26510696-Food-Toxicology

1068	UNIT 7 APPLICATIONS OF TOXICOLOGY

Clinical descriptions of adverse reactions to food are not new. Hippocrates (460 – 370 B.C.) first recorded adverse reactions to cow’s milk that caused gastric upset and urticaria, and Galen (A.D. 131–210) described allergic symptoms to goat milk. However, the immunologic basis of many adverse reactions to food was not established until the passive transfer of sensitivity to fish was described in the early 1960s (Frankland, 1987; Taylor et al., 1989). This test, which evolved into the (skin) prick test and later the radioallergosorbent (RAST) test, allowed a distinction to be made between immunologically based adverse reactions (true allergies) and adverse reactions with other causation.

Food Allergy Description Food hypersensitivity (allergy) refers to a reaction involving an immune-mediated response. Such a response is generally IgE-mediated, although IgG4- and cellmediated immunity also may play a role in some instances (Fukutomi et al., 1994). What generally distinguishes food allergy from other reactions is the involvement of immunoglobulins, basophils, or mast cells (the latter being a source of mediating substances including histamine and bradykinin for immediate reactions and prostaglandins and leukotrienes for slower-developing reactions) and a need for a prior exposure to the allergen or a crossreactive allergen. An allergic reaction may be manifest by one or more of the symptoms listed in Table 30-18. The list of foods known to provoke allergies is long and is probably limited only by what people are willing to eat. Although cutaneous reactions and anaphylaxis are the most common symptoms associated with food allergy, the body is replete with a repertoire of responses that are rarely confined to only a few foods.

A curious type of food allergy, the so-called exercise-induced food allergy, is apparently provoked by exercise that has been immediately preceded or followed by the ingestion of certain foods (Kivity et al., 1994), including shellfish, peach, wheat, celery, and “solid” food (Taylor et al., 1989). The exact mechanism is unknown, but it may involve enhanced mast-cell responsiveness to physical stimuli and/or diminished metabolism of histamine similar to red wine allergy (Taylor et al., 1989). On the other hand, food intolerance in patients with chronic fatigue may have less to do with allergic response and has been shown to be a somatization trait of patients with depressive symptoms and anxiety disorders (Manu et al., 1993).

Chemistry of Food Allergens Most allergens (antigens) in food are protein in nature, and although almost all foods contain one or more proteins, a few foods are associated more with allergic reactions than are others. For example, anaphylaxis to peanuts is more

Table 30-18

Symptoms of IgE-Mediated Food Allergies

Cutaneous	Urticaria (hives), eczema, dermatitis,
	pruritus, rash
Gastrointestinal	Nausea, vomiting, diarrhea, abdominal
	cramps
Respiratory	Asthma, wheezing, rhinitis, bronchospasm
Other	Anaphylactic shock, hypotension, palatal
	itching, swelling including tongue and
	larynx, methemoglobinemia*

*An unusual manifestation of allergy reported to occur in response to soy or cow milk protein intolerance in infants (Murray and Christie, 1993).

SOURCE: Adapted from Taylor et al., 1989, with permission.

common than is anaphylaxis to other legumes (e.g., peas, soybeans). Similarly, although allergies may occur from bony fishes, there is no basis for cross-reactivity to other types of seafood (e.g., mollusks and crustaceans), although dual (and independent) sensitivities may exist (Anderson and Sogn, 1984). Interestingly, patients who are allergic to milk can usually tolerate beef and inhaled cattle dander, and patients allergic to eggs can usually tolerate ingestion of chicken and feather-derived particles (Anderson and Sogn, 1984)—although in the “bird-egg” syndrome, patients can be allergic to bird feathers, egg yolk, egg white, or any combination of the three (DeBlay et al., 1994; Szepfalusi et al., 1994). Some of the allergenic components of common food allergens are listed in Table 30-19.

Table 30-19

Known Allergenic Food Proteins

FOOD	ALLERGIC PROTEINS
Cow’s milk	Casein (Dorion et al., 1994; Stoger
	and Wuthrich, 1993)
	-Lactoglobulin (Piastra et al., 1994;
	Stoger and Wuthrich, 1993)
	a-Lactalbumin (Bernaola et al., 1994;
	Stoger and Wuthrich, 1993)
Egg whites	Ovomucoid (Bernhisel-Broadbent et
	al., 1994)
	Ovalbumin (Fukotomi et al., 1994,
	Bernhiesel-Broadbent et al., 1994)
Egg yolks	Livetin (de Blay et al., 1994;
	Szepfalusi et al., 1994)
Peanuts	Ara h II (Dorion et al., 1994)
	Peanut I (Sachs et al., 1981)
Soybeans	-Conglycinin (7S fraction) (Rumsey
	et al., 1994)
	Glycinin (11S fraction) (Rumsey
	et al., 1994)
	Gly mIA (Gonzalez et al., 1992)
	Gly mIB (Gonzalez et al., 1992)
	Kunitz trypsin inhibitor (Brandon
	et al., 1986)
Codfish	Gad cI (O’Neil et al., 1993)
Shrimp	Antigen II (Taylor et al., 1989)
Green peas	Albumin fraction (Taylor et al., 1989)
Rice	Glutelin fraction (Taylor et al., 1989)
	Globulin fraction (Taylor et al., 1989)
Cottonseed	Glycoprotein fraction (Taylor et al.,
	1989)
Peach guava,	30-kDa protein (Wadee et al., 1990)
banana,
mandarin,
strawberry
Tomato	Several glycoproteins (Taylor et al.,
	1989)
Wheat	Gluten (Stewart-Tull and Jones, 1992)
	Gliadin (O’Hallaren, 1992)
	Globulin (O’Hallaren, 1992)
	Albumin (O’Hallaren, 1992)
Okra	Fraction I (Manda et al., 1992)

SOURCE: Modified from Taylor et al., 1989, with permission.

CHAPTER 30 FOOD TOXICOLOGY

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Although food avoidance is usually the best means of protection, it is not always possible because (1) the content of some prepared foods may be unknown (e.g., the presence of eggs or cottonseed oil), (2) there is the possibility of contamination of food from unsuspected sources [e.g., Penicillium in cheeses or meat, Candida albicans (Dayan, 1993; Dorion et al., 1994), and cow’s milk antigens in the breast milk of mothers who have consumed cow’s milk (Halken, et al., 1993)], (3) an allergen may be present in a previously unknown place [the insertion of Brazil nut DNA into soybeans and subsequent appearance of the allergic 2S protein in soybean products (Nordlee et al., 1996)], and (4) there is a lack of knowledge about the phylogenetic relationships between food sources (legumes include peas, soybeans, and peanuts; some Americans are not aware that ham is a pork product). While avoidance is not always possible, promising research in the area of probiotics (i.e., promotion of the growth of beneficial intestinal bacteria including lactobacilli or bifidobacteria) may help in management of food allergy (Kirjavainen et al., 1999; Arunachalam, 1999).

