Plastic contamination of the environment is a global problem whose magnitude justifies the consideration of plastics as emergent geomaterials with chemistries not previously seen in Earth’s history. At the elemental level, plastics are predominantly carbon. The comparison of plastic stocks and fluxes to those of carbon reveals that the quantities of plastics present in some ecosystems rival the quantity of natural organic carbon and suggests that geochemists should now consider plastics in their analyses. Acknowledging plastics as geomaterials and adopting geochemical insights and methods can expedite our understanding of plastics in the Earth system. Plastics also can be used as global-scale tracers to advance Earth system science.

Trillions of plastic fragments are afloat at sea, yet they represent only 1-2% of the plastics entering the ocean annually. The fate of the missing plastic and its impact on marine life remains largely unknown. To address these unknowns, we irradiated post-consumer microplastics (polyethylene, PE; polypropylene, PP; and expanded polystyrene, EPS), standard PE, and plastic-fragments collected from the surface waters of the North Pacific Gyre under a solar simulator. We report that simulated sunlight can remove plastics from the sea surface. Simulated sunlight also fragmented, oxidized, and altered the color of the irradiated polymers. Dissolved organic carbon (DOC) is identified as a major byproduct of sunlight-driven plastic photodegradation. Rates of removal depended upon polymer chemistry with EPS degrading more rapidly than PP, and PE being the most photo-resistant polymer studied. The DOC released as most plastics photodegraded was readily utilized by marine bacteria. However, one sample of PE microplastics released organics or co-leachates that inhibited microbial growth. Thus, although sunlight may remove plastics from the ocean's surface, leachates formed during plastic photodegradation may have mixed impacts on ocean microbes and the food webs they support.

The problem of plastic and microplastic (MP, 70%) and only 14.2% in Manta trawl samples. Submersible pump sampling using a 50 µm mesh retained a higher percentage of fibers, with a two magnitude higher abundance of MPs (357 ± 119 and 553 ± 19 n/m³ for 330 µm and 50 µm mesh, respectively) attributed to the floating debris encountered during sampling and the shallower sampling depth as well as smaller sampling volume. This study highlights the key factors that impact MP abundance and characteristics as well as the challenges to harmonizing MPs sampling methods in aquatic environments, which is also helpful for data compilation across studies.

Seagrass meadows are renowned for their associated ecosystem services and carbon sequestration capacity, with microorganisms playing a crucial role. However, the invasion of microplastics may disrupt these processes. Here, we conducted a one-month in-situ incubation of three prevalent types of microplastics in the seagrass meadow of Swan Lake, China. The results showed significant differences in microbial communities between the plastisphere and natural matrices. Cyanobacteria exhibited a strong preference for polyethylene terephthalate, and microplastic shape and their contact area with water may be key factors in shaping microbial communities. Meanwhile, microplastic invasion can shift carbon- and nitrogen-fixing microbes and related genes, thereby changing seagrass meadows’ carbon and nitrogen cycles. This may impact the carbon sequestration capacity of seagrass meadows and pose potential risks of water blooms. Additionally, the potential ecological risks posed by the large number of resistance genes adsorbed by microplastics in the ecosystem are also worthy of attention.