Robert J. Drimmie

Oxygen isotope exchange between sulphate and water during bacterial reduction of sulphate

The bacterial reduction of sulphate is accompanied by oxygen isotope exchange reactions. The mechanisms were not investigated in detail but it is suggested that the formation of sulphate-enzyme complexes as intermediary reaction products are facilitating the exchange of 18O between water and sulphate. Under the experimental conditions the observed fractionation factor is close to 25‰ at 30°C and approaches 27‰ at 17°C. Extrapolated values from a field study indicate a difference of ∼ 29‰ at ∼ 5°C.

Stable chlorine and carbon isotope measurements of selected chlorinated organic solvents

Abstract Stable Cl and C isotope ratio results for 3 selected chlorinated solvents, perchloroethylene (PCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) provided by 4 different manufacturers are presented. The isotope ratio for all compounds range between −3.5 and +6.0‰ for δ 37 Cl and from −37.2 to −23.3%. for δ 13 C . The greatest 37 Cl difference between manufacturers is observed in the TCE samples which show δ 37 CI values of −2.5%o for PPG, +2.43‰ for ICI and +4.4‰ for DOW. TCAs show a smaller range (−2.4 to +2.0‰), while the TCEs have slightly different 37 Cl contents. The 13 C data show the most distinct δ 13 C values for PCEs (−23.3 for DOW, −24.1 for Vulcan, −33.8 for PPG and −37.2‰ for ICI) while both TCEs and TCAs show a smaller δ 13 C range, but still distinct differences. These preliminary data suggest that each manufacturer and solvent type may have distinctive δ 637 Cl and δ 13 C values. These results show that by using a combination of 37 Cl and 13 C, there is a potential to indicate a specific source of chlorinated solvents, as well as an ability to delineate contamination episodes caused by these compounds in groundwaters.

Stable hydrogen, carbon and chlorine isotope measurements of selected chlorinated organic solvents

Stable hydrogen isotopes of two chlorinated solvents, trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA), provided by five different manufacturers, were determined and compared to their carbon and chlorine isotopic signatures. The isotope ratio for delta2H of different TCEs ranged between +466.9 per thousand and +681.9 per thousand, for delta13C between -31.57 per thousand and -27.37 per thousand, and for delta37Cl between -3.19 per thousand and +3.90 per thousand. In the case of the TCAs, the isotope ratio for delta2H ranged between -23.1 per thousand and +15.1 per thousand, for delta13C between -27.39 per thousand and -25.84 per thousand, and for delta37Cl between -3.54 per thousand and +1.39 per thousand. As well, a column experiment was carried out to dechlorinate tetrachloroethylene (PCE) to TCE using iron. The dechlorination products have completely different hydrogen isotope ratios than the manufactured TCEs. Compared to the positive values of delta2H in manufactured TCEs (between +466.9 per thousand and +681.9 per thousand), the dechlorinated products had a very depleted delta2H (less than -300 per thousand). This finding has strong implications for distinguishing dechlorination products (PCE to TCE) from manufactured TCE. In addition, the results of this study show the potential of combining 2H/1H analyses with 13C/12C and 37Cl/35Cl for isotopic fingerprinting applications in organic contaminant hydrogeology.

Temporal trends and future predictions of mercury concentrations in Northwest Greenland polar bear (Ursus maritimus) hair.

Hair samples from 117 Northwest Greenland polar bears (Ursus maritimus) were taken during 1892-2008 and analyzed for total mercury (hereafter Hg). The sample represented 28 independent years and the aim of the study was to analyze for temporal Hg trends. Mercury concentrations showed yearly significant increases of 1.6-1.7% (p < 0.0001) from 1892 to 2008 and the two most recent median concentrations from 2006 and 2008 were 23- to 27-fold higher respectively than baseline level from 1300 A.D. in the same region (Nuullit). This indicates that the present (2006-2008) Northwest Greenland polar bear Hg exposure is 95.6-96.2% anthropogenic in its origin. Assuming a continued anthropogenic increase, this model estimated concentrations in 2050 and 2100 will be 40- and 92-fold the baseline concentration, respectively, which is equivalent to a 97.5 and 98.9% man-made contribution. None of the 2001-2008 concentrations of Hg in Northwest Greenland polar bear hair exceeded the general guideline values of 20-30 μg/g dry weight for terrestrial wildlife, whereas the neurochemical effect level of 5.4 μg Hg/g dry weight proposed for East Greenland polar bears was exceeded in 93.5% of the cases. These results call for detailed effect studies in main target organs such as brain, liver, kidney, and sexual organs in the Northwest Greenland polar bears.

