Linking structural and compositional changes in archaeological human bone collagen: an FTIR-ATR approach

Collagen is the main structural and most abundant protein in the human body, and it is routinely extracted and analysed in scientific archaeology. Its degree of preservation is, therefore, crucial and several approaches are used to determine it. Spectroscopic techniques provide a cost-effective, non-destructive method to investigate the molecular structure, especially when combined with multivariate statistics (chemometric approach). In this study, we used FTIR-ATR spectroscopy to characterise collagen extracted from skeletons recovered from necropoleis in NW Spain spanning from the Bronze Age to eighteenth century AD. Principal components analysis was performed on a selection of bands and structural equation models (SEM) were developed to relate the collagen quality indicators to collagen structural change. Four principal components represented: (i) Cp1, transformations of the backbone protein with a residual increase in proteoglycans; (ii) Cp2, protein transformations not accompanied by changes in proteoglycans abundance; (iii) Cp3, variations in aliphatic side chains and (iv) Cp4, absorption of the OH of carbohydrates and amide. Highly explanatory SEM models were obtained for the traditional collagen quality indicators (collagen yield, C, N, C:N), but no relationship was found between quality and δ13C and δ15N ratios. The observed decrease in C and N content and increase in C:N ratios is controlled by the degradation of protein backbone components and the relative preservation of carbon-rich compounds, proteoglycans and, to a lesser extent, aliphatic moieties. Our results suggest that FTIR-ATR is an ideal technique for collagen characterization/pre-screening for palaeodiet, mobility and radiocarbon researchThis research was partially funded by the projects “Galician Paleodiet” (ED481D 2017/014), Consiliencia network (ED 431D2017/08), GPC (ED341B 2018/20) and “Antropoloxía dos restos óseos humanos de Galicia” (Dirección Xeral de Patrimonio Histórico), Xunta de Galicia. OLC is funded by Plan Galego I2C mod.B (ED481D 2017/014) and by Ministerio de Ciencia e Innovación (JIN project PID2019-111683RJ-100)S

Differentiation between pine woods according to species and growing location using FTIR-ATR

Attenuated total reflectance-Fourier transform infrared (FTIR-ATR) spectroscopy was applied to 120 samples of heartwood rings from eight individual pine trees from different locations in Spain. Pinus sylvestris cores were collected at the Artikutza natural park (Ps-ART). Pinus nigra cores were collected in Sierra de Cazorla (Pn-LIN) and in La Sagra Mountain (Pn-LSA). Three discriminant analysis tests were performed using all bands (DFT), lignin bands only (DFL) and polysaccharides bands only (DFP), to explore the ability of FTIR-ATR to separate between species and growing location. The DFL model enabled a good separation between pine species, whereas the DFP model enabled differentiation for both species and growing location. The DFT model enabled virtually perfect separation, based on two functions involving twelve FTIR bands. Discrimination between species was related to bands at 860 and 1655 cm−1, which were more intense in P. sylvestris samples, and bands at 1425 and 1635 cm−1, more intense in P. nigra samples. These vibrations were related to differences in lignin structure and polysaccharide linear chains. Discrimination between growing locations was mainly related to polysaccharide absorptions: at 900, 1085 and 1335 cm−1 more representative of Pn-LIN samples, and at 1105 and 1315 cm−1 mostly associated to Pn-LSA samples. These absorptions are related to β-glycosidic linkages (900 cm−1), cellulose and hemicellulose (C–O bonds, 1085 and 1105 cm−1) and content in amorphous/crystalline cellulose (1315 and 1335 cm−1). These results show that FTIR-ATR in combination with multivariate statistics can be a useful tool for species identification and provenancing for pine wood samples of unknown originS

Potential of pyrolysis-GC–MS molecular fingerprint as a proxy of Modern Age Iberian shipwreck wood preservation

