Physio-chemical degradation of single-use plastics in natural weather and marine environments.

Plastic pollution has reached concerning levels globally, with single-use plastic products (SUPs) comprising at least 50% of plastic waste. This study investigates the physical and chemical degradation of frequently used SUPs, including petroleum-based and bio-based plastics, in natural Northern European coastal weather and marine environments over a three-year period from 2019 to 2022. Addressing a critical knowledge gap, this research was based on a hypothesis that real-world ageing studies on SUPs would produce more accurate time- and process-lines for their transformation from macro-to microplastics than are available today based on the modeling studies more frequently used. The study employs optical examination, mechanical testing, Fourier Transform Infrared (FTIR) spectroscopy, and Gas Chromatography-Mass Spectrometry (GC-MS) to determine and relate physical and chemical changes with time. The results indicate that SUPs undergo significantly faster degradation in natural weather than predicted to date. Photooxidation emerges as the primary degradation pathway for all SUPs, emphasizing the role of light in plastic breakdown. Importantly, physical degradation to microplastics in natural environments is not always associated with significant chemical changes such as breaking chemical bonds. Black SUPs exhibit greater resistance to visible light and ultraviolet radiation than equivalent white and transparent examples. In marine environments, SUPs degrade measurably slower than in air, their degradation slowing with increasing distance from the water surface. Our findings indicate the urgent need for strategies that mitigate the impacts of photo-oxidation of SUPs. Such strategies may include a focus on the removal of post-use SUPs from pavements, roads, beaches, and water surfaces where photo-oxidation is faster than underwater and underground. Preferential use of black SUPs over white or transparent should also be considered.

Do weathered microplastics impact the planktonic community? A mesocosm approach in the Baltic Sea.

Microplastics (MPs) are ubiquitous pollutants of increasing concern in aquatic systems. However, little is still known about the impacts of weathered MPs on plankton at the community level after long-term exposure. In this study, we investigated the effects of weathered MPs on the structure and dynamics of a Baltic Sea planktonic community during ca. 5 weeks of exposure using a mesocosm approach (2 m3) mimicking natural conditions. MPs were obtained from micronized commercial materials of polyvinyl chloride, polypropylene, polystyrene, and polyamide (nylon) previously weathered by thermal ageing and sunlight exposure. The planktonic community was exposed to 2 µg L-1 and 2 mg L-1 of MPs corresponding to measured particle concentrations (10-120 µm) of 680 MPs L-1 and 680 MPs mL-1, respectively. The abundance and composition of all size classes and groups of plankton and chlorophyll concentrations were periodically analyzed throughout the experiment. The population dynamics of the studied groups showed some variations between treatments, with negative and positive effects of MPs exhibited depending on the group and exposure time. The abundance of heterotrophic bacteria, pico- and nanophytoplankton, cryptophytes, and ciliates was lower in the treatment with the higher MP concentration than in the control at the last weeks of the exposure. The chlorophyll concentration and the abundances of heterotrophic nanoflagellates, Astromoeba, dinoflagellate, diatom, and metazooplankton were not negatively affected by the exposure to MPs and, in some cases, some groups showed even higher abundances in the MP treatments. Despite these tendencies, statistical analyses indicate that in most cases there were no statistically significant differences between treatments over the exposure period, even at very high exposure concentrations. Our results show that weathered MPs of the studied conventional plastic materials have minimal or negligible impact on planktonic communities after long-term exposure to environmentally relevant concentrations.

Assessing the Impact and Suitability of Dense Carbon Dioxide as a Green Solvent for the Treatment of PMMA of Historical Value.

