
Chloride |
4.70
x 10-7 (iii) |
| Trichloroethylene |
4.3
x 10-7 (ii) |
|
(i)
URF is the unit lifetime risk associated with
a lifetime exposure (i.e. 70 years) to 1 ugm-3
of TAP.
(ii) 1999 WHO Air Quality Guidelines.
(iii) US EPA - Integrated Risk Information System
- On-line data as at 24 Dec 1999.
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In
addition to their carcinogenic health effects, TAPs
also have a number of other potential health effects
(WHO 1987). For example, 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.
Monitoring
of TAPs was initiated by EPD in 1997, at two of their
existing AQMSs, in Tsuen Wan (TWS), and in the Central/Western
area (CWS). A summary of monitoring results of years
1997 and 1998 is provided in Table 1.3b below.
|
Table
1.3b Levels of Toxic Air Pollutants in Hong Kong
|
| Pollutant |
1997-98
Average Concentrations (EPD)
|
|
Tsuen
Wan
|
Central/Western
|
|
1997 |
1998 |
1997 |
1998 |
| 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 |
| Benzo
[a] pyrene (ng m-3) |
0.35 |
0.41 |
0.21 |
0.29 |
| 1,3-Butadiene
(ug m-3) |
0.52 |
0.2 |
0.53 |
0.2 |
| Formaldehyde
(ug m-3) |
18.4 |
4.47 |
21.0 |
5.28 |
Data
on concentrations of TAPs have been obtained from EPD's
recent ambient monitoring programme from April 1999
to April 2000 for a number of TAPs including carbonyls
(Acetaldehyde and Formaldehyde), VOCs (1,3-Butadiene,
Tetrachloroethylene, Benzene, Methylene chloride, Trichloroethylene)
and PAHs (Anthracene, Benzo(a)anthracene, Benzo(a)pyrene
and Chrysene), to form a basis for comparison with the
survey results obtained from this study.
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