Characterization of a major refractory component of marine dissolved organic matter

Refractory carboxyl-rich alicyclic molecules (CRAM) are characterized in marine dissolved organic matter (DOM) using nuclear magnetic resonance spectroscopy and ultrahigh resolution mass spectrometry. CRAM are distributed throughout the water column and are the most abundant components of deep ocean DOM ever characterized. CRAM are comprised of a complex mixture of carboxylated and fused alicyclic structures with a carboxyl-C:aliphatic-C ratio of 1:2 to 1:7. CRAM are expected to constitute a strong ligand for metal binding, and multiple coordination across cations could promote aggregation and marine gel formation thereby affecting CRAM reactivity and the bioavailability of nutrients and trace metals. It appears CRAM are ultimately derived from biomolecules with structural similarities to sterols and hopanoids. The occurrence of CRAM in freshwater and terrestrial environments seems likely, considering the global distribution of biomolecules and the similarities of biogeochemical processes among environments.     

Tracing nitrogen in volcanic and geothermal volatiles from the Nicaraguan volcanic front

We report new chemical and isotopic data from 26 volcanic and geothermal gases, vapor condensates, and thermal water samples, collected along the Nicaraguan volcanic front. The samples were analyzed for chemical abundances and stable isotope compositions, with a focus on nitrogen abundances and isotope ratios. These data are used to evaluate samples for volatile contributions from magma, air, air-saturated water, and the crust. Samples devoid of crustal contamination (based upon He isotope composition) but slightly contaminated by air or air-saturated water are corrected using N₂/Ar ratios in order to obtain primary magmatic values, composed of contributions from upper mantle and subducted hemipelagic sediment on the down-going plate. Using a mantle endmember with δ¹⁵N = −5‰ and N₂/He = 100 and a subducted sediment component with δ¹⁵N = +7‰ and N₂/He = 10,500, the average sediment contribution to Nicaraguan volcanic and geothermal gases was determined to be 71%. Most of the gases were dominated by sediment-derived nitrogen, but gas from Volcán Mombacho, the southernmost sampling location, had a mantle signature (46% from subducted sediment, or 54% from the mantle) and an affinity with mantle-dominated gases discharging from Costa Rica localities to the south. High CO₂/N_{2 exc.} ratios (N_{2 exc.} is the N₂ abundance corrected for contributions from air) in the south are similar to those in Costa Rica, and reflect the predominant mantle wedge input, whereas low ratios in the north indicate contribution by altered oceanic crust and/or preferential release of nitrogen over carbon from the subducting slab. Sediment-derived nitrogen fluxes at the Nicaraguan volcanic front, estimated by three methods, are 7.8 × 10⁸ mol N/a from ³He flux, 6.9 × 10⁸ mol/a from SO₂ flux, and 2.1 × 10⁸ and 1.3 × 10⁹ mol/a from CO₂ fluxes calculated from ³He and SO₂, respectively. These flux results are higher than previous estimates for Central America, reflecting the high sediment-derived volatile contribution and the high nitrogen content of geothermal and volcanic gases in Nicaragua. The fluxes are also similar to but higher than estimated hemipelagic nitrogen inputs at the trench, suggesting addition of N from altered oceanic basement is needed to satisfy these flux estimates. The similarity of the calculated input of N via the trench to our calculated outputs suggests that little or none of the subducted nitrogen is being recycled into the deeper mantle, and that it is, instead, returned to the surface via arc volcanism.     

Assessment of the mycoflora of commercial poultry feeds sold in the humid tropical environment of Imo State, Nigeria

This study was carried out to identify the common moulds growing in selected commercial poultry feed sold in Owerri, Imo State, Nigeria. Forty-eight bulk samples derived froml92 bags of feeds were collected from broiler starter (BS), broiler finishers (BF), grower mash (GM) and layer mash (LM) across 4 different brands of ommercial poultry feeds, which included Livestock (LF), Top (TF) Guinea (GF) and Vital (VF) feeds. The feed samples were collected during the rainy season months of June, July and August. The common moulds isolated from these feeds were Aspergillus sp., Peicillium sp.,Mucor sp., Yeast sp., Rhizopus sp., Epicoecum sp., Gymnoaseus sp., Cladosporium sp., Mortierella sp. as well as Bacteria. Generally, more organisms were isolated in June than the other months with Mortierella sp. being the only one not isolated in that month. Vital feed with 8 different isolates had the highest diversity of fungal species while the others had between 4 and 5 species. Prevalence rates across the feed types, generally ranged from 18.76% in layer mash to 30.03% in broiler finisher. The four Aspergillus sp. isolated came from GM and BF. This study highlights the need for constant monitoring of moulds in commercial feedstuff produced in the humid tropical environments such as Imo state, Nigeria. There is also the need to routinely include fungal growth nhibitors in commercial feeds since moulds are capable of reducing the nutritional values of feedstuff as well as elaborating pathogenic toxins.     

