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(). 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.
() ERM (1997) op cit.