Publications

Freshwater and marine environments constitute the largest global reservoirs of the greenhouse gas methane (CH4) and natural abundance radiocarbon measurements (14C-CH4) can allow for high confidence interpretations about CH4 dynamics operating in these environments. Collecting sufficient amounts of CH4 sample for a standard, high precision 14C-accelerator mass spectrometry (AMS) analysis (∼ 200 μg carbon (C)) was previously unfeasible when sampling from low CH4 concentration waters, such as much of the surface ocean (∼ 2 nM), which would require collecting the CH4 from 8500 L of seawater. The method described here involves pumping 20,000–40,000 L of seawater up from depth through a dissolved gas extraction system, which enables the collection of a sample composed of 100s of L of gas in less than 4 h on station. The large volume extracted gas sample is compressed into a 1.7 L cylinder for transport from the ship to the home laboratory. The home laboratory preparation of each sample to a CH4-derived carbon dioxide aliquot for 14C-AMS analysis is carried out in 3 h on a flow-through vacuum line that simultaneously prepares aliquots for stable isotope analyses (δ13C-CH4 and δ2H-CH4). The total process blank of the method is small (5.0 μg CH4-C) and composes 1.2% of the average collected and prepared sample (424 ± 163 μg, from a recent campaign; n = 16). The 14C-CH4 blanks prepared on the vacuum line have acceptably low 14C content (0.23 ± 0.07 percent Modern Carbon (pMC); n = 7) relative to the 14C-dead (0 pMC) CH4 from which they are prepared.

Electrophilic compounds/metabolites present in humans, originating from endogenous processes or exogenous exposure, pose a risk to health effects through their reactions with nucleophilic sites in proteins and DNA, forming adducts. Adductomic approaches are developed to screen for adducts to biomacromolecules in vivo by mass spectrometry (MS), with the aim to detect adducts corresponding to unknown exposures from electrophiles. In the present study, adductomic screening was performed using blood samples from healthy children about 12 years old (n = 51). The frequencies of micronuclei (MN) in erythrocytes in peripheral blood were monitored as a measure of genotoxic effect/genotoxic exposure. The applied adductomic approach has been reported earlier by us and is based on analysis of N-terminal valine adducts in hemoglobin (Hb) by liquid chromatography tandem mass spectrometry (LC-MS/MS). High resolution MS was introduced for refined screening of previously unknown N-terminal Hb adducts. Measured adduct levels were compared with MN frequencies using multivariate data analysis. In the 51 individuals, a total of 24 adducts (whereof 12 were previously identified) were observed and their levels quantified. Relatively large interindividual variations in adduct levels were observed. The data analysis (with partial least-squares regression) showed that as much as 60% of the MN variation could be explained by the adduct levels. This study, for the first time, applies the combination of these sensitive methods to measure the internal dose of potentially genotoxic chemicals and genotoxic effects, respectively. The results indicate that this is a valuable approach for the characterization of exposure to chemical risk factors for the genotoxic effects present in individuals of the general population.