9b.1.1.1 This section presents the assessment of the potential health risk impact associated with the construction and operation phases of the IWMF located at the artificial island near SKC.
9b.1.1.2
With reference to the Section
·
Assess the potential health impacts of aerial emissions from the IWMF
during operational phase;
·
Assess the potential health impacts of biogas from sorting and recycling
plant;
·
Assess the potential health impacts of fugitive emissions during
transportation, storage and handling of the waste and ash; and
· Assess any other potential accidental events.
9b.2 Potential Health Impacts of Aerial Emissions from the IWMF during Operational Phase
9b.2.1.1
The artificial island near SKC
will need to be formed by reclamation on the southern side of the Shek Kwu
Chau, an island located to the south of the Chi Ma Wan Peninsula of Lantau
·
It is far from any major residential populations.
·
The nearest major group of sensitive receptors includes residents of
Cheung Chau (≈
· No other major industrial air emission sources exist in the nearby areas. Therefore, concerns about the cumulative impact of multiple sources on air quality are minimal for this site.
9b.2.2.1
Based on our desktop literature
search, the conduct of full quantified health risk assessments has become
fairly standard for incinerators, but there is generally no regulatory
requirement, nor official guidance on how to conduct risk assessments for
incinerators. For example, the WHO has general guidelines, but there are no
specific quantitative recommendations on assumptions or equations that should
be used. The risk assessment procedures used in the
9b.2.2.2 The purpose of the hazard identification step is to identify compounds of potential concern (COPC) for quantitative evaluation and to generate emissions estimates for short-term (acute) and long-term (chronic) exposures to the selected COPCs.
Compounds of Potential Concern
9b.2.2.3 An early step of the health risk assessment involved reviewing data for compounds potentially present in facility emissions (due to presence in the waste stream, presence in stack gas emissions as products of incomplete combustion, or as a result of emissions from fugitive sources associated with waste handling and the combustion process), and then identifying the most toxic, prevalent, mobile and persistent compounds. Based on this analysis, COPCs are selected for evaluation in the health risk assessment.
9b.2.2.4 The IWMF thermal treatment facility is currently in the planning stages. As such, facility specific stack gas emissions data are not available. Therefore, to identify COPCs and their associated emission rates, it was necessary to evaluate information from a variety of different sources.
9b.2.2.5 Sources of information for selection of COPCs included regulatory air quality requirements or stack gas permit limits such as those provided in the Environmental Protection Department’s (EPD) Guidance Note on the Best Practicable Means (BPM) for Incinerators (EPD, 2008). Additional consideration was given to identifying COPCs that may be considered Persistent, Bioaccumulative and Toxic (PBT) chemicals, often of particular concern through indirect (ingestion) exposure pathways.
COPCs
9b.2.2.6 The list of identified COPCs is provided below.
Trace Metals
·
Antimony
·
Arsenic
·
Beryllium
·
Cadmium
·
Chromium
·
Cobalt
·
Copper
·
Lead
·
Manganese
·
Mercury
·
Nickel
·
Thallium
·
Vanadium
· Zinc
Organic Compounds
·
Polychlorinated biphenyls (PCBs)
·
Polychlorinated dibenzodioxins and furans (dioxins/furans)
· Polynuclear aromatic hydrocarbons (PAHs)
Other Compounds
·
Carbon monoxide
·
Hydrochloric acid
·
Hydrogen fluoride
·
Nitrogen oxide
·
Particulate matter (respirable)
·
9b.2.2.7 These COPCs are representative of MSW thermal treatment facilities in general and are expected to represent those compounds or groups of compounds for which regulatory permit limits may be applicable and those that may be the most toxic, prevalent, mobile and persistent compounds in MSW emissions. Most of the compounds listed above are subject to the target concentration limits set by the EPD. For those COPCs (i.e. Beryllium, Zinc, PCBs & PAHs) not listed on the BPM, the emission rates are made reference to the “Quantitative risk assessment of stack emissions from municipal waste combustors[1].
9b.2.2.8 Long-term maximum stack emission rates (in grams per second) have been developed for each COPC identified. Because stack gas measurement data are not available for the planned MSW thermal treatment unit, emission factors upon which emission rates are based may be higher than actual emission rates. This is customary in permitting MSW thermal treatment units since (1) certain values (such as Target Emission Levels established as part of the EIA) may become permit limits; (2) emissions from MSW thermal treatment units are known to fluctuate as a result of variations in waste composition; and (3) it is prudent to take an approach that assures the emissions will not be understated. It is important to emphasize that the final design of the planned MSW thermal treatment unit will incorporate good engineering practices and air pollution control (APC) systems which will minimize actual emissions.
9b.2.2.9 Concentration limits have been established by the Hong Kong EPD (Guidance Note on the BPM for Incinerators (Municipal Waste Incineration), BPM 12/1 (08)) for most of the metals listed above as well as hydrogen chloride (HCl), nitrogen oxides (NOx), particulate matter and dioxins and furans. These concentration limits are proposed as the basis for estimating emission rates of those COPCs except NOx. For NOx, the target emission levels for the IWMF would be set as half of respective concentration limits stipulated in BPM 12/1 (08). The emission rates have been estimated by multiplying the target concentration limits and the stack gas flow rate, which were determined from preliminary design parameters for the combustion unit at the IWMF. For Be, Zn, PCBs & PAHs, the emission rates stated in the “Quantitative risk assessment of stack emissions from municipal waste combustors” is for the combustion of 1500 tonnes of waste per day. Since the design capacity of the IWMF is 3000 tpd, therefore two times the emission rates stated in the above paper have been adopted for the assessment. In accordance with the above paper, the anticipated normal emission rates for Be, Zn, PCBs & PAHs would only be 2% to 11% of their corresponding maximum emission rates, taking into consideration the waste composition and the incinerator design of the IWMF, the assumed emission rates for Be, Zn, PCBs & PAHs adopted in this assessment are indeed conservative.
9b.2.3 Air Dispersion and Deposition Modelling
9b.2.3.1 Air dispersion and deposition of aerial emissions from the planned MSW thermal treatment units have been predicted from a combination of modelling efforts to support the health risk assessment.
9b.2.3.2 Potential cumulative impacts due to dispersion of aerial emissions from the IWMF have been predicted at existing and planned/committed Air Sensitive Receivers (ASRs) with the use of Industrial Source Complex (ISC) model (for the near field ASR (i.e. SKC1)) and the Pollutants in the Atmosphere and their Transport over Hong Kong (PATH) Model. The proposed representative ASRs are listed in Table 9b.1. The detailed methodology for modelling air dispersion is presented in Section 3 of this EIA Report.
Table 9b.1 Identified Air Sensitive Receivers for
|
ASR |
Description |
Nature of ASR (1) |
Building Height, m |
Ground level, mPD |
Distance to Project Boundary, m |
|
SKC1 |
Shek Kwu Chau
Treatment and Rehabilitation Centre(2) |
G/IC |
6 |
74.1 |
278 |
|
SL1 |
Cheung Sha |
R |
9 |
34.8 |
5557 |
|
SL2 |
Tong Fuk |
R |
9 |
14.0 |
7113 |
|
TC1 |
|
CDA |
141 |
7.5 |
11428 |
|
TC2 |
|
CDA |
153 |
6.8 |
11245 |
|
TC3 |
Ling Liang Church
Sau Tak primary School |
G/IC |
21 |
6.4 |
11196 |
|
TC4 |
|
R |
108 |
9.3 |
10890 |
|
TC5 |
|
R |
129 |
11.1 |
11275 |
|
TC6 |
Yat Tung Estate -
Hong Yat House |
R |
105 |
9.7 |
10498 |
|
AP1 |
Chek Lap Kok Fire
Station |
C |
9 |
7.5 |
12646 |
|
AP2 |
Gate Gourmet
Catering Building |
C |
30 |
6.7 |
13116 |
|
AP3 |
DHL |
C |
30 |
5.4 |
13124 |
|
AP4 |
Regal Airport Hotel |
C |
90 |
5.3 |
14584 |
|
AP5 |
SkyCity Nine Eagles
Golf Course |
C |
- |
6.2 |
14264 |
|
AP6 |
SkyCity Nine Eagles
Golf Course |
C |
- |
6.2 |
14057 |
|
AP7 |
SkyCity Nine Eagles
Golf Course |
C |
- |
6.2 |
14319 |
|
AP8 |
Terminal 2 |
G/IC |
25 |
6.4 |
14213 |
|
SLW1 |
Sha Lo Wan House
No.1 |
R |
9 |
5.0 |
13421 |
|
SLW2 |
|
R |
9 |
4.9 |
13404 |
|
SLW3 |
Tin Sum |
R |
9 |
5.7 |
12242 |
|
KT1 |
Block 6, Lai King
Estate |
R |
42 |
40.1 |
22376 |
|
KT2 |
Block 7, Lai King
Estate |
R |
66 |
40.1 |
22306 |
|
KT3 |
Lai King Home |
R |
12 |
40 |
22301 |
|
KT4 |
|
G/IC |
6 |
38.5 |
22359 |
|
KT5 |
Lai Hong House, |
R |
135 |
25 |
22249 |
|
KT6 |
|
GIC |
30 |
38.9 |
22388 |
|
KT7 |
|
GIC |
- |
7.6 |
22380 |
|
KT8 |
Hoi Yin House, Hoi
Lai Estate |
R |
108 |
5.9 |
22563 |
Notes:
(1)
R –
Residential; G/IC –Government / Institution / Community; CDA - Comprehensive
Development Area; REC – Recreation; OU – Other Specified Uses
Deposition Modelling Analysis
9b.2.3.3 Deposition of facility-related COPCs were used to evaluate potential cumulative indirect exposure through the food chain as a result of COPCs that are deposited onto soil and then taken up into the food chain. ISC model was used to predict deposition rates for particles and vapours emitted from the IWMF stack. ISC deposition modelling analysis have been conducted in accordance with USEPA recommendations for conducting modelling in support of health risk assessment as outlined in the HHRAP guidance (USEPA, 2005). The modelling procedures and input requirements required for modelling are discussed below.
