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Fast and manageable determination of the microplastics in the sediment

The main goal of this research was to obtain a method and approach for microplastics determination in the sediment that would take care of possible density changes due to biofouling ; that could be used independently of the different upper size limit for microplastics ; to have ease of use so that it can be applied on the expedition ship and would be inexpensive. Separation of microplastics from the sediment, based on the difference in densities is a well-known and adopted approach, due to a nominally lower density of microplastics than the density of sediment. The novelty of the proposed approach is the use of sodium polytungstate or SPT (Na6[H2W12O40]), a non-toxic compound used as a heavy liquid for gravity separation. Due to its very high solubility in water, different density can be achieved, from 1.01 g/cm3 to 3.10 g/cm3. Prior to separation procedure, samples should be treated with H2O2 (30%) to remove organic matter and with HCl (10%) to remove carbonate particles. These steps are important because shells of some organisms and similar hollow objects remain in the lighter fraction and affect a determination of microplastics later on. A sample prepared in this way is then separated in the SPT solution (density 1.60 g/cm3). Microplastics particles float on top of the SPT solution and the remaining sediment sinks to the bottom. A solution is then frozen and the light fraction is easily separated. Extracted microplastics should be washed, dried and weighted, to calculate its amount in the sample. Final determination of extracted particles and verification of the type of microplastics is done by Fourier transform infrared spectroscopy (FTIR). A determination could be done by some other methods but proposed one has an advantage when a small amount of microplastics particles is extracted, e.g. 1 mg, by making KBr pellets.

Microplastics, Sediment, SPT, FT, IR

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