CASE TEACHING NOTES for "The Benign Hamburger" by Graham Peaslee, Hope College, Holland, MI Juliette M. Lantz, Siena College, Loudonville, NY Mary M. Walczak, St. Olaf College, Northfield, MN

Case Objectives:

1. Introduce an application of nuclear science that applies the basic definitions, addresses some of the myths of nuclear technology, and examines the societal, political, and economic issues surrounding the science of food irradiation.

2. Teach some of the scientific principles of electromagnetic radiation, interaction of radiation and matter, and chemical bonding. Distinguish between atomic and nuclear energy scales.

3. Research a topical and controversial subject; learn to separate fact from opinion and valid information sources from editorials. Advance scientific literacy skills.

4. Develop critical thinking skills and learn to support arguments and opinions with facts. Apply risk-benefit analysis principles.

Use of the Case:

This case was developed for use as an introduction to nuclear applications aside from those involving nuclear power generation and weapons. As such, it can be used in a variety of introductory science courses, such as chemistry, physics, biology, environmental science, and agricultural science.

Synopsis:

The executives at the Jill-at-the-Grill fast food chain must decide the future of the company. High levels of Escherichia coli O157:H7 bacteria in hamburgers sold at Jill-at-the-Grill restaurants have resulted in a food poisoning epidemic that has caused at least one death and over two hundred reported cases of food poisoning. The company CEO has assembled all his top aides for an emergency meeting to update the situation and decide what steps the organization should take to reverse the economic plunge company stock has taken in the last few days. They consider introducing irradiated beef into their stores to prevent another such catastrophe and to restore the public’s confidence in their restaurants. Concern about the safety of the irradiated food and the public’s acceptance of the irradiation process is discussed.

II) FACILITATING THE CASE

This case works well as a research-gathering exercise followed by an in-class discussion.

Variation 1: The case is given to students a few days prior to the discussion. Each student is given 2-5 questions from the following list, and is asked to do the background research necessary to answer their assigned questions. This has the effect of "seeding" the class with experts. During a normal class period, a full case discussion ensues. In one instance, the students were divided up into three groups: Jill-at-the-Grill executives, FDA research scientists, and concerned and alarmed citizens. In this role-playing mode, a class debate/discussion was held.

Variation 2: The whole class gathers and generates a list of questions that they think that the decision-makers at Jill-at-the-Grill would need answered before they could arrive at a final course of action. The students then divide up these questions and head off on a fact-finding mission. After a designated period of time (in one instance the students were given approximately one hour), the class reconvenes and a full case discussion ensues. This works best in an extended class period, such as a laboratory or workshop mode.

Questions assigned to students prior to class meeting:

What foods are currently irradiated in the U.S. and elsewhere?

What is pasteurization? How is it different from food irradiation?

Does the process of cooking food introduce toxic chemical species?

What are the public fears regarding irradiated food?

Does food irradiation have any global implications?

Does food irradiation have any local implications?

Which countries are most likely to use food irradiation?

What alternatives are there to food irradiation?

What is the definition of "organic food?"

Can irradiated food be organic?

Is irradiated food natural or unnatural?

What are the relative costs of food irradiation and post-harvest fumigants?

In what ways does the agricultural community stand to benefit from this technology?

Is irradiation technology used for any other purposes in the U.S.?

Do workers in a food irradiation facility receive any special training?

How are radioactive sources regulated in the U.S.?

Which countries permit food irradiation worldwide?

How does ⁶⁰Co decay?

How is ⁶⁰Co produced?

How are radioactive sources transported in the U.S. ?

List common sources of radiation that the average American encounters.

How much will food irradiation cost?

What is E. coli? Pair this question up with the next 3

Where is E. coli found?

Why is E. coli ingestion toxic to humans?

How does E. coli respond to irradiation?

How many people die each year from food poisoning?

How many workdays are lost to food poisoning each year?

What are the symptoms of food poisoning?

What are the major bacteriological causes of food poisoning?

What is the shelf life of beef?

Investigate the effect an E. coli outbreak has on a company's stock value (e.g., Odwalla Juice outbreak, October 1996, or Hudson Foods Recall, August 1997).

Is the RAR allegation "U.S. is using radiation waste for food irradiation" true?

Is the RAR allegation "Toxic chemical species are generated in the irradiation of food" true?

Is the RAR allegation "Irradiation reduces the nutritional value of food" true?

Is the RAR allegation that "Natural food warnings are eliminated" true?

Questions to facilitate case discussion:

The following questions are provided for use by the instructor in facilitating the case discussion. In addition to these questions, the instructor may choose to ask specific questions from the list above.

Introductory:

What issues are important to the CEO?