Demographics of Food Allergy Although children appear to be the most susceptible to food allergy, with adverse reactions occurring in 4 to 6 percent of infants, the incidence appears to taper off with maturation of the digestive tract, with only 1 to 2 percent of young children (4 to 15 years) susceptible (Fuglsang et al., 1993). The increase in the number of adults exhibiting food allergy

Table 30-20

Idiosyncratic Reactions to Foods

may be due in part to an expanded food universe—that is, an increased willingness to try different foods. In one study, allergies among young children were most commonly to milk and eggs, while allergies that developed later in life tended to be to fruit and vegetables (Kivity et al., 1994).

Familial relationships also play a role. Schrander and colleagues (1993) noted that among infants intolerant of cow’s milk protein, 65 percent had a positive family history (firstor seconddegree relatives) for atopy compared with 35 percent of healthy controls.

Food Toxicity (Poisoning) See “Substances for which Tolerances May Not Be Set” below.

Food Idiosyncrasy Food idiosyncrasies are generally defined as quantitatively abnormal responses to a food substance or additive; this reaction differs from the physiologic effect, and although it may resemble hypersensitivity, it does not involve immune mechanisms. Food idiosyncratic reactions include those that occur in specific groups of individuals who may be genetically predisposed. Examples of such reactions and the foods that are probably responsible are given in Table 30-20.

Probably the most common idiosyncratic reaction is lactose intolerance, a deficiency of the lactase enzyme needed for the metabolism of the lactose in cow’s milk. A lack of this enzyme re-

FOOD

REACTION

MECHANISM

REFERENCE

Fava beans	Hemolysis, sometimes
	accompanied by jaundice and
	hemoglobinuria; also, pallor,
	fatigue, nausea, dyspnea, fever and
	chills, abdominal and dorsal
	pain
Chocolate	Migraine headache

Pyramidene aglycones in fava bean cause	Chevion et al., 1985
irreversible oxidation of GSH in G-6-PD-
deficient erythrocytes by blocking
NADPH supply, resulting in oxidative
stress of the erythrocyte and eventual
hemolysis
Phenylethylamine-related (?)	Gibb et al., 1991;
	Settipane, 1987

Beets	Beetanuria: passage of red urine	Excretion of beetanin in urine after	Smith, 1991
	(often mistaken for hematuria)	consumption of beets
Asparagus	Odorous, sulfurous-smelling urine	Autosomal dominant inability to	Smith, 1991
		metabolize methanthiol of asparagus
		and consequent passage of methanthiol
		in urine
Red wine	Sneezing, flush, headache, diarrhea,	Diminished histamine degradation:	Wantke et al., 1994
	skin itch, shortness of breath	deficiency of diamine oxidase (?)
		Histamines present in wine

Cholineand	Fish odor syndrome: foul odor
carnitine-	of body secretions
containing
foods

Choline and carnitine metabolized to	Ayesh et al., 1993
trimethylamine in gut by bacteria,
followed by absorption but inability to
metabolize to odorless trimethylamine
N-oxide

Lactose	Abdominal pain, bloating, diarrhea	Lactase deficiency	Mallinson, 1987
intolerance
Fructose-	Abdominal pain, vomiting, diarrhea,	Reduced activity of hepatic aldolase	Frankland, 1987; Catto-
containing	hypoglycemia	B toward fructose-1-phosphate	Smith and Adams, 1993
foods

1070	UNIT 7 APPLICATIONS OF TOXICOLOGY

sults in fermentation of lactose to lactic acid and an osmotic effect in the bowel, with resultant symptoms of malabsorption and diarrhea. Lactose intolerance is lowest in northern Europe at 3 to 8 percent of the population; it reaches 70 percent in southern Italy and Turkey and nearly 100 percent in southeast Asia (GudmandHoyer, 1994; Anderson and Sogn, 1984).

Anaphylactoid Reactions Anaphylactoid reactions are historically thought of as reactions mimicking anaphylaxis (and other “allergic-type” responses, including though not limited to itching, chronic urticaria, angioedema, exacerbation of atopic eczema, rhinitis, bronchial obstruction, asthma, diarrhea and other intestinal disturbances, and vasomotor headaches) through direct application of the primary mediator of anaphylactic reactions: histamine. Ingestion of scombroid fish (e.g., tuna, mackerel, bonito) as well as some nonscombroid fish (mahimahi and bluefish) that have been acted upon by microorganisms (most commonly Proteus morganii, Proteus vulgaris, Clostridium spp., Escherichia coli, Salmonella spp., and Shigella spp.) to produce histamine may result in an anaphylactoid reaction also called scombrotoxicosis (Table 30-21) (Clark et al., 1999). The condition was reported to be mimicked by the direct ingestion of 90 mg of histamine in unspoiled fish (van Geldern et al., 1992), but according to Taylor (1986), the effect of simply ingesting histamine does not produce the equivalent effect. Instead, Taylor stated that histamine ingested with spoiled fish appears to be much more toxic than is histamine ingested in an aqueous solution, as a result of the presence of histamine potentiators in fish flesh. These potentiators included putrefactive amines (putrescine and cadaverine) and pharmacologic potentiators such as aminoguanidine and isoniazid (histaminase inhibitors). The mechanism of potentiation involves the inhibition of intestinal histaminemetabolizing enzymes (diamine oxidase), which causes increased

Table 30-21

Anaphylactoid Reactions to Food

histamine uptake. Scombrotoxicosis in the absence of high histamine levels (less than the U.S. FDA action level for tuna of 50 mg histamine/100 g fish) was reported by Gessner et al., 1996. Melnik et al., (1997) proposed that anaphylactoid responses may be the sum of several mechanisms: (1) an increased intake of biogenic amines (including histamine) with food, (2) an increased synthesis by the intestinal flora, (3) a diminished catabolism of biogenic amines by the intestinal mucosa, and (4) an increased release of endogenous histamine from mast cells and basophils by histaminereleasing food. Further, improvement was observed in 50 percent of patients with histamine intolerance and atopic eczema who maintained a histamine-depleted diet. Ijomah and coworkers (1991) claimed that dietary histamine is not a major determinant of scombrotoxicosis, since potency is not positively correlated with the dose and volunteers tend to fall into susceptible and nonsusceptible subgroups. Ijomah and coworkers (1991) suggested that endogenous histamine released by mast cells plays a significant role in the etiology of scombrotoxicosis, whereas the role of dietary histamine is minor. An exception to this endogenous histamine theory was described by Morrow and colleagues (1991), who found the expected increase in urinary histamine in scombroid-poisoned individuals but did not find an increase in urinary 9 ,11 -dhydroxy- 15-oxo-2,3,18,19-tetranorprost-5-ene-1,20-dioic acid, the principal metabolite of prostaglandin D2, a mast cell secretory product; thus, no mast-cell involvement was indicated. Rittweger et al. (1994) have reported an increase in urinary immunoreaction angiotensin I and angiotensin II following oral provocation tests to patients with a history of anaphylactoid reactions to drugs, foods, and food additives, but unfortunately there are no reports describing urinary angiotensin levels following oral histamine administration.

