Mikro- ja mesomuovit pohjoisella Itämerellä : kohtalo sedimentissä ja vaikutukset pohjaeläimiin

Marine litter, especially microplastics (plastic fragments < 5 mm), has been a subject of increasing interest in recent decade, due to its ubiquitous distribution in the marine environment. Most marine litter will eventually sink to the seafloor, and many field studies to date have confirmed the accumulation of microplastics in fine-grained soft sediments. The numbers of microplastics in the environment are expected yet to increase; thus, the seafloor sediments represent both current and future hotspots for microplastic pollution, making it important to investigate the fate and potential impacts of plastic litter in these habitats. In this thesis, the interactions between microplastics, the benthic invertebrate community and harmful contaminants were examined in four different mesocosm studies that together shed light on how the size, properties (polymer type and associated contaminants) and vertical distribution of plastics on the seafloor may affect the benthic fauna. The most common benthic invertebrates in the northern Baltic Sea, the Baltic clam Limecola balthica, polychaete Marenzelleria spp. and amphipod Monoporeia affinis, were selected for the experiments that investigated how the activities of the benthic community shape the vertical distribution of microplastics in the sediment. A follow-up study further examined the bacterial communities developing on the surface of different biodegradable (cellulose acetate, poly-L-lactic acid) and conventional (polyamide, polystyrene) mesoplastics together with the capacity of plastics to sorb polycyclic aromatic hydrocarbons (PAHs) from the sediment. Lastly, the effects of acute (5 days) and chronic (29 days) exposure to tyre rubber fragments on L. balthica were examined, using a suite of biomarkers and cell ultrastructural examination of clam tissues. The results demonstrate that bioturbation by common benthic fauna buried microplastics in the sediment up to a depth of 5 cm and at the same time reduced their bioavailability to the invertebrates feeding from the sediment surface. In the experiments, 25% of the exposed clams ingested microplastics from the sediment surface, but the availability of microplastics decreased with depth; only 1% of the clams were found to ingest microplastics that were placed at depths of 2–5 cm in the sediment. In addition to the location of the microplastics, their bioavailability was also governed by the species-specific particle-size range for ingestion. Furthermore, the redistribution of buried microplastics at the sediment surface by bioturbation was negligible, supporting the hypothesis of seafloors acting as a final sink for microplastics. When incubated in the sediments, the bacterial communities developed on biodegradable cellulose acetate diverged from the other polymer types examined and harboured potentially biodegrading bacteria. The results also showed that all the polymer types examined sorbed PAHs from the sediments, but had varying PAH sorption capacities, indicating that if ingested, the microplastics’ role as PAH vectors is dependent on the polymer type. However, comparison of the PAH concentrations in plastics and in the sediment also suggested that the ingestion of plastics is not likely to increase the PAH burden of deposit-feeders. In contrast, the contaminants already present in microplastics may pose elevated risk for benthic fauna, as was found in the study carried out with tyre rubber. Both PAHs and trace metals were quantified from the tyre rubber, and the clams exposed to an environmentally relevant concentration of tyre rubber fragments exhibited multiple sublethal responses, indicating oxidative stress and damage to vital cellular structures. In essence, this thesis provides novel information that contributes to fulfilling the current knowledge gaps regarding the fate and impacts of microplastics on the seafloor, and will further aid in assessing the potential risks microplastics pose to the benthic fauna, especially in the study area of the northern Baltic Sea. It remains unclear whether the impacts of microplastics could span from the individual to the population dynamics and ecosystem functioning, but the results obtained call for further research on the complex interactions taking place in the seafloor to better understand the impacts of microplastics on the marine environment.Merten roskaantuminen ja mikromuovit (< 5 mm muovihiput) ovat herättäneet viime aikoina laajaa huomiota. Suuri osa meriroskasta vajoaa lopulta merenpohjaan, ja koska merten mikromuovimäärien odotetaan edelleen kasvavan, merenpohjat edustavat sekä nykyisiä että tulevia mikromuovikeskittymiä. Siksi mikromuovien vaikutuksia näissä elinympäristössä on keskeistä selvittää. Väitöskirjassa tarkasteltiin kokeellisesti mikromuovien, pohjan eliöyhteisön ja haitallisten aineiden välisiä vuorovaikutuksia. Tutkimuksissa selvitettiin miten selkärangattomien pohjaeläinten toiminta muovaa mikromuovien jakautumista sedimentin eri kerroksiin ja sitä kautta vaikuttaa mikromuovien saatavuuteen eläimille. Myös pohjaeläinten syömien mikromuovien määriä ja kokoja tutkittiin. Tutkimuksissa tarkasteltiin erilaisten muovityyppien (biohajoavat ja perinteiset) pinnalle kehittyviä bakteeriyhteisöjä, sekä muovien roolia sedimenttiin varastoituneiden polysyklisten aromaattisten hiilivetyjen (PAH-yhdisteet) mahdollisina vektoreina. Lisäksi tutkittiin autonrenkaista jauhettujen mikromuovien vaikutuksia liejusimpukalle (Limecola balthica). Pohjaeläinten havaittiin altistuvan mikromuoveille erityisesti silloin, kun muovit sijaitsivat sedimentin pinnalla: neljännes altistetuista liejusimpukoista söi mikromuoveja sedimentin pinnalta, mutta syvemmällä sedimentissä sijanneita mikromuoveja löytyi vain 1 % liejusimpukoista. Bioturbaatio, eli eläinten liikkuminen ja ruokailu pohjasedimentissä, hautasi mikromuoveja syvempiin sedimenttikerroksiin ja vähensi siten mikromuovien saatavuutta. Bioturbaatio ei kuitenkaan merkittävästi palauttanut mikromuoveja sedimentin pinnalle, joten pehmeitä merenpohjia voidaan pitää pohjoisella Itämerellä mikromuovinieluina. Joidenkin biohajoavien muovityyppien aiheuttamat riskit merenpohjan eliöille voivat olla pienempiä kuin perinteisten muovien, sillä biohajoavan selluloosa-asetaatin pinnalle kehittyi muita tutkittuja muoveja monimuotoisempi bakteeriyhteisö, jonka joukossa oli mahdollisesti muovin hajotukseen kykeneviä ryhmiä. Myös tutkittujen muovityyppien kyky adsorboida PAH-yhdisteitä vaihteli. Koska PAH-yhdisteiden pitoisuudet muoveissa jäivät sedimenttien pitoisuuksia alhaisemmiksi, mikromuovien syöminen ei näytä lisäävän eläinten altistumista ympäristössä jo oleville PAH-yhdisteille. Sen sijaan materiaalissa valmiina olevat haitta-aineet voivat aiheuttaa suuremman riskin: autonrengaskumista mitattiin sekä raskasmetalleja että PAH-yhdisteitä, ja altistetuilla liejusimpukoilla todettiin oksidatiiviseen stressiin viittaavia biomarkkerivasteita ja soluelinvaurioita. On kuitenkin vielä epäselvää, heijastuvatko havaitut vaikutukset populaatiotasolle ja edelleen koko ekosysteemiin

