The alga Melosira arctica, which grows under Arctic sea ice, contains ten times as many microplastic particles as the surrounding seawater. This concentration at the base of the food web poses a threat to creatures that feed on the algae at the sea surface. Clumps of dead algae also transport the plastic with its pollutants particularly quickly into the deep sea – and can thus explain the high microplastic concentrations in the sediment there. Researchers led by the Alfred Wegener Institute have now reported this in the journal Environmental Science and Technology.