Organic contamination detection for isotopic analysis of water by laser spectroscopy.

RATIONALE: Hydrogen and oxygen stable isotope ratios (δ2 H, δ17 O, and δ18 O values) are commonly used tracers of water. These ratios can be measured by isotope ratio infrared spectroscopy (IRIS). However, IRIS approaches are prone to errors induced by organic compounds present in plant, soil, and natural water samples. A novel approach using 17 O-excess values has shown promise for flagging spectrally contaminated plant samples during IRIS analysis. A systematic assessment of this flagging system is needed to prove it useful. METHODS: Errors induced by methanol and ethanol water mixtures on measured IRIS and isotope ratio mass spectrometry (IRMS) results were evaluated. For IRIS analyses both liquid- and vapour-mode (via direct vapour equilibration) methods are used. The δ2 H, δ17 O, and δ18 O values were measured and compared with known reference values to determine the errors induced by methanol and ethanol contamination. In addition, the 17 O-excess contamination detection approach was tested. This is a post-processing detection tool for both liquid and vapour IRIS triple-isotope analyses, utilizing calculated 17 O-excess values to flag contaminated samples. RESULTS: Organic contamination induced significant errors in IRIS results, not seen in IRMS results. Methanol caused larger errors than ethanol. Results from vapour-IRIS analyses had larger errors than those from liquid-IRIS analyses. The 17 O-excess approach identified methanol driven error in liquid- and vapour-mode IRIS samples at levels where isotope results became unacceptably erroneous. For ethanol contaminated samples, a mix of erroneous and correct flagging occurred with the 17 O-excess method. Our results indicate that methanol is the more problematic contaminant for data corruption. The 17 O-excess method was therefore useful for data quality control. CONCLUSIONS: Organic contamination caused significant errors in IRIS stable isotope results. These errors were larger during vapour analyses than during liquid IRIS analyses, and larger for methanol than ethanol contamination. The 17 O-excess method is highly sensitive for detecting narrowband (methanol) contamination error in vapour and liquid analysis modes in IRIS.

17 O-excess as a detector for co-extracted organics in vapor analyses of plant isotope signatures.

RATIONALE: The stable isotope compositions of hydrogen and oxygen in water (δ2 H and δ18 O values) have been widely used to investigate plant water sources, but traditional isotopic measurements of plant waters are expensive and labor intensive. Recent work with direct vapor equilibration (DVE) on laser spectroscopy has shown potential to side step limitations imposed by traditional methods. Here, we evaluate DVE analysis of plants with a focus on spectral contamination introduced by organic compounds. We present 17 O-excess as a way of quantifying organic compound interference in DVE. METHODS: We performed isotopic analysis using the δ2 H, δ18 O and δ17 O values of water on an Off-Axis Integrated Cavity Output Spectroscopy (IWA-45EP OA-ICOS) instrument in vapor mode. We used a set of methanol (MeOH) and ethanol (EtOH) solutions to assess errors in isotope measurements. We evaluated how organic compounds affect the 17 O-excess. DVE was used to measure the isotopic signatures in natural plant material from Pinus banksiana, Picea mariana, and Larix laricina, and soil from boreal forest for comparison with solutions. RESULTS: The 17 O-excess was sensitive to the presence of organic compounds in water. 17 O-excess changed proportionally to the concentration of MeOH per volume of water, resulting in positive values, while EtOH solutions resulted in smaller changes in the 17 O-excess. Soil samples did not show any spectral contamination. Plant samples were spectrally contaminated on the narrow-band and were enriched in 1 H and 16 O compared with source water. L. laricina was the only species that did not show any evidence of spectral contamination. Xylem samples that were spectrally contaminated had positive 17 O-excess values. CONCLUSIONS: 17 O-excess can be a useful tool to identify spectral contamination and improve DVE plant and soil analysis in the laboratory and in situ. The 17 O-excess flagged the presence of MeOH and EtOH. Adding measurement of δ17 O values to traditional measurement of δ2 H and δ18 O values may shed new light on plant water analysis for source mixing dynamics using DVE.

PAH distributions in sediments in the oil sands monitoring area and western Lake Athabasca: Concentration, composition and diagnostic ratios.

Oil sands activities north of Fort McMurray, Alberta, have intensified in recent years with a concomitant debate as to their environmental impacts. The Regional Aquatics Monitoring Program and its successor, the Joint Canada-Alberta Implementation Plan for Oil Sands Monitoring (JOSM), are the primary aquatic programs monitoring this industry. Here we examine sediment data (collected by Ekman grabs) to investigate trends and sources of polycyclic aromatic hydrocarbons (PAHs), supplementing these data with sediment core studies. Total PAH (ΣPAH) concentrations were highest at Shipyard Lake (6038 ± 2679 ng/g) in the development center and lower at Isadore's Lake (1660 ± 777 ng/g) to the north; both lakes are in the Athabasca River Valley and lie below the developments. ΣPAH concentrations were lower (622-930 ng/g) in upland lakes (Kearl, McClelland) located further away from the developments. ΣPAH concentrations increased at Shipyard Lake (2001-2014) and the Ells River mouth (1998-2014) but decreased in nearshore areas at Kearl Lake (2001-2014) and a Muskeg River (2000-2014) site. Over the longer term, ΣPAH concentrations increased in Kearl (1934-2012) and Sharkbite (1928-2010) Lakes. Further (200 km) downstream in the Athabasca River delta, ΣPAH concentrations (1029 ± 671 ng/g) increased (1999-2014) when %sands were included in the regression model; however, 50 km to the east, concentrations declined (1926-2009) in Lake Athabasca. Ten diagnostic ratios based on anthracene, phenanthrene, fluoranthene, pyrene, benz[a]anthracene, chrysene, indeno[123-cd]pyrene, dibenz[a,h]anthracene, dibenzothiophene and retene were examined to infer spatial and temporal trends in PAH sources (e.g., combustion versus petrogenic) and weathering. There was some evidence of increasing contributions of unprocessed oil sands and bitumen dust to Shipyard, Sharkbite, and Isadore's Lakes and increased combustion sources in the Athabasca River delta. Some CCME interim sediment quality guidelines were exceeded, primarily in Shipyard Lake and near presumed natural bitumen sources.