9b.2.3.4
The modelling has been
performed with a unit (
9b.2.3.5 In addition to the physical stack parameters and exhaust stack parameters, particle size data on stack emission are required to perform deposition modelling.
9b.2.3.6
Unit-specific particle size data were not available
since the unit has not yet been built.
Therefore, the aerodynamic size distribution of emitted particulate was
based on published data for similar types
of units, which can be found in the open literature. For example, USEPA’s Technology Transfer
Network Clearing House for Emission Inventories and Emission Factors (http://www.epa.gov/ttn/chief/ap42/)
contains information on particle size distribution data and sized emission
factors for selected sources, including municipal solid waste
incinerators.
9b.2.3.7 In accordance with the HHRAP (USEPA, 2005), two different particle size distributions have been modelled. The distribution of particle mass was used to represent all metals except mercury when present. Semi-volatile organic species and some mercury species that tend to vaporize during combustion and condense on the surface of emitted flyash are represented by a surface area-weighted size distribution (“particle-bound”). Elemental mercury and a fraction of divalent mercury are modelled as vapours. This approach tends to produce more realistic deposition rates of these materials in the immediate vicinity of the source. The proposed particle distributions are shown in Table 9b.2.
Table 9b.2 Particle Size Distributions
|
Mean Particle Diameter (µm)(1) |
Mass Fraction(1) |
Surface Area Fraction(2) |
|
0.11 |
0.237 |
0.878 |
|
0.61 |
0.0661 |
0.0442 |
|
1.00 |
0.0577 |
0.0235 |
|
1.70 |
0.0717 |
0.0172 |
|
2.93 |
0.0785 |
0.0109 |
|
4.53 |
0.114 |
0.0102 |
|
6.68 |
0.174 |
0.0106 |
|
10.23 |
0.0877 |
0.00349 |
|
25.16 |
0.114 |
0.00184 |
|
(1) Compliance test at the Covanta Hempstead EfW
Facility (Radian, 1989) (2) Calculated based on assumed spherical particle diameter and mass fraction |
||
9b.2.3.8 The deposition modelling has been conducted based on the meteorological data extracted from the PATH model (i.e. MM5 hourly meteorological data).
Application of ISC
9b.2.3.9
ISC was applied to determine
long-term averages (based on one year modelled) of wet, dry, and total
deposition for vapours, particles, and particle-bound compounds. The modelling domain included an area in
the vicinity of the facility (
1)
wet
and dry deposition of particles, based on mass-weighted particle distribution
including plume depletion;
2)
wet
and dry deposition of particles, based on area-weighted particle size
distribution including plume depletion; and
3)
wet
and dry deposition of vaporous gases with plume depletion.
9b.2.4.1 In this step of the risk assessment process, hypothetical human receptors and potential exposure pathways through which such receptors may be exposed to facility-related COPCs were identified. Selection of such potential exposure scenarios was based on the characteristics of the facility and surrounding area, and activities that could take place in the vicinity of the facility. Dispersion of COPCs into the ambient air allows direct human exposure to COPCs through inhalation. COPCs that are deposited onto soil, water or plants (such as vegetables), are available for indirect exposure through the ingestion of soil, water, or produce. Additionally, the COPCs are potentially available to other secondary indirect pathways of exposure, including ingestion of locally raised agricultural products (beef, dairy, pork, and poultry products), or consumption of locally caught fish. The goal of the exposure assessment is to predict the magnitude of potential human exposure to COPCs in emissions from the facility through a variety of assumed exposure pathways.
9b.2.4.2
In the combustion risk
assessment process, the air dispersion and deposition modelling, discussed in Section 9b.2.3 above,
provides the foundation for all other environmental concentration modelling
efforts. The final air dispersion
and deposition modelling results were entered into the Lakes Environmental
Software model IRAP-h View (Version
9b.2.4.3
The HHRAP (USEPA, 2005)
suggests the evaluation of three pairs of potential receptors: a non-farming resident (child and
adult), a subsistence farmer (child and adult), and a subsistence fisher (child
and adult). However, the exact
receptors to be evaluated were made site-specific based on land use and human
activity patterns. Information on
land use in the vicinity of the artificial island near SKC was considered so
that the receptor scenarios chosen for the health risk assessment would be
appropriate for the
9b.2.4.4 The artificial island near SKC is not identified as having a large population of sensitive receptors in the vicinity. A more detailed discussion on land use, focused on a vicinity of the facility is presented below to ensure that the maximally impacted receptors were evaluated in the risk assessment.
Chronic Exposure Scenarios
9b.2.4.5 The locations of current exposure scenarios have been selected based on a combination of the air dispersion and deposition modelling results and actual land uses identified in the vicinity of each site. Inhalation exposure has been evaluated under each scenario. The locations of the ASRs as described in Section 9b.2.3 above were evaluated in the context of the air modelling results to ensure that the locations of the maximum ambient concentrations were included in the evaluation. The indirect pathways have only been evaluated under the relevant scenarios (i.e., ingestion of fish is only be evaluated under the fisher scenario) and in relevant locations (i.e., areas capable of supporting the activity).
Residential
9b.2.4.6 A reasonable resident scenario was evaluated at the off-site location with the highest estimated soil (corresponding to the location of maximum total deposition) concentration to ensure that potential exposures for a resident are not underestimated.
9b.2.4.7
There is a very small
population of approximately 200 people living on SKC in a rehabilitation centre
managed by the Society for the Aid and Rehabilitation of Drug Addicts
(SARDA). These residents are
considered as sensitive subpopulation and have been evaluated in the health
risk assessment. However, based on
descriptions of the programs offered at the rehabilitation facility, the
maximum length of treatment is typically less than 6 months. Therefore, patients at the treatment facility
would only be exposed on a short-term basis. If employee retention is good, some
employees at the rehabilitation centre could potentially be exposed on a more
long-term basis, particularly if they reside on site. However, there is a ferry dock on the
island, so it is more likely that staff employed at the drug treatment facility
commute back and forth to Cheung Chau or
Farming
9b.2.4.8
Most agricultural produce
consumed in Hong Kong is imported from neighbouring mainland
9b.2.4.9 Local land use in the vicinity of the artificial island near SKC with regards to agricultural production is described below in more detail.
9b.2.4.10
In accordance with the
information available from the Agriculture, Fisheries, and Conservation
Department
(http://www.afcd.gov.hk/english/publications/
publications_agr/files/Map_AFS_HK_10_2009.pdf), no locally accredited farms
are identified in outlying islands in
9b.2.4.11
It is possible that some gardening may take place
at the drug treatment facility on SKC, although this has not been
confirmed. It is not known whether
edible produce is grown on site.
However, even if edible produce is grown on site, patients would only be
exposed on a short-term basis and, therefore, exposure via produce grown at the
site is unlikely to be significant.
