Global patterns for the spatial distribution of floating microfibers: Arctic Ocean as a potential accumulation zone.

Despite their representativeness, most studies to date have underestimated the amount of microfibers (MFs) in the marine environment. Therefore, further research is still necessary to identify key processes governing MF distribution. Here, the interaction among surface water temperature, salinity, currents and winds explained the patterns of MF accumulation. The estimated density of floating MFs is ∼5900 ±â€¯6800 items m-3 in the global ocean; and three patterns of accumulation were predicted by the proposed model: (i) intermediate densities in ocean gyres, Seas of Japan and of Okhotsk, Mediterranean and around the Antarctic Ocean; (ii) high densities in the Arctic Ocean; and (iii) point zones of highest densities inside the Arctic Seas. Coastal areas and upwelling systems have low accumulation potential. At the same time, zones of divergences between westerlies and trade winds, located above the tropical oceanic gyres, are predicted to accumulate MFs. In addition, it is likely that the warm branch of the thermohaline circulation has an important role in the transport of MFs towards the Arctic Ocean, emphasizing that surface water masses are important predictors. This study highlights that the Arctic Ocean is a dead end for floating MFs.

A watershed-scale, citizen science approach to quantifying microplastic concentration in a mixed land-use river.

Microplastic (particles < 5 mm) pollution dynamics are well documented in oceans and increasingly studied in freshwater. We used a watershed-scale approach to examine spatial and temporal patterns in microplastic concentrations in the Gallatin River watershed (Montana, USA). At 72 sites, trained volunteers collected ∼1-L grab samples at 4 seasons per year over 2 years (n = 714 samples). Microplastics were found in 57% of the samples (mean = 1.2 particles L-1). The majority of particles were fibers (80%), 0.1-1.5 mm long. Chemical identification determined 93% of particles measured by µFT-IR were synthetic or semi-synthetic materials. Microplastic concentration differed significantly among dates, but showed no longitudinal pattern or relationship to land-use among subwatersheds. At two sites with gaging stations, microplastic was negatively related to discharge when compared across dates. This suggests stormwater is not a source of microplastic in this watershed, but instead dilutes microplastic inputs from other sources. We conclude that microplastic sources are diverse, and measurements of microplastic deposition, resuspension, and transport may be needed to clarify the role of land-use patterns on microplastic pollution. This large scale, citizen science based approach provides a model for future analysis which can further expand microplastic collection at the watershed scale.