In the Classroom
The Lead Project An Environmental Instrumental Analysis Case Study Vincent T. Breslin* Department of Science Education and Environmental Studies, Southern Connecticut State University, New Haven, CT 06515;
[email protected] Sergio A. Sañudo-Wilhelmy Marine Sciences Research Center, Waste Reduction and Management Institute, SUNY at Stony Brook, Stony Brook, NY 11794
We describe an environmental instrumental analysis course that examines the problem of lead contamination in paint, soil, and drinking water of suburban residential houses. This course combines classroom lectures illustrating instrumental techniques and analytical principles with mandatory laboratory exercises. In addition, students are required to perform analysis of field-collected samples, in collaboration with the local community. While instrumental analysis courses are turning toward project-based approaches (1–3), our approach is unique because students learn that instrumental analysis (or chemical analysis) is only a part of a series of tasks directed to address a question or hypothesis. This type of training and education of analytical chemists develops an ability to solve problems, to work as team members, and to present oral and written reports effectively. Why Lead? Despite the ban on lead-based paints and leaded gasoline in the United States in the 1970s and 1980s, 4.4% of American children aged 1–5 still have blood Pb levels high enough to cause irreversible damage (4 ). In addition, almost 12% of children living in older housing in large urban areas have elevated blood Pb levels and African-American children living in the major U.S. inner cities are affected disproportionately (about 22%) (4, 5). Pb exposure in young children results primarily from ingestion or inhalation of soil particles, drinking water, paint, and dust particles in and around the home and play areas (6, 7 ). Lead was used extensively as a corrosion inhibitor and pigment in both interior and exterior oil-based paints prior to 1978 and some paints were manufactured with Pb concentrations of 50% by weight (8). Therefore, weathering of leadbased exterior paint and deposition of paint chips and dust on soils remains a significant source of Pb to soils surrounding homes. Soil Pb concentrations at or above 500 µg g᎑1 will result in a 1–5% probability that a child will have a blood Pb concentration that equals or exceeds 10 µg dL᎑1 (9). Drinking water is another source of ingested Pb. Household plumbing fixtures, including metal pipes, faucets, and soldered joints, are possible sources of Pb in drinking water (10, 11). The lower the pH of the water and the lower the concentration of dissolved salts in the water, the greater is the solubility of Pb in the water (12). Leaching of Pb from plastic pipes has also been documented and was attributed to the use of Pb stearate, which was used as a stabilizer in the manufacture of polyvinyl plastics (13).
Course Requirements The instrumental analysis course gives students an opportunity to become competent in the laboratory with the techniques and instrumentation used in environmental analytical chemistry. The course was designed for junior- and senior-level science majors and first-year graduate students. Course enrollment has been restricted to 12 students (6–8 undergraduate, 4–6 graduate) owing to the need for close student supervision in the laboratory and to maximize student use of instrumentation. Students work in the laboratory as members of a team, usually 2 or 3 students per group. However, each student is responsible for maintaining a laboratory notebook, conducting instrumental analyses, and submitting written laboratory reports. In addition, each student is required to prepare and deliver an oral presentation describing the objectives, results, and implications of the laboratory analyses. Students are evaluated on the basis of classroom and laboratory participation, homework, and the quality of their written laboratory reports and oral presentations. Course Design The curriculum is divided into a series of modules including lectures, discussions, laboratory exercises, field collections, sample analysis, report writing, and presentations (Fig. 1). Course content and a description of the laboratory
Problem Definition
Sampling Design and Statistics
Analytical and Instrumental Principles
Sampling Protocols and Field Sampling
Sample Preparation and Analysis
Data Analysis and Interpretation
Final Report and Presentation
Figure 1. Environmental instrumental analysis course module sequence.
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and field activities for each of the modules are described in the following sections.
