This paper clarifies some conceptual shortcomings of the empirical environmental Kuznets curve (EKC) literature that arise because of the hitherto inadequate application of unit root and ...cointegration techniques. The literature to date has ignored the fact, and a fortiori the consequences, that powers of integrated processes are themselves not integrated processes. The paper explains why standard methods should not be applied and discusses some recently proposed viable estimation and testing approaches for cointegrating polynomial regressions. The application to CO₂ and SO₂ emissions data shows that using appropriate methods leads to strongly reduced evidence for a cointegrating EKC compared to typical but conceptually not sound findings.
Future plastic materials will be very different from those that are used today. The increasing importance of sustainability promotes the development of bio-based and biodegradable polymers, sometimes ...misleadingly referred to as 'bioplastics'. Because both terms imply "green" sources and "clean" removal, this paper aims at critically discussing the sometimes-conflicting terminology as well as renewable sources with a special focus on the degradation of these polymers in natural environments. With regard to the former we review innovations in feedstock development (
e.g.
microalgae and food wastes). In terms of the latter, we highlight the effects that polymer structure, additives, and environmental variables have on plastic biodegradability. We argue that the 'biodegradable' end-product does not necessarily degrade once emitted to the environment because chemical additives used to make them fit for purpose will increase the longevity. In the future, this trend may continue as the plastics industry also is expected to be a major user of nanocomposites. Overall, there is a need to assess the performance of polymer innovations in terms of their biodegradability especially under realistic waste management and environmental conditions, to avoid the unwanted release of plastic degradation products in receiving environments.
This review provides a critical discussion as to the future direction of plastic materials, including balancing factors such as biodegradability and longevity, effects of additive compounds, feedstock developments, and environmental considerations.
This study investigated the formation and size distribution of microscopic plastic particles during the degradation of different plastic materials. Particle number concentrations in the size range ...30 nm–60 μm were measured by nanoparticle tracking analysis (NTA) and Coulter Counter techniques. Each of the plastics used exhibited a measureable increase in the release of particles into the surrounding solution, with polystyrene (PS) and polylactic acid (PLA) generating the highest particle concentrations. After 112 d, particle concentrations ranged from 2147 particles ml−1 in the control (C) to 92,465 particles ml−1 for PS in the 2–60 μm size class; 1.2 × 105 particles ml−1 (C) to 11.6 × 106 for PLA in the 0.6–18 μm size class; and 0.2 × 108 particles ml−1 (C) to 6.4 × 108 particles ml−1 for PS in the 30–2000 nm size class (84 d). A classification of samples based on principal component analysis showed a separation between the different plastic types, with PLA clustering individually in each of the three size classes. In addition, particle size distribution models were used to examine more closely the size distribution data generated by NTA. Overall, the results indicate that at the beginning of plastic weathering processes chain scission at the polymer surface causes many very small particles to be released into the surrounding solution and those concentrations may vary between plastic types.
•Degradation of seven polymers in aquatic medium results in an increased formation of microscopic plastic particles.•Weathering of polystyrene and polylactic acid generated the highest number of particles, especially in the nanometer range.•Surface erosion of all seven materials produced particles from 30 nm up to 60 μm.•Particle concentration increased with decreasing particle diameter.•Degradation processes start with chain scission at the polymer surface releasing many very small particles.
The main trigger for liver injury in acquired cholestatic liver disease remains unclear. However, the accumulation of bile acids (BAs) undoubtedly plays a role. Recent progress in deciphering the ...pathomechanisms of inborn cholestatic liver diseases, decoding mechanisms of BA-induced cell death, and generating modern BA-derived drugs has improved the understanding of the regulation of BA synthesis and transport. Now is the appropriate time to reassess current knowledge about the specific role of BAs in hepatobiliary injury.
