Better approach needed for chemical spills

PUBLISHED : Tuesday, 14 March, 2000, 12:00am
UPDATED : Tuesday, 14 March, 2000, 12:00am

A truck overturned in Fuk Hi Street, Yuen Long, on February 5, resulting in a spillage of about 12 tonnes of styrene into a nullah that empties into Shan Pui Ho. The Fire Services Department was called in to deal with the situation by hosing down the contaminated area.

The Environmental Protection Department (EPD) took samples from the site, and later claimed that the chemical dissolved readily in water, and should 'vanish' quickly from the area. It also said that because of the relatively small volume of the leaked chemical, no further monitoring or action was necessary.

As part of our research programme, I and my research group of postgraduate students took water samples from just outside a floating bird hide inside the Mai Po Nature Reserve, a core conservation area inside a Wetland of International Importance established under the Ramsar Convention. Subsequent analysis of the water samples revealed traces (up to 0.1 parts per billion) of styrene. As this chemical, known to be toxic to a range of aquatic organisms, had not been detected in our samples previously, we took additional samples from several sites along the nullah and at Shan Pui Ho.

Our overall results indicate the sediments are contaminated with styrene, ranging from about two parts per million (ppm) near the spill site to 0.2 ppm at the point where the nullah enters Shan Pui Ho which drains directly into the Mai Po and Deep Bay mudflat. The official EPD response is still that the levels are extremely low, and thus it was correct not to instigate a monitoring programme to follow up on the incident.

The purpose of this letter is not to argue whether or not the levels are high. Nor am I arguing whether 12 tonnes of styrene is or is not a small amount. What has become obvious from this incident is the need to improve the way we handle this type of environmental emergency.

The strategy adopted by the EPD is of management decisions based entirely on concentrations, or in this case, anticipated concentrations in the environment (called a hazard-based approach) that fails to take into account the probability that a substance is potentially hazardous and may cause harm. A risk-based approach, one that I am advocating, considers the nature of the chemical, its ability to build up in body tissues, its solubility and susceptibility of the target organisms.

Also of relevance here is the dispersion pattern of the pollutant in nearby waters. The discovery of trace amounts of styrene in the nullah 300 metres upstream from the spill site clearly illustrates the importance of tidal regimes in the dispersion of the chemical and the need for field monitoring. Indeed, there are many good and scientifically sound techniques and methodologies for assessing and managing environmental risks in a spill situation, but guessing, as used by EPD, is not one of them.

I am very encouraged by the fact that the styrene levels detected are relatively low, albeit persistent, but not so much by the way that the incident was handled. We are fortunate this time, but what about next time? It is perhaps the right time for us to consider whether we need a special risk assessment and management procedure for ecologically/environmentally sensitive areas in Hong Kong.

PAUL LAM Associate Professor Department of Biology and Chemistry City University of Hong Kong