Teaching analytical atomic spectroscopy advances in an environmental chemistry class using a project-based laboratory approach: investigation of lead and arsenic distributions in a lead arsenate contaminated apple orchard
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- Amarasiriwardena, D. Anal Bioanal Chem (2007) 388: 307. doi:10.1007/s00216-007-1189-z
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Over the last quarter century environmental chemistry has matured as a significant field in chemical sciences. It has become one of the interdisciplinary meeting grounds where chemistry plays a central role in understanding contemporary environmental issues affecting all of us. Increasingly, environmental chemistry has become an important subfield along with inorganic chemistry, organic chemistry, biochemistry, physical chemistry and analytical chemistry. The awareness of chemistry, the social and political context of environmental issues, and a good grasp of associated analytical chemistry are also increasingly important for the contemporary environmental chemist; thus, environmental analytical chemistry should be an important part of any study of environmental chemistry.
I believe an environmental chemistry curriculum in a liberal arts college should entice students to appreciate the rewards of learning chemistry and to connect “real-world” issues. The expectations of the contemporary cohort of students are very diverse and interdisciplinary. Traditional laboratory exercises often do not enhance the investigation and inquiry skills of students but encourage a passive approach to experimentation and problem solving; therefore, there a strong trend is developing to shift the traditional concept-verification laboratories to inquiry-based science laboratories and teaching [1–3] and to call for student-active teaching pedagogies [4, 5]. Students become more involved and excited about learning environmental analytical chemistry through project-based, issue-oriented laboratories [3, 6, 7] dealing with authentic environmental [8, 9] questions than they do through recreating classical experiments. Not only do these kinds of projects persuade students to learn theoretical/conceptual material, but they offer practical field/laboratory investigation skills to explore “real-world” environmental issues and to experience the research-like atmosphere that traditional prescriptive, verification-oriented laboratories do not offer [9, 10].
Analytical atomic spectroscopy plays an important role in identification (what is it?) and then quantification (how much?) of pollutants. New developments in analytical instrumentation and methods have improved detection capabilities (i.e., low detection limits) and the ability to harvest chemical information about various species (i.e., chemical speciation). These new analytical developments have influenced the regulatory limits and have enhanced the characterization of mobility and transportation behaviors of environmental pollutants.
This paper will discuss how current advances in atomic spectroscopy and other instrumentation can be incorporated into an undergraduate environmental chemistry laboratory using a project-based approach. An example of a project related to a local environmental issue is discussed. In addition, the in-class project execution strategies, pedagogical goals, and rewards and limitations of such a project are discussed.
Typically, this is a multiweek research project on a local environmental issue with strong components in fieldwork and laboratory work in environmental analytical chemistry. Students work as small teams  as in a “workplace” environment, and students take leadership roles in designing the experiment, completing fieldwork, and laboratory work and data analysis, and they develop workplace ethics like teamwork, punctuality, and responsibility for achieving a given task . Finally, student teams present their findings to the class as a team. Each student writes his/her manuscript-style report for evaluation. In the following, I describe a typical project-based laboratory we have executed in our undergraduate environmental chemistry class that focused on trace metal analysis and analytical atomic spectrometry.
About the class
This upper-level environmental chemistry course used chemistry to explore contemporary environmental concerns in the hydrosphere, soils, and atmosphere. Topics included chemistry of natural waters, water pollution and wastewater treatment, toxic heavy metals and their complexation properties in soils, and inorganic and organic pollutants in the atmosphere. The course emphasized learning environmental chemical analysis methods and instrumentation in the environmental monitoring of water and soils. The class had seven students (sophomore to senior-year science “concentrators”) with diverse backgrounds, interests, and preparation. The diversity of student academic backgrounds in science also contributed to the successful execution of this project. All students had completed two semesters of introductory chemistry and had basic laboratory skills and proficiency. The class met twice a week for in-class lecture and discussion (80 min) with a weekly one afternoon laboratory session or fieldwork (4–5 h). The project began in the fourth week of the semester as soon as the weather was favorable for fieldwork during the late winter.
