Environmental plastics in the context of UV radiation, climate change, and the Montreal Protocol.

There are close links between solar UV radiation, climate change, and plastic pollution. UV-driven weathering is a key process leading to the degradation of plastics in the environment but also the formation of potentially harmful plastic fragments such as micro- and nanoplastic particles. Estimates of the environmental persistence of plastic pollution, and the formation of fragments, will need to take in account plastic dispersal around the globe, as well as projected UV radiation levels and climate change factors.

Plastics in the environment in the context of UV radiation, climate change and the Montreal Protocol: UNEP Environmental Effects Assessment Panel, Update 2023.

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) considers the interactive effects of solar UV radiation, global warming, and other weathering factors on plastics. The Assessment illustrates the significance of solar UV radiation in decreasing the durability of plastic materials, degradation of plastic debris, formation of micro- and nanoplastic particles and accompanying leaching of potential toxic compounds. Micro- and nanoplastics have been found in all ecosystems, the atmosphere, and in humans. While the potential biological risks are not yet well-established, the widespread and increasing occurrence of plastic pollution is reason for continuing research and monitoring. Plastic debris persists after its intended life in soils, water bodies and the atmosphere as well as in living organisms. To counteract accumulation of plastics in the environment, the lifetime of novel plastics or plastic alternatives should better match the functional life of products, with eventual breakdown releasing harmless substances to the environment.

The success of the Montreal Protocol in mitigating interactive effects of stratospheric ozone depletion and climate change on the environment.

The Montreal Protocol and its Amendments have been highly effective in protecting the stratospheric ozone layer, preventing global increases in solar ultraviolet-B radiation (UV-B; 280-315 nm) at Earth's surface, and reducing global warming. While ongoing and projected changes in UV-B radiation and climate still pose a threat to human health, food security, air and water quality, terrestrial and aquatic ecosystems, and construction materials and fabrics, the Montreal Protocol continues to play a critical role in protecting Earth's inhabitants and ecosystems by addressing many of the United Nations Sustainable Development Goals.

Roles of Silver-Chloride Complexations in Sunlight-Driven Formation of Silver Nanoparticles.

In aerobic natural surface water, a silver ion (Ag+) exists in various Ag+-Cl- complexes because of a strong affinity for a chloride ion (Cl-); however, little information is available about the role of the Ag+-Cl- complex in the formation of silver nanoparticles (AgNPs). This study demonstrates that soluble AgClx(x-1)- species act as a precursor of AgNPs under simulated sunlight irradiation. The AgNP photoproduction increases with Cl- levels up to 0.0025 M ([Ag+] = 5 × 10-7 M) and decreases with continued Cl- level increase (0.09 to 0.5 M). At [Cl-] ≤ 0.0025 M (freshwater systems), photoproduction of AgNP correlates with the formation of AgCl(aq), suggesting that it is the most photoactive species in those systems. Matching the ionic strength of experiments containing various Cl- levels indicates that the trend in AgNP photoproduction correlates with Cl- concentrations rather than ionic strength-induced effects. The photoproduction of AgNPs is highly pH-dependent, especially at pH > 8.3. The UV and visible light portions of the solar light spectrum are equally important in photoreduction of Ag+. Overall, we show evidence that AgClx(x-1)- species irradiated under sunlight conditions contributes to the formation of nanosized silver (Ag) in the environment.

Modeling framework for simulating concentrations of solute chemicals, nanoparticles, and solids in surface waters and sediments: WASP8 Advanced Toxicant Module.

Toxicant concentrations in surface waters are of environmental concern due to their potential impacts to humans and wildlife. Numerical models provide system insight, support management decisions, and provide scenario testing on the impacts of toxicants. The Water Quality Analysis Simulation Program (WASP) is a widely used framework for developing site-specific models for simulating toxicant concentrations in surface waters and sediments over a range of complexities and temporal and spatial scales. WASP8, with the Advanced Toxicant module, has been recently released, incorporating a complete architecture redesign for an increased number of state variables and different state variable types. WASP8 incorporates a new structure for simulating light intensity and photoreactions in the water column, including the distinction of 10 different wavelength bands, and nanoparticle heteroaggregation to solids. We present a hypothetical case study, using the Cape Fear River, North Carolina as a representative example for simulating solute chemicals, nanoparticles, and solids to demonstrate the new and updated capabilities of WASP8.

