Grantee Research Project Results
1998 Progress Report: Environmental Applications of Novel Instrumentation for Measurement of Lead Isotope Ratios In Atmospheric Pollution Source Apportionment Studies
EPA Grant Number: R826177Title: Environmental Applications of Novel Instrumentation for Measurement of Lead Isotope Ratios In Atmospheric Pollution Source Apportionment Studies
Investigators: Keeler, Gerald J. , Graney, Joseph R.
Institution: University of Michigan , The State University of New York at Binghamton
EPA Project Officer: Hahn, Intaek
Project Period: December 1, 1997 through November 30, 1998
Project Period Covered by this Report: December 1, 1997 through November 30, 1998
Project Amount: $99,776
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Safer Chemicals
Objective:
The measurement of lead isotope ratios coupled with other trace element determinations on a spatial and temporal basis can potentially be used to differentiate between, and trace, the local and regional movement of aerosols from different sources of pollution. The low concentrations of lead in precipitation and ambient aerosols, the potential for contamination during sampling, and the time and expense involved in measuring isotope ratios to high precision are reasons why this tracer approach has not been used extensively to date. The goals of this exploratory research project are to demonstrate 1) how precise measurements of lead isotope ratios from samples with low concentrations can be made in a time and cost efficient manner using a hybrid instrument, the Plasma54 and 2) how lead isotope ratios can be directly coupled with those of Hg and other trace element determinations for a better understanding of source/receptor relationships.
Progress Summary:
In year one of the project, work was focussed in the following areas:
- To obtain and contrast the results of Pb isotope measurements obtained from the Plasma54 with those obtained using conventional ICP-MS on standards and "as is" samples of precipitation. "As is" refers to samples of precipitation from which Pb isotope ratios were obtained without separation and pre-concentration of the Pb from other elements prior to analysis.
- To assess the concept of using lead isotopes as a tracer on several scales. We began this assessment by analyzing precipitation samples from two areas, in the south Florida/Everglades region where several well defined emission sources of atmospheric pollutants are located, and over a larger geographic area with numerous emission sources, the Great Lakes region.
- To determine when pre-concentration of the Pb would be required prior to measurement of Pb isotope ratios (by assessing analysis precision on "as is" samples) and to then develop a cost efficient method for pre-concentration of the Pb in such samples.
All of the precipitation samples on which Pb isotope ratios were determined have previously been analyzed for other trace element concentrations, including mercury (from co-located samples). We measured the isotopic ratios of lead using a Perkin Elmer Elan 5000 ICP-MS (PE 5000) prior to analysis of the same samples with the Plasma54. This procedure allowed for direct comparison of the accuracy and precision between the two methods. Following are examples of our findings from year one of the project.
Comparisons Using NIST SRM-981:
Precision and accuracy using the PE5000 and Plasma54 were assessed through replicate analyses of a solution of NIST SRM-981. A thallium spike solution was added to each sample to correct for fractionation during ionization. The Plasma54 differs from conventional ICP-MS technology in that the Plasma54 incorporates ICP sample introduction with magnetic sector multiple collector technology to measure isotope ratios. Therefore the Plasma54 should be able to achieve high precision analyses and fast, cost efficient throughput, because by design it combines the speed of ICP-MS with the precision of TIMS. The increased precision and accuracy of Pb isotope ratios from the SRM-981 galena standard using the Plasma54 versus the PE 5000 is apparent from Table 1. The accuracy and precision of the Pb isotope ratios obtained from samples containing only 2 ppb lead concentrations (in 15 minutes with only 0.5 ml of sample consumption) demonstrates the remarkable analytical capabilities of the Plasma54.
Table 1. Examples of Precision and Accuracy Results using the PE5000 and Plasma 54
PE 5000 | Plasma 54 | |||
Measured | 207Pb/206Pb | 208Pb/206Pb | 207Pb/206Pb | 208Pb/206Pb |
80 ppb Pb | 0.9235 + 0.22% | 2.164 + 0.14% | 0.91447 + 0.0012% | 2.1656 + 0.0019% |
80 ppb Pb | 0.9259 + 0.31% | 2.163 + 0.13% | 0.91449 + 0.0008% | 2.1655 + 0.0010% |
2 ppb Pb | 0.9189 + 0.37% | 2.161 + 0.20% | 0.91418 + 0.0323% | 2.1646 + 0.0330% |
2 ppb Pb | 0.9177 + 0.30% | 2.168 + 0.56% | 0.91459 + 0.0257% | 2.1641 + 0.0301% |
Certified | 0.91464 | 2.1681 | 0.91464 | 2.1681 |
Ave. Analysis Time | 5 minutes | 15 minutes | ||
Sample Consumption | 5 ml | 0.5 ml |
The solutions contained the stated concentration of NIST SRM-981(a galena standard with a certified isotopic composition) spiked with thallium (at the same concentration) in 0.2% HNO3. The % precision listed is one sigma.
Precipitation Samples from South Florida:
We have analyzed 70 precipitation samples from south Florida for Pb isotope ratios using the PE 5000, and have initiated comparisons of results with the Plasma54. (Table 2).