Class research project
The purpose of this project was to investigate spatial and vertical distribution of Pb and As of soils in a local apple orchard and to compare the results with soils from an uncontaminated site.
Lead arsenate was an effective inorganic pesticide widely used during the first half of the twentieth century in many apple orchards. This pesticide was used to contain leaf rollers, moths, and other chewing insects. Application of lead arsenate pesticide in apple orchards was phased out in the early 1950s with the introduction of organochlorine-based pesticides. The use of lead arsenate pesticides was terminated in 1988; however, the residues of lead arsenate pesticide still remain in most orchard soils [12–14], especially in western Massachusetts in New England [15–17]. Among the lead arsenate pesticides used in New England orchards acid lead orthoarsenate [Pb3(AsO4)2] is shown to be prevalent  although other formulations, like acid lead arsenate (PbHAsO4), acidic orthoarsenite (PbHAsO3), and basic orthoarsenate [Pb4(PbOH)(AsO4)], were available for the orchard keepers. They usually sprayed individual or combined mixtures of pesticide directly onto the tree’s canopy by using hand spray guns or brooms . Both lead and arsenic [especially As(III), or arsenite] are toxic for humans. Often As(V) is reduced to more toxic As(III) in the body , perhaps under anoxic conditions in the intestine. As New England orchards and farms are rapidly developed into housing subdivisions, home vegetable plots, and children’s playgrounds, they pose a lead and arsenic exposure risk, especially for children.
An old apple orchard in south Amherst, MA, USA (42 °19′ N, 72 °31′ W) located close to our campus was chosen for its proximity and easy access to the property. The approximately 11,000 m2 orchard area has nearly 80 mature apple trees grown in rows. The drip zone of the apple trees is around 2–3 m away from the trunk.
In one afternoon during the field/laboratory period, the whole class participated in sample collection and field related measurements (i.e., survey of the site, location of sites). Forty-three surface soil samples [(Hinesburg (HgB)—silty, lacustrine, and well-drained soil)] were collected on a grid using an aluminum soil corer, and samples were transferred into plastic bags. Two core samples (40–60-cm deep) were collected by a student team from the orchard using a 3-in.-diameter PVC pipe, and one control soil in the forested area (Sudbury A, very fine moderately drained) in campus was collected by another team. All samples were properly labeled and transferred to the laboratory for air-drying. Another team cataloged the samples and their sampling locations, site survey measurements, and related soil physical characteristics.
At the beginning of the semester, we discussed the safety issues related to working in the laboratory and in the field, and the proper disposal of chemical wastes. Each team leader was responsible for maintaining field/laboratory safety, cleanliness in the work area, and coordination of analytical tasks among the analytical teams.
Five grams of soil samples was mixed with distilled deionized water and stirred vigorously in a shaker for 30 min. The supernatant was decanted and measured for soil pH (using model Phi-310, Beckman Instruments) and for conductivity (using model 30, Yellow Springs Instrument Co., Yellow Springs, OH, USA), and for oxidation/reduction potential (ORP) (using model RE 300, Extech Instruments, OH, USA).
Air-dried soil samples were passed through a 2-mm sieve to remove plant debris and gravel. Two grams of dried soil samples was mixed with 1 M nitric acid solution and allowed to leach trace metals for 1 week. The soil’s nitric acid extracts were centrifuged at 2,000 rpm for 10 min (Sorval model GLC-2B, Dupont Instruments, Norwood, MA, USA), and the supernatants were decanted and appropriate dilutions were made before the inductively coupled plasma atomic emission spectroscopy (ICP-AES) and mass spectrometry (ICP-MS) measurements.
