A separation of plastic debris in Saigon river sediment using a microplastic sediment separator

Abstract

Plastic debris was separated from Saigon river sediment using a microplastic sediment separator (MPSS) for the first time. A separation fluid of ZnCl2 solution (1.6 kg/L) was used to separate lower density materials (floating on the top) from higher density materials (sinking in the bottom). Plastic and plastic-like materials were collected and analyzed by a FTIR spectrometer to determine plastic composition. The results show that a total of 350 items (0.0485 g) of plastic debris were extracted from 1,500.00 g dry sediment, including 11 items (0.0130 g) of macroplastics (> 5 mm) and 339 items (0.0355 g) of microplastics (0.3–5 mm). Polyethylene (PE), polypropylene (PP), and PE-PP mixture were the most major plastic types with 225, 85, and 21 items, respectively. Others, including polystyrene (PS), polyurethane (PU), silicon, rubber, and nylon were also found in the sediment sample. Fragments were the major shape with 300 items while other shapes of sheets, fibers and beads were also recorded. The advantages of MPSS are high capacity, high separation efficiency, and low-cost operation. The disadvantages of this apparatus are high pollution due to using ZnCl2, bottom stirrer is easily stuck, and uncertain efficiency with small microplastic particles (< 0.3 mm). A significant high number of microplastics in sediment environment indicates that microplastics could be a potential risk for benthic organisms and aquatic food web. Various types and shapes of plastics also suggests that macroplastics and microplastics in sediment could originate from various sources. It is said that, for the first time in Vietnam, plastic debris, particular with microplastics, can be efficiently extracted from a large amount of sediment sample (up to 1.5 kg dry sediment). These findings could be an interesting reference for researchers who may want to obtain a large amount of microplastics for further investigation of microplastic toxicology.