Three decades (1983-2010) of contaminant trends in East Greenland polar bears (Ursus maritimus). Part 2: Brominated flame retardants

Brominated flame retardants were determined in adipose tissues from 294 polar bears (Ursus maritimus) sampled in East Greenland in 23 of the 28years between 1983 and 2010. Significant linear increases were found for sum polybrominated diphenyl ether (ΣPBDE), BDE100, BDE153, and hexabromocyclododecane (HBCD). Average increases of 5.0% per year (range: 2.9-7.6%/year) were found for the subadult polar bears. BDE47 and BDE99 concentrations did not show a significant linear trend over time, but rather a significant non-linear trend peaking between 2000 and 2004. The average ΣPBDE concentrations increased 2.3 fold from 25.0ng/g lw (95% C.I.: 15.3-34.7ng/g lw) in 1983-1986 to 58.5ng/g lw (95% C.I.: 43.6-73.4ng/g lw) in 2006-2010. Similar but fewer statistically significant trends were found for adult females and adult males likely due to smaller sample size and years. Analyses of δ(15)N and δ(13)C stable isotopes in hair revealed no clear linear temporal trends in trophic level or carbon source, respectively, and non-linear trends differed among sex and age groups. These increasing concentrations of organobromine contaminants contribute to complex organohalogen mixture, already causing health effects to the East Greenland polar bears.

Isotopic and geochemical evidence of regional-scale anisotropy and interconnectivity of an alluvial fan system, Cochabamba Valley, Bolivia

Abstract A study of groundwater chemistry and isotopic composition was conducted in Cochabamba Valley, Bolivia of an alluvial fan aquifer system located along the northern edge of the valley. In total, 75 wells were sampled for major and minor (F−, Br−, Si4+, NO3−, Fetotal, H2S, PO34−) ion chemistry, 18O and 2H, and 3H. In the alluvial fan aquifer, groundwater flow patterns appear to be controlled by the unique hydrostratigraphy of the fan sediments. The radial morphology of alluvial fans and the entrenchment of channels in the apex of the fan are two probable causes of deposition of coarser, more permeable material along the axis of the fan. Geochemical and isotopic parameters give indirect evidence of these more permeable zones. Ratios of Na + Ca ++ are higher off the axis of the fan, which is most likely due to longer residence times so that diffusion of saline residual pore water or ion exchange reactions create more Na+-rich groundwater. Also, 3H concentrations down the flow system are higher along the axis of the alluvial fan, a direct indication of younger groundwater age along the axis. The distribution of other minor ions, such as F− and Si4+, and the redox parameters NO3−, Fetotal, SO42− and H2S suggest a shorter residence times along the axes. The even pattern of Na + Ca ++ and Na + K + ratios, and Si4+, NO3−, Fetotal, SO42−, H2S, and 3H concentrations along the flow system from wells varying 20 to 80 m in depth suggest that the aquifer–aquitard alluvial fan system is interconnected between different depths. Enriched groundwater 18O and 2H signatures in the distal end of the flow system in Area A are most likely the result of the introduction of evaporated waters from the surface, further evidence that the system is interconnected.

Characterizing shallow aquifers using tritium and 14C: periodic sampling based on tritium half-life

Abstract Thirteen water-production wells in glacial sediments in and around Waterloo, Ontario, (Canada) were sampled for major ions, 3H, 13C, 14C and 18O in 1976 and again in 1988 to gauge the movement of bomb-spike tritium and 14C through the Waterloo aquifer and also to assess the reliability of a hydrogeochemical interpretation of the dynamic character of an aquifer based only on single sampling episode. The suite of samples collected in 1976 was not able to indicate how fast the tritium spike was moving or even if each well-screen was intercepting the front end or tail end of the bomb-spike peak corresponding to infiltration of mid-1960s precipitation. The second sampling event portrayed movement which, qualitatively at least, gave information relating to the more permeable zones of the aquifer and direction of water movement. Water from all but one of the 13 wells sampled in 1988 registered a drop in tritium relative to the 1976 sampling. A well is deemed to be intercepting the front end of the peak of the bomb-spike if its 1988 tritium activity (±2 TU analytical uncertainty) is greater than one half that of the tritium activity of well water measured in 1976 (±8 TU uncertainty). Only one well and two shallow piezometers met this criterion. Ten wells had TU1988/TU1976 ratios which could be interpreted as either greater than or less than 0.5, if the analytical uncertainties of both analyses in this ratio are rigorously applied. Screens of two wells intercept the tail end of the spike because both their uncertainty-adjusted TU1988/TU1976 ratios range from 0.29 to 0.41. Carbon-14 activity for individual wells varied by no more than 6 Per cent Modern Carbon (PMC) between 1976 and 1988. Bomb-spike 14C is not so easily detected as tritium in passage through aquifers because the thermonuclear input of 14C into the atmosphere was much less intense (relative to pre-bomb, background levels) than that for tritium. Also, incongruent dissolution of dolomite, coupled with differing dissolution kinetics between dolomite and calcite, precipitates 14C-bearing calcite in the saturated zone. Although the chemistry of an aquifer can be reasonably characterized by a single sampling episode, the recharge rate and groundwater flow paths are best delineated from a geochemical perspective by multiple samplings in which a persistent chemical and/or isotopic tracer is sought out and repeatedly analyzed. In the Waterloo aquifer, these are tritium and Cl. The sameness of 14C activity in waters sampled 12 a apart makes this a poor candidate to use in this scheme.

