Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Prepare the 0.01 M lead nitrate solution. Dilute 10 mL of the 1 M lead nitrate solution up to 1000 mL with DI water. This is a 0.01 M lead nitrate solution. Mix well.
2. Prepare the 0.02% sodium rhodizonate solution just prior to the laboratory. Only prepare if a student group will need it that day.
3. Weigh 0.01 g of sodium rhodizonate and place into a 50-mL Erlenmeyer flask. Dilute up to 50 mL with DI water and mix well. Label the solution 0.02% sodium rhodizonate.

Safety Precautions

Lead nitrate is moderately toxic by ingestion, a body tissue irritant and a possible carcinogen. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The waste lead nitrate may be disposed of by a licensed hazardous waste disposal company according to Flinn Suggested Disposal Method #27f. Excess sodium rhodizonate solution may be disposed of down the drain with an excess of water according to Flinn Suggested Disposal Method #26b.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of three or for 10 groups of students. The laboratory work for this experiment will vary from one day to several days depending upon the remediation strategy. The most important element for success in an inquiry-based activity is student preparation. Sufficient class time should be allotted before lab to think through the investigational design of the experiment. The Prelab Questions section contains leading questions to stimulate class discussion.
• Guide students to begin testing a small amount of remediation compound by discussing the need to determine the most cost effective strategy possible.
• For best results use the 0.02% sodium rhodizonate solution within a couple of hours of when it is prepared.
• In laboratory testing, 0.02% sodium rhodizonate solution was able do detect lead nitrate down to 0.01656 g/L. This is 1100 times the EPA action level for lead.
• The standard concentration for sodium rhodizonate testing is a 0.2% solution. For dilute lead nitrate solutions, such as a 0.01 M solution, the yellow-orange color of a 0.2% solution overwhelms the pink-mauve color of a positive test.
• After students have tested a single remediation factor, allow students to retest the remediation process with a two factor strategy such as EDTA amended soil with sunflowers.
• Projects using duckweed, sunflower, and corn will all remediate lead nitrate over the course of several weeks. For sunflowers and corn, remove the plants from the soil and saturate the soil with deionized water. Allow the soil and water mixture to rest overnight then filter out the soil. Since lead nitrate is soluble, any lead nitrate available in the soil should be detected in the solution provided the lower detectable limit has not been exceeded.
• Apatite, Flinn Catalog No. AP4896, did not remediate the 0.01 M lead nitrate solution as single solid rocks. The rocks must be crushed to provide more surface area for remediation.

Teacher Tips

• Excess 0.02% sodium rhodizonate solution can be used to test for lead on other substances. The solution must come in contact with the source of lead. For example, a wall with one or more layers of lead-free paint will show a negative result even though lead paint exists under the top layers. Sinkers, metal strips or minerals, such as galena, are just of few possible samples.
• Extend the activity by having students research the health problems associated with lead, lead testing procedures, lead abatement procedures, or historical uses of lead.
• For more information about lead in the home, the EPA published a 67-page pamphlet in 1998 titled Lead in Your Home: A Parent’s Reference Guide. EPA publication number 747-B-98-002. The publication can be found online at http://www. epa.gov/lead/pubs/leadrev.pdf (Accessed April 2008).

Answers to Prelab Questions

1. Review the health concerns for lead and outline the safety precautions that are necessary when handling lead-containing compounds. Lead nitrate is moderately toxic by ingestion, a body tissue irritant and a possible carcinogen. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.
2. Conduct preliminary research using textbook and online resources regarding the remediation techniques discussed in the Background section. Summarize the findings in a table listing the advantages and disadvantages of each method.
   {10928_PreLabAnswers_Table_2}

Sample Data

50 mL of 0.04 M EDTA added to 50 mL 0.01 M lead nitrate produced a negative sodium rhodizonate test immediately.

15 g of plant fertilizer added to 50 mL 0.01 M lead nitrate produced a negative sodium rhodizonate test after 45 minutes.

15 g of zeolite added to 50 mL 0.01 M lead nitrate produced a negative sodium rhodizonate test after 45 minutes.

Answers to Questions

1. Write a paragraph discussing the observations and the outcome of the experiment as tested.

   Student answers will vary.

2. Write a paragraph discussing any modifications, if any, if the experiment were to be retested.

   Student answers will vary.

References

Environmental Protection Agency website http://www.epa.gov/lead/ (accessed May 2008).

