Sensible use of available information
Paul Lam (letter, South China Morning Post, March 14) accuses the Environmental Protection Department (EPD) of 'guessing' in formulating our response to the recent styrene spill.
I would like to provide a factual account of the information the EPD considered in making decisions on how to deal with the spill and leave your readers to decide if we have been 'guessing'.
The spill occurred on the first day of Chinese New Year. We were notified at about 1pm. As soon as we were notified, relevant staff went to the site while others checked on the characteristics of the chemical and the risks it posed.
We searched information compiled by the US Environmental Protection Agency (USEPA), the Canadian Council of Ministers of the Environment, and the World Health Organisation.
We found that styrene is relatively insoluble, will float on water, is highly volatile, evaporates rapidly and is biodegradable (not persistent). In the air, half the chemical will be degraded to derivatives in 2.5 hours. Based on this information we concluded, we believe reasonably, that the original chemical would decline to very low levels very rapidly.
We then checked the toxicity information.
Overseas ecotoxicological studies showed that the chemical is moderately toxic to aquatic life. For the fish and aquatic invertebrates tested, there was no observed effect at concentrations below 1.9 parts per million (ppm). For the alga tested, concentrations below 0.063ppm would have no effect.
We also checked on the potential of the chemical to accumulate in tissues. We found that based on its chemical characteristics the USEPA concluded styrene would not be expected to bioaccumulate or bioconcentrate in organisms and food chains.
Taking the foregoing into account we concluded that while there would be an impact immediately after the spill, the chances that effects would persist for a long period or extend over a wide area were very low, albeit not precisely quantifiable. We also concluded that we should focus on contamination in the water environment, because direct toxicity in the water posed the greater threat. We therefore arranged to collect samples from nearby areas including Mai Po Marshes.
The analytical results confirmed our judgment that the levels would decline rapidly within a few hours. The first samples, collected 11 hours after the spill, showed levels in the water of up to 0.41ppm. Samples taken on the following day, 24 hours after the spill, showed that the concentration in the water was in the range of 0.025 to 0.032ppm, well below reported toxic levels.
Given the need to focus on environmental outcomes, and that we do not possess unlimited resources, we had to consider at that stage whether there was any value in conducting further monitoring. Taking all the foregoing information into account we decided further monitoring would be unlikely to yield any substantive environmental benefit.
Dr Lam's team later collected samples and found levels of styrene in the water of Mai Po Nature Reserve to be less than 0.0001ppm. This is about 600 times below the lowest recorded toxic level and accorded well with our prediction of rapid dispersal and degradation.
I am not sure whether our actions as I have described them amount to 'guessing' rather than the 'risk-based approach' Dr Lam advocates. I leave readers to form their own views. But to me it represents the sensible utilisation of the information immediately to hand, coupled with the accumulated field experience of our officers, to exercise judgment in a professional manner in a difficult situation.
Dr Lam mentions that there exist many sound techniques for managing environmental risks in a spill situation. We shall be reviewing our procedures and actions in the light of the experience we have gained from this incident and would welcome any constructive advice Dr Lam has to offer us, which would have led to a more rapid or effective response.
Dr M. J. BROOM Principal Environmental Protection Officer for Director of Environmental Protection