Use of Stable Isotopes to Identify Sources of Mercury in Sediments: A Review and Uncertainty Analysis

Mass-dependent and mass-independent mercury isotope fractionation potentially generates unique source signatures that can be used to apportion contributions to sediment contamination. This article reviews findings from previous investigations that have used mercury isotopes to identify sources. It also discusses a mass balance mercury isotope fractionation model that simulates changes in isotopic source signatures in aquatic systems caused by natural biogeochemical cycling. According to the model, the extent of source signature alteration depends on chemical speciation, with more labile forms exhibiting greater isotopic fractionation. Apportionment is tractable when differences between δ²⁰²Hg of sources are larger than potential changes in isotopic signatures following the release of mercury into the environment.     

Applications of Anthropogenic Lead ArchaeoStratigraphy (ALAS Model) to Hydrocarbon Remediation

A model, which employs the use of high precision stable lead isotopic analyses, has been developed to estimate the age of hydrocarbon releases. The ALAS Model (Anthropogenic Lead ArchaeoStratigraphy) is based on calibrated, systematic increases in lead isotope ratios of gasolines caused by shifts in sources of lead ores used by the U.S. lead industry, including manufacturers of alkylleads, to more radiogenic Mississippi Valley Type (MVT) deposits. Acquisition of high quality samples (free product, gasoline-impacted soil and groundwater) of known age and subsequent analyses of the hydrocarbon component by high precision lead isotopic analyses by thermal ionization mass spectrometry (TIMS) have produced the ALAS Model calibration curve. Age uncertainties range from - 1 to 2 years for gasoline releases which occurred between 1965 and 1990, the major era of leaded gasoline usage. Analytical methods required to measure lead isotope ratios on ~5 nanograms of lead with precisions and accuracy of < - 0.1% (2 SEM ) are discussed in detail. Published lead isotopic measurements of gasoline-derived anthropogenic lead of samples throughout the United States are used to demonstrate the wide geographic range over which the ALAS Model may be applied. Two representative case studies involving an early 1970s free product release in California and the discrimination of a 1970s from modern unleaded gasoline release in Florida demonstrate the use of the model on single and multiple hydrocarbon releases, respectively, in different geographic regions of the United States. A third investigation focuses on the use of lead isotopes to correlate dissolved phase hydrocarbons with their source, in this case, unleaded (aka low lead) gasoline releases in New Jersey. Dissolved phase hydrocarbons (BTEX/MTBE) are shown to carry the lead isotopic signature of the unleaded gasoline into groundwater, allowing the specific source of the release to be identified. Investigations of lead isotopes as tracers of MTBE in groundwater are ongoing. However, both laboratory and field data indicate MTBE carries the lead isotopic signature of its unleaded gasoline source into groundwater, demonstrating the potential of the lead isotopic system as a discriminant of MTBE sources. Although developed to estimate the age of leaded gasoline releases, the ALAS Model has been successfully applied in studies requiring age dating of jet-A, diesel, kerosene, motor oil, and heating oil. These petroleum distillates are suspected of accidentally acquiring small, yet significant quantities of alkylleads during refining, allowing accurate ALAS Model ages to be determined. When lead levels in these petroleum distillates are within their normal range, typically tens to hundreds of ppb lead, it is possible to use lead isotopic ratios to correlate environmental releases of these products to their source or other releases.     

Applications of Anthropogenic Lead ArchaeoStratigraphy (ALAS Model) to Hydrocarbon Remediation

