First assessment of microplastic particles contamination using two complementary analysis methods from the source to the estuary of the Loire River, France

For the first time, microplastic contamination of the Loire River, from its source to the estuary, has been investigated. As part of the Loire Sentinelle project, water and sediment were sampled over a period of three months at 20 stations surrounding major cities and tributaries along this river, which stretches over 1,000 km. The microfiber were analysed from water and sediment samples by microscopy and particles from sediment samples by micro-Fourier transform infrared spectroscopy (especially fragments) to characterise their shape, nature, size, and colour. These data were compared to the sediment composition and other abiotic factors. The most striking result is the omnipresence of microplastics all along the Loire River. Microplastic particles found were mainly made of polypropylene and polyethylene, coloured in blue and black, and at concentrations of the same order as those found in other European rivers, namely between 86 and 1,761 mean microfibers/kg dw of sediment and about 0.13 microfibers/m3 of water. While sediment grain size did not seem to influence microplastic contamination, the latter appeared to increase at stations downstream of cities compared to upstream ones. Both techniques used in this study were complementary and enabled a comprehensive assessment of microplastic contamination.