Involved Members: Dr. Siu Gin CHEUNG, Prof. Paul Kwan Sing LAM, Prof. Kenneth Mei Yee LEUNG

In collaboration with Environmental Protection Department and Drainage Services Department of the Hong Kong SAR Government, SKLMP team led by Dr. Kai Zhang (former Research Associate at SKLMP and now Assistant Professor at Macau University of Science and Technology) developed scientifically robust standard methods for monitoring of microplastics (two size ranges: 0.3-5 mm and 0.02-0.3mm) in wastewater, seawater, freshwater and stormwater. The established standard methods will be applied for the longterm monitoring of microplastics in Hong Kong. The main results have been published in Water Research (Zhang et al. 2022). The study team found that local sewage treatment plants could effectively remove microplastics from wastewater with an average removal efficiency of 81%, 85% and 98% for chemically enhanced primary treatment, secondary treatment and tertiary treatment, respectively.

The concentrations of microplastics from local sewage effluents and stormwater drainages were comparatively low when compared with those reported in other countries. Nevertheless, given the high volume of flow, the estimated discharge of microplastics from sewage effluent remained high in Hong Kong, with 4.5-26.8 billion pieces of microplastics per day. The six major storm drainages could discharge up to 3.2 billion pieces of microplastics per year. We also found that the stormwater also contained elevated levels of plasticizers (10 different phthalate esters) and the six storm drainages could release up to 29.4 kg of phthalate esters per day (Cao et al., 2022). Based on the results, we recommended some tangible mitigation measures for reducing microplastics pollution. Our results were widely reported in local newspapers and radio programmes of RTHK (in early 2023).

References:

Zhang, K., Xu, S.P., Zhang, Y., Lo, Y.K., Liu, M.Y., Ma, Y., Chau, H.S., Cao, Y.R., Xu, X.Y., Wu, R.B., Lin, H.J., Lao, J.Y., Tao, D.Y., Lau, F.T.K., Chiu, S.C., Wong, G.T.N., Lee, K., Ng, D.C.M., Cheung, S.G., Leung, K.M.Y., Lam, P.K.S. (2022). A systematic Study of Microplastic Occurrence in the Urban Water Networks of a Metropolis. Water Research, 223, 118992. (impact factor 13.400)

Cao, Y.R., Xu, S.P., Zhang, K., Lin, H.J., Wu, R.B., Lao, J.Y., Tao, D.Y., Liu, M.Y., Leung, K.M.Y., Lam, P.K.S. (2022). Spatiotemporal Occurrence of Phthalate Esters in Stormwater Drains of Hong Kong, China: Mass Loading and Source Identification. Environmental Pollution, 308, 119683. (impact factor 9.988)