Environmental Protection Agency website for drinking water http://www.epa.gov/safewater/contaminants/index.html#1 (accessed April 2008).

National Library of Medicine Tox Town website http://toxtown.nlm.nih.gov/text_version/chemicals.php?id=16 (accessed May 2008).

National Safety Council website http://www.nsc.org/issues/index.htm (accessed May 2008).

North Carolina Cooperative Extension Service website http://www.bae.ncsu.edu/programs/extension/publicat/wqwm/he395.html (accessed April 2008).

Northwestern University Phytoremediation of lead decision tree. http://www.civil.northwestern.edu/EHE/HTML_KAG/Kimweb/MEOP/INDEX.HTM (accessed May 2008).

Apatite remediation of lead. http://www.soilremedy.com/HowApatiteIIworksPaper30.pdf (accessed May 2008).

Phosphorus remediation of lead using fertilizer. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1361759 (accessed May 2008).

http://lqma.ifas.ufl.edu/PUBLICATION/ma-99.pdf (accessed May 2008).

Introduction

The processes of life are a series of chemical reactions that occur in the body of a living organism. Living things obtain elements by eating and absorbing compounds from their environment. Many elements are beneficial for life while other elements can be harmful to an organism. Lead is an example of an element that is harmful to human beings.

Concepts

• Bioaccumulation
• Remediation
• Pathology of lead
• Phytoremediation

Background

Children are especially vulnerable to lead poisoning. Children need a lot of calcium for both bone and brain growth. The body treats lead like calcium; in fact the body will absorb lead instead of calcium if there is a shortage of calcium in the diet. Lead is absorbed into the bloodstream and then into the bones where it can slowly leach out into the bloodstream for an entire lifetime. The process of storing minerals is an example of bioaccumulation. Calcium is also an important part of nerve, muscle and kidney functions, so lead will interfere in these processes as well. Lead, like calcium, is able to cross the blood–brain barrier where it causes damage to all areas of the brain. Lead exposure can lead to learning disabilities, behavioral problems, decreased intelligence as well as speech, language, hearing and muscle coordination issues. Very high doses of lead can cause mental retardation, coma and even death. In adults, lead exposure can cause nerve, muscle, and memory problems as well as increased blood pressure and even cause fertility problems. Lead can enter the body by inhalation, ingestion of lead in water, food, soil, lead-paint dust or from lead in or on toys.

Lead occurs in food sources from the bioaccumulation of lead in streams, ponds, lakes and oceans. Ecosystem water can become contaminated with lead from manufacturing processes or from lead-containing minerals and mine tailings from the mining of those minerals. Acid rain or precipitation that becomes acidic due to the composition of the native rock leaches lead from the minerals (see Figure 1). Like most metals, lead is more soluble in acidic solutions than in basic solutions. Acidic lead–contaminated water flows into streams, ponds and lakes where it precipitates out of solution and deposits into the stream or lake bed. Vegetation and small organisms incorporate lead into their systems through absorption of lead found in the water and sediment. Lead accumulates in predator species as they consume the vegetation and small organisms. Lead has toxicological effects on many species, causing fertility and neurological problems and even death for the plants and animals.

There are many ways to remediate lead. Remediation is any process that reduces the amount of lead available for absorption into a body. The easiest method to remove lead from a site is to physically remove the lead from the area. For example, contaminated soil can be removed and hauled away to a hazardous waste landfill. Another common method of controlling exposure to lead is to seal the contaminated area under a layer of concrete or sod. This method is not remediation; it is actually an encapsulation technique since the lead is still present. The lead stays but the surrounding environment and people are sealed off from the lead. Other remediation methods use the chemistry of lead to trap lead molecules into an insoluble solid that cannot migrate through soil or water. Examples of lead-trapping chemicals are zeolite minerals, clay minerals, phosphorus, and chelating agents.

A zeolite is a type of man-made or natural mineral that has a micro-porous structure. The composition of the zeolite “traps” the lead in the micro-pores, removing the lead from the system. Clay minerals, like kaolin, also “trap” the lead by bonding with the lead. Phosphorus, in the form of phosphorus-rich minerals like apatite or as fertilizer, binds with the lead to form insoluble metal-phosphate complexes. Chelating agents, like EDTA, are complex chemical compounds that bind with metals, removing the metal from the surrounding system. EDTA is not only used to remove lead from the environment, it is also used intravenously to remove lead from the blood of people with lead poisoning.