Employees at the rehabilitation centre could potentially be exposed to
locally-grown produce on a long-term basis if they reside on site. However, as mentioned above, it is more
likely that staff employed at the drug treatment facility commute back and
forth to Cheung Chau or
Fishing
9b.2.4.12
Hong Kong’s commercial fishing activities are
conducted mainly in the waters of the adjacent continental shelf in the South
and
9b.2.4.13
The marine area near SKC is a fish spawning and
nursery ground. Although a
significant proportion of fishing by Hong Kong fishers is conducted in waters
adjacent to Hong Kong in the East China or
9b.2.4.14
A compliance check of the maximum permitted concentration of certain
metals present in foods due to the Project as stipulated in “Food Adulteration
(Metallic Contamination) Regulations” by the
Centre for Food Safety, was conducted based on the risk modelling results. Two schedules of the maximum permitted
concentration of certain metals present in specified foods are listed below.
Table 9b.3 First Schedule – Maximum permitted concentration of certain metals naturally present in specified foods
|
Metal |
Description of food |
Maximum permitted
concentration in parts per million |
|
Arsenic |
Solids being fish and fish products |
6 |
|
Solids being shellfish and shellfish products |
10 |
Table 9b.4 Second Schedule – Maximum permitted concentration of certain metals present in specified foods
|
Metal |
Description of food |
Maximum permitted
concentration in parts per million |
|
Antimony |
Cereals and vegetables |
1 |
|
Fish, crab-meat, oysters, prawns and
shrimps |
1 |
|
|
Meat of animal and poultry |
1 |
|
|
Arsenic |
Solids other than- |
1.4 |
|
All food in liquid form |
0.14 |
|
|
Cadmium |
Cereals and vegetables |
0.1 |
|
Fish, crab-meat, oysters, prawns and
shrimps |
2 |
|
|
Meat of animal and poultry |
0.2 |
|
|
Chromium |
Cereals and vegetables |
1 |
|
Fish, crab-meat, oysters, prawns and
shrimps |
1 |
|
|
Meat of animal and poultry |
1 |
|
|
Lead |
All food in solid form |
6 |
|
Mercury |
All food in solid form |
0.5 |
|
Tin |
All food in solid form |
230 |
Acute Exposure Scenarios
9b.2.4.15
Acute exposure has been evaluated at the selected
ASRs described in Section 9b.2.3.
Chronic Residential Pathways
9b.2.4.16
Chronic exposure has been evaluated for adult and
child residents via the following pathways:
·
Inhalation of vapours and particulates
·
Incidental ingestion of soil
· Ingestion of home-grown produce
9b.2.4.17
Fresh water is limited in Hong Kong, with
approximately 70-80% of fresh water coming directly from Dongjiang (the
Chronic Fisherman Pathways
9b.2.4.18
Exposure via the following pathways have been
evaluated for adult and child fishers:
·
Inhalation of vapours and particles
·
Incidental ingestion of soil
·
Ingestion of home-grown produce
· Ingestion of fish
Acute Pathways
9b.2.4.19
Acute exposure has been evaluated via the
inhalation pathway at the selected ASRs described in Section 9b.2.3.
9b.2.4.20
Except where noted in this EIA Report, the
equations and input parameters presented in the final HHRAP guidance (2005)
were used to estimate chemical concentrations in media and food sources for the
standard exposure scenarios (resident, farmer, fisher).
Body Weight
9b.2.4.21
The exposure dose is defined as the amount of COPC
taken into the receptor and is expressed in units of milligrams of COPC per
kilogram of body weight per day (mg/kg-day). Because exposure is normalized by body
weight (is in the denominator of the intake equation), small differences in
body weight can substantially increase or decrease estimated intakes. In general, Asians are smaller than
Americans. Therefore, use of the
body weight assumptions recommended in the HHRAP (USEPA, 2005) is not
appropriate and a population-specific body weight is proposed for use in this
assessment.
9b.2.4.22
The adult and child body weights used by the Hong
Kong EPD to develop Risk-Based Remediation Goals (RBRGs) are
Food Consumption Rates
9b.2.4.23
The WHO has implemented the Global Environment
Monitoring System/Food Contamination Monitoring and Assessment Programme
(GEMS/Food Regional Diets) to assess the levels and trends of potentially
hazardous chemicals in food and their significance for human health and trade
(WHO, 2003). As part of this
dietary exposure assessment mandate, GEMS/Food Regional Diets has developed
five regional diets which are currently used for predicting dietary intake of
pesticide residues according to internationally accepted methodologies. The GEMS/Food Regional Diets are based
on Food Balance Sheet (FBS) data compiled by the Food and Agriculture
Organization of the United Nations (FAO) from selected countries to represent
five regional dietary patterns. The
regions covered are Middle Eastern, Far Eastern, African, Latin American, and
European. Hong Kong is included in
the Far East region along with
9b.2.4.24
Table 9b.5 summarizes
consumption rates in grams per day (g/day) for relevant food items from the
GEMS/Food Regional Diets (WHO, 2003; http://www.who.int/foodsafety/chem/en/gems_regional_diet.pdf). The GEMS/ Food Regional Diets only
provide adult consumption rates.
Therefore, child meat consumption rates are assumed to be 15% of the
adult value and child vegetable consumption rates are assumed to be 30% of the
adult value. The percentages used
to adjust adult consumption rates for children are based on the ratio between
adult and child food consumption rates for the
Table 9b.5 Food Consumption Rates
|
Individual
Adult Consumption Rates from the GEMS/Food (2003) for the |
|||||||
|
Total
Vegetables |
Total
Fish |
Poultry
Products |
Pork |
||||
|
Adult |
Child (a) |
Adult |
Child (b) |
Adult |
Child (b) |
Adult |
Child (b) |
|
287 |
86.1 |
31.5 |
4.7 |
24.6 |
3.7 |
28.2 |
4.2 |
Notes:
(a) 30% of adult
consumption rate.
(b) 15% of adult
consumption rate.
9b.2.4.25
Based on detailed national surveys, average food
consumption estimates based on FBS data are about 15% higher than actual
average food consumption in the worst cases (e.g. certain fruits and other
highly perishable products). This
is partly because GEMS/Food Regional Diet values are given for the whole raw
agricultural commodity. This
approach is conservative because the production rate data are provided in
tons/day, but include edible and non-edible parts of such as bone and
shell. In addition, waste at the
household or individual level is not taken into account, which also
overestimates consumption.
9b.2.4.26
Two additional sources of fish consumption rates
for Asian populations were located in the open scientific literature that
quoted higher fish consumption rates.
A paper entitled “Mercury and Organochlorine Exposure from Fish
Consumption in Hong Kong” quotes an average Hong Kong fish consumption rate of
9b.2.4.27
Despite the higher fish consumption rates found in
these two papers, the GEMS/Food Regional Diets (WHO, 2003) consumption rates
were used in the health risk assessment for all food items for the following
reasons:
·
The consumption rates recommended in the GEMS/Food Regional Diet are already
being used to predict dietary intake of pesticide residues by the WHO and are,
therefore, internationally accepted for use in estimating chronic hazards and
risks;
·
The GEMS/Food Regional Diets provide data on all of the food
commodities, making it possible to use one source for all consumption rates,
thus avoiding the potential internal inconsistencies that could arise if
multiple sources of food consumption rates were used; and
· Original sources for the literature values could not be located for verification.
Estimation of Chemical Concentrations in Environmental Media
9b.2.4.28
Table 9b.6 summarizes the mechanisms by which environmental
media can become contaminated as a result of incinerator emissions. The table also summarizes the inputs
necessary for estimating those media concentrations. Equations and input parameters presented
in the HHRAP guidance (USEPA, 2005) were used to estimate chemical
concentrations in media and food sources.
The HHRAP guidance provides standard conservative fate and transport and
chemical-specific assumptions for each of the media and food sources of
interest. The HHRAP guidance was
developed for use in the
9b.2.4.29
Where the results of the risk assessment indicate
that a default assumption may be unrealistically influencing the results of the
assessment, site-specific refinements to the health risk assessment have been
made and documented accordingly.
9b.2.4.30
For those exposure scenarios for which default fate
and transport modelling parameters are not available in the HHRAP guidance,
site specific parameters have been derived, consistent with the recommendations
of the HHRAP guidance. Examples of
site-specific inputs would include the delineation of the extent of the
watersheds and water body surface areas (in the vicinity of the facility). Estimated input parameters for the
algorithms outlined in the HHRAP was based on knowledge of the site and its
vicinity (e.g., soil types, watershed areas, land slopes, etc.) obtained from
existing reports, topographic maps, and/or soil surveys. It should be noted that the HHRAP model
for evaluating watershed and water body impacts is designed and intended for
use in evaluating freshwater streams, rivers, ponds and lakes. Therefore, the local marine environment
was treated as a lake in the HHRAP modelling.
