Role of surface functionalities of nanoplastics on their transport in seawater-saturated sea sand

Zhiqiang Dong; Ling Zhu; Wen Zhang; Rui Huang; XiangWei Lv; Xinyu Jing; Zhenglong Yang; Junliang Wang; Yuping Qiu

doi:10.1016/j.envpol.2019.113177

Role of surface functionalities of nanoplastics on their transport in seawater-saturated sea sand

Environ Pollut. 2019 Dec;255(Pt 1):113177. doi: 10.1016/j.envpol.2019.113177. Epub 2019 Sep 5.

Authors

Zhiqiang Dong¹, Ling Zhu¹, Wen Zhang¹, Rui Huang², XiangWei Lv², Xinyu Jing², Zhenglong Yang³, Junliang Wang⁴, Yuping Qiu⁵

Affiliations

¹ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, China.
² State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China.
³ School of Materials Science and Engineering, Jiading Campus, Tongji University, Shanghai, 201804, China.
⁴ College of the Environment, Zhejiang University of Technology, Hangzhou, 310014, China.
⁵ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, China. Electronic address: ypqiu@tongji.edu.cn.

PMID: 31521995
DOI: 10.1016/j.envpol.2019.113177

Abstract

The transport and retention of nanoplastics (NP, 200 nm nanopolystyrene) functionalized with surface carboxyl (NPC), sulfonic (NPS), low-density amino (negatively charged, NPA^-), and high-density amino (positively charged, NPA⁺) groups in seawater-saturated sand with/without humic acid were examined to explore the role of NP surface functionalities. The mass percentages of NP recovered from the effluent (M_eff) with a salinity of 35 practical salinity units (PSU) were ranked as follows: NPC (19.69%) > NPS (16.37%) > NPA⁺ (13.33%) > NPA^- (9.78%). The homoaggregation of NPS and NPA^- was observed in seawater. The transport of NPA^- exhibited a ripening phenomenon (i.e., a decrease in the transport rate with time) due to the high attraction of NP with previously deposited NP, whereas monodispersed NPA⁺ presented a low M_eff value because of the electrostatic attraction between NPA⁺ and negatively charged sand. Retention experiments showed that the majority of NPC, NPS and NPA⁺ accumulated in a monolayer on the sand surface, whereas NPA^- accumulated in multiple layers. Suwannee River humic acid (SRHA) could remarkably improve the transportability of NPC, NPS, and NPA^- by increasing steric repulsion. The strong attraction between NPA⁺ and the deposited NPA⁺ in the presence of SRHA triggered the weak ripening phenomenon. As seawater salinity decreased from 35 PSU to 3.5 PSU, the increase in electrostatic repulsion of NP-NP and NP-sand enhanced the transport of NPC, NPS, and NPA^-, and the ripening of NPA^- breakthrough curves disappeared. In deionized water, NPC, NPS, and NPA^- achieved complete column breakthrough because the electrostatic repulsion between NP and sand intensified. However, the M_eff values of NPA⁺ in 3.5 PSU seawater and deionized water presented limited increments of 15.49% and 23.67%, respectively. These results indicated that the fate of NP in sandy marine environments were strongly affected by NP surface functionalities, seawater salinity, and coexisting SRHA.

Keywords: Humic acid; Nanoplastics; Seawater; Surface functionality; Transport.

MeSH terms

Humic Substances / analysis
Microplastics / analysis*
Nanoparticles / analysis
Polystyrenes / analysis
Salinity
Sand / chemistry*
Seawater / chemistry*
Silicon Dioxide / chemistry
Static Electricity
Water / chemistry
Water Pollutants, Chemical / analysis*

Substances

Humic Substances
Microplastics
Polystyrenes
Sand
Water Pollutants, Chemical
Water
Silicon Dioxide