A model, which employs the use of high precision stable lead isotopic analyses, has been developed to estimate the age of hydrocarbon releases. The ALAS Model (Anthropogenic Lead ArchaeoStratigraphy) is based on calibrated, systematic increases in lead isotope ratios of gasolines caused by shifts in sources of lead ores used by the U.S. lead industry, including manufacturers of alkylleads, to more radiogenic Mississippi Valley Type (MVT) deposits. Acquisition of high quality samples (free product, gasoline-impacted soil and groundwater) of known age and subsequent analyses of the hydrocarbon component by high precision lead isotopic analyses by thermal ionization mass spectrometry (TIMS) have produced the ALAS Model calibration curve. Age uncertainties range from  ± 1 to 2 years for gasoline releases which occurred between 1965 and 1990, the major era of leaded gasoline usage. Analytical methods required to measure lead isotope ratios on ∼5 nanograms of lead with precisions and accuracy of < ± 0.1% (2_SEM) are discussed in detail. Published lead isotopic measurements of gasoline-derived anthropogenic lead of samples throughout the United States are used to demonstrate the wide geographic range over which the ALAS Model may be applied. Two representative case studies involving an early 1970s free product release in California and the discrimination of a 1970s from modern unleaded gasoline release in Florida demonstrate the use of the model on single and multiple hydrocarbon releases, respectively, in different geographic regions of the United States. A third investigation focuses on the use of lead isotopes to correlate dissolved phase hydrocarbons with their source, in this case, unleaded (aka low lead) gasoline releases in New Jersey. Dissolved phase hydrocarbons (BTEX/MTBE) are shown to carry the lead isotopic signature of the unleaded gasoline into groundwater, allowing the specific source of the release to be identified. Investigations of lead isotopes as tracers of MTBE in groundwater are ongoing. However, both laboratory and field data indicate MTBE carries the lead isotopic signature of its unleaded gasoline source into groundwater, demonstrating the potential of the lead isotopic system as a discriminant of MTBE sources. Although developed to estimate the age of leaded gasoline releases, the ALAS Model has been successfully applied in studies requiring age dating of jet-A, diesel, kerosene, motor oil, and heating oil. These petroleum distillates are suspected of accidentally acquiring small, yet significant quantities of alkylleads during refining, allowing accurate ALAS Model ages to be determined. When lead levels in these petroleum distillates are within their normal range, typically tens to hundreds of ppb lead, it is possible to use lead isotopic ratios to correlate environmental releases of these products to their source or other releases.     

Determination of the origin of groundwater nitrate at an air weapons range using the dual isotope approach

Nitrate is one of the most common contaminants in shallow groundwater, and many sources may contribute to the nitrate load within an aquifer. Groundwater nitrate plumes have been detected at several ammunition production sites. However, the presence of multiple potential sources and the lack of existing isotopic data concerning explosive degradation-induced nitrate constitute a limitation when it comes to linking both types of contaminants. On military training ranges, high nitrate concentrations in groundwater were reported for the first time as part of the hydrogeological characterization of the Cold Lake Air Weapons Range (CLAWR), Alberta, Canada. Explosives degradation is thought to be the main source of nitrate contamination at CLAWR, as no other major source is present. Isotopic analyses of N and O in nitrate were performed on groundwater samples from the unconfined and confined aquifers; the dual isotopic analysis approach was used in order to increase the chances of identifying the source of nitrate. The isotopic ratios for the groundwater samples with low nitrate concentration suggested a natural origin with a strong contribution of anthropogenic atmospheric NOx. For the samples with nitrate concentration above the expected background level the isotopic ratios did not correspond to any source documented in the literature. Dissolved RDX samples were degraded in the laboratory and results showed that all reproduced degradation processes released nitrate with a strong fractionation. Laboratory isotopic values for RDX-derived NO(3)(-) produced a trend of high delta(18)O-low delta(15)N to low delta(18)O-high delta(15)N, and groundwater samples with nitrate concentrations above the expected background level appeared along this trend. Our results thus point toward a characteristic field of isotopic ratios for nitrate being derived from the degradation of RDX.     

Forensic Applications of Nitrogen and Oxygen Isotopes in Tracing Nitrate Sources in Urban Environments

Ground and surface waters in urban areas are susceptible to nitrate contamination from septic systems, leaking sewer lines, and fertilizer applications. Source identification is a primary step toward a successful remediation plan in affected areas. In this respect, nitrogen and oxygen isotope ratios of nitrate, in conjunction with hydrologic data and water chemistry, have proven valuable in urban studies from Austin, Texas, and Tacoma, Washington. In Austin, stream water was sampled during stremflow and baseflow conditions to assess surface and subsurface sources of nitrate, respectively. In Tacoma, well waters were sampled in adjacent sewered and un-sewered areas to determine if locally high nitrate concentrations were caused by septic systems in the un-sewered areas. In both studies, sewage was identified as a nitrate source and mixing between sewage and other sources of nitrate was apparent. In addition to source identification, combined nitrogen and oxygen isotopes were important in determining the significance of denitrification, which can complicate source assessment by reducing nitrate concentrations and increasing i 15 N values. The two studies illustrate the value of nitrogen and oxygen isotopes of nitrate for forensic applications in urba areas.     

