Development and validation of an in situ high-resolution technique for measuring antibiotics in sediments

Important biogeochemical processes occur in sediments at fine scales. Sampling techniques capable of yielding information with high resolution are therefore needed to investigate chemical distributions and fluxes and to elucidate key processes affecting chemical fates. In this study, a high-resolution diffusive gradients in thin-films (DGT) technique was systematically developed and tested in a controlled sediment system to measure organic contaminants, antibiotics, for the first time. The DGT probe was used to resolve compound distributions at the mm scale. It also reflected the fluxes from the sediment pore-water and remobilization from the solid phase, providing more dynamic information. Through the fine scale detection, a reduction of re-supply was observed over time, which was concentration and location dependent. Compared to the Rhizon sampling method, antibiotic concentrations obtained by DGT probes were less than the pore-water concentrations, as DGT measures the labile fraction of the compounds. The DGT probe was also tested on an intact sediment core sampled from a lake in China and used to measure the distribution of labile antibiotics with depth in the core at the mm scale. ENVIRONMENTAL IMPLICATION: The abuse of antibiotics and widespread of their residues influences the ecosystem, induces the generation of super-bacteria, and finally poses threat to human health. Sediments adsorbs pollutants from the aquatic environment, while may also release them back to the environment. We systematically developed DGT probe approach for measuring antibiotics in sediment in situ in high resolving power, it provides information at fine scale to help us investigate biogeochemical processes take place in sediment and sediment-water interface.

Medical aspects of the tour by Martin Martin (c 1660-1719) of the Western and Northern Islands of Scotland, Circa 1695

This review is based investigations on the Western Isles, Scotland, by Martin Martin, a notable Scottish Highlander, academic and medical doctor, of the 17th-18th century. His extensive observations of the geography and peoples of these Isles were recorded in his books, "On the Description of the Western Islands of Scotland Circa 1695" and "A Late Voyage to St Kilda". In these books and subsequent papers there were some noteworthy observations on the occurrence (and as he says non-occurrence) of "epidemical" diseases and conditions afflicting the peoples of The Isle of Skye and the Western Isles of Scotland in this period, and these are discussed in this review. Martin also gives details of a wide variety of remedies that were observed or reported by inhabitants around that time. Some of these remedies are interesting for their relevance to the period but others are of doubtful merit. These are reviewed here more for their significance in the understanding of the diseases and conditions of humans and even in some cases animals at that time. Introductions by Charles Withers and R.W. Munro, 11 and re-assessments of the contributions of Martin and colleagues of that time have given insight into the health and condition of peoples of the Western Isles of Scotland(the Occidental) (Martin 1695; Martin 1716).

Spatiotemporal distribution, sources apportionment and ecological risks of PAHs: a study in the Wuhan section of the Yangtze River

This study investigated the sources, contamination and ecological risks of polycyclic aromatic hydrocarbons (PAHs) based on their spatiotemporal distribution in aquatic environment in the Wuhan section of the Yangtze River (WYR). The fugacity ratio evaluation indicated that sediment was secondary release sources of two- and three-ring PAHs and sinks of four- and five-ring PAHs. The total concentrations of PAHs (Σ16PAHs) ranged from 2.51 to 102.5 ng/L in water with the dominant contribution of 47.8% by two-ring PAHs. Σ16PAHs in sediments varied from 5.90 to 2926 ng/g with the contribution of 35.4% by four-ring PAHs. The higher levels of PAHs occurred around developed industrial areas during the wet season, which was related to local industrial emissions and influenced by rainfall/runoff. Annual flux of Σ16PAHs was estimated of 28.77 t. The PMF model analysis revealed that petroleum and industrial emissions were the dominant sources in water accounting for 58.5% of the total pollution, although traffic emission was the main source for sediment accounting for 44.6%. Risk assessments showed that PAHs in water were at low risks, whereas about 44% of the sediments were identified as medium risks. Therefore, energy structure adjustment and further implement of regulation and monitoring are necessary to reduce PAH emissions.

Annual flux estimation and source apportionment of PCBs and PBDEs in the middle reach of Yangtze River, China

This work is the first time to investigate the annual flux, spatiotemporal changes and sources of PCBs and PBDEs in water and sediment from the middle reach of Yangtze River (Wuhan, China), which was particularly based on the monthly monitoring data in a one-year-round study. The concentrations of PCBs and PBDEs in water were <LOD-3.41 ng/L and <LOD-3.01 ng/L, while they were <LOD-0.23 ng/g and 0.04-3.01 ng/g in sediments, respectively. Sediment-water partitioning data suggested an overall tendency for PCBs and PBDEs of transferring from water to sediment. PMF analysis showed that the possible sources of PCBs included fuel emissions (36.7 %), e-waste (26.4 %), paint and coatings (13.6 %), Aorclor1248 (12.4 %) and waste/biodegradation processes (10.8 %), while the potential sources for PBDEs were debromination of highly brominated PBDEs (56.1 %), industrial Penta-BDEs (16.6 %), e-waste (14.1 %) and atmospheric deposition (13.3 %). The annual fluxes were estimated for PCBs and PBDEs with 578 kg and 1360 kg, respectively. The results of risk assessment revealed that PCBs and PBDEs were at low or minimal risks in the study area, although the potential threat to the ecosystem should not be ignored due to their bio-accumulative effect and high toxicity particularly when these compounds are transferred through the food chain.

Input-export fluxes of heavy metals in the Cochin estuary, southwest coast of India

Cochin estuary (CE) is one of the largest tropical estuaries along the southwest coast of India, sustaining rich bio-resources. Several studies enlighten the environmental changes in the CE caused by anthropogenic activities. In the present study, an attempt has been made to quantify the heavy metal (dissolved and particulate) fluxes brought by the six rivers into the CE with their exchange into the coastal ocean through the major inlet at Cochin during a steady flow period (October-November 2015). The water flux across the inlet was quantified using an acoustic doppler current profiler. The measured daily input of dissolved metals from the rivers was 2.43 × 10³ kg Fe, 334 kg Zn, 259 kg Ni, and 83 kg Cr, while that of particulate metals were 85.30 × 10³ kg Fe, 8. 6 × 10³ kg Mn, 236.9 kg Cr, and 111.9 kg Zn. The net export of metals through the Cochin inlet (per tidal cycle) was 3.3 × 10³ kg Fe, 515 kg Cr, 150 kg Zn, and 5 kg Ni in dissolved form and 3.32 × 10⁵ kg Fe, 1747 kg Mn, 1636 kg Cr, 1397 kg Zn, and 586 kg Ni in particulate form. The high concentrations of metals during ebb tides are clear indications of their contribution from the industrial conglomerates (industrial units of metallurgy, catalyst, fertilizer, and pesticides) located in the Periyar River. The significance of this study is that the export fluxes may increase further during the summer monsoon (June to September), which may impact the abundant fishery emanating in the coastal environment during the period due to intense upwelling.

