Changing nutrient cycling in Lake Baikal, the world's oldest lake.

Lake Baikal, lying in a rift zone in southeastern Siberia, is the world's oldest, deepest, and most voluminous lake that began to form over 30 million years ago. Cited as the "most outstanding example of a freshwater ecosystem" and designated a World Heritage Site in 1996 due to its high level of endemicity, the lake and its ecosystem have become increasingly threatened by both climate change and anthropogenic disturbance. Here, we present a record of nutrient cycling in the lake, derived from the silicon isotope composition of diatoms, which dominate aquatic primary productivity. Using historical records from the region, we assess the extent to which natural and anthropogenic factors have altered biogeochemical cycling in the lake over the last 2,000 y. We show that rates of nutrient supply from deep waters to the photic zone have dramatically increased since the mid-19th century in response to changing wind dynamics, reduced ice cover, and their associated impact on limnological processes in the lake. With stressors linked to untreated sewage and catchment development also now impacting the near-shore region of Lake Baikal, the resilience of the lake's highly endemic ecosystem to ongoing and future disturbance is increasingly uncertain.

The potential of fluorescent dyes-comparative study of Nile red and three derivatives for the detection of microplastics.

During the last years, microplastics in the environment came to the fore in environmental science research. For an appropriate risk assessment, it is essential to know the levels of microplastic contamination in the environment. In the field of microplastic detection, extensive research has been carried out in recent years. While common methods such as Raman spectroscopy and pyrolysis GC-MS are time-consuming and require trained staff and expensive equipment, there is the need for a cheap and easily applicable method. Staining microplastics with the fluorescent dye Nile red (NR) has a high potential to fulfill these criteria. In our work, we tested Nile red and newly developed derivatives, with the aim of achieving greater selectivity for plastic particles and more intense fluorescence. In addition, the influence of using different solvents and water at different pH values in the dyeing process was investigated by analyzing solid sample fluorescence spectra of dyed microplastics and natural particles. Finally, the method developed from the acquired knowledge was tested for sea salt. Graphical abstract.

Accurate Reference Gas Mixtures Containing Tritiated Molecules: Their Production and Raman-Based Analysis.

Highly accurate, quantitative analyses of mixtures of hydrogen isotopologues-both the stable species, H2, D2, and HD, and the radioactive species, T2, HT, and DT-are of great importance in fields as diverse as deuterium-tritium fusion, neutrino mass measurements using tritium ß-decay, or for photonuclear experiments in which hydrogen-deuterium targets are used. In this publication we describe a production, handling, and analysis facility capable of fabricating well-defined gas samples, which may contain any of the stable and radioactive hydrogen isotopologues, with sub-percent accuracy for the relative species concentrations. The production is based on precise manometric gas mixing of H2, D2, and T2. The heteronuclear isotopologues HD, HT, and DT are generated via controlled, in-line catalytic reaction or by ß-induced self-equilibration, respectively. The analysis was carried out using an in-line intensity- and wavelength-calibrated Raman spectroscopy system. This allows for continuous monitoring of the composition of the circulating gas during the self-equilibration or catalytic evolution phases. During all procedures, effects, such as exchange reactions with wall materials, were considered with care. Together with measurement statistics, these and other systematic effects were included in the determination of composition uncertainties of the generated reference gas samples. Measurement and calibration accuracy at the level of 1% was achieved.

In-line calibration of Raman systems for analysis of gas mixtures of hydrogen isotopologues with sub-percent accuracy.

Highly accurate, in-line, and real-time composition measurements of gases are mandatory in many processing applications. The quantitative analysis of mixtures of hydrogen isotopologues (H2, D2, T2, HD, HT, and DT) is of high importance in such fields as DT fusion, neutrino mass measurements using tritium ß-decay or photonuclear experiments where HD targets are used. Raman spectroscopy is a favorable method for these tasks. In this publication we present a method for the in-line calibration of Raman systems for the nonradioactive hydrogen isotopologues. It is based on precise volumetric gas mixing of the homonuclear species H2/D2 and a controlled catalytic production of the heteronuclear species HD. Systematic effects like spurious exchange reactions with wall materials and others are considered with care during the procedure. A detailed discussion of statistical and systematic uncertainties is presented which finally yields a calibration accuracy of better than 0.4%.

