Plastic litter is an ever-increasing global issue and one of this generation's key environmental challenges. Microplastics have reached oceans via river transport on a global scale, but outside two mega-cities, Paris (France) and Dongguan (China), there is a lack of information on atmospheric microplastic deposition or transport. Here we present the observations of atmospheric microplastic deposition in a remote, pristine, mountain catchment (French Pyrenees). We analyse five months of samples representing atmospheric wet and dry deposition and identify fibres up to ~750 µm long and fragments ≤300µm as microplastics. We document relative daily counts of 249 fragments, 73 films and 44 fibres per square metre depositing on the catchment. Air mass trajectory analysis shows microplastic transport through the atmosphere over a distance of up to 95km. We suggest that microplastics can reach and affect remote, sparsely inhabited areas through atmospheric transport.

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In this study, we conducted synchrotron radiation Fourier transform infrared (IR) spectroscopy, potentiometric titration, and metal sorption experiments to characterize metal-cyanobacteria sorption reactions. Infrared spectra were collected with samples in solution for intact cyanobacterial filaments and separated exopolymeric sheath material to examine the deprotonation reactions of cell surface functional groups. The infrared spectra of intact cells sequentially titrated from pH 3.2 to 6.5 display an increase in peak intensity and area at 1400 cm(-1) corresponding to vibrational COO- frequencies from the formation of deprotonated carboxyl surface sites. Similarly, bulk acid-base titration of cyanobacterial filaments and sheath material indicates that the concentration of proton-active surface sites is higher on the cell wall compared to the overlying sheath. A three-site model provides an excellent fit to the titration curves of both intact cells and sheath material with corresponding pKa values of 4.7 +/- 0.4, 6.6 +/- 0.2, 9.2 +/- 0.3 and 4.8 +/- 0.3, 6.5 +/- 0.1, 8.7 +/- 0.2, respectively. Finally, Cu2+, Cd2+, and Pb2+ sorption experiments were conducted as a function of pH, and a site-specific surface complexation model was used to describe the metal sorption data. The modeling indicates that metal ions are partitioned between the exopolymer sheath and cell wall and that the carboxyl groups on the cyanobacterial cell wall are the dominant sink for metals at near neutral pH. These results demonstrate that the cyanobacterial surfaces are complex structures which contain distinct surface layers, each with unique molecular functional groups and metal binding properties.

Silici®ed deposits, such as sinters, occur in several modern geothermal environments, but the mechanisms of silici®cation (and crucially the role of microorganisms in their construction) are still largely unresolved. Detailed examination of siliceous sinter, in particular sections of microstromatolites growing at the Krisuvik hot spring, Iceland, reveals that biomineralization contributes a major component to the overall structure, with approximately half the sinter thickness attributed to silici®ed microorganisms. Almost all microorganisms observed under the scanning electron microscope (SEM) are mineralized, with epicellular silica ranging in thickness from < 5 lm coatings on individual cells, to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick. Within the overall pro®le, there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite:`microbial' layers are predominantly consisting of ®lamentous, intact, vertically aligned, biomineralized cyanobacteria, identi®ed as Calothrix and Fischerella sp.; and weakly laminated silica layers which appear to be devoid of any microbial component. The microbial layers commonly have a sharply de®ned base, overlying the weakly laminated silica, and a gradational upper surface merging into the weakly laminated silica. These cyclic laminations are probably explained by variations in microbial activity. Active growth during spring/ summer allows the microorganisms to keep pace with silici®cation, with the cell surfaces facilitating silici®cation, while during their natural slow growth phase in the dark autumn/winter months silici®cation exceeds the bacteria's ability to compensate (i.e. grow upwards). At this stage, the microbial colony is probably not essential to microstromatolite formation, with silici®cation presumably occurring abiogenically. When conditions once again become favourable for growth, recolonization of the solid silica surface by free-living bacteria occurs: cell motility is not responsible for the laminations. We have also observed that microbial populations within the microstromatolite, some several mm in depth, appear viable, i.e. they still have their pigmentation, the trichomes are not collapsed, cell walls are unbroken, cytoplasm is still present and they proved culturable. This suggests that the bulk of silici®cation occurred rapidly, probably while the cells were still alive. Surprisingly, however, measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light (PAL) only transmitted through the uppermost 2 mm. Therefore the`deeper' microbial populations must have either: (i) altered their metabolic pathways; (ii) become metabolically inactive; or (iii) the deeper populations may be dominated by different microbial assemblages from that of the surface. From these collective observations, it now seems unequivocal that microstromatolite formation is intimately linked to microbial ...