Why would anyone irradiate food?

What is at stake if Jill-at-the-Grill makes the wrong decision?

How many of you have experienced food poisoning?

How many of you know somebody that has experienced food poisoning?

Irradiation: Facts vs. Opinions

Are irradiated foods in the U.S. required to be labeled as such?

Does any government agency monitor food irradiation?

Does food irradiation raise the temperature of the foods being irradiated?

What is gamma radiation and how is it different from microwave radiation?

What effect does gamma radiation have on matter? Food and bacteria in particular?

On a molecular level, what changes occur in food as a result of irradiation?

What residues are left behind when gamma rays pass through food?

What advantages are there to irradiating food?

What are free radicals? Why are they a health concern? Why are they suspected to be toxic?

How does the food irradiation process differ from that of nuclear explosions and reactors?

What is the relationship between nuclear materials proliferation and food irradiation?

Compare the magnitude of nuclear energy to that of atomic (electronic) energy.

Decision Forcing:

Is radiation natural or unnatural?

Should irradiated food be labeled as such?

Would you eat a hamburger at Jill-at-the-Grill tomorrow if they made no policy changes?

Would you eat a hamburger at Jill-at-the-Grill tomorrow if they used irradiated beef?

What percentage of your friends and family would support food irradiation, without any additional information on the subject? With additional information?

Summary:

What should Jill-at-the-Grill do? What should the press release say?

Introductory Chemistry
        Topics that would be especially appropriate for this audience include nuclear processes and the effect of radiation on matter. The discussion could focus on an explanation of how irradiation works to kill disease-causing microorganisms, the range of the electromagnetic spectrum and the interaction of various energies of light with molecules, and the public perception of the nuclear industry and technology.

Environmental Chemistry, Environmental Science
        Topics that would be especially appropriate for this audience include the difference between various nuclear technologies (food irradiation, power plants, bombs) and the safety of any nuclear facility. The discussion could focus on the level of scientific literacy necessary to function as a responsible citizen, world food supplies and food preservation technologies, government regulatory functions, and the harmful effects of various radiation dosages.

Introductory Biology
        Topics that would be especially appropriate for this audience include bacteria and the public policy issues related to food irradiation. The discussion could focus on bacterial infections, the role of bacteria in the human GI tract, the role of bacteria in food preservation technologies, the history of various epidemics, FDA regulatory policies, and the societial issues resulting from such a proposition.

Students are sometimes quick to dismiss RAR’s allegations, as they seem to be merely emotional appeals. Asking the students to examine each allegation for truth often reveals that RAR makes some good points that many citizens would consider important - hence, Jill-at-the-Grill can't afford to disregard this group entirely.

At the other extreme it is possible to find students with an emotional and vocal fear of anything "nuclear," and this outcry can distract the entire class. Usually steering the discussion towards the effects of food poisoning can in turn lead to a discussion of the benefits of food irradiation, and allow the nuclear issues to be introduced more gradually.

1) Have students write Jill-at-the-Grill’s press release, outlining their course of action and justifying their choice to the general public.

2) Have students submit the answers to their individual research questions in written form, including what they learned from their own research and what they learned from the class discussion.

3) A quiz can be given at the end of the discussion period asking students to state their decision and to provide relevant information to support that decision. A useful feedback question to include on such a quiz is what have the students learned from class discussion as compared to their own reading/research, and what important scientific principles were discussed.

Student Feedback

Following the case discussion, students were asked to write responses to questions such as:

What was the most important thing you learned from the class discussion?

What was one thing you learned about food irradiation from your research or from the class discussion?

Samples of student responses to these questions are included here.

"From the discussion in class I learned that irradiating food kills the bacteria which inhabit food by breaking the bonds of the molecules within the bacteria. It does this by striking the electrons involved with gamma rays which frees some of the electrons from the molecules creating free radicals and ions."

"Perhaps the most valuable thing that I learned from today’s discussion is all the factors that go into making such decisions - in regards to the scientific background which eventually becomes social knowledge. In this discussion I primarily learned of the interconnectedness of the scientific with the political with the social."

III) ANALYSIS OF KEY SUBJECTS

1) Nuclear reactions and nomenclature:

There are several types of nuclear reactions that occur naturally, and some that are induced by technological means. In the early twentieth century, only three types of natural radiation were identified; they were categorized as alpha (a), beta (b) and gamma (g)-rays. These rays were eventually discovered to emanate from the nucleus of an atom, while a fourth type of radiation (the x-ray) was found to emit from the atomic shells of electrons surrounding the nucleus. Since the strong force which holds the nucleus together is much greater in magnitude than the electromagnetic force which governs all the electromagnetic emissions of atoms, the nuclear emissions of a, b, and g-rays are typically much more energetic than x-rays and other atomic processes. However, the emission of these particles is very similar to the atomic processes that students often encounter in introductory science. Just as excited atoms will rearrange their electron configurations and emit electromagnetic radiation to decay or de-excite from an excited state to a ground state, nuclei will undergo rearrangement of their protons and neutrons and emit particles or electromagnetic radiation to de-excite into more stable nuclear configurations.

