Fate of nanoplastics in the environment: Implication of the cigarette butts

Highlights

• The nanoplastic sorption by cigarette filters was evaluated in pure and freshwater.

• The sorption was addressed for nanoplastics of various morphologies and dispersity.

• A kinetic approach gives cigarette filters partition coefficient within 10²-10⁴.

Abstract

Fate, transport and accumulation of nanoplastics have attracted considerable attention in the past few years. While actual researches have been focused on nanoplastics dispersed or aggregated in different environmental system, no study have been focused on the possibility that nanoplastics are co-transported with other natural or anthropogenic materials. Therefore, the large quantity of debris released in the environment, such as cigarette butts (CGB), could be part of the nanoplastics fate and behavior. Here we show the considerable sorption capacities of cigarette filters for nanoplastics. To address this topic, we chose polystyrene-based nanoplastics with similar state of charge (according to the physico-chemical characteristic of the zeta potential −45 to −40 mV) but with different sizes (50–800 nm) and morphologies. A kinetic approach to sorption in fresh water (pH = 8.05; 179.5 μS cm⁻¹) at room temperature was carried out by means of the flow field flow analysis method (AF4) to determine the partition coefficients and water sampling rates between nanoplastics and cigarette butts. Using different models of, more or less environmentally relevant, nanoplastics (NPTs) and adequate analytical strategies, we found partition coefficients between the NPTs and CGBs ranged from 10² to 10⁴ in freshwater conditions. We demonstrated that the physical features of the NPTs (size and morphology) have an influence on the sorption behaviour. Asymmetrical shaped NPTs with broader size distribution seems to be mostly retained in the CGBs after longer equilibration time. This result shows the importance of the NPTs features on the mechanisms governing their transfer and fate in the environment through environmental matrices, especially when other materials are involved. We anticipate our work to be a starting point for investigating the co-transport of NPTs with other materials present in the environment (natural and anthropogenic).

Introduction

Plastic pollution has attracted considerable attention from the public sector in recent years. While a large majority of the relevant research has been performed on microsized plastic particles, only a few groups of researchers focused their work on nanoscale plastics (Li et al., 2020; Shen et al., 2019; Wagner and Reemtsma, 2019). It was now admitted that the fragmentation of plastic particles releases a considerable number of nanoplastics (NPTs) (Gigault et al., 2016; Hartmann et al., 2019; Lambert and Wagner, 2016a, 2016b). Similar to other classic nanoparticles, NPTs may interact with various species, whether naturally present or (un)intentionally released within the environment. These interactions can enhance NPT transport through different natural interfaces (soil-freshwater-estuarine system-ocean) or promote their accumulation in specific areas (Alimi et al., 2018; da Costa et al., 2016; Dong et al., 2019).

Among all the types of debris found in the environment, cigarette butts (CGBs) are one of the most predominant, and worldwide cigarette consumption is estimated to reach approximately 9 trillion by 2025 (Araújo and Costa, 2019; Mackay et al., 2002). It is estimated that more than 750 000 metric tons of CGBs end up as litter worldwide per year, which corresponds to approximately 4.5 10¹² CGB units released into our environment each year (Novotny and Slaughter, 2014). Because CGBs are composed of cellulose acetate, they can interact with several organic and metallic pollutants in the environment (Chevalier et al., 2018). Pu et al. recently demonstrated that CGB based-materials act as a powerful Uranium sorbent (106 mg g⁻¹) (Pu et al., 2019). In air, CGBs were demonstrated to sorb and release particles with different size distribution (Hengstberger and Stark, 2009). In aqueous media, due to the large quantity of CGBs and nanoplastics released, co-transport of NPTs and other contaminants with CGBs have to be investigated for environmental and health perspectives. Indeed, NPT-CGB interaction and synergy could complicate the fate and impact of both of these emergent pollutants, whose behaviour is already challenging.

The main objective of this work is to investigate the sorption capacities of NPTs on cigarette filters to evaluate the general problem of the co-transport possibility of these nanoplastics in the environment. In this work, different kinds of nanoplastics were chosen. The first type of NPTs tested is the one commonly used in environmental studies on the impacts of NPTs on aquatic organisms and the transfer and environmental fate of NPTs. These NPTs are monodisperse and spherical (Pessoni et al., 2019). On the other hand, the second type of NPTs was chosen to be anisotropic and was obtained by mechanical fragmentation as described elsewhere (Davranche et al., 2019; El Hadri et al., 2020; Gillibert et al., 2019). Both of these NPT series are identical in terms of chemical composition (polystyrene base) and have similar surface functionality, as revealed by their similar values of the zeta-potential physico-chemical parameter. A kinetic approach to analyze NPT sorption on unused cigarette filters was performed, the partition coefficients and mass transfer coefficients in fresh water have been evaluated.