Problem Definition The class starts with the definition of the questions or hypotheses to be tested. The students receive in advance a series of articles on Pb in the environment. Although they are told that the objective of the class is to determine Pb levels at houses along the north shore of Suffolk County, Long Island, New York, they need to formulate several working hypotheses. The typical hypotheses to be tested by the class involve whether Pb contamination is a problem limited to the inner cities or whether it affects affluent residential areas as well, and whether Pb contamination still persists despite the ban of lead in paint and gasoline 20 years ago. Other questions relate to the age of the houses and the levels of Pb found in their surroundings (paint, soil, and water), and whether Pb levels in surface soils decline with distance from the house and with depth. Students have also hypothesized that soil composition (grain size, concentration of major geochemical carriers such as Al and Fe) and physicochemical variables of the water (e.g., pH, temperature) influence the levels of Pb in the samples. Sampling Design and Statistics After the problem is defined, a sampling strategy is designed that will provide the data needed to test the questions or hypothesis. In this part of the class, students list the parameters to be analyzed, type of samples required, and number of samples and replicates needed to address temporal and spatial variability. They consult classical instrumental and analytical chemistry textbooks to identify the possible analytical protocols to be used in the research project (based on adequate detection limits, availability, etc). They also discuss the criteria involved in selecting possible sampling locations. For example, houses sampled for this study are selected on the basis of the age of the house and the paint pigment used on the exterior surface. The residential areas sampled in this study are located away from major highways and industry that could act as nonpoint sources of Pb. Houses sampled represent a time span of 170 years, from the 1800s to the 1970s. Sampling was generally restricted to houses with white or gray painted exterior surfaces where Pb-based pigment contents would be expected to be highest. In this module, students are also introduced to basic statistical analysis (mean, standard deviation, linear regressions) and error propagation analysis and to the meaning of outliers in a data set. An important objective of this module is to teach the concepts of accuracy and precision, limit of detection, and determination of blanks (field and laboratory, including containers and reagents), and the use of standard reference materials. Quality control in sample collection and analysis, and sources of error such as matrix interference, inadequate detection limits, signal resolution, and background signal are also described. Students are required to read and discuss several articles on sampling design and the statistical power of the sampling design to address the hypothesis. This module ends with homework dealing with all of the concepts learned in this part of the class.
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Analytical and Instrumental Principles and Required Laboratory Experiments Once the parameters to be analyzed are clearly defined (e.g., Pb, Al, Fe in soils and in water, pH, alkalinity, grain size), a series of lectures is used to explain the basic principles behind each analytical technique and instrumentation. These include gravimetric analysis for grain-size determination, UV– vis spectroscopy for Fe quantification (ferrozine), fluorescence for Al analysis (lumogalion technique using standard addition protocols), and flame and graphite furnace atomic absorption spectroscopy for Al, Fe, and Pb in soils and water. In this module, students learn about matrix interferences and the advantages of standard addition protocols over non-matrixmatched calibration standards and single-point standard additions. Each lecture (90 minutes) is followed later in the week by a 3-hour laboratory exercise. Sampling Protocols and Field Sampling In this part of the class, students are introduced to different types of samples (dissolved versus particulate, discrete versus pooled), and to several sampling techniques (coring for sediments and soils and trace-metal-clean protocols for water collections). They learn about proper sample container selection (Teflon, polyethylene, etc.) and preparation (acidrinsed) and sample storage (cold, freezing, and acidification of water samples). One of the major objectives of this module is to show that inadequate sample preparation, storage, and handling can strongly influence the outcome of the project. For the Pb project, soil samples were collected using a Soil Test Zero Contamination hand-held soil corer lined with PTFE plastic core liners. Samples were collected adjacent to the house foundation (0.15–1 