5                     human health risk assessment

Introduction

5.1               The Human Health Risk Assessment (HHRA) in the EIA Report, which focused on assessing the potential risks/impacts to human health due to chronic exposure to the contaminants present in the SCISTW effluent discharge, predicted that the contaminants present in the chlorinated/dechlorinated SCISTW CEPT effluent discharge would not induce unacceptable risk/impact to human health.

 

5.2               Contaminant concentrations in marine water are recommended to be monitored in the effluent quality and water quality monitoring of the Post Project Monitoring (PPM) Programme.  The monitoring aims to achieve the following objectives:

 

·             To check whether the Project would cause an increase in contaminant concentrations in seawater

·             To verify the predictions of the HHRA; and

·             To verify the predictions of the Ecological Risk Assessment (ERA) 

Effluent Contamination Concentration Monitoring

5.3               The requirements, methodology, equipment, sampling location and schedule (for both baseline and impact monitoring) of the effluent contaminant concentration monitoring shall be consistent with the indicative effluent quality monitoring programme as discussed in Section 4 of the EM&A Manual.  Table 5.1 presents the list of contaminants to be analyzed in the effluent contaminant concentration monitoring, the corresponding analysis method as well as detection limit.  HOKLAS accredited analysis methods can also be used for the contaminant concentration determination.

 

Table 5.1      List of Contaminants and Analytical Methods to be Applied

               

Determinant

Suggested Analytical Method

Suggested Detection Limit (μg/L)

Total residual chlorine

APHA 4500CL: G

5*

Bromoform

USEPA 8260 (Purge & Trap GCMS)

0.1*

Bromodichloromethane

0.1*

Chloroform

0.1*

Dibromochloromethane

5

Bromoacetic acid

APHA 6251

2

Chloroacetic acid

2

Dibromoacetic acid

2

Dichloroacetic acid

2

Trichloroacetic acid

2

Methylene chloride

USEPA 8260 (Purge and Trap GCMS)

20

Carbon tetrachloride

0.5

Chlorobenzene

0.5

1,1-dichloroethane

0.5

1,2-dichloroethane

0.5

1,1-dichloroethylene

0.5

1,2-dichloropropane

0.5

Tetrachloroethylene

0.5

1,1,1-trichloroethane

0.5

1,1,2-trichloroethane

0.5

Trichloroethylene

0.5

2-chlorophenol

USEPA 8270/GCMS

0.5

2,4-dichlorophenol

0.5

p-chloro-m-cresol

0.5

Pentachlorophenol

0.5*

2,4,6-trichlorophenol

0.5

Bis(2-chloroethoxy)methane

0.5

1,4-dichlorobenzene

0.5

Hexachlorobenzene

0.01*

Hexachlorocyclopentadiene

2.5

Hexachloroethane

0.5

1,2,4-trichlorobenzene

0.5

Alpha-BHC

0.01*

Beta-BHC

0.01*

Gamma-BHC

0.01*

Aluminium

USEPA 200.7

1

Antimony

1

Arsenic

1

Barium

1

Chromium III

1

Copper

1

Lead

1

Mercury

0.1*

Nickel

1

Selenium

1

Silver

1

Tin

1

Vanadium

1

Zinc

1

Ammonia

APHA 4500NH: G

10

Sulphide

APHA 20e 4500-S2-

10

TCDD

USEPA 1613

1 TEQ rg/L

Toluene

USEPA 1624

10

Diazinon

USEPA 1657

0.01

Malathion

USEPA 1657

0.01

Note: * The suggested detection limit was in light of the concentration of interest (COI) for human health and/or ecological resources, which was based on local/international authority approved standard.  Determinant at concentration below COI is not expected to induce concern to human health and ecological resources.

