The role of crystallinity and particle morphology on the sorption of dibutyl phthalate on polyethylene microplastics: Implications for the behavior of phthalate plastic additives

Shi Yao,Huihui Cao,Hans Peter H Arp,Jia Li,Yongrong Bian,Zubin Xie,Francesco Cherubini,Xin Jiang,Yang Song

doi:10.1016/j.envpol.2021.117393

Abstract

The sorption behavior of phthalate additives in plastic and microplastic litter is an important process controlling the exposure, net health risk and ecotoxicity of these co-occurring pollutants. Plastic crystallinity and particle morphology are hypothesized to be important variables for microplastics sorption behavior, but to date there have been few direct studies to explicitly test for the influence of these parameters. To address this, in this study we explored the sorption of dibutyl phthalate (DBP) as a probe molecule to diverse polyethylene microplastics including irregularly-shaped pure polyethylene microplastics (IPPM), black plastic film microplastics (BPFM), white plastic film microplastics (WPFM), and commercial microspheres (CM), which had crystallinities ranging from 17 to 99%. Sorption kinetics for all materials could be well represented with both a pseudo-first-order (R2 = 0.87–0.93) and pseudo-second-order model (R2 = 0.87–0.93). Further, sorption was highly linear in the concentration range of 0.5–10 mg L−1, with no greater performance from a linear sorption model (R2 = 0.96–0.99) than the non-linear Freundlich or Temkin sorption models. The partition coefficient (Kd) of DBP sorption onto IPPM, BPFM, WPFM and CMs were 1974.55 L kg−1, 1483.85 L kg−1, 1477.45 L kg−1 and 509.37 L kg−1, respectively, showing a significant decrease with increasing crystallinity (r2 = 0.98). The particle size of microplastics (27–1000 μm) is, however, an indecisive factor affecting their sorption behavior for DBP in this study. This study provides new insight that crystallinity plays a governing role on the sorption of phthalate from microplastic. This should be considered in future exposure studies and assessments of phthalates from plastics and microplastics.

Highlights

The ubiquity of plastic in daily life has led to some to call this age the "Plastic-age” (Shen et al, 2019)
The surfaces of the commercial microspheres (CM) were relatively smooth compared with the irregularly-shaped pure polyethylene microplastics (IPPM), white plastic film microplastics (WPFM) and black plastic film microplastics (BPFM) samples
The particle size of PE microplastics is an indecisive factor affecting their sorption for dibutyl phthalate (DBP), but the morphology and the crystallinity of PE microplastics is important in determining their sorption capacities

Summary

Introduction

The ubiquity of plastic in daily life has led to some to call this age the "Plastic-age” (Shen et al, 2019). There is a current focus on how the plastic-age has led to ecological and environmental threats to the earth, such as from emissions of microplastics (Thompson et al, 2004) or harmful plastic additives (Gong and Xie, 2020). It is estimated that about 900,000 tons of microplastics enter the terrestrial environment each year (Horton et al, 2017). Microplastics have been widely distributed due to their small size and fast migration (Gong and Xie, 2020). Fresh water, air and soil environments all contain quantifiable levels of microplastic, with commonly occurring plastic types being polyethylene (PE),

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