5
HAZARD
TO HEALTH
5.1 Introduction
The waters north of Lantau have
historically been important fishing grounds and are presently fished by shrimp
and hang trawlers based primarily in Tuen Mun Port. These fishermen's catches comprise shrimps and crabs, as well
as fish species of relatively low commercial value such as croakers, ponyfish,
pufferfish and gobies.
The waters of North-west and West
Lantau are also recognised as the primary habitat of the Indo-Pacific Humpback
dolphin (Sousa chinensis) within Hong
Kong waters. This species, which
is listed in Appendix 1 of the Convention on International Trade in Endangered
Species (CITES), has a limited distribution in Hong Kong waters due to its
preference for shallow, coastal estuarine habitat and is thought to be
threatened by continuing development in the Pearl River Delta.
Although the East of Sha Chau Study
Area is not considered to be part of the main area of sightings of the dolphins
it is regarded as a sensitive receiver.
The operations at the East of Sha Chau facility are designed to minimise
the dispersion of contaminated sediments during disposal and to prevent the
long-term migration of contaminants through the placement of a clean mud
cap.
However, as
losses of contaminated sediment will nevertheless occur during placement, and
as the area serves as habitat for marine species which may be consumed by
humans and/or Sousa chinensis, the
risk of adverse impacts must be addressed by the monitoring programme. Pathways of contaminant release to
sensitive receivers (ie humans and dolphins) include ingestion of contaminated
sediment, ingestion of dissolved and suspended contaminants in water, and
ingestion of organisms with contaminant residues.
5.2 Objectives
The objective of this risk assessment
is to determine whether disposal operations at East of Sha Chau are predicted
to pose unacceptable risk to humans and dolphins. The assessment considers the effects of the consumption of
seafood and marine prey species by humans and Sousa chinensis respectively.
Predicted concentrations of contaminants of concern from the
bioaccumulation assessment (Annex B) and historical data from the
previous monitoring programmes are used as the basis for the analysis.
In terms of other potential risks, it
should be noted that there have been no records of marine traffic associated
with disposal operations being a cause of dolphin death. As the proposed operations are similar
to those currently in operation, marine traffic associated with the new facility
are, therefore, not considered to pose any additional risk to dolphins.
5.3 Methodology
Pathways of contaminant
release to sensitive receivers (ie human and dolphins) include ingestion of contaminated
sediment, ingestion of dissolved and suspended contaminants in water, and
ingestion of organisms with contaminant residues. Illustration of these pathways for the East of Sha Chau area
is provided in Figure 5.3a.
Pathways of contaminant release to sensitive receivers (ie human and dolphins)
include ingestion of contaminated sediment, ingestion of dissolved and
suspended contaminants in water, and ingestion of organisms with contaminant
residues. Illustration of these
pathways for the East of Sha
Chau area is provided in Figure 5.3a.
Figure 5.3a Exposure Pathways
The methodology
utilised in this risk assessment to human health and the health of marine
mammals follows the guidelines of the US Environmental Protection Agency (USEPA
1989 ([1]), 1992 ([2]), 1997 ([3]), 2000 ([4])) and will incorporate a four-step approach
involving problem formulation, characterisation of exposure, characterisation
of ecological or human health effects, and risk characterisation. This methodology has been utilised in the East of Sha Chau area
during the monitoring programmes undertaken by the Civil Engineering and
Development Department since 1997 (ERM 2002 ([5])) and is based on the methodology presented in
Clarke et al. 2000 ([6]).
The methodology for the risk assessment
to human health and the health of marine mammals is presented in Annex C.
5.4 Human
Health Risk Assessment Results
As previously discussed, the intent
of this evaluation is to determine the potential risks to the various populations
of Hong Kong, resulting from dredged material disposal at the proposed East of
Sha Chau Contaminated Mud Disposal Facility. The exposure pathway is assumed to be consumption of food by
members of the various populations included in the assessment:
·
Population 1 - Hong Kong people in general;
·
Population 2 - Hong Kong fishermen; and,
·
Population 3 - East Sha Chau fishermen.
The methodology is designed to
provide a conservative estimate of the risks to these populations. As discussed in Annex C the evaluation has been conducted in order to provide two
estimates of risk:
·
Carcinogenic risk to the three populations through the
consumption of contaminated seafood.
