Occurrence, distribution and characteristics of beached plastic production pellets on the island of Malta (central Mediterranean)

The distribution, abundance and chemical characteristics of plastic production pellets on beaches of the island of Malta have been determined. Pellets were observed at all locations visited and were generally most abundant (>1000 m⁻² at the surface) on the backshores of beaches with a westerly aspect. Most pellets were disc-shaped or flattened cylinders and could be categorised as white, yellow, amber or brown. The polymeric matrix of all pellets analysed by infrared spectroscopy was polyethylene and the degree of yellowing or darkening was associated with an increase in the carbonyl index, hence extent of photo-oxidation or aging. Qualitatively, pellets are similar to those reported for other regions of the Mediterranean in surveys spanning three decades, suggesting that they are a general and persistent characteristic of the region.     

The pollution of the marine environment by plastic debris: a review

The deleterious effects of plastic debris on the marine environment were reviewed by bringing together most of the literature published so far on the topic. A large number of marine species is known to be harmed and/or killed by plastic debris, which could jeopardize their survival, especially since many are already endangered by other forms of anthropogenic activities. Marine animals are mostly affected through entanglement in and ingestion of plastic litter. Other less known threats include the use of plastic debris by "invader" species and the absorption of polychlorinated biphenyls from ingested plastics. Less conspicuous forms, such as plastic pellets and "scrubbers" are also hazardous. To address the problem of plastic debris in the oceans is a difficult task, and a variety of approaches are urgently required. Some of the ways to mitigate the problem are discussed.     

Diffuse pollution by persistent organic pollutants as measured in plastic pellets sampled from various beaches in Greece

Plastic pellets found stranded on beaches are hydrophobic organic materials and thus, they are a favourable medium for persistent organic pollutants to absorb to. In the present study, plastic pellets are used to determine the diffuse pollution of selected Greek beaches. Samples of pellets were taken from these beaches and were analyzed for PCBs, DDTs, HCHs, and PAHs. The observed differences among pellets from various sampling sites are related to the pollution occurring at each site. Plastic pellets collected in Saronikos Gulf beaches demonstrate much higher pollutant loading than the ones collected in a remote island or close to an agricultural area. Based on data collected in this study and the International Pellet Watch program, pollution in Saronikos Gulf, Greece, is comparable to other heavily industrialized places of the world. The present study demonstrates the potential of pellet watch to be utilized as a detailed-scale monitoring tool within a single country.     

Persistent organic pollutants carried by synthetic polymers in the ocean environment

Thermoplastic resin pellets are melted and formed into an enormous number of inexpensive consumer goods, many of which are discarded after a relatively short period of use, dropped haphazardly onto watersheds and then make their way to the ocean where some get ingested by marine life. In 2003 and 2004 pre-production thermoplastic resin pellets and post-consumer plastic fragments were collected and analyzed for contamination for persistent organic pollutants (POPs). Samples were taken from the North Pacific Gyre, and selected sites in California, Hawaii, and from Guadalupe Island, Mexico. The total concentration of PCBs ranged from 27 to 980 ng/g; DDTs from 22 to 7100 ng/g and PAHs from 39 to 1200 ng/g, and aliphatic hydrocarbons from 1.1 to 8600 microg/g. Analytical methods were developed to extract, concentrate and identify POPs that may have accumulated on plastic fragments and plastic pellets. The results of this study confirm that plastic debris is a trap for POPs.     

Desorption kinetics of hydrophobic organic contaminants from marine plastic pellets

This study investigated the desorption behavior of polychlorinated biphenyls (PCBs) from marine plastic pellets. Long-term desorption experiments were conducted using field-collected polyethylene (PE) pellets. The results indicate that the desorption kinetics highly depends on the PE-water partition coefficients of PCB congeners. After 128 d of the experiment, the smallest congener considered (CB 8) had desorbed nearly completely (98%), whereas major fractions (90–99%) of highly chlorinated congeners remained in the pellets. An intraparticle diffusion model mostly failed to reproduce the desorption kinetics, whereas an aqueous boundary layer (ABL) diffusion model well approximated the data. The desorption half-lives are estimated to 14 d to 210 years for CB 8 to CB 209 in an actively stirred solution (ABL thickness: 30 μm). Addition of methanol to water enhanced the desorption to a large extent. A need for further work to explore roles of organic matter in facilitating solute transfer is suggested.     

