When strong typhoon Vicente hit Hong Kong, 150 tonnes of “polypropylene” plastic pellets scattered into the neighbouring sea. The local fish culture zones have been affected. Over a hundred dead fish were found in the rafts and residual plastic pellets were found inside fish offal. Government departments and environmental groups mobilized volunteers to salvage and clean up the plastic pellets. However, the government said it is safe for the public to consume local fish, just be mindful of any plastic pellet inside fish intestine with thorough cleaning. In this issue, Dr Leung Ka-sing, Visiting Associate Professor of PolyU’s Department of Applied Biology and Chemical Technology, will enlighten us on this topic.

1/ Will seawater pollutants pollute the plastic pellets? Would this incident contaminate the food chain?

“Polypropylene” is an inert and heat-resistant plastic material, with good chemical stability. It is resistant to most organic solvents as well as acids and alkalis. Its melting point is much higher than 100°C (boiling point of water), making it an excellent material for food containers. “Polypropylene” pellets are less dense than water. They will float on and drift with water. Therefore, the chance is slim for them to be polluted by marine pollutants and then contaminate the food chain.

2/ Reports said that fish, after accidentally swallowed plastic pellets, will develop digestive problems affecting their growth. Is this correct?

In fact, how will the plastic pellets affect the fish depends on the size of the fish. Plastic pellets will not get into tiny fish, while big fish can easily excrete the pellets out from their bodies. For some fish, the plastic pellets may accumulate inside their intestines, thus affecting their eating and growth.

3/ Reports said that the non-toxic plastic pellets will neither absorb the toxins in the sea, nor be directly absorbed by living organisms. However, when the fish with plastic pellets inside their intestines are cooked and exposed to heat, will the plastic pellet substances undergo changes? If humans eat those fish, will their health be affected?

Under normal cooking temperature, “polypropylene” pellets will not have significant changes. When entering the human body, the plastic pellets will not be digested or absorbed, but excreted, thus will not affect the human health. The best measure is to avoid eating fish intestine, or cook fish after careful visual inspection of the intestine.

4/ Some people described this incident as ecological catastrophe. In the long run, how will it affect the natural ecology of our coast and the water quality?

“Polypropylene” pellets will float with the sea waves and be washed ashore, but will not affect the water quality. There is no significant difference in the ecological impact between these pellets and general plastic wastes.