Table 9b.6 Mechanisms for Environmental Media Contamination
|
Pathway |
Mechanisms of Media Contamination |
Input |
|
Direct Inhalation |
Air concentration of a
pollutant based on air quality modelling run as described in Section 3b. |
1. Vapour phase air concentration |
|
Soil Ingestion |
Soil may become
contaminated by emissions through direct deposition onto the soil. The soil equation includes a loss term
which accounts for the loss of contaminant from the soil after deposition by
several mechanisms, including leaching, erosion, runoff, degradation, and
volatilization. |
2. Emission rates 3. Modelled vapour phase air
concentration, wet deposition from vapour phase, dry deposition from particle
phase, and wet deposition from particle phase 4. Soil concentration due to
deposition |
|
Consumption of
aboveground produce |
Produce may become
contaminated by emissions through direct deposition onto the plant, direct
uptake of vapour phase contaminant, and root uptake of contaminants deposited
on the soil. |
1. Emission rates 2. Modelled vapour phase air
concentration, wet deposition from vapour phase, dry deposition from particle
phase, and wet deposition from particle phase 3. Soil concentration due to
deposition 4. Air-to-plant biotransfer factors |
|
Consumption of Animal
Products |
Animal tissue may be
contaminated through ingestion of contaminated forage, grain, silage, and
soil by livestock or wildlife. |
1. Emission rates 2. Modelled vapour phase air concentration,
wet deposition from vapour phase, dry deposition from particle phase, and wet
deposition from particle phase 3. Soil concentration due to
deposition 4. Forage and silage concentrations 5. Beef concentration due to plant
and soil ingestion by cattle 6. Milk concentration due to plant
and soil ingestion by cows |
|
Consumption of
Drinking Water and Fish |
Contaminant
concentrations in a water body are partitioned between dissolved phase,
suspended sediment, and benthic sediment. Contaminant concentrations in fish are
calculated from the contaminant concentrations in the water body. |
1. Soil concentration averaged across
the watershed 2. Total contaminant load to the
water body due to runoff, soil erosion, and direct deposition 3. Dissolved water concentration 4. Total water column concentration 5. Sediment concentration 6. Bioconcentration and/or
bioaccumulation factors 7. Biota-to-sediment accumulation
factors |
9b.2.4.31
Table 9b.7 presents a summary of the water body and watershed
parameters that have been identified for input to the risk assessment. Equations for evaluating exposure and
risk are presented in Appendix 9.1.
Table 9b.7 Summary of General Water Body and Watershed Parameters
|
Parameter |
Unit |
Fate & Transport Variable |
|
Average Annual Runoff |
cm/year |
220 |
|
Average Wind Speed |
m/s |
5.1 |
|
Water Body Surface Area |
m2 |
1.6 x 108 |
|
Total Watershed Area Receiving
Pollutant |
m2 |
6 x 107 |
|
Average Volumetric Flow Rate |
m3/year |
3.8 x 1012 |
|
Depth of Water Column |
m |
14 |
|
USLE Rainfall Factor |
per year |
550 |
9b.2.5.1
The purpose of the toxicity assessment is to
identify the types of adverse health effects a COPC may potentially cause, and
to define the relationship between the dose of a compound and the likelihood or
magnitude of an adverse health effect (response). Adverse health effects are typically
characterized in the health risk assessment as carcinogenic or non-carcinogenic
for long-term exposure and acute hazard for short-term exposure.
Toxicity Criteria / Guidelines for Long-Term Exposure
9b.2.5.2
COPCs are classified as to whether they exhibit
cancer and non-cancer health effects and whether health effects can result from
ingestion or inhalation of the chemical.
9b.2.5.3
The toxicity of each COPC is based on toxicity
factors developed by relevant studies.
The toxicity factors are referred to as dose-response values, and are
derived for both inhalation and oral routes of exposure. The dose-response values derived by
evaluation of potential carcinogenic health effects resulting from long-term
exposure to COPCs are called cancer slope factors [CSFs; expressed in units of
(mg/kg-day)-1] for oral exposure pathways, and unit risk factors
[URFs; expressed in units of (ug/m3)-1] for direct inhalation
exposure pathways. The
dose-response values derived for evaluation of potential non-carcinogenic
health effects resulting from long-term exposure to COPC are called reference
doses (RfDs) or tolerable daily intakes (TDI) expressed in units of mg/kg-day
for oral exposure pathways and reference concentrations (RfCs) or tolerable
concentrations in air (TCA) expressed in mg/m3) for inhalation
exposure pathways. For some COPCs,
both cancer and non-cancer toxicity factors are available because the chemical
has been associated with both cancer and non-cancer health effects. The health risk assessment includes an
evaluation of both potentially carcinogenic and non-carcinogenic COPCs.
Other
COPCs
9b.2.5.5
For the other COPCs, the following sources of
information have been reviewed to determine the toxicity factors for use in
evaluating exposure and risk through inhalation and other indirect pathways
(i.e., ingestion of food, soil, water)
·
Air Quality Guidelines (AQG) values by the World Health Organization
(WHO)
·
World Health Organization (WHO) documents
·
USEPA’s Integrated Risk Information System (IRIS)
·
Publications of the USEPA’s Superfund Technical Support Center (STSC)
(only toxicological indices which have supporting documentation on their
derivation)
· Other relevant international publications of toxicology studies
9b.2.5.7
Table 9b.8 contains all of the toxicity criteria used in the
risk assessment. For the sake of
sensitivity test, the selected toxicity factors have been taken as the most
conservative toxicity factors, if available, from the sources of information
reviewed under Section 9b.2.5.4 above.
Table 9b.8 Toxicity Factors for the Risk Assessment
|
COPCs |
Inhalation Unit Risk Factor (μg/m3)-1 |
Inhalation RfC (μg/m3) |
Cancer Slope Factor (mg/kg-day)-1 |
Oral RfD/TDI (mg/kg-day) |
|
Sb |
NA |
1 HSE (2005) |
NA |
0.006 WHO(2008) |
|
As |
0.0015 WHO (2000) |
NA(a) |
1.5 IRIS (2009) |
0.002 WHO (2008) |
|
Be |
0.0024 IRIS (2009) |
0.02 IRIS (2009) |
NA |
0.002 IRIS (2009) |
|
Cd |
0.0018 IRIS (2009) |
NA(b) |
NA |
0.0005 (water) 0.001 (food) IRIS (2009) |
|
Cr (VI) |
0.04 WHO (2000) |
0.1 (particulate) IRIS (2009) |
NA |
0.003 IRIS (2009) |
|
Co |
NA |
0.2 HSE (2005) |
NA |
NA |
|
Cu |
NA |
2 HSE (2005) |
NA |
NA |
|
Dioxins |
NA |
NA(c) |
150000 HEAST (1997) |
2.3 x 10-9 WHO (2001) |
|
HCl |
NA |
20 IRIS (2009) |
NA |
NA |
|
HF |
-- |
3 HSE (2005) |
-- |
-- |
|
Pb |
NA |
0.5 WHO (2000) |
NA |
0.0035 WHO (2008) |
|
Mn |
NA |
0.15 WHO (2000) |
NA |
0.06 WHO (2008) |
|
Hg |
NA |
1 WHO (2000) |
NA |
0.002 WHO (2008) |
|
Ni |
0.0004 WHO (2000) |
NA(d) |
NA |
0.012 WHO (2008) |
|
PCBs |
NA |
NA(e) |
2 IRIS (2009) |
NA |
|
PAHs |
0.09 (B(a)P) WHO (2000) |
3 (Naphthalene) IRIS (2009) |
0.5 (B(a)P) WHO (2008) |
0.02 (Naphthalene) IRIS (2009) |
|
Tl |
NA |
0.2 HSE (2005) |
NA |
0.00008 (chloride /carbonate) IRIS (2009) |
|
V |
NA |
1 WHO (2000) |
NA |
NA |
|
Zn |
NA |
NA(f) |
NA |
0.3 IRIS (2009) |
Note
(a)
Arsenic is a human
carcinogen. Present risk estimates have been derived from studies in exposed
human populations in
(b)
International Agency for
Research on Cancer has classified cadmium and cadmium compounds as human
carcinogens, having concluded that there was sufficient evidence that cadmium
can produce lung cancers in humans and animals exposed by inhalation. Yet
because of the identified and controversial influence of concomitant exposure
to arsenic in the epidemiological study, however, no reliable unit risk can be
derived to estimate the excess lifetime risk for lung cancer. (Reference: WHO
Air Quality Guidelines – 2nd Edition)
(c)
An air quality guideline
for Dioxins is not proposed because direct inhalation exposures constitute only
a small proportion of the total exposure, generally less than 5% of the daily
intake from food. (Reference: WHO Air Quality Guidelines – 2nd Edition)
(d)
Even if the dermatological
effects of nickel are the most common, such effects are not considered to be
critically linked to ambient air levels. Nickel compounds are human carcinogens
by inhalation exposure. The present data are derived from studies in
occupationally exposed human populations.