Total organic carbon in soils and its relation with manganese concentrations in soils and vegetation close to an abandoned manganese mine

This study aimed at quantifying the total organic carbon (TOC) present in soils within the proximity of the Kgwakgwe Mn oxide ore abandoned mine, Botswana, and establish its relationship with Mn concentrations in soils and vegetation based on multivariate and Geographical Information Systems (GIS) analytical techniques. Four hundred soil samples and 200 vegetation set samples were obtained from a 4 km² area close to the abandoned mine. The TOC in soil samples were determined using a carbon/hydrogen/moisture determinator, and Mn concentrations in soils and vegetation by atomic absorption spectrophotometry. Results were processed using the statistical package for social science (SPSS), GIS, and Remote Sensing (RS) techniques with the Integrated Land and Water Information System (ILWIS), Geosoft Oasis Montaj and ArcGIS software packages. The values for TOC in the soil samples from the study area ranged from 0 wt % to 7.91 wt %, with a mean of 1.90 wt %, and at the control area, from 4.07 wt % to 4.86 wt %. The range of concentrations of Mn in soils was from 36 mg/g to 24908 mg/g and for Mn concentrations in the vegetation samples from 26 mg/g to 3611 mg/g with a mean of 598 mg/g. Results of correlation coefficients depicted very weak negative association except Mn in soils/Mn in leaves which was weak but positive. The statistical data yielded four clusters as follows: cluster one consisted mainly of Mn in leaves, cluster two was constituted of Mn in soils, and cluster four had TOC. Cluster three was dominated by the three parameters but with negative t statistic. The spatial presentation of data presented revealed little or no vegetation in the south eastern area and those close to the mine workings, and some significant vegetation in the north western part of the study area. The low TOC in the soils is associated to low vegetation cover which is considered to have been influenced by the soil clay fraction mineralogy and high concentrations of Mn.     

Cadmium absorption and accumulation in different parts of kidney beans, radishes and pumpkins

This study is done to measure the absorption and distribution of cadmium in different parts of kidney beans, radishes and pumpkins. Three parts of a field was chosen. In one part 65 ppm of cadmium nitrate was added to water and in the other part 130 ppm, the last part was irrigated with normal water. Samples were digested by EPA 3050 method. Cadmium concentration was measured by Unicam 919 absorption unit. Beans accumulate cadmium mostly in root (70 ppm) and a little amount is mobilized through upper parts (12–16ppm), but kidneys did not accumulate a significant amount. In radishes the roots did not accumulate a significant amount of cadmium but stems had 4 ppm and leaves had 25 ppm. Cadmium concentration in soil does not affect its concentration in different parts of pumpkins and beside the stems and leaves (4 ppm) the other parts' concentrations were insignificant. In regard to the results of this study the cadmium concentrations in edible parts of the samples (kidney beans, radish roots and pumpkin fruit) were less than the U.S. EPA standards for agriculture and human beings.     

Heterogeneous organic matter from the surface horizon of a temperate zone marsh

Abundance, bulk chemical composition and sources of the organic matter in the surface horizon of the permanently water-covered part of an intermittently water-covered marsh were investigated. Lipids, insoluble non-hydrolysable macromolecular organic matter and black carbon fractions were isolated and examined via Rock-Eval pyrolysis, elemental analysis, Fourier transform infrared spectroscopy, isotopic (δ¹³C, δ¹⁵N) methods and high resolution transmission electron microscopy. Integration of bulk Rock-Eval data, elemental and isotopic composition, together with spectroscopic features, suggested immature Type III organic matter derived mainly from C₃ vascular plants. The distribution of n-alkanes from the non-aromatic lipid fraction exhibited the importance of emergent macrophytes and terrestrial plants, as well as a moderate input of submerged/floating macrophytes to the source biomass. Mathematical deconvolution of a Rock-Eval pyrogram revealed highly heterogeneous organic matter composed of a mixture of thermally labile biopolymers (36%) at various stages of decomposition, as well as humic substances and highly refractory organic matter (64%) in the whole sample. Markedly lower heterogeneity and aliphaticity, together with a higher proportion of humic substances and highly refractory organic matter (ca. 84%) were observed in the macromolecular fraction. An abundant contribution of black carbon to the macromolecular fraction was indicated by mathematical deconvolution of the Rock-Eval pyrogram and was clearly shown by the isolation of this fraction and chemical oxidation. The black carbon fraction appeared to account for ca. half of the macromolecular fraction, the carbon in these two fractions representing 30% and 14% of the initial carbon, respectively. The electron microscopy observations directly evidenced the presence of black carbon, which was comprised of both amorphous poorly organized particles and highly ordered onion-shaped particles.     

