The bioaccumulation of contaminants by prey organisms and
consequent biomagnification of contaminants up the food chain has long been an
issue of concern for the disposal of contaminated mud at East Sha Chau. Although the public at large may not
appreciate the technical details of a biomonitoring programme, especially
concerning mobile populations, they are well aware of the potential for
contaminated mud disposal to taint seafood products. These issues have been voiced not only in meetings with the
Advisory Council on the Environment (ACE) but also during presentations of the
findings of the EIA for CMP IV at District Board meetings([1]). In recognition of these issues, a comprehensive
biomonitoring programme which will address public concerns about contamination
of seafood in the area through use of the data in a risk assessment framework
should be undertaken for the disposal activities at the active pits.
As well as examining the influence of contaminated sediment
disposal on contaminant levels in demersal fisheries resources, the impact of
disposal on the abundance and structure of demersal fisheries should also be
assessed. Consequently, there are
two objectives for this task:
·
Biomonitoring of Contaminants - To identify any increases
in the concentrations of contaminants in tissues of demersal marine life
adjacent to and remote from the active
pits.
·
Trawling, Sorting & Analysis - To assess the impact of
contaminated mud disposal at the active
pits on the fisheries resources of the North Lantau area.
In accordance with the predictions of the EIA and the
objectives for the Study, the impact hypothesis for this task is as follows:
There is no increase in tissue
or whole body contaminant concentration over time in selected target species.
In order to reflect the dual workstreams under this task,
two sets of null hypotheses should be tested:
H0 The concentrations of contaminants in
tissue and whole body samples of demersal marine life adjacent to the active pits are not greater than
contaminant concentrations from samples collected at stations remote from the active pits.
H0 The concentrations of contaminants in
tissue and whole body samples of demersal marine life do not increase over
time.
H0 There are no differences in the
composition or abundance of demersal fisheries resources near to and remote
from the active pits Facility.
H0 There are no differences in the
composition or abundance of demersal fisheries resources over time.
Samples of the target species should be collected twice per year
(July/August in the wet season and January/February in the dry seasons)
specifically from two stations, one located north of Lung Kwu Chau as a
reference area (TNA) and the other located on the northern edge of Pit A (INA)
(Figure 6.4a). However, in order to obtain sufficient
tissue and whole body samples from impact and reference stations, samples
collected at different impact and reference stations (eg INA and INB, and TNA
and TNB) will be combined where necessary.
The precise location of the sampling stations should be
confirmed in advance of the commencement of the disposal activities and agreed
with EPD.
Due to concerns regarding the collection of sufficient
quantities of target species, catch from the first trawl survey of each season
(trawl for catch characterisation) should be retained in a frozen state for
joint processing with the biomonitoring samples in the following month.
Five replicate tows should be conducted at each station and
composite samples prepared from all nets and tows at each station during each
of the sampling events. Replicate
data points should be obtained whenever the abundance of target species allows
laboratory analysis of more than one tissue/whole body sample for each target
species at each station. The
design to be developed should address the following key issues:
·
Rigour
of the dataset to allow for statistical testing of observed differences;
·
Data
required for the risk assessment;
·
Composite
samples to minimise the variance between fish and improve the reliability of
detecting any significant trends; and,
·
Analysing
replicate samples, whenever possible, to provide cost effective statistical
rigour.
The design of the sampling programme should encompasses the
following key issues:
·
Temporal
variation in fisheries assemblages; and,
·
Spatial
variation of mobile assemblages of demersal fisheries resources.
Samples should be collected for analysis four times each year
(twice in the dry season and twice in the wet season) to account for temporal
variation in the fisheries assemblages.
The samples should be collected from 5 replicate trawls (each with 6
nets) undertaken along a transect.
Two replicate transects should be sampled at each site. Two sites should be located in each of
two areas (impact areas and reference areas) (Figures 6.4a and 6.4b). The exact position of the sampling
locations should be confirmed prior to the commencement of the disposal
activities and agreed with EPD.