The newest type of remediation is called phytoremediation. Some species of plants are able to accumulate significant amounts of lead in their tissues before the lead becomes toxic to the plant. Many of these plants are now used as part of the remediation plan to “clean-up” the lead contamination surrounding old mines or other heavily polluted sites. In order to remediate the lead, seeds of specific species are planted at the desired remediation site. After several weeks or years the plants are harvested and removed from the site as hazardous waste. Allowing the plants to decompose on site would recycle the lead back into the soil. Different species of plants may be used over the course of several years, with short rooting plants used first, followed by long rooting plants in subsequent years. For example, several crops of corn, followed by sunflowers, with poplar or aspen trees planted for long term control.

Remediation is also used to treat lead-contaminated storm water. In urban areas, the first few minutes of a rainstorm washes surface contaminants, including lead, down storm water drains. Many urban areas collect storm water for processing before discharging it back into the environment. Storm water processing includes filtration and remediation. The filter system typically begins with a coarse membrane filter, a thick layer of glass fibers or a layer of sand to remove large particles of debris from the storm water. The second filtration layer is usually fine membrane filter which removes smaller particles and protozoa from the water. Metals and organic compounds are removed by a thick layer of activated carbon followed by a layer of zeolite, a clay mineral or apatite. Finally another coarse filter ensures the carbon and other filtering particles are not discharged into the environment. The storm water can then be discharged back into the environment without polluting the local rivers and streams.

There are many methods that can be used to test for lead. One of the simplest methods is the sodium rhodizonate test. Sodium rhodizonate is a chemical that changes color when exposed to lead. The yellow-orange colored sodium rhodizonate reacts with lead to form a purple or pink complex. Only a few drops of a sodium rhodizonate solution are enough to indicate the presence of lead. Although differences in color can be seen, rhodizonate tests are not considered conclusive. One of the reasons for this is because other metals such as cadmium, silver, tin and barium react with sodium rhodizonate to form a purple or pink complex. A positive rhodizonate test indicates the need for further testing. Another limitation of rhodizonate testing is its lower detection limit or LDL. Below a certain level of lead concentration the pink color is no longer visible. Unfortunately the LDL is above the EPA action level for lead in water. In a lab, water samples can be concentrated by slowly evaporating the water from the sample, leaving the lead behind to react with the rhodizonate. This concentrating is best completed in the laboratory where other quantitative tests can be used instead of the rhodizonate test. The final limitation with the rhodizonate test involves the shelf-life of the sodium rhodizonate solution. Once prepared, the solution must be used within a couple of hours. In spite of these drawbacks, sodium rhodizonate is a good field screening tool for samples collected around contaminated sites.

Experiment Overview

The purpose of this inquiry-based experiment is to design and carry out a procedure to determine a method to remediate lead from a lead nitrate solution.

Materials

Prelab Questions

1. Review the health concerns for lead and outline the safety precautions that are necessary when handling lead-containing compounds.
2. Conduct preliminary research using textbook and online resources regarding the remediation techniques listed. Summarize the findings in the table listing the advantages, disadvantages, and limitations of each method.
   {10928_PreLab_Table_1}
3. From the list of materials, determine which remediation strategy you wish to test. You will be given 50 mL of a 0.01 M lead nitrate solution as the contaminant. A 0.02% sodium rhodizonate solution will be used to test the effectiveness of the remediation strategy. Consider the following questions while planning your experiment:
   1. The independent variable in an experiment is the variable that is changed by the experimenter, while the dependent variable responds to (depends on) changes in the independent variable. Choose the dependent and independent variables for your proposed experiment.
   2. What other variables will affect the results in this experiment? How can these variables be controlled?
   3. Estimate the lowest amount of remediation compound that is necessary to remediate 50 mL of a 0.01 M lead nitrate solution.
   4. Estimate the amount of time necessary to complete the remediation strategy.
   5. Write a step-by-step procedure for the experiment. Include the specific safety precautions that must be followed.

Safety Precautions

Lead nitrate is moderately toxic by inhalation and ingestion, a body tissue irritant and a possible carcinogen. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Verify the procedure (see the Prelab Questions) with your instructor and review all safety precautions.
2. Carry out the procedure and record all data and observations in a suitable data table.
3. Answer the Post-Lab Questions.
4. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10928_Student1.pdf