Yet assuming a linear dose response, no safe level for nickel compounds
can be recommended. (Reference: WHO Air Quality Guidelines – 2nd
Edition)
(e)
An air quality guideline
for PCBs is not proposed because direct inhalation exposures constitute only a
small proportion of the total exposure, in the order of 1-2% of the daily
intake from food. (Reference: WHO
Air Quality Guidelines – 2nd Edition)
(f)
No information from
WHO. With reference to IRIS (2009),
available data are not suitable for the derivation of an RfC for zinc. (Reference: http://www.epa.gov/iris/subst/0426.htm#refinhal)
(g)
Sources of References:
WHO (1998): http://www.who.int/ipcs/publications/en/exe-sum-final.pdf
WHO (2000): http://www.euro.who.int/document/e71922.pdf
WHO (2001): http://www.who.int/ipcs/food/jecfa/summaries/en/summary_57.pdf
WHO (2008): http://www.who.int/water_sanitation_health/dwq/fulltext.pdf
USEPA (IRIS, 2009): http://www.epa.gov/iris/index.html
HSE (2005): Health and
Safety Executive. EH40/2005 Workplace exposure limits
HEAST (1997): Health
Effects Assessment Summary Tables (HEAST). Fiscal Year 1997 Update". Office of Solid Waste and Emergency
Response. EPA-540-R-97-036. July 1997
9b.2.5.8
Discussed below are a few special cases for which
the specification of toxicity criteria / guidelines is somewhat more
complex.
9b.2.5.9
For the purpose of health risk assessment, chromium
and chromium compounds need to be speciated into trivalent and hexavalent
chromium species with trivalent chromium or Cr(III) being non-toxic and
hexavalent chromium or Cr(VI) is toxic.
With reference to the 2005 National Emissions Inventory Data prepared by
USEPA, the percentage of Cr (VI) in total Cr is 19% for emissions of large
municipal waste combustors.
Therefore, a 19% Cr(VI) speciation factor is applied to the total Cr emissions
in this health risk assessment.
Lead
9b.2.5.10
USEPA has not derived RfDs for lead due to
uncertainties about the health effects and dose-response associated with
exposures to lead. Based on
findings that neurobehavioral effects in young children occur at exposure
levels below those that have caused cancer in laboratory animals, an Integrated
Exposure Uptake Biokinetic (IEUBK) Model for Lead in Children has been
developed by USEPA (USEPA, 2002b).
USEPA guidance (USEPA, 2005) has recommended the use of this IEUBK model
in combustor health risk assessments.
9b.2.5.11
Several recent combustor facility risk studies have
yielded extremely low incremental concentrations of lead in the modelled
environmental media. Those
concentrations are often so low that they are difficult to evaluate in the
IEUBK model (due to threshold format restrictions). Therefore, the WHO (WHO, 2003) Tolerable
Daily Intake (TDI) of 0.0035 mg/kg-day has been used to evaluate potential
health risks associated with exposure to lead from the IWMF.
Polycyclic Aromatic Hydrocarbons (PAHs)
9b.2.5.12
Consistent with USEPA guidance (USEPA, 2005), the
health risk assessment has considered both potential carcinogenic effects and
non-carcinogenic toxicity for the potential PAH constituents. Potentially carcinogenic polycyclic
aromatic hydrocarbon (PAH) are ranked in order of potency in relation to
benzo(a)pyrene. For those PAH
compounds that are potentially carcinogenic, the risk analysis has used the
USEPA-developed comparative potency factors to derive cancer slope factors
representative of these compounds and their potential toxicity relative to
benzo(a)pyrene (USEPA, 1993), which are mostly consistent with those endorsed
by the WHO (WHO, 1998). The only
differences are for benzo(k)fluoranthene (WHO value of 0.1 vs. U.S. EPA value
of 0.01) and chrysene (no WHO potency factor vs. the U.S. EPA recommended
0.001). Potential non-carcinogenic
effects of PAHs has been evaluated using the RfD for naphthalene recommended by
USEPA if total PAHs are evaluated or individual PAH toxicity factors
recommended by USEPA if emission rates for individual PAHs are located in the
literature.
9b.2.5.13
Although there are hundreds of dioxin and furan
compounds, those compounds for which potential human health impacts can be
quantitatively evaluated are the dibenzodioxin, and dibenzofuran congeners
which have four chlorine molecules attached in positions 2, 3, 7, and 8 on the
central ring structure. A CSF has
been developed only for 2,3,7,8-tetrachloro-dibenzo-p-dioxin (2,3,7,8-TCDD).
9b.2.5.14
The WHO has established (1998) and re-evaluated
(2005) toxicity equivalency factors (TEFs) for dioxins and related
compounds. Other congeners are
assigned WHO TEFs that relate their toxicities to that of 2,3,7,8-TCDD (Van den
Berg et al., 2005). This concept
parallels that used for evaluating PAHs, as explained above.
9b.2.5.15
For this evaluation, since emission rates were
based on the combined concentration limit for dioxins and furans, there was no
need to apply the WHO TEFs (emissions were not estimated for individual
congeners). Potential carcinogenic
health risks associated with the dioxin and furans have been evaluated in
accordance with the approach developed by USEPA, and recommended in the 2005
HHRAP as follows: Risks have been
calculated for combined dioxin and furans using the cancer slope factor for
2,3,7,8-TCDD listed in HEAST (USEPA, 1997).
9b.2.5.16
Dioxin and furan congeners may also have some risk
of non-carcinogenic toxicity associated with them; however, there are no
established RfDs with which to evaluate this hazard.
Polychlorinated Biphenyls
9b.2.5.17
Moderately chlorinated PCB congeners can have
dioxin-like effects. This
sub-category includes PCB congeners with four or more chlorine atoms and few
substitutions in the ortho positions (positions designated 2, 2', 6, or
6'). They are sometimes referred to
as “coplanar” PCBs, because the rings can rotate into the same plane if not
blocked from rotation by ortho-substituted chlorine atoms. In this configuration, the shape of the
PCB molecule is very similar to that of a dioxin molecule. Studies have shown that these
dioxin-like congeners can react with the aryl hydrocarbon receptor; the same
reaction believed to initiate the adverse effects of dioxins and furans.
9b.2.5.18
A recent revision of the TEF scheme was undertaken
by the WHO (Van den Berg et al, 2005) in connection with a review of the WHO
recommended Tolerable Daily Intake.
The proposed scheme included coplanar congeners of PCBs within the
overall TEQ scheme, by defining TEFs for 12 coplanar PCBs on the basis that
their mode of action and the responses elicited in biological systems parallel
those of the 2,3,7,8-positional dioxins and furans. The WHO-TEQ of the sample would be
represented by the summation of the products of the concentrations of 17 dioxin/furan
congeners and 12 PCB congeners by their respective TEFs. Risks from coplanar PCBs have been
estimated by computing a toxicity equivalency quotient (TEQ) for PCBs, and then
applying the slope factor for 2,3,7,8-TCDD.
9b.2.5.19
In addition to the coplanar (dioxin-like) PCB
congeners, the remaining PCBs have also been evaluated in the risk
assessment. After considering the
accumulated research on PCBs and a number of studies of the transport and
bioaccumulation of various congeners, USEPA derived three new CSFs to replace
the former single CSF for PCBs. The
upper-bound CSF designated for use when evaluating food-chain exposures and
ingestion of soil is used to evaluate cancer risk associated with the remaining
PCBs (the non-dioxin-like PCBs) in the mixture as recommended by USEPA.
Toxicity Criteria / Guidelines for Short-Term Exposure
9b.2.5.20
As currently recommended in the HHRAP guidance, it
is proposed that potential risks due to short-term inhalation exposure (such as
irritant or respiratory health effects) be evaluated in addition to the more
commonly evaluated chronic risks to human health discussed above. Therefore, a screening level evaluation
of short-term health effects has been conducted by comparing predicted
short-term (maximum 1-hour) air concentrations against the findings of relevant
toxicology studies.
Classical COPCs of the HKAQO
9b.2.5.21
For the classical COPCs of the HKAQO with potential
acute health effects, the contribution of the IWMF project to the predicted
cumulative short-term (hourly average) concentrations of these classical COPCs
at the air sensitive receivers are analysed as part of this health risk
assessment and compared against the findings of relevant toxicology studies.