Carbon and hydrogen isotope effects during sorption of organic contaminants on carbonaceous materials

Stable carbon and hydrogen isotopes can be an efficient means to validate biodegradation of organic contaminants in groundwater since it results in an isotopic fractionation. A prerequisite in applying this method in the field is the proof that other processes decreasing the contaminant concentration are conservative with respect to isotope effects. In this paper we show for carbon isotopes of halogenated hydrocarbon compounds [trichloroethene (TCE), cis-dichloroethene (c-DCE), vinylchloride (VC)] and carbon and hydrogen isotopes of BTEX compounds (benzene, toluene, p-xylene) that no significant fractionation occurs during equilibrium sorption onto activated carbon, lignite coke and lignite. In general, effects were in the range of the reproducibility limit of the analytical instrument (0.5 per thousand for delta13C, and 8 per thousand for delta2H). This observation was made for fractions sorbed of less than 5% to more than 95%. Also for rate-limited sorption of TCE onto activated carbon, no significant fractionation in carbon isotopes could be observed. These findings support the assumption that for these classes of compounds, sorption processes in aquifer systems are conservative with respect to isotope effects.     

Measurement of 13C/12C of chloroacetic acids by gas chromatography/combustion/isotope ratio mass spectrometry

This paper describes a novel analytical methodology using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) to measure the 13C/12C ratios of chloroacetic acids (CAAs). CAAs are a major class of environmental pollutants that are widely distributed throughout the world, often at relatively high concentrations, and are of concern due to their toxic effects, particularly on plants. The 13C/12C of CAA reagents was measured by IRMS subsequent to offline combustion. Aqueous solutions of these CAAs were derivatized to the corresponding methyl chloroacetates (MCAAs) with acidic methanol with a known isotopic composition, extracted into pentane, and analyzed by GC/C/IRMS. Measured 13C/12C ratios of derivatized MCAAs were in agreement with calculated values within 1 per thousand for monochloroacetic acid and trichloroacetic acid and within 2 per thousand for dichloroacetic acid, suggesting that methylation and other analytical methodology steps do not isotopically fractionate derivatized MCAAs. 13C/12C ratios of reagent CAAs from different sources had varying isotopic signatures suggesting differences in source carbon and/or production methods. Our results underscore the potential of stable isotopes to serve as tracers of environmental sources of CAAs.     

Forensic Applications of Nitrogen and Oxygen Isotopes in Tracing Nitrate Sources in Urban Environments

Ground and surface waters in urban areas are susceptible to nitrate contamination from septic systems, leaking sewer lines, and fertilizer applications. Source identification is a primary step toward a successful remediation plan in affected areas. In this respect, nitrogen and oxygen isotope ratios of nitrate, in conjunction with hydrologic data and water chemistry, have proven valuable in urban studies from Austin, Texas, and Tacoma, Washington.In Austin, stream water was sampled during stremflow and baseflow conditions to assess surface and subsurface sources of nitrate, respectively. In Tacoma, well waters were sampled in adjacent sewered and un-sewered areas to determine if locally high nitrate concentrations were caused by septic systems in the un-sewered areas. In both studies, sewage was identified as a nitrate source and mixing between sewage and other sources of nitrate was apparent. In addition to source identification, combined nitrogen and oxygen isotopes were important in determining the significance of denitrification, which can complicate source assessment by reducing nitrate concentrations and increasing δ¹⁵N values. The two studies illustrate the value of nitrogen and oxygen isotopes of nitrate for forensic applications in urban areas.     

