This study evaluates the effects of biological factors of fish and seasonality on Polycyclic Aromatic Hydrocarbon (PAH) accumulation in red mullet (Mullus barbatus) tissue. Specimens were collected monthly with a bottom trawl net in an offshore fishing ground in the Northern and Central Adriatic Sea (Geographical Sub Area 17) throughout 2016.The edible fillets of 380 individuals were analyzed for the concentrations of individual PAH, total PAH, and low, medium and high molecular weight (MW) PAHs. PAH bioaccumulation was related to their physicochemical characteristics (MW, and logarithm of the octanol-water partition coefficient, log Kₒw), some biological parameters of fish (body size, age, sex, reproductive stage and total lipid content), and catch season.The PAH bioaccumulation pattern and the effects of the different factors varied according to PAH MW. The heavier (medium and high MW) PAHs showed higher levels in winter-autumn and in pre-spawners compared with spawners and post-spawners. Our findings suggest that an important detoxification mechanism, albeit limited to the heavier PAHs, acts in the spawning and post-spawning stage. Low MW PAHs appeared to be unaffected by reproductive stage, lipid content and seasonality. Reproductive stage and seasonality seem to play an important role in the accumulation of heavier PAH, whereas total lipid content and age seem to exert a limited influence, and body size no effect at all.

Freshwater systems serve as important sources and transportation routes for marine microplastic pollution, and inadequate attention has been paid to this situation. Data on microplastic pollution of typical seagoing rivers in northern China are lacking. In the current study, we investigated the distribution and characteristics of microplastics in the main stream of the Haihe River, which flows through a metropolis with a high population density and level of industrialization and then flows into the Bohai Sea. The microplastic samples were collected by manta trawls with pore sizes of 333 μm, and the microplastic concentrations ranged from 0.69 to 74.95 items/m³. Fibers dominated in the surface water of the Haihe River; their shapes that were categorized as fibers, film, foam, fragments, and spheres, and contributed 17.4–86.7% of the total microplastics studied. The size distribution of the microplastics was concentrated in a range of 100–1000 μm, with 54.7% of the total sizes corresponding to the 333-μm trawl. Micro-Fourier transform infrared (μ-FT-IR) spectra showed that the main components were polyethylene, poly(ethylene-propylene) copolymer, and polypropylene. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) measurements revealed scratches, micropores, and cracks on the surfaces of the microplastics due to mechanical friction, chemical oxidation and degradation processes. The results of this study confirmed the high abundance and high diversity of microplastics in an urban river and indicated appreciable impacts from point-source inputs on the microplastic pollution, such as effluents from wastewater treatment plants (WWTPs).

Microplastics may lose buoyancy and occur in deeper waters and ultimately sink to the sediment and this may threaten plankton inhabiting in various water layers and benthic organisms. Here, we conduct the first survey on microplastics in the water column and corresponding sediment in addition to the surface water in the Bohai Sea. A total of 20 stations covering whole Bohai Sea were selected, which included 6 stations specified for water column studying. Seawater was sampled every 5 m, with maximal depth of 30 m in the water column using Niskin bottles coupled with a ship-based conductivity, temperature and depth sensor (CTD) system and surface sediment samples were collected using box corer. The results indicated that higher microplastic levels accumulated at a depth range of 5–15 m in the water column in some stations, suggesting the surface water survey was not sufficient to reflect microplastics loading in a water body. Fibers predominated microplastic types in both seawater and sediment of the Bohai Sea, which accounted for 75%–96.4% of the total microplastics. However the relatively proportion of the fibers in the deeper water layers and sediment was lower than that in the surface water. Microplastic shapes are more diverse in the sediment than in the seawater in general. The microplastic sizes changed with depth in the water column and the proportion of the size-fraction < 300 μm increased with depth, probably as a result of rapid biofouling on the small microplastics due to their higher specific surface area. Such depth distribution also implied that sampling with manta net (>330 μm) that commonly used in the oceanographic survey might underestimate microplastics abundance in the water column. Further studies are recommended to focus on the sinking behavior of microplastics and their effects on marine organisms.