Smith (1991) described sulfite-induced bronchospasm (sometimes leading to asthma), which was first noticed as an acute sen-

FOOD

REACTION

MECHANISM

REFERENCE

Western Australian	Erythema and urticaria of the skin,
salmon (Arripis	facial flushing and sweating,
truttaceus)	palpitations, hot flushes of the
	body, headache, nausea, vomiting,
	and dizziness
Fish (spiked	Facial flushing, headache
with histamine)
Cape yellow tail	Skin rash, diarrhea, palpitations,
(fish) (Seriola	headache, nausea and abdominal
lalandii)	cramps, paresthesia, unusual taste
	sensation, and breathing difficulties
Sulfite sensitivity	Bronchospasm, asthma
Tuna, albacore,	Reaction resembling an acute allergic
mackerel, bonito,	reaction
mahimahi, and
bluefish
Cheese	Symptoms resembling acute allergic
	reaction

Scombroid poisoning; high histamine	Smart, 1992
levels demonstrated in the fish
Histamine poisoning; histamine	Van Gelderen et al.,
concentration in plasma correlated	1992
closely with histamine dose ingested
Scombroid poisoning, treated with	Muller et al., 1992
antihistamines
Sulfite oxidase deficiency to meta-	Smith, 1991
bisulfites in foods and wine
Scombroid poisoning treated with	Lange, 1988
antihistamines and cimetidine
Responds to antihistamines; histamine	Taylor, 1986
poisoning?

CHAPTER 30 FOOD TOXICOLOGY

1071

sitivity to metabisulfites sprayed on restaurant salads (and salad bars) and in wine. Sulfite is normally detoxicated rapidly to inorganic sulfate by the enzyme sulfite oxidase. In sensitive individuals, there is apparently a deficiency in this enzyme, making them supersensitive to sulfites. (The FDA has taken the position that the addition of sulfite to food is safe only when properly disclosed on the food label.)

Pharmacologic Food Reactions Also referred to as “false food allergies” (Moneret-Vautrin, 1987), these adverse reactions are characterized by exaggerated responses to pharmacologic agents in food (Table 30-22). These reactions are distinguished from other classifications because they are not associated with a specific anomaly of metabolism (e.g., lactose intolerance or favism) but may be a receptor anomaly instead. These, then, are common pharmacologic agents acting in a very predictable manner, but at exceptionally low levels.

Metabolic Food Reactions Metabolic food reactions are distinct from other categories of adverse reactions in that the foods are more or less commonly eaten and demonstrate toxic effects only when eaten to excess or improperly processed (Table 30-23). The susceptible population exists as a result of its own behavior—that is, the “voluntary” consumption of food as a result of a limited food supply or an abnormal craving for a specific food. Such an abnormal craving was reported by Bannister and associates (1977), who noted hypokalemia leading to cardiac arrest in a 58-year-old woman who had been eating about 1.8 kg of licorice per week. In “glycyrrhizism,” or licorice intoxication, glycyrrhizic acid is the active component, with an effect resembling that of aldosterone, which suppresses the renin-angiotensin-aldosterone axis, resulting in the loss of potassium. Clinically, hypokalemia with alkalosis, cardiac arrhythmias, and muscular symptoms, together with sodium retention, edema, and severe hypertension are observed. The syndrome may develop at a level of 100 g licorice per day but gradually abates upon withdrawal of the licorice (Tonnesen, 1979).

This category also includes the ingestion of improperly prepared food such as cassava or cycad, which, if prepared properly will result in a toxin-free food. For example, cycad (Cacaos circinalis) is a particularly hardy tree in tropical to subtropical habitats around the world. Cycads often survive when other crops have been destroyed (e.g., a natural disaster such as a typhoon or drought) and therefore may serve as an alternative source of food. Among people who have used cycads for food, the method of detoxification is remarkably similar despite the wide range of this plant: the seeds and stems are cut into small pieces and soaked in water for several days; they are then dried and ground into flour. The effec-

Table 30-22

Pharmacologic Reactions to Food

tiveness of leaching the toxin (cycasin) from the bits of flesh is most directly dependent on the size of the pieces, the duration of soaking, and the number of water changes. Shortcuts in processing may have grave consequences (Matsumoto, 1985).

Importance of Labeling

Food labeling allows susceptible individuals to avoid foods containing ingredients that may be harmful to them, such as allergens or substances they may be intolerant of, such as lactose. Thus, if a food contained an allergy-causing protein, this would have to be indicated on the label. The FDA has indicated that, at this time, they are not aware of any information that foods developed through genetic engineering differ as a class in any attribute from foods developed through conventional means, and that such foods would therefore not warrant a special label (Thompson, 2000). FDA allows companies to include on the label of a product any statement as long as the statement is truthful and not misleading.

TOLERANCE SETTING FOR

SUBSTANCES IN FOODS

Pesticide Residues

A pesticide is defined under the FD&C Act as any substance used as a pesticide, within the meaning of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), in the production, storage, or transportation of raw agricultural commodities (food in its raw or natural state) [section 201(q)]. The Pesticide amendments of 1956 to the FD&C Act (section 408) were the first amendments to the FD&C Act requiring premarket clearance evaluations of the safety of chemicals added to food. Currently, the U.S. Environmental Protection Agency (EPA) is responsible for evaluating the safety of pesticides before issuing tolerances.

The regulation of pesticides and their safety is accomplished under both FIFRA and the FD&C Act. FIFRA governs the registration of pesticides. Registration addresses specific uses of a pesticide, and without such registration a pesticide cannot be lawfully sold for such use in the United States. A major part of the registration process involves tolerance setting. Pesticides intended for use on food crops must be granted tolerances or exempted from tolerances under the FD&C Act.