For example, a-decay is the emission of 2 protons and 2 neutrons as a helium nucleus, often represented as , a-emission typically occurs in the de-excitation of heavy nuclei:

This example is the typical a-particle decay which occurs in household smoke detectors. The radioactive source in the smoke detector emits a continuous stream of charged alpha particles which generates a small electrical current in a circuit. When smoke particles interfere with the flow of the alpha particles, the circuit is interrupted and an alarm sounds.

Beta decay is the emission of an electron from the nucleus, which can only occur if a neutron in the nucleus decays into a proton and an electron. Many light elements decay by this mechanism:

This reaction is the basis of the widely-used "radiocarbon dating" process. Carbon-14 is formed naturally in the atmosphere when cosmic rays interact with nitrogen causing a process known as electron capture:

These carbon-14 isotopes are naturally incorporated into living things as part of the carbon cycle. Radiocarbon dating takes advantage of the fact that when living things die they stop exchanging carbon with the surroundings, including the radioactive carbon-14 isotope. Since carbon-14 decays with a known half-life of 5370 years, the amount of carbon-14 that has disappeared from an object (relative to atmospheric levels) can be used to determine the number of years that have passed since the death of the entity.

Gamma decay is the emission of purely electromagnetic radiation from the nucleus. Since this radiation does not change the proton or neutron number in the nucleus, there is no transmutation of the element and the same nucleus remains after the emission, just in a lower excited state. A typical example is:

This particular decay of Ni is the only source of gamma rays used for food irradiation currently in the U.S. A ⁶⁰Co source is used, which spontaneously undergoes beta-decay with a half-life of 5.3 years to form ⁶⁰Ni in an excited state (⁶⁰Ni*). The subsequent instantaneous g-decay may be compared to the atomic emission of x-rays, except in this case the protons and neutrons re-arrange in the nucleus into a more stable state with an accompanying emission of radiation. Gamma rays are nothing more than very energetic electromagnetic radiation, at the high energy end of the electromagnetic spectrum beyond x-rays, light waves, microwaves, and radio frequencies.

There are several forms of radioactive decay, which any general chemistry textbook will discuss in detail. One sure to arise in this case discussion will be fission, the process whereby a heavy nucleus decays into two lighter nuclei. Since the lighter nuclear products are so much more stable, a significant quantity of energy is released in the decay process. The amount of energy released in this process can be calculated from binding energy systematics of products minus reactants, which is often done in general chemistry textbooks. Fission is the basic process occurring in nuclear power plants and weapons. A typical chain reaction begins when a low-energy neutron initiates the fission process:

The produced neutrons react further with other ²³⁵U atoms and thereby propagate the chain reaction. It should be noted that ⁹⁵Sr and ¹³⁸Xe are only examples of the many possible product isotopes. However, many of the reaction products are unstable and will subsequently decay to other species, which leads to a mixture of "fission products" in fission fuel waste. It is these subsequent decays which make the waste highly radioactive for many years after the "useful" fission reaction has occurred. It should be noted the ⁶⁰Co isotope is an unlikely product in the ²³⁵U fission process.

All radiation interacts with matter as it passes through it, and most of this interaction is dominated by the stopping process. This stopping process is usually an atomic rather than a nuclear process, because radiation will most often "hit" the atomic electrons. Collisions with atomic electrons will cause excitation of these electrons, and because of energy conservation, kinetic energy is lost from the incident radiation. Sometimes all the incident energy can be lost in a single collision and sometimes many collisions are required, depending on the incident energy and type of interaction. The interactions of radiation and matter are central to the application of electromagnetic technology today, and this topic is also the basis for food irradiation. Some examples of these interactions are listed below starting with the highest energy electromagnetic waves and progressing to lower energy electromagnetic waves. (It should be noted that alpha and beta particles also interact with matter, and typically significantly more energy is released in the stopping process, which is more dangerous to biological systems due to the physical size of these particles and their charge. However, since charged particles interact so strongly with the material they pass through, they consequently have a very short penetration depth. Thus, to obtain significant radiation deep into a material, a penetrating radiation such as gamma-radiation must be used.)