Method for rapid biofilm cultivation on microplastics and investigation of its effect on the agglomeration and removal of microplastics using organosilanes.

Since microplastics were recognized as a global environmental problem in the early 2000s, research began on possible solutions such as the removal of microplastics from waters. A novel and promising approach for this purpose is microplastics agglomeration-fixation using organosilanes. In this study, it is investigated how biofilm coverage of microplastics affects this process. The biofilm was grown on the microplastics by cultivating it for one week in a packed bed column operated with biologically treated municipal wastewater enriched with glucose. The biofilm was characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and Fourier-Transform infrared spectroscopy (FT-IR). The results show a partial coverage of the microplastics with attached bacteria and extracellular polymeric substances (EPS) after 7 days of incubation. Comparing five polymer types (polyethylene, polypropylene, polyamide, polyester, and polyvinyl chloride) and three organosilanes, the biofilm coverage caused a reduced removal efficiency for all combinations tested as it changes the surface chemistry of the microplastics and therefore the interaction with the organosilanes tested in this study. Treatment of biofilm covered microplastic with ultrasound partly recovers the removal. However, the results underline the importance of simulated environmental exposure when performing experiments for microplastic removal.

Influence of various production methods on the microplastic contamination of sea salt produced in Java, Indonesia.

The extensive research on microplastics (MPs) in the last years has shown that it is not just an environmental problem anymore. As it can also be found in human food, it poses a potential risk for human health and food safety. Especially sea salt, which is produced by the evaporation of seawater, including its microplastic contamination, has been reported with different levels of MP contamination. Therefore, in this preliminary study, we investigated if different solar evaporation methods (traditional, geomembrane, and tunnel) influence the concentration of microplastic particles in sea salt production in Indonesia, one of the countries with the highest estimated level of plastic waste input into the ocean. The results show a significantly higher MP contamination in sea salt produced traditionally compared to the geomembrane and tunnel methods.

Pre-packed vacuum bone cement mixing systems. A further step in reducing methylmethacrylate exposure in surgery.

OBJECTIVES: Polymethylmethacrylate bone cements are widely used in orthopaedic and trauma surgery as well as in dentistry. The toxic side effects of inhaled methylmethacrylate (MMA) fumes generated during mixing have been well studied. Vacuum cement mixing systems have been shown to reduce the risk of airborne MMA significantly compared to handmixing. In an effort to further reduce MMA exposure, the latest generation of mixing devices are pre-packed with the ingredients and thus allow preparation in nearly closed circuits. Until now, there has been no study proofing the efficacy of those systems in protecting theatre staff from MMA vapours. METHODS: A pre-packed vacuum mixing system (Optipac®) was compared with two standard systems (Palamix® and Easymix®) regarding MMA emission. The latter systems require loading with the bone cement compounds prior to mixing. Following a standardized procedure, 10 mixes were performed with each system and the emission of MMA vapours in the breathing zone was recorded using photoionization detection over a period of 3 min. RESULTS: The mean MMA exposure was reduced when using the pre-packed system compared to the devices that require filling with the components. The highest emission peaks were recorded during the mixing and preparation steps in all systems. CONCLUSIONS: Modern pre-packed vacuum mixing systems further help to reduce the occupational hazards created by bone cement preparation. However, MMA fumes can still be detected using this technique. Although this is an important step in reducing MMA exposure in the operating theatre, further technical effort has to be taken to eliminate the continuous leakage of monomer from the devices while mixing and to minimize necessary manipulation for final delivery.

Comparative study of the influence of linear and branched alkyltrichlorosilanes on the removal efficiency of polyethylene and polypropylene-based microplastic particles from water.

