Microplastics in urban stormwater drains and sewage treatment works
In recent years, scientists found that microplastic pollution in the marine environment has become a serious ecological problem due to the widespread use of plastic products in our society. Because of their tiny size of less than 5 millimetres in diameter and their persistence in the environment, microplastics can be easily ingested by marine organisms. During this process, microplastics may also release their potentially harmful additives and toxic pollutants that accumulated from the surrounding environment into marine organisms, causing indirect harm and ultimately threatening the health and safety of humankind.
Few studies have been conducted on the abundance of microplastics in urban stormwater drains and their emissions to the coastal marine environment through sewage and stormwater drainage networks. Under the guidance of SKLMP Director Prof. Kenneth Mei Yee Leung and SKLMP members Dr. Siu Gin Cheung and Prof. Paul Kwan Sing Lam, the SKLMP research team led by Dr. Kai Zhang (former SKLMP Research Associate, current Assistant Professor at Macau University of Science and Technology), in collaboration with the Hong Kong Environmental Protection Department and Drainage Services Department, thoroughly investigated three sewage treatment works (STWs) including Stonecutters Island, Sha Tin and Shek Wu Hui STWs, as well as six main stormwater drains covering most regions of Hong Kong during 2021. The final results show that although the STWs are effective in removing microplastics from wastewater, they are still the major source of microplastic emissions in Hong Kong, discharging approximately 4.48 to 26.8 billion microplastic particles every day into the surrounding ocean, much more than the 224 million to 3.21 billion particles from the six stormwater drains.
These findings have been published in the journal Water Research and the SKLMP research team has developed scientifically robust standard methods for monitoring microplastics (two size ranges: 0.3-5 mm and 0.02-0.3mm) in wastewater, seawater, freshwater and stormwater, which will also be applied to the long-term monitoring of microplastics in Hong Kong in the future.