m) and away from the house (9–12 m). The soils surrounding these houses were classified as either Plymouth loamy sand or Haven loam (14). In the laboratory, a surface soil layer (0–5 cm) and a deep soil layer (20–25 cm) were extruded and sampled from each of the cores. The soil samples were then oven-dried at 90 °C for 24 hours and transferred to plastic bags for storage. Paint samples were obtained from each exterior wall of each house. Paint chips were oven-dried at 90 °C for 24 hours and stored in plastic bags prior to acid digestion. Clean techniques were used for water collection for lead analysis in drinking water. Since a first-flush water sample is desirable (usually very early in the morning), the homeowners were provided with acid-washed polyethylene sample containers and instructed by faculty on the proper sample collection technique. Thirty-milliliter tap-water samples were collected from 10 houses after 0, 1, 3, 5, and 10 minutes of flushing. The samples were acidified to a pH of 1.5 (Q-HNO3). All tapwater sample and analytical manipulations were conducted in a class-100 clean room. Sample Preparation and Analysis Lectures for this module describe several procedures used to isolate or concentrate the analyte before quantification, including filtration protocols, solid digestion, and preconcentration techniques such as liquid–liquid extraction and the use of resins. In the lab, the students digest both paint and soil samples (0.2–0.7 g) collected in field sites according
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to U.S. EPA Method 3050a (15). Analysis of soil and paint digests for Pb was conducted in a separate laboratory period using an air–acetylene flame on a Perkin-Elmer Zeeman 5000 AAS at a wavelength of 283.3 nm. Two Pb-containing standard reference materials, Community Bureau of Reference (BCR) 146 sewage sludge (1255 ± 41 µg g᎑1) and National Institute of Standards and Technology (NIST) 2582 paint (208.8 ± 4.9 µg g᎑1) were also acid-digested and analyzed by flame AAS by a procedure similar to that used for the soil and paint samples. Analysis of water samples for Pb was conducted using a graphite atomizer on a Hitachi Z-8100 Polarized Zeeman AAS equipped with an autosampler.
Data Analysis and Interpretation This module is divided in two sections: Lead Recovery from Certified Materials (for accuracy and reliability) and Field Results (lead in exterior house paint, soil and drinking water). Lead Recovery from Certified Materials Data accuracy and reliability is illustrated using the students’ results from analysis of the standard reference materials (NIST 2582 paint and BCR 146 sewage sludge). Mean student group recoveries for the NIST 2582 Pb in paint were similar to the certified value—for example, 214 and 208.8 µg g᎑1, respectively (Fig. 2). Results of the analyses of the BCR 146 sewage sludge by the student groups showed more variability (850–1250 µg g᎑1); however the overall class mean value (1120 µg g᎑1) was similar to the certified Pb value. These results demonstrate that the acid-digest-AAS method is effective in extracting and measuring the Pb content of materials similar to those analyzed in this study. Field Results Lead in Exterior House Paint. The lead content of the exterior house paints sampled in our study ranged from 30 µg g᎑1 to 33.0% (1% = 10,000 µg g᎑1). As the students hypothesized, the Pb content of exterior paint is inversely correlated with the year the house was built (r 2 = ᎑.93); paint Pb content increases with the age of the house (Fig. 3). In general, Pb content is highest in exterior paints sampled from houses built before 1900. The level of Pb in paint from one house built in 1845 was anomalously low (300 µg g᎑1); this is the only house painted with a red pigment. The allowable Pb content in paint has been reduced as a result of the increased awareness of the health risks associated with ingestion of Pb-based paints. In 1971 the Lead Based Paint Poisoning Prevention Act was passed, and since 1979 no paint may contain more than 0.06 weight percent Pb (600 µg g᎑1). However, the class results suggest that the Pb content of the exterior paint is still a major environmental hazard. For example, all of the houses built before 1900 that we have analyzed contain more than 10% Pb in the paint. Lead in Soil. Surface soil samples collected adjacent to the house foundation have Pb contents ranging from 17 to 10,000 µg g᎑1. Surface soil Pb contents also correlate with the age of the house (r 2 = .88); the highest soil Pb levels are proximate to foundations of houses constructed before 1900 (Fig. 3). One notable exception was the surface soil Pb
Figure 2. Measured and certified lead contents for standard reference materials BCR 146 lead in sewage sludge (䊉) and NIST 2582 lead in paint (䊊) for student groups from 1997 to 1999. Solid line represents the mean value for lead in BCR 146; dashed line represents the mean value for lead in NIST 2582.
