Testing citizen science as a tool for monitoring surface water microplastics

The use of citizen science in the collection of surface water marine microplastics (MP) samples with manta trawl was tested in the Baltic Sea, where the collection of surface water samples is often hampered by environmental conditions. Sampling was carried out at 7 locations around the Baltic Sea with a custom-made manta trawl which was operated onboard a sailing boat. The total concentrations of ≥ 0.3 mm MP in the samples ranged from 0.45 to 1.98 MP m^-3. Based on the results and experiences from this study, citizen science could be introduced into the toolbox of monitoring large MP. When the common basic constraints of surface water sampling within a regional sea are defined and agreed upon, citizen science could be used for strengthening the power of assessments on the state of the marine environment by increasing the spatial coverage of the monitored area.

Comparative study of three sampling methods for microplastics analysis in seawater

Microplastics, as an emerging pollutant, are widely spread in the oceans. The sampling method is the most basic and important factor affecting the reported microplastic abundance data. Three sampling methods, most commonly used for microplastic collection, including direct filtration with 0.45 μm pore size membrane, 20 μm sieve pre-concentration followed by 0.45 μm filtration and Manta trawling with a 150 μm mesh size net were studied. The results showed that there were orders of magnitude difference in abundance of microplastic across the three methods with 0.45 μm direct filtration yielding 1600.0-4000.0 items/m³, 20 μm sieve pre-concentration yielding 10.0-50.0 items/m³, and 150 μm trawl net yielding 0.13-0.24 items/m³. The polymer types of microplastic collected by the three methods were similar, but polymer proportions were different. PES and rayon dominated in the samples collected by direct filtration and sieve pre-concentration. PES and PP accounted for a higher proportion in the trawling samples. The abundance and polymer types of microplastics had a clear correlation between direct filtration and sieve pre-concentration (p < 0.05). More microplastic shapes were found in trawling samples. The average and median sizes of microplastics increased with increasing pore or mesh size. According to the size fraction and standard deviation of microplastic size in different samples of each method, the stability of method decreased with increasing pore or mesh size. The trawling method had a higher sampling efficiency, but its stability was weaker than the other two methods. Our results suggested that an appropriate method should be selected upon actual sampling condition and available tools during the research process to improve the credibility of the results.

Pelagic microplastics in surface water of the Eastern Indian Ocean during monsoon transition period: Abundance, distribution, and characteristics

Microplastics (MPs) have been documented in almost all marine environments, including coastal regions, the open ocean, and the deep sea. However, relatively little knowledge was available about MP pollution in the open ocean, especially the Indian Ocean. We conducted field observations at 36 stations in the Eastern Indian Ocean (EIO), using a typical manta trawl with a mesh size of 330 μm for surface water sampling. Ours is the first study to obtained comprehensive and comparable baseline data about MPs in the EIO, including abundance, spatial distribution and characteristics. Abundance of MPs in the EIO varied from 0.01 items m^-2 to 4.53 items m^-2, with an average concentration of 0.34 ± 0.80 item m^-2. The mean concentration of MPs in the Bay of Bengal (BoB) was 2.04 ± 2.26 items m^-2 and 0.16 ± 0.17 items m^-2 in the open ocean of the EIO. These results illustrate the high spatial heterogeneity of MPs distribution. Micro-FTIR analysis of polymer composition showed that the vast majority of MPs consisted of polypropylene (PP, 51.11%) and polyethylene (PE, 20.07%). Our data show that MP pollution in the EIO, whether in the epeiric sea or the open ocean, is among the highest of the world's oceans. The BoB is likely to become a MP hotspot due to the vast input of land-based plastics and the presence of multiscale recirculation gyres. These results are absolutely thought provoking: The EIO needs more attention on MPs.

Microplastics and other anthropogenic particles in the surface waters of the Chesapeake Bay

Microplastics are a ubiquitous environmental contaminant whose distributions have been correlated with land-use and population density. Although there are numerous studies quantifying microplastics in the environment, local studies help inform sources, pathways, and policy. Here, we measure the concentration of microplastics in the surface waters across the Chesapeake Bay - the largest estuary in the USA. Thirty surface water samples from throughout the Chesapeake Bay were collected with a manta trawl. Samples were manually processed for microplastics and other anthropogenic particles. Fourier-transform infrared spectroscopy (FTIR) was used to determine the chemical composition of the particles. Higher concentrations were found near major cities and where larger rivers or tributaries met the Chesapeake Bay. Fragments, films, and fibres were the most common morphologies found, and polyethylene and polypropylene were the most common plastic types. These results can be used to inform mitigation strategies for microplastic pollution in the Chesapeake Bay region.

Sea-surface microplastic concentrations along the coastal shelf of KwaZulu-Natal, South Africa

Ocean pollution is a global issue; yet limited quantitative data on microplastic concentrations are available for the South African coastal shelf. Estuarine outlets within industrial areas that are found along the coastline serve as conduits for plastics and other pollutants to the ocean. This study investigated coastal plastic concentrations around KwaZulu-Natal. Forty-three manta trawl samples were collected and analysed over a period of one year. An average of 4.01 ± 3.28 plastic particles/100 m² was found in surface trawls. Plastic concentrations in winter were significantly higher than those in summer (5.54 ± 3.26 and 2.96 ± 2.94 particles/100 m² respectively). The highest concentrations of plastics were found south of the city of Durban, with the highest concentration at Isipingo winter with 12.2 particles/100 m². Among the summer samples, the highest concentration of particles was off Amanzimtoti (9.54 particles/100 m²). The main plastic forms were fragments, films and fibres that were commonly white, clear, opaque, blue and black in colour. High plastic concentrations in the Durban area and sites close-by were expected due to the high levels of urbanization in the area, however, the difference in concentrations found between winter and summer was not expected and may have been due to the prevailing wind and/or current conditions on the sampling date.

Abundance and composition of near surface microplastics and plastic debris in the Stockholm Archipelago, Baltic Sea

We collected plastic debris in the Stockholm Archipelago using a manta trawl, and additionally along a transect in the Baltic Sea from the island of Gotland to Stockholm in a citizen science study. The samples were concentrated by filtration and organic material was digested using hydrogen peroxide. Suspected plastic material was isolated by visual sorting and 59 of these were selected to be characterized with Fourier transform infrared spectroscopy. Polypropylene and polyethylene were the most abundant plastics identified among the samples (53% and 24% respectively). We found nearly ten times higher abundance of plastics near central Stockholm than in offshore areas (4.2×10⁵plastics km^-2 compared to 4.7×10⁴plastics km^-2). The abundance of plastic debris near Stockholm was similar to urban areas in California, USA, and the overall abundance in the Stockholm Archipelago was similar to plastic abundance reported in the northwestern Mediterranean Sea.

Distribution and abundance of surface water microlitter in the Baltic Sea: A comparison of two sampling methods

Two methods for marine microlitter sampling were compared in the Gulf of Finland, northern Baltic Sea: manta trawl (333μm) and a submersible pump (300 or 100μm). Concentrations of microlitter (microplastics, combustion particles, non-synthetic fibres) in the samples collected with both methods and filter sizes remained <10particlesm(-3). The pump with 100μm filter gave higher microlitter concentrations compared to manta trawl or pump with 300μm filter. Manta sampling covers larger areas, but is potentially subjected to contamination during sample processing and does not give precise volumetric values. Using a submerged pump allows method controls, use of different filter sizes and gives exact volumetric measures. Both devices need relatively calm weather for operation. The choice of the method in general depends on the aim of the study. For monitoring environmentally relevant size fractions of microlitter the use of 100μm or smaller mesh size is recommended for the Baltic Sea.