Fourier transform infrared (FTIR) spectroscopy has been extensively used in microplastic (MP) pollution research since 2004. The aim of this review is to discuss and highlight the recent advances in FTIR (spectroscopy and chemical imaging) techniques that are used to characterize various polymer types of MPs and to trace their fate and transport in different environmental matrices. More than 400 research papers dealing with FTIR techniques in MP pollution research, which are published between January 2010 and December 2019, have been identified from the Scopus and Web of Science databases. The MPs present in sediment, water (marine and freshwater), biota, air/dust, waste water treatment plants and salt are further classified according to (1) characterization and identification, (2) weathering and aging, (3) ecotoxicology, and (4) analytical methods. The results revealed that the ATR-FTIR technique is mostly used to identify and characterize the MPs found in water and sediment. The µFTIR (FTIR imaging) is extensively used to study the ingestion of MPs in biota (both marine and freshwater). In this article, we have summarized the current knowledge of application of FTIR spectroscopy to MP research and provided insights to future challenges for understanding the risk of MPs.

Abundance and seasonal trophodynamics (specific growth rate, daily production, and grazing mortality) of the major picophytoplankton components, Synechococcus cyanobacteria (Syn) and picoeukaryotes (Pico-E), were studied at three stations in Sevastopol Bay and adjacent coastal waters (the Black Sea) in 2014 by flow cytometry and the dilution method. Pico-E abundance was shown to increase along the nutrient and pollution gradient from the coastal waters outside the bay (annual average of 7.3 ± 5.4 × 10³ cells mL^–1) to the eastern corner of the bay (28.7 ± 11.4 × 10³ cells mL^–1), while no relation was found between the water pollution status and Syn abundance (9.9 ± 8.7 × 10³ cells mL^–1; at all the stations, n = 27). Matter flows through the communities (daily production for Syn and Pico-E 0^–16.6 and 0^–19.3 µg C L^–1 day^–1, respectively; grazing mortality for Syn and PicoE 0–3.6 and 0–21.2 µg C L^–1 day^–1, respectively) were comparable to or even exceeded their biomass stocks (>0.05–6.8 and 0.9–26.5 µg C L^–1 for Syn and PicoE, respectively), indicating high biomass turnover rates. The highest flow-to-stock ratio (up to 6 for Syn) and a significant imbalance between daily production (P) and grazing mortality (G) were observed in the most polluted and eutrophic waters of the bay in spring (Pico-E: P/G < 1) and late summer (Syn: P/G > 1). Black River inflow to the bay was hypothesized to be among the mechanisms maintaining this pronounced and long-term imbalance in the open system without any negative consequences for the picophytoplankton assemblages.

Intense pollution of marine environments with plastic waste, including micro- and nanoplastics, is a new and poorly studied threat measured in tens of million tonnes annually. Despite a huge scale of the problem, almost nothing is known about pathways and mechanisms of involvement of micro- and nanoplastics in marine food webs, trophic processes, global biogeochemical cycles. In this study, a hypothesis is considered and experimentally verified about the role exopolymers from marine phytoplankton play in flocculating micro- and nanoplastics and forming their aggregates in marine environments to transfer and deposit them further in bottom sediments. In experiments with non-axenic cultures of the cryptophyte Rhodomonas salina (RHO) and the green alga Tetraselmis suecica (TET) exposed to micro-polystyrene particles (MP, 4.3 μm diam., about 0.4 × 106 particles/ml, 16 mg/L), microalgal exudates were shown to promote MP flocculation and immobilization on vertical glass surfaces. The highest levels of MP were “cleared” from the medium by the TET culture which released more extracellular polysacharides. Hetero-aggregation of MP and algal cells was not observed, probably owing to turbulent mixing and cell motility. Abundant bacterial consortia relealed in the cultures (up to 9 × 106 cells ml-1) could be an additional source of exopolymers and serve an agent of MP flocculation and adhesion. Thus, the results obtained highlight the potential for phytoplankton exudates to interact with micro- and nanoplastics, and potentially affect their bioavailability and vertical transport in marine environments.

Climate warming can directly affect biological processes in marine environments. Here, we investigated if warming (+2 °C) can change dynamics in viral and prokaryotic populations in the cold seasons in natural seawaters. We monitored the changes in viral production and prokaryotic growth rate. The prokaryotic average gross growth rates were 0.08 and 0.34 h⁻¹ in November and 0.06 and 0.41 h⁻¹ in December in the in situ and warming experiments, respectively. We found that warming water temperature resulted in a significant increase in prokaryotic growth rates. In warming experiments, the overall viral production rate was about 0.77–14.4 × 10⁵ viruses mL⁻¹ h⁻¹, and a rough estimate of prokaryotic mortality was about 5.6–6.8 × 10⁴ cells mL⁻¹ h⁻¹. Based on our estimation, burst sizes of about 21 and 14 viruses prokaryotes⁻¹ were measured under the experimental warming period. Moreover, the results found that an increased water temperature in the subtropical western Pacific coastal waters increases prokaryotic growth rates, enhances viral production, and changes the carbon fluxes in the trophic interactions of microbes.