Gamma radiation is high-energy electromagnetic radiation that will pass through most material without being stopped. Gamma rays typically have frequencies from 10²⁰ to 10²⁴ Hz, which correspond to energies of approximately 10⁸ kJ/mol. Higher energy gamma rays do exist - they are called cosmic rays because they are only produced naturally in astronomical processes. A more traditional unit of energy for nuclear processes is an electron volt (eV); gamma rays typically possess millions of electron volts of energy (MeV) (Conversion factor 1.6 x 10^-19 eV = 1 J). In contrast, typical atomic energy levels measure a few eV’s; this corresponds to the energy which binds electrons to an atom. Since electromagnetic waves are not particles per se, their interactions with charged particles such as electrons are governed by quantum mechanics. One of the odd features of this interaction is that since the energy of a gamma ray is so high, the probability of an interaction is low for any given collision with an atom. Thus, gamma radiation requires several feet of shielding material (lead and concrete are usually used due to their high density) to stop it completely. When gamma radiation does interact with atomic electrons by one of several processes, the end result is that many electrons (typically thousands) will be removed from their atoms (ionized) by a single gamma ray. Losing electrons will cause the formation of free radicals (molecular species with unpaired electrons) and will often destroy molecular bonds (shared pairs of electrons).

X-rays are slightly lower in energy than gamma rays. These electromagnetic waves have frequencies around 10¹⁸ Hz, which correspond to energies of 10⁴ kJ/mol or several keV. X-rays can pass through a substantial amount of material, such as several inches of muscle and tissue, but they are stopped quite readily by dense materials such as bones. X-rays have sufficient energy to ionize electrons as well, and the fact that they can disrupt chemical bonds causes them to be classified as carcinogenic. Exposure to too many x-rays will cause the mutation of cells (by destroying genetic material) which can lead to the onset of cancer. However, the medical diagnostics available from x-ray use outweigh the risks associated with the high energy electromagnetic radiation exposure for most people.

Ultraviolet, visible, and infrared light are electromagnetic radiation with less energy than x-rays. These electromagnetic waves have frequencies around 10¹²to 10¹⁶ Hz, which correspond to energies of a few tenths to a few tens of kJ/mol or several eV. UV exposure carries the same danger as x-rays because UV waves can induce bond-breaking processes. Considerable UV exposure has been linked to various types of cancer, which is a frequent topic in the news surrounding the use of tanning salons. Visible light and infrared light will not ionize electrons typically, but they can cause electronic, vibrational, and rotational excitations in molecules. Electronic transitions result when electrons are excited to higher energy levels, but they are not ejected from the molecule. Vibrational and rotational excitations cause thermal excitation (heating) of a molecule. Ultraviolet, visible, and infrared radiation are typically used to study the composition of chemical species in the field of spectroscopy (the interaction of radiation with matter).

Microwaves are still lower in energy on the electromagnetic spectrum. They typically have frequencies around 10¹⁰ Hz, which corresponds to energies of less than a J/mol or a fraction of an eV. Microwaves are stopped by any molecule (typically water) that can absorb them via molecular rotations and vibrations (thermal heat). We use this technology to heat food rapidly inside a container (i.e., a microwave oven) that protects the surroundings from excess microwave radiation with a thin shield of metal. A description of how microwaves work should be provided in most general chemistry textbooks; a good one appears on p. 488 of Chemistry and Chemical Reactivity by Kotz and Treichel, 3rd edition, Saunders College Publishing, 1996.

The lowest energy electromagnetic wave are radiowaves, which range in frequency from 1 to 10⁸ Hz. The energy associated with these waves is too low to cause many molecular excitations at all, which explains why we can surround ourselves with radio stations without a noticeable increase in cancer rates.

The principle behind food irradiation is that by passing highly-ionizing and penetrating radiation (gamma-rays) through a foodstuff, a significant portion of the bacteria will be killed outright and the rest will undergo radical mutation that will prevent reproduction of the bacteria. Thus a single irradiation can cause the elimination of food-spoiling bacteria as well as bacteria that are human pathogens. This will result in foodstuffs that have longer shelf-lives and that have less pathogenic (disease-causing) organisms.

