The research began in the fall semester 2005. Research accomplished since that time includes the topics listed below which are not intended to be taken as chronological or sequential.
- Samples were analyzed for total lead, lead isotope ratios and elements that may correlate to the lead source.
- Samples were analyzed for total lead, lead isotope ratios and elements that may correlate to the lead source.
Reproducibility experiments have been carried out to asses sample homogeneity and soil sampling methods.
Lead standards have been analyzed to assess method limits in both total lead and lead isotope ratio measurements.
I. Experimental Section as of Spring 2006
In this project, Chem 1184 students work with geology/geography students to test the hypothesis that that variability in lead isotop ratio is sufficient to distinguish between multiple sources of lead contamination in the soil in Omaha: the Asarco lead smelter, emissions/residues from leaded gasoline and lead from lead paint. To test the hypothesis, multiple experiments need to be carried out which collecting soil samples from a variety of locations all around Omaha.
While individual experiments will be completed each semester, the total quantity of samples is expected to be sufficient to require several semesters’ worth of analysis, and probably lead to additional experiments to be conducted in later semesters. Local experiments are needed to discriminate the effect of any contribution from lead in paint. Statistical tests will be applied to demonstrate that a relationship does or does not exist. Elements commonly found in the same lead ores such as arsenic, antimony, zinc and bismuth, will be used as additional evidence of the lead source(s).
This research could encompass 100 square miles and easily generate 1000’s of soil samples, requiring computer based manipulation and graphical display. Geology students will also be responsible for this effort, also contributing to the extended duration of this project.
A. Geology Sampling Protocol
Geology students collected the soil samples. The samples were labeled with unique sample numbers that will be used throughout the data analysis procedures. The location of each sample was recorded using address and/or GPS location.
B. Chemical Analysis Procedure
Soil samples were provided by geology students via the lab instructor. There were 12 total field samples, 8 small and 4 large. The eight small samples were used as is and the four large samples were each split into quarters resulting in a total of 24 instrument samples.
1. Soil Sample Preparation
Soil samples were ground to a fine powder in a mortar and pestle. Small samples were then digested (Step 2). Large samples were then transferred to butcher paper in one neat, symmetrical pile. The pile was then quartered. These quarters were then separated and identified by appending a, b, c, and d to the name of the original sample.
2. Soil Digestion
An aliquot of each soil sample weighing between 0.990 and 1.010 g was transferred quantitatively to a clean labeled Erlenmeyer flask. Next 10 mL of distilled water and 10 mL of concentrated nitric acid were added to the flask. The flask was covered with a Tuttle cap, placed on a hotplate in the fume hood and heated to just under boiling for 1 hour, with occasional swirling.
After 1 hour, the Tuttle cap was removed momentarily to allow any remaining nitrogen dioxide to escape from the flask before removing it from the fume hood. The flask was allowed cool and then 25 mL of distilled water was added.
3. Filtration and Dilution of Sample
The sample was filtered a long stemmed funnel fitted with Whatman #1 filter paper into a clean 100 mL volumetric flask. The residual soil and the filter paper were washed several times with small portions of distilled water. Distilled water was then added to the flask to bring the volume up to the mark on the neck. The tightly capped volumetric flask was then inverted 10 times to ensure complete mixing.
One mL of this solution was then transferred by pipet to a clean 25 mL volumetric flask. Water was added to bring the volume up to the mark. The flask was then inverted ten times to ensure complete mixing. A labeled ICP-MS sample tube was filled ¾ full with this solution and submitted for analysis.
II. Results and Discussion
Your part in the project will begin with an examination of the raw data. Previous classes have discussed their results and drawn conclusions from them. You should begin your work with an independent look at the data, make your own observations, have an unbiased discussion, and draw your own conclusions.
Next, examine the map of total lead generated by geology/geography from last semester.
Chemistry 1184 students will answer a set of questions from this reading that must be completed before the Lead Project Lab. Write out the answers to these questions in your lab notebook.
The duplicate copies of this pre-lab assignment will be collected by your lab instructors at the beginning of the Lead Project lab.