Focus

A problem-based, self-directed approach to the teaching of the principles of environmental and human toxicology

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Focus on Education and Training

A problem-based, self-directed approach to the teaching of the principles of environmental and human toxicology

1. Background

McMaster University's pioneering contributions to problem-based, self-directed instruction is recognized in medicine,^1,2 occupational health,³ pharmacology⁴ and engineering.⁵ This approach to learning shifts the attention from the teacher or instructor to the learner. It places more emphasis on process that facilitates acquisition by the students of information and motivational skills, thereby encouraging them to take greater responsibility for their own learning.

In problem-based learning (PBL), real situations (case studies) or paper problems provide the vehicle for learning. The students identify issues, knowledge concepts and the data needed to understand and/or solve or manage a problem; learning objectives are set and pursued by the learners and therefore the process is self-directed. Small-group learning (maximum of 8–10 students per tutorial group) fits PBL as it caters to the individual, encourages cooperation and generates critical thinking. There are no formal lectures. The tutor is a facilitator, while the tutor and learners themselves constitute important resources. The problem, peers, tutor and resources assist “guided discovery”. Student assessment involves summative evaluation (to facilitate decisions about performance in a course; i.e., assign academic grades) and formative evaluation (feedback to enhance student learning by optimizing the learning dynamics).⁶

The course described in this article (Pharmacology 4C03; Principles of Toxicology) is offered within the Honours Biology and Pharmacology Programme in the Biology Department at McMaster University.⁴ It is a five year co-op programme, three four-month terms of which are spent in work related to pharmacology, toxicology or pharmaceutics. In their first year students take year-I science, while in the second year the focus is on chemistry, biology, biochemistry and statistics courses with some room for electives. A co-op work term occurs during each of the last 3 years, and is interspersed with academic terms featuring courses in biology and pharmacology, as well as a laboratory course, a senior thesis and electives. All the pharmacology courses are taught in a small group setting using the PBL format; others taken are not.

2. Pharmacology 4C03

2.1. Course objectives

One objective of this course is to provide information about the mechanisms whereby chemicals given as therapeutic agents, encountered naturally in foods, in the work place or the general environment produce toxic effects. Both chemical and biological determinants of toxicity are examined, as well as the fundamental principles of toxicology (absorption, distribution and excretion; exposures and pathways to man; dose-response relationships; antagonism and synergism; and analytical aspects).

2.2. Format

Student contact consists of one 3 h tutorial per week for one term (13 weeks). Case studies constitute the vehicles for learning and the knowledge and information needed to understand, resolve and/or manage the problem described is the basis for the study objectives.

In a typical tutorial, the students begin by agreeing upon an agenda based on the previous week's study objectives. Usually, one or two students take the lead voluntarily and others generate discussion by asking questions or by requesting more details. After a suitable break, the discussion is resumed. Handouts or overheads are frequently employed by the students to support their participation. Before the end of the tutorial, new study objectives are set. In these deliberations, the problem scenario is likely to be consulted again. The work load is then divided and assigned. The students, alone or in small teams, consult suitable sources in preparation for the next tutorial. Most often original research articles or subject-specific critical reviews are selected.

Before the session is adjourned, the students engage in a brief period of formative evaluation. It involves personal and peer assessment of preparedness and participation, the communication and interpersonal skills exhibited, and it is determined if group dynamics can be improved, or whether the group objectives were achieved. The appropriateness of the case scenario is also addressed.

2.3. Evaluation

Student evaluation is based upon: class participation (20%); class presentation (10%); written assignment (20%); mid-term Evaluation Exercise (15%); and end-of-term Evaluation Exercise (35%).

The assignment and Evaluation Exercises constitute the summative student evaluation component of the course. Learner competencies assessed include: knowledge; application of knowledge; reasoning ability; judgment; decision-making; problem-solving, technical, information retrieval and critical appraisal skills. Assessment of class participation and class presentations (including one formal talk) are more subjective evaluation aspects and student participation in this is invited.

2.4. Course schedule

Table 1

Table 1  

WEEK	PROBLEM OR ACTIVITY^a
a Time will be allotted for formal student presentations based on the assignment.
1	Introduction to Course and to Self-directed, Problem-Based Learning
2 & 3	Aflatoxin: A Food Contaminant
4 & 5	Toxic Encephalopathy from a Seafood Toxin
6	Case Study on Lead Exposure: How Clean is Clean?
7	Mid-Term Evaluation Exercise
8^a	Case Study on Lead Exposure: How Clean is Clean?
9^a & 10^a	Reproductive Impact of Endocrine-Disruptive Chemicals^b
11^a & 12^a	Particulates, Acid Aerosols and Oxidant Pollutants^b
13	Final Evaluation Exercise

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2.5. Scope of coverage

With each case study, selected references are provided to introduce the student to the literature. The coverage for each problem usually includes the following aspects, if applicable: epidemiology, exposure, pathways to man, metabolism (including biotransformation), toxicokinetics, pathogenesis, target organ, structure-function relationships, risk assessment and regulation, analytical chemistry aspects, and preventive measures. Critical appraisal of the evidence is to be emphasized throughout the course.

2.6. A typical case scenario

Reproductive impact of endocrine-disruptive contaminants. Fish of the carp family (cyprinids) living downstream from where effluent from a sewage-treatment work (STW) entered a river, were bisexual (hermaphrodites). Hermaphrodites occur very rarely among healthy cyprinids. When caged trout were placed in the STW effluent channel, the results summarized in the figure below were obtained. Vitellogenesis may be taken as a biomarker of estrogenic contamination of the aquatic environment. It illustrates the widespread concern about developmental effects in wildlife and humans of estrogen-like substances and other endocrine-disruptive chemicals.