Source characterization of ozone precursors by complementary approaches of vehicular indicator and principal component analysis

Measurements of speciated non-methane hydrocarbons (NMHCs) were conducted in an ozone non-attainment metropolis with pronounced industrial emissions in addition to traffic ones. Highly variable and complex natures of industrial sources make their composition profiles difficult to determine. In the circumstances of no reliable source profiles, two simple complementary approaches were attempted to characterize sources of NMHCs. First, a robust vehicular indicator, 3-methylpentane (3MC5A), which is an intrinsic component of gasoline, was used to estimate contributions of traffic versus non-traffic sources for major NMHCs with high ozone-forming potentials (OFPs), such as ethene, toluene, xylene, isoprene, etc. Second, the method of principal component analysis (PCA) was employed to further discern non-traffic emissions into various source groups. A total of 454 ambient samples were sampled in the urban-industrial complex metropolis (Kaohsiung, Taiwan) to build up a large dataset to be tested by the two complementary approaches. It was found that four types of emissions, i.e., traffic, household fuel leakage, industrial, and biogenic, were responsible for the observed ambient NMHCs. The industrial contribution was significant for ethene and toluene (with 48–67% and 33–62%, respectively), whereas xylene was found to be mainly vehicular. In addition, isoprene revealed its biogenic nature. OFPs arising from vehicular, industrial and biogenic contributions could be further assessed for the purpose of emission control of NMHCs in the ozone non-attainment area.     

The Use of Stable Isotopes to Differentiate Specific Source Markers for MTBE

The recent controversy over the use of MTBE within gasoline to boost oxygen content and decrease carbon monoxide emissions to the atmosphere has led to a proposed phase-out of this compound by 2002. This paper is a preliminary investigation into the use of gas chromatography isotope-ratio mass spectrometry (GCIRMS) to determine both carbon and hydrogen isotopic compositions of MTBE as a means of differentiating sources of MTBE. Three pure MTBE samples were purchased from chemical distributors. Little variation of the i 13 C values were observed although the samples had isotopically distinct i -D values. Four different methods of obtaining carbon isotope ratios of neat MTBE, MTBE in gasoline, and MTBE in water are described, and the precision and accuracy of each is discussed. The carbon isotopic compositions of MTBE within 10 gasoline samples from three different areas of the United States show a wide range of carbon isotope compositions. This novel method of MTBE analysis could be valuable in forensic investigations.     

The Use of Stable Isotopes to Differentiate Specific Source Markers for MTBE

The recent controversy over the use of MTBE within gasoline to boost oxygen content and decrease carbon monoxide emissions to the atmosphere has led to a proposed phase-out of this compound by 2002. This paper is a preliminary investigation into the use of gas chromatography isotope-ratio mass spectrometry (GCIRMS) to determine both carbon and hydrogen isotopic compositions of MTBE as a means of differentiating sources of MTBE. Three pure MTBE samples were purchased from chemical distributors. Little variation of the δ¹³C values were observed although the samples had isotopically distinct δ-D values. Four different methods of obtaining carbon isotope ratios of neat MTBE, MTBE in gasoline, and MTBE in water are described, and the precision and accuracy of each is discussed. The carbon isotopic compositions of MTBE within 10 gasoline samples from three different areas of the United States show a wide range of carbon isotope compositions. This novel method of MTBE analysis could be valuable in forensic investigations.     

Forensic Evaluation of Metals (Cr,Cu, Pb,Zn), Isotopes (δ13C and δ15N), and C:N Ratios in Freshwater Sediment

A forensic approach was used to evaluate sediments from Portão Stream, including analysis of metals, carbon (C) and nitrogen (N) stable isotopes, and C:N ratios. Samples collected at various points located along the stream were tested in order to investigate a possible illegal leachate input. The studied stream is heavily impacted by sewage and industrial discharges from two cities along its course. Among the metals analyzed, chromium (Cr) was noticeably the main pollutant, showing the highest levels, above regulatory limits, downstream from some potential sources of effluents enriched with this metal. Isotope analyses revealed a general trend of depletion in the heavier isotope along the stream for C and N. The exception was one point near a hazardous waste landfill, where relatively more enriched δ¹³C and δ¹⁵N values were found. The isotope and metal analysis results indicated that this site was affected by a particular source, demonstrating the combination of these parameters could be used for the discrimination of sources in a heavily polluted stream. Nevertheless, further investigations are necessary to provide a comprehensive evaluation of the biogeochemical processes involved in the incorporation of leachate in sediments to use this analysis as evidence for the illegal leachate discharge.     

