Sandro Francesconi

Characterisation of proteinaceous binders and drying oils in wall painting samples by gas chromatography-mass spectrometry

Abstract A reliable analytical procedure has been developed for the characterisation of drying oils and proteinaceous binders in samples of painted artworks. The method is based on microwave assisted acid hydrolysis followed by the extraction of the lipid component with diethyl ether. Fatty acids were determined after saponification of the organic phase and derivatisation with N-tert.-Butyl methylsilyl-N-methyltrifluoroacetamide. Amino acids present in the acid aqueous phase were derivatised with the same silyl agent. The separation and quantitative determination of derivatives was performed by gas chromatography–mass spectrometry. Detection limits of fatty acids (lauric, myristic, palmitic, stearic, oleic, suberic, azelaic and sebacic acid) and amino acids were in the range 50–100 pg. The mean recovery of the procedure for lipid determination was about 70% and that for proteins 100% with a reproducibility better than 10% for 1 mg samples. The overall procedure was validated by analysing suitable reference wall painting samples. The identification of the proteinaceous binders was achieved by principal component analysis performed on the fourteen amino acid relative percentages while the identification of the drying oils was based on the values of palmitic to stearic ratio and azelaic to palmitic ratio. A general pattern recognition scheme based on these values and on the amounts of dicarboxylic acids and the presence of cholesterol was developed to distinguish between proteinaceous binder, “tempera grassa” and drying oils. The application of the proposed procedure to samples from “The Legend of True Cross” (1452) by Piero della Francesca allowed the identification of “tempera grassa” made of egg and linseed oil.

Polychlorobiphenyls and polycyclic aromatic hydrocarbons in the sea-surface micro-layer and the water column at Gerlache Inlet, Antarctica

The enrichment of PCBs (polychlorobiphenyls) and PAHs (polycyclic aromatic hydrocarbons) in the sea-surface micro-layer and depth profile of these pollutants in the water column were investigated at Gerlache Inlet, Terra Nova Bay, Antarctica. Depth profile samplings were repeated three times during the Antarctic summer (from November to February). PCBs and PAHs showed a concentration range in the water column of 30-120 pg l(-1) and 150-400 pg l(-1), respectively, and these values were very much dependent on the suspended matter content. A nearly two-fold decrease in the pollutant concentration was also observed in the depth profile obtained in February, i.e. late summer, which might be correlated both with the high content of suspended matter and the reduction of the pollutant input. Moreover, isomer ratios of PAHs, such as LMW/HMW and PHE/ANT, highlight that the main PAH source might be petrogenic in nature, whereas the pyrolytic source seems to be less important. Sea surface micro-layer (SML) and sub-surface sea water (SSW) samples were simultaneously collected in the same site by a remote controlled rotating drum-based sampling system, a prototype named MUMS (Multi-User Micro-layer Sampler). Sea surface micro-layer samples showed a total content of PCBs and PAHs in the range 400-450 pg l(-1) and 2000-3000 pg l(-1), respectively, whereas the mean content of the sub-surface sea water samples was 48 pg l(-1) and 325 pg l(-1), respectively. The mean enrichment factors of PCBs and PAHs in sea-surface micro-layer were about 10 and 7, respectively. The surface excess concentrations of PCBs and PAHs were about 35 000 and 200 000, respectively. A fairly good correlation was observed between the concentration of pollutants and water solubility. Based on the assumption that POPs are confined in a very thin top layer of the SML about 0.01-0.001 microm thick, namely the sea-surface nano-layer, and also on an estimated thickness of the sampled sea-surface layer of about 100 microm, an enrichment factor of 10(5)-10(6) for the sea-surface nano-layer was calculated. Such a very high concentration increase was related to the two-fold increase of PAH concentration observed in the underlying 20 cm of the water column in late summer.

Enrichment, isolation and biodegradation potential of psychrotolerant polychlorinated-biphenyl degrading bacteria from the Kongsfjorden (Svalbard Islands, High Arctic Norway)☆

Persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), have been detected in abiotic Arctic matrices: surface sediments and seawater from coastal areas in the Kongsfjorden were collected and analyzed. Levels of PCBs varied depending on the sampling site. Total PCB concentrations were between 11.63 (site C2W) and 27.69pgl-1 (site AW). These levels were comparable to those reported previously in lake sediments from the northern Svalbard. The occurrence and biodegradation potential of cold-adapted PCB-oxidizing bacteria in seawater and sediment along the fjord was also evaluated. After enrichment with biphenyl, 246 isolates were obtained with 45 of them that were able to grow in the presence of the PCB mixture Aroclor 1242, as the sole carbon source. The catabolic gene bphA was harbored by 17 isolates with affiliates to the genera Algoriphagus, Devosia and Salinibacterium that have been never reported as able to utilize PCBs, thus deserving further investigation. The total removal of Aroclor 1242 and selected PCB congeners was evaluated at 4 and 15°C for eight bphA-harboring isolates and Gelidibacter sp. DS-10. With few exceptions, tested strains showed greater efficiency at 15 than at 4°C. Isolates were able to reduce most chromatographic peaks by >50%, with some di- and trichlorobiphenyls that were quite totally removed (>90%).