Get the Lead Out! An Interdisciplinary Case Study for Science Students
Part I- Lake County Emergency
At Lake County Community Hospital, Dr. Barbara Elliot raced to the emergency room. T ere, she found 6-year-old Suzy Smith, whom she had seen just yesterday with what the doctor had thought was a case of flu. Suzy's mother, Jane Smith, sighed with relief when Dr. Elliot stepped into the room.
"Thank goodness you're here! Suzy can't seem to keep any food down. She's so pale and weak ... I'm worried about her."
"Let's have her spend the night, Jane, so I can keep an eye on her. I suspect there is something going on here besides the flu. I'd like to run a series of tests on her."
After checking Suzy's vital signs, the doctor got the little girl settled into a hospital room.
Dr. Barbara Elliot was new to Lake County, Colorado. During the year she had been practicing there, she had observed that a large number of her pediatric patients had similar symptoms: sleeplessness, stomach ache, vomiting, diarrhea, and anemia. The doctor was becoming convinced that there was an underlying problem-some common cause.
When Dr. Elliot got back Suzy's blood test results, she was alarmed to see that the blood contained elevated lead levels. Her thoughts immediately shifted to the abandoned mining district only a few miles away. Was it possible that this was the source of lead in Suzy's blood? Could contamination from the old mines be responsible for the large number of sick children she had seen over the past year?
Background
The mining district of Lake County, Colorado, is about 120 miles west of Denver and was the site of gold mining as early as 1859. In the 1870s, silver and lead were also mined. During World War II, large amounts of zinc, lead, and copper were extracted at the site.
Mining at the location has since ceased, but there remains a large quantity of resultant waste at what is known as the "California Gulch Site," a 15-square-mile area that serves as a watershed. Among the waste products from mining operations are mine tailings, slag piles, waste rock piles, and abandoned mine shafts.
Questions for Part 1
1. (a) Describe a general process of mining lead from ore, including the name and formula for the primary ore that contains lead.
(b) Define terms used in the process such as ore, smelt, gangue, refine, slag, and mine tailings.
2. During the smelting process, sulfur dioxide gas is produced. When dissolved into water, what compound is produced? Write the chemical equation(s) for this process.
3. What is a watershed? What might be some possible environmental effects of an area like this being mined for lead based on your answers to questions 1 and 2? (Hint: What is the effect of an acid on an insoluble compound such as lead(II) sulfide?)
4. What are considered safe levels of lead in human blood in parts per million (ppm)?
5. What are some of the effects of overexposure to lead for adults? For children?
6. How are patients with high levels of lead in their blood treated?
Part II-Water Testing in Lake County
Based on the elevated lead levels in children that she and her colleagues had seen, Dr. Eliot believed that lead ores from the nearby mining district may have contaminated both the soil and water in the area. Contained within this 15-square-mile area is the California Gulch watershed. It empties into the nearby Arkansas River and provides the community with agricultural irrigation, recreation, and municipal drinking water.
Dr. Elliot and several other prominent citizens have been able to successfully persuade local officials to contract an environmental study of the area's soil and water. You are a chemist who works with the contracted environmental lab. Your primary area of concern is water testing for the presence of lead in groundwater samples using atomic absorption spectrophotometry (AA). Colleagues will be testing for other metals in the water. Residential soil samples from Lake County will also be tested.
Questions
1. Outline how flame spectrophotometry works by explaining the following:
• The absorption of light energy at characteristic wavelengths.
• The proportionality of light absorbed to sample concentration using Beer's Law.
2. Define and diagram the basic parts of an atomic absorption spectrophotometer including the nebulizing chamber (or aspirator), the flame, light source, monochromator, and detector.
3. Why must all equipment in this analysis be acid washed?
4. What concentration (ppm) of lead in drinking water is considered dangerous ("action level") by the U.S. Environmental Protection Agency (EPA)
Part III-Lead Remediation in Lake County
Samples of groundwater in and around Lake County have been shown to have lead levels as high as 8 ppm as a result of your water analysis. These concentrations are well above the EPA action level of 0.015 ppm. Analysis of residential soils has found levels there to be as high as 1000 ppm; therefore, the EPA has begun evaluating the site for remediation.
There are two major categories of remediation for "heavy" metals such as lead. One method requires the physical movement of contaminated soil to a treatment facility and subsequent transfer of "clean" soil to the affected area. The second method involves phytoremediation, the removal of toxic substances by living plants. Because funding is limited, this second method has been chosen.
The following are four types of phytoremediation: phytoaccumulation, phytodegradation, rhizodegradation, and phytovolatization. Research indicates that phytoaccumulation is ideally suited for the Lake County site.
You are a member of the EPA's Superfund Response Team. You and your team must now decide on the most effective way to implement phytoaccumulation in the Lake County area. As part of your research, you should access the following websites in order to answer the questions below:
• A Resource Guide: The Phytoremediation of Lead in Urban, Residential Soils, Joseph L. Fiegl, et al., Northwestern University.
https://www.civil.northwestern.edu/ehe/html_kag/kimweb/MEOP/Index.htm
• Phytoremediation, by Kelly E. Belz, 1997, in Groundwater Pollution Primer, Virginia Polytechnic Institute and State University.
https://www.cee.vt.edu/ewr/environmental/teach/gwprimer/phyto/phyto.html
Questions for Part 3
1. Give comparative costs for the two major types of remediation discussed in paragraph two above-i.e., (a) removal and replacement of contaminated soils or (b) phytoremediation.
2. Why are heavy metals, such as lead, difficult to remove using phytoremediation?
3. Explain the process of each of the four types of phytoremediation: phytoaccumulation, phytodegradation, rhizodegradation, and phytovolatization.
4. Which of the four processes described in question 3 is the best choice for the clean-up of lead at the Lake County site (i.e., why might the other three techniques not be as effective)?
5. What is a hyperaccumulator?
6. Give at least two ways in which the uptake of lead though phytoaccumulation can be enhanced.
7. What plant(s) might be the best choice for phytoremediation at the Lake County site?