The contaminants assessed in this way are those where carcinogenic
effects have been demonstrated and an oral Slope Factor (SF) is known.
·
An estimate of the hazard to each population through
the consumption of contaminated seafood.
The contaminants assessed in this way are those where hazardous effects have
been demonstrated and a Reference Dose (RfD) is known.
Several of the organic contaminants
were consistently recorded below the detection limits in marine monitoring
programmes ([7]) . For
this reason the organic contaminants included
as part of this assessment were as follows:
·
Total PCBs
·
Low MW PAH
·
High MW PAH
All of the inorganic contaminants
listed in ETWBTCW 34/2002 have been included in the assessment.
5.4.1
Carcinogenic
Risk Assessment Results
Carcinogenic risk
may be defined as the daily intake multiplied by the carcinogenic slope factor
(SF). The resultant value reflects
the additional lifetime carcinogenic risk from exposure to the particular
Contaminant of Concern (COC). The
intake is measured in terms of mg kg-1 (body weight) day-1
and has been calculated using the data presented in Annex B.
The majority of the SF values for
each of the COCs were taken from the US EPA's IRIS database, as discussed in Annex C of this report. As discussed in Annex C, the assessment of risk associated with the intake of
carcinogens in the edible portion of seafood is calculated over the entire
lifetime of the members of the population of concern.
Values for
incremental lifetime risk have been calculated for each COC and are summed to
provide an estimate of the Total Incremental Lifetime Risk to which each of the
populations of concern are exposed.
The justification for use of an additive approach is presented in Annex C. Once the incremental lifetime risk has been calculated the
next step is to evaluate the magnitude of acceptability of the incremental risk
due to the project. At present the
US EPA has defined acceptable incremental lifetime risks for carcinogens as
within the range of 10-4 to 10-6 for multiple contaminants
and 10-4 for single contaminants. Higher risks have, however, been deemed acceptable if there
were special extenuating circumstances (LaGrega et al 1994) ([8]).
Results
The incremental lifetime risk values for East of Sha
Chau are presented in
Table 5.1
Table
5.1Table 5.1Table
5.1Table 5.1. The single contaminant incremental
lifetime risk levels are acceptable for all of the contaminants for each of the
exposure populations. The total
incremental lifetime risk levels are also acceptable for the East of Sha Chau
scenario.
Table 5.1 Calculations of Dose and
Subsequent Incremental Carcinogenic Risk Levels (contaminant
intake from seafood using mg kg-1
day-1)
|
Contaminants |
Oral Slope
Factor |
Incremental
Lifetime Risk |
||
|
|
(mg/kg/day)-1 |
HK People |
HK Fishermen |
East Sha Chau Fishermen |
|
Background |
|
|
|
|
|
Low
MW PAH |
3.4´10-1 |
2.48´10-9 |
2.85´10-8 |
4.49´10-7 |
|
High
MW PAH |
3.44´10-1 |
7.43´10-9 |
8.55´10-8 |
1.35´10-6 |
|
Total
PCBs |
2 |
7.02´10-9 |
7.56´10-8 |
1.27´10-6 |
|
Arsenic |
1.5 |
4.90´10-8 |
5.98´10-7 |
8.87´10-6 |
|
Lead |
8.5´10-3 |
2.46´10-10 |
2.77´10-9 |
4.45´10-8 |
|
Total Lifetime Risk |
|
6.62´10-8 |
7.90´10-7 |
1.20´10-5 |
|
East of Sha Chau |
|
|
|
|
|
Low
MW PAH |
3.4´10-1 |
1.00´10-10 |
6.30´10-9 |
1.90´10-8 |
|
High
MW PAH |
3.4´10-1 |
3.4´10-10 |
1.95´10-8 |
6.00´10-8 |
|
Total
PCBs |
2 |
2.17´10-9 |
5.74´10-8 |
3.90´10-7 |
|
Arsenic |
1.5 |
4.00´10-10 |
2.20´10-8 |
8.00´10-7 |
|
Lead |
8.5´10-3 |
1.60´10-11 |
1.70´10-10 |
3.10´10-9 |
|
Total Incremental Lifetime Risk |
|
3.03´10-9 |
1.05´10-7 |
5.52´10-7 |
5.4.2
Hazard
Assessment Results (Non-carcinogens)
The measure used
to establish the risk of toxic effects for non-carcinogenic substances is
referred to as the Hazard Quotient (HQ).
