Sediment

EPD does not gather data on TBT in the routine monitoring of sediments in Hong Kong waters. Few data are therefore available regarding TBT contamination of either local sediments or biota.

Most sediments analysed for TBT in this baseline Study were below the detection limit of 20 ug Sn kg-1. TBT was detected at above the detection limit in three stations (see Sections 2.3.3 and 4.2.2). The highest TBT concentrations recorded, tended to be associated with station WS1 which is located south of Tsing Yi and the upper concentrations recorded ranged from 81.8 - 107.0 ug Sn kg-1. These high TBT levels are probably associated with intensive shipping activity (TBT antifouling paints) and nearby shipbuilding and repair operations.

TBT concentrations previously recorded by ERM (1999) in sediments at the East Sha Chau CMP IV(47) revealed maximum levels of 10 ug Sn kg-1. TBT in sediments collected in the East Lamma Channel reference area sampled during the SSSP(48) recorded mean concentrations of 11 ug Sn kg-1 which is lower than values recorded in this baseline Study at Tsing Yi, but higher than levels recorded at most other sampling stations. Considerably higher TBT levels were recorded during the SSSP. TBT concentrations in excess of 200 ug Sn kg-1 were recorded at many stations with some exceptionally high levels (11,618 ug Sn kg-1 ) recorded in the Causeway Bay Typhoon Shelter.

High TBT concentrations have been recorded also in sediments from the typhoon shelter at Pak Sha Wan (Sai Kung), marinas at Marina Cove and Hebe Haven, Causeway Bay, and, at the Tiu Cham Wan fish culture zone (Sai Kung) where values of 1690.0, 1160.0, 960.0, 990.0 and 1100.0 mg TBT kg-1 were reported(49). TBT sediment concentrations in Causeway Bay Typhoon Shelter, Tsing Yi North, Aberdeen, Victoria Harbour and Hebe Haven were previously measured during A Study of Tributyltin Contamination of the Marine Environment of Hong Kong conducted in 1998 by Aspinwall who recorded levels of 312.5, 1163.0, 74.0, 16.5 and 39.0 ug Sn kg-1(50) . Spatial variation of TBT values in sediment recorded in this baseline Study along with values reported previously in Hong Kong are presented on Figure 4.2a.

Many international studies have measured TBT contamination in sediments from the marine environment. TBT in the sediments of a naval station in San Diego Bay have been recorded at 26 - 44 mg TBT kg-1 (dry weight)(51) which is similar to the values reported from Hong Kong. In the UK, however, values of an order of magnitude higher have been recorded (TBT and DBT) in a marina in Poole Harbour ranging from 0.02, 0.01 and 0.03 ug Sn kg-1 (dry weight) at the Harbour mouth to 0.52, 0.57 and 1.05 ug Sn kg-1 (dry weight) at a site 100 m from the marina(52). In 1988, sediment fractions (< 60 mm) TBT concentrations from the Netherlands reached levels as high as 1200 ug Sn kg-1 (dry weight)(53).

Biota

There are few measurements of TBT in the tissues of local marine organisms. In this baseline Study, TBT was only rarely recorded in biota tissues (Table 3.4a and 3.4b). The Gizzard Shad (Clupanodon thrissa) which is a pelagic fish was found to contain high tissue TBT (21 - 32 ug Sn kg-1) and values ranging from 21 - 33 ug Sn kg-1 were recorded in the burrowing Mantis Shrimp (Oratosquilla interrupta). Generally, the Mantis Shrimp was the only species to show TBT at detectable levels consistently over the four trawling surveys. TBT in bivalve (Perna viridis) tissues collected from Kat O (Northeastern New Territories) were usually below detection limits (10 ug Sn kg-1 wet weight) and highest concentrations detected in three individuals (50% of bivalve tissues analysed) ranged from 13 - 18 ug Sn kg-1(54) . These values represent lower ranges of TBT contamination recorded in this baseline Study though the bivalves sampled were distant from major TBT inputs.

There have been several international studies on TBT contamination of marine biota. Langston et al (1987) measured TBT in benthic organisms from Poole Harbour in the UK and recorded maximum concentrations of 1.12, 3.05 and 11.45 ug Sn kg-1(dry weight) for Litorina littorea, Scrobicularia plana and Mya arenaria, respectively(55). TBT was recorded in mussel (Mytilus edulis) tissues in the Netherlands at concentrations of 2300 - 1350 ug kg-1 (dry weight) in marinas and 130 - 530 ug kg-1 (dry weight) in reference stations(56). The TBT concentrations recorded elsewhere are, therefore, considerably higher than recorded values in this Study, although changes in the use of this biocide have generally reduced global marine inputs from smaller.