Surface cleaning of plastic materials of historical value can be challenging due to the high risk of inducing detrimental effects and visual alterations. As a result, recent studies have focused on researching new approaches that might reduce the associated hazards and, at the same time, minimize the environmental impact by employing biodegradable and green materials. In this context, the present work investigates the effects and potential suitability of dense carbon dioxide (CO2) as an alternative and green solvent for cleaning plastic materials of historical value. The results of extensive trials with CO2 in different phases (supercritical, liquid, and vapor) and under various conditions (pressure, temperature, exposure, and depressurization time) are reported for new, transparent, thick poly(methyl methacrylate) (PMMA) samples. The impact of CO2 on the weight, the appearance of the samples (dimensions, color, gloss, and surface texture), and modifications to their physicochemical and mechanical properties were monitored via a multi-analytical approach that included optical microscopy, Raman and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopies, and micro-indentation (Vickers hardness). Results showed that CO2 induced undesirable and irreversible changes in PMMA samples (i.e., formation of fractures and stress-induced cracking, drastic decrease in the surface hardness of the samples), independent of the conditions used (i.e., temperature, pressure, CO2 phase, and exposure time).

Microplastics in marine beach and seabed sediments along the coasts of Dar es Salaam and Zanzibar in Tanzania.

Microplastics (MPs) pollution in the marine environment has been one of the biggest challenge in developing countries due to a lack of proper solid waste management strategies. This study reports the distribution and types of MPs in beach and seabed zones of the Dar es Salaam and Zanzibar coasts. A total of 641 MPs were identified across all sites, of which 84 % and 16 % originated from beach and seabed sediments, respectively. Fragment and fibers were the most common types in both seabed and beach zone confirming the secondary sources of the MPs. Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), revealed four types of polymers with polyethylene (PE) (56%) and polyester (PS) (24 %) being the most common. Microplastics were more abundant on beaches than in seabed zone. A larger abundance of PE and PS reveals a wide range of MPs entering the Ocean.

Real time degradation studies on polyurethane household sponges in Danish weather and marine environments.

Polyurethane (PUR) ether sponges represent a widely-used cleaning tool with a short service lifetime resulting in the production of high quantities of waste. However, the fate of PUR in natural environments is poorly understood. In this study, sponges were exposed to the natural environments of Danish weather and seawater for two years. Physiochemical changes were monitored using visual, microscopic, spectroscopic and chromatographic techniques. Results from Attenuated Total Reflection-Fourier Transform Infrared spectroscopy and change in mass indicated that photo-oxidation was the primary degradation pathway of polyurethane ether- based sponges with a specific surface degradation rate of 12,500 µm year-1 in Danish weather. Significantly, analysis by gas chromatography-mass spectrometry showed the release to the environment of toxic substance TDI as a product of photo-oxidation. Although PUR degraded more slowly in seawater than in weather, flame retardant TMCP leached from sponges to water, indicating potential health risks of PUR waste to aquatic life.

Microplastics in Marine Nearshore Surface Waters of Dar es Salaam and Zanzibar, East Africa.

Limited information exists on the occurrence of microplastics (MPs) in East African coastal waters. A 300 µm manta net was used to collect surface water from 8 sites in the regions Dar es Salaam (DES) and Zanzibar (ZZ) during low and high tides. DES had a higher (p < 0.05) abundance of MPs than ZZ. Fragments and fibers were the dominant MP types at all sites. The number of fibers was significantly higher (p = 0.002) in DES than in ZZ. MPs were more prevalent during high tide in both DES and ZZ. The MPs within the 2-5 mm size range were identified most often. White and blue MPs were the most common in study sites comprising 45% and 18% of the total MPs respectively. Three polymers polypropylene (PP) high-density polyethylene (HDPE) and low-density polyethylene (LDPE) were identified. The occurrence of MPs in nearshore waters of DES and ZZ is probably due to their proximity to industrial areas, poor solid waste management, and high population pressure.

Microplastics in Kenya's marine nearshore surface waters: Current status.

Microplastics (MPs) were collected at six locations along Kenya's marine nearshore surface waters using a 300 µm mesh-size manta net. The samples were washed over a 125-µm mesh size sieve No.120 into a glass jar and preserved in 70% ethanol. MPs were sorted, counted visually under a dissecting microscope then identified using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. A total of 1473 particles with an overall mean concentration of 0.58 ± 1.29 MPs m-3, were collected. Fragments were the most common types representing 55% of the total MPs, followed by films (40%) and fibers (2%). Polypropylene (PP) was dominant (52%), high-density polyethylene (HDPE) comprised 38% and low density polyethylene (LDPE) 10% of the total MPs. This study provided baseline information, in which Malindi was identified as a hot spot for MPs pollution. Furthermore, the outcomes will assist policy formulations and management strategies aimed at controlling marine plastics.