Methane and carbon dioxide cycles in lakes of the King George Island, maritime Antarctica

Freshwater ecosystems are important contributors to the global greenhouse gas budget and a comprehensive assessment of their role in the context of global warming is essential. Despite many reports on freshwater ecosystems, relatively little attention has been given so far to those located in the southern hemisphere and our current knowledge is particularly poor regarding the methane cycle in non-perennially glaciated lakes of the maritime Antarctica. We conducted a high-resolution study of the methane and carbon dioxide cycle in a lake of the Fildes Peninsula, King George Island (Lat. 62°S), and a succinct characterization of 10 additional lakes and ponds of the region. The study, done during the ice-free and the ice-seasons, included methane and carbon dioxide exchanges with the atmosphere (both from water and surrounding soils) and the dissolved concentration of these two gases throughout the water column. This characterization was complemented with an ex-situ analysis of the microbial activities involved in the methane cycle, including methanotrophic and methanogenic activities as well as the methane-related marker gene abundance, in water, sediments and surrounding soils. The results showed that, over an annual cycle, the freshwater ecosystems of the region are dominantly autotrophic and that, despite low but omnipresent atmospheric methane emissions, they act as greenhouse gas sinks.

Pond mitigation in dissolved and particulate pesticide transfers: Influence of storm events and seasonality (Auradé agricultural catchment, SW-France)

In agricultural headwater catchments, wetlands such as ponds are numerous and well known to partly dissipate contamination. Most of the pesticides are transferred from soils to the aquatic environment during flood events. This study reports the annual/seasonal behaviour of 6 pesticides (metolachlor, boscalid, epoxiconazole, tebuconazole, aclonifen and pendimethalin) in such an environment. Because it is rarely considered, the study focussed on the high frequency of the distribution of pesticides between dissolved and particulate phases, as well as the main controlling factors of their upstream-downstream transfer. The pond removal rate was calculated to evaluate the wetland efficiency in pesticide mitigation. We conducted a one-year high frequency hydrochemical survey, with particular emphasis on flood events, in the upper Auradé catchment (SW-France), an area of long-term conventional agriculture on highly erosive carbonated soils. The inlet and outlet of the pond were instrumented for water level measurements and water sampling. The highest concentrations were observed for tebuconazole and, in general, the presence of the molecules during the year depended on the season. The pond showed satisfactory efficiency in pesticide attenuation for the six molecules considered, although the removal rate depended on the molecule and the bearing phase (from 28.4% for boscalid to 89.4% for aclonifen in the dissolved phase and from 22.1% for pendimethalin to 96.8% for metolachlor in the particulate fraction). Interestingly, the more hydrophilic the molecule (low LogK_OW), the more efficient the pesticide removal rate was for its particulate fraction, and the opposite for hydrophobic molecules (high LogK_OW). Flood events carried a large amount of Total Suspended Solid (TSS) bearing hydrophobic molecules from a major legacy of upper catchment soils, although 52% of the pesticides were transported by the dissolved fraction. Significant resuspension of TSS from the pond was evidenced by the annual mass balance with four tons of TSS released, while the positive rate of pesticide removal involved other effective mechanisms such as exchange and complexation. Although these constructed wetlands may be beneficial for pesticide mitigation, the results highlighted the need for improved land management in the upstream catchment during the different seasons to avoid bare soils that pose a risk of high surface water contamination, especially due to the presence of hydrophobic molecules in combination with a high erosive context.

Particle size distribution, wet deposition and scavenging effect of per- and polyfluoroalkyl substances (PFASs) in the atmosphere from a subtropical city of China

Per- and polyfluoroalkyl substances (PFASs) as emerging organic pollutants have received great attention, but the scavenging efficiency of particulate PFASs by wet deposition was rarely studied. For the first time, we reported the scavenging efficiency of PFASs on different particle sizes. In this study, both rainwater and particle samples were collected for a whole year from Xiamen, a subtropical city of China. Particulate PFASs ranged from 4.11 to 67.41 pg m^-3, with an average value of 26.56 pg m^-3, and perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) were the main compounds. Perfluorocarboxylic acids (PFCAs) were predominantly observed on fine particles (<1 μm), while PFOS and 6:2 chlorinated polyfluoroalkyl ether sulfonic acid (6:2 Cl-PFESA) had large proportions on coarse particles (1-2.5 μm and 2.5-10 μm). In the rainwater, PFASs ranged from 0.20 to 180.65 ng L^-1, with an average value of 10.71 ng L^-1, and perfluorobutanoic acid (PFBA), PFOA were the main compounds. The wet deposition flux of ∑PFASs was 5200 mg km^-2 yr^-1, exhibiting high fluxes during the wet season (March to September). The scavenging efficiency of particulate PFOS and PFOA ranged from 68%-98% during the rainfall, and wash-out of the raindrops was found to be one of the main scavenging mechanisms. In addition, the precipitation duration and intensity influenced the scavenging efficiency. The scavenging capacity of PFCAs was large on fine particles, while for per-and polyfluoroalkyl sulfonic acids, the scavenging capacity was high on coarse particles. Our results showed that wet deposition effectively removed medium to long carbon chain (≥C6) PFASs in the atmosphere.

Spatial and temporal distributions of microplastics and their macroscopic relationship with algal blooms in Chaohu Lake, China

Microplastics are emerging pollutants with sizes less than 5 mm, and they are ubiquitous. The occurrence of algal blooms has become a major problem affecting water quality in Chaohu Lake. To understand the relationship between the microplastic distribution and algal bloom density from a macroscopic point of view in Chaohu Lake, we collected microplastic samples from water and sediments during the wet and dry seasons and collected satellite remote sensing images of the algae density in recent years. The research results showed that the spatial and temporal distributions of microplastics were uneven and varied greatly. The average abundances of microplastics in the water samples were 2133 ± 1534 n•m^-3 in the dry season and 1679 ± 1577 n•m^-3 in the wet season, and the average abundance of microplastics in sediments was 308 ± 231 n•kg^-1. The abundance of microplastics in the estuaries was higher than those in other locations, and it was higher in the western part of the lake than in the eastern part. The microplastics in water and sediments presented different sizes, colors, shapes and compositions. The abundance, distribution and migration of microplastics were mainly affected by population density, rainfall, runoff, hydrodynamic force and wind direction. At a more macroscopic level, the distribution of microplastics was similar to that of algal blooms, TN and TP to some extent, especially in the early stage of algal bloom outbreaks, and the algal density was significantly positively correlated with the flux of microplastics into the lake. Microplastics, as carriers of algae, could promote the growth of algae blooms in the early stage, while in the later stage, microplastics and algal blooms could aggregate and coprecipitate through adsorption or adhesion and then inhibit the growth of algae.

Visualizing physiological parameters in cells and tissues using genetically encoded indicators for metabolites

The study of metabolism is undergoing a renaissance. Since the year 2002, over 50 genetically-encoded fluorescent indicators (GEFIs) have been introduced, capable of monitoring metabolites with high spatial/temporal resolution using fluorescence microscopy. Indicators are fusion proteins that change their fluorescence upon binding a specific metabolite. There are indicators for sugars, monocarboxylates, Krebs cycle intermediates, amino acids, cofactors, and energy nucleotides. They permit monitoring relative levels, concentrations, and fluxes in living systems. At a minimum they report relative levels and, in some cases, absolute concentrations may be obtained by performing ad hoc calibration protocols. Proper data collection, processing, and interpretation are critical to take full advantage of these new tools. This review offers a survey of the metabolic indicators that have been validated in mammalian systems. Minimally invasive, these indicators have been instrumental for the purposes of confirmation, rebuttal and discovery. We envision that this powerful technology will foster metabolic physiology.

