Preliminary investigation on effects of size, polymer type, and surface behaviour on the vertical mobility of microplastics in a porous media

Ved Prakash Ranjan; Anuja Joseph; Hari Bhakta Sharma; Sudha Goel

doi:10.1016/j.scitotenv.2022.161148

Preliminary investigation on effects of size, polymer type, and surface behaviour on the vertical mobility of microplastics in a porous media

Sci Total Environ. 2023 Mar 15:864:161148. doi: 10.1016/j.scitotenv.2022.161148. Epub 2022 Dec 23.

Authors

Ved Prakash Ranjan¹, Anuja Joseph², Hari Bhakta Sharma³, Sudha Goel⁴

Affiliations

¹ Environmental Engineering and Management, Department of Civil Engineering, Indian Institute of Technology, Kharagpur, West Bengal 721302, India. Electronic address: vedprakgpian@iitkgp.ac.in.
² School of Environmental Science and Engineering, Indian Institute of Technology, Kharagpur, West Bengal 721302, India.
³ Department of Civil Engineering, Sikkim Manipal Institute of Technology, Majitar, Rangpo, Sikkim 737136, India.
⁴ Environmental Engineering and Management, Department of Civil Engineering, Indian Institute of Technology, Kharagpur, West Bengal 721302, India.

PMID: 36572318
DOI: 10.1016/j.scitotenv.2022.161148

Abstract

Due to the ubiquitous nature of microplastic (MP), knowledge of its fate and migration in subsurface environments like soil becomes extremely important to understand underlying ecological risk. The fate and migration of MP in subterranean settings like sand are governed by the retention/transport properties influenced by the interaction of sand and MPs. In this study, sand column experiments under simulated rainfall conditions were conducted for 180 days to assess the vertical migration of mixed MPs consisting of polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET). Sand column experiments were subjected to 60 wet-dry cycles over 180 days. The effects of polymer type, microplastic size, sand particle size, and surface roughness on the migration of MPs were evaluated. Results showed that the smallest-sized fragmented PE particles had the highest migration potential compared to PET and PE. The ratios of the diameters of MP particles and sand particles (d_MP/d_sand) played a significant role in determining the penetration depth of the various sizes of MPs. The MP particles with d_MP/d_sand 0.11 showed greater penetration depth in sand media and were detected in the column effluent water after 60 days of a column run. In addition, surface roughness, low ionic strength water, irregularly shaped particles, and wet and dry cycles contributed to the migration of MPs in the sand column. Three new absorbance peaks corresponding to the hydroxyl, CO stretch, and carbonyl groups evolved in the extracted PE MPs sample from different depths, as shown by FTIR analysis, suggesting that PE MPs had been oxidised. XPS analysis revealed changes in the surface properties of the MPs, indicating that oxidation occurred at the top layer, causing structural deterioration of the PE MPs. However, oxidation of the surface bonds was restricted in the layers underneath due to a lack of oxygen. The finding of the study suggests that in a natural environment, such accumulation and migration of MPs in sandy soil can increase the possibilities to the underlying groundwater contamination.

Keywords: Microplastics pollution; Plastic waste; Porous media; Vertical migration; Wet-dry cycle.