The HQ is composed of two components: the daily intake of the particular
COC from all dietary sources measured in terms of mg kg-1 (body
weight) day-1 and used as the numerator, and the recommended
Reference Dose (RfD) which is used as the denominator. The RfD values for each of the COCs
were taken from the US EPA's IRIS database, as discussed in Annex C of this report. The calculation of the HQ involves
dividing the daily intake value (dose) by the RfD value (discussed in Annex C).
According to the
guidelines presented in US EPA (1989)([9]) and those in EVS (1996c)([10]), HQs can be interpreted in a conservative risk
assessment as follows:
HQ
< 1 the risk
of an adverse effect occurring is low (as the intake of the COC is lower than
the RfD);
HQ 1
to 10 there is some
risk of an adverse effect occurring, however, typically within the bounds of
uncertainty; and,
HQ
> 10 the
risk of adverse effects on human health is moderate to high (depending on the
HQ) as the intake of COCs is an order of magnitude, or more, higher than the
RfD.
As can be seen from the above
ranges, the greater the value of the HQ the greater the level of concern. However, it should be noted that the HQ
does not define a linear dose-response relationship and therefore the numerical
value should not be regarded as a direct estimate of risk (US EPA 1989)([11]). It is
especially important to note that a Hazard Quotient exceeding 1 does not necessarily mean that adverse
effects will occur. HQs are
specific to each particular COC and do not provide an indication of the total
hazard to the population of concern through intake of all the COCs in their
diet. The approach used to address
this, as well as the
assumption and uncertainties areas discussed in Annex C, will be additive and consequently is considered a
conservative method. The sum of
all the HQs for each COC is referred to as the Hazard Index (HI). The HI is interpreted in the same way as described for HQs
above.
Results
Once the RfD values and intake
values were obtained for each COC, the HQs were calculated for the three
populations of concern in both the East of Sha Chau and Background areas (
Table 5.2Table
5.2Table 5.2Table 5.2Table
5.2). The
table indicates that all of the HQ values for both populations were less than
one.
Table 5.2 Hazard Quotients for Populations
of Concern (contaminant
intake from seafood using mg kg-1
day-1)
|
Contaminants |
RfD |
Hazard
Quotient |
||
|
|
mg/kg/day |
HK People |
HK
Fishermen |
East Sha
Chau Fishermen |
|
East of Sha Chau |
|
|
|
|
|
Low
MW PAH |
2´10-2 |
3.32´10-6 |
4.47´10-5 |
6.02´10-4 |
|
High
MW PAH |
5´10-4 |
4´10-4 |
5.41´10-3 |
7.25´10-2 |
|
Arsenic |
3´10-4 |
1.92´10-2 |
1.21´10-2 |
1.74´10-1 |
|
Cadmium |
1´10-3 |
2.48´10-4 |
1.36´10-2 |
4.49´10-2 |
|
Chromium |
3´10-3 |
6.85´10-5 |
7.72´10-4 |
1.24´10-2 |
|
Copper |
4.3´10-2 |
1.61´10-4 |
2.78´10-3 |
2.91´10-2 |
|
Lead |
1.43´10-3 |
1.89´10-4 |
2.12´10-3 |
3.42´10-2 |
|
Mercury |
2.2´10-4 |
6.24´10-4 |
1.38´10-2 |
1.13´10-1 |
|
Nickel |
2´10-2 |
1.22´10-5 |
1.51´10-4 |
2.21´10-3 |
|
Silver |
5´10-3 |
1.77´10-5 |
3.2´10-4 |
3.2´10-3 |
|
Zinc |
3´10-1 |
1.1´10-4 |
1.76´10-3 |
1.99´10-2 |
|
Hazards Index |
|
2.1´10-2 |
5.28´10-2 |
5.06´10-1 |
|
Background |
|
|
|
|
|
Low
MW PAH |
2´10-2 |
3.19´10-6 |
3.67´10-5 |
5.77´10-4 |
|
High
MW PAH |
5´10-4 |
3.82´10-4 |
4.4´10-3 |
6.93´10-2 |
|
Arsenic |
3´10-4 |
9.20´10-4 |
1.16´10-2 |
1.73´10-1 |
|
Cadmium |
1´10-3 |
5.49´10-5 |
1.56´10-3 |
9.95´10-3 |
|
Chromium |
3´10-3 |
5.02´10-5 |
5.84´10-4 |
9.09´10-3 |
|
Copper |
4.3´10-2 |
1.57´10-4 |
2.74´10-3 |
2.85´10-2 |
|
Lead |
1.43´10-3 |
1.77´10-4 |
2´10-3 |
3.21´10-2 |
|
Mercury |
2.2´10-4 |
3.77´10-4 |
4.08´10-3 |
6.84´10-2 |
|
Nickel |
2´10-2 |
1.17´10-5 |
1.46´10-4 |
2.13´10-3 |
|
Silver |
5´10-3 |
1.65´10-5 |
3.08´10-4 |
2.99´10-3 |
|
Zinc |