Accelerated weathering affects the chemical and physical properties of marine antifouling paint microplastics and their identification by ATR-FTIR spectroscopy.

Microplastics prepared from commercial marine antifouling paints were weathered by UV-C irradiation representing between 25 and 101 days of real-time, outdoor exposure. Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy of the degraded paint particles showed that weathering induced chemical changes in the material, including the release of volatile components and the formation of hydrophilic groups. The chemical changes and increased reactivity of the paint binder were associated with alterations in their physical properties and increased leaching of metals in freshwater conditions. Changes in the spectra obtained from weathered paint samples reduced their match with spectra of unaged materials, resulting in a poorer similarity index, the Score when using automatic identification tools for microplastics. The results suggest that spectra of weathered, as well as pristine paint microplastics, should be consulted when applying analytical pipelines to identify microplastics extracted from natural matrices.

A nationwide assessment of plastic pollution in the Danish realm using citizen science.

Plastic pollution is considered one of today's major environmental problems. Current land-based monitoring programs typically rely on beach litter data and seldom include plastic pollution further inland. We initiated a citizen science project known as the Mass Experiment inviting schools throughout The Danish Realm (Denmark, Greenland and the Faeroe Islands) to collect litter samples of and document plastic pollution in 8 different nature types. In total approximately 57,000 students (6-19 years) collected 374,082 plastic items in 94 out of 98 Danish municipalities over three weeks during fall 2019. The Mass Experiment was the first scientific survey of plastic litter to cover an entire country. Here we show how citizen science, conducted by students, can be used to fill important knowledge gaps in plastic pollution research, increase public awareness, establish large scale clean-up activities and subsequently provide information to political decision-makers aiming for a more sustainable future.

Microplastics in beach sediments and cockles (Anadara antiquata) along the Tanzanian coastline.

Little is known about the prevalence of microplastics (MPs) in East Africa. In the present study, sediments were sampled at 18 sites along the Tanzanian coast that exhibit different levels of anthropogenic activity and were extracted using floatation methodology. Cockles (Anadara antiquata) were collected only from eight sites and MPs were extracted following NaOH digestion. MPs were most abundant at Mtoni Kijichi Creek (MKC, 2972 ± 238 particles kg-1 dry sediment), an industrial port in Dar es Salaam, and significantly higher than all other sites where the abundance range was 15-214 particles kg-1 dry sediment (p < 0.05, one-way ANOVA). Fragments and fibers were found at all sites. Polypropylene and polyethylene were identified polymers. MPs were found in cockles from all sampled sites with both frequencies of occurrence and MPs per individual subject to site-specific variation. This study provides a baseline of MP data in a previously uninvestigated area.

'The Plastic Nile': First Evidence of Microplastic Contamination in Fish from the Nile River (Cairo, Egypt).

The presence of microplastics (MPs) in the world's longest river, the Nile River, has yet to be reported. This small-scale study aimed to provide the first information about MPs in the Nile River by sampling the digestive tracts of two fish species, the Nile tilapia (Oreochromis niloticus, n = 29) and catfish (Bagrus bayad, n = 14). Fish were purchased from local sellers in Cairo, and then their gastrointestinal tracts were dissected and examined for MPs. Over 75% of the fish sampled contained MPs in their digestive tract (MP prevalence of 75.9% and 78.6% for Nile tilapia and catfish, respectively). The most abundant MP type was fibers (65%), the next most abundant type was films (26.5%), and the remaining MPs were fragments. Polyethylene (PE), polyethylene terephthalate (PET) and polypropylene (PP) were all non-destructively identified by attenuated total reflectance Fourier transform infrared spectroscopy. A comparison with similar studies from marine and freshwater environments shows that this high level of MP ingestion is rarely found and that fish sampled from the Nile River in Cairo are potentially among the most in danger of consuming MPs worldwide. Further research needs to be conducted, but, in order to mitigate microplastic pollution in the Nile River, we must act now.

Considerations on the use of equilibrium models for the characterisation of HOC-microplastic interactions in vector studies.

