Over the past five or six decades, contamination and pollution of the world’s enclosed seas, coastal waters and the wider open oceans by plastics and other synthetic, non-biodegradable materials (generally known as ‘marine debris’) has been an ever-increasing phenomenon. The sources of these polluting materials are both land- and marine-based, their origins may be local or distant, and the environmental consequences are many and varied. The more widely recognized problems are typically associated with entanglement, ingestion, suffocation and general debilitation, and are often related to stranding events and public perception. Among the less frequently recognized and recorded problems are global hazards to shipping, fisheries and other maritime activities. Today, there are rapidly developing research interests in the biota attracted to freely floating (i.e. pelagic) marine debris, commonly known as ‘hangers-on and hitch-hikers’ as well as material sinking to the sea floor despite being buoyant. Dispersal of aggressive alien and invasive species by these mechanisms leads one to reflect on the possibilities that ensuing invasions could endanger sensitive, or at-risk coastal environments (both marine and terrestrial) far from their native habitats.

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Environmental implications of plastic debris in marine settings--entanglement, ingestion, smothering, hangers-on, hitch-hiking and alien invasions.

This book describes how manmade litter, primarily plastic, has spread into the remotest parts of the oceans and covers all aspects of this pollution problem from the impacts on wildlife and human health to socio-economic and political issues. Marine litter is a prime threat to marine wildlife, habitats and food webs worldwide.

The book illustrates how advanced technologies from deep-sea research, microbiology and mathematic modelling as well as classic beach litter counts by volunteers contributed to the broad awareness of marine litter as a problem of global significance. The authors summarise more than five decades of marine litter research, which receives growing attention after the recent discovery of great oceanic garbage patches and the ubiquity of microscopic plastic particles in marine organisms and habitats.

In 16 chapters, authors from all over the world have created a universal view on the diverse field of marine litter pollution, the biological impacts, dedicated research activities, and the various national and international legislative efforts to combat this environmental problem. They recommend future research directions necessary for a comprehensive understanding of this environmental issue and the development of efficient management strategies. This book addresses scientists, and it provides a solid knowledge base for policy makers, NGOs, and the broader public.

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Marine Anthropogenic Litter

Plastics contamination in the marine environment was first reported nearly 50 years ago, less than two decades after the rise of commercial plastics production, when less than 50 million metric tons were produced per year. In 2014, global plastics production surpassed 300 million metric tons per year. Plastic debris has been detected worldwide in all major marine habitats, in sizes from microns to meters. In response, concerns about risks to marine wildlife upon exposure to the varied forms of plastic debris have increased, stimulating new research into the extent and consequences of plastics contamination in the marine environment. Here, I present a framework to evaluate the current understanding of the sources, distribution, fate, and impacts of marine plastics. Despite remaining knowledge gaps in mass budgeting and challenges in investigating ecological impacts, the increasing evidence of the ubiquity of plastics contamination in the marine environment, the continued rapid growth in plastics production...

Plastics in the Marine Environment

Rafting of marine and terrestrial organisms has been reported from a variety of substrata and from all major oceans of the world. Herein we present information on common rafting organisms and on ecological interactions during rafting voyages. An extensive literature review revealed a total of 1206 organisms, for which rafting was confirmed or inferred based on distributional or genetic evidence. Rafting organisms comprised cyanobacteria, algae, protists, invertebrates from most marine but also terrestrial phyla, and even a few terrestrial vertebrates. Marine hydrozoans, bryozoans, crustaceans and gastropods were the most common taxa that had been observed rafting. All major feeding types were represented among rafters, being dominated by grazing/boring and suspension-feeding organisms, which occurred on all floating substrata. Besides these principal trophic groups, predators/scavengers and detritus-feeders were also reported. Motility of rafting organisms was highest on macroalgae and lowest on abiotic substrata such as plastics and volcanic pumice. Important trends were revealed for the reproductive biology of rafting organisms. A high proportion of clonal organisms (Cnidaria and Bryozoa) featured asexual reproduction, often in combination with sexual reproduction. Almost all rafting organisms have internal fertilisation, which may be due to the fact that gamete concentrations in the rafting environment are too low for successful fertilisation of external fertilisers. Following fertilisation, many rafting organisms incubate their offspring in/on their body or deposit embryos in egg masses on rafts. Local recruitment, where offspring settle in the immediate vicinity of parents, is considered an important advantage for establishing persistent local populations on a raft, or in new habitats. Some organisms are obligate rafters, spending their entire life cycle on a raft, but the large majority of reported rafters are considered facultative rafters. These organisms typically live in benthic (or terrestrial) habitats, but may become dispersed while being confined to a floating item. Substratum characteristics (complexity, surface, size) have important effects on the composition of the rafting community. While at sea, ecological interactions (facilitation, competition, predation) contribute to the community succession on rafts. Organisms capable to compete for and exploit resources on a raft (space and food) will be able to persist throughout community succession. The duration of rafting voyages is closely related to rafting distances, which may cover various geographical scales. In chronological order, three features of an organism gain in importance during rafting, these being ability to (1) hold onto floating items, (2) establish and compete successfully, and (3) develop persistent local populations during a long voyage. Small organisms that do not feed on their floating substratum and with asexual reproduction or direct development combine all these features, and appear to be most suited for long-distance dispersal on rafts and successful colonisation after reaching new habitats. All available evidence suggests that rafting is an important process for the population dynamics of many organisms and that it also has had and continues to have a strong influence on coastal biodiversity.

