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Modified Heavy Minerals Separation Procedure as a Tool in the Microplastics Analysis

Microplastics (MP) can be defined as a plastic particle of size in the range from 0.5 to 5 mm, although there is an ongoing debate on the definition and the minimum size limit (CHUBARENKO et al., 2016). Plastics are synthetic organic polymers, which are derived from the polymerization of monomers extracted from oil or gas (COLE et al., 2011), with low density, in the range between 0.8-1.4 g cm-3, as an important characteristic of MP. Sediment is one of the media where microplastics are present and therefore is regularly analyzed. Analysis of microplastics can be divided in two main processes: separation of microplastics (a) and microplastics determination (b). Both of these steps have challenges and yet there is no analytical procedure to follow but some recommendations. The most used process for microplastics separation from the sediment includes zinc chloride solution, and separation is based on different density of the microplastics and solution (LÖDER & GERDTS, 2015). Due to the toxicity of ZnCl2 solution (ERGONUL et al., 2012), in our research we modified heavy minerals separation procedure and successfully separated MP from sediment, with the chemical that can fit into the “Green Chemistry” philosophy. A known mass of homogenized and dry sediment is mixed with the sodium polytungstate or SPT (Na6[H2W12O40]) solution of adjusted density at 1.60 g cm-3. After stirring and centrifugation solution is frozen, to achieve better separation of particles with the lower density. Prior to the density separation, sediment samples are treated with the hydrogen peroxide (H2O2, 30%) to remove organic matter. This step is of great importance when biofouling is present, due to the density increase of particle of interest. One of the possible steps, depending on the mineralogy of the sample, is carbonate removal, with the hydrochloric acid (HCl, 10%). When small shells or tests are abundantly represented in the sample, this step is recommended. After MP separation is performed, particles are weighted to determine the amount of MP in sediment and ready for the further determination by an instrument of choice (HIDALGO- RUZ et al. 2012).

Microplastics, sediment, SPT, density separation

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