All food irradiation facilities use ⁶⁰Co or ¹³⁷Cs as a source of radioactivity, though in the U.S., only ⁶⁰Co is currently used. Both of these isotopes appear as products in a nuclear reactor, but ⁶⁰Co is too light to be produced in any appreciable quantity as a fission product. Instead, it is produced by inserting the one naturally occurring isotope of cobalt (⁵⁹Co) into a reactor core, and bombarding it with a high flux of neutrons. A fraction of the cobalt nuclei will absorb neutrons to become cobalt-60:

This particular isotope of cobalt subsequently decays via beta emission to an excited state of ⁶⁰Ni*:

The half-life for this decay is about 5.3 years. The ⁶⁰Ni* instantly decays to its ground state via emission of characteristic gamma rays:

In other countries the cesium isotope is produced in much the same way, by adding four neutrons to the naturally-occurring ¹³³Cs. It is true that significant quantities of ¹³⁷Cs are also produced as waste products in fission reactions, and it might be conceivable to separate this isotope out from radioactive waste. However, this would be a messy and expensive process and for these reasons is unlikely to be a goal of the U.S. government, as the RAR claims.

Both of these isotopes are isolated and sold as commercial gamma-ray sources and used with special government licenses by individual companies as a radiation source. Irradiation is used for a number of other processes including medical and dental x-rays, medical irradiation (cancer treatment), medical and non-medical tracers, sterilizing pharmaceutical products, making non-stick cookware, the manufacture of some plastic food wraps and tires, gemstone irradiation, and fundamental research at university centers. These isotopes are not fissionable (they are too light) and they cannot induce radioactivity in other materials, as gamma rays do not change the proton and neutron numbers of any nucleus they hit.

The factors that are most important in determining the radiation chemistry of food irradiation include (1) the radiation dose, (2) the chemical composition of the food itself, (3) the physical state of the food (fresh or frozen), and (4) the ambient atmosphere. An excellent synopsis of the chemistry involved is reported in the Federal Register record of the Food and Drug Administration (FDA) petition to make the irradiation of beef legal (Federal Register 62 FR 64107 December 3, 1997). The efficacy of the treatment of beef to substantially reduce pathogens such as E. coli, Salmonella and Clostridium botulinum has been demonstrated by many scientific studies reported to the FDA. Tests on irradiated foodstuffs have been performed since the mid-1950s in the U.S., and the first products approved by the FDA were wheat and white potatoes in the 1960s. During the 1980s, the FDA approved petitions for irradiation of spices and seasonings, pork, fresh fruits, and dry or dehydrated substances. Poultry received approval in 1990. Based on this efficacy and the demonstrated lack of toxicity and insignificant nutrient loss, the FDA approved red meat irradiation in this country in December 1997. Basically, meat irradiation is approved in this country up to a dosage of 4.5 kGy (unit described below) for fresh meats, and up to a dosage of 7.0 kGy for frozen meats. This is true of meat and meat by-products that are "primarily from bovine, ovine, porcine and equine sources" as specified by the FDA.

The biological effects of ionizing radiation are directly proportional to the amount of ionization produced in living tissue. The more ionization produced, the greater the lethal effect on bacteria. The amount of ionization is also proportional to the energy and the type of radiation deposited. Thus, units of radiation dose are related to the amount of radiation deposited per unit mass of tissue. A kGy (kilogrey) corresponds to a radiation flux of 1 kJ/kg of matter. In older units, this would be equivalent to 100,000 rad/kg of matter. Rads are equivalent to rems for gamma radiation. For comparison, a typical dental x-ray has a radiation flux of 70 mrem, annual radiation exposure for an average U.S. citizen is around 200 mrem, and a chest x-ray is approximately 300 mrem. This means that fresh meat would receive the equivalent of approximately 1.5 million chest x-rays to kill the bacteria.

At these irradiation levels most foods, including meats, do not show any visible effects. Some citrus fruits and eggs, however, show cellular ruptures at low irradiation levels and, although this is not determined to be dangerous, it makes the appearance of the product unpopular with consumers. The incidence of Salmonella is shown to drop over 100,000-fold after irradiation at less than 1 kGy. However, since E. coli is even less resistant to irradiation than the Salmonella, contamination levels should decrease even more during a similar irradiation. The shelf-life for all irradiated foodstuffs is longer than non-irradiated foodstuffs, although the hamburger meat discussed in this case would still need to be refrigerated or frozen as is the current practice for non-irradiated meat. This longer shelf-life is the reason the United Nations Food and Agriculture Organization (UN-FAO) is heavily promoting the use of food irradiation in third-world countries, since it is estimated that about one-quarter of the world's food is lost post-harvest to spoilage or pests. According to UN statistics, 39 nations have approved food irradiation for preservation and post-harvest decontamination, and many are involved in the commercial irradiation of food. These include countries such as Argentina, Bangladesh, Belgium, Brazil, Chile, China, Denmark, Finland, France, Hungary, India, Indonesia, Israel, Japan, Netherlands, Norway, Philippines, Russia, Thailand, United States, and Yugoslavia.