Fig. 1 The effect of effluent from a sewage-treatment works on the plasma vitellogenin concentration of male rainbow trout. One cage containing 20 male trout was placed directly in the effluent channel of a sewage-treatment works (STW), and another (control) was maintained in a laboratory supplied with high-quality spring water. Plasma samples were collected after 1, 2, and 3 weeks and assayed for vitellogenin. Exposure to effluent caused a pronounced increase in the plasma vitellogenin concentration (p < 0.001 at all observation times). Results are mean ± SEM (n = 20). The SEMs shown in the original figure are omitted from the histograms because they were of small magnitude. (Adapted with permission from Sumpter and Jobling.⁷)

2.7. Example of an evaluation exercise component

The evaluation exercises are conducted in the context of case scenarios and thus reflect the approach taken in the tutorial. Below a typical scenario and questions are reproduced, which are used in the evaluation of students' knowledge and other summative attributes pertaining to the tutorial problem highlighted above. By mutual agreement, study guidelines for the evaluation exercise were drawn up and toxicological outcomes were limited to reproductive and developmental effects since cancer, biotransformation and neurotoxicity had been included in the previous evaluation exercise.

Case scenario. Detailed environmental surveys completed in 1998 showed, based on soil and plant analyses, that some of the First Nation Cree communities in the James Bay region of Ontario were contaminated with PCBs reaching as high as 21,000 ppm in soil and 550 ppm in vegetation (the corresponding acceptable criteria levels in Ontario are 5.0 ppm and <1 ppb, respectively). Others were contaminated with pesticides (especially p,p-DDE and p,p-DDT) or PAHs (polycyclic aromatic hydrocarbons). Elevation of organochlorine contaminants have also been shown to occur in bottom-feeding fish caught in nearby river channels and in the blood of adults living in the contaminated communities.

The following questions were used in a recent examination.

Investigators studying endocrine disruption frequently use the Vitellogenin Assay. What is vitellogenin? Describe the vitellogenin assay and illustrate how this might be used to test for the presence of estrogens and estrogen-like compounds in the waters surrounding the contaminated communities in the scenario.

PCBs, DDT/DDE and some PAHs are representative of compounds known to be endocrine disrupters. Based on available evidence for detrimental effects of contaminants with estrogenic/anti-estrogenic or androgenic/anti-androgenic activities among wildlife, succinctly summarize your concerns for the sexual development and reproductive health of birds (e.g. eagles), mammals (e.g., black and polar bear; caribou and moose; marine mammals such as whale and seal), fish and invertebrates of the Hudson-Bay/James Bay lowlands of Ontario. OR Based on available human evidence and any supporting animal (experimental and/or wildlife) evidence, state/describe your concerns for possible detrimental effects on the reproductive and developmental health of people living in native communities contaminated with endocrine disrupting organochlorines and polycyclic aromatic hydrocarbons.

Describe the underlying (fundamental) mechanism(s) of action corresponding to the endocrine-disrupting effects of two outcomes described in your answer to 1(b).

3. Concluding remarks

During the tutorials of the 2 weeks allotted, the topics covered in some depth in relation to endocrine-disrupting chemicals typically include: roles of estrogens and androgens in sexual development; sources and types of estrogens (i.e., endogenous, phytoestrogens, synthetic); biotransformation; bioaccumulation and bioconcentration; toxicokinetics; mechanisms of action of hormones; biomarkers of exposure; effects of specific hormones or endocrine-disrupting chemicals documented in wildlife and humans and the strength of the evidence; bioassays available to assess potencies; and analytical methods for quantitative measurements. The estrogen-related risks established for breast cancer constitute a major focus.

Students enjoy the broad scope of the course and the opportunity to learn basic concepts in the context of real, holistic situations. Motivation remains high throughout the course, and each year new developments in the published literature are identified and consulted. Clearly, the educational rewards are not limited to the students.

References

1. V. R. Neufeld, C. A. Woodward and S. M. MacLeod, Acad. Med, 1989, 64, 423.
2. J. M. Blake, G. R. Norman and E. K. M. Smith, Lancet, 1995, 345, 899.
3. D. K. Verma, H. S. Shannon, D. C. F. Muir, E. Nieboer and A. T. Haines, J. Soc. Occup. Med., 1988, 38, 101.
4. P. K. Rangachari, Am. J. Physiol. (Adv. Physiol. Educ. 5), 1991, 260, S14.
5. D. R. Woods, A. N. Hrymak, R. R. Marshall, P. E. Wood, C. M. Crowe, T. W. Hoffman, J. D. Wright, P. A. Taylor, K. A. Woodhouse and C. G. K. Bouchard, J. Eng. Educ., 1997, 86, 75.
6. Evaluation Methods: A Resource Book, ed. S. Shannon and G. R. Norman, McMaster University, Hamilton, ON, 1995.
7. J. P. Sumpter and S. Jobling, Environ. Health Perspect., 1995, 103(Suppl), 173.

Evert Nieboer
Department of Biochemistry, McMaster University, 1200 Main St. West, Hamilton, ON Canada, L8N 3Z5 and Institute of Community Medicine, University of Troms, Troms, N-9037, Norway.
E-mail: nieboere@mcmaster.ca

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