Formulation Controls the Potential Neuromuscular Toxicity of Polyethylene Photoproducts in Developing Zebrafish.

Sunlight transforms plastic into water-soluble products, the potential toxicity of which remains unresolved, particularly for vertebrate animals. We evaluated acute toxicity and gene expression in developing zebrafish larvae after 5 days of exposure to photoproduced (P) and dark (D) leachates from additive-free polyethylene (PE) film and consumer-grade, additive-containing, conventional, and recycled PE bags. Using a "worst-case" scenario, with plastic concentrations exceeding those found in natural waters, we observed no acute toxicity. However, at the molecular level, RNA sequencing revealed differences in the number of differentially expressed genes (DEGs) for each leachate treatment: thousands of genes (5442 P, 577 D) for the additive-free film, tens of genes for the additive-containing conventional bag (14 P, 7 D), and none for the additive-containing recycled bag. Gene ontology enrichment analyses suggested that the additive-free PE leachates disrupted neuromuscular processes via biophysical signaling; this was most pronounced for the photoproduced leachates. We suggest that the fewer DEGs elicited by the leachates from conventional PE bags (and none from recycled bags) could be due to differences in photoproduced leachate composition caused by titanium dioxide-catalyzed reactions not present in the additive-free PE. This work demonstrates that the potential toxicity of plastic photoproducts can be product formulation-specific.

Synergy between Sunlight, Titanium Dioxide, and Microbes Enhances Cellulose Diacetate Degradation in the Ocean.

Sunlight chemically transforms marine plastics into a suite of products, with formulation─the specific mixture of polymers and additives─driving rates and products. However, the effect of light-driven transformations on subsequent microbial lability is poorly understood. Here, we examined the interplay between photochemical and biological degradation of fabrics made from cellulose diacetate (CDA), a biobased polymer used commonly in consumer products. We also examined the influence of ∼1% titanium dioxide (TiO2), a common pigment and photocatalyst. We sequentially exposed CDA to simulated sunlight and native marine microbes to understand how photodegradation influences metabolic rates and pathways. Nuclear magnetic resonance spectroscopy revealed that sunlight initiated chain scission reactions, reducing CDA's average molecular weight. Natural abundance carbon isotope measurements demonstrated that chain scission ultimately yields CO2, a newly identified abiotic loss term of CDA in the environment. Measurements of fabric mass loss and enzymatic activities in seawater implied that photodegradation enhanced biodegradation by performing steps typically facilitated by cellulase. TiO2 accelerated CDA photodegradation, expediting biodegradation. Collectively, these findings (i) underline the importance of formulation in plastic's environmental fate and (ii) suggest that overlooking synergy between photochemical and biological degradation may lead to overestimates of marine plastic persistence.

The M/V X-Press Pearl Nurdle Spill: Contamination of Burnt Plastic and Unburnt Nurdles along Sri Lanka's Beaches.

In May 2021, the M/V X-Press Pearl cargo ship caught fire 18 km off the west coast of Sri Lanka and spilled ∼1680 tons of spherical pieces of plastic or "nurdles" (∼5 mm; white in color). Nurdles are the preproduction plastic used to manufacture a wide range of end products. Exposure to combustion, heat, and chemicals led to agglomeration, fragmentation, charring, and chemical modification of the plastic, creating an unprecedented complex spill of visibly burnt plastic and unburnt nurdles. These pieces span a continuum of colors, shapes, sizes, and densities with high variability that could impact cleanup efforts, alter transport in the ocean, and potentially affect wildlife. Visibly burnt plastic was 3-fold more chemically complex than visibly unburnt nurdles. This added chemical complexity included combustion-derived polycyclic aromatic hydrocarbons. A portion of the burnt material contained petroleum-derived biomarkers, indicating that it encountered some fossil-fuel products during the spill. The findings of this research highlight the added complexity caused by the fire and subsequent burning of plastic for cleanup operations, monitoring, and damage assessment and provides recommendations to further understand and combat the impacts of this and future spills.

Plastic Formulation is an Emerging Control of Its Photochemical Fate in the Ocean.

Sunlight exposure is a control of long-term plastic fate in the environment that converts plastic into oxygenated products spanning the polymer, dissolved, and gas phases. However, our understanding of how plastic formulation influences the amount and composition of these photoproducts remains incomplete. Here, we characterized the initial formulations and resulting dissolved photoproducts of four single-use consumer polyethylene (PE) bags from major retailers and one pure PE film. Consumer PE bags contained 15-36% inorganic additives, primarily calcium carbonate (13-34%) and titanium dioxide (TiO2; 1-2%). Sunlight exposure consistently increased production of dissolved organic carbon (DOC) relative to leaching in the dark (3- to 80-fold). All consumer PE bags produced more DOC during sunlight exposure than the pure PE (1.2- to 2.0-fold). The DOC leached after sunlight exposure increasingly reflected the 13C and 14C isotopic composition of the plastic. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that sunlight exposure substantially increased the number of DOC formulas detected (1.1- to 50-fold). TiO2-containing bags photochemically degraded into the most compositionally similar DOC, with 68-94% of photoproduced formulas in common with at least one other TiO2-containing bag. Conversely, only 28% of photoproduced formulas from the pure PE were detected in photoproduced DOC from the consumer PE. Overall, these findings suggest that plastic formulation, especially TiO2, plays a determining role in the amount and composition of DOC generated by sunlight. Consequently, studies on pure, unweathered polymers may not accurately represent the fates and impacts of the plastics entering the ocean.

Advances in offline approaches for trace measurements of complex organic compound mixtures via soft ionization and high-resolution tandem mass spectrometry.

Complex airborne mixtures of organic compounds can contain 10,000's of diverse compounds at trace concentrations. Here, we incorporate high-resolution mass spectrometry into our integrated offline sampling-to-analysis measurement system for routine molecular-level speciation of complex mixtures in gas- or particle-phase samples with detection limits of 2-20 pg L-1 (i.e. 0.2-1.9 ppt in 6 L samples). Analytes desorbed from custom adsorbent tubes (or filter extracts) were separated via gas chromatography (GC) and simultaneously analyzed by an electron ionization quadrupole mass spectrometer (EI-MS), and by atmospheric pressure chemical ionization (APCI) combined with a high-resolution quadrupole time-of-flight mass spectrometer (Q-TOF) with a resolution of 25,000-40,000 M/ΔM in HR-TOF and MS/MS modes. We demonstrated our system with simple standards, a Macondo crude oil standard as a reference for complex mixtures of common airborne compounds, and ambient samples using GC-TOF and GC-MS/MS. We speciated complex mixtures at mass accuracy error (i.e. mass tolerance) down to 8 ± 2 ppm (e.g. resolving analytes of mass 270.000 u with 0.003 u accuracy) using a targeted approach with 3000 molecular formulas, including hydrocarbons and functionalized analytes containing oxygen, sulfur, nitrogen, or phosphorous. This extended from compounds with 10 to 32 carbon atoms and up to 16 hydrocarbon formulas per carbon number, and a similar range for functionalized compound classes. We also demonstrated our MS/MS capabilities to differentiate structural isomers and determine the presence of specific functional groups; and our direct-TOF capability, which bypasses high-temperature chromatographic separation to preserve functionalized analytes.