One student team prepared a series of multielement standard solutions with Cu, Ni, Pb, and Zn in 2% (v/v) nitric acid in an appropriate calibration range (0.1–10 μg/mL) using the serial dilution method. Nitric acid extracted trace metal solutions were also diluted to fit into the calibration range. Samples were analyzed by ICP-AES (Optima 2000, PerkinElmer Instruments, Shelton, CT, USA). The most sensitive, yet less interfering analytical wavelengths [Zn(II) 206.200 nm, Cu(I) 327.393 nm, Pb(II) 220.353 nm, Ni(II) 231.604 nm] were selected by the students using wavelength tables. Arsenic in soil samples was analyzed by ICP-MS (Elan 6000, PerkinElmer Instruments, Shelton, CT, USA) and the students became aware of potential interference of [40Ar35Cl]+ from chlorine in the sample. On the basis of the chemistry of these soils, the students agreed that chlorine residues in the soil samples were minimal.
A summary of the project outcome and the most common interpretation of the results and ensuing discussion reported in the students’ reports (environmental chemistry class, spring 2004) follows.
The pH range of the orchard soil is 4.76–6.26, indicating the acidic nature of New England soils and the soil is oxic with an ORP range from +210 to +343 mV. Soil electrical conductivity ranged from 15 to 62 μS/cm in the soils examined.
Finally, many students came up with remediation strategies for this contaminated site. One potential remediation approach recommended was to remove the top soil layer (first 30 cm) and to bury and cap it with a clay layer in a secure site. Several other students suggested application of phytoremediation methods.
Pedagogical approach and execution of the project
As a class, the students designed and formulated the research question; a brief research proposal and statement of work was prepared ahead of the project. The class was divided into small working teams [8, 9] of three students. These teams were responsible for various aspects of the project (Fig. 1), and some tasks were rotated so that every student had an opportunity to master all analytical tasks, including field, laboratory, sample preparation, and analytical instrument operation skills.
Project laboratory process
Facets of the project laboratory
Location of the activity
Research proposal and statement of work
Formulation of a research question
Understanding the research question using primary literature
Survey of available resources: instruments, chemicals, planning, etc.
Refining the research question
Statement of work (laboratory work, data analysis phase, time for writing of the thesis, revisions, final draft, preparation of oral presentation material)
Field work: site survey, site selection, soil sample collection
Laboratory: sample preparation, standard solution preparation, instrument calibration, sample analysis
Data analysis and interpretation
Communication and reporting
Writing individual report/self-revision
Pedagogical goals for the project laboratory
Environmental chemistry learning: anthropogenic and natural lead and arsenic sources; mobilization and transport phenomena of lead and arsenic compounds; chemical speciation; health implications
Analytical: introduce student to site selection and soil sampling techniques; sample preparation and trace metal extraction methods; multielement standard preparation methods; hands-on experience with: pH, ORP, ICP-AES, and ICP-MS measurements; preparation of calibration curves for the appropriate concentration range
Data analysis using spreadsheet software and making appropriate graphs; statistics
Environmental analytical chemistry: understanding theoretical and practical underpinnings of analytical atomic spectrometry
Field: sampling; site selection; GPS and mapping
Written: submission of manuscript-style paper
This project helped students characterize the analytical advantages and limitations of plasma spectrometry, and it also encouraged them to look at an analytical question in a broad context. We encouraged students to bring their interdisciplinary research interests into these project-based inquiry laboratories.
Analytical and environment chemistry
The project offered students an opportunity to work on a local agricultural and environmental issue using the theoretical knowledge gained from the class. Moreover, the students were not only exposed to an authentic environmental analytical chemistry issue, but they also experienced the analytical chemical challenges associated with working on “real-world” samples. The instructor’s role was to be an enthusiastic facilitator and resourceful consultant. The project also enhanced the interdisciplinary scientific knowledge base of both parties (i.e., students and faculty) involved. This project promoted active learning skills in analytical chemical sciences, and it is an excellent way of promoting learning of environmental analytical chemistry for senior students including majors and nonmajors.
This project was an elegant way to introduce students to the modern analytical chemistry theory behind analytical techniques and instrumentation and to the process of research. The approach also facilitated understanding of basic operational principles of modern environmental analytical instrumentation. The class atmosphere was research-like, and collegial; the students were passionate about the project. All students participated as genuine stakeholders of the project and not as passive learners.