Research and application of method of oxygen isotope of inorganic phosphate in Beijing agricultural soils

Phosphorus (P) in agricultural ecosystems is an essential and limited element for plants and microorganisms. However, environmental problems caused by P accumulation as well as by P loss have become more and more serious. Oxygen isotopes of phosphate can trace the sources, migration, and transformation of P in agricultural soils. In order to use the isotopes of phosphate oxygen, appropriate extraction and purification methods for inorganic phosphate from soils are necessary. Here, we combined two different methods to analyze the oxygen isotopic composition of inorganic phosphate (δ¹⁸O_P) from chemical fertilizers and different fractions (Milli-Q water, 0.5 mol L^?1 NaHCO₃ (pH = 8.5), 0.1 mol L^?1 NaOH and 1 mol L^?1 HCl) of agricultural soils from the Beijing area. The δ¹⁸O_P results of the water extracts and NaHCO₃ extracts in most samples were close to the calculated equilibrium value. These phenomena can be explained by rapid P cycling in soils and the influence of chemical fertilizers. The δ¹⁸O_P value of the water extracts and NaHCO₃ extracts in some soil samples below the equilibrium value may be caused by the hydrolysis of organic P fractions mediated by extracellular enzymes. The δ¹⁸O_P values of the NaOH extracts were above the calculated equilibrium value reflecting the balance state between microbial uptake of phosphate and the release of intracellular phosphate back to the soil. The HCl extracts with the lowest δ¹⁸O_P values and highest phosphate concentrations indicated that the HCl fraction was affected by microbial activity. Hence, these δ¹⁸O_p values likely reflected the oxygen isotopic values of the parent materials. The results suggested that phosphate oxygen isotope analyses could be an effective tool in order to trace phosphate sources, transformation processes, and its utilization by microorganisms in agricultural soils.     

Geochemistry of high arsenic groundwater in Chia-Nan plain, Southwestern Taiwan: possible sources and reactive transport of arsenic

Major ion, trace element, and stable isotope analyses were performed on groundwater samples collected during November 2005 and 2006 in Chia-Nan plain of southwestern Taiwan to examine As mobilization in aquifers. The high concentrations of As, Fe and Mn in the groundwater is consistent with low Eh values (under moderately reduced state). Moreover, the observed Na/Cl and SO(4)/Cl molar ratios in groundwater demonstrate the influence of seawater intrusion. Seawater intrusion could provide required electron acceptors (i.e., SO(4)) for bacterial sulfate reduction and promote reducing conditions that are favorable for As mobilization. The concurrent increases in the concentrations of Fe and Mn from 2005 to 2006 may be caused by bacterial Fe(III) and Mn(IV) reduction. Geochemical modeling demonstrate that As(III) is the dominant As species and the presence of Fe-bearing carbonates, sulfides, and oxide phases may locally act as potential sinks for As. Mud volcano fluids were also collected and analyzed to assess the possible source of As in the Chia-Nan plain groundwater. The oxygen and hydrogen isotopic signatures indicate that the As-rich mud volcano fluids may have been modified by chemical exchange with (18)O-rich crustal rocks and possibly originated from mixing of deep brines with circulating meteoric water. Thus As in the Chia-Nan plain groundwater may have been evolved from deep crustal fluids or rock sources. The hydrogeochemistry and widespread As enrichment in groundwater of Chia-Nan plain result from multiple processes, e.g., de-watering of deep crustal fluids, seawater intrusion, and biogeochemical cycling of Fe, As, and S in alluvial sediments.     

Atmospheric Pb isotopic composition and trace metal concentration as revealed by epiphytic lichens:: an investigation related to two altitudinal sections in Eastern France