Other COPCs
9b.2.5.22 For other COPCs with potential acute health effects, for the purpose of this risk assessment, the following sources of information have been reviewed to determine the inhalation reference level for use in evaluating exposure and risk through inhalation:
·
·
Acute inhalation exposure guidelines (AEGL-1) (USEPA, 2010);
·
Level 1 emergency planning guidelines (ERPG-1; DoE, 2010);
·
Temporary Emergency Exposure limits (TEEL-1; DoE, 2010); and
· AEGL-2 values (USEPA, 2010).
9b.2.5.23
If no AEGL-1 value is available, but an AEGL-2
value is available, the AEGL-2 value was selected only if it is a more
protective value (lower in concentration) than an ERPG-1, or a TEEL-1 value if
either of these values is available.
9b.2.5.24
The adopted exposure limits/reference levels for
short term exposure of COPCs are presented in Table 9b.9.
Table 9b.9 Exposure Limits/Reference Levels for COPCs Acute Exposure
|
COPC |
Exposure Limit/Reference Level (μg/m3, 1-hr
averaging time) |
Source |
|
Sb |
1,500/10 = 150 |
TEEL-1 |
|
As |
30 /10 = 3 |
TEEL-1 |
|
Cd |
30/10 = 3 |
TEEL-1 |
|
Cr (VI) |
30/10 = 3 |
TEEL-1 |
|
Co |
3,000/10 = 300 |
TEEL-1 |
|
Cu |
100 |
Cal/EPA Acute
REL |
|
Dioxins |
No guideline |
- |
|
HCl |
2,100 |
Cal/EPA Acute
REL |
|
HF |
240 |
Cal/EPA Acute
REL |
|
Pb |
150/10 = 15 |
TEEL-1 |
|
Mn |
3,000/10 = 300 |
TEEL-1 |
|
Hg |
0.6 |
Cal/EPA Acute
REL |
|
Ni |
6.0 |
Cal/EPA Acute
REL |
|
Tl |
300/10 = 30 |
TEEL-1 |
|
V |
150/10 = 15 |
TEEL-1 |
9b.2.6.1
In the risk characterization step, the potential
human health risks associated with COPC emissions from the MSW thermal
treatment unit have been estimated.
The risk characterization step combined the results of both the exposure
assessment and the dose-response assessment to estimate the incremental
potential risks to human health.
Classical COPCs of the HKAQO
9b.2.6.2
The highest cumulative annual average SO2
concentrations predicted at the hot spot areas (see Section 3b) based on territory-wide scale model results (PATH
model) would range from 6 to 17 μg/m3. The average contribution by the IWMF
would range from 0.23 to 3.21%.
Nevertheless, there is still considerable scientific uncertainty as to
whether SO2 is the pollutant responsible for the observed adverse
air effects or, rather a surrogate for particulate matters[2]. While it is not possible to totally rule
out its adverse health effects, the potential additional health effects are
likely to be small.
9b.2.6.3
For the RSP, the highest cumulative annual average
RSP concentrations predicted at the hot spot areas based on territory-wide
scale model results (PATH model) would range from 39 to 46 μg/m3. The average contributions by the IWMF
would be below 0.07%. As such, the
associated adverse health effects of RSP due to the IWMF are likely to be very
small and are unlikely to be quantifiable[3].
9b.2.6.4
For NO2, the highest cumulative annual
average NO2 concentrations predicted at the hot spot areas based on Territory-wide
scale model results (PAHT model) would range from 13 to 40 μg/m3. The average contribution by the IWMF
would range from 0.04 to 1.49%. The
associated additional risk for adverse health effects of NO2 due to the
IWMF are likely to be very small. .
As such, it is very unlikely that the NO2 emitted by the IWMF
will cause significant long-term adverse health effects.
9b.2.6.5
The detailed percentage contributions of SO2,
NO2 and RSP by the IWMF are presented in Appendix 9.3.
Other COPCs
9b.2.6.6
The cumulative non-carcinogenic health impact due
to chronic inhalation, includes the impact arising from the IWMF plus the
background contribution are presented in Appendix 9.4. Cumulative chronic health impact of the
IWMF at all receptors are assessed and compared with the exposure
limits/reference levels. It is
concluded that the effect are insignificant when compared to the proposed
exposure limits/reference levels.
No adverse chronic inhalation health effects are expected and no risks
due to long-term exposure are expected.
9b.2.6.7
The potential for chemicals to cause adverse non-carcinogenic
health effects has been assessed by dividing estimated exposure doses
(determined for the exposure scenarios described above) by appropriate
dose-response values, such as reference doses (RfDs). The resulting ratio is referred to as
the "chemical-specific risk ratio" or hazard quotient. For individual chemicals, hazard
quotients have been added across exposure pathways to determine the total
non-carcinogenic hazard index (HI) for each receptor potentially exposed to
facility-related COPC in the environment.
9b.2.6.8
The USEPA has determined that exposure to a
chemical is not expected to cause significant adverse health effects if this
total risk ratio, or HI, for all exposure pathways has a total value of 1 or
less. The most recent USEPA risk
management guidance (USEPA, 1998) describing management decisions for
combustion facilities recommends, however, that it be assumed that 75% of this
value is reserved for exposures that may come from other background sources. Thus, the guidance indicates that the
remaining HI = 0.25 should serve as an initial screening benchmark for
exposures that may be associated with the subject facility operations.
9b.2.6.9
Since a total HI of less than or equal to 1.0
generally indicates no significant risk of adverse non-carcinogenic human
health effects, the more conservative approach of 0.25 would also support such
a conclusion. The USEPA further
recommends that if the resulting summation exceeds 0.25, the HI analysis should
be re-examined and refined, such that only those chemicals exhibiting the same
or similar toxicity endpoints (i.e., they affect the same target organ) are
summed. Since chemicals may display
a variety of effects depending on concentration, the toxic endpoint is defined
in this context as the most sensitive non-carcinogenic health effect used to
derive the RfD.
9b.2.6.10
With reference to risk assessment results on
non-carcinogenic hazard presented in Appendix 9.5, it can be
concluded that the Hazard Index at all receptors falls under 0.25. The highest hazard quotient occurs at
receptor TC4 with a value of 0.01.
Therefore, the exposure of the receptors for the artificial island near
SKC to the non-carcinogenic COPCs is not expected to cause significant adverse
health effects.
9b.2.6.11
Potential incremental ("excess") lifetime
cancer risks have been calculated for each receptor by multiplying the
appropriate CSF by the site-specific exposure dose level determined for each of
the exposure scenarios described above.
The cancer risks from each carcinogenic COPC and from each exposure
pathway have been added together to estimate the total cancer risk for each
receptor. The equation for
estimating cancer risk is presented below:
Cancer
Riski = I
x ED x EF x CSF/AT x 365
Where:
I = Intake
(mg/kg-d)
ED = Exposure
duration (years)
EF = Exposure
frequency (days/year)
CSF = Cancer
slope factor (mg/kg-day)-1
AT = Averaging
time (days)
365 = Days/year
9b.2.6.12
Total cancer risk are
calculated as follows:
Total Cancer
Risk = Σi Cancer riski
9b.2.6.13
The USEPA risk management guidance[4] (USEPA,
1998) suggests a target risk level of 1x10-5 as an acceptable total
for all contributions of carcinogenic risk at a designated individual receptor
from the Project. In accordance with
the USEPA risk management guidance, if a calculated risk falls within the
target values, the authority may, without further investigation, conclude that
the proposed project does not present an unacceptable risk.
9b.2.6.14 The predicted total carcinogenic risk at the representative receptors are summarized in Appendix 9.5. The results indicated that the predicted total carcinogenic risk from the Project at all receptors are less than 1x10-5. The highest total cancer risk occurs at receptor TC4 with a value of 2.76x10-6. Therefore, it is expected that the Project would not present an unacceptable risk.
9b.2.6.15
Since the assessment results meet both the cancer
risk and non-cancer hazard index criteria, no further analysis is presumed to
be necessary.
Risks Due to Short-Term Exposure
9b.2.6.16
In addition to the potential long-term risk to
human health presented by COPCs emitted from the facility, short-term or acute
risk has been evaluated for direct inhalation COPCs. Acute exposure has been estimated, based
on maximum one-hour average air concentrations predicted from the atmospheric
dispersion modelling described in Section
3b. To determine the likelihood
of adverse acute effects, maximum predicted one-hour average air concentrations
are compared with criteria for short-term inhalation exposures.
Classical COPCs (CO, SO2 & NO2)
9b.2.6.17
The average contribution of 1-hr SO2
concentrations by the IWMF are predicted at the hot spot areas (see Section 3b) to be in the range of 0.15%
to 10.72%. The highest cumulative
1-hr average SO2 concentration with the operation of the IWMF would
be 179µg/m3 based on territory-wide scale model results (PATH model),
which is below the short term exposure level with observable acute health
effects in vulnerable groups[5]. Therefore, the associated acute health
effect would be negligible.
