7    Human Health and Ecological Risk Assessment


7.1    Background


The waters north of Lantau have historically been important fishing grounds and are presently fished by shrimp and hang trawlers based primarily at Castle Peak.  These fishermen's catches comprise mainly shrimps and crabs, as well as fish species of relatively low commercial value such as pony fish, puffer fish and gobies ([1]).  The North of Lantau area also is recognized 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. 

Disposal operations at the facility will be designed to minimize the dispersion of contaminated sediments during disposal and to prevent the long-term migration of contaminants through placement of a clean sand and 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 the Indo-Pacific Humpback Dolphin, 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.

The EIA has indicated that the consumption of seafood collected within the vicinity of the pits does not pose an unacceptable public health risk to any of the sub-populations of concern.  In order to verify the predictions of the EIA a programme of monitoring the concentration of contaminants of concern in seafood is recommended.  The data from such a programme would also be of value to determining the risks to the Indo-Pacific Humpback Dolphin.

Consequently, a risk assessment should be performed at least on an annual basis to verify that no unacceptable risk are occurring to either human health or marine mammals as a result of consuming prey species from the waters in the vicinity of the pits of North Lantau.  The details of the EM&A programme for assessing hazard to health of humans and marine mammals are presented below.

7.2    Objective


The objective of the risk assessment component of the monitoring programme is to determine whether disposal operations at the active pits are posing an unacceptable risk to humans and dolphins through consumption of seafood/marine prey species from the North Lantau area.  This objective should be addressed through a standardized risk assessment methodology which cost effectively builds on existing risk assessment methodologies and databases and overcomes some of the previous studies’ limitations.


7.3    Hypothesis


Given the above discussion of objectives, the impact hypotheses for this component of the monitoring programme are defined as follows:

For Human Health:


IH1:   Risks to human health from consumption of commercial species captured adjacent to the active pits are no greater than risks associated with consumption of species remote from the active pits;


IH2:   Risks to human health from consumption of commercial species captured adjacent to the active pits are below the screening risk criterion (see Section 7.5).

For Dolphins:

IH1:   Risks to dolphins from consumption of prey species captured adjacent to the active pits are no greater than risks associated with consumption of prey species remote from the active pits;


IH2:   Risks to dolphins from consumption of prey species captured adjacent to the active pits are below the screening risk criterion (see Section 7.5).


7.4    Sampling Design


Data required for the risk assessment should consist of:


·                contaminant concentrations in commercial/prey species collected from stations adjacent to and remote from the active pits;

·                toxicology data for humans and dolphins;

·                gastro-intestinal tract absorption factors;

·                literature-derived human consumption rates and patterns for seafood;

·                literature-derived data on exposure of humans from other food groups;

·                literature-derived data on contaminant levels in marine mammals;

·                data collected by the Swire Institute of Marine Science (SWIMS) and AFCD on contaminant levels in stranded Sousa chinensis carcasses; and,

·                existing natural history information for the Indo-Pacific Humpback Dolphin and related species (eg diet composition and feeding range).


The primary data input to the risk assessment should derive from the bi-annual trawl (ie tissue collection) monitoring events.  The risk assessment shall be performed on an annual basis.


7.5    Use of Data


The risk assessment shall follow the guidelines of the US Environmental Protection Agency ([1]) (2) and shall incorporate a four-step approach involving problem formulation, estimation of exposure, characterization of ecological or human health effects (injury), and risk characterization.  Each of these steps is described below with reference to how each applies to both human health and ecological risk assessment.

Problem Formulation:  Also known as hazard definition (3), the problem formulation will describe the sensitive populations (eg the general Hong Kong population, subsistence fishermen, the Indo-Pacific Humpback Dolphin) and identify biological effects of concern potentially associated with the CMP operations at the active facility.  Identification of these effects should include a discussion of contaminants of concern, measurement endpoints and a conceptual model embodying the mechanisms of contaminant migration.


Estimation of Exposure:  The purpose of the exposure estimation is to determine the intake of each contaminant of concern by potentially exposed individuals.  This step shall consider the various routes of contaminant release and their migration from the site to sensitive receivers.  Factors such as fate and transport processes, the concentrations in the ambient environment, and the maximum short-term or average lifetime doses should be assessed. 

For human populations exposure factors presented in previous reports ([1]) (2) shall be critically evaluated to determine if further modification is necessary.  These factors, which include amounts of seafood consumed, origin of seafood products, and methods of preparation (eg raw versus cooked, whole body vs tissue only) shall be evaluated for the general population and any sensitive subpopulations (eg subsistence fishermen fishing in the East of Sha Chau area). 


Characterization of Effects:  The effects assessment is designed to quantify the relationship between the degree of exposure to a substance and the extent of toxic injury or disease.  This step in the assessment shall use data derived from dose response studies on laboratory animals or, less frequently, on exposed human populations and clinical trials.  For non-carcinogenic substances, once the relationship between doses and responses is established, a threshold which represents the highest contaminant concentration that is not expected to result in an adverse effect, ie the reference dose (RfD) or a No Observed Adverse Effect Level (NOAEL) can be established.  This threshold shall then compare to the dose derived from the exposure assessment above to produce the risk characterization. 


For humans, dose-response relationships must be considered separately for carcinogens and non-carcinogens.  When dealing with carcinogens, a cancer potency factor (CPF) or Slope Factor (SF) for each contaminant of concern shall be used.  For non-carcinogens, the NOAEL or LOAEL (lowest observed adverse effect level) shall be used as the threshold value.  Data on CPFs, and NOAEL/LOAEL values are available through the U.S. EPA's IRIS (Integrated Risk Information System) and HEAST (Health Effects Assessment Summary Tables) databases.  The relationship between contaminant concentrations in toothed cetacean tissues and the concentrations in their prey items will be assessed in this programme. 


Risk Characterization:  The risk characterization shall integrate the results of the exposure and effects assessments to estimate the risks and consequences of contaminant exposures.  In this step, the estimated exposure should be divided by the threshold value to obtain a Hazard Quotient (HQ).  Generally HQ values below 1 are considered to represent a very low risk of adverse effects, whereas HQ values above 10 indicate a moderate to high level of risk. 


For human populations, the general approach to evaluating HQs can be applied to this Project.  However, the human health risk characterization produced for this Project should be updated through the use of continually collected tissue and other environmental monitoring data to reflect current conditions.  This Study's human health risk assessment will improve the robustness of previous studies through a careful reconsideration of all exposure and effects parameters, with particular focus on background doses and seafood consumption patterns. 


([1])     ERM (1997) Fisheries Resources and Fishing Operations in Hong Kong Waters.  Draft Final Report prepared AFD.

([2])     U.S. Environmental Protection Agency. 1992. Framework for Ecological Risk Assessment. EPA/630/R‑92/001. Risk Assessment Forum, U.S. EPA, Washington, DC.

([3])     U.S. Environmental Protection Agency. 1996. Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments (Draft). U.S. EPA.

([4])     Suter, G W II. (1993).  Ecological Risk Assessment.  Lewis Press, Boca Raton, FL, 538 pp.

([5])     Shaw, B (1995) Evaluation of risks to human health in Hong Kong from consumption of chemically contaminated seafood:  A risk assessment approach, MSc thesis, Environmental Management Programme, University of Hong Kong.

([6])     EVS (1996) Contaminated Mud Disposal at East Sha Chau:  Comparative Integrated Risk Assessment. Prepared for CED.