Biological Weighting Functions for Evaluating the Role of Sunlight-Induced Inactivation of Coliphages at Selected Beaches and Nearby Tributaries.

Coliphages can indicate contamination of recreational waters and previous studies show that sunlight is important in altering densities of coliphages, other indicator microorganisms, and pathogens in aquatic environments. Here, we report on laboratory studies of light-induced inactivation of two coliphage groups-male-specific (F+) and somatic coliphage-under various conditions in phosphate-buffered water (PBW). Strains isolated from wastewater treatment facilities and laboratory strains (MS2 and phiX174 coliphages) were evaluated. Inactivation rates were determined in a series of irradiations using simulated solar radiation passed through light filters that blocked different parts of the ultraviolet spectral region. Inactivation rates and spectral irradiance from these experiments were then analyzed to develop biological weighting functions (BWFs) for the light-induced inactivation. BWFs were used to model the inactivation of coliphages over a range of conditions in aquatic environments that included two beach sites in Lake Michigan and one in Lake Erie. For example, modeled effects of sunlight attenuation, using UV absorption data from the three Great Lakes beach sites, inferred that direct photoinactivation rate constants, averaged over a one-meter water column in swimmable areas, were reduced 2- to 5-fold, compared to near-surface rate constants.

Using Integrated Environmental Modeling to Assess Sources of Microbial Contamination in Mixed-Use Watersheds.

Microbial fate and transport in watersheds should include a microbial source apportionment analysis that estimates the importance of each source, relative to each other and in combination, by capturing their impacts spatially and temporally under various scenarios. A loosely configured software infrastructure was used in microbial source-to-receptor modeling by focusing on animal- and human-impacted mixed-use watersheds. Components include data collection software, a microbial source module that determines loading rates from different sources, a watershed model, an inverse model for calibrating flows and microbial densities, tabular and graphical viewers, software to convert output to different formats, and a model for calculating risk from pathogen exposure. The system automates, as much as possible, the manual process of accessing and retrieving data and completes input data files of the models. The workflow considers land-applied manure from domestic animals on undeveloped areas; direct shedding (excretion) on undeveloped lands by domestic animals and wildlife; pastureland, cropland, forest, and urban or engineered areas; sources that directly release to streams from leaking septic systems; and shedding by domestic animals directly to streams. The infrastructure also considers point sources from regulated discharges. An application is presented on a real-world watershed and helps answer questions such as: What are the major microbial sources? What practices contribute to contamination at the receptor location? What land-use types influence contamination at the receptor location? and Under what conditions do these sources manifest themselves? This research aims to improve our understanding of processes related to pathogen and indicator dynamics in mixed-use watershed systems.

Capturing Microbial Sources Distributed in a Mixed-use Watershed within an Integrated Environmental Modeling Workflow.

Many watershed models simulate overland and instream microbial fate and transport, but few provide loading rates on land surfaces and point sources to the waterbody network. This paper describes the underlying equations for microbial loading rates associated with 1) land-applied manure on undeveloped areas from domestic animals; 2) direct shedding (excretion) on undeveloped lands by domestic animals and wildlife; 3) urban or engineered areas; and 4) point sources that directly discharge to streams from septic systems and shedding by domestic animals. A microbial source module, which houses these formulations, is part of a workflow containing multiple models and databases that form a loosely configured modeling infrastructure which supports watershed-scale microbial source-to-receptor modeling by focusing on animal- and human-impacted catchments. A hypothetical application - accessing, retrieving, and using real-world data - demonstrates how the infrastructure can automate many of the manual steps associated with a standard watershed assessment, culminating in calibrated flow and microbial densities at the watershed's pour point.