Seafloor sediments as microplastic sinks in the northern Baltic Sea : Negligible upward transport of buried microplastics by bioturbation

Microplastics (MPs) are ubiquitous in the marine environment. High concentrations of MPs are found from seafloor sediments, which have been proposed to act as their final sinks. Because bioturbation is an important process affecting the burial of MPs, a mesocosm experiment was established to study whether sediment infauna may also promote MP return to the sediment surface. Thin layers of frozen sediment containing an environmentally realistic concentration (500 μm and 100–300 μm) were added to depths of 2 cm and 5 cm in the experimental cylinders filled with sediment. The displacement of these MPs, made of acrylonitrile butadiene styrene (ABS), by a community of common benthic invertebrates in the northern Baltic Sea (clam Limecola balthica, polychaete Marenzelleria spp., gammarid Monoporeia affinis) was studied in a 10-week experiment. After the experiment, the MPs were extracted from each sediment layer and the animals were examined for MP ingestion. The results indicated that the transportation of MPs to the sediment surface by bioturbation was negligible. Thus, in the Baltic Sea, the seafloor may act as a sink for once sedimented MPs, reducing simultaneously the MP exposure of the macrofauna feeding on the sediment surface.peerReviewe

Bioturbation transports secondary microplastics to deeper layers in soft marine sediments of the northern Baltic Sea

Microplastics (MPs) are observed to be present on the seafloor ranging from coastal areas to deep seas. Because bioturbation alters the distribution of natural particles on inhabited soft bottoms, a mesocosm experiment with common benthic invertebrates was conducted to study their effect on the distribution of secondary MPs (different-sized pieces of fishing line < 1 mm). During the study period of three weeks, the benthic community increased MP concentration in the depth of 1.7-5.1 cm in the sediment. The experiment revealed a clear vertical gradient in MP distribution with their abundance being highest in the uppermost parts of the sediment and decreasing with depth. The Baltic clam Macoma balthica was the only study animal that ingested MPs. This study highlights the need to further examine the vertical distribution of MPs in natural sediments to reliably assess their abundance on the seafloor as well as their potential impacts on benthic communities

