Comparison of different salt solutions for density separation of conventional and biodegradable microplastic from solid sample matrices

Abstract

Microplastics are the new emerging pollutants ubiquitously detectable in aquatic and terrestrial ecosystems. Fate and behavior, as well as ecotoxicity, are of increasing environmental concern, particularly in sediments and soils as natural sinks. For a global environmental risk assessment, reliable and easy to apply analytical methods are mandatory to obtain comparable data. This is based on the isolation of microplastics out of the solid sample matrices prior to instrumental detection. Thus, this study provides an easy to apply approach for density separation. The technique emerged from a comparative study using different salt solutions to isolate conventional, and for the first time biodegradable, microplastics from different solid sample matrices, i.e., sand, artificial soil, and compost. Four solutions (water, sodium chloride, sodium hexametaphosphate, and sodium bromide) of different densities were applied followed by oxidizing digestion. Finally, the impact of the procedures on size and surface properties of microplastics was tested. Dependent on the sample matrix, the highest recovery rates of 87.3–100.3% for conventional polymers, and 38.2–78.2% for biodegradable polymers, were determined with sodium bromide. It could be shown that the type of solid sample matrix influences the recovery rates and has to be considered when choosing a sample preparation technique. Graphical abstract

Characterizing the Microplastic Content of Biosolids in Southern Ontario, Canada

“…Digestions were performed on shaker tables set to 175 revolutions/min in a fume hood for 24 h. Samples were then returned to a drying oven set to 65 °C to remove residual H 2 O 2 . Samples were rehydrated with 100 mL of 905 g NaBr/L H 2 O (ρ = 1.53 g/cm 3 ), and a stir bar was added to each beaker (Radford et al, 2021;Schutze et al, 2022). Sodium bromide was used over other common salt solutions (NaCl, ZnCl 2 ) because of its ability to separate out higher-density plastics such as polyester (ρ = 1.24-1.40 g/cm 3 ) and polyvinyl chloride (ρ = 1.29-1.44 g/cm 3 ; Radford et al, 2021).…”

The Abundance of Microplastics in Sediment Siak River Pekanbaru City

“…The dried sediment was then pulverized using a mortar and pestle. Furthermore, the density separation stage by mixing a saturated NaCl solution as much as 3 times the weight of the sediment into the sediment, then stirring for 2 minutes (Rani et al, 2023;Schütze et al, 2022). After stirring the sediment sample bath is allowed to stand for 1 hour, the light plastic will separate and will be at the top.…”

Assessing the efficiency of microplastics extraction methods for tropical beach sediments and matrix preparation for experimental controls

“…Saturated NaCl solution was used as the density separation solution as it is a more economical and practical approach; higher density solutions are usually expensive and are not cost-efficient for the sole purpose of preparing 'clean' beach sediments. On the other hand, Method 2 involved subjecting the beach sediments in aluminum pans to a furnace at 550°C for 4 h (Schütze et al, 2022). Lastly, Method 3 employed a density separation method using saturated NaCl (single extraction) followed by subjecting the beach sediments to a furnace at 550°C for 4 hours (Shim et al, 2016), as shown in Figure 2.…”

“…However, obtaining a reference material in the form of 'clean' beach sediments is very difficult and not commercially plausible (Silva et al, 2018;Cadiou et al, 2020). While some studies have employed their own protocol for 'cleaning' beach sediments (Shim et al, 2016;Bridson et al, 2020;Schütze et al, 2022), no controlled comparisons have yet been made that can inform future harmonization efforts. Thus, there is a need to optimize towards an efficient method for removing plastic contamination in beach sediments.…”