During Fall 1996, epiphytic lichens were collected along altitudinal sections in two areas of France (the Vosges mountains in the North-East, and the Alps, in Haute-Savoie) in order to verify any geographic distribution of atmospheric metals on a small scale. These lichens have various Pb isotopic compositions (²⁰⁶Pb/²⁰⁷Pb=1.126–1.147) which are correlated with the altitude of sampling. Lichens sampled near valleys display isotopic ratios significantly less radiogenic than those sampled at several hundred to thousand meters of altitude. In the Vosges sections, Pb concentrations and isotopic compositions of lichens may be used to define three zones: (1) valley: Pb-rich and non-radiogenic ratios, (2) transition: low-Pb and intermediate isotopic compositions, (3) mountain: heterogeneous Pb concentrations but more radiogenic and homogeneous Pb isotopic composition. Other metals (Zn, Cu, Cd, As), when normalised one to another, are not fractionated between these zones and display homogeneous relative abundance along the altitudinal sections of both sites. Variation of ²⁰⁶Pb/²⁰⁷Pb ratios with altitude is interpreted in terms of mixing of at least two pollution sources: one being the petrol (leaded and/or unleaded) combustion, and the other being of industrial origin. The latter is characterised by a more radiogenic isotopic composition. The Pb isotopic composition of flue gas residues from different municipal solid waste combustors in the Rhine valley and in other areas of France would suggest that these plants might be an important source of industrial Pb in the atmosphere. If the average industrial Pb in France has a ²⁰⁶Pb/²⁰⁷Pb close to 1.15, between 60 and 80% of the total Pb in lichens from the Rhine valley would come from gasoline combustion, whereas 85–90% of the Pb would have an industrial origin in lichens from higher altitude in the Vosges mountains. Although lichens from the Alps were collected at higher altitude, the percentage of industrial Pb for these lichens would be slightly lower (65%). Major winds and convection winds in the different valleys must then play an important role in term of distribution of atmospheric Pb in function of altitude.     

The Use of the Isotopic Composition of Individual Compounds for Correlating Spilled Oils and Refined Products in the Environment with Suspected Sources

Correlation of crude oils, or refined products, in the environment with suspected sources is typically undertaken through the use of GC and GCMS and in certain cases bulk carbon isotope compositions. However, with crude condensates, or refined products in particular, the absence, or low concentration, of biomarkers precludes their successful use for making unique correlations. An alternative and, sometimes, complimentary technique for correlation of such products is evolving through the use of combined gas chromatography-isotope ratio mass spectrometry (GCIRMS). This approach permits determination of the carbon and hydrogen isotopic composition of individual compounds in the crude oil or refined product to produce isotopic fingerprints for use in correlation studies. In this paper, it is proposed to review applications of GCIRMS to the correlation of various spilled products with their suspected sources in different environments. Whilst not proposing that this technique will replace GC or GCMS; it is proposed that GCIRMS is a very powerful tool to be used in conjunction with GC and GCMS to make such correlations. Although isotopic fractionation has been observed in some of the lighter components such as benzene and toluene, higher carbon numbered compounds, say above C 10 , do not appear to undergo any significant isotopic fractionation as a result of weathering. Furthermore with refined products, isotopic fractionation of the lighter components has the potential to demonstrate the onset of natural attenuation of refined products in the environment.     

The Use of the Isotopic Composition of Individual Compounds for Correlating Spilled Oils and Refined Products in the Environment with Suspected Sources

Correlation of crude oils, or refined products, in the environment with suspected sources is typically undertaken through the use of GC and GCMS and in certain cases bulk carbon isotope compositions. However, with crude condensates, or refined products in particular, the absence, or low concentration, of biomarkers precludes their successful use for making unique correlations. An alternative and, sometimes, complimentary technique for correlation of such products is evolving through the use of combined gas chromatography–isotope ratio mass spectrometry (GCIRMS). This approach permits determination of the carbon and hydrogen isotopic composition of individual compounds in the crude oil or refined product to produce isotopic fingerprints for use in correlation studies. In this paper, it is proposed to review applications of GCIRMS to the correlation of various spilled products with their suspected sources in different environments. Whilst not proposing that this technique will replace GC or GCMS; it is proposed that GCIRMS is a very powerful tool to be used in conjunction with GC and GCMS to make such correlations. Although isotopic fractionation has been observed in some of the lighter components such as benzene and toluene, higher carbon numbered compounds, say above C₁₀, do not appear to undergo any significant isotopic fractionation as a result of weathering. Furthermore with refined products, isotopic fractionation of the lighter components has the potential to demonstrate the onset of natural attenuation of refined products in the environment.     