Target species should be identified in advance of the
commencement of disposal activities. The species list should be devised with
reference to the previous biomonitoring programmes for the East Sha Chau
CMPs. The species list should also
include alternative species such that in case sufficient samples of target
species cannot be obtained, analysis of the alternative species should be
carried out.
The data should be analysed using analysis of variance
techniques to test for differences between the two sampling sites. Once a time series of data (sequential
sampling events) has been gathered, differences should be tested between the
stations and between the different sampling events to examine any temporal
trends in contaminant levels in the target species.
Catch composition should be analysed using partially nested
analysis of variance techniques to account for changes in catches between and
within sites in the North Lantauregion
and between different sampling times.
As with the previous examples, any significant differences should be
further tested through the use of multiple comparison tests.
If significant increases are detected in the levels of
contaminants in fisheries resources in this programme it will indicate that
bioaccumulation is occurring. However, as demersal fisheries resources are
generally mobile (except burrowing species such as the gobies Trypauchen and Oxyurichthys), increases may not necessarily be due to disposal at
the disposal facility. Other contaminant sources such as
discharges from the Pearl River, the local sewage outfalls or non point source
pollution may cause such increases.
To account for these confounding effects, the results from this
Project’s sediment and water chemistry programmes along with the most recent
sediment toxicity test results so that the sources of any increases can be
identified. Should there be
evidence that effects are due to the
active facility, the monitoring and disposal programme shall be reviewed
and revised where necessary as agreed with CEDD/EPD.
The contaminants of concern for this project should be
measured separately, firstly in tissue samples (soft tissue) and secondly in
whole body samples obtained from the species list established for this
project. The species to be
examined should be chosen based on two criteria:
·
The
degree to which the organisms are exposed to contaminants in the sediments;
and,
·
The
position of the organisms in the food chain and the trophic level of their
predators (ie, humans or Indo-Pacific Humpback Dolphin).
In the laboratory, each sample should be analysed for
species composition, number of species, abundance and biomass. Each biomonitoring sample should be
sorted for target species; target species selection should be based on the
abundance and potential sample mass available for each species captured. In preparing samples for analysis,
different species will not be mixed.
Each tissue sample for laboratory analysis should consist of three or
more organisms, with priority given to larger individuals with no more than 2
fold difference in length. Length
and weight of all individual organisms represented by the composite sample
shall be recorded and individuals for tissue sample analysis dissected with a
sterilised (with hexane) titanium knife and a composite sample prepared. Frozen composite samples of at least 55
g wet weight (5 g for metal analysis, 30 g for organic analysis, 20 g for TBT
analysis) should be sent to the laboratory for analysis.
The analytical parameters for tissue and whole body testing
are given below.
(a) Inorganic
Contaminants;
(b) Polycyclic
Aromatic Hydrocarbons (PAHs);
(c) Total
Polychlorinated Biphenyls (PCBs);
(d) Organochlorine
Pesticides (DDE & DDT); and,
(e) Tributyltin
(TBT).
Moisture content of the tissue and whole body samples will
also be measured.
Catches from the trawl vessel should be processed to record
the number and abundance of individuals of commercial fisheries resources in
the samples as well as the number of species present.
Trawl sampling should be conducted by a shrimp trawler
equipped with a GPS system to ensure accurate positioning of each trawl. Five replicate trawls, with six nets
deployed in each, should be conducted for 10 minutes at each station. If more than one of the six nets are
retrieved in a damaged condition, the samples should be rejected and the trawl
repeated. To ensure the maximum
quality of the benthic trawl samples, several control measures have been
incorporated into the sampling programme, including:
·
no
more than three consecutive trawls should be conducted at a station and
resampling should only occur after a minimum of two hours has elapsed;
·
subsequent
trawls at each station should be shifted to avoid repetitive sampling over the
same area of seabed; and,
·
the
first station sampled in each survey should be selected at random to minimise
the diurnal influences on catches.
Catches from all six nets in each trawl should be combined
to form one sample. Each sample
should be immediately washed and stored in sterilised (with hexane) glass
jars. All samples should be chilled
to 4oC and transported to the laboratory for further sorting and
analysis.