5 Quantifying microplastics in beach sand and river sediment using thermal analytical methods

Microplastics are emerging contaminants that have gained significance in the recent years. To understand the generation, transport, and transformation of microplastics in the environment, it is important to be able to identify plastics by their type and quantify their levels in environmental matrices. This study reviewed existing thermal analytical techniques employed in microplastics research and discussed their advantages and limitations. As a case study, we examined microplastics in beach sand and river sediment samples collected at two locations in Massachusetts, USA using pyrolysis-gas chromatography- mass spectrometry (PY-GC-MS). Multiple-step pretreatment processing based on size fractionation, density separation, wet peroxide oxidation, and solvent extraction was necessary to remove inorganic constituents and natural organic matter in samples prior to PY-GC-MS analysis. Pretreatment sequence was optimized separately for beach sand and river sediment as the latter carried very high levels of plant debris and organic matter. PET was identified in the fine fraction (< 100 μm) of the beach sand at 8.1 mg/kg and it was not detected in the medium size fraction (100 μm - 1.2 mm). This suggests the degradation of macro-plastics on beach due to UV exposure and mechanical abrasion caused by water and sand. For the river sediment sample, PET was detected in both the fine and medium fractions and the mass concentrations were on the order of 1 mg/kg. PP was also detected in both fractions of the river sediment at 0.1 - 0.3 mg/kg. The results validate the ability of PY-GC-MS in conjunction with appropriate pretreatments to quantitatively analyze low levels of microplastics in the coastal and terrestrial environments.