Microplastics are a global environmental pollution. Due to this fact, new solutions are needed to reduce the amount in various aquatic environments. A new concept introduced by Herbort and Schuhen from the year 2016 describes the agglomeration of microplastics in water using silicon-based precursors. In the study presented here, alkyltrichlorosilanes with different linear and branched alkyl groups and a chain length between 1 and 18 carbon (C-) atoms are investigated for their suitability to fix microplastics (mixtures of polyethylene (PE) and polypropylene (PP)) and to form larger agglomerates. As the alkyl group has a major influence on the reaction rate and agglomeration behavior, we present here the extensive data collection of the evaluation of the best case. The removal efficiency is determined gravimetrically. The reaction behavior and the fixation process are characterized by hydrolysis kinetics. 29Si-MAS-NMR spectroscopy, IR spectroscopy, and thermogravimetry (TGA) are used to characterize the chemical composition of the agglomerates. Finally, the use of optical coherence tomography (OCT) allows the visualization of the formed agglomerates. The results show that the different alkyl groups have a strong impact on the suitability of the alkyltrichlorosilanes for the agglomeration, as they influence the hydrolysis and condensation kinetics in water and the affinity to the microplastics. Best suited for microplastic removal were intermediate chain length between 3 and 5 C-atoms.

Oxygen consumption in seasonally stratified lakes decreases only below a marginal phosphorus threshold.

Areal oxygen (O2) consumption in deeper layers of stratified lakes and reservoirs depends on the amount of settling organic matter. As phosphorus (P) limits primary production in most lakes, protective and remediation efforts often seek to reduce P input. However, lower P concentrations do not always lead to lower O2 consumption rates. This study used a large hydrochemical dataset to show that hypolimnetic O2 consumption rates in seasonally stratified European lakes remain consistently elevated within a narrow range (1.06 ± 0.08 g O2 m-2 d-1) as long as areal P supply (APS) exceeded 0.54 ± 0.06 g P m-2 during the productive season. APS consists of the sum of total P present in the productive top 15 m of the water column after winter mixing plus the load of total dissolved P imported during the stratified season, normalized to the lake area. Only when APS sank below this threshold, the areal hypolimnetic mineralization rate (AHM) decreased in proportion to APS. Sediment trap material showed increasing carbon:phosphorus (C:P) ratios in settling particulate matter when APS declined. This suggests that a decreasing P load results in lower P concentration but not necessarily in lower AHM rates because the phytoplankton community is able to maintain maximum biomass production by counteracting the decreasing P supply by a more efficient P utilization. In other words, in-lake organic matter production depends only on APS if the latter falls below the threshold of 0.54 g P m-2 and correspondingly, the atomic C:P ratio of the settling material exceeds ~155.

Correction: Diatom evidence of 20th century ecosystem change in Lake Baikal, Siberia.

[This corrects the article DOI: 10.1371/journal.pone.0208765.].

A new approach for the agglomeration and subsequent removal of polyethylene, polypropylene, and mixtures of both from freshwater systems - a case study.

Based on a new concept for the sustainable removal of microplastics from freshwater systems, a case study for a pH-induced agglomeration and subsequent removal of polyethylene and polypropylene particles from water is presented. The two-step-based process includes firstly a localization and secondly an aggregation of microplastic particles (250-350 µM) in a physicochemical process. The research describes a strong increase in the particle size independent of pH of the aquatic milieu induced by the addition of trichlorosilane-substituted Si derivatives. The resulting Si-based microplastic aggregates (particle size after aggregation is 2-3 cm) could be easily removed by use of, e.g., sand traps. Due to the effect that microplastic particles form agglomeration products under every kind of process conditions (e.g., various pH, various polymer concentrations), the study shows a high potential for the sustainable removal of particles from wastewater.

Diatom evidence of 20th century ecosystem change in Lake Baikal, Siberia.