Titanium nanoparticles fate in small-sized watersheds under different land-uses

Surface waters from three catchments having contrasting land-uses (forested, agricultural, and urban) were sampled monthly and analysed for nanoparticulate titanium dioxide (NPs-TiO₂) by single particle ICPMS and electron microscopy. We report one-year of data for NPs-TiO₂ having average number and mass concentrations of 9.1 × 10⁸ NPs-TiO₂ particles L^-1 and 11 µg NPs-TiO₂ L^-1 respectively. An increase in concentration during warmer months is observed in the forested and agricultural catchments. Both concentrations of NPs-TiO₂ are within the range of recently reported values using similar analytical approaches. The positive correlations for NPs-TiO₂ mass concentration or particle number with the concentration of some trace elements and DOC in the forested and agricultural catchments suggest the detected NPs-TiO₂ in these two systems are mostly from geogenic origin. Additionally, microscopy imaging confirmed the presence of NPs in the three catchments. Furthermore, the land-area normalized annual flux of NPs-TiO₂ (1.65 kg TiO₂ year^-1 km^-2) was highest for the agricultural catchment, suggesting that agricultural practices have a different impact on the NPs-TiO₂ dynamics and exports than other land-uses (urban or forestry). A similar trend is also found by the reanalysis of recent literature data.

Cyanobacteria blooms potentially enhance volatile organic compound (VOC) emissions from a eutrophic lake: Field and experimental evidence

Eutrophication promotes massive cyanobacteria blooms (CBBs), leading to the release of volatile organic compounds (VOCs). To investigate the effects of cyanobacteria on VOC emissions, field campaigns were carried out in eutrophic Chaohu Lake at six sites with different microalgae densities during CBBs in summer 2019, and incubation experiments were performed in the laboratory. The results showed that the lake water was the primary source of VOCs at six sampling sites in Chaohu Lake during CBBs, with an average total VOC flux of 81.2 ± 20.6 μg m^-2 h^-1. Alkanes were the most abundantly emitted VOCs, with a share of 23.1-63.7% of total emitted VOCs, followed by aromatics (16.6-46.3%). The fluxes of total VOCs were significantly greater at sites B and/or C than at site A in July, and at site B' and/or C' than at site A' in August in Chaohu Lake. The fluxes of total VOCs from living and decayed cyanobacteria in the experimental treatments were two orders of magnitude higher than the corresponding values in the control treatments in the laboratory incubation. Taken together, these results suggested that CBBs potentially enhanced VOC emissions from the eutrophic lake, and that cyanobacteria acted as an important source of VOCs. Additionally, non-methane hydrocarbons (i.e., alkanes, alkenes, and aromatics) predominated among the released VOCs during the stabilization and senescence stages, while oxygenated volatile organic compounds (i.e. alcohols, aldehydes, ketones, esters, and furans) prevailed during the apoptosis stage and aromatics and volatile organic sulfur compounds predominated during the decomposition stage, suggesting that VOC emissions varied markedly at different life stages.

The influence of near-field fluxes on seasonal carbon dioxide enhancements: results from the Indianapolis Flux Experiment (INFLUX)

BACKGROUND

Networks of tower-based CO₂ mole fraction sensors have been deployed by various groups in and around cities across the world to quantify anthropogenic CO₂ emissions from metropolitan areas. A critical aspect in these approaches is the separation of atmospheric signatures from distant sources and sinks (i.e., the background) from local emissions and biogenic fluxes. We examined CO₂ enhancements compared to forested and agricultural background towers in Indianapolis, Indiana, USA, as a function of season and compared them to modeled results, as a part of the Indianapolis Flux (INFLUX) project.

RESULTS

At the INFLUX urban tower sites, daytime growing season enhancement on a monthly timescale was up to 4.3-6.5 ppm, 2.6 times as large as those in the dormant season, on average. The enhancement differed significantly depending on choice of background and time of year, being 2.8 ppm higher in June and 1.8 ppm lower in August using a forested background tower compared to an agricultural background tower. A prediction based on land cover and observed CO₂ fluxes showed that differences in phenology and drawdown intensities drove measured differences in enhancements. Forward modelled CO₂ enhancements using fossil fuel and biogenic fluxes indicated growing season model-data mismatch of 1.1 ± 1.7 ppm for the agricultural background and 2.1 ± 0.5 ppm for the forested background, corresponding to 25-29% of the modelled CO₂ enhancements. The model-data total CO₂ mismatch during the dormant season was low, - 0.1 ± 0.5 ppm.

CONCLUSIONS

Because growing season biogenic fluxes at the background towers are large, the urban enhancements must be disentangled from the biogenic signal, and growing season increases in CO₂ enhancement could be misinterpreted as increased anthropogenic fluxes if the background ecosystem CO₂ drawdown is not considered. The magnitude and timing of enhancements depend on the land cover type and net fluxes surrounding each background tower, so a simple box model is not appropriate for interpretation of these data. Quantification of the seasonality and magnitude of the biological fluxes in the study region using high-resolution and detailed biogenic models is necessary for the interpretation of tower-based urban CO₂ networks for cities with significant vegetation.

Seasonal variations in arsenic mobility and bacterial diversity: The case study of Huangshui Creek, Shimen Realgar Mine, Hunan Province, China

Rivers throughout the world have been contaminated by arsenic dispersed from mining activities. The biogeochemical cycling of this arsenic has been shown to be due to factors such as pH, Eh, ionic strength and microbial activity, but few studies have examined the effects of both seasonal changes and microbial community structure on arsenic speciation and flux in mining-affected river systems. To address this research gap, a study was carried out in Huangshui Creek, Hunan province, China, which has been severely impacted by long-term historic realgar (α-As₄S₄) mining. Water and sediment sampling, and batch experiments at different temperatures using creek sediment, were used to determine the form, source and mobility of arsenic. Pentavalent (AsO₄³) and trivalent arsenic (AsO₃^3-) were the dominant aqueous species (70-89% and 30-11%, respectively) in the creek, and the maximum concentration of inorganic arsenic in surface water was 10,400 μg/L. Dry season aqueous arsenic concentrations were lower than those in the wet season samples. The sediments contained both arsenate and arsenite, and relative proportions of these varied with season. 8.3 tons arsenic per annum were estimated to be exported from Huangshui Creek. Arsenic release from sediment increased by 3 to 5 times in high water temperature batch experiments (25 and 37 °C) compared to those carried out at low temperature (8 °C). Our data suggest that the arsenic-containing sediments were the main source of arsenic contamination in Huangshui Creek. Microbial community structured varied at the different sample sites along the creek. Redundancy analysis (RDA) showed that both temperature and arsenic concentrations were the main controlling factors on the structure of the microbial community. Protecbacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Verrucomicrobia, and Planctomycetes were the stable dominant phyla in both dry and wet seasons. The genera Flavobacterium, Hydrogenophaga and Sphingomonas occurred in the most highly arsenic contaminated sites, which removed arsenic by related metabolism.Our findings indicate that seasonal variations profoundly control arsenic flux and species, microbial community structure and ultimately, the biogeochemical fate of arsenic.

