A temporal sediment record of microplastics in an urban lake, London, UK

A radionuclide-dated (210Pb and 137Cs) sediment core collected from Hampstead Pond No. 1, a North London lake, was used to provide novel data on the historical accumulation of microplastic waste in the urban environment. Microplastics were extracted from sediments by sieving and dense-liquid separation. Fibres of anthropogenic origin dominated the assemblage. Microplastics were first identified by microscopy before Raman spectroscopy of selected particles was used to determine the composition of synthetic polymers and dyes. Polystyrene microplastic particles were identified, in addition to synthetic fibres of polyacrylonitrile, polyvinyl chloride and fibres containing synthetic dyes. Concentrations of total microplastics in the sediment samples ranged from detection level to 539 particles per kilogram of dried sediment. Proliferation of microplastics is evident in the core from the late 1950s to the present. Relatively low numbers of particles were found in older sediments, comparable to laboratory blanks, highlighting the difficulty of extending a plastic chronostratigraphy back to the early twentieth century. This study shows that, with optimisation, routine extraction of microplastics from radionuclide-dated lake sediments can add an important temporal perspective to our understanding of microplastics in aquatic systems.