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The Ecology of Rafting in the Marine Environment. II. The Rafting Organisms and Community

Biofouling on buoyant marine plastics: An experimental study into the effect of size on surface longevity.

Samples of low-density polyethylene, free from additives, were heated at temperatures between 284° and 355°C under high-purity nitrogen. Changes in molecular weight distribution (MWD), molecular weight averages, and degree of long-chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). At 284° and 315°C, the MWD's were shifted toward higher molecular weights and the Mw values increased. At 333° and 355°C, the MWD's shift toward lower molecular weight, but the high molecular weight, tail is largely retained. Mw decreases slowly at 333°C. At 355°C, Mw undergoes a rapid initial drop which levels off. Mw/Mn and the degree of LCB increase with heating time and temperature. Olefinic unsaturation increases. The vinyl groups show a larger relative increase than do the trans-vinylene and vinylidene groups. At 355°C, the peak of the unimodal DSC thermogram is shifted to ∼3°C higher temperature. A lower melting peak then develops, and after 72 and 90 min the two peaks are about equal in size. The density increases from 0.922 g/cm3 to 0.930 g/cm3 for samples heated at 355°C, and the weight loss was 1.5% after 90 min. A reaction scheme for the thermal degradation of polyethylene is discussed. Initiation is suggested to be accomplished by scission of allylic CC bonds. Propagation proceeds by both intra- and intermolecular hydrogen abstraction, followed by β-scission. Termination can occur by both combination and disproportionation. Combination reactions are suggested to account for the observed formation of LCB and high molecular weight material. Due to changes in the degree of LCB during the degradation, viscometry alone will not give a proper measure of the changes in molecular weight.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/app.1974.070181023

Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. II. Structural changes occuring in low-density polyethylene at an oxygen content less than 0.0005%

Samples of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and tetratetracontane (n-C44H90) free from additives were heated in air at temperatures between 120 and 180°C. As a comparison, “as received” HDPE containing unspecified additives has also been included.



The structural changes have been studied with gel chromatography, viscometry, infrared spectroscopy, differential scanning calorimetry, and gravimetric measurements.



LDPE, HDPE, and n-C44H90 follow the same course of thermooxidative degradation when they are free from additives and present in the molten state. Both molecular-diminishing and enlargement reactions occur. At temperatures below 150°C molecular enlargement is not observed until after rather long exposure times, whereas at higher temperatures enlargement occurs immediately. The difference is because “peroxide curing” becomes increasingly important above 150°C, whereas ester formation is operating at all temperature levels. Degradation below Tm is restricted to the amorphous phase that results in a different degradation pattern.



In accelerated testing work extrapolations of the Arrhenius type in the prediction of structural change are thus not justified, even within the actual narrow temperature range. Neither are changes in commonly used standards like carbonyl content justified as a measure of the changes; for example, in mechanical properties.



The stabilizer in the unpurified HDPE not only influences the induction period but also the course of the thermooxidative degradation.

Thermooxidative degradation of polyethylene. I and II. Structural changes occurring in low‐density polyethylene, high‐density polyethylene, and tetratetracontane heated in air

FISHERMEN from Smogen, Sweden have remarked that when they trawl along the bottom of the Skagerack they almost invariably collect sheets of plastic in their nets.

Plastic films on the bottom of the Skagerack

The thermal and thermo-oxidative degradation of reprecipitated and “as received” samples of different types of high-density polyethylene (HDPE) have been studied. Two of the samples were of conventional Phillips type, being essentially linear and having one vinyl group per molecule. The other two HDPE's were also produced by chromium catalysts, but according to Union Carbide's fluidized bed process. In one of these resins the molecules had vinyl end groups while the other resin was fully saturated.



Contrary to earlier statements concerning the thermal degradation of polyethylene it was found that HDPE is not degraded according to a random scission type of mechanism. Instead both molecular diminishing and enlargement are found to occur simultaneously. This is, however, in accordance with our recent findings on low-density polyethylene (LDPE).



The samples were heated at temperatures between 284 and 355°C under high purity grade nitrogen during thermal degradation and under nitrogen containing up to 1.14% oxygen during thermo-oxidative degradation. Changes in molecular weight distribution and degree of long chain branching (LCB) were followed by gel chromatography and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry. Both reprecipitated and “as-received” samples gave identical results.