3´10-1 |
9.98´10-5 |
1.2´10-3 |
1.81´10-2 |
|
Hazards Index |
|
2.28´10-3 |
2.87´10-2 |
4.14´10-1 |
The
summation of the HQ values to produce the HI also indicates that for both areas
the HI was less than one. The
exposure pathway examined in this risk assessment is focussed on exposure to
COCs via ingestion of seafood from within a specific area only. It is acknowledged that other pathways,
such as other seafood sources and foods other than seafood will also expose the
study populations to the COCs and thereby could affect the HI value. Hence chemicals with a HQ (as well as
the HI) of less than one does not necessarily imply that there is no risk. Concerning the East of Sha Chau
fishermen sub-populations the HI value for the East of Sha Chau is 0.506 of
which 34% is related to Arsenic and 22% due to Mercury. It is noted that exposure to Arsenic
and Mercury from other pathways, such as via air (inhalation), water (drinking)
and dermal contact are minor when compared to the diet and of the diet seafood
contains the largest source of these COCs (FEHD 2002) ([12]). The results of this assessment indicated that the
incremental
risk of an adverse effect occurring from consuming
seafood collected at East of Sha Chau is low.
5.5
Marine
Mammal Risk Assessment
As previously discussed, the intent of
this evaluation is to provide a determination of the potential risks to the
Indo-Pacific Humpback Dolphin population in the waters of Hong Kong, resulting
from dredged material disposal in East of Sha Chau proposed mud disposal
facility. The exposure pathway has
been assumed to be consumption of contaminated food by dolphins residing in
potentially impacted areas near the mud pits, and in an area representative of
background conditions.
Estimates of risk were determined by dividing the
estimated dose by the TRV to derive a Hazard Quotient (HQ). An HQ exceeding 1 indicates the
potential for systemic toxicity to the exposed organism. Based on the results of this screening
assessment, Silver was identified as of potential concern in relation to the
diet of Indo-Pacific Humpback dolphins from coastal waters near Hong Kong (
Table 5.3
Table 5.3Table
5.3Table 5.3Table 5.3). The HQ estimated for this chemical
exceeded 1 for both the East of Sha Chau and Background scenarios. No exceedances were observed for any of
the other HQ values.
Table 5.3 Estimate of Risk to the Indo-Pacific Humpback Dolphin East of
Sha Chau and Background area resulting from consumption of prey species. (contaminant intake from seafood
using mg kg-1
day-1)
|
Contaminants |
Dose (PC) |
Dose (PC) |
TRV |
Hazard
Quotient |
|
|
|
mg/kg/day |
mg/kg/day |
mg/kg/day |
|
|
|
|
East of Sha
Chau |
Background |
|
East of Sha
Chau |
Background |
|
Low
MW PAH |
1.62
´ 10-3 |
1.22
´ 10-3 |
0.03 |
0.05412 |
0.04054 |
|
High
MW PAH |
4.92
´ 10-4 |
3.65
´ 10-4 |
0.03 |
0.16387 |
0.12162 |
|
Total
PCBs |
8.80
´ 10-4 |
3.80
´ 10-4 |
0.04 |
0.02189 |
0.00947 |
|
Arsenic |
1.54
´ 10-1 |
1.47
´ 10-1 |
0.01 |
0.79998 |
0.73654 |
|
Cadmium |
2.57
´ 10-2 |
1.01
´ 10-2 |
0.2 |
0.12835 |
0.05069 |
|
Chromium |
8.50
´ 10-3 |
7.64
´ 10-3 |
570.82 |
0.00001 |
0.00001 |
|
Copper |
6.69
´ 10-1 |
6.67
´ 10-1 |
3.17 |
0.21091 |
0.21060 |
|
Lead |
1.62
´ 10-2 |
1.57
´ 10-2 |
1.67 |
0.00975 |
0.00941 |
|
Mercury |
6.14
´ 10-3 |
1.22
´ 10-3 |
0.27 |
0.02276 |
0.00453 |
|
Nickel |
2.95
´ 10-1 |
2.96
´ 10-1 |
8.34 |
0.03545 |
0.03544 |
|
Silver |
2.22
´ 10-2 |
2.05
´ 10-2 |
0.004 |
5.54211 |
5.13724 |
|
Zinc |
1.93
´ 10-0 |
1.35
´ 10-0 |
33.37 |
0.05776 |
0.04062 |
|
Hazards Index |
|
|
|
7.04690 |
6.39668 |
|
Note: values in bold indicate
that a possibility of risk may occur and warrants closer investigation. |
|||||
The HQ value for Silver in dolphin prey from East of
Sha Chau is 5.54 and 5.14 from Background areas and are essentially
equivalent.