A comprehensive framework for evaluating the environmental health and safety implications of engineered nanomaterials.

Engineered nanomaterials (ENM) are a growing aspect of the global economy, and their safe and sustainable development, use, and eventual disposal requires the capability to forecast and avoid potential problems. This review provides a framework to evaluate the health and safety implications of ENM releases into the environment, including purposeful releases such as for antimicrobial sprays or nano-enabled pesticides, and inadvertent releases as a consequence of other intended applications. Considerations encompass product life cycles, environmental media, exposed populations, and possible adverse outcomes. This framework is presented as a series of compartmental flow diagrams that serve as a basis to help derive future quantitative predictive models, guide research, and support development of tools for making risk-based decisions. After use, ENM are not expected to remain in their original form due to reactivity and/or propensity for hetero-agglomeration in environmental media. Therefore, emphasis is placed on characterizing ENM as they occur in environmental or biological matrices. In addition, predicting the activity of ENM in the environment is difficult due to the multiple dynamic interactions between the physical/chemical aspects of ENM and similarly complex environmental conditions. Others have proposed the use of simple predictive functional assays as an intermediate step to address the challenge of using physical/chemical properties to predict environmental fate and behavior of ENM. The nodes and interactions of the framework presented here reflect phase transitions that could be targets for development of such assays to estimate kinetic reaction rates and simplify model predictions. Application, refinement, and demonstration of this framework, along with an associated knowledgebase that includes targeted functional assay data, will allow better de novo predictions of potential exposures and adverse outcomes.

NanoRelease: Pilot interlaboratory comparison of a weathering protocol applied to resilient and labile polymers with and without embedded carbon nanotubes.

A major use of multi-walled carbon nanotubes (MWCNTs) is as functional fillers embedded in a solid matrix, such as plastics or coatings. Weathering and abrasion of the solid matrix during use can lead to environmental releases of the MWCNTs. Here we focus on a protocol to identify and quantify the primary release induced by weathering, and assess reproducibility, transferability, and sensitivity towards different materials and uses. We prepared 132 specimens of two polymer-MWCNT composites containing the same grade of MWCNTs used in earlier OECD hazard assessments but without UV stabilizer. We report on a pilot inter-laboratory comparison (ILC) with four labs (two US and two EU) aging by UV and rain, then shipping for analysis. Two labs (one US and one EU) conducted the release sampling and analysis by Transmission Electron Microscopy (TEM), Inductively Coupled Plasma- Mass Spectrometry (ICP-MS), UltravioleteVisible Spectroscopy (UVeVis), Analytical Ultracentrifugation (AUC), and Asymmetric Flow Field Flow Fractionation (AF4). We compare results between aging labs, between analysis labs and between materials. Surprisingly, we found quantitative agreement between analysis labs for TEM, ICP-MS, UVeVis; low variation between aging labs by all methods; and consistent rankings of release between TEM, ICP-MS, UVeVis, AUC. Significant disagreement was related primarily to differences in aging, but even these cases remained within a factor of two.

Phototransformation-Induced Aggregation of Functionalized Single-Walled Carbon Nanotubes: The Importance of Amorphous Carbon.

Single-walled carbon nanotubes (SWCNTs) with proper functionalization are desirable for applications that require dispersion in aqueous and biological environments, and functionalized SWCNTs also serve as building blocks for conjugation with specific molecules in these applications. In this study, we examined the phototransformation of carboxylated SWCNTs and associated amorphous carbon impurities in the presence or absence of H2O2 under simulated sunlight conditions. We found that while carboxylated SWCNTs were rather unreactive with respect to direct solar photolysis, they photoreacted in the presence of H2O2, forming CO2 and strongly aggregated SWCNT products that precipitated. Photoreaction caused SWCNTs to lose oxygen-containing functionalities, and interestingly, the resulting photoproducts had spectral characteristics similar to those of parent carboxylated SWCNTs whose amorphous carbon was removed by base washing. These results indicated that photoreaction of the amorphous carbon was likely involved. The removal of amorphous carbon after indirect photoreaction was confirmed with thermogravimetric analysis (TGA). Further studies using carboxylated SWCNTs with and without base washing indicate that amorphous carbon reduced the extent of aggregation caused by photoreaction. The second-order rate constant for carboxylated SWCNTs reacting with (•)OH was estimated to be in the range of 1.7-3.8 × 10(9) MC(-1) s(-1). The modeled phototransformation half-lives fall in the range of 2.8-280 days in typical sunlit freshwaters. Our study indicates that photosensitized reactions involving (•)OH may be a transformation and removal pathway of functionalized SWCNTs in the aquatic environment, and that the residual amorphous carbon associated with SWCNTs plays a role in SWCNT stabilization.