Tolerances for raw agriculture commodities (RAC’s) were established under section 408 of the FD&C Act. If the pesticide chemical was found to concentrate in any of the processed fractions from the processing studies on the food crops (usually at least 1.5 or 2.0 of the residue concentration in the RAC), the residues in the

FOOD	REACTION	MECHANISM	REFERENCE
Cheese, red wine	Severe headache, hypertension	Tyramine from endogenous or ingested	Settipane, 1987
		tyrosine
Nutmeg	Hallucinations	Myristicin	Anderson and Sogn, 1984
Coffee, tea	Headache, hypertension	Methylxanthine (caffeine) acting as a	Anderson and Sogn, 1984
		noradrenergic stimulant
Chocolate	Headache, hypertension	Methylxanthine (theophylline) acting	Anderson and Sogn, 1984
		as a noradrenergic stimulant

1072	UNIT 7 APPLICATIONS OF TOXICOLOGY
Table 30-23
Metabolic Food Reactions
FOOD	REACTION	MECHANISM	REFERENCE
Lima beans,	Cyanosis	Cyanogenic glycosides releasing	Anderson and Sogn, 1984
cassava roots,		hydrogen cyanide on contact with
millet (sorghum)		stomach acid
sprouts, bitter
almonds, apricot
and peach pits
Cabbage family,	Goiter (enlarged thyroid)	Isothiocyanates, goitrin, or	Anderson and Sogn, 1984;
turnips, soybeans,		S-5-vinyl-thiooxazolidone	vanEtten and Tookey,
radishes, rapeseed		interferes with utilization of iodine	1985
and mustard
Unripe fruit of	Severe vomiting, coma,	Hypoglycin A, isolated from the	Evans, 1985
the tropical tree	and acute hypoglycemia	fruit, may interfere with oxidation
Blighia sapida,	sometimes resulting in death,	of fatty acids, so that glycogen
common in	especially among the	stores have to be metabolized for
Caribbean and	malnourished	energy, with depletion of carbo-
Nigeria		hydrates, resulting in hypoglycemia
Leguminosae,	Lathyritic symptoms:	L-2-4-Diaminobutyric acid inhibition	Evans, 1985
Cruciferae	neurological symptoms of	of ornithine transcarbamylase of the
	weakness, leg paralysis, and	urea cycle, inducing ammonia toxicity
	sometimes death
Licorice	Hypertension, cardiac	Glycyrrhizic acid mimicking	Farese et al., 1991
(glycyrrhizic acid)	enlargement, sodium	mineralocorticoids
	retention
Polar bear and	Irritability, vomiting, increased	Vitamin A toxicity	Bryan, 1984
Chicken liver	intracranial pressure, death
Cycads	Amyotrophic lateral sclerosis	Cycasin (methylazoxymethanol);	Matsumoto, 1985; Sieber
(cycad flour)	(humans), hepatocarcino-	primary action is methylation,	et al., 1980
	genicity (rats and nonhuman	resulting in a broad range of
	primates)	effects from membrane destruction
		to inactivation of enzyme systems

processed fraction(s) were considered to be intentional food additives and were required to be assigned “Food Additive Tolerances” under Section 409 of the act. If the pesticide chemical in question had been classified by the EPA as a human or animal carcinogen, the Delaney clause would then be invoked, and the section 409 food additive tolerance(s) could be denied on that basis.

Under the new Food Quality Protection Act (FQPA) of 1996, section 201(s) of the FD&C Act excludes pesticides from the definition of food additive — even in the case of concentration of residues in processed fractions. Consequently, the Delaney clause is no longer applicable for pesticides. The Delaney clause has not been repealed from section 409 and continues to apply to intentional food additives other than pesticides. In the case of concentration of pesticide residues in a processed fraction above the section 408 tolerances established for the RAC, an additional tolerance for that processed fraction is still established, but now under section 408 rather than section 409.

The FQPA requires that an additional tenfold safety factor “shall be applied for infants and children to take into account potential preand post-natal toxicity and completeness of the data with respect to exposure and toxicity to infants and children.” Therefore the “default” assumption is that the additional 10 safety

factor will be applied to the chemical safety assessment resulting in a total safety factor of 1000 . It further states, however, that “the Administrator may use a different margin of safety for the pesticide chemical residue only if, on the basis of reliable data, such margin will be safe for infants and children.” Therefore, the additional 10 safety factor may be reduced depending on such things as adequacy of exposure assessment, adequacy of the toxicologic data-base, and the nature and severity of any adverse effects observed in these studies, the most important being the adequacy of the toxicologic data base.

Drugs Used in Food-Producing Animals

An animal drug “means any drug intended for use for animals other than man” [section 201(w) of the FD&C Act]. Animal drugs, which typically are used for growth promotion and increased food production, present a complex problem in the safety assessment of animal drug residues in human food. Determination of the potential human health hazards associated with animal drug residues is complicated by the metabolism of an animal drug, which results in residues of many potential metabolites. The sensitivity of modern analytic methodologies designed to quantitate small amounts of

CHAPTER 30 FOOD TOXICOLOGY

1073

drugs and their various metabolites has made evaluation more complex.

The primary factors that must be considered in the evaluation of animal drugs are (1) consumption and absorption by the target animal, (2) metabolism of the drug by the target food animal, (3) excretion and tissue distribution of the drug and its metabolites in food animal products and tissues, (4) consumption of food animal products and tissues by humans, (5) potential absorption of the drug and its metabolites by humans, (6) potential metabolism of the drug and its metabolites by humans, and (7) potential excretion and tissue distribution in humans of the drug, its metabolites, and the secondary human metabolites derived from the drug and its metabolites. Thus, the pharmacokinetic and biotransformation characteristics of both the animal and the human must be considered in an assessment of the potential human health hazard of an animal drug.

When an animal drug is considered GRAS, the safety assessment of the drug is handled as described under the section on GRAS, above. With respect to new animal drugs, safety assessment is concerned primarily with residues that occur in animal food products (milk, cheese, etc.) and edible tissues (muscle, liver, etc.). Toxicity studies in the target species (chicken, cow, pig, etc.) should provide data on metabolism and the nature of metabolites along with information on the drug’s pharmacokinetics. If this information is not available, these studies must be performed using the animal species that is likely to be exposed to the drug. During this phase, the parent drug and its metabolites are evaluated both qualitatively and quantitatively in the animal products of concern (eggs, milk, meat, etc.). This may involve the development of sophisticated analytic methodologies. Once these data are obtained, it is necessary to undertake an assessment to determine potential human exposure to these compounds from the diet and other sources. If adequate toxicity data are available, it is possible to undertake a safety assessment pursuant to the establishment of a tolerance.

