peer reviewed | Trace elements (TEs) remain of significant toxicological concern as many are critical for global decarbonisation. TEs accumulate in sediments so benthic polychaetes (e.g. Hediste diversicolor and Alitta virens) are highly relevant for ecotoxicology. However, ecological/biological differences could influence TE accumulation and biomonitoring suitability. Exploiting multiple sympatric populations (Solent, UK), we measure sediment and tissue concentrations generating EFs (enrichment factors), AEIs (Adverse Effects Indexes) and tissue bioaccumulation factors. We also assess stable isotope compositions to elucidate diet influences. Despite diverse anthropogenic activity in the Solent, the majority of TEs present low levels of sediment contamination at the sites. For Ni, Pb and As, a combination of mean AEIs >1 and some sediment concentrations exceeding SQVs (Sediment Quality Values) indicate a slight toxicological risk. For Cu and Hg, high EFs and AEI scores confirm they are the greatest risk, thus requiring source identification/control. However, only mean As tissue concentrations reflect contaminated sites, therefore, identifying the As-source(s) is also a priority. Sediment and tissue concentration relationships were generally negative and not significant for both species. Although a significant negative relationship for Cd for A. virens requires further investigation, the lack of evidence for TE bioaccumulation from sediment may limit both species' biomonitoring suitability for low-contamination sites. Species differences in tissue concentration were also TE specific: H. diversicolor had significantly higher concentrations for Ag, Cu, Hg, Ni and Zn, whilst the reverse was true for Cd, Fe, Cr and As. Whilst ecological differences and that feeding sources are site and species-specific (as evidenced by C, N and S stable isotopes analysis) cannot be ignored, the diverse tissue concentrations strongly suggest different TE regulation strategies per species. Together these data will be important for ecotoxicologists and regulators to select the 'best' polychaete biomonitor and assess TE toxicity under future global decarbonisation trajectories for TE inputs. | 14. Life below water

Wear and tear on fishing gear is a sparsely investigated source of microplastic pollution in the sea. In Norway, Danish seine ropes and trawls are the fishing gears that contribute most to this pollution. The main reason for this pollution is that the seine ropes are dragged along the seabed over a considerable distance, creating a friction force that results in high ropes wear. This note reports the findings after examining the wear of Danish seine ropes used in Norwegian fisheries. The results show that, in Norway alone, an average of 77 to 97 tons of plastic will be added to the sea annually due to this specific fishing gear. Aggregated to include all fly dragging, anchor seining, and pair seining globally, this number is estimated to be about 311 tons per year. | publishedVersion

Longlining is a widely used fishing method. During longline fishing, some of the snoods connecting the hooks to the mainline are often lost at sea. Since snoods are made of nylon or polyester, lost snoods contribute to marine plastic pollution. Replacing nylon or polyester with a new material made of biodegradable plastics can potentially reduce macro- and microplastic pollution that is caused by lost snoods. In this study, we estimated the risk for snood loss in a longline fishery targeting haddock (Melanogrammus aeglefinus (Linnaeus, 1758)) and Atlantic cod (Gadus morhua (Linnaeus, 1758)) in Barents Sea. Further, we compared catch efficiency in this fishery for snoods made of biodegradable and nylon materials. No significant differences were found between the two materials. Therefore, catch efficiency does not represent a barrier for using biodegradable materials in snoods. | publishedVersion

Fuzzy Cognitive Mapping (FCM) is a participatory modelling tool used to explore complex systems by facilitating interdisciplinary cooperation and integrating a variety of knowledge systems. Here FCM was used to explore marine microfiber pollution. Through individual interviews with representatives from the research, industry, water and environmental sectors, five stakeholder FCMs were developed and used to produce an aggregated community FCM in a stakeholder workshop. Stakeholder FCMs and the revised community FCM were used to compute how the modelled system reacted to changes under two scenarios developed during the stakeholder workshop; (i) Green Shift and (ii) increased textile consumption and production. Significant differences were observed in scenario results from the stakeholder-based models and the community-based model. For societal challenges characterized by unknowns around the problem and potential solutions, inclusion of a variety of knowledge systems through FCM and deliberation processes contribute to a more holistic picture of the system and its uncertainties. | publishedVersion

Spatial uptake patterns of microplastics (MP) by marine species are largely unexplored under field conditions. A novel “biodeposit trap” that measure uptake and egestion of MP by suspension-feeders through the analysis of their biodeposits, was designed and used to estimate the spatial variation of these processes by mussels in field conditions. Traps containing wild or farmed mussels or control empty shells were deployed at three sites characterised by different MP concentrations and water flow conditions. A different MP dimensional composition was observed between MP pools present in biodeposit and control traps, with the latter shifted towards higher dimensional range (0.05–5 mm). Conversely, mussels accumulated small MP (0.02–0.05 mm) into their biodeposits without any significant difference between wild and farmed specimens. MP uptake rates were on average 4–5 times higher at the site where MP contamination was expected to be highest and where water flow conditions were considered moderate. | publishedVersion