Bioturbation transports secondary microplastics to deeper layers in soft marine sediments of the northern Baltic Sea

Microplastics (MPs) are observed to be present on the seafloor ranging from coastal areas to deep seas. Because bioturbation alters the distribution of natural particles on inhabited soft bottoms, a mesocosm experiment with common benthic invertebrates was conducted to study their effect on the distribution of secondary MPs (different-sized pieces of fishing line <1 mm). During the study period of three weeks, the benthic community increased MP concentration in the depth of 1.7-5.1 cm in the sediment. The experiment revealed a clear vertical gradient in MP distribution with their abundance being highest in the uppermost parts of the sediment and decreasing with depth. The Baltic clam Macoma balthica was the only study animal that ingested MPs. This study highlights the need to further examine the vertical distribution of MPs in natural sediments to reliably assess their abundance on the seafloor as well as their potential impacts on benthic communities.Peer reviewe

Size matters more than shape: Ingestion of primary and secondary microplastics by small predators

Experimental studies have shown how microplastics are taken up by various aquatic organisms. Most of these studies have been carried out with small ( 200 μm and ABS > 100 μm) in comparison to primary microplastic beads (90 μm). Our results show that fragments of secondary plastics may end up in the food web but only in small amounts, and that the size of the fragments more than their shape is a crucial nominator influencing the numbers of plastics ingested. Future research aiming to resolve the effects of microplastics in the ecosystems should concentrate on environmentally relevant plastics and concentrations.Peer reviewe

Polycyclic aromatic hydrocarbon sorption and bacterial community composition of biodegradable and conventional plastics incubated in coastal sediments

Resistant to degradation, plastic litter poses a long-term threat to marine ecosystems. Biodegradable materials have been developed to replace conventional plastics, but little is known of their impacts and degradation in marine environments. A 14-week laboratory experiment was conducted to investigate the sorption of polycyclic aromatic hydrocarbons (PAHs) to conventional (polystyrene PS and polyamide PA) and bio-based, biodegradable plastic films (cellulose acetate CA and poly-L-lactic acid PLLA), and to examine the composition of bacterial communities colonizing these materials. Mesoplastics (1 cm(2)) of these materials were incubated in sediment and seawater collected from two sites in the Gulf of Finland, on the coast of the highly urbanized area of Helsinki, Finland. PS sorbed more PAHs than did the other plastic types at both sites, and the concentration of PAHs was consistently and considerably smaller in plastics than in the sediment. In general, the plastic bacterial biofilms resembled those in the surrounding media (water and/or sediment). However, in the sediment incubations, the community composition on CA diverged from that of the other three plastic types and was enriched with Bacteroidia and potentially cellulolytic Spirochaetia at both sites. The results indicate that certain biodegradable plastics, such as CA, may harbour potential bioplastic-degrading communities and that PAH sorption capacity varies between polymer types. Since biodegradable plastics are presented as replacements for conventional plastics in applications with risk of ending up in the marine environment, the results highlight the need to carefully examine the environmental behaviour of each biodegradable plastic type before they are extensively introduced to the market. (C) 2020 The Author(s). Published by Elsevier B.V.peerReviewe

Degradation rates and bacterial community compositions vary among commonly used bioplastic materials in a brackish marine environment

Plastic pollution threatens both terrestrial and aquatic ecosystems. As a result of the pressures of replacing oil-based materials and reducing the accumulation of litter in the environment, the use of bioplastics is increasing, despite little being known about their accurate biodegradation in natural conditions. Here, we investigated the weight attrition and degradation behavior of four different bioplastic materials compared to conventional oil-based polyethylene during a 1-year in situ incubation in the brackish Baltic Sea and in controlled 1 month biodegradation experiments in the laboratory. Bacterial communities were also investigated to verify whether putative plastic-degrading bacteria are enriched on bioplastics. Poly-l-lactic acid showed no signs of degradation, whereas poly(3-hydroxybutyrate/3-hydroxyvalerate) (PHB/HV), plasticized starch (PR), and cellulose acetate (CA) degraded completely or almost completely during 1-year in situ incubations. In accordance, bacterial taxa potentially capable of using complex carbon substrates and belonging, e.g., to class Gammaproteobacteria were significantly enriched on PHB/HV, PR, and CA. An increase in gammaproteobacterial abundance was also observed in the biodegradation experiments. The results show substantial differences in the persistence and biodegradation rates among bioplastics, thus highlighting the need for carefully selecting materials for applications with risk of becoming marine litter