Degradation of plastic carrier bags in the marine environment

There is considerable concern about the hazards that plastic debris presents to wildlife. Use of polymers that degrade more quickly than conventional plastics presents a possible solution to this problem. Here we investigate breakdown of two oxo-biodegradable plastics, compostable plastic and standard polyethylene in the marine environment. Tensile strength of all materials decreased during exposure, but at different rates. Compostable plastic disappeared from our test rig between 16 and 24 weeks whereas approximately 98% of the other plastics remained after 40 weeks. Some plastics require UV light to degrade. Transmittance of UV through oxo-biodegradable and standard polyethylene decreased as a consequence of fouling such that these materials received ～ 90% less UV light after 40 weeks. Our data indicate that compostable plastics may degrade relatively quickly compared to oxo-biodegradable and conventional plastics. While degradable polymers offer waste management solutions, there are limitations to their effectiveness in reducing hazards associated with plastic debris.     

Microplastics as contaminants in the marine environment: a review

Since the mass production of plastics began in the 1940s, microplastic contamination of the marine environment has been a growing problem. Here, a review of the literature has been conducted with the following objectives: (1) to summarise the properties, nomenclature and sources of microplastics; (2) to discuss the routes by which microplastics enter the marine environment; (3) to evaluate the methods by which microplastics are detected in the marine environment; (4) to assess spatial and temporal trends of microplastic abundance; and (5) to discuss the environmental impact of microplastics. Microplastics are both abundant and widespread within the marine environment, found in their highest concentrations along coastlines and within mid-ocean gyres. Ingestion of microplastics has been demonstrated in a range of marine organisms, a process which may facilitate the transfer of chemical additives or hydrophobic waterborne pollutants to biota. We conclude by highlighting key future research areas for scientists and policymakers.     

Analysis of bacterial diversity and metals in produced water, seawater and sediments from an offshore oil and gas production platform

Produced water is one of the largest waste products routinely discharged into the ocean from offshore oil and gas platforms. This study analyzed bacterial communities and metals in the produced water, surrounding seawater, and sediment around the Thebaud platform. The bacterial community within the produced water was different from the seawater (SAB = 13.3), but the discharge had no detectable effect on the bacterial communities in the seawater (SAB > 97). In contrast, genomic analysis of sediments revealed that the bacterial community from 250 m was different (SAB = 70) from other locations further from the discharge, suggesting that the produced water had a detectable effect on the bacterial community in the sediment closest to the discharge. These near-field sediments contained elevated concentrations of manganese and iron that are associated with the produced water effluent. The results suggested that the discharge of produced water has influenced the bacterial community structure of sediments adjacent to the platform.     

Seabirds indicate changes in the composition of plastic litter in the Atlantic and south-western Indian Oceans

I compare plastic ingested by five species of seabirds sampled in the 1980s and again in 1999-2006. The numbers of ingested plastic particles have not changed significantly, but the proportion of virgin pellets has decreased 44-79% in all five species: great shearwater Puffinus gravis, white-chinned petrel Procellaria aequinoctialis, broad-billed prion Pachyptila vittata, white-faced storm petrel Pelagodroma marina and white-bellied storm petrel Fregetta grallaria. The populations sampled range widely in the South Atlantic and western Indian Oceans. The most marked reduction occurred in great shearwaters, where the average number of pellets per bird decreased from 10.5 to 1.6. This species migrates between the South and North Atlantic each year. Similar decreases in virgin pellets have been recorded in short-tailed shearwaters Puffinus tenuirostris in the Pacific Ocean and northern fulmars Fulmarus glacialis in the North Sea. More data are needed on the relationship between plastic loads in seabirds and the density of plastic at sea in their foraging areas, but the consistent decrease in pellets in birds suggests there has been a global change in the composition of small plastic debris at sea over the last two decades.     

