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
Although the South Brothers 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 South
Brothers 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 South Brothers 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 South
Brothers 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
Population
1 -
Population
2 -
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.
?/span>
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 ETWBTC
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.
?/span>
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 South Brothers are
presented in Table 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 South Brothers 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 |
|
|
Background |
|
|
|
|
|
Low MW PAH |
3.4?/span>10-1 |
2.48?/span>10-9 |
2.85?/span>10-8 |
4.49?/span>10-7 |
|
High MW PAH |
3.44?/span>10-1 |
7.43?/span>10-9 |
8.55?/span>10-8 |
1.35?/span>10-6 |
|
Total PCBs |
2 |
7.02?/span>10-9 |
7.56?/span>10-8 |
1.27?/span>10-6 |
|
Arsenic |
1.5 |
4.90?/span>10-8 |
5.98?/span>10-7 |
8.87?/span>10-6 |
|
Lead |
8.5?/span>10-3 |
2.46?/span>10-10 |
2.77?/span>10-9 |
4.45?/span>10-8 |
|
Total Lifetime Risk |
|
6.62?/span>10-8 |
7.90?/span>10-7 |
1.20?/span>10-5 |
|
South Brothers |
|
|
|
|
|
Low MW PAH |
3.4?/span>10-1 |
0 |
0 |
0 |
|
High MW PAH |
3.4?/span>10-1 |
1.00?/span>10-11 |
1.00?/span>10-10 |
0 |
|
Total PCBs |
2 |
1.31?/span>10-9 |
1.24?/span>10-8 |
2.20?/span>10-7 |
|
Arsenic |
1.5 |
0 |
0 |
1.00?/span>10-8 |
|
Lead |
8.5?/span>10-3 |
8.00?/span>10-12 |
9.00?/span>10-11 |
1.50?/span>10-9 |
|
Total Incremental Lifetime
Risk |
|
1.33?/span>10-9 |
1.26?/span>10-8 |
2.32?/span>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
?/span>
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 South Brothers and Background areas (Table
5.2).?The table indicates that all
of the HQ values for both populations were less than one.
?/span>
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 |
|
|
South Brothers |
|
|
|
|
|
Low
MW PAH |
2?/span>10-2 |
3.19?/span>10-6 |
3.67?/span>10-5 |
5.77?/span>10-4 |
|
High
MW PAH |
5?/span>10-4 |
3.83?/span>10-4 |
4.41?/span>10-3 |
6.94?/span>10-2 |
|
Arsenic |
3?/span>10-4 |
9.53?/span>10-4 |
1.16?/span>10-2 |
1.73?/span>10-1 |
|
Cadmium |
1?/span>10-3 |
1.98?/span>10-4 |
1.05?/span>10-2 |
3.58?/span>10-2 |
|
Chromium |
3?/span>10-3 |
5.93?/span>10-5 |
6.78?/span>10-4 |
1.07?/span>10-2 |
|
Copper |
4.3?/span>10-2 |
1.59?/span>10-4 |
2.06?/span>10-3 |
2.88?/span>10-2 |
|
Lead |
1.43?/span>10-3 |
1.83?/span>10-4 |
2.06?/span>10-3 |
3.31?/span>10-2 |
|
Mercury |
2.2?/span>10-4 |
5.35?/span>10-4 |
1.10?/span>10-2 |
9.69?/span>10-2 |
|
Nickel |
2?/span>10-2 |
1.20?/span>10-5 |
1.49?/span>10-4 |
2.17?/span>10-3 |
|
Silver |
5?/span>10-3 |
1.66?/span>10-5 |
3.10?/span>10-4 |
3.03?/span>10-3 |
|
Zinc |
3?/span>10-1 |
1.07?/span>10-4 |
1.61?/span>10-3 |
1.94?/span>10-2 |
|
Hazard Index |
|
2.61?/span>10-3 |
4.51?/span>10-2 |
4.75?/span>10-1 |
|
Background |
|
|
|
|
|
Low
MW PAH |
2?/span>10-2 |
3.19?/span>10-6 |
3.67?/span>10-5 |
5.77?/span>10-4 |
|
High
MW PAH |
5?/span>10-4 |
3.82?/span>10-4 |
4.4?/span>10-3 |
6.93?/span>10-2 |
|
Arsenic |
3?/span>10-4 |
9.20?/span>10-4 |
1.16?/span>10-2 |
1.73?/span>10-1 |
|
Cadmium |
1?/span>10-3 |
5.49?/span>10-5 |
1.56?/span>10-3 |
9.95?/span>10-3 |
|
Chromium |
3?/span>10-3 |
5.02?/span>10-5 |
5.84?/span>10-4 |
9.09?/span>10-3 |
|
Copper |
4.3?/span>10-2 |
1.57?/span>10-4 |
2.74?/span>10-3 |
2.85?/span>10-2 |
|
Lead |
1.43?/span>10-3 |
1.77?/span>10-4 |
2?/span>10-3 |
3.21?/span>10-2 |
|
Mercury |
2.2?/span>10-4 |
3.77?/span>10-4 |
4.08?/span>10-3 |
6.84?/span>10-2 |
|
Nickel |
2?/span>10-2 |
1.17?/span>10-5 |
1.46?/span>10-4 |
2.13?/span>10-3 |
|
Silver |
5?/span>10-3 |
1.65?/span>10-5 |
3.08?/span>10-4 |
2.99?/span>10-3 |
|
Zinc |
3?/span>10-1 |
9.98?/span>10-5 |
1.2?/span>10-3 |
1.81?/span>10-2 |
|
Hazards Index |
|
2.28?/span>10-3 |
2.87?/span>10-2 |
4.14?/span>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. ?/span>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 do not necessarily
imply that there is no risk.?
