Nicasio T. Jiménez-Morillo

Post-fire recovery of soil organic matter in a Cambisol from typical Mediterranean forest in Southwestern Spain

Wildfire is a recurrent phenomenon in Mediterranean ecosystems and contributes to soil degradation and desertification, which are partially caused by alterations to soil organic matter (SOM). The SOM composition from a Cambisol under a Mediterranean forest affected by a wildfire is studied in detail in order to assess soil health status and better understand of soil recovery after the fire event. The soil was sampled one month and twenty-five months after the wildfire. A nearby unburnt site was taken as control soil. Soil rehabilitation actions involving heavy machinery to remove burnt vegetation were conducted sixteen months after the wildfire. Immediately after fire the SOM increased in topsoil due to inputs from charred vegetation, whereas a decrease was observed in the underlying soil layer. Twenty-five months after fire soil-pH increased in fire-affected topsoil due to the presence of ashes, a decrease in SOM content was recorded for the burnt topsoil and similar trend was observed for the water holding capacity. The pyro-chromatograms of burned soils revealed the formation of additional aromatic compounds. The thermal cracking of long-chain n-alkanes was also detected. Solid-state 13C NMR spectroscopy supported the increase of aromatic compounds in the fire-affected topsoil due to the accumulation of charcoal, whereas the deeper soil sections were not affected by the fire. Two years later, soil parameters for the unburnt and burnt sites showed comparable values. The reduction of the relative intensity in the aromatic C region of the NMR spectra indicated a decrease in the charcoal content of the topsoil. Due to the negligible slope in the sampling site, the loss of charcoal was explained by the post-fire restoration activity, degradation, leaching of pyrogenic SOM into deeper soil horizons or wind erosion. Our results support that in the Mediterranean region, fire-induced alteration of the SOM is not lasting in the long-term.

Pyrolysis-gas chromatography-isotope ratio mass spectrometry of polyethylene

Polyethylene is probably the most used plastic material in daily life and its accurate analysis is of importance. In this communication the chemical structure of polyethylenes is studied in detail using conventional analytical pyrolysis (Py-GC/MS), bulk stable isotopic analysis (IRMS) and pyrolysis compound specific stable isotopic analysis (Py-CSIA) to measure stable isotope proportions (δ(13)C, δ(15)N and δD) of polyethylene pyrolysis compounds. Polyethylene pyrolysis yields triplet peaks of n-alkanes, α-alkenes and α,ω-alkanedienes. No differences were found for bulk δ(13)C among different polyethylene types. However, conspicuous differences in δD were evident. It was possible to assign structure δ(13)C and δD values to specific polyethylene pyrolysis products in the range 12-18 carbon chain length. Conspicuous differences were found for the pyrolysis products with unsaturated moieties showing significant higher δD values than saturated chains (alkanes) that were deuterium depleted. In addition, a full isotopic fingerprinting (δ(13)C, δ(15)N and δD) for a dye (o-chloroaniline) contained in a polyethylene is reported. To the best of our knowledge this is the first application Py-CSIA to the study of a synthetic polymer. This hyphenated analytical technique is a promising tool to study synthetic materials, providing not only a fingerprinting, but also allowing the traceability of the polymerization process and the origin of the materials.

Molecular characterisation of a bio-based active packaging containing Origanum vulgare L. essential oil using pyrolysis gas chromatography–mass spectrometry

BACKGROUND Environmental, economic and safety challenges motivate shift towards safer materials for food packaging. New bioactive packaging techniques, i.e. addition of essential plant oils (EOs), are gaining attention by creating barriers to protect products from spoilage. Analytical pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) was used to fingerprint a bioactive polylactic acid (PLA) with polybutylene succinate (PBS) (950 g kg(-1) :50 g kg(-1) ) film extruded with variable quantities (0, 20, 50 and 100 g kg(-1) ) of Origanum vulgare EO. RESULTS Main PLA:PBS pyrolysis products were lactide enantiomers and monomer units from the major PLA fraction and succinic acid anhydride from the PBS fraction. Oregano EO pyrolysis released cymene, terpinene and thymol/carvacrol peaks as diagnostic peaks for EO. In fact, linear correlation coefficients better than 0.950R(2) value (P < 0.001) were found between the chromatographic area of the diagnostic peaks and the amount of oregano EO in the bioplastic. CONCLUSION The pyrolytic behaviour of a bio-based active package polymer including EO is studied in detail. Identified diagnostic compounds provide a tool to monitor the quantity of EO incorporated into the PLA:PBS polymeric matrix. Analytical pyrolysis is proposed as a rapid technique for the identification and quantification of additives within bio-based plastic matrices.

