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Arctic sea ice has alarmingly high concentrations of microplastics (MPs). Additionally, sea ice reduction in the Arctic is opening new opportunities for the oil and maritime industries, which could increase oil pollution in the region. Yet knowledge of the effects of co-exposure to MPs and crude oil on Arctic zooplankton is lacking. We tested the influence of MPs (polyethylene, 20.7 μm) on polycyclic aromatic hydrocarbon (PAH) bioaccumulation and oil toxicity in the key arctic copepod Calanus hyperboreus after exposure to oil with and without dispersant. Up to 30% of the copepods stopped feeding and fecal pellet production rates were reduced after co-exposure to oil (1 μL L -1 ) and MPs (20 MPs mL -1 ). The PAH body burden was ~3 times higher in feeding than in non-feeding copepods. Copepods ingested both MPs and crude oil droplets. MPs did not influence bioaccumulation of PAHs in copepods or their fecal pellets, but chemical dispersant increased bioaccumulation, especially of ≥4 ring-PAHs. Our results suggest that MPs do not act as vectors of PAHs in Arctic marine food webs after oil spills, but, at high concentrations (20 MPs mL -1 ), MPs can trigger behavioral stress responses (e.g., feeding suppression) to oil pollution in zooplankton., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Microplastics (MPs) are polluting the Arctic, but our understanding of their abundance, distribution, and sources is limited. This study quantified MPs down to 10 μm in marine waters of the most populated region in Greenland. A new plastic-free pump-filter system was used to collect MPs from surface waters in the fjord Nuup Kangerlua close to Nuuk. Additionally, we took samples by horizontal tows with a bongo net (300 μm mesh-size). The median concentrations were 142 MPs m -3 and 0.12 MPs m -3 in the pump and bongo samples, respectively. The most abundant polymer was polyester across stations and sampling types. Fibers were the dominant shape in the bongo samples, while non-fibrous particles dominated in the pump samples. MP abundance was lower in the fjord and increased close to Nuuk and towards the open ocean, indicating that Nuuk is an important point source for MPs. In both samples, concentrations of MPs increased with decreasing size, illustrating the importance of quantifying the smallest fraction of MPs. Thus, the use of methods allowing for a quantification of the smallest MPs is vital to reduce the underestimation of MP concentrations in the environment. The smallest size fraction is also most available to plankton-feeding marine invertebrates and an important entry point for MPs into marine food webs. At the found concentrations, immediate adverse effects on the pelagic food webs are unlikely. However, growing anthropogenic activities could increase the risk of MPs to affect the sensitive Arctic ecosystem., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Microplastics (MPs) are contaminants of emerging concern in the Arctic, but knowledge of their potential effects on Arctic plankton food webs remains scarce. We experimentally investigated ingestion and effects of MPs (20 μm polyethylene spheres) on the arctic copepods Calanus finmarchicus, C. glacialis and C. hyperboreus. These species dominate arctic zooplankton biomass and are relevant target species to investigate the potential impacts of MPs on the Arctic marine ecosystem. Females of each species were exposed to two concentrations of MPs (200 and 20,000 MPs L -1 ) in combination with different food (diatom) concentrations, reflecting high (3000-5000 cells mL -1 , spring phytoplankton bloom) and low (50-500 cells mL -1 , pre/post bloom) food conditions. MPs did not affect negatively fecal pellet production rates in any of the species at the studied exposure concentrations. However, egg production rates of copepods exposed to MPs were 8 times higher compared with the controls, which suggests that MP exposure can cause stress-induced spawning in arctic copepods. Microscopic examination of the fecal pellets confirmed ingested MPs in the three species (up to aprox. 1000 MPs cop -1 d -1 ). The number of MPs per pellet decreased exponentially with increasing food concentration. The daily ingestion of MPs per copepod was higher at low- food concentrations (250-500 cells mL -1 ). At our exposure conditions, the presence of MPs inside C. hyperboreus fecal pellets did not affect their sinking rates. Overall, our experimental research show that 1) acute exposure to virgin polyethylene MPs has a low impact on arctic Calanus species at environmentally relevant MP concentrations, independent of food availability, and 2) arctic copepods influence the environmental fate of plankton-sized MPs by exporting buoyant MPs from the surface layer to the sea floor via fecal pellets., (Copyright © 2020 Elsevier B.V. All rights reserved.)