Fate and transport of nanoplastics in complex natural aquifer media: Effect of particle size and surface functionalization

Zefeng Song; Xinyao Yang; Fangmin Chen; Fangyuan Zhao; Ying Zhao; Lili Ruan; Yinggang Wang; Yuesuo Yang

doi:10.1016/j.scitotenv.2019.03.102

Fate and transport of nanoplastics in complex natural aquifer media: Effect of particle size and surface functionalization

Sci Total Environ. 2019 Jun 15:669:120-128. doi: 10.1016/j.scitotenv.2019.03.102. Epub 2019 Mar 8.

Authors

Zefeng Song¹, Xinyao Yang², Fangmin Chen³, Fangyuan Zhao⁴, Ying Zhao⁴, Lili Ruan⁴, Yinggang Wang⁴, Yuesuo Yang⁴

Affiliations

¹ Key Lab of Eco-restoration of Regional Contaminated Environment (Shenyang University), Ministry of Education, Shenyang 110044, China; Institute of Resources and Environment, Hebei GEO University, Shijiazhuang 050031, China.
² Key Lab of Eco-restoration of Regional Contaminated Environment (Shenyang University), Ministry of Education, Shenyang 110044, China. Electronic address: yangxinyao@hotmail.com.
³ Key Lab of Eco-restoration of Regional Contaminated Environment (Shenyang University), Ministry of Education, Shenyang 110044, China; Liaoning Provincial Key Lab of Urban Integrated Pest Management and Ecological Security, Shenyang University, Shenyang 110044, China.
⁴ Key Lab of Eco-restoration of Regional Contaminated Environment (Shenyang University), Ministry of Education, Shenyang 110044, China.

PMID: 30878920
DOI: 10.1016/j.scitotenv.2019.03.102

Abstract

Environmental processes of nanoplastics in heterogeneous natural groundwater systems remain unclear. In this study, the control of particle size and surface functional groups on the fate and transport of nanoplastics in an organic matter (OM) rich aquifer was explored using batch and column tests. The carboxyl-modified 200 nm (200CNP), carboxyl-modified 50 nm (50CNP), and amino-modified 50 nm (50ANP) polystyrene latex beads were used as surrogates for nanoplastics of contrasting sizes and surface functional groups. Aquifer sand and natural groundwater sampled from an agriculture-impacted shallow sandy aquifer were processed to obtain granule beds with/out surface minerals and groundwater containing different-sized fractions of OM. Results show that particle size controlled the hetero-aggregation rate of nanoplastics with OM and Ca²⁺: a larger size resulting in a lower reaction rate led to a higher stability of 200CNP than 50CNP and 50ANP. Meanwhile, surface functional groups appeared to affect the affinity of OM and Ca²⁺ to nanoplastics, i.e. the amino group allowed the adsorption of dissolved OM on the particle but inhibited the adsorption of Ca²⁺ and suspended OM, while the carboxyl group allowed adsorption of the all. The resulting variable OM coatings formed on the different nanoplastics played a critical role in determining the particle stability and mobility, i.e. the suspended OM increased both the particle stability and mobility while the dissolved OM reduced both. These findings suggest that: 1. Depending on the OM properties, the influence of particle size and surface group on the nanoplastic processes might be secondary to the OM impact; 2. In evaluating the OM impact, not only the OM concentration but also the size and surface physiochemistry of the OM should be characterized. The insight gained is important to predict the concentration evolution pattern of weathered nanoplastics in OM-impacted sandy aquifers.

Keywords: Aggregation; Batch test; Calcium ion; Column study; Nanoplastic transport; Organic-matter-rich natural groundwater.