Radiocarbon and stable isotopes in water and dissolved constituents, Milk River aquifer, Alberta, Canada

Abstract Origin and age of groundwater in the Milk River aquifer (Alberta, Canada) was the focal point of the present study. To answer related questions, wells in this aquifer were sampled and 2 H and 18 O in water, 13 C and 2 H in methane, 34 S and 18 O in SO 4 , 13 C and 14 C in dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC), and tritium contents determined. Stable isotope analyses on ground-water permitted the recognition of at least three different zones within the aquifer: starting at the recharge zone modern-type groundwaters are encountered for the first few kilometers. These are followed by groundwater with slightly higher 18 O and 2 H contents, i.e. waters which do not show a glacial signature and were probably recharged under warmer climatic conditions. Groundwater in the third zone is characterized by higher salinities and a pronounced oxygen isotope shift. They show the gradual admixture of far more saline formation waters from the Alberta Basin. Sulphate-S and sulphate-O isotope values indicate a till source for the SO 4 . However, SO 4 in wells close to the area where SO 4 virtually disappears show isotopic values which suggest that SO 4 -reduction is occurring, although other studies could not find bacterial populations of SO 4 reducers. Methane is present in most wells and, based on C and H isotope data, has a biogenic origin. Methane production occurs close to some wells and/or it diffuses from the confining shales into the aquifer. Radiocarbon is measurable only in the first 20 km from the recharge zone, however, transformation of measured concentrations to “water ages” is very difficult because of the complexity of the geochemical system. Comparison with 14 C data on DOC was, therefore, very interesting and this new technique may complement the DIC radiocarbon dating. Two wells near the recharge zone yielded DIC, DOC-High Molecular Weight (HMW) and DOC-Low Molecular Weight (LMW) results. The DIC dates were much older than DOC dates but the differenve in years between the wells for all three types of C were within 1000 a of each other. The DOC dates led to the conclusion that the initial DIC radiocarbon content was as low as 30% modern when the water entered the aquifer. The age of the water 20 km from the recharge zone was assessed at ∼20,000 a, resulting in a velocity of ∼1 m/a. This result is much higher than estimates by other techniques.

Sulfate in brines in the crystalline rocks of the Canadian shield

Abstract Deep groundwaters in crystalline rocks typically are very saline and are characterized by a rather unique Ca-Na-Cl-dominated chemistry. Sulfate is present in variable amounts and may be linked to both the geochemical evolution of these fluids as well as to recent processes initiated through mining activities. It is possible to distinguish on the basis of isotopic compositions between brine sulfate and secondary sulfate formed by oxidation of Sulfides: The latter is characterized by δ 34 S values which reflect the local mineral sulfide precursor and δ 18 O close to or below 0%. SMOW. The isotopic composition of the brine sulfate is characterized by δ 18 O and δ 34 S values which resemble marine isotopic compositions at some localities, at others they could be explained as being of magmatic/hydrothermal origin. It is likely that the sulfate participated in the geochemical evolution of these brines. Thus, its isotopic composition reflects geochemical processes rather than a primary origin. No evidence for the influence of bacterial reduction was found.

Dissolved gases in the Milk River aquifer, Alberta, Canada

Abstract Geochemical relations between the noble gases, 40 Ar/ 36 Ar ratio, N 2 and CH 4 contents of groundwaters from the Milk River aquifer, Albert, Canada, have been investigated. The CH 4 contents for many of the groundwaters are several times their N 2 contents and cause degassing to occur as the hydrostatic pressure decreases during their ascent in the wells. Recharge temperatures, derived for those groundwaters that were not degassed, indicate that the youngest groundwaters were recharged under cooler climatic conditions than prevailed during earlier recharge. This conclusion is supported by the stable isotope compositions of the groundwater. The 4 He concentration in the groundwater varies with depth according to the theoretical concentration/depth profile for accumulated radiogenic 4 He in the aquifer and its adjacent shales. The corresponding flux of 4 He to the atmosphere is 4 He production rate. Excess radiogenic 40 Ar is associated with CH 4 and both gases originated within the adjacent shales. The CH 4 is biogenic and was produced in an aqueous environment which ranged from marine to freshwater as the connate fluids in these marine shales were replaced. The degassing process has been modelled to explain the residual dissolved gas contents of the groundwater and to show that the CH 4 /N 2 ratio in situ was ∼12.