To comply with the congressional intent regarding the use of animal drugs in food-producing animals as required in the “no residue” provision of the Delaney clause, the FDA began to build a system for conducting risk assessment of carcinogens in the early 1970s (FDA, 1977). In the course of developing a policy and/or regulatory definition for “no residue,” the FDA was compelled to address the issue of residues of metabolites of animal drugs known to induce cancer in humans or animals. As the number of metabolites may range into the hundreds, it became apparent that, as a practical matter, not every metabolite could be tested with the same thoroughness as the parent animal drug. This forced the FDA to consider threshold assessment for the first time. Threshold assessment combines information on the structure and in vitro biological activity of a metabolite for the purpose of determining whether carcinogenicity testing is necessary (Flamm et al., 1994). If testing is necessary and the substance is found to induce cancer, the FDA’s definition states that a lifetime risk of one in a million as determined by a specified methodology is equivalent to the meaning of “no residue” as intended by Congress.

Unavoidable Contaminants

Certain substances—such as polychlorinated biphenyls (PCB’s) or heavy metals—are unavoidable in food because their widespread industrial applications or their presence in the earth’s crust have resulted in their becoming a persistent and ubiquitous contaminant in the environment. As a result, foods and animal feeds, principally

those of animal and marine origin, contain unavoidable contaminants at some level. Tolerances for residues of unavoidable contaminants are established for foods and food ingredients to ensure that they are safe under expected or intended conditions of use.

Heavy Metals There are 92 natural elements; approximately 22 are known to be essential nutrients of the mammalian body and are referred to as micronutrients (Concon, 1988). Among the micronutrients are iron, zinc, copper, manganese, molybdenum, selenium, iodine, cobalt, and even aluminum and arsenic. However, among the 92 elements, lead, mercury, and cadmium are familiar as contaminants or at least have more specifications setting their limits in food ingredients (e.g., Food Chemicals Codex, 1996). The prevalence of these elements as contaminants is due to their ubiquity in nature but also to their use by humans.

Lead Although the toxicity of lead is well known, lead may be an essential trace mineral. A lead deficiency induced by feeding rats 50 ppb (versus 1000 ppb in controls) over one or more generations produced effects on the hematopoietic system, decreased iron stores in the liver and spleen, and caused decreased growth (Kirchgessner and Reichmayer-Lais, 1981), but apparently not as a result of an effect on iron absorption (Reichmayer-Lais and Kirchgessner, 1985). Although the toxic effects of lead are discussed elsewhere in this text, it is important to note that the effects are profound (especially in children) and appear to be long-lasting, since mechanisms for excretion appear to be inadequate in comparison to those for uptake (Linder, 1991).

Over the years, recognition of the serious nature of lead poisoning in children has caused the World Health Organization (WHO) and FDA to adjust the recommended tolerable total lead intake from all sources of not more than 100 g/day for infants up to 6 months of age and not more than 150 g/day for children from 6 months to 2 years of age to the considerably lower range of 6 to 18 g/day as a provisional tolerable range for lead intake in a 10-kg child.

Initiatives to reduce the level of lead in foods, such as the move to eliminate lead-soldered seams in soldered food cans that was begun in the 1970s and efforts to eliminate leachable lead from ceramic glazes, have resulted in a steady decline in dietary lead intake. Although food and water still contribute lead to the diet, data from the FDA’s Total Diet Study indicated a reduction in mean dietary lead intake for adult males from 95 g/day in 1978 to 9 g/day in the period 1986–1988 (Shank and Carson, 1992).

Some lead sources are difficult to curtail, as lead often survives food processing; for example, lead in wheat remains in the finished flour (Linder, 1991). Therefore, reducing the contribution from dietary sources remains a challenge, but elimination of leadsoldered cans, lead-soldered plumbing, and especially the removal of tetraethyl lead as a gasoline additive have produced substantial reductions in lead ingestion. What is needed now is continued vigilance of largely imported lead-based ceramic ware, leadcontaining calcium supplements, and lead leaching into groundwater (Shank and Carson, 1992).

Arsenic Arsenic is a ubiquitous element in the environment; it ranks 20th in relative abundance among the elements of the earth’s crust and 12th in the human body (Concon, 1988). (Since arsenic is discussed in detail elsewhere in this text, the discussion here is limited to its relationship to foods.) There is some competition for arsenic absorption with selenium, which is known to reduce arsenic toxicity; arsenic is also known to antagonize iodine metabolism and inhibit various metabolic processes, as a result affecting a num-

1074	UNIT 7 APPLICATIONS OF TOXICOLOGY

ber of organ systems. There are a number of sources of arsenic, including drinking water, air, and pesticides (Newberne, 1987), but arsenic consumed via food is largely in proportion to the amount of seafood eaten (74 percent of the arsenic in a market basket survey came from the meat-poultry-fish group, of which seafood consistently has the highest concentration) (Johnson et al., 1981). Although arsenic is used as an animal feed additive, this source does not contribute much to the body burden, as 0.1% arsanilic acid or docecylamine-p-chlorophenylarsonate fed to turkeys resulted in tissue residues of only 0.31 and 0.24 ppm in fresh muscle (Underwood, 1973).

Acute poisoning with arsenic often results from mistaking arsenic for sugar, baking powder, and soda and adding it to food. The time between exposure and symptoms is 10 min to several days, and the symptoms include burning of the mouth or throat, a metallic taste, vomiting, diarrhea (watery and bloody), borborigmi (rumbling of the bowles caused by movement of gas in the GI tract), painful tenesmus (spasm of the anal or vesical sphincter), hematuria, dehydration, jaundice, oliguria, collapse, and shock. Headache, vertigo, muscle spasm, stupor, and delirium may occur (Bryan, 1984).

Cadmium Cadmium is a relatively rare commodity in nature and is usually associated with shale and sedimentary deposites. It is often found in association with zinc ores and in lesser amounts in fossil fuel. Although rare in nature, it is a nearly ubiquitous element in American society because of its industrial uses in plating, paint pigments, plastics, and textiles. Exposure of humans often occurs through secondary routes as a result of dumping at smelters and refining plants, disintegration of automobile tires (which contain rubber-laden cadmium), subsequent seepage into the soil and groundwater, and inhalation of combustion of cadmium-containing materials. The estimated yearly release of cadmium from automobile tires ranges from 5.2 to 6.0 metric tons (Davis, 1970; Lagerwerff and Specht, 1971).