Lichen response to changes in atmospheric sulphur: isotopic evidence.

In June of 1997, several thalli of the lichen species Alectoria sarmentosa were transplanted from a remote area (Bonavista) to an urban area (St John's) on the island of Newfoundland, Canada. The purpose was to assess the response of these epiphytic lichens to a change in the level of atmospheric sulphur pollution as measured by sulphur concentration and isotopic composition. The dominant source of atmospheric sulphur in the Bonavista area is sea spray, therefore, lichens growing there have relatively high sulphur isotopic compositions and low concentrations (approximately + 15 per/thousand, 250 ppm). Atmospheric sulphur in the St John's area is dominated by anthropogenic sources, primarily oil burning. Lichens in this area have lower isotopic compositions and higher concentrations (approximately + 6 per thousand, 500 ppm). The transplanted lichens were monitored monthly for a period of 1 year. In all experiments the sulphur isotopic composition decreased and the sulphur concentration increased linearly. It is estimated that, within 18 months, transplanted A. sarmentosa would be indistinguishable from the same species naturally growing in the transplant site, both in terms of sulphur concentration and isotopic composition.     

Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb–Zn refinery

The present paper examines the use of zinc isotopes as tracers of atmospheric sources and focuses on the potential fractionation of Zn isotopes through anthropogenic processes. In order to do so, Zn isotopic ratios are measured in enriched ores and airborne particles associated with pyrometallurgical activities of one of the major Pb–Zn refineries in France. Supporting the isotopic investigation, this paper also compares morphological and chemical characteristics of Zn particles collected on dry deposition plates (“environmental samples”) placed within a 5 km radius of the smelter, with those of Zn particles collected inside the plant (“process samples”), i.e. dust collected from the main exhaust system of the plant. To ensure a constant isotopic “supply”, the refinery processed a specific set of ores during the sampling campaigns, as agreed with the executive staff of the plant. Enriched ores and dust produced by the successive Zn extraction steps show strong isotope fractionation (from ?0.66 to +0.22‰) mainly related to evaporation processes within the blast furnaces. Dust from the main chimney displays a δ⁶⁶Zn value of ?0.67‰. Application of the Rayleigh equation to evaluate the fractionation factor associated with the Zn vapor produced after a free evaporation gives a range of α_ore/vapor from 1.0004 to 1.0008. The dry deposits, collected on plates downwind of the refinery, display δ⁶⁶Zn variations of up to +0.7‰. However, it is to be noted that between 190 and 1250 m from the main chimney of the refinery, the dry deposits show a high level of large (>10 μm) Zn, S, Fe and O bearing aggregates characterized by positive δ⁶⁶Zn values (+0.02 to +0.19‰). These airborne particles probably derive from the re-suspension of slag heaps and local emissions from the working-units. In contrast, from 1720 to 4560 m, the dry deposits are comprised of small (PM10) particles, including spherical Zn-bearing aggregates, showing negative δ⁶⁶Zn values (?0.52 to ?0.02‰). Our results suggest that the source of the distal dry fallouts is the main chimney plume, whose light Zn isotopic signature they preserve. Based on Zn isotopic analysis in combination with morphological and chemical characteristics of airborne particles, the present study suggests the traceability of smelter dusts by Zn isotopes.     

Understanding the source of water for selected springs within Mojave Trails National Monument,California

While water sources that sustain many of the springs in the Mojave Desert have been poorly understood, the desert ecosystem can be highly dependent on such resources. This evaluation updates the water resource forensics of Bonanza Spring, the largest spring in the southeastern Mojave Desert. The source of spring flow at Bonanza Spring was evaluated through an integration of published geologic maps, measured groundwater levels, water quality chemistry, and isotope data compiled from both published sources and new samples collected for water chemistry and isotopic composition. The results indicate that Bonanza Spring has a regional water source, in hydraulic communication with basin fill aquifer systems. Neighboring Lower Bonanza Spring appears to primarily be a downstream manifestation of surfacing water originally discharged from the Bonanza Spring source. Whereas other springs in the area, Hummingbird, Chuckwalla, and Teresa Springs, each appear to be locally sourced as “perched” springs. These conclusions have important implications for managing activities that have the potential to impact the desert ecosystem.