9b.2.6.18
For CO, the average contribution of 1-hr CO
concentrations by the IWMF are predicted at the hot spot areas to be less than
0.11%. The predicted highest
cumulative 1-hr average CO concentration is 1712µg/m3 based on territory-wide
scale model results (PATH model) and is far below international safe levels[6]. Therefore, adverse health effect of CO
contribution from the IWMF is negligible.
9b.2.6.19
For NO2, the predicted highest
cumulative 1-hr average NO2 concentration is 275µg/m3
based on territory-wide scale model results (PATH model). The predicted 1-hr average
concentration is below the level with clear observable acute health effects in
many short term experimental toxicology studies[7]. Nevertheless, the average contribution
of 1-hr average NO2 concentration at the hot spot areas by the IWMF
is predicted to be in the range of 0.03% to 5.34%. Therefore, the acute adverse health
effects of NO2 due to the IWMF would be very small and are unlikely
to be quantifiable.
9b.2.6.20
In summary, the IWMF would make only small
additional contributions to local concentration of CO, SO2 and NO2. While it is not possible to rule out
adverse health effects from the IWMF with complete certainty, the impact on
health from small additional air pollutants is likely to be very small and
unlikely to be quantifiable.
Other COPCs
9b.2.6.21 The cumulative non-carcinogenic health impact due to direct inhalation, includes the impact arising from the IWMF plus the background contribution are presented in Appendix 9.6. Cumulative acute health impact of the IWMF at all receptors are assessed and compared with the exposure limits/reference levels. It is concluded that the effect are insignificant when compared to the proposed exposure limits/reference levels. No adverse acute effects are expected.
Maximum Permitted Concentration of Certain Metals present in Foods
9b.2.6.22 In order to determine the compliance of the maximum permitted concentration of certain metals present in foods due to the Project as stipulated in “Food Adulteration (Metallic Contamination) Regulations” by the Centre for Food Safety, a compliance check was conducted based on the risk modelling results. The concentrations of the metals listed in Table 9b.3 and Table 9b.4 at each receptor location were compared with the maximum permitted concentrations.
9b.2.6.23
Based on the assessment results presented in Appendix 9.7, it is concluded that food grown in the vicinity of all receptor
locations would comply with the maximum permitted concentrations stipulated by
the Centre for Food Safety. The concentrations of Antimony, Arsenic, Cadmium,
Chromium, Lead and Mercury at all receptor locations fall under the maximum
permitted concentrations listed in the first and second schedules in Table 9b.3 and Table
9b.4.
9b.2.6.24
Within any risk assessment process, a number of
assumptions and simplifications are made in recognition of the lack of complete
scientific knowledge and inherent variability in many of the parameters used in
risk assessment models. In some
cases, the values may vary widely between a conservative upper confidence limit
and a mean value. In other cases,
measurement data are too sparse to develop a statistically robust estimate of
the mean. In those cases, judgments
must be made in selecting an assumed value that is credible, but unlikely to be
exceeded when future measurements become available.
9b.2.6.25
The health risk assessment is a complex process,
requiring the integration of the followings:
·
Release of COPCs into the environment;
·
Transport of the COPCs by air dispersion, in a variety of different and
variable environments;
·
Potential for adverse health effects in human, as extrapolated from
animal studies; and
· Probability of adverse effects in a human population that is highly variable genetically, and in age, activity level and lifestyle.
9b.2.6.26
Uncertainty can be introduced in the assessment at
many steps of the process. The
following paragraphs discuss the uncertainties associated with each stage of
the assessment.
Hazard Identification
9b.2.6.27
COPCs are identified based on the air pollutants
listed in EPD’s BPM12/1. This list
of chemicals may not cover all the chemicals emitted from the stack of the IWMF
which could pose a threat to human health, which may underestimate the
risk. However, it is considered
that although the COPCs identified may not be exhaustive, it appeared
sufficiently comprehensive for the purpose of the assessment because BPM12/1
serves the purpose to prevent the air pollutant emissions from incinerator
stack from harming the environment and human health or creating nuisance.
9b.2.6.28
The adopted emission factors of COPCs from the IWMF
stack for air quality modelling are based on the target exhaust gas
concentration limits proposed for the IWMF. It is considered that this assumption
would overestimate the risk because COPC emission rate from IWMF would not
reach the allowed maximum rate all the time. Moreover, the emission factors for
individual heavy metals (except Hg) are based on the “exhaust gas concentration
for combined metal species”[8], this
would further overestimate the risk.
Exposure Assessment
9b.2.6.29
In this stage of the assessment, air dispersion
model is used to predict the COPC dispersion in air and the COPC concentrations
at potential human receptors. As
computer models are simplifications of reality requiring exclusion of some
variables that influence predictions, of which would introduce uncertainty in
the prediction of COPC concentration at potential human receptors and may in
turn overestimate or underestimate the risk.
9b.2.6.30
Moreover, the air quality modelling results adopted
for exposure assessment are modelled based on the worst case scenario which
would not occur all the time. This
conservative approach in air quality modelling would overestimate the risk.
9b.2.6.31
The characteristic parameter values for human
receptors used in the HHRA are adopted from the default values suggested in
USEPA (2005). The values adopted
may not precisely reflect the conditions of potential human receptors
identified, which may overestimate or underestimate the risk.
Dose-response Assessment
9b.2.6.32
The toxicity criteria / guidelines[9] adopted
from agencies would introduce uncertainty to the HHRA. These toxicity criteria / guidelines are
used as single-point estimates throughout the analysis with uncertainty and
variability associated with them.
Moreover, the arbitrary application of safety factor to occupational
exposure limit for derivation of toxicity criteria / guidelines for long term
COPC exposure is another source of uncertainty. This uncertainty may overestimate or
underestimate the risk. However, it
should be noted that much of the uncertainty and variability associated with
the toxicity criteria / guidelines shall be accounted for in the process that
the agencies setting verified toxicity criteria / guidelines.
9b.3 Potential Health Impacts of Biogas from Sorting and Recycling Plant
9b.3.1.1
This section reviewed the potential health impact
associated with biogas in sorting and recycling plant (i.e. Mechanical
Treatment) operations. Mechanical
Treatment Plant includes the following components:
·
Municipal Solid Waste (MSW) receiving, storage and feeding system
·
Mechanical treatment system including shredding and sorting facilities
·
Products and by-products storage and handling system
·
Odour control system
· Process control and monitoring system
9b.3.1.2
In a mechanical treatment process for mixed MSW
treatment, mechanical part is used mainly to pre-treat the waste for the
subsequent treatment process, and meanwhile recover the recyclable materials,
such as metals, plastic and paper.
9b.3.2 Description of Potential Biogas Emissions
9b.3.2.1
The objectives of mechanical treatment process
include preparation and sorting / separation of waste. Waste preparation is to split the refuse
bags, remove bulky waste and shred and homogenise the waste into smaller
particle sizes suitable for separation processes. The mechanical sorting processes then
separate the prepared wastes into the following parts:
·
Recyclable materials including metals, paper and plastics;
·
Inappropriate constituents for subsequent biological treatment,
including:
·
Over-size refuse such as textiles, wood and residual paper and plastics;
· Under-size refuse such as glass, sands and residual metals.
9b.3.2.2
In the consideration of
9b.3.2.3
Since mechanical treatment will not generate the
biogas, potential health impact to the staff due to biogas emission from mechanical
treatment is not expected.
9b.3.3.1
In accordance with the description in Section 9b.3.2 above, biogas will not be generated in the
mechanical treatment process.
Potential health impact to the staff and nearby sensitive receivers due
to biogas from sorting and recycling plant is therefore not expected.
9b.4 Potential Health Impacts of Fugitive Emissions during Transportation, Storage and Handling of Waste and Ash
9b.4.1.1
This section reviewed the potential health impact
associated with fugitive emissions during transportation, storage and handling
of waste and ash during operation of the IWMF.
9b.4.2 Description of Operation Process
9b.4.2.1
The containers of mixed MSW from various existing
Refuse Transfer Stations (probably from Island East (IETS), Island West (IWTS)
and
9b.4.2.2
At the waste reception hall of the incineration
plant, mixed MSW from the containers would be unloaded into the bunker. The
waste is then transferred by overhead cranes into the combustion chamber for burning.
Ash will be collected at the bottom of the combustion chamber and passes to the
ash storage pit through an ash extractor and magnetic separator for ferrous
metal recovery. These ashes, commonly known as bottom ash, would be delivered
in containers to the landfill for final disposal or reuse.