There are free radicals produced during the radiation process, and these create new chemical species that result in the death of the pathogenic and non-pathogenic bacteria and spores. There have been many studies conducted over the past 40 years on the level of free-radical production in irradiated foodstuffs. At the approved dosages, there are no free radicals detected that would not be produced in subsequent storage and cooking of the meat. This seems to be independent of the meat type or the ambient atmosphere. However, frozen meat requires more irradiation than fresh meat. In a frozen structure, the free radicals are less likely to migrate away from the ionization site, and a higher fraction of them recombine in place to form the original molecule. With no real evidence of any toxic, carcinogenic, or teratogenic substances being introduced by irradiation after numerous studies, the FDA deemed this process to be safe for the meat industry.

There is some concern about the loss of nutrients in the meat after irradiation noted in the application to approve beef irradiation in the U.S. by the FDA. There is a small but reproducible loss of proteins and vitamins during the irradiation process. Proteins are polypeptide chains of amino acids that have a primary structure (sequence of acids), a secondary structure (coiling or pleating of peptide chains), and a tertiary structure (the three-dimensional shape of the large molecule). Denaturation of proteins occurs when the secondary and tertiary structures of a protein are lost through heating or irradiation, and this results in a loss of biological function. Irradiation of beef at approved levels results in the denaturing of some proteins, at levels that range from a few percent to twenty percent. Proteins play a central role in a variety of biochemical processes, primarily as enzymes that catalyze various reaction pathways and as transport and storage molecules. A protein that has been denatured will have lost its tertiary structure and will not necessarily function, since shape often critically affects the performance of enzymatic proteins, for example. However, since proteins are available from a wide variety of food sources, a small loss of protein in meat is deemed by the FDA to be a negligible loss, considering the average daily intake of the American consumer.

Meat also contains large amounts of B vitamins, which are types of molecules that assist the function of many enzymes that are essential for human biochemistry. For example, vitamin B12 catalyzes the intramolecular migration of hydrogen, and regulates the reduction of ribonucleotides (RNA) to deoxyribonucleotides (DNA). This vitamin is unique in that it cannot be synthesized except by microorganisms, and humans have to ingest a certain amount of it to avoid pernicious anemia. Food irradiation can cause some degradation of the B vitamins, at levels that range from a few percent to twenty percent. Since this nutrient loss is similar to the aging and cooking process, and simply exacerbates it, the FDA has concluded that irradiation adds no toxicity to the food. The nutrient loss caused by irradiation has been estimated using thiamine (vitamin B1), the most radiation-sensitive B vitamin. Even at a 50% degradation level of thiamine in red meat, the average U.S. consumer would still be well over the recommended daily allowance of thiamine. For more reading on this topic, consult ("Biochemistry," L. Stryer, Freeman (1995)).

Meat is a nutrient-rich substrate that supports the growth of a variety of microorganisms. During the initial processing stages (slaughter, skinning, butchering) these microorganisms are diverse and scattered throughout the meat product. Microorganisms present include non-pathogenic spoilage bacteria, including organisms from the Pseudomonas-Moraxella-Acinetobacter group and others. Pathogenic organisms, including Salmonella, Escherichia coli O157:H7, listeria monocytogenes, staphylococcus aureus, can all be present, although usually at relatively low levels. Spores of various pathogens, which are the "resting stage" of certain bacteria in which the bacterial cell has become enclosed in a resistant coating as a response to an adverse environment, have been isolated in raw meat as well. Among these are the well-known Clostridium botulinum. The growth of all these microorganisms is determined by several factors, including temperature, ambient oxygen level, pH, and the number of spores present.

E. coli is a bacterium - a single-celled organism. Like all bacteria, under the proper conditions it can quickly multiply. When an organism has a bacterial infection, single-celled disease-causing bacteria have invaded the organism and multiplied to a level higher than the organism can tolerate without exhibiting signs. The human body’s defense against such invasions is to produce antibodies and white blood cells that attack and kill the bacteria.

The name E. coli represents many strains of bacteria. Some of these strains are normally found in the large (and to a lesser extent small) intestine of humans. Not all strains of E. coli are pathogenic. Some strains contain a gene for a toxin which is what makes the strain pathogenic. Other beneficial strains of E. coli aid in digestion or produce B-complex vitamins and Vitamin K.

The E. coli O157:H7 strain does contain the gene for the toxin and is therefore pathogenic. When in the gastrointestinal tract, this toxin typically causes diarrhea and abdominal cramps which can be mild or severe. The illness manifests itself 3-5 days after eating contaminated food and is resolved in 5-10 days. Most people recover without treatment. The use of antibiotics has not been shown to speed recovery.