Chemistry of dry and wet atmospheric deposition over the Balearic Islands, NW Mediterranean: Source apportionment and African dust areas

Wet and dry aerosol deposition samples were collected from September 2010 to August 2012 at a remote background site in the Mallorca Isle (Western Mediterranean). Ions and major and trace elements were determined in soluble and insoluble fractions. Temporal variations of chemical components are discussed and interpreted. The overall pattern associated to long-range-transport air masses is studied: Dry/Wet deposition ratios, charges and composition depend clearly on the meteorological scenario. E.g. Dry/Wet ratio is 1:1 when air comes from North Africa, in contrast to a 1:9 ratio under the mainland Europe influence. Moreover, an innovating source apportionment study was conducted integrating both dry and wet deposition samples. Six sources were revealed, including marine aerosols (32%); two different mineral factors, African dust (15%) and regional dust (12%); two anthropogenic factors, one related to road traffic (8%) and another to regional sources (17%); and a mixed factor having biomass burning emissions and others sources (17%). Temporal variations and influence from long-range-transport air masses are also investigated. Fertilization deposition trends have also been explored, observing nutrients settling, as well as nitrate and sulphate, due to their agricultural interest. An important peak during January-February 2012 is studied in depth. Having in mind the strong impact of African dust on the global deposition budget, the analysis of elemental ratios between key dust components was investigated in order to identify major source areas affecting Western Mediterranean: Western Sahara, Algeria-Hoggar Massif and Tunisia-Libya. Differences among these regions are evident. E.g. the impact of industrial emissions is well-detected under outbreaks from Tunisia-Libya, with relatively high content of Ni and Pb.

Mercury biogeochemical cycling: A synthesis of recent scientific advances

The focus of this paper is to briefly discuss the major advances in scientific thinking regarding: a) processes governing the fate and transport of mercury in the environment; b) advances in measurement methods; and c) how these advances in knowledge fit in within the context of the Minamata Convention on Mercury. Details regarding the information summarized here can be found in the papers associated with this Virtual Special Issue of STOTEN.

A global perspective on mercury cycling in the ocean

Mercury (Hg) is a ubiquitous metal in the ocean that undergoes in situ chemical transformations in seawater and marine sediment. Most relevant to public health is the production of monomethyl-Hg, a neurotoxin to humans that accumulates in marine fish and mammals. Here we synthesize 30 years of Hg measurements in the ocean to discuss sources, sinks, and internal cycling of this toxic metal. Global-scale oceanographic survey programs (i.e. CLIVAR and GEOTRACES), refined protocols for clean sampling, and analytical advancements have produced over 200 high-resolution, full-depth profiles of total Hg, methylated Hg, and gaseous elemental Hg throughout the Atlantic, Pacific, Arctic, and Southern Oceans. Vertical maxima of methylated Hg were found in surface waters, near the subsurface chlorophyll maximum, and in low-oxygen thermocline waters. The greatest concentration of Hg in deep water was measured in Antarctic Bottom Water, and in newly formed Labrador Sea Water, Hg showed a decreasing trend over the past 20 years. Distribution of Hg in polar oceans was unique relative to lower latitudes with higher concentrations of total Hg near the surface and vertical trends of Hg speciation driven by water column stratification and seasonal ice cover. Global models of Hg in the ocean require a better understanding of biogeochemical controls on Hg speciation and improved accuracy of methylated Hg measurements within the international community.

Historical sedimentary deposition and flux of PAHs, PCBs and DDTs in sediment cores from the western Adriatic Sea

The sources and depositional history of polycyclic aromatic hydrocarbons (PAHs) and organochlorine compounds (OCs) over the last century were investigated in sediment cores from the North Adriatic Sea (Po River prodelta) and the South-Western Adriatic Margin (SWAM). Contaminant concentrations were higher in the Po River prodelta. ∑₁₆PAHs ranged from 193 to 533 ng g^-1, ∑₅PCBs ranged from 0.9 to 5.2 ng g^-1 and ∑DDTs (p,p'-DDD + p,p'-DDE) ranged from 0.1 to 2.5 ng g^-1. In the SWAM, ∑PAHs ranged from 11 to 74 ng g^-1 while ∑PCB and ∑DDT concentrations were close to the MQL. Accordingly, contaminant fluxes were much higher in the northern (mean values of 152 ± 31 ng cm² y^-1 and 0.70 ± 0.35 ng cm² y^-1 for PAHs and OCs, respectively) than in the southern Adriatic (2.62 ± 0.9 ng cm² y^-1 and 0.03 ± 0.02 ng cm² y^-1 for PAHs and OCs, respectively). The historical deposition of PAHs seemed to be influenced by the historical socioeconomic development and by changes in the composition of fossil fuel consumption (from petroleum derivatives to natural gas) in Italy from the end of the 19th century to the present. Similarly, vertical variations in DDT concentrations matched its historical use and consumption in Italy, which started around in the mid-late 1940s to fight typhus during the II World War. Contaminant concentrations detected in sediments does not seem to pose ecotoxicological risk for marine organisms in the Adriatic Sea.

Greenhouse gas emissions from intact riparian wetland soil columns continuously loaded with nitrate solution: a laboratory microcosm study

In this study, we aimed at determining greenhouse gas (GHG) (CO₂, CH₄, and N₂O) fluxes exchange between the soil collected from sites dominated by different vegetation types (Calamagrostis epigeios, Phragmites australis, and Carex schnimdtii) in nitrogenous loaded riparian wetland and the atmosphere. The intact soil columns collected from the wetland were incubated in laboratory and continuously treated with [Formula: see text]-enriched water simulating downward surface water percolating through the soil to become groundwater in a natural system. This study revealed that the soil collected from the site dominated by C. epigeios was net CO₂ and N₂O sources, whereas the soil from P. australis and C. schnimdtii were net sinks of CO₂ and N₂O, respectively. The soil from the site dominated by C. schnimdtii had the highest climate impact, as it had the highest global warming potential (GWP) compared with the other sites. Our study indicates that total organic carbon and [Formula: see text] concentration in the soil water has great influence on GHG fluxes. Carbon dioxide (CO₂) and N₂O fluxes were accelerated by the availability of higher [Formula: see text] concentration in soil water. On the other hand, higher [Formula: see text] concentration in soil water favors CH₄ oxidation, hence the low CH₄ production. Temporally, CO₂ fluxes were relatively higher in the first 15 days and reduced gradually likely due to a decline in organic carbon. The finding of this study implies that higher [Formula: see text] concentration in wetland soil, caused by human activities, could increase N₂O and CO₂ emissions from the soil. This therefore stresses the importance of controls of [Formula: see text] leaching in the mitigation of anthropogenic N₂O and CO₂ emissions.