Pollution by plastic and microplastic impacts the environment globally. Knowledge on the ageing mechanisms of plastics in natural settings is needed to understand their environmental fate and their reactivity in the ecosystems. Accordingly, the study of ageing processes is gaining focus in the context of the environmental sciences. However, laboratory-based experimental research has typically assessed individual ageing processes, limiting environmental applicability. In this study, we propose a multi-tiered approach to study the environmental ageing of polyethylene plastic fragments focusing on the combined assessment of physical and biological processes in sequence. The ageing protocol included ultraviolet irradiation in air and in a range of water solutions, followed by a biofouling test. Changes in surface characteristics were assessed by Fourier transform infrared spectroscopy, scanning electron microscopy, and water contact angle. UV radiation both in air and water caused a significant increase in the density of oxidized groups (i.e., hydroxyl and carbonyl) on the plastic surface, whereby water solution chemistry influenced the process both by modulating surface oxidation and morphology. Biofouling, too, was a strong determinant of surface alterations, regardless of the prior irradiation treatments. All biofouled samples present (i) specific infrared bands of new surface functional groups (e.g., amides and polysaccharides), (ii) a further increase in hydroxyl and carbonyl groups, (iii) the diffuse presence of algal biofilm on the plastic surface, and (iv) a significant decrease in surface hydrophobicity. This suggests that biological-driven alterations are not affected by the level of physicochemical ageing and may represent, in real settings, the main driver of alteration of both weathered and pristine plastics. This work highlights the potentially pivotal role of biofouling as the main process of plastic ageing, providing useful technical insights for future experimental works. These results also confirm that a multi-tiered laboratory approach permits a realistic simulation of plastic environmental ageing in controlled conditions. | publishedVersion

peer reviewed | Plastic debris are accumulating in the marine environment and aggregate microorganisms that form a new ecosystem called the plastisphere. Better understanding the plastisphere is crucial as it has self-sufficient orga- nization and carries pathogens or organisms that may be involved in the pollutant adsorption and/or plastic degradation. To date, the plastisphere is mainly described at the taxonomic level and the functioning of its microbial communities still remains poorly documented. In this work, metagenomic and metaproteomic analyzes were performed on the plastisphere of polypropylene and polyethylene plastic debris sampled on a pebble beach from the Mediterranean Sea. Our results confirmed that the plastisphere was organized as self-sufficient eco- systems containing highly active primary producers, heterotrophs and predators such as nematode. Interestingly, the chemical composition of the polymer did not impact the structure of the microbial communities but rather influenced the functions expressed. Despite the fact that the presence of hydrocarbon-degrading bacteria was observed in the metagenomes, polymer degradation metabolisms were not detected at the protein level. Finally, hydrocarbon degrader (i.e., Alcanivorax) and pathogenic bacteria (i.e., Vibrionaceae) were observed in the plas- tispheres but were not very active as no proteins involved in polymer degradation or pathogeny were detected. This work brings new insights into the functioning of the microbial plastisphere developed on plastic marine debris.

peer reviewed | Mercury (Hg) concentrations have significantly increased in oceans during the last century. This element accumulates in marine fauna and can reach toxic levels. Seafood consumption is the main pathway of methylmercury (MeHg) toxicity in humans. Here, we analyzed total Hg (T-Hg) concentrations in two oceanic squid species (Ommastrephes bartramii and Thysanoteuthis rhombus) of an increasing commercial interest off Martinique, French West Indies. Stable isotope ratios reveal a negative linear relationship between δ15N or δ13C in diamondback squid samples. No significant trend was observed between δ34S values and T-Hg concentrations, contrasting with the sulfate availability and sulfide abundance hypotheses. This adds to a growing body of evidence suggesting Hg methylation via sulfate-reducing bacteria is not the main mechanism driving Hg bioavailability in mesopelagic organisms. All squid samples present T-Hg levels below the maximum safe consumption limit (0.5 ppm), deeming the establishment of a commercial squid fishery in the region safe for human consumption.

Microplastic fibres (MPFs) often make up the largest fraction of microplastic pollution in aquatic environments, yet little is known about their degradative fate and persistence. This study investigates the environmentally relevant photodegradation of common MPFs: polyester (PET), polyamide (PA) and polyacrylonitrile (PAN), their respective additive chemical profile, together with their potential for additive leaching. MPFs were subject to ultraviolet (UV) exposure in seawater and freshwater media over 10 months. PET and PA MPFs showed significant fragmentation and surface changes following UV exposure, additionally PA showed evidence of chemical changes. PAN did not undergo significant photodegradation in the same exposure period. Chemicals tentatively identified in MPFs and aqueous leachates via non-target gas chromatography-mass spectrometry include monomers, UV stabilisers and degradation products. Characterisation of several bisphenols (BPs) and benzophenones (BzPs) was performed via ultraperformance liquid chromatography tandem mass spectrometry. Bisphenol A, bisphenol S and benzophenone-3 were quantified in all MPFs and wool at concentrations between 4.3 - 501 ng/g, with wool displaying the highest sum concentration of BPs and BzPs at 863 and 27 ng/g, respectively. | publishedVersion

Sediment samples were randomly taken in March and August 2017 at the strandlines of nine locations along the coast of Slovenia (Adriatic Sea, Mediterranean). Microparticles were isolated by density separation in saturated aqueous NaCl-solutions and analysed by infrared spectroscopy (ATR-FTIR). 11.3% of these particles were unambiguously confirmed as microplastics. Another 8.2% showed plastic characteristics but failed ATR-FTIR validation. 4.3% were naturally organic. The rest was unidentified material (76.2%). The average microplastic densities were 0.5 ± 0.5 MP kg−1 in March and 1.0 ± 0.8 MP kg−1 in August. The microplastics comprised fragments, fibres, films, and foams. The characteristics of the microplastics suggest origin from single-used plastic products and from aquaculture. Compared to other studies and sites, the microplastic pollution of the Slovenian coast appeared low. The validity of the results is discussed with respect to microplastic distribution and patchiness, sampling strategies, methodology, and scientific claims.