Even though pyrolysis in combination with gas chromatography and mass spectrometry (Py-GC–MS) is widely used for molecular characterization of wood, its abilities to determine the taxonomy (species), provenance and the nature and intensity of degradation of archaeological woods are hardly explored. We performed principal component analysis (PCA) on Py-GC–MS data of sound woods and shipwreck woods of Pinus sp. and Quercus sp., to identify the impact of diagenesis on pyrolysis fingerprints. It was found that the proportion of most polysaccharide products decreased significantly upon diagenesis with the exception of 3-hydroxy-2-methyl-2-cyclopenten-1-one, which remains relatively well preserved. Furthermore, the guaiacyl lignin products were generally well preserved with the exception of 4-propylguaiacol, the relative contribution of which decreased considerably. New indices are proposed to establish the preservation state of shipwreck wood (shipwreck wood preservation index; SWPI) on the basis of polysaccharides (SWPIPS) and guaiacyl lignin (SWPILG) and syringyl lignin (SWPILS) fingerprints. Stepwise multiple linear regressions analyses applied on FTIR data of the same samples are indicative of the consistency of both techniques and the potential to identify changes in wood chemistry as a result of degradation. Other factors that influence wood composition, such as the differences between soft- and hardwood lignin and sap- and heartwood were also recognizedThis study was developed within the framework of the ForSeaDiscovery project funded by the European Research Council through the Seventh Framework Programme under grant agreement number 607545. We thank the editor and the anonymous reviewer for their time and insightful commentsS

Structural equation modelling of mercury intra-skeletal variability on archaeological human remains

Archaeological burial environments are useful archives to investigate the long-term trends and the behaviour of mercury. In order to understand the relationship between mercury, skeletons and soil, we applied Partial Least Squares - Structural Equation Modelling (PLS-SEM) to a detailed, multisampling (n = 73 bone samples +37 soil samples) design of two archaeological graves dating to the 6th to 7th centuries CE (A Lanzada site, NW Spain). Mercury content was assessed using a DMA-80, and data about bone structure and the grave soil/sediments were obtained using FTIR-ATR spectroscopy. The theoretical model is supported by proxies of bone structure, grave soil/sediments, and location of the bone within the skeleton. The general model explained 61 % of mercury variance. Additionally, Partial Least Square – Prediction Oriented Segmentation (PLS-POS) was also used to check for segmentation in the dataset. POS revealed two group of samples depending on the bone phase (hydroxyapatite or collagen) controlling the Hg content, and the corresponding models explained 86 % and 76 % of Hg variance, respectively. The results suggest that mercury behaviour in the graves is complex, and that mercury concentrations were influenced by i) the ante-mortem status of the bone matrix, related to the weight of each bone phase; ii) post-mortem evolution of bone crystallinity, where bone loses mercury with increasing alteration; and iii) the proximity of the skeletal pieces to mercury target organs, as decomposition and collapse of the thoracic and abdominal soft tissues causes a secondary mercury enrichment in bones from the body trunk during early post-mortem. Skeletons provide a source of mercury to the soil whereas soil/sediments contribute little to skeletal mercury contentPresent research was funded by Estudo de esqueletos humanos e de secuencias edafosedimentarias do xacemento de A Lanzada (2017-CP035) funded by Deputación Provincial de Pontevedra. The study was also supported by the projects “Pollutio” Plan Nacional (PID2019-111683RJ-I00) Spanish Ministerio de Ciencia e Innovacion, “Epidemias del hambre” Beca Leonardo a Investigadores y Creadores Culturales 2020 (2020-PO048) de la Fundación BBVA and “Grupos de Referencia Competitiva” (ED431C 2021/32) by Xunta de Galicia. NAF was funded by Convenio de Colaboración entre a Axencia Galega de Innovación, a Consellería de Cultura, Educación e Universidade, a USC e CSIC para fomentar a actividade Investigadora do persoal investigador finalista nas convocatorias de axudas do ERC no Marco do H2020. OLC is funded by a Ramón y Cajal senior fellowship (RYC2020-030531-I)S