Table 2. Examples of Results using the PE 5000 and Plasma 54 from Florida Samples
PE 5000 | Plasma 54 | ||||
Sample | Pb Conc. | 207Pb/206Pb | 208Pb/206Pb | 207Pb/206Pb | 208Pb/206Pb |
MNS-28 | 2.59 | 0.8284 + 0.47% | 2.029+ 0.40% | 0.8210 + 0.013% | 2.018 + 0.015% |
IND-22 | 1.61 | 0.8322 + 0.40% | 2.026+ 0.16% | 0.8265 + 0.023% | 2.028 + 0.020% |
MNS-1 | 1.42 | 0.8333 + 0.37% | 2.028 + 0.52% | 0.8328 + 0.062% | 2.039 + 0.044% |
SOT-3 | 1.26 | 0.8399 + 0.26% | 2.036 + 1.02% | 0.8361 + 0.038% | 2.048 + 0.039% |
The isotope ratios obtained from individual samples measured by the PE5000 and the Plasma54 are similar (within analytical error). Unfortunately, the precision of the measurements obtained using the PE5000 temper our ability to fingerprint Pb emission sources in south Florida because most of the Pb isotope ratios overlap when measurement uncertainty is accounted for. However, the increase in precision obtained using the Plasma54 indicates that differences in Pb isotope ratios are present. The next step will be to determine if the differences in isotope ratios are sufficient for emission source differentiation and apportionment.
Precipitation Samples from the Great Lakes Region:
We have analyzed 60 precipitation samples from the Great Lakes region for Pb isotope ratios using the PE 5000, and have initiated comparisons of results with the Plasma54 (see Table 3).
Table 3. Examples of Results using the PE 5000 and Plasma 54 from Great Lakes Samples
PE 5000 | Plasma 54 | ||||
Sample | Pb Conc. | 207Pb/206Pb | 208Pb/206Pb | 207Pb/206Pb | 208Pb/206Pb |
SHN-6 | 2.91 | 0.7857 + 0.45% | 1.939 + 0.31% | 0.7847 + 0.023% | 1.951 + 0.028% |
BON-7 | 1.19 | 0.8349 + 0.24% | 2.040 + 0.38% | 0.8321 + 0.029% | 2.044 + 0.021% |
BON-12 | 0.91 | 0.7963 + 0.26% | 1.964 + 0.37% | 0.7989 + 0.030% | 1.981+ 0.027% |
CWP-5 | 0.51 | 0.8672 + 0.21% | 2.083 + 0.34% | 0.8675 + 0.078% | 2.094 + 0.050% |
SBD-12 | 0.24 | 0.8280 + 0.76% | 2.032 + 1.02% | 0.8291 + 0.278% | 2.060 + 0.465% |
Pb isotope ratios were measured on "as is" samples. Pb concentrations expressed in ug/L (ppb). The % precision listed is one sigma.
The isotope ratios from individual samples measured by the PE5000 and the Plasma54 are similar (within analytical error). Note the wide range in the isotope ratios among samples collected from different locations as well as different rain events at the same location. Therefore, in this sample set, results using the PE5000 to measure differences in isotope ratios might be adequate to suggest differences in lead sources. Note the increase in precision of the ratios obtained using the Plasma54, especially when Pb concentrations are greater than 0.50 ppb. Unfortunately, the precision of the Pb isotope ratios obtained using the Plasma54 from precipitation samples with Pb concentrations below 0.50 ppb is probably inadequate for purposes of source apportionment. Pre-concentration of the Pb will be needed from such samples in order to increase the precision of the isotope ratio measurements. Nonetheless, the precision of Pb isotope ratios obtained from precipitation samples containing ppb levels of Pb with the Plasma54 (without pre-concentration) is remarkable.
Pb Pre-concentration Method Development:
A technique for efficient extraction and pre-concentration of lead from precipitation has been tested. In most Pb isotope studies, the Pb is separated from other elements and concentrated using sequential HCl-HBr column chromatography with AG 1X8 anion exchange resin. However, this procedure involves numerous time and reagent consuming steps. Because one of the goals of this study was to develop a time and cost efficient method for measuring Pb isotope ratios, a different pre-concentration approach was used. Specifically a new Pb selective resin called PbSpecTM was used (available from Eichrom Industries). Briefly the method entails passing a 50 ml aliquot of a precipitation sample over 0.1-0.3 grams of the pre-cleaned resin, and then eluting the Pb from the resin using dilute sulfuric acid. Pb recoveries are greater than 90% of the expected value, Pb concentration in the collected eluant are 10-20x that present in the original sample, and Pb contribution from the process blanks average less than 0.25% of the total Pb measured, provided the resin is pre-cleaned prior to use.
Future Activities:
In year two we will continue to analyze precipitation samples with the Plasma 54 using both the "as is" as well as pre-concentrated modes. In year two we also plan to analyze Pb isotopic compositions from several sets of ambient aerosol samples that were collected during the same time frame as the precipitation samples. Initially, we will prepare several papers concerning analytical method development and results. Our long term goal is to couple the results from measurement of Pb isotope ratios with those of Hg and other trace element concentrations and fluxes for a better understanding of source/receptor relations. This will be accomplished by combining lead isotope ratios and other trace elements measurements with meteorological data and 3-D trajectory calculations using Regional Atmospheric Modeling (RAMS) and lagrangian particle diffusion (LPDM) and HY-SPLIT transport models (NOAA-ARL).Journal Articles:
No journal articles submitted with this report: View all 4 publications for this projectSupplemental Keywords:
geochemistry, heavy metals, industry, particulate material, transportation, RFA, Scientific Discipline, Air, Geographic Area, Ecology, particulate matter, Environmental Chemistry, Chemistry, State, mobile sources, Engineering, Chemistry, & Physics, Great Lakes, ambient aerosol, precipitation, particulates, aerosol particles, atmospheric particles, air quality models, tracer isotopes, air sampling, municipal incineration, lead isotope ratios, combustion, Florida, acid rain, atmospheric deposition, FLA, source apportionment studiesProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.