Lesley Ann Chesson

Stable isotopes are valuable biogeochemical markers for solving problems faced by society today, such as distinguishing authentic from adulterated foods and beverages or tracing the origins of illicit drugs. Hydrogen and oxygen isotopes in water exhibit distinct continental patterns (isoscapes), which provide useful region-of-origin information. We ourselves reflect the stable isotope ratios of the water we drink and the food we eat: our hair records any isotopic changes to our diets, which can often be related to location. This latter aspect can be of interest to law enforcement in determining the origins and travel histories of unidentified murder victims.

Analyses of stable isotope ratios of pollen present within complex matrices may be useful in sample provenance or climate change applications. We developed a method for separating pollen from honey and preparing pollen for hydrogen and oxygen stable isotope ratio analysis. The method combined several treatments: ethanol dilution to separate pollen; hexane washing to remove wax; and acetolysis to digest all but the external layer of pollen granules. There were large isotopic effects associated with treatments but effects were consistent between replicate applications of the method. We used the method to separate pollen from 45 honey samples from across the United States. Pollen δ²H and δ¹⁸O isotope values were significantly positively correlated (P < 0.05), but there was little variation in δ²H values explained by δ¹⁸O values (r² = 0.17). Pollen δ²H values were significantly correlated with δ²H values of precipitation predicted for hive locations (P < 0.05, r² = 0.24), but there was no significant correlation between pollen and precipitation δ¹⁸O values (P = 0.34, r² = 0.03). These results suggest hydrogen and oxygen stable isotope analysis of pollen may not be as useful as analysis of liquid honey or beeswax in investigating provenance.

Strontium isotope analysis has proven useful in geo‐location investigations of organic and inorganic materials and may complement the region‐of‐origin information provided by hydrogen and oxygen stable isotope analysis. In this study, we analyzed 99 drinking (tap) water samples collected from 95 municipal water systems across the USA to investigate the potential that ⁸⁷Sr/⁸⁶Sr can be used to provenance samples from managed hydrological systems. Results from a leaching and exchange experiment demonstrated that non‐ideal storage conditions did not prohibit Sr isotope analysis of previously archived water samples stored in glass. Tap water samples were analyzed via multi‐collector inductively coupled plasma mass spectrometry, which was preceded by a novel, automated, in‐line Sr purification method. Measured tap water ⁸⁷Sr/⁸⁶Sr was compared to expected ⁸⁷Sr/⁸⁶Sr for collection location, which was predicted using four published isotope landscape (isoscape) models: age of bedrock (bedrock model), age plus major and minor lithology of bedrock (major bedrock model), weathering of Sr from rock (local water model), and surface fluxes within watershed (catchment model). The geologic history of the geographic regions represented by collected tap waters was diverse and we therefore expected significant covariation in measured and modeled ⁸⁷Sr/⁸⁶Sr values. Tap water exhibited large ranges in both Sr concentration (0–1.9 mg/L) and ⁸⁷Sr/⁸⁶Sr (0.7037–0.7320). Measured tap water ⁸⁷Sr/⁸⁶Sr ratios were significantly and positively correlated with predictions based on bedrock and catchment models. However, these bedrock and catchment models explained relatively little of the tap water Sr isotopic variation (∼10% and 17%, respectively), suggesting that the factors affecting drinking water ⁸⁷Sr/⁸⁶Sr are complex and more numerous than the variables included in current water models. This could be due to the reliance of some municipal water systems on groundwater, rather than surficial water sources; the natural movement of water across distinct geologic gradients; and/or the managed transport of water from source to point‐of‐use. Although published isoscape models for predicting Sr isotopic variation within the continental USA are reasonable approaches for estimating surface water ⁸⁷Sr/⁸⁶Sr, additional efforts are needed to develop a prediction model specifically for tap water ⁸⁷Sr/⁸⁶Sr.

