Plastics can be found in all ecosystems across the globe. This type of environmental pollution is important, even if its impact is not fully understood. The presence of small plastic particles at the micro- and nanoscales is of growing concern, but nanoplastic has not yet been observed in natural samples. In this study, we examined four size fractions (meso-, large micro-, small micro-, and nanoplastics) of debris collected in the North Atlantic subtropical gyre. To obtain the nanoplastic portion, we isolated the colloidal fraction of seawater. After ultrafiltration, the occurrence of nanoscale particles was demonstrated using dynamic light scattering experiments. The chemical fingerprint of the colloids was obtained by pyrolysis coupled with gas chromatography-mass spectrometry. We demonstrated that the signal was anthropogenic and attributed to a combination of plastics. The polymer composition varied among the size classes. At the micro- and nanoscales, polyvinyl chloride, polyethylene terephthalate, polystyrene and polyethylene were observed. We also observed changes in the pyrolytic signals of polyethylene with decreasing debris size, which could be related to the structural modification of this plastic as a consequence of weathering.

[1] To obtain better constraints on the control of seasonal hydrological variations on dissolved organic carbon (DOC) dynamics in headwater catchments, we combined hydrometric monitoring with high-frequency analyses of DOC concentration and DOC chemical composition (specific UV adsorption, 13 C) in soil and stream waters during one complete hydrological cycle in a small lowland catchment of western France. We observed a succession of four hydrological periods, each corresponding to specific DOC signatures. In particular, the rise of the upland water table at the end of the rewetting period yielded to a strong increase of the specific UV absorbance (from 2.5 to 4.0 L mg C À1 m À1 ) and of the 13 C values (from À29 to À27%) of the soil DOC. Another striking feature was the release of large amounts of DOC during reduction of soil Fe-oxyhydroxides at the end of the highflow period. Comparison of hydrometric data with DOC composition metrics showed that soils from the upland domains were rapidly DOC depleted after the rise of the water table in these domains, whereas wetland soils acted as quasi-infinite DOC sources. Results from this study showed that the composition and ultimate source of the DOC exported to the stream will depend on the period within the annual hydrological cycle. However, we found that the aromatic DOC component identified during the high-flow period will likely represent the dominant DOC component in stream waters on an annual basis, because most of the annual stream DOC flux is exported during such periods.Citation: Lambert, T., A.-C. Pierson-Wickmann, G. Gruau, A. Jaffrezic, P. Petitjean, J.-N Thibault, and L. Jeanneau (2013), Hydrologically driven seasonal changes in the sources and production mechanisms of dissolved organic carbon in a small lowland catchment, Water Resour. Res., 49,[5792][5793][5794][5795][5796][5797][5798][5799][5800][5801][5802][5803]