Distribution and ecological risk assessment of palm stearin in coastal marine environments of Hong Kong after an accidental pollution in Pearl River Estuary, South China

Abstract

On 3 August 2017, two container vessels collided in the Pearl River Estuary, southwest of Hong Kong, leading to release over 1,000 tonnes of palm stearin into adjacent waters. About 200 tonnes of the stearin reached south coasts of Hong Kong after two days. However, toxicity of palm stearin to marine organisms is unknown. This study, therefore, aimed to examine its contamination levels in seawater, sediment and animal samples collected from seven locations along the south coasts of Hong Kong; determine its toxicities to selected marine organisms including microalgae (Isochrysis galbana and Chaetoceros gracilis), the copepod (Tigriopus japonicus), the artemia (Artemia franciscanas), and the fish (Oryzias melastigma), and derive interim water quality guidelines (WQG) of the palm stearin and thereby assess its ecological risks to local marine ecosystems. Samples of the palm stearin, surface seawater, sediment and three intertidal gastropods were collected twice (within seven days and four months after the incident) in six locations along the south coast of Hong Kong. Fatty acids in these samples were detected using gas chromatography-mass spectrometry. Standard toxicity tests were conducted with the selected species. The results showed that all seawater samples collected from the six sites were heavily contaminated by the palm stearin after one week of the accidental pollution. We also found that although the palm stearin had little effects on marine animals, it was toxic to microalgae species as reflected by growth inhibition. Its toxic mechanisms on the microalgae may be associated with its adsorption onto microalgal cells, and reudction of light prenetration to the cells due to obstruction from the stearin and palm oil. At present, we are generating additional toxicity data on other microalgal species (Thalassiosira weissflogii and Tetraselmis suecica). Using all toxicity data generated from this study, we will ultimately determine an interim WQG for the palm stearin, and use this WQG to assess its ecological risks to local marine ecosystems. This study represents the first comprehensive investigation on the ecological risk of the palm stearin in the world, and the results will facilitate informed decision-making by the environmental authority.