Sediment was collected at ten stations in Hong Kong waters ranging from the mouth of Tolo Harbour/Mirs Bay to Deep Bay and thus covered the ten Water Control Zones (WCZs) in Hong Kong waters (Figure 2.1a) and the three hydrographic zones of local waters (ie Eastern zone comprised of mostly high salinity oceanic waters; the Central transitional zone comprised of mixed waters from the Eastern and Western zones; and, the Western zone comprised of estuarine waters owing to influence from the Pearl River). Existing EPD marine sediment quality monitoring stations were used for the sampling locations in order to provide consistency with EPD's long-term dataset.

Many elements of the monitoring programme were based on those previously developed for the monitoring programme for the East Sha Chau Contaminated Mud Pits. This programme is Hong Kong's largest and most comprehensive marine monitoring programme and has formulated methodology by consensus with EPD, AFD, CED and the Government Chemist. Use of this methodology for the SUSDEV baseline study facilitates a direct comparison with the 30 months of data collected at East Sha Chau.

The following organic contaminants of concern were analysed in sediments collected from locations in Hong Kong:

These contaminants have been selected as existing data on pesticides (eg DDT) and tributyltin in local sediments are limited. Information on PCBs and PAHs can be obtained from EPD's routine sediment monitoring programme.

The specific analytes to be tested and the required methods and detection limits were based on the monitoring programme for East Sha Chau Contaminated Mud Pits and are described in Table 2.1a.

Note 1: The TBT MDL shown in the table complies with Government's requirements for the East Sha Chau CMP IV EM&A programme. The actual TBT MDL used in the East Sha Chau CMP IV EM&A programme is 0.5 ug Sn kg-1

It should be noted that most laboratories in Hong Kong which analyse organic compounds calculate total PAHs by summing the concentrations of each of the individual PAHs, and do not possess the equipment which would allow them to perform a basic analysis for total PAHs. A similar situation exists for pesticides and hence Total DDT is reported.

The sediment samples were collected four times during the baseline SUSDEV 21 Studies. Sampling was conducted twice in both the wet and dry seasons to allow for any temporal differences in contaminant levels that are known to occur due to such events as different rates of deposition in sediment caused by urban run-off pulses associated with storm events. Sediment sampling was conducted on the following days:

• 1 December 1998 (dry season) (stations DS3, NS4, WS1, VS3);

• 2 December 1998 (dry season) (stations ES2, PS6, MS15, MS5, TS2);

• 3 December 1998 (dry season) (station SS3);

• 26 January 1999 (dry season) (stations ES2, PS6, MS15, MS5, TS2);

• 27 January (dry season) (stations DS3, NS4, WS1, VS3, SS3);

• 15 June 1999 (wet season) (stations DS3, NS4, WS1, SS3, VS3);

• 16 June 1999 (wet season) (stations ES2, PS6, MS15, MS5, TS2);

• 11 August 1999 (wet season) (stations DS3, NS4, WS1, VS3, SS3); and,

• 12 August 1999 (wet season) (stations TS2, MS15, MS5, ES2, PS6).

The sediment sampling frequency employed was used so as to provide coverage of both wet and dry seasons and allow replication of data within each season. Data replication is required in order to provide a statistically robust analyses of toxic organic contamination of sediments and improve the overall SUSDEV 21 baseline results.