Copper Adsorption to Microplastics and Natural Particles in Seawater: A Comparison of Kinetics, Isotherms, and Bioavailability

Abstract

The growing use of plastics has led to microplastics (MPs) being ubiquitously distributed in marine environments. Although previous studies have emphasized MPs as important metal-transport vectors, few have considered the differences between these anthropogenic particles and their coexisting natural counterparts in sequestering metals in seawater. Here, we compared Cu adsorption to pristine and naturally aged MPs (polystyrene and polyethylene) with that to algae particles and sediments and assessed the bioavailability of the adsorbed Cu by a gut juice extraction assay. Adsorption kinetics and isotherms consistently showed that natural particles bound far more Cu to their surfaces than MPs. The rougher surfaces, greater specific surface areas, and lower ζ-potentials of natural particles contributed to their stronger Cu adsorption capacity than pristine or aged MPs. Natural particles also contained more diverse functional groups for binding Cu, with oxygen-containing groups playing a dominant role. Adsorbed Cu on natural particles was less extractable by sipunculan gut juice than that on MPs, indicating their higher Cu affinity. Overall, our study suggests that natural particles outcompete MPs in carrying metals in the water column and transferring them to marine organisms in today’s environmental context. This work provides new insights for assessing the risks of MPs in marine environments.

A review of microplastic fibres: generation, transport, and vectors for metal(loid)s in terrestrial environments

“…Cojocariu et al (2017) 122 quantied the sorption of Pb and Cu to recycled PET bres, reporting Pb and Cu sorption to be 48.9 mg g À1 and 30.7 mg g À1 respectively. These sorption values are several orders of magnitude higher than others reported thus far in the literature, 35,36,[118][119][120] although it should be noted that a physicochemical characterisation of the PET bres was not provided in this study, so bre size and specic surface area are not known. Recently, Han et al (2021) 123 investigated the sorption of Pb, Cu and Cr onto PET microplastics of varying size fractions (<0.9 mm; 0.9-2 mm; 2-5 mm).…”

“…This was partly attributed to the increased specic surface area, and more negative zeta potentials of the aged microplastics. 120 The sorption of metals and metalloids onto microplastic surfaces is strongly inuenced by the chemical properties of the metal or metalloid and the physicochemical properties of the microplastic surfaces. 35,36,[118][119][120] Previous studies investigating metal and metalloid sorption onto microplastics have mainly focussed on microplastic types commonly found in marine environments, such as PE, PS and PVC.…”

“…120 The sorption of metals and metalloids onto microplastic surfaces is strongly inuenced by the chemical properties of the metal or metalloid and the physicochemical properties of the microplastic surfaces. 35,36,[118][119][120] Previous studies investigating metal and metalloid sorption onto microplastics have mainly focussed on microplastic types commonly found in marine environments, such as PE, PS and PVC. Data for metal and metalloid sorption onto PET microplastic surfaces are scarce in the literature in comparison with other polymer types.…”

“…Langmuir modelling of isotherm data revealed maximum sorption capacities for Cu, Ni and Zn were 16.7 μg g −1 , 10.6 μg g −1 and 12.7 μg g −1 respectively, however, the data are not reported for the virgin nylon microplastics. Chen et al (2021) 120 compared the sorption of Cu onto virgin and aged PS and PE microplastics, finding aged microplastics to have a higher sorption capacity (Table 2). This was partly attributed to the increased specific surface area, and more negative zeta potentials of the aged microplastics.…”

“…This was partly attributed to the increased specific surface area, and more negative zeta potentials of the aged microplastics. 120…”