For all the HDPE's an increase in heating time and temperature and oxygen content was found to increase the formation of low molecular weight material, long chain branches, volatile products, carbonyl-, ether-, and olefinic groups, discoloration, and insoluble material. Although there was much in common between LDPE and HDPE there were also certain noticeable differences, even within the HDPE group. These differences are suggested to be due to different catalyst residues in the HDPE's causing, e.g., the fully saturated material to degrade at 100°C lower temperature than expected.

Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. IV. Structural changes occurring in different types of high-density polyethylene

Classical methods for determinations of molecular weight distribution of PVC have been compared with gel permeation chromatography (GPC) measurements. Two PVC samples representing extreme values of polydispersity for common commercial resins, have been characterized by GPC and precipitation fractionation, using the tetrahydrofuran/H2O system. The concept of universal calibration and a correction for incomplete resolution have been applied to GPC data. Intrinsic viscosities and molecular weight averages have been determined both for the fractions and the original polymers.



Different ways to calculate molecular weight distributions from the fractions have been compared. It was found that the modified BEALL method using the SCHULZ distribution function for the fractions, gives the most accurate molecular weight distribution if spurious peaks could be eliminated. Among the methods using molecular weight averages for the whole polymer in combination with a distribution function, the SCHULZ distribution function showed the best agreement with GPC. Distribution functions based on one molecular weight average only seemed to give less satisfactory results.



Association of PVC molecules in tetrahydrofuran causes anomalous behaviour during the fractionation procedure and with other characterization methods. It was found that the amount of aggregates increases with syndiotacticity. To avoid the undesired influence of such supermolecular structures a heat treatment of the PVC solutions was used. The deviation from linearity in log [η] vs. log Mw plots was thus found to be due to aggregation and not to long chain branching.



Klassische Methoden zur Bestimmung der Molekulargewichtvserteilung von PVC wurden mit den Ergebnissen der Gelchromatographie (GPC) verglichen. Zwei PVC-Proben, die in bezug auf die Polydispersitat Extrema der Handelsware darstellen, wurden durch GPC und durch Fallungsfraktionierung im System Tetrahydrofuran/H2O charakterisiert. Der Bestimmung der GPC-Daten wurde das Konzept der Universalkalibrierung zugrunde gelegt; fur unvollstandige Auflosung wurde eine Korrektur eingefuhrt. Die Grenzviskositaten und die mittleren Molekulargewichte wurden sowohl fur die Fraktionen als auch fur die ursprunglichen Polymeren ermittelt.



Verschiedene Methoden der Berechnung der Molekulargewichtsverteilung von Fraktionen wurden verglichen. Falls sich das Auftreten von Peaks, deren Herkunft nicht auf die Molekulargewichts-Verteilung der Probe zuruckgefuhrt werden kann („spurious peaks”), vermeiden last, liefert die modifizierte BEALL-Methode bei Verwendung der SCHULZschen Verteilungsfunktion die besten Werte fur die Molekulargewichtsverteilung. Unter den Methoden, die auf einer Verwendung der mittleren Molekulargewichte des gesamten Polymeren in Verbindung mit einer Verteilungsfunktion beruhen, zeigt die Methode, die die SCHULZsche Verteilungsfunktion verwendet, die beste Ubereinstimmung mit den Ergebnissen der GPC. Verteilungsfunktionen, denen nur ein Wert fur das mittlere Molekulargewicht zugrunde liegt, gaben weniger zufriedenstellende Resultate.



Die Assoziation der PVC-Molekule in Tetrahydrofuran fuhrt bei diesem Polymeren wahrend des Fraktionierungsvorgangs und bei anderen Charakterisierungsmethoden zu einem anormalen Verhalten. Die Assoziation nimmt mit der Syndiotaktizitat der Probe zu. Um den uuerwunschten Einflus solcher ubermolekularer Strukturen zu vermeiden, wurde eine Warmebehandlung der PVC-Losungen durchgefuhrt. Die Abweichung der log [η] vs. log Mw-Kurven von der Linearitat wurde auf diese Weise auf eine Assoziation und nicht auf eine Kettenverzweigung zuruckgefuhrt.

Arne Holmström

Papers

Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. II. Structural changes occuring in low-density polyethylene at an oxygen content less than 0.0005%

Thermooxidative degradation of polyethylene. I and II. Structural changes occurring in low‐density polyethylene, high‐density polyethylene, and tetratetracontane heated in air

Plastic films on the bottom of the Skagerack

Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. IV. Structural changes occurring in different types of high-density polyethylene

A comparison between different ways to obtain molecular weight distributions of PVC and a study on the anomalies of PVC in tetrahydrofuran solutions