Microscopic plastic items (microplastics) are ubiquitously present in aquatic ecosystems. With decreasing size their availability and potential to accumulate throughout food webs increase. However, ...little is known on the uptake of microplastics by freshwater invertebrates. To address this, we exposed species with different feeding strategies to 1, 10 and 90 µm fluorescent polystyrene spheres (3-3 000 particles mL
). Additionally, we investigated how developmental stages and a co-exposure to natural particles (e.g., food) modulate microplastic ingestion. All species ingested microplastics in a concentration-dependent manner with Daphnia magna consuming up to 6 180 particles h
, followed by Chironomus riparius (226 particles h
), Physella acuta (118 particles h
), Gammarus pulex (10 particles h
) and Lumbriculus variegatus (8 particles h
). D. magna did not ingest 90 µm microplastics whereas the other species preferred larger microplastics over 1 µm in size. In C. riparius and D. magna, size preference depended on the life stage with larger specimens ingesting more and larger microplastics. The presence of natural particles generally reduced the microplastics uptake. Our results demonstrate that freshwater invertebrates have the capacity to ingest microplastics. However, the quantity of uptake depends on their feeding type and morphology as well as on the availability of microplastics.
We report on recurrent shear localization by formation of strictly alternating shear and matrix bands during equal-channel angular pressing (ECAP) of a 6000 series aluminum alloy. The strain ...partitioning process is documented by analyzing the deformation of a grid of indents as well as reconstructing the corresponding flow lines. Interestingly, shear strains of ∼3.6 in the shear bands considerably exceed the conventional maximum shear strain achievable in a single ECAP pass, whereas much lower strains occur in the matrix bands, maintaining on average the macroscopic deformation that is expected for ECA-pressing with a 90° die. Microstructural analysis by electron back-scatter diffraction (EBSD) and scanning transmission electron microscopy documents the different stages of microstructural evolution in shear and matrix bands and confirms the pronounced differences associated with the novel strain partitioning process. Furthermore, an EBSD-based analysis of texture evolution for billets with different orientations with respect to the initial extrusion direction demonstrates the important role that texture softening plays in triggering shear localization in two characteristic orientations as opposed to homogeneous deformation in the third orientation. Shear banding during ECAP is often interpreted in the light of failure mechanisms and cracking; the present study demonstrates that stable strain partitioning facilitates the fabrication of bulk laminated materials by ECAP.
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•Most bioplastics and plant-based materials contain toxic chemicals.•Cellulose and starch-based products induce the strongest in vitro toxicity.•Most samples contain >1000 chemical ...features; the maximum is 20,000 features.•The material type does not predict toxicity or chemical composition.•Bio-based/biodegradable materials and conventional plastics are similarly toxic.
Plastics contain a complex mixture of known and unknown chemicals; some of which can be toxic. Bioplastics and plant-based materials are marketed as sustainable alternative to conventional plastics. However, little is known with regard to the chemicals they contain and the safety of these compounds. Thus, we extracted 43 everyday bio-based and/or biodegradable products as well as their precursors, covering mostly food contact materials made of nine material types, and characterized these extracts using in vitro bioassays and non-target high-resolution mass spectrometry. Two-third (67%) of the samples induced baseline toxicity, 42% oxidative stress, 23% antiandrogenicity and one sample estrogenicity. In total, we detected 41,395 chemical features with 186–20,965 features present in the individual samples. 80% of the extracts contained >1000 features, most of them unique to one sample. We tentatively identified 343 priority compounds including monomers, oligomers, plastic additives, lubricants and non-intentionally added substances. Extracts from cellulose- and starch-based materials generally triggered a strong in vitro toxicity and contained most chemical features. The toxicological and chemical signatures of polyethylene (Bio-PE), polyethylene terephthalate (Bio-PET), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polylactic acid (PLA), polyhydroxyalkanoates (PHA) and bamboo-based materials varied with the respective product rather than the material. Toxicity was less prevalent and potent in raw materials than in final products. A comparison with conventional plastics indicates that bioplastics and plant-based materials are similarly toxic. This highlights the need to focus more on aspects of chemical safety when designing truly “better” plastic alternatives.
We discuss several major econometric problems that have been ignored in the empirical environmental Kuznets curve (EKC) literature thus far. These are: First, the use of nonlinear transformations of ...integrated regressors and second, in a panel context, cross-sectional dependence in the data. Both problems fundamentally invalidate the use of widely applied time series and panel unit root and cointegration techniques. We use the important special case of the relationship between GDP and CO
2 (and SO
2) emissions to show and discuss in detail that the seemingly strong evidence for an inverted U-shaped relationship between these variables obtained with commonly used methods is entirely spurious and vanishes when resorting to estimation strategies that take the discussed problems into account.
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