Lake Baikal has been experiencing limnological changes from recent atmospheric warming since the 1950s, with rising lake water temperatures, reduced ice cover duration and reduced lake surface-water mixing due to stronger thermal stratification. This study uses lake sediment cores to reconstruct recent changes (c. past 20 years) in Lake Baikal's pelagic diatom communities relative to previous 20th century diatom assemblage records collected in 1993 and 1994 at the same locations in the lake. Recent changes documented within the core-top diatom records agree with predictions of diatom responses to warming at Lake Baikal. Sediments in the south basin of the lake exhibit clear temporal changes, with the most rapid occurring in the 1990's with shifts towards higher abundances of the cosmopolitan Synedra acus and a decline in endemic species, mainly Cyclotella minuta and Stephanodiscus meyerii and to a lesser extent Aulacoseira baicalensis and Aulacoseira skvortzowii. The north basin, in contrast, shows no evidence of recent diatom response to lake warming despite marked declines in north basin ice cover in recent decades. This study also shows no diatom-inferred evidence of eutrophication from deep water sediments. However, due to the localised impacts seen in areas of Lake Baikal's shoreline from nutrient pollution derived from inadequate sewage treatment, urgent action is vital to prevent anthropogenic pollution extending into the open waters.

The historical record of PCB and PCDD/F deposition at Greifensee, a lake of the Swiss plateau, between 1848 and 1999.

Dated sediment cores provide an excellent way to investigate the historical input of persistent organic pollutants into the environment and to identify possible sources of pollution. The vertical distribution of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/F) and polychlorinated biphenyls (PCB) was investigated in a sediment core from Greifensee to elucidate the historical trends of PCDD/F and PCB inputs between 1848 and 1999. Concentrations of PCB and PCDD/F increased by more than one order of magnitude between 1930 and 1960. PCB and PCDD/F concentrations were 5700 ng/kg dry weight (dw) and 160 ng/kg dw, respectively, in sediments originating from the late 1930s and reached a maximum of 130,000 ng/kg dw and 2400 ng/kg dw, respectively, in the early 1960s. From 1960 on, concentrations decreased to the 1930s level by the mid 1980s. A remarkable shift in the PCDD/F pattern was observed after the early 1940s. Before 1940, the PCDD/F pattern was PCDF dominated (ratio of PCDD to PCDF=0.41+/-0.11), while the PCDD started to be the major species after the early 1940s (ratio of PCDD to PCDF=1.46+/-0.38). The temporal trends of PCB and PCDD/F correlate surprisingly well with each other. This might be due to the coincidence of two factors. The introduction of PCB on the market in the 1930s resulted in emissions due to the widespread use of these industrial chemicals. In the same time period, waste incineration became an increasingly popular way to get rid of garbage, boosting the PCDD/F emissions significantly. The rapid decline of PCDD/F and PCB concentrations in the sediment starting in the early 1960s reflects the result of better emission control techniques in thermal processes and the improvement of waste water treatment in the catchment of Greifensee.

Early diagenetic processes generate iron and manganese oxide layers in the sediments of Lake Baikal, Siberia.

Distinct layers of iron(III) and manganese(IV) (Fe/Mn) oxides are found buried within the reducing part of the sediments in Lake Baikal and cause considerable complexity and steep vertical gradients with respect to the redox sequence. For the on-site investigation of the responsible biogeochemical processes, we applied filter tube samplers for the extraction of sediment porewater combined with a portable capillary electrophoresis instrument for the analyses of inorganic cations and anions. On the basis of the new results, the sequence of diagenetic processes leading to the formation, transformation, and dissolution of the Fe/Mn layers was investigated. With two exemplary cores we demonstrate that the dissolution of particulate Fe and Mn is coupled to the anaerobic oxidation of CH4 (AOM) either via the reduction of sulphate (SO4(2-)) and the subsequent generation of Fe(II) by S(-II) oxidation, or directly coupled to Fe reduction. Dissolved Fe(II) diffuses upwards to reduce particulate Mn(IV) thus forming a sharp mineral boundary. An alternative dissolution pathway is indicated by the occurrence of anaerobic nitrification of NH4(+) observed at locations with Mn(IV). Furthermore, the reasons and consequences of the non-steady-state sediment pattern and the resulting redox discontinuities are discussed and a suggestion for the burial of active Fe/Mn layers is presented.