Compound-specific stable carbon isotopic signature of carbohydrate pyrolysis products from C3 and C4 plants

BACKGROUND Pyrolysis-compound specific isotopic analysis (Py-CSIA: Py-GC-(FID)-C-IRMS) is a relatively novel technique that allows on-line quantification of stable isotope proportions in chromatographically separated products released by pyrolysis. Validation of the Py-CSIA technique is compulsory for molecular traceability in basic and applied research. In this work, commercial sucrose from C4 (sugarcane) and C3 (sugarbeet) photosystem plants and admixtures were studied using analytical pyrolysis (Py-GC/MS), bulk δ(13)C IRMS and δ(13)C Py-CSIA. RESULTS Major pyrolysis compounds were furfural (F), furfural-5-hydroxymethyl (HMF) and levoglucosan (LV). Bulk and main pyrolysis compound δ(13)C (‰) values were dependent on plant origin: C3 (F, -24.65 ± 0.89; HMF, -22.07 ± 0.41‰; LV, -21.74 ± 0.17‰) and C4 (F, -14.35 ± 0.89‰; HMF, -11.22 ± 0.54‰; LV, -11.44 ± 1.26‰). Significant regressions were obtained for δ(13)C of bulk and pyrolysis compounds in C3 and C4 admixtures. Furfural (F) was found (13)C depleted with respect to bulk and HMF and LV, indicating the incorporation of the light carbon atom in position 6 of carbohydrates in the furan ring after pyrolysis. CONCLUSION This is the first detailed report on the δ(13)C signature of major pyrolytically generated carbohydrate-derived molecules. The information provided by Py-CSIA is valuable for identifying source marker compounds of use in food science/fraud detection or in environmental research.

Analytical pyrolysis and stable isotope analyses reveal past environmental changes in coralloid speleothems from Easter Island (Chile).

This study comprises an innovative approach based on the combination of chromatography (analytical pyrolysis and pyrolysis compound-specific isotope analysis (Py-CSIA)), light stable isotopes, microscopy and mineralogy analyses to characterize the internal layering of coralloid speleothems from the Ana Heva lava tube in Easter Island (Chile). This multidisciplinary proxy showed that the speleothems consist of banded siliceous materials of low crystallinity with different mineralogical compositions and a significant contribution of organic carbon. Opal-A constitutes the outermost grey layer of the coralloids, whereas calcite and amorphous Mg hydrate silicate are the major components of the inner whitish and honey-brown layers, respectively. The differences found in the mineralogical, elemental, molecular and isotopic composition of these distinct coloured layers are related to environmental changes during speleothem development. Stable isotopes and analytical pyrolysis suggested alterations in the water regime, pointing to wetter conditions during the formation of the Ca-rich layer and a possible increase in the amount of water dripping into the cave. The trend observed for δ(15)N values suggested an increase in the average temperature over time, which is consistent with the so-called climate warming during the Holocene. The pyrolysis compound-specific isotope analysis of each speleothem layer showed a similar trend with the bulk δ(13)C values pointing to the appropriateness of direct Py-CSIA in paleoenvironmental studies. The δ(13)C values for n-alkanes reinforced the occurrence of a drastic environmental change, indicating that the outermost Opal layer was developed under drier and more arid environmental conditions.