In some people, usually young children and the elderly, the effects can be very serious and require hospitalization. There are two more serious illnesses than can result from E. coli O157:H7 infection: hemorrhagic colitis and hemolytic uremic syndrome. Hemorrhagic colitis is characterized by the sudden onset of severe gastrointestinal symptoms, including bloody diarrhea. Hemolytic uremic syndrome involves the destruction of red blood cells, kidney failure, and neurological complications (e.g., seizures and strokes). Hemolytic uremic syndrome is a life-threatening illness that requires intensive care, blood transfusion, and kidney dialysis. About 16% of the E. coli O157:H7 infection cases reported annually develop hemorrhagic colitis, though less than 5% develop hemolytic uremic syndrome.

Food handling procedures are regulated by the Food and Drug Administration in the U.S. A summary of these procedures may be found at: http://vm.cfsan.fda.gov/~dms/fc-toc.html.

There are a complex set of rules that should be followed for all retail food preparation in the U.S., and enforcement is done primarily through the use of routine inspections conducted by the individual states. These inspections are full reviews of the food establishment operations and facilities and their impact on food safety. They include assessment of employee and management health, practices, and knowledge of food safety; food flows, source, storage, thawing, preparation (including cooking temperatures and times) and post-preparation processes; equipment and facility construction; cleaning and sanitizing processes; water sources; sewage disposal; and vermin control. A typical fast-food restaurant would qualify as a type 2 risk establishment, and qualify for two routine inspections per year, if there were no regular health code violations.

The basic approved method for destroying pathogens in raw food is to cook food by raising all parts of it to a specific temperature and maintaining that temperature for a specified period of time. For example, to prepare a hamburger, the meat must be cooked at a temperature of 145^oF for 3 minutes or at 150^oF for 1 minute. See the food code listed in: http://vm.cfsan.fda.gov/~dms/fc-toc.html for further details.

Other food topics that are likely to arise in the case discussion include the production and marketing of organic foodstuffs and pasteurization. Organic foods are those which are grown without any synthetically compounded fertilizers, pesticides, growth regulators, and livestock feed additives. They are not necessarily exposed to less bacteria than foods grown using non-organic methods and, to the extent that they are slaughtered in the same manner as non-organically grown livestock, they will be similarly exposed to the E. coli that inhabits the upper intestine of the animals.

Pasteurization is a thermal treatment applied to many foods to kill pathogens or food spoilage microorganisms. Foods that are consumed directly (e.g., milk) are pasteurized to kill pathogens. Other foods are pasteurized to kill food spoilage bacteria thereby increasing shelf life. Milk and dairy products can be pasteurized by a number of different time-temperature treatments. Several different time-temperature combinations have been approved as equivalent, such as 161^oF for 15 seconds, or 201^oF for 0.1 second. Heat treatment at these times and temperatures destroys the most heat resistant non-sporeforming pathogen found in milk, Coxiella brunetii. Milk pasteurization has effectively eliminated the spread of diseases such as diphtheria and brucellosis, which were widespread at the end of the nineteenth century.

References for Case Itself

This case was based upon the New York Times article

Egan, Timothy, "Tainted Hamburger Raises Doubts on Meat Safety," January 27, 1993, v142, page 6.

Other materials used in developing this case were the American Dietetic Association’s position paper on food irradiation which can be found on the world wide web at: http://www.eatright.org/Public/GovernmentAffairs/92_adap0200.cfm

"Syracuse U Dining Halls Ban Irradiated Foods," Chronicle of Higher Education, August 3, 1988, p. A2.

General Reading:

Food Irradiation: A Most Versatile 20th Century Technology for Tomorrow, Overview of a Symposium held at the Annual Meeting of the Institute of Food Technologists, Chicago, IL, June 25-29, 1989, Food Technology, July 1989.

Gunther, Judith Anne, "The Food Zappers," Popular Science, January, 1994, p. 72.

Morganthau, Tom, "E. coli Alert," Newsweek, September 1, 1997, pp. 26-32.

Morrison, R. M., Buzby, J. C., Jordan Lin, C.-T., "Irradiating Ground Beef to Enhance Food Safety," Food Review, Jan-Apr 1997, URL: http://www.ers.usda.gov/publications/foodreview/jan1997/jan97e.pdf

Preventing Foodborne Illness: Escherichia coli O157:H7 URL: http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm

Zurer, Pamela, "Food Irradiation: A Technology at Turning Point," Chemical & Engineering News, May 5, 1986, p.46-56.

References on the FDA Decision, December 1997:

An absolute must, the Federal Register documentation from the FDA when it approved beef irradiation in December 1997: http://vm.cfsan.fda.gov/~lrd/fr97123a.html

Kolata, Gina, F.D.A., "Saying Process is Safe, Approves Irradiating Red Meat: Move Could Eliminate Most Dangerous Bacteria," New York Times, December 3, 1997, v147, page 1.

