Density Separation of Microplastics from solid sample matrices

, Schütze Berit, Thomas Daniela, Brunotte Habil Joachim.

While extent of contamination and effects of MPs in aquatic systems are under current study, terrestrial ecosystems have only recently come into focus (Rillig et al. 2012). Main sources are expected to be application of sewage sludge and compost as well as fragmentation of macroplastics in soil. As it is estimated that plastic release in terrestrial systems is 4-23 times higher than into the oceans (Horton et al. 2017), there is an urgent need to quantify contents and specify effects in soil. Definitions of microplastic as well as sample treatment methods and measurement techniques for MP analysis differ strongly within the scientific community. Consequently, previous studies calculated strongly varying concentrations of 0.34-43,000 particles/kg soil and 500 μm from soil was developed based on previously applied methods. Furthermore, tests of influence during separation of MPs were conducted by measuring surface changes with ATR-FTIR as well as changes in size of particles. Artificial substrates and compost with varying content of organic matter were tested. Four different solutions were applied in density separation to separate MPs from substrates: distilled water (ρ = 1.0 g/cm³), NaCl (ρ = 1.19 g/cm³), sodium hexametaphosphate (SHMP) (ρ = 1.30 g/cm³) and NaBr (ρ = 1.53 g/cm³). Furthermore, organic matter was removed by digestion with H2O2. Recovery rates of 87.3-100.3 % for conventional polymers (PE, PP, PVC, PET) and 38.2-78.2 % (PLA, PBS, MaterBi film) for biodegradable polymers were measured with NaBr that showed highest recovery of applied density solutions.

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