Rivers and effluents have been identified as major pathways for microplastics of terrestrial sources. Moreover, lakes of different dimensions and even in remote locations contain microplastics in striking abundances. This study investigates concentrations of microplastic particles at two lakes in central Italy (Lake Bolsena, Lake Chiusi). A total number of six Manta Trawls have been carried out, two of them one day after heavy winds occurred on Lake Bolsena showing effects on particle distribution of fragments and fibers of varying size categories. Additionally, 36 sediment samples from lakeshores were analyzed for microplastic content. In the surface waters 2.68 to 3.36 particles/m3 (Lake Chiusi) and 0.82 to 4.42 particles/m3 (Lake Bolsena) were detected, respectively. Main differences between the lakes are attributed to lake characteristics such as surface and catchment area, depth and the presence of local wind patterns and tide range at Lake Bolsena. An event of heavy winds and moderate rainfall prior to one sampling led to an increase of concentrations at Lake Bolsena which is most probable related to lateral land-based and sewage effluent inputs. The abundances of microplastic particles in sediments vary from mean values of 112 (Lake Bolsena) to 234 particles/kg dry weight (Lake Chiusi). Lake Chiusi results reveal elevated fiber concentrations compared to those of Lake Bolsena what might be a result of higher organic content and a shift in grain size distribution towards the silt and clay fraction at the shallow and highly eutrophic Lake Chiusi. The distribution of particles along different beach levels revealed no significant differences.

Integrative passive sampling with devices such as semipermeable membrane devices generally relies on rigs for month-long static exposures in water. We evaluate here whether mobile exposures of passive samplers can provide reliable estimates of dissolved contaminant concentrations. Mobile exposures were obtained by towing samplers fastened to the end of a benthic trawl net. Significant and reproducible absorption of polycyclic aromatic hydrocarbons during 5 h-long deployments was made possible by high sampling rates resulting from high water turbulences during towing at 1.2–1.5 knots. Sampling rates (72–215 L d⁻¹) estimated from the dissipation of performance reference compounds were supported by in situ calibration with samplers exposed for a 30 days in the vicinity of the test site. Higher fluoranthene and pyrene absorption in samplers exposed to the trawling-induced sediment plume could be attributed to desorption from re-suspended sediments. This mode of exposure has the potential to be used in monitoring programmes.

To study the spatial distribution of sea surface plastics in marine protected and non-protected areas, 65 sea surface trawls were carried out using a Hydro-bios manta net coupled with a 335-μm mesh. A total of 19 sampling sites along the coastal waters of Mallorca, the “Parque Nacional Marítimo-Terrestre del Archipiélago de Cabrera” and Menorca in the Balearic Islands as well as along coastal waters of The Natural Park of Columbretes Islands (NW Mediterranean Sea) were sampled. A total of 10,637 plastic items were identified and a subset of these items was categorized by shape, color, size and polymer composition. Plastic particles were found at each sampling site and in all samples. No microscale nor mesoscale variability in floating marine plastics abundance (particles/m²) was encountered throughout the study area where similar values were found in protected areas with no local land-based contamination sources, such as Columbretes [0.04 (±0.03) particles/m²], and in high anthropized areas, such as the island of Mallorca [0.04 (±0.07) particles/m²]. However, differences were found in characteristics of plastic items (shape, polymer, and size range), with the protected area of Columbretes characterized by the presence of the highest density of very small plastic items composed mainly of fragments (93%). Quantified plastics from the marine environment were composed mainly of polyethylene (PE, 63.3%), polypropylene (PP; 24.9%), polycarbonate (PC; 4.6%) and polystyrene (PS, 3.3%). The polymer composition showed a homogenous composition between islands and differences were detected only amongst Columbretes and the other islands. Results from this study provide further evidence of the ubiquity of plastics in the marine environment and highlight that remote and protected areas, such as Columbretes, are not exempt from plastic pollution, but receptor areas for small and aged floating plastics composed mainly by fragments, which might have potentially harmful effects on protected ecosystems.