Although, like mercury, cadmium can form alkyl compounds, unlike mercury, the alkyl derivatives are relatively unstable and consumption almost always involves the inorganic salt. Of two historical incidents of cadmium poisoning, one involved the use of

Table 30-24

Examples of Levels of Chlorinated Hydrocarbons in British Food

cadmium-plated containers to hold acidic fruit slushes before freezing. Up to 13 to 15 ppm cadmium was found in the frozen confection, 300 ppm in lemonade, and 450 in raspberry gelatin. Several deaths resulted. A more recent incident of a chronic poisoning involved the dumping of mining wastes into rice paddies in Japan. Middle-aged women who were deficient in calcium and had had multiple pregnancies seemed to be the most susceptible. Symptoms included hypercalciuria; extreme bone pain from osteomalacia; lumbago; pain in the back, shoulders, and joints; a waddling gait; frequent fractures; proteinuria; and glycosuria. The disease was called itai itai (“ouch-ouch disease”) as a result of the pain with walking. The victims had a reported intake of 1000 g/day, approximately 200 times the normal intake in unexposed populations (Yamagata and Shigematsu, 1970). Cadmium exposure also has been associated with cancer of the breast, lung, large intestine, and urinary bladder (Newberne, 1987).

Chlorinated Organics Chlorinated organics have been with us for some time, and given their stability in water and resistance to oxidation, ultraviolet light, microbial degradation, and other sources of natural destruction, chlorinated organics will continue to reside in the environment for some time to come, albeit in minute amounts. However, with the introduction of chlorinated hydrocarbons as pesticides in the 1930s, diseases associated with an insect vector such as malaria were nearly eliminated. In the industrialized world, chlorinated organics brought the promise of nearly universal solvents, and their extraordinary resistance to degradation made them suitable for use as heat transfer agents, carbonless copy paper, and fire retardants (Table 30-24).

As persistent as these substances are in the environment and despite the degree of toxicity that might be implied, the possible hazard from chlorinated substances is relatively low. Ames et al. (1987) described a method for interpreting the differing potencies of carcinogens and human exposures: the percentage HERP (human exposure dose/rodent potency dose). Using this method, they demonstrated that the hazard from trichloroethylene-contaminated water in Silicon Valley or Woburn, Massachusetts, or the daily dietary intake from DDT (or its product, DDE) at a HERP of 0.0003

Chlorinated Hydrocarbons, ug/kg

FOOD	CHCl3	CCl4	TCE	TCEY	TTCE	PCE	HCB	HCBD	Per CE
Milk	5.0	0.2		0.3	—	—	1.0	0.08	0.3
Cheese	33.0	5.0		3.0	0.0	0.0	0.0	0.0	2.0
Butter	22.0	14.0		10.0	—	—	—	2.0	13.0
Chicken eggs	1.4	0.5		0.6	0.0	0.0	0.0	0.0	0.0
Beef steak	4.0	7.0	3.0	16.0	0.0	0.0	0.0	0.0	0.9
Beef fat	3.0	8.0	6.0	12.0					1.0
Pork liver	1.0	9.0	4.0	22.0	0.5	0.4			5.0
Margarine	3.0	6.0	—		0.8				7.0
Tomatoes	2.0	4.5	—	1.7	1.0		70.1	0.8	1.2
Bread (fresh)	2.0	5.0	2.0	7.0	—	—	—	—	1.0
Fruit drink (canned)	2.0	0.5	—	5.0		0.8			2.0

KEY: CHCl3 chloroform; CCl4 carbon tetrachloride; TCE trichloroethane; TCEY trichloroethylene; TTCE tetrachloroethane; PCE pentachloroethane; HCB hexachlorobenzene; HCBD hexachlorobutadiene; Per CE perchloroethylene.

SOURCE: Modified from McConnell et al., 1975, with kind permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington OX5 1GB, UK.

CHAPTER 30 FOOD TOXICOLOGY

1075

to 0.004 percent is considerably less than the hazard presented by the consumption of symphytine in a single cup of comfrey herb tea (0.03 percent) or the hazard presented by aflatoxin in a peanut butter sandwich (0.03 percent). The FDA’s authority to set tolerances has been used only once in establishing levels for polychlorinated biphenyls (21 CFR 109.15 and 109.30).

Although the possibility always exists, there have been only a few incidents of mass poisonings via food, two of which involved contaminated cooking oil. The first became known as yusho, or rice oil disease, from rice oil contamination by polychlorinated biphenyls (PCBs). The most vulnerable individuals were newborn infants of poisoned mothers. The liver and skin were the most severely affected. Symptoms included dark brown pigmentation of nails; acne-like eruptions; increased eye discharge; visual disturbances; pigmentation of the skin, lips, and gingiva; swelling of the upper eyelids; hyperemia of the conjunctiva; enlargement and elevation of hair follicles; itching; increased sweating of the palms; hyperkeratotic plaques on the soles and palms; and generalized malaise. Recovery requires several years (Anderson and Sogn, 1984). The second incident has become known as Spanish toxic oil syndrome, and although details are still not fully known, it occurred after aniline-contaminated rapeseed oil was distributed as cooking oil in Spain in 1981. Approximately 20,000 people were affected and there were several deaths. Because symptoms were unique— including respiratory effects, eosinophilia, and muscle wasting— but not typical of aniline poisoning, the exact etiologic agent is still unknown. Because the source of the aniline may have been improperly cleaned tank trucks that had imported industrial chemicals, three hypotheses have been offered: the etiologic agent may have been (1) a contaminant in the aniline, (2) a contaminant introduced during transportation, or (3) a reaction product of normal oil components and the potential contaminants (the fraction of the oil most commonly associated with toxicity contained C18:3 anilide, also called oleyl anilide and “fatty acid anilide”) (Borda et al., 1998; Posada de la Paz et al., 1996; Wood et al., 1994).

Nitrosamines, Nitrosamides, and N-Nitroso Substances Nitrogenous compounds such as amines, amides, guanidines, and ureas can react with oxides of nitrogen (NOx) to form N-nitroso compounds (NOCs) (Hotchkiss et al., 1992). The NOCs may be divided into two classes: the nitrosamines, which are N-nitroso derivatives of secondary amines, and nitrosamides, which are N-nitroso derivatives of substituted ureas, amides, carbamates, guanidines, and similar compounds (Mirvish, 1975).