5.6 Conclusion
5.6.1
Human
Health Risk Assessment
The risk assessment work conducted
for this Study has employed two approaches to predict the effects on human
health of consuming seafood collected from the East of Sha Chau area. The first approach examined the risks associated
with exposure to carcinogens and the second examined the hazards to human
health associated with exposure to non-carcinogens. Three populations with differing potential to be exposed to
seafood from the East of Sha Chau were examined. The first population represented the average exposure to
seafood from the Study Area by members of the Hong Kong population as a whole
and was referred to as Hong Kong People. The second population of concern
reflected the high end of risk and was considered to represent members of the
Hong Kong fishing community and was referred to as Hong Kong Fishermen.
The third population represented the absolute highest risk of exposure
to the seafood at East of Sha Chau and was considered as representative of
members of the fishing community that fish within the Study Area and was
referred to as East Sha Chau Fishermen.
The carcinogenic risk assessment has
indicated that the lifetime risks associated with consumption of seafood were
below the acceptability criterion for both the East of Sha Chau and the
Background areas. Results of the
hazard assessment indicated that risks associated with consumption of seafood
were low for
both the East of Sha Chau and comparable reference areas.
5.6.2
Ecological
Risk Assessment
Based on the risk evaluations
conducted for this Study, it does not appear that Indo-Pacific Humpback dolphin
prey organisms are predicted to bioaccumulate chemical contaminants from the
East of Sha Chau contaminated mud pits to higher concentrations than in prey of
the same species from nearby reference locations.
The only contaminant with a Hazard
Quotient greater than one (indicating the possibility of adverse risk) was
Silver. Silver has a very low
solubility in seawater and hard fresh waters ([13]). It tends to precipitate and
bind to the gills of fish in fresh water and is unlikely to be assimilated
efficiently from food by marine organisms, including dolphins. Although concentration of silver in
Indo-Pacific Humpback dolphin tissue has been analysed as part of a Hong Kong study, no data has been
reported to date ([14]).
Internationally,
Becker et al ([15]) reported elevated concentrations of Silver,
Mercury, and Selenium in the liver of beluga whales, Delphinapterus leucas, and pilot whales, Globicephala melas from Alaska.
The concentration of Silver in beluga whale liver was in the range of
10.1 to 107 mg kg-1 wet wt and was positively correlated with
concentrations of Selenium. The
authors postulated that Silver, like Mercury, is sequestered (detoxified) in the liver as an
insoluble silver-selenium complex.
Thus, cetaceans may be tolerant to Silver in their food, as they are for
Mercury ([16]) Silver and Mercury may exhibit toxic effects only
when accumulated in liver and kidney to a concentration that exceeds the capacity of the
sequestration system. In all
cases, the risk to dolphins consuming prey from the Background areas was
equivalent to that for dolphins consuming prey from the East of Sha Chau area. This prediction concurs with the
findings of a recent
risk assessment published by Hung et al (2004) ([17]).
These results indicate that disposal
of contaminated sediments into the mud pits at East of Sha Chau is not
predicted to contribute to an increased risk of harm to Indo-Pacific Humpback dolphins.