Air-water exchange of pesticidal persistent organic pollutants in the lower stretch of the transboundary river Ganga, India

The lower stretch of the perennial transboundary river Ganga is known as the Hooghly River (HR) in India. Despite the strict ban, HR has been evidenced with residues of pesticidal persistent organic pollutants (POPs) from primary and secondary sources. Hence surface water sampling and passive air sampling (PAS) were conducted along the urban and suburban transects and discharge points to study the fate of pesticidal (POPs along the HR. Excluding the discharge points, the mean concentration of hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT) and endosulfan (ENDO) were 6 ng/L, 4 ng/L and 36 ng/L in surface water and 888 pg/m³, 1689 pg/m³ and 429 pg/m³ in atmosphere respectively. Percentage composition and diagnostic ratios strongly suggest ongoing use of technical HCH, DDT and endosulfan. Elevated endosulfan in surface water has been related to its usage during fishing. Except for p,p'-DDE, α-Endo and β-Endo, fluxes at the air-water interface showed net deposition from air to water for all the OCPs in urban and suburban transects. The estimated eco-toxicological risk assessment showed risk on lower trophic organisms due to DDT and lindane mostly at the discharge points. Endosulfan can pose potential risk to the edible fishe species in the HR.

Quantifying greenhouse gas emissions from municipal solid waste dumpsites in Cameroon

Open dumpsites that receive municipal solid waste are potentially significant sources of greenhouse gas (GHG) emissions into the atmosphere. There is little data available on emissions from these sources, especially in the unique climate and management of central Africa. This research aimed at quantifying CH₄, N₂O and CO₂ emissions from two open dumpsites in Cameroon, located in Mussaka-Buea, regional headquarters of the South West Region and in Mbellewa-Bamenda, regional headquarters of the North West Region. Emissions were measured during the wet season (May 2015 and August 2016) at the Mussaka and Mbellewa dumpsites respectively. Dumpsite surfaces were partitioned into several zones for emission measurements, based on the current activity and the age of the waste. Static flux chambers were used to quantify gas emission rates thrice a day (mornings, afternoons and evenings). Average emissions were 96.80 ± 144 mg CH₄ m^-2 min^-1, 0.20 ± 0.43 mg N₂O m^-2 min^-1 and 224.78 ± 312 mg CO₂ m^-2 min^-1 in the Mussaka dumpsite, and 213.44 ± 419 mg CH₄ m^-2 min^-1, 0.15 ± 0.15 mg N₂O m^-2 min^-1 and 1103.82 ± 1194 mg CO₂ m^-2 min^-1 at the Mbellewa dumpsite. Emissions as high as 1784 mg CH₄ m^-2 min^-1, 2.3 mg N₂O m^-2 min^-1 and 5448 mg CO₂ m^-2 min^-1 were measured from both dumpsites. Huge variations observed in emissions between the different zones on the waste surface were likely a result of the heterogeneous nature of the waste, different stages in waste decomposition and different environmental conditions within the waste. Management activities that disturb waste, such as spreading and compressing potentially increase gas emissions, while covering waste with a layer of soil potentially mitigate gas emissions. Recommendations were for dumpsites to be upgraded to sanitary landfills, and biogas production from such landfills should be exploited to reduce CH₄ emissions.

Extraction of levetiracetam for therapeutic drug monitoring by transdermal reverse iontophoresis

Recently, transdermal reverse iontophoresis across the skin has been investigated as a novel technology for the purpose of diagnosis as well as therapeutic drug monitoring. Accordingly, the objective of this study was to investigate ex vivo and in vivo transdermal extraction of levetiracetam, an antiepileptic drug, across the pig ear skin by reverse iontophoresis. Reverse iontophoresis experiments were performed using three chambered diffusion cells. Extractions profiles were generated in phosphate buffers at different current intensities, pH and ionic strength as well donor drug concentrations. This was followed by ex vivo extraction in gels and in vivo extractions using New Zealand rabbits. Results indicate that levetiracetam was extracted at both anode and cathode. Flux values were unaffected by increase in current intensities (0.5 mA and 0.6 mA) but affected by pH and ionic strength. Neither in cathodal nor in anodal extraction, flux values did show a proportional relationship with the donor drug concentration. At low and medium concentration levels, flux values did not show any major change but the extraction flux at high donor concentration was much higher. In contrast, in vivo experiment with rabbits resulted in wide variation of fluxes with very high fluxes recorded at the cathodal end. Reasons attributed to this difference may include lower current intensity, and species variation. The most significant finding of this study is that measurable amounts of the levetiracetam were extracted at both the ends indicating its feasibility for non-invasive drug monitoring.

Inventories of heavy metal inputs and outputs to and from agricultural soils: A review

Heavy metal pollution of agricultural soils is an important issue around the world. To understand the overall pollution process, accurate determination of every input and output pathway of heavy metals to and from soils is essential. Hence, input and output inventory, a quantitative analysis method of heavy metals balance in agricultural soils, has been widely used. However, due to differences in geography, climate, socioeconomic factors, industrial and agricultural production, substantial variation exists among existing input and output inventories for different countries and regions. In this study, we systematically analyzed these differences and the findings will improve the compilation of inventories worldwide.

Mercury transport and fate models in aquatic systems: A review and synthesis

Mercury contamination in aquatic systems has been an issue to the natural ecosystem and human health. Environmental models have become a valuable decision-making tool and play a significant role in mercury pollution control and management. This paper gives an overview of currently available models for simulating mercury transport and fate in aquatic systems. The mercury transformation mechanisms included in these models were identified, as well as data limitations in the models' application. Future advances in understanding mercury transport, cycling, and biogeochemistry in both water column and sediment will improve the robustness of current modeling applications. Moreover, additional field data are critically needed to better predict the concentrations of multi-phase mercury species in various aquatic systems, including measurements in the water column, benthic sediments, and organisms. Field data are also crucial for model calibration and validation. Without this information it will not be possible to adequately understand the environmental factors controlling mercury fate in aquatic systems. The insufficient quantity of adequate measurements and the unsatisfactory accuracy of mercury models are, in numerous cases, supplemented by mass balances since they diminish the unreliability of models. Mercury science evolves gradually with the advancement of science and technology, which requires that mathematical modeling of mercury transport and transformation should be consistently updated.

Risk estimation and annual fluxes of emerging contaminants from a Scottish priority catchment to the estuary and North Sea

Emerging contaminants (ECs) such as endocrine-disrupting chemicals (EDCs) and pharmaceuticals and personal care products (PPCPs) attracted global concern during the last decades due to their potential adverse effects on humans and ecosystems. This work is the first study to assess the spatiotemporal changes, annual fluxes and ecological risk of ECs (4 EDCs and 6 PPCPs) by different monitoring strategies (spot and passive sampling) over 12 months in a Scottish priority catchment (River Ugie, Scotland, 335 km²). Overall, the total concentration in water ranged from <LOD to 55.13 ng/l (mean 5.14 ng/l) for EDCs and 0.24 to 361.2 ng/l (mean 51.16 ng/l) for PPCPs, respectively. Ibuprofen and carbamazepine were observed to be the dominant contaminants in the River Ugie. The total annual fluxes of 4 EDCs transported to the Ugie estuary and North Sea were estimated to be 409 and 294 g based on the spot and passive sampling data, respectively, while they were 4636 and 4517 g for 6 PPCPs by spot and passive sampling, respectively. The spatiotemporal trend suggested that human activities and medication usages were the primary source of the contaminants. The overall comparison of the two sampling strategies supported the hypothesis that passive sampling tends to integrate the contaminants over a period of exposure and allows quantification of contamination at low concentration. The ecological risk assessment showed that bisphenol A posed the highest risks with 21.5% of the spot samples, resulting in a risk quotient >1. This suggests that mitigation measures might need to be taken to reduce the input of emerging contaminants into the river and its adjacent estuary and sea.