Assessing the Effects of UVA Photocatalysis on Soot-Coated TiO2-containing Mortars

The deposition of soot on building surfaces darkens their colour and leads to undesirable black crusts, which are one of the most serious problems on the conservation of built cultural heritage. As a preventive strategy, self-cleaning systems based on the use of titanium dioxide (TiO2) coatings have been employed on building materials for degrading organic compounds deposited on building surfaces, improving their durability and performance. In this study, the self-cleaning effect of TiO2-containing mortars coated with diesel soot has been appraised under laboratory conditions. The mortar samples were manufactured using lime putty and two different doses of TiO2 (2.5% and 5%). The lime mortars were then coated with diesel engine soot and irradiated with ultraviolet A (UVA) illumination for 30days. The photocatalytic efficiency was evaluated by visual inspection, field emission scanning electron microscopy (FESEM) and colour spectrophotometry. Changes in the chemical composition of the soot particles (including persistent organic pollutants) were assessed by analytical pyrolysis (Py-GC/MS) and solid state 13C NMR spectroscopy. The FESEM and colour spectrophotometry revealed that the soot-coated TiO2-containing mortars promoted a self-cleaning effect after UVA irradiation. The combination of analytical pyrolysis and 13C solid state NMR showed that the UVA irradiation caused the cracking of polycyclic aromatic structures and n-alkyl compounds of the diesel soot and its transformation into methyl polymers. Our findings also revealed that the inclusion of TiO2 in the lime mortar formulations catalysed these transformations promoting the self-cleaning of the soot-stained mortars. The combined action of TiO2 and UVA irradiation is a promising proxy to clean lime mortars affected by soot deposition.

Laccase SilA from Streptomyces ipomoeae CECT 3341, a key enzyme for the degradation of lignin from agricultural residues?

The role of laccase SilA produced by Streptomyces ipomoeae CECT 3341 in lignocellulose degradation was investigated. A comparison of the properties and activities of a laccase-negative mutant strain (SilA−) with that of the wild-type was studied in terms of their ability to degrade lignin from grass lignocellulose. The yields of solubilized lignin (acid precipitable polymeric lignin, APPL) obtained from wheat straw by both strains in Solid State Fermentation (SSF) conditions demonstrated the importance of SilA laccase in lignin degradation with the wild-type showing 5-fold more APPL produced compared with the mutant strain (SilA−). Analytical pyrolysis and FT-IR (Fourier Transform Infrared Spectroscopy) confirmed that the APPL obtained from the substrate fermented by wild-type strain was dominated by lignin derived methoxyphenols whereas those from SilA− and control APPLs were composed mainly of polysaccharides. This is the first report highlighting the role of this laccase in lignin degradation.

Wildfire effects on lipid composition and hydrophobicity of bulk soil and soil size fractions under Quercus suber cover (SW-Spain)

ABSTRACT Soil water repellency (hydrophobicity) prevents water from wetting or infiltrating soils, triggering changes in the ecosystems. Fire may develop, enhance or destroy hydrophobicity in previously wettable or water‐repellent soils. Soil water repellency is mostly influenced by the quality and quantity of soil organic matter, particularly the lipid fraction. Here we report the results of a study on the effect of fire on the distribution of soil lipids and their role in the hydrophobicity grade of six particle size fractions (2–1, 1–0.5, 0.5–0.25, 0.25–0.1, 0.1–0.05 and <0.05 mm) of an Arenosol under Quercus suber canopy at the Doñana National Park (SW‐Spain). Hydrophobicity was determined using water drop penetration time test. Field emission scanning electron microscopy (FESEM) was used to assess the presence and morphology of the inorganic and organic soil components in the particle size fractions. Soil lipids were Soxhlet extracted with a dichloromethane‐methanol mixture. Fatty acids (FAs) and neutral lipids were separated, derivatized, identified and quantified by gas chromatography/mass spectrometry and gas chromatography/flame ionization detection. The hydrophobicity values of soil samples and fractions were statistically different (P < 0.05), for both, the unburnt and burnt soils, and particle size fractions. All samples displayed a similar distribution of FAs, straight‐chain saturated acids in the C14–C32 range, and neutral lipids (n‐alkan‐1‐ols, n‐alkanes), only differing in their relative abundances. Among possible biogeochemical mechanisms responsible for the changes in soil lipids, the observed depletion of long chain FAs (C≥24) in the coarse fraction is best explained by thermal cracking caused by the heat of the fire. The enrichment of long chain FAs observed in other fractions suggests possible exogenous additions of charred, lipid‐rich, material, like cork suberin or other plant‐derived macromolecules (cutins). Principal component analysis was used to study the relationships between hydrophobicity with soil organic matter and its different components. Extractable organic matter (EOM) and specifically long chain FAs content were positively correlated to soil hydrophobicity. Therefore, the latter could be used as biomarkers surrogated to hydrophobicity in sandy soils. Graphical abstract: Figure. No Caption available. HighlightsSoil fractions affected or not by fire shows heterogeneous hydrophobicity behavior.The study of free lipids fractions detected the presence of different carbon pools.Fire caused a transfer of partly charred compounds from coarse to fine fractions.Hydrophobicity was positively correlated with long chain fatty acids.