Old cannery wastes,a potential source of trace metals in the marine environment

High levels of lead and zinc have been measured in the California Mussel Mytilus californianus taken from southern Monterey Bay as part of the California State Mussel Watch programme. The levels of lead and zinc increase steadily from Cypress Point towards Cannery Row. The California State Water Resources Control Board (which funded but did not conduct the State Mussel Watch) has attributed the high levels to heavy metals contributed by sewage. The state mussel watch data reports have not considered the historic canning wastes from more than 30 canneries along Cannery Row as a possible source of trace metals. Leachates from old cannery wastes may be a major source of lead and zinc in mussels in southern Monterey Bay and must be considered in assessing any data from the State Mussel Watch programme.     

Organic pollutants in microplastics from two beaches of the Portuguese coast

Microplastics pose a threat to coastal environments due to their capacity to adsorb persistent organic pollutants (POPs). These particles (less than 5 mm in size) are potentially dangerous to marine species due to magnification risk over the food chain. Samples were collected from two Portuguese beaches and sorted in four classes to relate the adsorption capacity of pollutants with color and age. Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and DDTs were analysed on pellets through gas chromatography mass spectrometry (GC-MS), and types of plastic were identified using Fourier transformed infra-red spectroscopy (micro-FTIR). Microplastics were mostly polyethylene and polypropylene. Regarding sizes, some fibres ranged from 1 to 5 μm in diameter and were 500 μm in length. The majority of samples collected had sizes above 200 μm. Black pellets, unlike aged pellets, had the highest concentrations of POPs except for PAHs in Fonte da Telha beach. PAHs with higher concentrations were pyrene, phenantrene, chrysene and fluoranthene. Higher concentrations of PCBs were found for congeners 18, 31, 138 and 187. Further investigation is necessary to understand the relationship between plastic degradation and adsorption for different pollutants.     

The usefulness of transplantation studies in monitoring of metals in the marine environment: South African experience

Due to their close proximity to the point sources of pollution, estuaries and harbours are exposed to metals. Mussels are used worldwide to monitor marine pollution due to their ability to take up contaminants and the ease of transplantation. Mussels were collected from two reference sites and transplanted in Richards Bay Harbour (2006 and 2010) and in three harbours. Transplanted and resident mussels were removed after 6 weeks exposure and metal concentrations were analysed using ICP-MS techniques. Transplanted mussels had higher metal concentrations than the resident mussels. This was attributed to regulation of metals by the resident mussels. Metal regulation was greater in mussels that are continuously submerged as opposed to those that undergo tidal influences. For monitoring it is essential that the reference population for transplantation is considered carefully as upwelling events in the pristine reference location results in significant increases in metal bioaccumulation.     

Microplastics in the marine environment

This review discusses the mechanisms of generation and potential impacts of microplastics in the ocean environment. Weathering degradation of plastics on the beaches results in their surface embrittlement and microcracking, yielding microparticles that are carried into water by wind or wave action. Unlike inorganic fines present in sea water, microplastics concentrate persistent organic pollutants (POPs) by partition. The relevant distribution coefficients for common POPs are several orders of magnitude in favour of the plastic medium. Consequently, the microparticles laden with high levels of POPs can be ingested by marine biota. Bioavailability and the efficiency of transfer of the ingested POPs across trophic levels are not known and the potential damage posed by these to the marine ecosystem has yet to be quantified and modelled. Given the increasing levels of plastic pollution of the oceans it is important to better understand the impact of microplastics in the ocean food web.     

Biomagnification in marine systems: the perspective of an ecologist

Biomagnification is the process where xenobiotic substances are transferred from food to an organism resulting in higher concentrations compared with the source. It is widely believed that this is a general phenomenon for marine food webs. An analysis of 148 papers with biomagnification in the title shows that under half show biomagnification. Of studies on metals only organic mercury shows biomagnification and most metals are regulated and excreted and do not biomagnify. Of the studies on organic compounds 67% claimed to show biomagnification. However, bioconcentration (uptake from the surrounding water) is the most usual way that organic compounds are accumulated in organisms from invertebrates to and including fish. Only in sea-birds and marine mammals is food intake the major route and where biomagnification can be clearly shown. Body concentrations of organic compounds vary with lipid content and thus in order to compare across species normalisation to uniform lipid content should be done. Yet often this is not done so data purporting to show biomagnification merely relate to differing lipid content in the different species studied. Finally suggestions are made as to how data can be collected to better interpret the process of biomagnification in marine food webs.     