A field experimental study on non-methane hydrocarbon (NMHC) emissions from a straw-returned maize cropping system

Non-methane hydrocarbons (NMHCs) play an important role in the atmospheric environment. However, NMHC emissions from agricultural fields, especially their variations with straw return, are poorly understood. Therefore, a field study comprising two treatments, i.e., (1) S0 (straw removal) and (2) S1 (incorporation of maize straw at a rate of 9000 kg ha^-1), was conducted in a straw-returned maize cropping system to characterize NMHC emissions as well as to estimate the effect of straw return on those emissions. Using a Gas Chromatography-Mass Spectrometer (GC-MS) method, 28 types of NMHCs were identified. The total NMHC emission from S0 was 2018 g ha^-1, where 1-methyl-3-propyl-benzene, (1-methylethyl)-benzene, and toluene were obviously predominant, whereas the total NMHC emission from S1 was 1903 g ha^-1, where 1-methyl-3-propyl-benzene, 2-methyl-pentane, and (1-methylethyl)-benzene were the main species. The results showed that straw return had opposing effects on NMHC emissions, ranging from -55.4% to 478.6%. Overall, the total NMHC emission with returned straw alone decreased by 2963 ng kg straw^-1 h^-1. Furthermore, NMHC fluxes had higher correlations with soil temperature than with soil moisture or pH. Notably, the higher correlations of NMHC fluxes with 10 cm soil temperature than with 5 cm soil temperature indicate that soil in the deeper layer might play a more important role in NMHC fluxes. The results also suggest that more field study is needed to accurately estimate the effect of straw return on NMHC emissions from agroecosystems and fully understand its underlying mechanism.

Emerging ensembles of kinetic parameters to characterize observed metabolic phenotypes

Background

Determining the value of kinetic constants for a metabolic system in the exact physiological conditions is an extremely hard task. However, this kind of information is of pivotal relevance to effectively simulate a biological phenomenon as complex as metabolism.

Results

To overcome this issue, we propose to investigate emerging properties of ensembles of sets of kinetic constants leading to the biological readout observed in different experimental conditions. To this aim, we exploit information retrievable from constraint-based analyses (i.e. metabolic flux distributions at steady state) with the goal to generate feasible values for kinetic constants exploiting the mass action law. The sets retrieved from the previous step will be used to parametrize a mechanistic model whose simulation will be performed to reconstruct the dynamics of the system (until reaching the metabolic steady state) for each experimental condition. Every parametrization that is in accordance with the expected metabolic phenotype is collected in an ensemble whose features are analyzed to determine the emergence of properties of a phenotype. In this work we apply the proposed approach to identify ensembles of kinetic parameters for five metabolic phenotypes of E. Coli, by analyzing five different experimental conditions associated with the ECC2comp model recently published by Hädicke and collaborators.

Conclusions

Our results suggest that the parameter values of just few reactions are responsible for the emergence of a metabolic phenotype. Notably, in contrast with constraint-based approaches such as Flux Balance Analysis, the methodology used in this paper does not require to assume that metabolism is optimizing towards a specific goal.

Electronic supplementary material

The online version of this article (10.1186/s12859-018-2181-7) contains supplementary material, which is available to authorized users.

Characterization of dissolved organic carbon in rainwater of an urban/coastal site in Mediterranean area

Concentration and optical characteristics of dissolved organic matter were studied in rainwater in the urban/coastal city of Thessaloniki, Northern Greece for 2-yr sampling period (2014-2016). The concentration of DOC ranged from 0.33-24.5mg/L with higher values measured in spring-summer period. Higher aromaticity and fluorescence intensity was observed in winter. Chromophoric organic matter represents a significant fraction of DOC that is highly correlated with fluorescence during cold period. Three factor spectral profiles of fluorescence were elucidated, with peaks at protein-like and humic-like area at different intensities. Fluorophores at shorter wavelengths are more susceptible to changes. DOC showed negative relationship with precipitation height, particularly during autumn and spring suggesting washout effect. NMR spectra showed the dominance of aliphatic protons in rainwater. Levoglucosan, sucrose and arabitol were determined in rainwater at concentrations <0.07-2.2μg/L, <0.03-5.1μg/L and <0.03-2.1μg/L, respectively showing impact of biomass combustion and biogenic emissions.

A method for the assessment of long-term changes in carbon stock by construction of a hydropower reservoir

Sustainability of hydropower reservoirs has been questioned since the detection of their greenhouse gas (GHG) emissions which are mainly composed of carbon dioxide and methane. A method to assess the impact on the carbon cycle caused by the transition from a natural river system into a reservoir is presented and discussed. The method evaluates the long term changes in carbon stock instead of the current approach of monitoring and integrating continuous short term fluxes. A case study was conducted in a subtropical reservoir in Brazil, showing that the carbon content within the reservoir exceeds that of the previous landuse. The average carbon sequestration over 43 years since damming was 895 mg C m[Formula: see text] and found to be mainly due to storage of carbon in sediments. These results demonstrate that reservoirs have two opposite effects on the balance of GHGs. By storing organic C in sediments, reservoirs are an important carbon sink. On the other hand, reservoirs increase the flux of methane into the atmosphere. If the sediments of reservoirs could be used for long term C storage, reservoirs might have a positive effect on the balance of GHGs.

Effects of enhanced bioturbation intensities on the toxicity assessment of legacy-contaminated sediments

Many benthic communities within estuarine ecosystems are highly degraded due to the close proximity of urban and industrial contamination sources. The maintenance of recolonised, healthy ecosystems following remediation is a challenge, and better techniques are required for monitoring their progressive recovery. Rates of ecosystem recovery are influenced by the changes in the concentrations and forms of contaminants, the sensitivity of recolonising organisms to bioavailable contaminants, and a range of abiotic and biotic factors influencing the exposure of organisms to the contamination. Here we investigate the influence of bioturbation by an active amphipod (Victoriopisa australiensis) on the bioavailability of metals and hydrocarbons in highly contaminated sediments. Changes in contaminant bioavailability were evaluated by assessing sublethal effects to a smaller cohabiting amphipod (Melita plumulosa). For predominantly metal-contaminated sediments, the presence of V. australiensis generally increased survival and reproduction of M. plumulosa when compared to treatments with only M. plumulosa present (from 42 to 93% survival and 3-61% reproduction). The decrease in toxic effects to M. plumulosa corresponded with lower dissolved copper and zinc concentrations in the overlying waters (14-9 μg Cu L^-1, and 14 to 6 μg Zn L^-1 for absence to presence of V. australiensis). For sediments contaminated with both hydrocarbons and metals, the increased bioturbation intensity by V. australiensis resulted in decreased reproduction of M. plumulosa, despite lower dissolved metal exposure, and indicated increased bioavailability of the hydrocarbon contaminants. Thus, the presence of a secondary active bioturbator can enhance or suppress toxicity to co-inhabiting organisms, and may depend on the contaminant class and form. The results highlight the need to consider both abiotic and biotic interactions when using laboratory studies to evaluate the ability of organisms to recolonise and reproduce within benthic environments degraded by contamination, or for more general extrapolation for sediment quality assessment purposes.

