Weathering Plastics as a Planetary Boundary Threat: Exposure, Fate, and Hazards

Abstract

We described in 2017 how weathering plastic litter in the marine environment fulfils two of three criteria to impose a planetary boundary threat related to "chemical pollution and the release of novel entities": (1) planetary-scale exposure, which (2) is not readily reversible. Whether marine plastics meet the third criterion, (3) eliciting a disruptive impact on vital earth system processes, was uncertain. Since then, several important discoveries have been made to motivate a re-evaluation. A key issue is if weathering macroplastics, microplastics, nanoplastics, and their leachates have an inherently higher potential to elicit adverse effects than natural particles of the same size. We summarize novel findings related to weathering plastic in the context of the planetary boundary threat criteria that demonstrate (1) increasing exposure, (2) fate processes leading to poorly reversible pollution, and (3) (eco)toxicological hazards and their thresholds. We provide evidence that the third criterion could be fulfilled for weathering plastics in sensitive environments and therefore conclude that weathering plastics pose a planetary boundary threat. We suggest future research priorities to better understand (eco)toxicological hazards modulated by increasing exposure and continuous weathering processes, to better parametrize the planetary boundary threshold for plastic pollution.

Environmental hazard of polypropylene microplastics from disposable medical masks: acute toxicity towards Daphnia magna and current knowledge on other polypropylene microplastics

“…Similar to other plastic items, once medical masks are disposed of into the natural environment, they undergo weathering processes, including ultraviolet radiation, temperature fluctuations, increased humidity, biodegradation, physical abrasion and chemical oxidation. Weathering affects the physicochemical properties of plastics, and eventually leads to their fragmentation into microplastics and nanoplastics [ 15 – 19 ]. The degradation of plastics is highly dependent on the polymer type and any chemical additives [ 20 , 21 ].…”

Locomotor behavior of Neocaridina palmata: a study with leachates from UV-weathered microplastics

“… Sarker et al (2020) observed that long-term environmental weathering reduced the toxicity of a high-density PE bag and PVC matting towards a marine microbe. A comparatively lower hazard can result from aged plastics taken from the environment because the release of chemicals already occurs during the aquatic lifetime ( Gardon et al, 2020 ; Arp et al, 2021 ). In contrast, Luo et al (2020) has shown that aged MPs (<500 µm PE that includes chrome yellow) caused an inhibition in algal cells because a comparably higher amount of chromium and lead was released.…”

“…As already described by Bridson et al (2021) and discussed here, the adverse effects of plastic leachates are not under debate. However, the extent to which hazardous chemicals are released due to weathering and affect aquatic organisms is of specific concern ( Arp et al, 2021 ).…”

“…Therefore, harmful compounds associated with plastics must be identified and removed entirely from the production process. To begin with, manufacturers could disclose and reduce the chemicals used in plastics ( Gardon et al, 2020 ), especially because weathered plastics release chemicals into the aquatic environment of yet unknown impacts on aquatic biota ( Arp et al, 2021 ).…”

“…Plastic chemicals have also been detected in rivers ( e.g ., organophosphates, phthalates and bisphenols) and some of them even exceeded the Environmental Quality Standards (EQS) as the maximum allowable concentration of defined substances in surface waters ( Schmidt et al, 2019 , 2020 ; Bolívar-Subirats et al, 2021 ). Besides, degradation products formed due to weathering processes ( e.g ., UV irradiation and hydrolysis) are often overlooked, but display an emerging chemical fraction once plastics enter the aquatic environment ( Arp et al, 2021 ).…”