Effects of stratospheric ozone depletion, solar UV radiation, and climate change on biogeochemical cycling: interactions and feedbacks.

Climate change modulates the effects of solar UV radiation on biogeochemical cycles in terrestrial and aquatic ecosystems, particularly for carbon cycling, resulting in UV-mediated positive or negative feedbacks on climate. Possible positive feedbacks discussed in this assessment include: (i) enhanced UV-induced mineralisation of above ground litter due to aridification; (ii) enhanced UV-induced mineralisation of photoreactive dissolved organic matter (DOM) in aquatic ecosystems due to changes in continental runoff and ice melting; (iii) reduced efficiency of the biological pump due to UV-induced bleaching of coloured dissolved organic matter (CDOM) in stratified aquatic ecosystems, where CDOM protects phytoplankton from the damaging solar UV-B radiation. Mineralisation of organic matter results in the production and release of CO2, whereas the biological pump is the main biological process for CO2 removal by aquatic ecosystems. This paper also assesses the interactive effects of solar UV radiation and climate change on the biogeochemical cycling of aerosols and trace gases other than CO2, as well as of chemical and biological contaminants. Interacting effects of solar UV radiation and climate change on biogeochemical cycles are particularly pronounced at terrestrial-aquatic interfaces.

Probing Photosensitization by Functionalized Carbon Nanotubes.

Carbon nanotubes (CNTs) photosensitize the production of reactive oxygen species that may damage organisms by biomembrane oxidation or mediate environmental transformations of CNTs. Photosensitization by derivatized carbon nanotubes from various synthetic methods, and thus with different intrinsic characteristics (e.g., diameter and electronic properties), has been investigated under environmentally relevant aquatic conditions. We used the CNT-sensitized photoisomerization of sorbic acid ((2E,4E)-hexa-2,4-dienoic acid) and singlet oxygen formation to quantify the triplet states ((3)CNT*) formed upon irradiation of selected single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs). The CNTs used in our studies were derivatized by carboxyl groups to facilitate their dispersion in water. Results indicate that high-defect-density (thus well-stabilized), small-diameter, and semiconducting-rich CNTs have higher-measured excited triplet state formation and therefore singlet oxygen ((1)O2) yield. Derivatized SWCNTs were significantly more photoreactive than derivatized MWCNTs. Moreover, addition of sodium chloride resulted in increased aggregation and small increases in (1)O2 production of CNTs. The most photoreactive CNTs exhibited comparable photoreactivity (in terms of (3)CNT* formation and (1)O2 yield) to reference natural organic matter (NOM) under sunlight irradiation with the same mass-based concentration. Selected reference NOM could therefore be useful in evaluating environmental photoreactivity or intended antibacterial applications of CNTs.

Photochemical transformation of graphene oxide in sunlight.

Graphene oxide (GO) is promising in scalable production and has useful properties that include semiconducting behavior, catalytic reactivity, and aqueous dispersibility. In this study, we investigated the photochemical fate of GO under environmentally relevant sunlight conditions. The results indicate that GO readily photoreacts under simulated sunlight with the potential involvement of electron-hole pair creation. GO was shown to photodisproportionate to CO2, reduced materials similar to reduced GO (rGO) that are fragmented compared to the starting material, and low molecular-weight (LMW) species. Kinetic studies show that the rate of the initially rapid photoreaction of GO is insensitive to the dissolved oxygen content. In contrast, at longer time points (>10 h), the presence of dissolved oxygen led to a greater production of CO2 than the same GO material under N2-saturated conditions. Regardless, the rGO species themselves persist after extended irradiation equivalent to 2 months in natural sunlight, even in the presence of dissolved oxygen. Overall, our findings indicate that GO phototransforms rapidly under sunlight exposure, resulting in chemically reduced and persistent photoproducts that are likely to exhibit transport and toxic properties unique from parent GO.