Inputs, dynamics and potential impacts of silver (Ag) from urban wastewater to a highly turbid estuary (SW France)

Although silver (Ag) has been listed as a priority pollutant for the aquatic environment by the European Union (Directive 2006/11/EC), the use of Ag-based products with antimicrobial effects is increasing in Europe, as well as North America and Asia. This study investigates personal care products (PCP) as a potential source of Ag in wastewater, as well as the dynamics and fate of Ag in the influent and effluent of a major urban wastewater treatment plant (WWTP) located on the fluvial part of the Gironde Estuary. Typical household PCPs marked as using Ag contained concentrations of up to 0.4 mg kg^-1 making them likely contributors to urban Ag released into the aquatic environment. Silver concentrations in influent wastewater generally occurred during mid-week working hours and decreased during the night and on weekends clearly indicating the dominance of urban sources. Up to 90% of the total Ag in wastewater was bound to particles and efficiently (>80%) removed by the treatment process, whereas 20% of Ag was released into the fluvial estuary. Silver concentrations in wastewater effluents clearly exceeded estuarine concentrations and may strongly amplify the local Ag concentrations and fluxes, especially during summer rainstorms in low river discharge conditions. Further work should focus on environmental effects and fate of urban Ag release due to immediate localized outfall and/or the adsorption on estuarine particles and subsequent release as dissolved Ag chloro-complexes within the estuarine salinity gradient.

Modelling macronutrient dynamics in the Hampshire Avon river: A Bayesian approach to estimate seasonal variability and total flux

The macronutrients nitrate and phosphate are aquatic pollutants that arise naturally, however, in excess concentrations they can be harmful to human health and ecosystems. These pollutants are driven by river currents and show dynamics that are affected by weather patterns and extreme rainfall events. As a result, the nutrient budget in the receiving estuaries and coasts can change suddenly and seasonally, causing ecological damage to resident wildlife and fish populations. In this paper, we propose a statistical change-point model with interactions between time and river flow, to capture the macronutrient dynamics and their responses to river flow threshold behaviour. It also accounts for the nonlinear effect of water quality properties via nonparametric penalised splines. This model enables us to estimate the daily levels of riverine macronutrient fluxes and their seasonal and annual totals. In particular, we present a study of macronutrient dynamics on the Hampshire Avon River, which flows to the southern coast of the UK through the Christchurch Harbour estuary. We model daily data for more than a year during 2013-14 in which period there were multiple severe meteorological conditions leading to localised flooding. Adopting a Bayesian inference framework, we have quantified riverine macronutrient fluxes based on input river flow values. Out of sample empirical validation methods justify our approach, which captures also the dependencies of macronutrient concentrations with water body characteristics.

Evaluation of spot and passive sampling for monitoring, flux estimation and risk assessment of pesticides within the constraints of a typical regulatory monitoring scheme

In many agricultural catchments of Europe and North America, pesticides occur at generally low concentrations with significant temporal variation. This poses several challenges for both monitoring and understanding ecological risks/impacts of these chemicals. This study aimed to compare the performance of passive and spot sampling strategies given the constraints of typical regulatory monitoring. Nine pesticides were investigated in a river currently undergoing regulatory monitoring (River Ugie, Scotland). Within this regulatory framework, spot and passive sampling were undertaken to understand spatiotemporal occurrence, mass loads and ecological risks. All the target pesticides were detected in water by both sampling strategies. Chlorotoluron was observed to be the dominant pesticide by both spot (maximum: 111.8ng/l, mean: 9.35ng/l) and passive sampling (maximum: 39.24ng/l, mean: 4.76ng/l). The annual pesticide loads were estimated to be 2735g and 1837g based on the spot and passive sampling data, respectively. The spatiotemporal trend suggested that agricultural activities were the primary source of the compounds with variability in loads explained in large by timing of pesticide applications and rainfall. The risk assessment showed chlorotoluron and chlorpyrifos posed the highest ecological risks with 23% of the chlorotoluron spot samples and 36% of the chlorpyrifos passive samples resulting in a Risk Quotient greater than 0.1. This suggests that mitigation measures might need to be taken to reduce the input of pesticides into the river. The overall comparison of the two sampling strategies supported the hypothesis that passive sampling tends to integrate the contaminants over a period of exposure and allows quantification of contamination at low concentration. The results suggested that within a regulatory monitoring context passive sampling was more suitable for flux estimation and risk assessment of trace contaminants which cannot be diagnosed by spot sampling and for determining if long-term average concentrations comply with specified standards.

Sulfur-based denitrification: Effect of biofilm development on denitrification fluxes

Elemental sulfur (S(o)) can serve as an electron donor for denitrification. However, the mechanisms and rates of S(o)-based denitrification, which depend on a biofilm development on a solid S(o) surface, are not well understood. We used completely-mixed reactors packed with S(o) chips to systematically explore the behavior of S(o)-based denitrification as a function of the bulk nitrate (NO3(-)) concentration and biofilm development. High-purity (99.5%) and agricultural-grade (90% purity) S(o) chips were tested to explore differences in performance. NO3(-) fluxes followed a Monod-type relationship with the bulk NO3(-) concentration. For high-purity S(o), the maximum NO3(-) flux increased from 0.4 gN/m(2)-d at 21 days to 0.9 g N/m(2)-d at around 100 days, but then decreased to 0.65 gN/m(2)-d at 161 days. The apparent (extant) half-saturation constant for NO3(-) KSapp, based on the bulk NO3(-) concentration and NO3(-) fluxes into the biofilm, increased from 0.1 mgN/L at 21 days to 0.8 mgN/L at 161 days, reflecting the increasing mass transfer resistance as the biofilm thickness increased. Nitrite (NO2(-)) accumulation became significant at bulk NO3(-) concentration above 0.2 mgN/L. The behavior of the agricultural-grade S(o) was very similar to the high-purity S(o). The kinetic behavior of S(o)-based denitrification was consistent with substrate counter-diffusion, where the soluble sulfur species diffuse from the S(o) particle into the base of the biofilm, while NO3(-) diffuses into the biofilm from the bulk. Initially, the fluxes were low due to biomass limitation (thin biofilms). As the biofilm thickness increased with time, the fluxes first increased, stabilized, and then decreased. The decrease was probably due to increasing diffusional resistance in the thick biofilm. Results suggest that fluxes comparable to heterotrophic biofilm processes can be achieved, but careful management of biofilm accumulation is important to maintain high fluxes.