Nitrosamines are stable compounds, while many nitrosamides have half-lives on the order of minutes, particularly at pH 6.5. Both classes have members that are potent carcinogens, but by different mechanisms. In general, the biological activity of an NOC is thought to be related to alkylation of genetic macromolecules. N-nitrosamines are metabolically activated by hydroxylation at an-carbon. The resulting hydroxyalkyl moiety is eliminated as an aldehyde, and an unstable primary nitrosamine is formed. The nitrosamine tautomerizes to a diazonium hydroxide and ultimately to a carbonium ion. Nitrosamides spontaneously decompose to a carbonium ion at physiologic pH by a similar mechanism (Hotchkiss et al., 1992). This is consistent with in vitro laboratory findings because nitrosamines require S9 for activity and nitrosamides are mutagenic de novo.

NOCs originate from two sources: environmental formation and endogenous formation (Table 30-25). Environmental sources have declined over the last several years but still include foods (e.g.,

Table 30-25

Sources of Dietary NOCs

The use of nitrate and/or nitrite as intentional food additives, both of which are added to fix the color of meats, inhibit oxidation, and prevent toxigenesis

Drying processes in which the drying air is heated by an open flame source. NOx is generated in small amounts through the oxidation of N2, which nitrosates amines

in the foods. This is the mechanism for contamination of malted barley products

NOCs can migrate from food contact materials such as rubber bottle nipples

NOCs can inhabit spices which may be added to food Cooking over open flames (e.g., natural gas flame) can

result in NOC formation in foods by the same mechanism as drying

SOURCE: Hotchkiss et al., 1992, with permission.

nitrate-cured meats) and beverages (e.g., malt beverages), cosmetics, occupational exposure, and rubber products (Hotchkiss, 1989). NOCs formed in vivo may actually constitute the greatest exposure and are formed from nitrosation of amines and amides in several areas, including the stomach, where the most favorable conditions exist (pH 2 to 4), although consumption of H2-receptor blockers or antacids decreases the formation of NOCs.

Environmentally, nitrite is formed from nitrate or ammonium ions by certain microorganisms in soil, water, and sewage. In vivo, nitrite is formed from nitrate by microorganisms in the mouth and stomach, followed by nitrosation of secondary amines and amides in the diet. Sources of nitrate and nitrite in the diet are given in Table 30-26. Many sources of nitrate are also sources of vitamin C. Another possibly significant source of nitrate is well water; although the levels are generally in the range of 21 M, average levels of 1600 M (100 mg/L) have been reported (Hotchkiss et al., 1992). However, on the average, western diets contain 1 to 2 mmol nitrate per person per day (Hotchkiss et al., 1992). Nitrosation reactions can be inhibited by preferential, competitive neutralization of nitrite with naturally occurring and synthetic materials such as vitamin C, vitamin E, sulfamate, and antioxidants such as BHT, BHA, gallic acid, and even amino acids or proteins (Hotchkiss, 1989; Hotchkiss et al., 1992).

N-nitrosoproline is the most common nitrosoamine present in humans and is excreted virtually unchanged in the urine. The basal rate of urinary excretion of nitrosoproline, which is claimed to be noncarcinogenic, is 2 to 7 g/day in subjects on a low-nitrate diet (Oshima and Bartsch, 1981). Epidemiologic studies have not provided evidence of a causal association between nitrate exposure and human cancer, nor has a causal link been shown between N-nitroso compounds preformed in the diet or endogenously synthesized and the incidence of human cancer (Gangolli 1999).

Food-Borne Molds and Mycotoxins Molds have served humans for centuries in the production of foods (e.g., ripening of cheese) and have provided various fungal metabolites with important medicinal uses; they also may produce metabolites with the potential to produce severe adverse health effects. Mycotoxins represent a diverse group of chemicals that can occur in a variety of plant foods. They also can occur in animal products derived from ani-

1076		UNIT 7 APPLICATIONS OF TOXICOLOGY
Table 30-26
Nitrate and Nitrite Content of Food
	NITRATE,	NITRITE,		NITRATE,	NITRITE,
VEGETABLES	PPM	PPM	MEAT	PPM	PPM
Artichoke	12	0.4	Unsmoked side bacon	134	12
Asparagus	44	0.6	Unsmoked back bacon	160	8
Green beans	340	0.6	Peameal bacon	16	21
Lima beans	54	1.1	Smoked bacon	52	7
Beets	2400	4	Corned beef	141	19
Broccoli	740	1	Cured corned beef	852	9
Brussels sprouts	120	1	Corned beef brisket	90	3
Cabbage	520	0.5	Pickled beef	70	23
Carrots	200	0.8	Canned corn beef	77	24
Cauliflower	480	1.1	Ham	105	17
Celery	2300	0.5	Smoked ham	138	50
Corn	45	2	Cured ham	767	35
Radish	1900	0.2	Belitalia (garlic)	247	5
Rhubarb	2100	NR*	Pepperoni (beef)	149	23
Spinach	1800	2.5	Summer sausage	135	7
Tomatoes	58	NR	Ukranian sausage (Polish)	77	15
Turnip	390	NR	German sausage	71	17
Turnip greens	6600	2.3

*NR not reported.

SOURCE: Hotchkiss et al., 1992, with permission

mals that consume contaminated feeds. The current interest in mycotoxicoses was generated by a series of reports in 1960–1963 that associated the death of turkeys in England (so-called turkey X disease) and ducklings in Uganda with the consumption of peanut meal feeds containing mold products produced by Aspergillus flavus (Stoloff, 1977). The additional discovery of aflatoxin metabolites (for example, aflatoxin M1) led to more intensive studies of mycotoxins and to the identification of a variety of these compounds associated with adverse human health effects, both retrospectively and prospectively.

Moldy foods are consumed throughout the world during times of famine, as a matter of taste, and through ignorance of their adverse health effects. Epidemiologic studies designed to ascertain the acute or chronic effects of such consumption are few. Data from animal studies indicate that the consumption of food contaminated with mycotoxins has a high potential to produce a variety of human diseases (Miller, 1991).

With some exceptions, molds can be divided into two main groups: “field fungi” and “storage fungi.” The former group contains species that proliferate in and under field conditions and do not multiply once grain is in storage. Field fungi are in fact superseded and overrun by storage fungi if conditions of moisture and oxygen allow. Thus, for instance, Fusarium spp., a field fungus commonly found on crops, is seldom found after about 6 weeks of storage, its place being taken by Aspergillus and Penicillium, both of which represent several species of storage fungi (Harrison, 1971). However, the presence of mold does not guarantee the presence of mycotoxin, which is elaborated only under certain conditions. Further, more than one mold can produce the same mycotoxin (e.g., both Aspergillus and Penicillium may produce the mycotoxin cyclopiazonic acid) (Truckness et al., 1987; El-Banna et al., 1987). Also, more than one mycotoxin may be present in an intoxication; that is, as in the outbreak of turkey X disease, there

is evidence that aflatoxin and cyclopiazonic acid both exerted an effect, but the profound effects of aflatoxin overshadowed those of cyclopiazonic acid (Miller, 1989). Although there are many different mycotoxins and subgroups (Table 30-27), this discussion is confined largely to two of the more toxicologically and economically important ones: the aflatoxins and trichothecenes.