Temporal trends, congener patterns, and sources of octa-, nona-, and decabromodiphenyl ethers (PBDE) and hexabromocyclododecanes (HBCD) in Swiss lake sediments.

With the recent ban of pentabromodiphenyl ether (technical PentaBDE) and octabromodiphenyl ether (technical OctaBDE) mixtures in the European Union (EU) and in parts of the United States, decabromodiphenyl ether (technical DecaBDE) remains as the only polybrominated diphenyl ether (PBDE) based flame retardant available, today. The EU risk assessment report for DecaBDE identified a high level of uncertainty associated with the suitability of the current risk assessment approach for secondary poisoning by debromination of DecaBDE to toxic lower brominated diphenylethers. Addressing this still open question, we investigated concentrations and temporal trends of DecaBDE, NonaBDE, and OctaBDE congeners in the sediments of Greifensee, a small lake located in an urban area close to Zürich, Switzerland. PBDE appeared first in sediment layers corresponding to the mid 1970s. While total Tri-HeptaBDE (BDE-28, -47, -99, -100, -153, -154 and -183) concentrations leveled off in the mid 1990s to about 1.6 ng/g dw (dry weight), DecaBDE levels increased steadily to 7.4 ng/g dw in 2001 with a doubling time of 9 years. Hexabromocyclododecanes (HBCD) appeared in Greifensee sediments in the mid 1980s. They are an important class of flame retardants that are being used in increasing amounts, today. As was observed for DecaBDE, HBCD concentrations were continuously increasing to reach 2.5 ng/g dw in 2001. Next to DecaBDE, all 3 NonaBDE congeners (BDE-208, BDE-207, and BDE-206) and at least 7 out of the 12 possible OctaBDE congeners (BDE-202, BDE-201, BDE-197/204, BDE-198/203, BDE-196/200, BDE-205, and BDE-194) were detected in the sediments of Greifensee. Highest concentrations were found in the surface sediments with 7.2, 0.26, 0.14, and 1.6 ng/g dw for Deca-, Nona-, Octa-, and the sum of Tri-HeptaBDE, respectively. While DecaBDE and NonaBDE were found to increase rapidly, the increase of OctaBDE was slower. Congener patterns of Octa- and NonaBDE present in sediments of Greifensee did not change with time. Consequently, there was no evidence for sediment mediated long-term transformation of PBDE within the observed time span of almost 30 years. Despite the high persistence of DecaBDE, environmental debromination occurs, as shown by the detection of a shift in congener patterns of Octa- and NonaBDE in sediments, compared to the respective congener patterns in technical PBDE products. The OctaBDE congener BDE-202 was detected in sediments, representing a transformation product that is not reported in any of the technical PBDE products. Comparison of OctaBDE congener patterns in sediments with OctaBDE congener patterns from known sources reveals that (i) they were distinctively different from the congener patterns in technical PBDE products and (ii) that they were similar to the OctaBDE patterns in house dust and photodegradation products of DecaBDE, suggesting contributions from these sources.

Efficacy of vacuum bone cement mixing systems in reducing methylmethacrylate fume exposure: comparison of 7 different mixing devices and handmixing.

BACKGROUND: Polymethylmethacrylate (PMMA) bone cements are mainly used for implant fixation in joint replacement surgery. During cement preparation for application, all staff in the operating theatre are exposed to methylmethacrylate (MMA) fumes, which are known to have toxic side effects. METHODS AND RESULTS: In this study we found that vacuum mixing of bone cement with 7 commercially available mixing devices significantly reduced the emission of MMA vapors in the breathing zone when compared with classic hand mixing in an open bowl. Gas chromatography appears to be more sensitive for detection of MMA fumes than Photo Inonization Detection. INTERPRETATION: According to present knowledge, even repeated mixing of PMMA bone cement during a normal working day does not seem to constitute an increased health risk, particularly if vacuum mixing is implemented.