The association of hydrophobic organic contaminants (HOCs) to microplastics (MPs) in the aquatic environment and the possible perturbation of how biota and HOCs interact (i.e. 'MP vector effect') is a much researched topic in the emergent field of aquatic MP pollution. Consensus on whether the vector-effect is relevant can in part be ascertained using laboratory experimentation. Such studies, of which there are now many examples, have as a mandatory component a characterisation of the HOC-MP interaction. However, important considerations must be made when planning and executing such laboratory experiments, and subsequently when choosing equilibria models to fit sorption curves, as it is necessary to recognize that simplified conceptual models (i.e. Freundlich or Langmuir models) do not fit all HOC-MP interactions under all circumstances. The sorption equilibrium of HOCs to most plastic particles occurs as a combination of surface adsorption in the crystalline regions of the polymer (typically characterized by Langmuir models) and internal partition into amorphous regions (modelled with Freundlich relations), but this is rarely recognized. In this discussion we highlight some considerations needed when both characterizing the interactions between MPs and HOCs and improving the environmental realism of vector studies through the use of, for instance, weathered particles, adequate time for HOC-MP equilibria to be reached and working at lower concentrations. Increasing environmental realism of vector studies corresponds to a greater complexity in the equilibria model, but ultimately allows better understanding of any potential HOC-MP vector effect in nature.

Influence of polyethylene microplastic beads on the uptake and localization of silver in zebrafish (Danio rerio).

This study aimed to determine whether the uptake and localization of Ag in zebrafish was affected by the presence of polyethylene microplastic beads (PE MPBs). Zebrafish were exposed to 1 µg Ag L(-1) (radiolabelled with (110m)Ag) for 4 and 24 h in the presence or absence of PE MPBs (10, 100 or 1000 MPBs mL(-1)), and one treatment in which MPBs (1000 MPBs mL(-1)) were incubated with Ag to promote adsorption. The presence of MPBs, at any of the tested doses, had no effect on the uptake or localization of Ag. However, exposure to the Ag-incubated MPBs (∽75% of the Ag bound to MPBs) significantly reduced Ag uptake at both time points and also significantly increased the proportion of intestinal Ag. This study demonstrates that microplastics can alter the bioavailability and uptake route of a metal contaminant in a model fish species.

Hydrolysis of Baltic amber during thermal ageing--an infrared spectroscopic approach.

To enable conservation of amber in museums, understanding of chemical changes is crucial. While oxidation has been investigated particularly well for this natural polymer, further degradation phenomena in relation to humidity and pollutants are poorly studied or still unknown. Attenuated total reflectance-Fourier transform infrared spectroscopy was explored with regard to Baltic amber. A systematic spectroscopic survey of a wide range of thermally aged model amber samples, exposed to different microclimatic conditions, showed significant changes in their spectra. Samples aged in a humid and acidic environment or exposed to a humid and alkaline atmosphere generally exhibited a higher absorbance intensity of carbonyl groups at frequencies assigned to acids than unaged samples, samples aged in drier conditions and samples immersed in an alkaline solution. Baltic amber comprises succinate ester, which may be hydrolysed into communol and succinic acid. The survey thus provided evidence about the progress of hydrolytic reactions during degradation of Baltic amber. Infrared spectroscopy was shown to have significant potential for providing qualitative and quantitative chemical information on hydrolysis of amber, which will be of interest for the development of preventive conservation techniques for museum collections of amber objects.

Evidence concerning oxidation as a surface reaction in Baltic amber.

The aim of this study was to provide evidence about oxidation as a surface reaction during degradation of Baltic amber. A clear understanding of the amber-oxygen interaction modalities is essential to develop conservation techniques for museum collections of amber objects. Pellet-shaped samples, obtained from pressed amber powder, were subjected to accelerated thermal ageing. Cross-sections of the pellets were analyzed by infrared micro-spectroscopy, in order to identify and quantify changes in chemical properties. The experimental results showed strong oxidation exclusively at the exterior part of cross-sections from samples subjected to long-term thermal ageing, confirming that oxidation of Baltic amber starts from the surface.