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.
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.
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;
AND
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;
AND
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).
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.
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.