Polychlorinated biphenyls (PCBs) in sediments from the western Adriatic Sea: Sources, historical trends and inventories

Sources, historical trends and inventories of polychlorinated biphenyls (PCBs) were investigated in sediments collected in five transects along the north-south axis of the western Adriatic Sea. The concentration of total PCBs (∑28 PCBs) ranged from <LOD (limit of detection) to 9.0ngg(-1) in the sediment cores and between 0.1 and 2.2ngg(-1) in recent sediments. Chronological records of PCB concentrations displayed a common pattern with historical PCB production and use, with the maximum peak values detected between the 1960s and the 1980s. Sediments deposited within the last two decades presented a ~40% to ~80% PCB reduction in comparison to the peak levels, reflecting the ban on PCB production and use since the late 1970s. PCB levels along with the presence of high-chlorinated congeners decreased southwards, indicating the Po River as the major source of PCBs in the western Adriatic Sea. This is further corroborated by the estimated inventories of PCBs, which were ~4-7 times higher in the Po River prodelta (256ngcm(-2)) in comparison to the middle and southern Adriatic, respectively, and about 100 times higher than the in the deep Adriatic Sea.

Optimizing laboratory-based radon flux measurements for sediments

Radon flux via diffusion from sediments and other materials may be determined in the laboratory by circulating air through the sample and a radon detector in a closed loop. However, this approach is complicated by the necessity of having to determine the total air volume in the system and accounting for any small air leaks that can arise if using extended measurement periods. We designed a simple open-loop configuration that includes a measured mass of wet sediment and water inside a gas-tight reaction flask connected to a drying system and a radon-in-air analyzer. Ambient air flows through two charcoal columns before entering the reaction vessel to eliminate incoming radon. After traveling through the reaction flask, the air passes the drier and the radon analyzer and is then vented. After some time, the radon activity will reach a steady state depending upon the airflow rate. With this approach, the radon flux via diffusion is simply the product of the steady-state radon activity (Bq/m(3)) multiplied by the airflow rate (mL/min). We demonstrated that this setup could produce good results for materials that produce relatively high radon fluxes. We also show that a modified closed system approach, including radon removal of the incoming air by charcoal filtration in a bypass, can produce very good results including samples with very low emission rates.

Characteristics of N2O production and transport within soil profiles subjected to different nitrogen application rates in China

To better understand the effect of N fertilizer on the responses of subsoil N2O to N2O emissions in a high-yield plot, we investigated the subsurface N2O concentrations at seven mineral soil depths and analyzed the subsoil N2O fluxes between soil horizons. This study was conducted from 2012 to 2013 in farmland located in the semi-humid area of the Changwu station, Shaanxi, and the results showed that the application of N fertilizer triggered the highest amount of N2O production and effluxes in the various soil layers. With an increase of N fertilizer, N2O effluxes and production significantly increased; the mean variation of 380 kg N ha(-1) treatment was much greater than that of 250 kg N ha(-1) treatment, particularly after fertilization during the maize growing season (MS). N2O concentrations increased within 30 cm and maintained low and stable values. However, N2O fluxes and production decreased with depth (below 30 cm) and then remained low (approximately zero or even negative) at depths of 30-90 cm. The cumulative N2O fluxes in the 0-15 cm soil layer accounted for 99.0% of the total amount in the soil profile, and high fluxes coincided with periods of relatively high production rates. The cumulative production of N2O also remained in step with the cumulative fluxes. In addition, more N fertilizer was applied, greater production occurred in the topsoil. A significantly positive relationship was found between N2O fluxes and mineral N, and a negative relationship was found between the fluxes and the water-filled pore space (WFPS) in the shallow soil. N2O effluxes increased with increasing amounts of N fertilizer, which was primarily due to nitrification on the Loess Plateau.

Residual fluxes of water and nutrient transport through the main inlet of a tropical estuary, Cochin estuary, West Coast, India

Determining robust values for estuarine material fluxes has been a complex task and an interdisciplinary research challenge. With the advent of acoustic Doppler profilers (ADPs) having bottom-track capability and which provides three-dimensional current velocity profiles, more accurate estimation of cross-sectional fluxes is far accomplished in unsteady and bidirectional flow conditions of estuaries. This paper reports for the first time the discharge measurements conducted across Cochin inlet using ADP to examine the spring-neap variability in residual fluxes of water and nutrients during dry season. Cross-sectional current velocity profiles and salinity profiles were captured using ADP and conductivity temperature depth (CTD) instrumentation. Samples of surface and bottom water were also collected at 3-h intervals. The results indicated that there is a distinct transition from the neap to spring tides related to flow and salinity structure. The neap tide was partially mixed with large diurnal inequalities whereas the spring tide was well-mixed with symmetric tides. During ebb, an increase in the concentrations of nitrate, nitrite, phosphate, and silicate was noticed indicating upstream sources for their inputs. In contrast, elevated levels of ammonia were found in the estuary throughout the period of observation. There was net residual outflow during both tides, and the computed residual water fluxes of neap doubled that of spring. The strong ebb currents and the increased nutrient concentrations during ebb resulted in the export of all nutrients (except ammonia during spring) into the sea. The findings of this study highlight the consequences of anthropogenic interventions in the estuary and their effects on the fluxes of ecologically relevant substances.

Turnover and release of P-, N-, Si-nutrients in the Mexicali Valley (Mexico): interactions between the lower Colorado River and adjacent ground- and surface water systems

A study on dissolved nitrate, ammonium, phosphate and silicate concentrations was carried out in various water compartments (rivers, drains, channels, springs, wetland, groundwater, tidal floodplains and ocean water) in the Mexicali Valley and the Colorado River delta between 2012 and 2013, to assess modern potential nutrient sources into the marine system after river damming. While nitrate and silicate appear to have a significant input into the coastal ocean, phosphate is rapidly transformed into a particulate phase. Nitrate is, in general, rapidly bio-consumed in the surface waters rich in micro algae, but its excess (up to 2.02 mg L(-1) of N from NO3 in winter) in the Santa Clara Wetland represents a potential average annual source to the coast of 59.4×10(3)kg N-NO3. Despite such localized inputs, continuous regional groundwater flow does not appear to be a source of nitrate to the estuary and coastal ocean. Silicate is associated with groundwaters that are also geothermally influenced. A silicate receiving agricultural drain adjacent to the tidal floodplain had maximum silicate concentrations of 16.1 mg L(-1) Si-SiO2. Seepage of drain water and/or mixing with seawater during high spring tides represents a potential source of dissolved silicate and nitrate into the Gulf of California.

Lipidomics of essential fatty acids and oxygenated metabolites

Polyunsaturated fatty acids in mammals may be oxygenated into a myriad of bioactive products through di- and monooxygenases, products that are rapidly degraded to control their action. To evaluate the phenotypes of biological systems regarding this wide family of compounds, a lipidomics approach in function of time and compartments would be relevant. The current review takes into consideration most of the diverse oxygenated metabolites of essential fatty acids at large and their immediate degradation products. Their biological function and life span are considered. Overall, this is a fluxolipidomics approach that is emerging.