Sensitivity of whole wood stable carbon and oxygen isotope values to milling procedures.

RATIONALE: Milling of wood samples is a widely applied preparation method for pooling tree-rings from different trees or periods of several years for determination of δ(13)C and δ(18)O values. In this study, whole wood samples were milled using different procedures in order to evaluate potential effects of this preparation method on δ(13)C and δ(18)O values. METHODS: Subsamples of a 5 cm(3) wood piece of a single tree-ring from a lowland white fir were used. The samples were milled with different setups: (i) two and three stainless-steel balls, (ii) 3, 5 and 8 min milling time, and (iii) discontinuous and continuous milling. The δ(13)C values were measured using an elemental analyser connected to an IsoPrime mass spectrometer and δ(18)O values using a Thermo Scientific MAT 253 mass spectrometer and a TC/EA connected by a ConFlo IV. RESULTS: The results show that varying the milling procedure does not alter the δ(13)C and δ(18)O values in comparison to non-milled blank samples. For shorter milling times, an increased variance of δ(18)O values is recorded, probably caused by isotopic gradient between early- and latewood portions of the tree-ring and thereby biasing the insufficiently homogenised samples. No overheating effects on the δ(13)C and δ(18)O values were detected. CONCLUSIONS: Milling of wood samples for carbon and oxygen isotope analyses is an appropriate preparation method.

Exposure to toxic agents alters organic elemental composition in human fingernails.

BACKGROUND AND OBJECTIVE: The human fingernail plate is highly keratinized. The keratin structure is held together by disulfide bonds. The organic elements sulfur and nitrogen occur almost exclusively in amino acids of the nail plate. This study analyzed whether occupational exposure to harmful chemical agents alters the organic elemental composition in fingernails. SUBJECTS AND METHODS: Participants were 71 occupationally exposed workers (49 hairdressers, 22 painters) and 49 unexposed controls. Aspects of exposure were assessed by questionnaire. Nail clippings of index and little fingers were analyzed for sulfur (S), nitrogen (N), carbon (C), and hydrogen (H) contents, using an automatic elemental analyzer (Vario EL III, Elementar Analysensysteme, Hanau, Germany). C/N, N/S, and C/S ratios were calculated. Reliability of elemental measurements was tested in a subset. RESULTS: Reliability analysis of elemental measurements showed a very good agreement. Both painters and hairdressers displayed in their fingernails significantly lower percentages of sulfur, but higher percentages of carbon than unexposed controls. A trend was observed in that sulfur content was lowest in those hairdressers who reported structural changes in their fingernails. As a consequence, the C/S and N/S ratios were significantly increased in both exposed groups. CONCLUSION: The occupational use of harmful substances leads to decreased sulfur levels in the exposed persons, probably due to diminution of sulfur-rich proteins in the nails, resulting from destruction of disulfide-bonds by alkaline and acid groups. Thus, the C/S ratio seems to be a useful indicator for the amount of damage of nail protein by harmful agents.

Organic elemental composition in fingernail plates varies between sexes and changes with increasing age in healthy humans.

BACKGROUND: Keratin, an alpha-helical fibrous protein, is the primary component of human nail plates. No data on age-related changes in healthy subjects are present. OBJECTIVE: This study investigated whether keratin amount and composition, as indicated by organic elemental composition of fingernails, varies with aging and between sexes. METHODS: Nail clippings from 225 healthy individuals (93 males, 132 females), aged 20-90 years, were analyzed for carbon (C), nitrogen (N), and sulfur (S) contents with an automatic elemental analyzer. C/N and N/S ratios were calculated. The C/N ratio is indicative of keratin composition, i.e. the ratio of alpha-amino acids and protein. The relationship of elemental composition with dietary intake was analyzed by standardized food record. RESULTS: Females have in their nails more sulfur (p < 0.001) and less nitrogen (p = 0.001), and thereby, a lower N/S ratio than males, whereas their carbon content is not different. With aging, the carbon content increases (p < 0.01, both sexes) and the nitrogen content decreases (p = 0.05, females), both leading to an increased C/N ratio (p < 0.001). By contrast, the sulfur content and the N/S ratio do not change with aging (p > 0.05). The carbon content correlates positively with macronutrient intake in females. Nitrogen and sulfur contents are not related with dietary intake. CONCLUSIONS: Results suggest that the N/S ratio is indicative of sex differences and the C/N ratio of aging in healthy humans. The increasing carbon content with ongoing age could be explained by loss of inorganic material from the nails, followed by a subsequent increase of organic material. The increasing C/N ratio gives evidence that keratin composition changes towards a higher amount of alpha-amino acids with aging.

Comparison of δ(13)C and δ(18)O from cellulose, whole wood, and resin-free whole wood from an old high elevation Pinus uncinata in the Spanish central Pyrenees.

δ(13)C and δ(18)O values from sapwood of a single Pinus uncinata tree, from a high elevation site in the Spanish Pyrenees, were determined to evaluate the differences between whole wood and resin-free whole wood. This issue is addressed for the first time with P. uncinata over a 38-year long period. Results are also compared with published isotope values of α-cellulose samples from the same tree. The differences in δ(13)C and δ(18)O between whole wood and resin-free whole wood vary within the analytical uncertainty of 0.3 and 0.5 ‰, respectively, indicating that resin extraction is not necessary for sapwood of P. uncinata. Mean differences between cellulose and whole wood are 0.9 ‰ (δ(13)C) and 5.0 ‰ (δ(18)O), respectively. However, further analyses of different species and other sites are needed to evaluate whether the findings reported here are coherent more generally.