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 |
G/IC |
6 |
74.1 |
278 |
|
SL1 |
Cheung Sha |
R |
9 |
34.8 |
5557 |
|
SL2 |
Tong Fuk |
R |
9 |
14.0 |
7113 |
|
SL3 |
Sea Ranch |
R |
12 |
24.0 |
3001 |
|
CC1 |
|
R |
6 |
16.0 |
3605 |
|
CC2 |
Round Table 3rd
Village |
R |
6 |
40.0 |
4039 |
|
CC3 |
|
R |
15 |
45.9 |
4504 |
|
CC4 |
Horizon Villa |
R |
9 |
15.0 |
5023 |
|
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
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/tc_chi/agriculture/agr_accfarm/agr_accfarm_num/agr_accfarm_num.html),
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
·
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 available from WHO and IRIS, or from other sources of
information reviewed under Section 9b.2.5.5 above if both WHO and IRIS factors are not
available.
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 |
0.0004 IRIS |
|
As |
0.0043 IRIS |
NA(a) |
1.5 IRIS (2009) |
0.0003 (g) IRIS |
|
Be |
0.0024 IRIS |
0.02 IRIS (2009) |
NA |
0.002 IRIS (2009) |
|
Cd |
0.0018 IRIS |
NA(b) |
NA |
0.0005 (water) 0.001 (food) IRIS |
|
Cr (VI) |
0.04 WHO (2000) |
0.1 (particulate) IRIS |
NA |
0.003 IRIS |
|
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 |
NA |
NA |
|
HF |
-- |
3 HSE (2005) |
-- |
-- |
|
Pb |
NA |
0.5 WHO (2000) |
NA |
NA (h) |
|
Mn |
NA |
0.05 IRIS |
NA |
0.06 WHO (2011) |
|
Hg |
NA |
1 WHO (2000) |
NA |
0.002 WHO (2011) |
|
Ni |
0.0004 WHO (2000) |
NA(d) |
NA |
0.012 WHO (2011) |
|
PCBs |
NA |
NA(e) |
2 IRIS |
NA |
|
PAHs |
0.09 (B(a)P) WHO (2000) |
3 (Naphthalene) IRIS |
7.3 (B(a)P) IRIS |
0.02 (Naphthalene) IRIS |
|
Tl |
NA |
0.2 HSE (2005) |
NA |
0.00008 (chloride /carbonate) IRIS |
|
V |
NA |
1 WHO (2000) |
NA |
NA |
|
Zn |
NA |
NA(f) |
NA |
0.3 IRIS |
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, available
data are not suitable for the derivation of an RfC for zinc. (Reference: http://www.epa.gov/iris/subst/0426.htm#refinhal)
(g)
Joint FAO/WHO Expert
Committee on Food Additives (JECFA) recently re-evaluated arsenic and concluded
that the existing provisional tolerable weekly intake (PTWI) was very close to
the lower confidence limit on the benchmark dose for a 0.5% response calculated
from epidemiological studies and was therefore no longer appropriate. The PTWI
was therefore withdrawn.
(h)
Based on the dose–response
analyses, JECFA estimated that the previously established PTWI of 25 μg/kg
body weight is associated with a decrease of at least 3 intelligence quotient
(IQ) points in children and an increase in systolic blood pressure of approximately
3 mmHg (0.4 kPa) in adults. These changes are important when viewed as a shift
in the distribution of IQ or blood pressure within a population. JECFA
therefore concluded that the PTWI could no longer be considered health
protective, and it was withdrawn.
(i)
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 (2011): http://www.who.int/water_sanitation_health/dwq/guidelines/en/index.html
USEPA (IRIS): 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).
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 (PATH 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 0.02.
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 3.23x10-6. 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 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 and inert
materials. The recyclables would be collected, stored for delivery to other
recycling sites. 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.4.3.1
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 3.23 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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