Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Prepare the water sample solution
   1. Dilute 30 mL of the 0.05 M lead nitrate solution up to 300 mL with DI water. This is a 0.005 M lead nitrate solution. Mix well. Label the solution Water Sample.
2. Prepare the 0.02% sodium rhodizonate solution just prior to the laboratory.
   1. Weigh out 0.1 g of sodium rhodizonate and place into a 500-mL Erlenmeyer flask.
   2. Dilute up to 500 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 individually. This laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab, and the data compilation and questions may be completed the day after the lab.
• In laboratory testing, 0.02% sodium rhodizonate solution was able to 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 water sampling the yellow-orange color of a 0.2% solution overwhelms the pink-mauve color of a positive test.
• For best results use the 0.02% sodium rhodizonate solution the day that it is prepared.

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 a 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).

Further Extensions

• Extend the activity by having students research the health problems associated with lead, lead testing procedures, lead abatement procedures or historical uses of lead.

Answers to Prelab Questions

1. Periodically, the Food and Drug Administration (FDA) will make a recommendation that pregnant women and small children refrain from eating certain species of fish due to heavy metal contamination. Explain why the FDA would be especially concerned for these two groups of people.

   Small children and pregnant women are of particular concern due to the possible concentration of lead entering their bodies. Lead damage to the brain or other systems of small or unborn children will affect them for the rest of their lives. Also, due to their smaller size, the same amount of lead is a higher dose in their bodies.

2. The level of lead is often higher in bottom feeding or bottom dwelling animals than in other species. Explain how the density of lead may factor into this phenomenon.

   Lead is a very dense element. Particles of lead will sink to the bottom of streams, ponds, and lakes where it becomes part of the sediment. Animals that live in or feed on this sediment will have more opportunities to ingest the lead into their systems.

Sample Data

Answers to Questions

1. Based on the test results, should additional analysis be conducted on the water sample? Explain.

   Yes, the water sample tested positive using the rhodizonate testing procedure. Additional samples should be collected and sent to a laboratory to determine which metal it contains and how much metal it contains.

2. A stream runs through an abandoned surface mine. Draw a diagram to indicate the best locations for collecting water samples to test for lead contamination of the stream by the mine tailings. Justify your choices.

   Samples should be collected both upstream and downstream of the mine. If the samples collected upstream test positive for lead then another site is responsible for at least some of the lead contamination.

3. In the Background section, the remediation of lead using plants was described. Some remediation plans call for the removal of all plants that currently grow on the site. What is the reason behind this recommendation?

   Plants currently growing on the site are usually lead tolerant species that likely contain a high level of lead in their tissues. Removing these plants as hazardous waste will remediate the lead that they contain. This way subsequent plantings will remove additional lead from the area.

4. Some states have considered banning lead fishing sinkers and skeet shooting in nature preserves. Discuss why these sources of lead are a concern for state wildlife officials.

   Lead fishing sinkers can be lost into the water if the line becomes snagged or cut. The ammunition used in skeet shooting contains lead. The lead shot lands in the water or on the ground. In both cases, the lead leaches from the sinker or pellets and enters the ecosystem.

References

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

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

North Carolina Cooperative Extension Service website, http://www.bae.ncsu.edu/programs/extension/publicat/wqwm/he395.html (accessed April 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 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
• Pathology of lead
• Water pollution

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 blood stream and then into the bones where it can slowly leach out for an entire lifetime. The process of storing minerals is an example of bioaccumulation. Since calcium is also an important part of nerve, muscle and kidney functions, 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 increase blood pressure and even cause fertility problems. Lead can enter the body by inhalation of dust containing lead, 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 found 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 acid solutions than in basic solutions. The lead-containing water flows into streams, ponds and lakes where the acidic solution is diluted causing the lead to precipitate. The amount of lead found in the water, soil and sediment depends upon how close it is to the lead-containing minerals. In general, the further the water, soil, or sediment is from the lead-containing mineral, the lower the amount of lead it contains. Vegetation and small organisms incorporate lead into their systems through absorption of lead found in the 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.

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. In order to remediate the lead, seeds are planted in the desired remediation site. After several weeks 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.

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. Rhodizonate is an inexpensive and quick testing technique. 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. 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. In spite of these drawbacks, sodium rhodizonate is a good field screening tool for surface water samples around contaminated sites.

Experiment Overview

The purpose of this experiment is to determine the presence or absence of lead in a sample of water using the sodium rhodizonate screening procedure.

Materials

Prelab Questions

1. Periodically, the Food and Drug Administration (FDA) will make a recommendation that pregnant women and small children refrain from eating certain species of fish due to heavy metal contamination. Explain why the FDA would be especially concerned for these two groups of people.
2. The level of lead is often higher in bottom feeding or bottom dwelling aquatic animals than in other aquatic or terrestrial species. Explain how the density of lead may factor into this phenomenon.

Safety Precautions

The water sample contain lead nitrate which 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. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Using the marker or wax pencil, label one water sampling tube “water sample” and the other “control.”
2. Using a clean large-bulb pipet, transfer 10 mL of distilled water into the water sampling tube labeled control.
3. Using the graduated pipet, add 1 mL of 0.02% sodium rhodizonate solution to the control sample.
4. Screw on the cap of the water sampling tube and invert it several times to mix the sample.
5. Record the color of the sample on the Lead in Water Worksheet.
6. Repeat steps 2–4 for the water sample.
7. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10926_Student1.pdf