9b.4.2.3
The hot flue gases from the combustion chambers
would flow through the boiler, releasing thermal energy which turns the water
in the boiler tubes into steam. The steam produced would be used to drive the
turbine to generate electricity. The cooled flue gases would be treated by flue
gas treatment system including scrubbers, activated carbon powder injection and
fabric filter systems. The cleaned flue gases would then be released to the
atmosphere via the stack. A
relatively smaller amount of fly ash and residues would be collected from the
boiler and flue gas equipments. The fly ash and residues would then be
stabilized with cement or other suitable material before final disposal.
9b.4.2.4
As regards the containers of waste delivered to the
mechanical treatment plant, they would be unloaded into a storage pit. The
waste would then be shredded and separated by mechanical treatment systems for
sorting of recyclable metals, recyclable plastics, oversize refuse, inert
materials and organic matters. The recyclables would be collected, stored for
delivery to other recycling sites. The organic matters would be further treated
by biological processes. The inert materials would be delivered to the landfill
for disposal. The oversize sorting residues would be combusted in the
incineration plant or disposed of at landfills.
9b.4.2.5
The separated organic fraction of the waste would
be treated by biological processes for stabilization and possible recovery of
resources. Anaerobic digestion involves
controlled biological degradation of organic wastes in the absence of
oxygen. The process involves the
anaerobic decomposition of organic wastes to produce a methane-rich biogas fuel
and residual solids that can be used for making compost. The biogas produced in the digester is
primarily composed of methane and carbon dioxide, with traces of hydrogen
sulphide and ammonia. In the
anaerobic digestion process, the organic materials would be degraded by microbial
activity in the absence of oxygen to produce biogas. The biogas would be collected and used
to generate electricity and/ or heat.
9b.4.3.1
As described above, the containers of MSW will be
delivered to the IWMF site by marine vessels. The existing enclosed-type container for
transportation of MSW from RTS to landfills will be adopted for the future
transportation of waste and ash to and from the IWMF.
9b.4.3.2
Potential fugitive emission from waste would be
expected during unloading to waste storage pit and transferring waste by
overhead cranes grab into the combustion chamber. Ash will be generated after combustion
and it will be collected at the bottom of combustion chamber. The ash will be conveyed to the ash
storage pit automatically through enclosed extractor. Closed grab will be used to grab the ash
to ash hopper and then transfer the ash to enclosed-type container.
9b.4.4.1
With reference to existing experience of waste
transportation between RTS and landfills, potential fugitive emission during
transportation of waste and ash is not expected by using the existing
enclosed-type containers. Besides,
given that the containers of MSW will be delivered to the IWMF site by marine
vessels, the potential health impacts associated with the transportation of
waste to the IWMF would be similar to those that associated with the current
transportation of waste to the landfill and are considered insignificant.
9b.4.4.2
With regards to the storage and handling of waste
and ash, given that all the reception halls and ash storage pits will be fully
enclosed with slightly negative air pressure and closed grab will be use to
grab waste and ash, leakage of any fugitive emissions to the outdoor
environment is not expected.
9b.4.4.3
In order to minimize the potential health impacts
to the workers working inside the plant, the following health risk control
measures will be implemented. With
the implementation of the following measures, the potential health impacts
associated with the transportation, storage and handling of waste and ash are
considered to be insignificant.
·
Provide signage for clear indication of the travelling route of
waste/ash trucks;
·
Monitor and control the traffic flow inside the reception hall of the
plant;
·
Vehicle cleaning system should be provided to clean the waste/ash trucks
before they leave the plant;
·
Apply good practice during unloading of MSW to waste storage pit
including: provide signage to assist waste/ash truck drivers to stop at
appropriate unloading position; provide sufficient training to waste/ash truck
drivers;
·
Detection device / alarm should be installed to prevent overfilling of
waste and ash storage pit;
·
In case manual handling of waste/ash is needed, the workers involved
should wear personal protective equipment;
·
The on-site workers responsible for maintenance and cleaning of
equipment or vehicles contaminated with waste/ash should wear personal
protective equipment; and
· Emergency plan should be established and implemented to handle the situation of accidental incineration units shut down.
9b.5 Health Impacts Associated with other Potential Accidental Events
9b.5.1.1
The IWMF will be designed and operated as a modern
facility. The operator must also be
well trained to avoid any accidental events. The possible accidental events associated
with health impacts and their corresponding preventive measures are listed in Table 9b.10
Table 9b.10 Potential Accidental Events and Preventive Measures
|
Risks |
Preventive Measures |
|
Aerial emissions (emission discharge exceed the discharge limit) |
Ø
Use of best
available techniques in emission stack design, implement continuous and
regular emission monitoring |
|
Transportation, storage and handling |
Ø
Implement good
waste/ash transportation, storage and handling practices (see Section 9.4) Ø
Plan transport
routes to avoid highly populated / sensitive areas Ø
Develop procedures
for and deploy as necessary emergency response including spill response for
accidents involving transport vehicles Ø
Enforce strict
driver skill standards and implement driver / navigator and road / marine
safety behaviour training |
|
Chemical spillage and leakage |
Ø
Implement proper
chemicals and chemical wastes handling and storage procedures Ø
Develop and
implement spill prevention and response plan including provision of spill
response equipment and trained personnel |
|
Employee health and safety |
Ø
Implement industry
best practice with reference to international standards and guidelines |
9b.5.1.2
To further avoid or minimize the potential health
impacts associated with other potential accidental events, an emergency
response plan should be developed and properly implemented for the IWMF. It should be noted that the emergency
response plan should be specific to the final design and operation of the
IWMF. With the implementation of
the preventive measures outlined in Table 9b.10 above and
an effective emergency response plan for the IWMF, the health impacts
associated with any potential accidental events could be minimized if not
avoided.
9b.6.1.1 The cancer risk arising from exposure to compounds of potential concern (COPCs) associated with the emissions of the IWMF is evaluated in this section. The highest cancer risk arising from the IWMF is predicted to be 2.76 x10-6 and it is considered that the Project would not present an unacceptable risk and no further analysis is necessary. The highest predicted total Hazard Index (HI) at all receptors are well below 0.25, which is derived from a conservative approach. Cumulative acute non-carcinogenic health impact of the IWMF imposed to the worst impacted human receptors were assessed and compared with local and overseas guideline levels. It was concluded that the levels of non-carcinogenic chemicals were found to be insignificant when compared to the adopted/derived reference levels. For the classical COPCs of the HKAQO, while it is not possible to rule out adverse health effects from the IWMF with complete certainty, the impact on health from small additional air pollutants is likely to be very small and unlikely to be quantifiable.
9b.6.1.2
The compliance check of the maximum permitted
concentration of certain metals present in foods due to the Project as
stipulated in “Food Adulteration (Metallic Contamination) Regulations” by the
Centre for Food Safety, a compliance check was conducted. The concentrations of Antimony, Arsenic,
Cadmium, Chromium, Lead and Mercury at all receptors fall under the maximum permitted
concentrations listed in the first and second schedules of the Regulations.
9b.6.1.3
Biogas will not be generated in the mechanical
treatment process of the mechanical treatment plant. Potential health impact to the staff and
nearby sensitive receivers due to biogas from sorting and recycling plant is
therefore not expected.
9b.6.1.4
The existing practices of waste transportation will
be followed. With regards to the
storage and handling of waste and ash, given that all the reception halls and
ash storage pits will be fully enclosed with slightly negative air pressure and
closed grab will be use to grab waste and ash, leakage of any fugitive
emissions to the outdoor environment is not expected. With the implementation of the
recommended health risk control measures, the potential health impacts
associated with the transportation, storage and handling of waste and ash are
considered to be insignificant.
9b.6.1.5
The IWMF will be designed and operated as a modern
facility. The operator must also be
well trained to avoid any accidental events. The possible accidental events
associated with health impacts and their corresponding preventive measures are
identified. To further avoid or
minimize the potential health impacts associated with other potential
accidental events, an emergency response plan should be developed and properly
implemented for the IWMF. It should
be noted that the emergency response plan should be specific to the final
design and operation of the IWMF.
With the implementation of the recommended preventive measures and an
effective emergency response plan for the IWMF, the health impacts associated
with any potential accidental events could be minimized if not avoided.
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[6] Toxicological Profile for
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[8] 0.05mg/m3 as
the limit for total concentration of Cd and Tl; 0.5mg/m3 as the
limit for total concentration of Sb, As, Pb, Co, Cr, Mn, V and Ni.
[9] Unit risk factors,
air quality standards/occupational exposure limit value for long term COC
exposure as well as exposure limits and reference level for acute COC exposure.