Many typical neuston trawls can only be used during relatively calm sea states and slow tow speeds. During two expeditions to the Bay of Bengal and the eastern South Pacific we investigated whether the new, high-speed AVANI trawl (All-purpose Velocity Accelerated Net Instrument) collects similar amounts and types of microplastics as two established scientific trawl designs, the manta trawl and the DiSalvo neuston net. Using a 335 μm net, the AVANI trawl can collect microplastics from the sea surface at speeds up to 8 knots as it “skis” across the surface, whereas the manta and DiSalvo neuston trawls must be towed slowly in a less turbulent sea state and often represent shorter tow lengths. Generally, the AVANI trawl collected a greater numerical abundance and weight of plastic particles in most size classes and debris types than the manta trawl and DiSalvo neuston net, likely because these trawls only skim the surface layer while the AVANI trawl, moving vertically in a random fashion, collects a “deeper” sample, capturing the few plastics that float slightly lower in the water column. However, the samples did not differ enough that results were significantly affected, suggesting that studies done with these different trawls are comparable. The advantage of the AVANI trawl over traditional research trawls is that it allows for collection on vessels underway at high speeds and during long transits, allowing for a nearly continuous sampling effort over long distances. As local surface currents make sea surface abundance widely heterogeneous, widely spaced short-tow trawls, such as the manta and DiSalvo trawls, can catch or miss hotspots or meso-scale variability of microplastic accumulations, whereas the AVANI trawl, if utilized for back-to-back tows of intermediate distances (5–10 km), can bridge variable wind conditions and debris concentrations potentially reducing variance and provide a greater resolution of spatial distribution.

Particle size plays an important role in determining the behaviour, fate and effects of microplastics (MPs), yet little is known about MPs <300 μm in aquatic environments. Therefore, we performed the first assessment of MPs in marine surface waters around the Whitsunday Islands region of the Great Barrier Reef Marine Park, Australia, to test for the presence of small MPs (50–300 μm) in-situ. Using a modified manta net, we demonstrate that MPs were present in all marine surface water samples, with a mean sea surface concentration of 0.23 ± 0.03 particles m⁻³. Microplastics were mainly blue, clear and black fibres and fragments, consisting of polyethylene terephthalate, high-density polyethylene and polypropylene plastic polymers. Tourism and marine recreation were considered the major contributing sources of MPs to surface waters around the Whitsunday Islands. Between 10 and 124 times the number of MPs exist in the 50 μm–300 μm size class, compared with the 1 mm–5 mm size range. This finding indicates that the global abundance of small MPs in marine surface waters is grossly underestimated and warrants further investigation. Research into the occurrence, characteristics and environmental fate of MPs <300 μm is needed to improve our understanding of the cumulative threats facing valuable ecosystems due to this smaller, potentially more hazardous size class.

Microplastics (MPs) are long-lasting anthropogenic pollutants, observed in all types of natural environments. The MPs abundance and their temporal variability in beach sands, surface waters (manta trawl), and suspended sediments (sediment trap) were assessed in Mazatlán, Mexico, a tourism destination on the northern Pacific coast, under the hypothesis that MP contamination is influenced by rainfall and population density. The MP concentrations in beach sands from urban and rural areas nearby Mazatlán (4–36 MPs m⁻²) and in surface waters (1.7–2.0 MPs m⁻³) were comparable between type of sampling sites; whereas the MP fluxes in sediment trap samples varied widely (40–782 MPs m⁻² day⁻¹) with highest values during the rainfall season. The MPs recovered were mostly white/clear (48–54%), and the prevailing shapes were fragments in beach sands and surface waters (59–80%), and fibers (75%) in suspended sediments. The synthetic polymers polypropylene, polyethylene, and polyethylene terephthalate were the most abundant in the study area.

Plastic pollution is ubiquitous and not even remote protected islands are safe from it. Floating debris can adsorb toxic compounds that concentrate on their surface, being available to the animals that ingest them. For this reason, a baseline study of plastic pollution was conducted in the remote Revillagigedo Archipelago, in the Mexican Pacific Ocean. In 47 manta net samples an average of 4.8 plastics/1000m² was found, 73% of the pieces being <5 mm. Polyethylene and polypropylene were the most common polymers found. The chemical analysis of organic pollutants revealed that organochlorine pesticides, polycyclic aromatic hydrocarbons and polychlorinated biphenyls are adsorbed on the plastics collected in the area. Filter feeding megafauna such as humpback whales, manta rays and whale sharks could ingest contaminated micro and macroplastics. Plastics were found also on the beach, where they are available to the ingestion by terrestrial animals, including endemic species endangered to extinction.