Figure 3. Relationship between the year the house was built and the lead content in surface soils (䊊) (– – – regression line), and the lead content in exterior paint (䊉) ( ––– regression line).
content for the house built in 1840. This house had a high exterior paint Pb content (22.7%) but a comparatively low surface soil Pb content adjacent to the house foundation (680 µg g᎑1). This soil sample was collected from an area where topsoil and sod had been recently placed. All houses with a surface soil Pb content exceeding 1000 µg g᎑1 had relatively high exterior paint Pb contents (>10%). Consistent with the students’ hypotheses, surface soil Pb concentrations decreased with distance from the foundation of the house. For houses with foundation surface soil contents >1000 µg g᎑1, the surface soil Pb content decreased 5–800-fold at a distance of 9–12 m from the foundation. Surface soil Pb content away from the house foundations ranged from 9 to 260 µg g᎑1.
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The strong covariance between Pb concentrations in exterior house walls and in the soils adjacent to the house foundations clearly suggests that the exterior paint is the source of the high Pb levels measured in the soils. The Pb concentrations in soils of the houses built in 1885, 1875, and 1800 exceeded the U.S. EPA soil abatement criteria of 5000 µg g᎑1. The Pb content of surface soils adjacent to the foundation at 4 other houses built after 1900 also exceeded the 400 µg g᎑1, warranting further evaluation and exposurereduction activities (16 ). While the level of Pb in surface soils declined with distance from the house, the Pb content in surface soil away from the foundation of houses built before 1900 was about 10 times higher than the level considered background for similar Long Island soils (8–25 µg g᎑1) (17, 18). Although soil-Pb concentrations are expected to be higher in large cities, and lower in smaller cities and towns (5), our preliminary results suggested that high Pb levels in soils may also be found in suburban environments with older homes. In fact, in this study, the Pb content in soils adjacent to the foundations of older houses was comparable to or even considerably higher than that reported in major urban areas such as New Orleans (5). Lead in Drinking Water. Lead content in drinking water was highest in the first-drawn water sample collected at each house (Fig. 4). The house built in 1845 had the highest initial drinking water Pb content, 24 µg L᎑1; it was the only residential drinking water sample to exceed the maximum allowable drinking water limit of 15 µg L᎑1. For the remaining drinking water samples, the first-drawn Pb content ranged from 0.2 to 9 µg L᎑1. High Pb content in the first-drawn water sample is likely due to lead leaching from pipes and plumbing fixtures during prolonged contact (8–12 hours). After the first-drawn sample, the Pb content of drinking water generally decreased with flushing time. With the exception of the house built in 1845, the drinking water Pb content decreased to 2 µ g L᎑1 even after 10 minutes of flushing. Although a previous study found a relationship between the age of the plumbing and drinking water Pb content (12), no such relationship was found in this study. The students concluded that soil Pb levels around old homes of Suffolk County were higher than those measured in large cities owing to weathering of exterior paint. Several of the houses in this study were selected primarily because they were constructed before 1900 and had not undergone significant exterior renovations. There are many houses in Suffolk County, NY, and elsewhere that meet these criteria. Homeowners need to be aware of the potential for high Pb contents in soils and the possible adverse health effects associated with a high-Pb environment. The presence of Pb in such high concentrations adjacent to the houses poses a significant health risk to children living in these homes.
Final Report and Presentations Students are responsible for submitting a lab report for every instrumental technique used in the class (see Analytical and Instrumental Principles and Required Laboratory Experiments section). The reports are written in the format of a
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Figure 4. Drinking water lead content as a function of flushing time. The symbols represent the year the house was built: 䉬, 1840; 䉭, 1845; 䊏, 1875; 䊐, 1885; 䉫, 1930; 䉱, 1930; 䉲, 1938; 䊉, 1945; 䉮, 1953; and 䊊, 1975.