Seawater Contaminant Concentration Monitoring

5.4               The requirements, methodology, equipment, monitoring locations and schedule (for both baseline and impact monitoring) of the contaminant concentration monitoring shall be consistent with the indicative water quality monitoring programme as discussed in Section 4 of the EM&A Manual.  The list of contaminants to be analyzed in the seawater contaminant concentration monitoring, the corresponding analysis method as well as detection limit are same to those listed for effluent contaminant concentration monitoring.

Statistical Analysis of Monitoring Data

5.5               After the data of the first set of baseline marine water quality monitoring has been obtained, a statistical power analysis shall be conducted to verify and review the number of replicates required for subsequent baseline and impact monitoring sessions.  

5.6               The monitoring data (contaminant concentrations in marine water) should be analyzed using analysis of variance techniques to test for differences between sampling locations.  Once a time series of data (sequential sampling events) has been gathered, difference should be tested between the stations and between the different sampling events to examine any temporal trends in contaminant concentrations in seawater.  The statistical analysis of monitoring data would provide information to identify any difference of contaminant concentration in seawater in spatial and temporal terms.

 

5.7               The main objective of the proposed monitoring programme is to check whether the Project would cause an increase in contaminant concentrations in seawater.  Therefore, once the impact monitoring programme for the year is complete, the impact monitoring data obtained for the year should be compared with the baseline monitoring data using statistical analysis technique to determine whether there is increase of contaminant concentrations in seawater after implementation of the Project.  Should the statistical analysis reveal that contaminant concentrations in marine water increase after implementation of the Project, the monitoring data collected in effluent quality monitoring shall be used to provide information to investigate whether such increase is due to the effluent discharged by the Project.   

Human Health Risk Assessment

5.8               If increase of seawater concentration of contaminant (one or more) is found to be due to operation of the Project, human health risk assessment and ecological risk assessment using the impact monitoring data obtained for the year should be conducted to verify that the human health risk/impact and ecological risk due to contaminants discharged from SCISTW effluent is acceptable.  The details of the human health risk assessment are presented below and details of the ecological risk assessment are presented in Section 6 of the EM&A Manual.

 

5.9               The HHRA shall follow the approach and methodology adopted in the EIA Study which has been presented in Appendix D.  The HHRA will consist of the following 5 stages:

 

·             Problem Formulation

·             Hazard Identification

·             Exposure Assessment

·             Dose-response Assessment

·             Risk/hazard Characterization

 

5.10            Apart from the chemical analysis data obtained from the monitoring programme, the following data are needed in the HHRA:

 

·             Human receptor parameter values including seafood consumption rate and frequency

·             Parameters related to contaminants including bioconcentration factor, food chain multiplier and dermal exposure related parameters

·             Health benchmarks (i.e. cancer slope factor and reference dose) of contaminants

 

5.11            The above data items used in the EIA Study should be reviewed and updated by the Environmental Consultant (if more up-to-date data is available) when performing the HHRA.  Should the HHRA results reveal that there is potential occurrence of unacceptable human health risk, a review of HHRA shall be conducted, which shall involve:

 

·             Identifying major exposure pathway[1] to contaminants contributing to the calculated health risk

·             Reviewing and using more realistic exposure assumptions related to the identified major exposure pathway to refine the HHRA results

·             If potential occurrence of unacceptable human health risk is still found in the refined HHRA, measures to prevent potential contaminant exposure (e.g. restriction of water related activities at location near SCISTW effluent diffuser, restriction of fisheries activities within the ZID of the HATS effluent[2]) shall be considered

·             Extension of ambient water contaminant concentration monitoring programme (in terms of location[3] and duration) may be considered to obtain data for more realistic risk estimation

 


[1]  Note: HHRA conducted in the EIA Study revealed that seawater ingestion and dermal contact during swimming activity would be the major exposure pathways contributing to the estimated health risk.

[2] Restriction of fisheries activities within the ZID of the HATS effluent has been currently exercised.

[3] Bathing beaches and fish cultural zones near the HATS effluent diffuser.