Kolata, Gina and Drew, Christopher, "Long Quest for Safer Food Revisits Radiation Method," New York Times, December 4, 1997, v147, page 1.

Other Interesting and Related Web Sites:

The Nuclear Information and Resource Service's Toolbox at http://www.nirs.org/toolbox/toolhome.htm

International: Joint FAO/IAEA Programme Nuclear Techniques in Food and Agriculture http://www.iaea.org/programmes/nafa/dx/index.html

International: Consumers International http://www.consumersinternational.org

American Meat Institute: http://www.meatami.org/irradok.htm

American Nuclear Society: http://www.ans.org/main.html

Foundation for Food Irradiation: http://www.food-irradiation.com/

Leader of the RAR?: http://www.pure-food.com/

USDA article on methyl bromide alternatives: http://www.ars.usda.gov/is/np/mba/oct97/index.htm.

Food irradiation, other countries: http://www.fao.org/sd/rtdirect/rtre0010.htm and http://www.iaea.org/programmes/nafa/dx/

Food handling regulations, FDA Food Code: http://vm.cfsan.fda.gov/~dms/fc-toc.html

References on the Case Teaching Method

Austin, J.E. "Teaching Notes: Communicating the Teacher’s Wisdom," © President and Fellows of Harvard College, 1993, #5-793-105.

Barnes, L.B.; Christensen, C.R.; Hansen, A.J. Eds. "Teaching and the Case Method," 3rd Edition, Harvard Business School Press: Boston, MA, 1994.

Boehrer, J.; Linsky, M. "Teaching with Cases: Learning to Question." In M.D. Svinicki (ed.), The Changing Face of College Teaching, New Directions for Teaching and Learning, No. 42, Jossey-Bass, San Francisco, 1990.

Boehrer, J. "How to Teach a Case" © President and Fellows of Harvard College, 1995, #N18-95-1285.0.

Christensen, C.R.; Garvin, D.A.; Sweet, A. Eds. "Education for Judgement: The Artistry of Discussion Leadership," Harvard Business School Press: Boston, MA, 1991.

Conant, J.B.; Nash, L.K.; Roller, D.; Roller D.H.D. Harvard Case Histories in Experimental Science, Vol. 1 and 2, Conant, J.B.; Nash, L.K. Eds. Harvard University Press: Cambridge, MA, 1964.

Coppola, B.P. "Progress in Practice: Teaching and Learning with Case Studies", The Chemical Educator, 1996, 1(4), S1430-4171 (96) 04050-2.

Herreid, C. F. "Case Studies in Science - A Novel Method of Science Education" J. College Science Teaching, 1994, 221-9.

Hitchner, S.B., Jr. "Preparation of Teaching Notes," " © President and Fellows of Harvard College, 1977, #N14-77-189.0.

Lantz, J.M.; Walczak, M. M. "The Elements of a Chemistry Case: Teaching Chemistry Using the Case Discussion Method," Chem. Educator, 1(6), 1997 S 1430-1471 (97) 06070-6.

Robyn, D. "What Makes a Good Case?" © President and Fellows of Harvard College, 1985, #N15-86-673.0.

Wheatley, Jack, "The Use of Case Studies in the Science Classroom", J. College Science Teaching, 1986, 428-31.

Other Cases by Lantz and Walczak

Lantz, J.M.; Walczak, M. M. "The Elements of a Chemistry Case: Teaching Chemistry Using the Case Discussion Method," Chem. Educator, 1(6), 1997 S 1430-1471 (97) 06070-6.   This article contains the case "Hommers Mining Dilemma."

Peaslee, G.; Lantz, J.M.; Walczak, M. M. "The Benign Hamburger," J. College Science Teaching, 1998, v28 n1 p21-24.

For other cases by Lantz and Walczak, visit our web site: http://www.stolaf.edu/people/walczak/cases.html

This case was written at the Pew Faculty Development Workshop: Writing Cases for Introductory Science Courses, September 26-29, 1996, at Colorado College. We thank the Pew Midstates Science and Mathematics Consortium for making that workshop and several other workshops on the case teaching method possible. The Pew Consortium also supported this work through the Short Term Consultation Program. Publication of this case on the Case Studies in Science website was made possible with support from the National Science Foundation (NSF Award #9752799).

We also thank Dr. Mike Swift for numerous valuable discussions on bacteria, viruses, and other microorganisms, and many other colleagues at various Pew workshops who gave us their invaluable feedback and insight on this case.