manuscript to be submitted for publication, including abstract, introduction, methods (including figures of merit), results, discussion, and conclusions. Since course enrollment is limited, the instructors are able to carefully review and edit the lab reports. We discuss the revisions with each student individually, and students are required to submit the previous report with each new submission to make sure that they are not repeating the same mistakes. This process of careful editing and revision has resulted in vast improvements in students’ report writing abilities. At the semester’s end, each student has a well-written laboratory report, which several of them have used during employment interviews. Homeowners and interested students and faculty were invited to the final student presentations to be informed of the results of the lead analyses and to ask questions concerning the implications of the analyses. Students who present the results of the analyses in a public forum have done so with enthusiasm and a sense of responsibility. Participating homeowners were impressed with the quality of the presentations and the results of the analyses. Homeowners with high lead contents in their soil, paint, or drinking water were made aware of the dangers associated with lead exposure and were given information to allow them to remediate the problem or to minimize their exposure. For most students the oral presentation of their results from this project was the only presentation of this type made during their undergraduate career. Students learned important public speaking skills and techniques for preparing and presenting environmental data to a diverse audience. One of the measures of the success of the course has been the students’ reviews of it. Students have been generally enthusiastic about participating in the sampling and analytical activities. Those who pursue research careers are better
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equipped to perform analytical determinations of environmental samples. All students gain a better understanding and appreciation of the difficulties of conducting and evaluating environmental analytical measurements. Former students have indicated that participation in this course has been an important factor in receiving job offers from environmental consulting firms and analytical service companies. Acknowledgments This manuscript contains data and information compiled from student final reports submitted for MAR 308/533 Instrumental Analysis, spring 1997–1999, at SUNY at Stony Brook. Students worked in small groups conducting the sampling and analytical procedures described in this report. We thank the homeowners for allowing the collection of paint, soil, and drinking water samples necessary to conduct this study. This manuscript is MSRC contribution #1229. Literature Cited 1. Kesner, L.; Eyring, E. M. J. Chem. Educ. 1999, 76, 920. 2. Fitch, A.; Wang, Y.; Mellican, S.; Macha, S. Anal. Chem. News Features 1996, 68, 727A. 3. Zaimi, O.; Blizzard, A. C.; Sorger, G. J. J. Coll. Sci. Teach. 1994, 24 (Nov), 105. 4. Settle, F. Am. Lab. 1995, 27 (Jun), 6. 5. Mielke, H. W. Am. Sci. 1999, 87, 62. 6. Mielke, H. W.; Reagan, P. L. Environ. Health Perspect. 1998, 106, 217.
7. Lanphear, B. P.; Matte, T. D.; Rogers, J.; Clickner, R. P.; Dietz, B.; Bornschein, R. L.; Succop, P.; Mahaffey, K. R.; Dixon, S.; Galke, W.; Rabinowitz, M.; Farfel, M.; Rohde, C.; Schwartz, J.; Ashley, P.; Jacobs, D. E. Environ. Res. 1998, 79, 51. 8. Stapleton, R. M. Lead Is a Silent Hazard; Walker: New York, 1994; p 224. 9. Lead: Identification of Dangerous Lead Levels; Fed. Regist. 1998, 63, 30301. 10. Gardels, M. C.; Sorg, T. J. J. Am. Water Works Assoc. 1989, 81, 101. 11. Consumer Reports 1993, 58 (Feb), 73. 12. Lee, R. G.; Becker, W. C.; Collins, D. W. J. Am. Water Works Assoc. 1989, 81, 52. 13. New York State Lead Poisoning Prevention Advisory Council Annual Report; The Council: Albany, NY, 1995. 14. Warner, J. W.; Hanna, W. E.; Landry, R. J.; Wulforst, J. P.; Neely, J. A.; Holmes, R. J.; Rice, C. E. Soil Survey of Suffolk County, New York; U.S. Department of Agriculture Soil Conservation Service/Cornell Agricultural Experiment Station; U.S. Government Printing Office: Washington, DC, 1975; No. 0-473-964. 15. U.S. Environmental Protection Agency. Test Methods for Evaluating Solid Wastes, Vol. 1A, 3rd ed.; SW-846; Office of Solid Waste and Emergency Response: Washington, DC, Nov 1986; Method 3050a. 16. Guidance on Identification of Lead-Based Paint Hazards; Fed. Regist. 1995, 60 (175), Part V, 60 CFR 47248 with attachments. 17. Sanok, W. J.; Ebel, J. G. Jr.; Manzell, K. L.; Gutenmann, W. H.; Lisk, D. J. Chemosphere 1995, 30, 803. 18. Breslin, V. T. Water Air Soil Pollut. 1999, 109, 163–178.
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