Published datasets of proteinaceous animal tissues suggest that co‐variation between amino acid hydrogen ( δ ² H) and oxygen ( δ ¹⁸ O) isotope ratios is a common feature in systems where isotopic variation is driven by geographic or temporal variation in the δ ² H and δ ¹⁸ O values of environmental water. This has led to the development of models relating tissue δ ² H and δ ¹⁸ O values to those of water, with potential application in a number of fields. However, the strength and ubiquity of the influence of environmental water on protein isotope ratios across taxonomic groups, and thus the relevance of predictive models, is an open question. Here we report strong co‐variation of δ ² H and δ ¹⁸ O values across a suite of terrestrial and aquatic animal meats purchased in American food markets, including beef, poultry (chicken and turkey), chicken eggs, pork, lamb, freshwater fish, and marine fish. Significant isotope co‐variation was not found for small collections of marine bivalves and crustaceans. These results imply that isotopic signals from environmental water were propagated similarly through most of the diverse natural and human‐managed foodwebs represented by our samples. Freshwater fish had the largest variation in δ ² H and δ ¹⁸ O values, with ranges of 121 ‰ and 19.2 ‰, respectively, reflecting the large isotopic variation in environmental freshwaters. In contrast marine animals had the smallest variation for both δ ² H (7 ‰ range, crustaceans) and δ ¹⁸ O (3.0 ‰ range, bivalves) values. Known‐origin beef samples demonstrated direct relationships between the variance of environmental water isotope ratios and that of collected meats. Copyright © 2011 John Wiley & Sons, Ltd.

Hydrogen ( δ ² H) and oxygen ( δ ¹⁸ O) stable isotope analysis is useful when tracing the origin of water in beverages, but traditional analytical techniques are limited to pure or extracted waters. We measured the isotopic composition of extracted beverage water using both isotope ratio infrared spectroscopy (IRIS; specifically, wavelength‐scanned cavity ring‐down spectroscopy) and isotope ratio mass spectrometry (IRMS). We also analyzed beer, sodas, juices, and milk ‘as is’ using IRIS. For IRIS analysis, four sequential injections of each sample were measured and data were corrected for sample‐to‐sample memory using injections (a) 1‐4, (b) 2‐4, and (c) 3‐4. The variation between δ ² H and δ ¹⁸ O values calculated using the three correction methods was larger for unextracted (i.e., complex) beverages than for waters. The memory correction was smallest when using injections 3‐4. Beverage water δ ² H and δ ¹⁸ O values generally fit the Global Meteoric Water Line, with the exception of water from fruit juices. The beverage water stable isotope ratios measured using IRIS agreed well with the IRMS data and fit 1:1 lines, with the exception of sodas and juices ( δ ² H values) and beers ( δ ¹⁸ O values). The δ ² H and δ ¹⁸ O values of waters extracted from beer, soda, juice, and milk were correlated with complex beverage δ ² H and δ ¹⁸ O values ( r = 0.998 and 0.997, respectively) and generally fit 1:1 lines. We conclude that it is possible to analyze complex beverages, without water extraction, using IRIS although caution is needed when analyzing beverages containing sugars, which can clog the syringe and increase memory, or alcohol, a known spectral interference. Copyright © 2010 John Wiley & Sons, Ltd.

This study investigated the impact of purchase location on the stable isotope ratios of beverages by measuring the delta(2)H and delta(18)O values of bottled water, soda, beer, and tap water collected across the contiguous United States. Measured beverage delta(2)H and delta(18)O values generally fit the Global Meteoric Water Line (GMWL), suggesting region-of-origin information is recorded in beverage water. Tap water delta(2)H and delta(18)O values were strongly correlated with the stable isotope ratios of bottled water and soda purchased in the same location. Beer water delta(2)H and delta(18)O values were also correlated with tap water, although not as strongly. Variability in delta(2)H and delta(18)O values among beverages purchased at a single location ranged from 2 to 41 per thousand and from 0.3 to 5.2 per thousand, respectively, but was generally moderate in most locations. It was concluded that the isotopic composition of local tap water is a reasonable proxy for consumers' fluid intake in most U.S. cities.