Photoreactivity of unfunctionalized single-wall carbon nanotubes involving hydroxyl radical: chiral dependency and surface coating effect.

Single-wall carbon nanotubes (SWCNTs) have a variety of potential and demonstrated applications, and their production rates are increasing rapidly. This increase in production has motivated research on their transport and potential transformation and their toxicity in the environment. In this work, we examined the direct and indirect photoreactivity of SWCNTs under sunlight conditions. We found that the direct photoreactivity of pristine SWCNTs is generally low; however, indirect photoreaction involving ·OH may be significant in natural aquatic environments. Environmental photochemical reactions generating ·OH lead to distinct changes in SWCNT fluorescence efficiency in the near-infrared (NIR) region, Raman spectra, and light attenuation spectra in the UV, visible, and NIR regions, indicating that covalent functionalization of SWCNTs occurs. The reactivity of SWCNTs to ·OH is dependent on the specific chiral structure of the SWCNTs and the surfactant associated with it. An operationally defined second-order rate constant (based on the decrease in NIR fluorescence signals) for all SWCNT chiral species reacting with ·OH was estimated to be (2.91 ± 1.30) × 10(10) M(-1 )s(-1). Our work suggests that photochemical reactions may be a significant transformation pathway of SWCNTs in aquatic systems.

Quenching and sensitizing fullerene photoreactions by natural organic matter.

Effects of natural organic matter (NOM) on the photoreaction kinetics of fullerenes (i.e., C60 and fullerenol) were investigated using simulated sunlight and monochromatic radiation (365 nm). NOM from several sources quenched (slowed) the photoreaction of C60 aggregates in water (aqu/nC60), but sensitized (accelerated) photoreaction of fullerenol. Kinetic studies indicated that the quenching occurred through a static mechanism involving NOM molecules adsorbed on the aqu/nC60 surface. Quenching constants for the photoreaction of aqu/nC60 correlated approximately with optical parameters related to the aromaticity and molecular size of the NOM. Association of aqu/nC60 particles with NOM was investigated indirectly via the study of the aggregation kinetics of colloidal C60 in the presence and absence of NOM as a function of NaCl strength at pH 7. In contrast to aqu/nC60, the photoreaction efficiencies of the hydrophilic fullerene, fullerenol, increased linearly with increasing NOM concentrations and kinetic parameters for the sensitized photoreactions increased as the spectral slope coefficients and ratio of absorption coefficients at 254 to 365 nm (E2:E3) of the NOM increased. The results indicate that triplet excited states of the NOM are key intermediates in the photosensitized reactions.

Sunlight-driven reduction of silver ions by natural organic matter: formation and transformation of silver nanoparticles.

Photobiogeochemical reactions involving metal species can be a source of naturally occurring nanoscale materials in the aquatic environment. This study demonstrates that, under simulated sunlight exposure, ionic Ag is photoreduced in river water or synthetic natural water samples that contain natural organic matter (NOM), forming Ag nanoparticles (AgNPs) that transform in size and shape and precipitate out upon extended irradiation. We show that the dissolved oxygen concentration does not appear to affect AgNP formation rates, indicating that reactive transients such as superoxide, hydrated electron, and triplet NOM do not play a large role. By varying pH and NOM concentrations and adding competing cations on the AgNP formation, we present three lines of evidence to show that Ag ion photoreduction likely involves ionic Ag binding to NOM. Our work suggests that photochemical reactions involving ionic Ag and NOM can be a source of nanosized Ag in the environment.