Pyrogenic organic matter from palaeo-fires during the Holocene: A case study in a sequence of buried soils at the Central Ebro Basin (NE Spain)

We studied the fire record and its environmental consequences during the Holocene in the Central Ebro Basin. This region is very sensitive to environmental changes due to its semiarid conditions, lithological features and a continuous human presence during the past 6000 years. The study area is a 6 m buried sequence of polycyclic soils developed approximately 9500 years ago that is exceptionally well preserved and encompasses four sedimentary units. The content and size distribution of macroscopic charcoal fragments were determined throughout the soil sequence and the analysis of the composition of charcoal, litter and sediments via analytical pyrolysis (Py-GC/MS). The high amount of charcoal fragments recovered in most horizons highlights the fire frequencies since the beginning of the Neolithic, most of which were probably of anthropogenic origin. In some soil horizons where charcoal was not found, we detected a distribution pattern of lipid compounds that could be related to biomass burning. On the other hand, the low number of pyrolysates in the charcoal could be attributed to high-intensity fires. No clear pattern was found in the composition of pyrolysates related to the age of sediments or vegetation type. The most ancient soil (Unit 1) was the richest in charcoal content and contains a higher proportion of larger fragments (>4 mm), which is consistent with the burning of a relatively dense vegetation cover. This buried soil has been preserved in situ, probably due to the accumulation of sedimentary materials because of a high-intensity fire. In addition, the pyrogenic C in this soil has some plant markers that could indicate a low degree of transformation. In Units 2-4, both the amount of charcoals and the proportions of macrofragments >4 mm are lower than those in Unit 1, which coincides with a more open forest and the presence of shrubs and herbs. The preservation of this site is key to continuing with studies that contribute to a better assessment of the consequences of future disturbances, such as landscape transformation and climate change.

Ultra-high resolution mass spectrometry of physical speciation patterns of organic matter in fire-affected soils

Fire is one of the most important modulating factors of the environment and the forest inducing chemical and biological changes on the most reactive soil component, the soil organic matter (SOM). Assuming the complex composition of the SOM, we used an ultra-high resolution mass spectrometry analysis technique to assess the chemical composition and fire-induced alterations in soil particle size fractions (coarse and fine) from a sandy soil in a Mediterranean oak forest at Doñana National Park (Southwest Spain). Electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) showed that the coarse fraction of soils not affected by fires consisted mainly of polyphenolic compounds consistent with little-transformed SOM and fresh biomass, whereas the fine fraction was enriched in protein and lipid like homologues suggesting microbially reworked SOM. In fire-affected SOM, the coarse fraction contained a high proportion of aromatic compounds, consistent with inputs of charred litter or in situ chemical transformation of the SOM. Analysis of the fine fraction revealed two differentiated chemical families pointing to the existence of two carbon pools; a native microbial-derived moiety composed of lipids and polypeptide compounds, and a secondary, pyrogenic or thermally-altered moiety rich in aromatic compounds. This work represents the first application of ultra-high resolution mass spectrometry to study the chemical composition of SOM in different particle size fractions.