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 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 Hong Kong, resulting from dredged material disposal at the proposed South Brothers 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.

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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.

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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

East Sha Chau 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

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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.

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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

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.

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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 Hong Kong (Table 5.3?? Estimate of Risk to the Indo-Pacific Humpback Dolphin South Brothers 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

 

 

 

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 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 South Brothers 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 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.


 ).?The HQ estimated for this chemical exceeded 1 for both the South Brothers 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 South Brothers 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

 

 

 

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.?

 

5.7    Conclusion

 

5.7.1    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 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 South Brothers 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 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.

 

5.7.2    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 ([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 South Brothers area.?This prediction concurs with the findings of a recent risk assessment published by Hung et al (2004)  ([17]).

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.


 



([1]) ????US EPA (1989) Assessing Human Health Risks from Chemically Contaminated Fish and Shellfish.?A Guidance Manual.?EPA-503/8-89/002.

([2]) ????US EPA (1992) Framework for ecological risk assessment.? EPA/630/R-92/001, Risk Assessment Forum, Washington, DC.

([3]) ????US EPA (1997) Ecological risk assessment guidance for superfund.?Process for Designing and Conducting Ecological Risk Assessments.?EPA-540-R97-006.

([4]) ????US EPA (2000) Guidance for assessing chemical contaminant data for use in fish advisories.?Volume 2.? Risk assessment and fish consumption limits.? EPA-823-B-00-008.

([5]) ????ERM (2002) Environmental Monitoring and Audit for Contaminated Mud Pit IV at East of Sha Chau.?Final Report for Civil Engineering Department.

([6]) ????Clarke SC, Jackson AP and Neff J (2000) Development of a risk assessment methodology for evaluating potential impacts associated with contaminated mud disposal in the marine environment. Chemosphere. 41:169-76.

([7])???There is a lack of bioaccumulation and bioconcentration factors available in the literature for TBT and it is therefore not included in the Risk Assessment.?This limitation does not limit the conservative nature of the assessment because background levels of TBT in sediment and dredged materials around the East of Sha Chau area are generally undetectable or very low.? This statement is backed up by monitoring data collected at CMPIV since 1997 which has consistently recorded TBT in sediment and tissue samples below levels of concern. ?/span>

([8]) ?? LaGrega M.D., P.L. Buckingham, J.C. Evans. and The ERM Group (1994)? Hazardous Waste Management.? McGraw-Hill Inc 1146pp.

([9]) ?? US EPA (1989) Assessing Human Health Risks from Chemically Contaminated Fish and Shellfish.?A Guidance Manual.?EPA-503/8-89/002.

([10])??? EVS (1996c) Contaminated Mud Disposal at East Sha Chau: Comparative Integrated Risk Assessment.? Prepared for the Hong Kong?/span>Civil Engineering Department.

([11]) ? US EPA (1989) Assessing Human Health Risks from Chemically Contaminated Fish and Shellfish.?A Guidance Manual.?EPA-503/8-89/002.

([12]) ? FEHD (2002) Dietary Exposure to Heavy Metals of Secondary School Students.? Food and Environmental hygiene Department, HKSARG.

([13]) ? Janes N and RC Playle (1995) Modeling silver binding to gills of rainbow trout (Oncorhynchus mykiss). Environmental Toxicology Chemistry. 14:1847-1858.

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