Pedogenic Processes in a Posidonia oceanica Mat

Scientists studying seagrasses typically refer to their substratum as sediment, but recently researchers have begun to refer to it as a soil. However, the logistics of sampling underwater substrata and the fragility of these ecosystems challenge their study using pedological methods. Previous studies have reported geochemical processes within the rhizosphere that are compatible with pedogenesis. Seagrass substratum accumulated over the Recent Holocene and can reach several meters in thickness, but studies about deeper layers are scarce. This study is a first attempt to find sound evidence of vertical structuring in Posidonia oceanica deposits to serve as a basis for more detailed pedological studies. A principal component analysis on X-Ray Fluorescence-elemental composition, carbonate content and organic matter content data along a 475 cm core was able to identify four main physico-chemical signals: humification, accumulation of carbonates, texture and organic matter depletion. The results revealed a highly structured deposit undergoing pedogenetical processes characteristic of soils rather than a mere accumulation of sediments. Further research is required to properly describe the substratum underneath seagrass meadows, decide between the sediment or soil nature for seagrass substrata, and for the eventual inclusion of seagrass substrata in soil classifications and the mapping of seagrass soil resourcesThis work has been funded by project SUMILEN (CTM2013- 47728-R, MINECO). C. Leiva-Dueñas was supported by a PhD scholarship funded by the Spanish Ministry of Science and Innovation (FPU15/01934); O. Serrano was supported by an ARC DECRA DE170101524. Authors would like to thank the use of RIAIDT-USC analytical facilities. This is a paper from the Group of Benthic Ecology 2014 SGR 120S

Arqueología en la ACEGA 2: el área arqueológica de O Peto (Vedra, A Coruña)

Cadernos de Arqueoloxía e Patrimonio (CAPA)[EN] The archaeological area of O Peto was discovered during the construction of the highway Santiago-Alto de Santo de Domingo. This site shows the existence of archaeological structures near of the galician Iron Age hillforts. In fact O Peto is an artificialized space (where a set of several structures was exhumed) that belongs to a prerroman iron mining complex that suffered several changes in the beginning of Romanization.[ES] El área arqueológica de O Peto se descubrió durante el control arqueológico de la construcción de la Autopista Santiago-Alto de Santo Domingo. Se trata de un ejemplo significativo de la existencia de estructuras anejas en el entorno inmediato del recinto habitacional de los castros de la Edad del Hierro. Constituye un espacio claramente artificializado en el que se superponen estructuras excavadas en la roca, de naturaleza y finalidad diferentes. A este respecto se configura un espacio construido –aparentemente multifuncional- que experimentó sucesivos procesos de ampliación, redefinición, sellado intencionado y abandono entre la Edad del Hierro y Época Romana. La información aportada por la excavación indica que este yacimiento albergó un complejo minerometalúrgico caracterizado tecnológicamente por la utilización de hornos bajos prerromanos sin sangrado de escoria que procesarían el mineral extraído en el propio yacimiento.Proyecto financiado por la Dirección Xeral de Investigación e Desenvolvemento da Consellería de Innovación, Industria e Comercio (Xunta de Galicia) con cargo a la convocatoria Programa de Tecnoloxías para a Innovación- Tecnoloxías da Construcción e da Conservación do Patrimonio do ano 2004. Código de Proxecto: PGIDIT04CCP606003PRPeer reviewe

Arqueología en la ACEGA 2: el área arqueológica de O Peto (Vedra, A Coruña)

Cadernos de Arqueoloxía e Patrimonio (CAPA)[EN] The archaeological area of O Peto was discovered during the construction of the highway Santiago-Alto de Santo de Domingo. This site shows the existence of archaeological structures near of the galician Iron Age hillforts. In fact O Peto is an artificialized space (where a set of several structures was exhumed) that belongs to a prerroman iron mining complex that suffered several changes in the beginning of Romanization.[ES] El área arqueológica de O Peto se descubrió durante el control arqueológico de la construcción de la Autopista Santiago-Alto de Santo Domingo. Se trata de un ejemplo significativo de la existencia de estructuras anejas en el entorno inmediato del recinto habitacional de los castros de la Edad del Hierro. Constituye un espacio claramente artificializado en el que se superponen estructuras excavadas en la roca, de naturaleza y finalidad diferentes. A este respecto se configura un espacio construido –aparentemente multifuncional- que experimentó sucesivos procesos de ampliación, redefinición, sellado intencionado y abandono entre la Edad del Hierro y Época Romana. La información aportada por la excavación indica que este yacimiento albergó un complejo minerometalúrgico caracterizado tecnológicamente por la utilización de hornos bajos prerromanos sin sangrado de escoria que procesarían el mineral extraído en el propio yacimiento.Proyecto financiado por la Dirección Xeral de Investigación e Desenvolvemento da Consellería de Innovación, Industria e Comercio (Xunta de Galicia) con cargo a la convocatoria Programa de Tecnoloxías para a Innovación- Tecnoloxías da Construcción e da Conservación do Patrimonio do ano 2004. Código de Proxecto: PGIDIT04CCP606003PRPeer reviewe