Characterisation of plastic microbeads in facial scrubs and their estimated emissions in Mainland China

Abstract

Plastic microbeads are often added to personal care and cosmetic products (PCCPs) as an abrasive agent in exfoliants. These beads have been reported to contaminate the aquatic environment and are sufficiently small to be readily ingested by aquatic organisms. Plastic microbeads can be directly released into the aquatic environment with domestic sewage if no sewage treatment is provided, and they can also escape from wastewater treatment plants (WWTPs) because of incomplete removal. However, the emissions of microbeads from these two sources have never been estimated for China, and no regulation has been imposed on the use of plastic microbeads in PCCPs. Therefore, in this study, we aimed to estimate the annual microbead emissions in Mainland China from both direct emissions and WWTP emissions. Nine facial scrubs were purchased, and the microbeads in the scrubs were extracted and enumerated. The microbead density in those products ranged from 5219 to 50,391 particles/g, with an average of 20,860 particles/g. Direct emissions arising from the use of facial scrubs were estimated using this average density number, population data, facial scrub usage rate, sewage treatment rate, and a few conservative assumptions. WWTP emissions were calculated by multiplying the annual treated sewage volume and estimated microbead density in treated sewage. We estimated that, on average, 209.7 trillion microbeads (306.9 tonnes) are emitted into the aquatic environment in Mainland China every year. More than 80% of the emissions originate from incomplete removal in WWTPs, and the remaining 20% are derived from direct emissions. Although the weight of the emitted microbeads only accounts for approximately 0.03% of the plastic waste input into the ocean from China, the number of microbeads emitted far exceeds the previous estimate of plastic debris (>330 μm) on the world's sea surface. Immediate actions are required to prevent plastic microbeads from entering the aquatic environment.