Fragmentation and release of pristine and functionalized carbon nanotubes from epoxy-nanocomposites during accelerated weathering.

There is an increasing volume of nano-enabled materials in the market. Once composites containing nano-additives are disposed of, weathering could deteriorate their structures, releasing nanoparticles and risking exposure of humans and aquatic organisms. Composite degradation due to environmental aging continues, including structural deterioration resulting in cracking, fragmentation, and release of microplastics and nano-additives to the environment. This research aims to study the degradation and release of initially embedded nanomaterials (NMs) from composites and their toxicity. The molecular interaction of carbon nanotube (CNT)/polymer composites is critical for modifying the polymer properties. This study investigated the interactions of functional multiwalled carbon nanotube (MWCNT) composites which affect their release during accelerated weathering processes. Different epoxy-MWCNT composites were prepared by filling a polymer with pure MWCNTs and MWCNTs functionalized with acid (-COOH) and amine (-NH2) groups. The physical and chemical changes of aged composites were characterized by gravimetric analysis, contact angle measurements, FTIR, SEM, and laser confocal microscopy. A loss of hydrophobicity was observed for composite surfaces long before surface cracks materialized. Released polymer fragments and nanoparticles were analyzed in wash water using TEM, FTIR and Raman spectroscopy. The environmental risks for long-term use of CNT-polymer composites and the influence of fillers on the extent of chemical photodegradation depended on the combination of polymer and fillers. If nanoparticles are released from the matrix, the high surface-to-volume ratio and reactivity of NMs make them highly dynamic in environmental systems. Exposure to these released NMs could negatively affect human health and the environment. This study provides fragmentation and CNT particle release data that could describe how molecular-level interactions between functionalized CNTs and epoxy polymers affect the aging and release of CNTs. A toxicity assessment based on a reactive oxygen species (ROS) formation assay and MTS assay for cell viability and activity of the released polymer and CNT fragments and leachate showed moderate levels of cytotoxicity of released materials as compared to pristine epoxy plates.

Weathering Effects on Degradation of Low-Density Polyethylene-Nanosilica Composite with Added Pro-oxidant.

Nanomaterials are increasingly used in polymer composites to enhance their properties, such as mechanical performance and durability, increased electrical conductivity, and improved optical clarity. Here results are presented of a study simulating effects of weathering on degradation of a nanosilica-low-density polyethylene (LDPE) composite. Release of nanosilica from LDPE composites is a potential source of toxic SiO2. Nanosilica based LDPE composites were weathered under carefully controlled conditions by exposure to simulated sunlight. The effects of an added pro-oxidant on weathering was examined. Weathering of the composites with pro-oxidant was determined by quantifying changes in infrared spectroscopic properties (Fourier transform infrared spectroscopy / FTIR); mechanical properties, atomic force microscopy (AFM), scanning electron microscopy and other procedures. Wavelength effects on weathering rates were determined in a series of irradiations using simulated solar radiation passed through light filters that blocked different parts of the ultraviolet spectral region. Rates and spectral irradiance were then analyzed to develop spectral weighting functions (SWFs) that quantify wavelength effects on the sunlight-induced weathering of the pro-oxidant amended composites.

Environmental effects of ozone depletion and its interactions with climate change: progress report, 2011.

The parties to the Montreal Protocol are informed by three panels of experts. One of these is the Environmental Effects Assessment Panel (EEAP), which deals with two focal issues. The first focus is the effects of increased UV radiation on human health, animals, plants, biogeochemistry, air quality, and materials. The second focus is on interactions between UV radiation and global climate change and how these may affect humans and the environment. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than believed previously. As a result of this, human health and environmental problems will be longer-lasting and more regionally variable. Like the other panels, the EEAP produces a detailed report every four years; the most recent was published in 2010 (Photochem. Photobiol. Sci., 2011, 10, 173-300). In the years in between, the EEAP produces less detailed and shorter progress reports, which highlight and assess the significance of developments in key areas of importance to the parties. The next full quadrennial report will be published in 2014-2015.