Microplastics in sediments of the River Thames Basin, UK

This dataset provides numbers and types of plastic particles extracted from sediment samples of three tributaries of the river Thames: the River Leach, the River Lambourn and The Cut. These rivers are regularly monitored for a range of water quality and biological characteristics as part of the ongoing CEH Thames initiative project. Four sampling sites were selected based on the average percentage of effluent present in the river and population equivalent density to represent scenarios ranging from low sewage input and population equivalent density (Leach and Lanbourn) through an intermediate site (the Cut) to a site with high sewage input and population equivalent density (also in the Cut). The samples were collected between late August and early September 2014. The data provides information on the site characteristics, dry weight of sediment analysed (in grams), number of microplastic particles extracted and characteristics of particles (including shape, colour and polymer type). Types of polymers identified include: polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, nylon and polyester.

The average percentage effluent present in the river was estimated using the Low Flows 2000 (LF2000) WQX (Water Quality eXtension) model. The population equivalent density was calculated using population within the catchment area (of known area) served by the upstream sewage treatment works. This site characteristic data is given in the datasheet ThamesMicroplastics_SamplingLocations. Four replicate sediment samples were taken at each site using a stainless steel scoop, collected into a 1 L glass jar. In the laboratory the 1 L sediment samples were wet-sieved and sediment in the size ranges 1-2 mm and 2-4 mm was retained for further analysis. Microplastic particles were extracted using a number of steps, consisting of manual sorting and density separation with zinc chloride solution (1.7-1.8 kg/L). Each sample comprised a different volume and weight following size-sieving, therefore the inclusion of dry weight data allows for the conversion of total microplastic particles into a concentration (e.g. particles/kg dry sediment) for comparability between samples (ThamesMicroplastics_NumberOfParticles). A subsample (20%) of particles were characterised by type and colour, with composition determined using Raman spectroscopy (ThamesMicroplastics_ParticleCharacteristics). Further details on the methods used for particle extraction and characterisation are available in the supporting information.