Toxic Substances Monitoring Programme

Since 2004, the EPD has expanded its activities by developing a new toxic substances monitoring programme, which focuses on the monitoring of trace levels of toxic chemicals such as dioxins, pesticides, and heavy metals. These chemicals persist in the environment: they build up in the food chain and can harm marine organisms and humans who consume contaminated seafood.

The toxic substances monitoring programme came about as a result of a 'Study of Toxic Substances Pollution in Hong Kong' conducted by the EPD from 1999 to 2003. The study gathered preliminary information about the levels of trace toxic chemicals in the marine environment and assessed the risks they could pose to the ecosystem and to human health. It concluded that although Hong Kong's marine environment was not widely polluted with toxic chemicals at levels causing concern, there was a definite need to monitor a number of trace toxic pollutants that held potential risks in some areas.

Following up on the recommendations of the study, in 2004 the Water Monitoring Section of the EPD initiated the toxic substances monitoring programme. The objectives of the programme were, first, to gain a clearer picture of the levels of trace toxic pollutants in the marine environment (i.e. in water, sediment and biota), and in sources of pollution (e.g. sewage, rivers, and storm runoff). Second, the programme aimed to monitor whether existing levels of toxic pollutants posed any special hazards either to the environment or to human health which might need to be addressed.

Monitoring was set up according to a three-year cycle, with the first two years focused on the monitoring of toxic chemicals in the marine environment and the third year on the monitoring of land-based pollution sources.

Dioxins/Furans are persistent organic pollutants which are harmful even at very low levels

In the first two years (2004-05), the programme monitored 13 chemicals in marine water, 21 chemicals in bottom sediments, and nine chemicals in marine biota. The trace organics that were analysed included dioxins/furans, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dichloro-diphenyltrichloroethane and its metabolites (DDTs), and organotin compounds (TBTs). Toxic metals covered by the monitoring included cadmium (Cd), copper (Cu) and mercury (Hg). Under the programme, EPD staff collected samples of marine water and bottom sediment from across seven different Water Control Zones representing the full geographical range of Hong Kong waters: Mirs Bay, Tolo Harbour, Junk Bay, Victoria Harbour, Southern, North Western and Deep Bay. At the same time, samples of marine biota including fish, bivalves, shrimps and mantis shrimps were collected from five Water Control Zones.

Sorting samples of marine biota on board vessel for the toxic substances monitoring programme

The initial findings of the 2004-05 monitoring programme were largely consistent with the conclusions of the 'Study of Toxic Substances Pollution in Hong Kong', namely that levels of toxic substances were low in most Hong Kong marine environment and not of major concern. It was found, however, that some heavy metals in sediment from Victoria Harbour occurred at particularly higher levels.

Toxic substances monitoring will continue in 2006 with a special focus on pollution sources such as raw sewage, effluent from sewage treatment plants, river water, and storm run-off. Hong Kong is party to the Stockholm Convention on Persistent Organic Pollutants (POPs), and as part of its implementation of the Convention, the toxic substances monitoring programme will be further expanded in the future to include all 12 POPs covered by the Convention.

Bioindicators Monitoring Programme

Dissecting the gonad of a pony fish Leiognathus brevirostris, used in the bioindicators monitoring programme

Another recent initiative by the EPD has been a new Bioindicators Monitoring Programme, launched in 2004. The EPD's water monitoring programme from the 1980s onward had mostly focused on physico-chemical parameters of marine water and sediment. Biomonitoring had been restricted to the monitoring of sewage bacteria and phytoplankton as part of the general marine water quality monitoring. There had been no monitoring of effects of toxic pollution on marine organisms.

Generally, biomonitoring is a good way to assess the ecological health of the marine environment. In particular, it can be vital in determining whether organisms have suffered any damage at different biological levels (biochemical, cytological, physiological, organismal, community) and if so, in relating that damage to pollution. .

Between 2001 and 2003, the EPD undertook a study on the 'Development of a Biological Indicator System for Monitoring Marine Pollution'. Amongst other things, the study recommended the setting up of a bioindicators monitoring programme that would track the biological effects of pollution. The objectives of the programme would be to monitor the biological responses of indicator species with respect to changes in water quality; to compare biological effects of pollution across Hong Kong waters; and to assess the overall ecological health of Hong Kong's marine environment.

The study recommended that the programme should monitor a total of 13 bioindicators at different levels of biological organisation. The indicators were as follows:

• Ethoxyresourufin O-deethylase (EROD) in fish liver
• Lysosomal integrity of mussels
• Body burden of heavy metals and trace organics in mussels
• Condition Factor (CF) of fish
• Hepatosomatic Index (HSI) of fish
• Gonadosomatic Index (GSI) of fish
• Fin erosion of fish
• Epidermal hyperplasia of fish
• Imposex of gastropods
• Diversity indices of benthos (benthic community)
• Log normal distribution of benthos
• ABC (Abundance and Biomass Comparison) plots of benthos
• Multivariate statistics of benthos
  

When the EPD began the programme in 2004 and 2005, it included the first nine bioindicators above, while the other four community indicators, monitored once every three years, were included in 2006.

The new bioindicators monitoring programme was carried out in six zones which took into account the pollution levels in different areas of Hong Kong waters. The six zones were Zone 1 (Deep Bay), Zone 2 (Western Waters), Zone 3 (Tolo Harbour and Inner Mirs Bay), Zone 4 (Port Shelter and Outer Mirs Bay), Zone 5 (Southern Waters) and Zone 6 (Victoria Harbour and Junk Bay).

Of the bioindicators described above, the programme showed that fish in Hong Kong waters were generally free from pollution-related fin erosion and epidermal hyperplasia. Certain other bioindicators posed some concern however, such as imposex of gastropods, which can be triggered by TBT compounds (used as antifoulant on the hulls of ships). TBT compounds can disrupt the reproduction of sea snails by changing their sex, even when it occurs at very low levels in marine water.

Mussels are able to accumulate toxic substances in their bodies, and have been used as bioindicators in many places. Early data have shown that levels of PCBs and PAHs in green mussels near urban centres such as Tsim Sha Tsui are higher than elsewhere in Hong Kong, although PCB contamination in all the mussels analysed was low.

These two new programmes are supplementing the existing marine water monitoring programme, and together they are helping the EPD get a more comprehensive picture than ever before of the state of Hong Kong's marine environment and the moves that need to be made to protect and restore it.