Natural attenuation and bioremediation of Prestige fuel oil along the Atlantic coast of Galicia (Spain)

Heavy fuel oil spilled from the oil tanker Prestige in November 2002 affected hundreds of km of Spanish shoreline. We carried out a two year study at two highly contaminated sites in order to monitor natural attenuation of the residues coating shore rocks and to test the effectiveness of bioremediation with an oleophilic fertilizer (S200). The methodology included an innovative approach for oil load calculation (based on image analysis techniques), the analysis of the fate of hydrocarbons by means of chemical biomarkers and different microbiological techniques for isolating and examining hydrocarbon degraders.Considerable hydrocarbon depletion from shorelines (≈100% for light-medium linear alkanes and ≈35% for aromatics such as pyrene) was observed within the first months after the spill. However, this natural attenuation effect dramatically slowed down in the following year, although partial enhancement (especially for the aromatic fraction) was attained as a result of the application of S200 to stimulate indigenous microorganisms. In addition, one of the main outcomes of this work concerns the remarkable hydrocarbon depletion achieved at points where fresh water flowed through the shore rocks. The study of samples collected where this natural attenuation phenomenon took place made it possible to isolate heterotrophic bacteria and fungi that are likely to cooperate with cyanobacteria in hydrocarbon biodegradation. The overall results strongly advocate the implementation of new bioremediation approaches, including alternatives such as the use of natural fresh water to irrigate polluted areas.     

The petroleum generation potential and effective oil window of humic coals related to coal composition and age

A worldwide data set of more than 500 humic coals from the major coal-forming geological periods has been used to analyse the evolution in the remaining (Hydrogen Index, HI) and total (Quality Index, QI) generation potentials with increasing thermal maturity and the ‘effective oil window’ (‘oil expulsion window’). All samples describe HI and QI bands that are broad at low maturities and that gradually narrow with increasing maturity. The oil generation potential is completely exhausted at a vitrinite reflectance of 2.0–2.2%R_o or T_max of 500–510 °C. The initial large variation in the generation potential is related to the original depositional conditions, particularly the degree of marine influence and the formation of hydrogen-enriched vitrinite, as suggested by increased sulphur and hydrogen contents. During initial thermal maturation the HI increases to a maximum value, HI_max. Similarly, QI increases to a maximum value, QI_max. This increase in HI and QI is related to the formation of an additional generation potential in the coal structure. The decline in QI with further maturation is indicating onset of initial oil expulsion, which precedes efficient expulsion. Liquid petroleum generation from humic coals is thus a complex, three-phase process: (i) onset of petroleum generation, (ii) petroleum build-up in the coal, and (iii) initial oil expulsion followed by efficient oil expulsion (corresponding to the effective oil window). Efficient oil expulsion is indicated by a decline in the Bitumen Index (BI) when plotted against vitrinite reflectance or T_max. This means that in humic coals the vitrinite reflectance or T_max values at which onset of petroleum generation occurs cannot be used to establish the start of the effective oil window. The start of the effective oil window occurs within the vitrinite reflectance range 0.85–1.05%R_o or T_max range 440–455 °C and the oil window extends to 1.5–2.0%R_o or 470–510 °C. For general use, an effective oil window is proposed to occur from 0.85 to 1.7%R_o or from 440 to 490 °C. Specific ranges for HI_max and the effective oil window can be defined for Cenozoic, Jurassic, Permian, and Carboniferous coals. Cenozoic coals reach the highest HI_max values (220–370 mg HC/g TOC), and for the most oil-prone Cenozoic coals the effective oil window may possibly range from 0.65 to 2.0%R_o or 430 to 510 °C. In contrast, the most oil-prone Jurassic, Permian and Carboniferous coals reach the expulsion threshold at a vitrinite reflectance of 0.85–0.9%R_o or T_max of 440–445 °C.     

Visualization experiments of iron precipitates: Application for in-situ arsenic remediation

Laboratory experiments were carried out to acquire more insight and understanding of the phenomena associated with the in-situ arsenic remediation. Visualization techniques are the most informative for the detection of Fe(II) while flowing in soils. Green Rust (GR) was considered as representative of in-situ iron precipitates. In a visualization flat cell, the change in color of GR to orange, due to oxidation, was monitored by a digital camera and the images were analyzed giving the spatial and temporal distribution of Fe(II). Moreover, both oxygen and pH changes in time were recorded in two sections along the flow direction in the cell. The measured and calculated concentration profiles were compared and the actual reaction rates were predicted. The reaction rate constants measured in this study, under flowing conditions, are in a good agreement with the values obtained from batch experiments reported in the literature.     

Hydrochemical and isotopical tracers in the lacustrine aquifer of the Cerro Prieto area, Baja California, México

A series of patterns in the chemical and isotopic composition of the groundwater of the Cerro Prieto area have been recognized. These patterns were used to define four hydrochemical and isotopical zones in the area. One of these areas located at the east side was found to be the source of recharge, while another in the central part is where an older aquifer exist in lacustrine deposits. The low permeability of the area causes the aquifer to act as an aquitard, which at least is partly surrounded by an interface zone where mixing of waters occurs. Tritium and radiocarbon method revealed that the aquitard is an isolate system whose residence time is of 32 ka.