The data obtained from the project laboratory provided ample opportunity to grapple with the uncertainty of a measurement (i.e., precision and accuracy, detection limits, sensitivity) and to delve into basic statistical analysis skills (standard deviation, regression analysis, t test, etc.) using spreadsheet software.
One of the highlights of this project laboratory was strong encouragement of teamwork among the members of the class and building a community of investigators (Fig. 1). The students learned how to work as a team, to accomplish goal-oriented tasks, and to develop the good work ethics needed to be successful team members. Often senior students on each team served as mentors for rookies in the research environment.
We also put strong emphasis on building communication skills both in written and oral communications. Fifteen-minute individual presentations included introduction to the background of the project, hypothesis, experimental approach, results and discussion, major conclusion, and proposal of remediation strategies for the contaminated site. Question-and-answer sessions were engaging and thoughtful. The atmosphere was conference-like and we even served donuts, apple cider, and coffee. These oral presentations were a great opportunity to pinpoint major flaws and shortcomings in students’ data analysis and to give them quick feedback before submission of the final paper. Usually, at least one revision of their manuscript-style paper was encouraged.
This environmental chemistry class was limited to ten students, and this size is ideal for upper-level courses where course enrollments are around ten to 15 students. For large classes the tactical help of a teaching assistant can be employed to ease the pressure on the instructor. Careful planning of the project and logistics (i.e., fieldwork, consideration of weather, sample preservation) and proper synchronization of the class discussions with laboratory work are vital for successful completion of the project laboratory. The content coverage of this project is in-depth, and less emphasis was put into the breadth of the coverage. Finally, compared with traditional concept-based laboratories, the students in this class were expected to spend a little extra time in the field or laboratory.
Beyond this class, some students continued to work on related spin-off projects like As and Sb speciation studies [17, 20] of these soils for senior theses research. As described in the students’ self-evaluations from this course, it is clear the students enjoyed doing this project and clearly benefited from the course format and concepts and analytical chemistry skills learned from it.
Quotes from students’ self-evaluations
“...We learned ways to quantify it, and the effect of the pollution on humans and the techniques behind trace metal analysis, which was probably one of the most valuable things in the class. Another part of the class I really enjoyed was integrated approach to learning about the pollution; not only did we learn the chemistry behind the reactions but we also learned its effects on health. I never had the opportunity to apply chemistry in this kind of way....”—CT
“I worked extremely hard in this class, in participating in the labs, in preparing for presentations, and in keeping up with the readings. I really enjoyed the lab, and learned a lot from writing it up, and doing the research for the introduction.... All in all I felt extremely challenged by this class, but felt I learned a lot and am proud of my work in it....”—SH
“...I am now familiar with the chemical instrumentation techniques such as ICP-AES, ICP-MS and pH, conductivity, and ORP meters.... The most challenging part in this class was the presentation. I had to spend hours to prepare for it. However, it gave me good opportunities to study the primary literature....”—NT
“...I am prepared for this summer research ... as well as future research at Hampshire and beyond....”—DM
“The final paper was a write-up of an extensive study that we had been conducting for more than half of the semester. It involved analyzing soil samples from an apple orchard contaminated with lead arsenate. This was an exciting and very practical field study that was also a lot of fun. The real hands-on approach to environmental chemistry was exactly what I wanted. I was challenged in many ways and feel very proud of my accomplishments throughout the semester....I am incredibly satisfied with how much I have learned about environmental chemistry and how to conduct an extensive study....”—SS
Very special thanks are extended to the hard work, dedication, and enthusiasm of students in the environmental chemistry class (NS 366, spring 2004) at Hampshire College. This project was partially funded by financial and instrumental support from the Howard Hughes Foundation Grant (grant no. 71100-503803) awarded to Hampshire College, and the Pittsburgh Conference Memorial College Grant. The author would also like to thank Dr. Ramon Barnes (University Research Institute for Analytical Chemistry, Amherst, MA, USA) and Dr. Merle Bruno and Ms. Joan Barrett at Hampshire College for their valuable comments about the manuscript. Special thanks also to Ms. Kristen Shrout for her assistance with laboratory instruments.