It was found that benzenepolycarboxylic acids (BPCA) do naturally occur in soils. They can be assumed as black carbon degradation products. We propose an improved method to analyse black carbon degradation products in soil. Method optimization comprised extraction duration, sample clean‐up, and chromatographic separation conditions. The method is also suitable for subsequent isotope ratio mass spectrometry of individual BPCA. Accuracy was checked with quartz sand and soil samples spiked with known amounts of BPCA. In soil samples with varying properties we compared contents of black carbon and black carbon degradation products, i.e., total and free BPCA contents, respectively. Results show that our proposed method can extract black carbon degradation products from soil after 48 h of extraction with 500 mM NaOH compared to 72 h of the original method. Polyvalent cations should be removed by Dowex 50 W X 8, 200–400 mesh, while original cation removal with Merck cation exchange resin was not successful. Free BPCA can be separated and quantified directly by ion exchange chromatography followed by ultraviolet spectroscopy or isotope ratio mass spectrometry, while the original method involved another two days for derivatization and isolation of derivatized BPCA. Recovery of spiked BPCA to a range of different soil samples was 81 ± 19%. Free BPCA concentrations of a Cambisol, Chernozem, Ferralsol, and Anthrosol varied between 0 and 0.24 g kg−1 contributing 0–38% of total black carbon concentration. Free BPCA correlated with total black carbon, total organic carbon, and negatively with pH. However, further studies with a larger set of samples are necessary to systematically investigate conditions for black carbon degradation and, thus free BPCA formation in soils.
Most visitors of a sauna appreciate the heat pulse that is perceived when water is poured on the stones of a sauna stove. However, probably only few bathers are aware that this pleasant heat pulse is caused by latent heat being released onto our skin due to condensation of water vapour. In order to quantify the proportion of condensation water versus sweat to dripping water of test persons we conducted sauna experiments using isotopically labelled (δ(18)O and δ(2)H) thrown water as tracer. This allows differentiating between 'pure sweat' and 'condensation water'. Two ways of isotope mass balance calculations were applied and yielded similar results for both water isotopes. Accordingly, condensation contributed considerably to dripping water with mean proportions of 52 ± 12 and 54 ± 7% in a sauna experiment in winter semester 2011/12 and 30 ± 13 and 33 ± 6% in a sauna experiment in winter semester 2012/13, respectively, depending on the way of calculating the isotope mass balance. It can be concluded from the results of our dual isotope labelling sauna experiment that it is not all about sweat in the sauna.
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