Trace metals in harbour and slipway sediments from the island of Malta, central Mediterranean

Sediment samples collected from large harbours and public slipways on the island of Malta have been analysed for geochemically important metals (Al, Ca, Fe, Mn) and contaminant metals (As, Cd, Co, Cr, Cu, Ni, Pb, Sn, Zn) following fractionation (<63 μm) and digestion in aqua regia. Absolute and Al-normalised concentrations of contaminant metals exhibited relatively little dispersion both among different samples from the same location and between samples from different locations, notable exceptions including lower concentrations of Cr and Sn on the slipways than in the harbours. Sources of contaminant metals are attributed to diffuse and specific waste inputs from urban surroundings and boating and shipping activities. Overall, concentrations are similar to those reported for other large harbours in urban settings where equivalent sample fractionation-digestion has been performed. Relative to various sediment quality guidelines, Pb is predicted to exert the greatest threat to the marine environment of Malta.     

The Role of Particulate Matter in the Mobilization of Trace Metals during Anaerobic Digestion of Solid Waste Material Die Bedeutung der partikulären Substanz für die Mobilisierung von Spurenmetallen beim anaeroben Abbau fester Abfallstoffe

Metal ions bound to particulate matter represent the greatest portion (i.e. > 95%) of the total metal content found in leachate from reactor experiments where solid waste material was anaerobically digested. This seems true even though strong complexing agents are in solution which increase the solubility of Pb and Cu by a factor up to 10⁴… 10⁵ over that theoretically predicted according to the solubility of the corresponding sulfide mineral. A titrimetric characterization of the metal ion binding sites of the particulate matter suggests that the metal binding properties of the particulate matter are mainly due to organic, aminoacid-type compounds (amines. thio groups, carboxylic groups) probably of bacterial origin. The change of the concentration of the binding sites with time, together with the change of the composition of the particulate matter indicates that bacterial flocs are suspended in the leachate during the switch from acidogenic to methanogenic conditions — either due to the detachment of bacterial films from the solid material by the intensive gas production or due to the formation of syntrophic methanogenic bacterial associations or a combination of both. A combination of the two factors, strong affinity of bacterial mass to metal ions on the one hand, and suspending of the bacterial mass in the leachate on the other hand, will therefore imply a great mobilizing potential for trace metals. Consequently, the highest concentrations of particulate bound Cd were found in reactor experiments where sewage sludge contaminated with Cd was added to the waste material. An increase of the concentration of dissolved cadmium over the solubility of cadmium sulfide, however, could not be observed.     

The control of the production process of phytoplankton by the physical structure of the aquatic environment with special reference to its optical properties

This tutorial was designed for nonbiologists requiring an introduction to the nature and general timescales of phytoplankton responses to physical forcing in aquatic environments. As such, an effort was made to highlight biological markers which might assist in identifying, measuring and/or validating physical processes controlling the variability in the distribution, abundance, composition and activity of phytoplankton communities. Given the recent advances in environmental optics and remote sensing capabilities, a special emphasis was placed on the nature and utility of phytoplankton optical properties in current bio-optical modelling efforts to predict temporal and spatial variability in phytoplankton productivity and growth.     

Effects of plastic fines on the instability of sand

The effects of plastic fines on the instability of sand were studied in this article. For this purpose, the results of undrained monotonic triaxial compression tests conducted on specimens of sand with variation in fines content from 0% to 30% are presented. The specimens were prepared in two different initial dry unit densities and were subjected to two different confining pressures. The results of the tests are shown in four groups. They demonstrate that an increase in plastic fines leads to an increase in the instability, followed by a decrease with a further increase in fines content. It is also seen that the slope of the steady-state lines in p’-q space increases with increase in fines content, but after certain fines content, it begins to decrease. A reverse trend is observed for the slope of instability lines; it decreases at lower fines content, followed by an increase with a further increase in fines content.