Concerning the East of Sha Chau fishermen sub-population the HI value
for the South Brothers is 0.475 of which 36% is related to Arsenic and 20% 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 South Brothers is low.
?/span>
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 South Brothers 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
|
Contaminants |
Dose (PC) |
Dose (PC) |
TRV |
Hazard Quotient |
|
|
|
mg/kg/day |
mg/kg/day |
mg/kg/day |
|
|
|
|
South Brothers |
Background |
|
South Brothers |
Background |
|
Low
MW PAH |
1.22
?/span> 10-3 |
1.22
?/span> 10-3 |
0.03 |
0.04 |
0.04054 |
|
High
MW PAH |
3.65
?/span> 10-4 |
3.65
?/span> 10-4 |
0.03 |
0.12 |
0.12 |
|
Total
PCBs |
3.83
?/span> 10-4 |
3.80
?/span> 10-4 |
0.04 |
0.01 |
0.01 |
|
Arsenic |
7.37
?/span> 10-3 |
1.47
?/span> 10-1 |
0.01 |
0.74 |
0.74 |
|
Cadmium |
1.24
?/span> 10-2 |
1.01
?/span> 10-2 |
0.2 |
0.06 |
0.05 |
|
Chromium |
7.73
?/span> 10-3 |
7.64
?/span> 10-3 |
570.82 |
<0.01 |
<0.01 |
|
Copper |
6.68
?/span> 10-1 |
6.67
?/span> 10-1 |
3.17 |
0.21 |
0.21 |
|
Lead |
1.58
?/span> 10-2 |
1.57
?/span> 10-2 |
1.67 |
0.01 |
0.01 |
|
Mercury |
1.95
?/span> 10-3 |
1.22
?/span> 10-3 |
0.27 |
0.01 |
<0.01 |
|
Nickel |
2.96
?/span> 10-1 |
2.96
?/span> 10-1 |
8.34 |
0.04 |
0.04 |
|
Silver |
2.06
?/span> 10-2 |
2.05
?/span> 10-2 |
0.004 |
5.15 |
5.14 |
|
Zinc |
1.44
?/span> 10-0 |
1.35
?/span> 10-0 |
33.37 |
0.04 |
0.04 |
|
Hazards Index |
|
|
|
6.42 |
6.40 |
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 South Brothers is 5.15 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
South Brothers 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 South Brothers were
examined.?The first population
represented the average exposure to seafood from the Study Area by members of
the
The
carcinogenic risk assessment has indicated that lifetime risks associated with
consumption of seafood were below the acceptability criterion for both the South
Brothers and the Background areas.?
Results of the hazard assessment indicated that risks associated with
consumption of seafood were low for the South Brothers and comparable with
reference areas.
5.6.2 Ecological
Risk Assessment
Based
on the risk assessment, it does not appear that Indo-Pacific Humpback dolphin
prey organisms are predicted to bioaccumulate contaminants 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 ().?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 ().?Internationally, Becker et al () 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
().?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 South Brothers area.?This
prediction concurs with the findings of a recent risk assessment published by
Hung et al (2004) ().
These
results indicate that the disposal of contaminated sediments at the proposed
South Brothers is not predicted to contribute to an increased risk of harm to
Indo-Pacific Humpback dolphins.