Aflatoxins Among the various mycotoxins, the aflatoxins have been the subject of the most intensive research because of the extremely potent hepatocarcinogenicity and toxicity of aflatoxin B1 in rats. Epidemiologic studies conducted in Africa and Asia suggest that it is a human hepatocarcinogen, and various other reports have implicated the aflatoxins in incidences of human toxicity (Krishnamachari et al., 1975; Peers et al., 1976).

Generally, aflatoxins occur in susceptible crops as mixtures of aflatoxins B1, B2, G1, and G2, with only aflatoxins B1 and G1 demonstrating carcinogenicity. A carcinogenic hydroxylated metabolite of aflatoxin B1 (termed aflatoxin M1) can occur in the milk from dairy cows that consume contaminated feed. Aflatoxins may occur in a number of susceptible commodities and products derived from them, including edible nuts (peanuts, pistachios, almonds, walnuts, pecans, Brazil nuts), oil seeds (cottonseed, copra), and grains (corn, grain sorghum, millet) (Stoloff, 1977). In tropical regions, aflatoxin can be produced in unrefrigerated prepared foods. The two major sources of aflatoxin contamination of commodities are field contamination, especially during times of drought and other stresses, which allow insect damage that opens the plant to mold attack, and inadequate storage conditions. Since the discovery of their potential threat to human health, progress has been made in decreasing the level of aflatoxin in specific commodities. Control measures include ensuring adequate storage conditions and careful monitoring of susceptible commodities for aflatoxin level and the banning of lots that exceed the action level for aflatoxin B1.

	CHAPTER 30 FOOD TOXICOLOGY		1077
Table 30-27
Selected Mycotoxins Produced by Various Molds
			COMMODITIES
MYCOTOXIN	SOURCE	EFFECT	CONTAMINATED
Aflatoxins B1, B2, G1, G2	Aspergillus flavus, parasiticus	Acute aflatoxicosis, carcinogenesis	Corn, peanuts, and
			and others
Aflatoxin M1	Metabolite of AFB1	Hepatotoxicity	Milk
Fumonisins B1, B2, B3,	Fusarium moniliforme	Carcinogenesis	Corn
B4, A1, A2
Trichothecenes	Fusarium, Myrothecium	Hematopoietic toxicity, meningeal	Cereal grains, corn
		hemorrhage of brain, “nervous’’
		disorder, necrosis of skin,
		hemorrhage in mucosal epithelia
		of stomach and intestine
T-2 toxin	Trichoderma		Corn, barley, sorghum
Trichodermin	Cephalosporium
Zearalenones	Fusarium	Estrogenic effect	Corn, grain
Cyclopiazonic acid	Aspergillus, Penicillium	Muscle, liver, and splenic toxicity	Cheese, grains, peanuts
Kojic acid	Aspergillus	Hepatotoxic?	Grain, animal feed
3-Nitropropionic acid	Arthrinium sacchari,	Central nervous system impairment	Sugarcane
	saccharicola, phaeospermum
Citreoviridin	Penicillium citreoviride,	Cardiac beriberi	Rice
	toxicarium
Cytochalasins E, B, F, H	Aspergillus and Penicillium	Cytotoxicity	Corn, cereal grain
Sterigmatocystin	Aspergillus versiolar	Carcinogenesis	Corn
Penicillinic acid	Penicillium cyclopium	Nephrotoxicity, abortifacient	Corn, dried beans,
			grains
Rubratoxins A, B	Penicillium rubrum	Hepatotoxicity, teratogenic	Corn
Patulin	Penicillium patulatum	Carcinogenesis, liver damage	Apple and apple
			products
Ochratoxin	A. ochraceus, P. viridicatum	Balkan nephropathy, carcinogenesis	Grains, peanuts, green
			coffee
Ergot alkaloids	Cladosporium purpurea	Ergotism	Grains

Aflatoxin B1 is acutely toxic in all species studied, with an LD50 ranging from 0.5 mg/kg for the duckling to 60 mg/kg for the mouse (Wogan, 1973). Death typically results from hepatotoxicity. This aflatoxin is also highly mutagenic, hepatocarcinogenic, and possibly teratogenic. A problem in extrapolating animal data to humans is the extremely wide range of species susceptibility to aflatoxin B1. For instance, whereas aflatoxin B1 appears to be the most hepatocarcinogenic compound known for the rat, the adult mouse is essentially totally resistant to its hepatocarcinogenicity.

Aflatoxin B1 is an extremely reactive compound biologically, altering a number of biochemical systems. The hepatocarcinogenicity of aflatoxin B1 is associated with its biotransformation to a highly reactive electrophilic epoxide that forms covalent adducts with DNA, RNA, and protein. Damage to DNA is thought to be the initial biochemical lesion resulting in the expression of the pathologic tumor growth (Miller, 1978). Species differences in the response to aflatoxin may be due in part to differences in biotransformation and susceptibility to the initial biochemical lesion (Campbell and Hayes, 1976; Monroe and Eaton, 1987).

Although the aflatoxins have received the greatest attention among the various mycotoxins because of their hepatocarcinogenicity in certain species, there is no compelling evidence that they have the greatest potential to produce adverse human health effects.

Trichothecenes Trichothecenes represent a group of toxic substances of which it is likely that several forms may be consumed concomitantly. They represent many different chemical entities all containing the trichothecene nucleus, and are produced by a number of commonly occurring molds, including Fusarium, Myrothecium, Trichoderma, and Cephalosporium. The trichothecenes were first discovered during attempts to isolate antibiotics, and although some show antibiotic activity, their toxicity has precluded their pharmacologic use. Trichothecenes most often occur in moldy cereal grains. There have been many reported cases of trichothecene toxicity in farm animals and a few in humans. One of the more famous cases of presumed human toxicity associated with the consumption of trichothecenes occurred in Russia during 1944 around Orenburg, Siberia. The disruption of agriculture caused by World War II led to the overwintering of millet, wheat, and barley in the field. Consumption of these grains resulted in vomiting, skin inflammation, diarrhea, and multiple hemorrhages, among other symptoms. This exposure was fatal to over 10 percent of the affected individuals (Ueno, 1977). The extent of toxicity associated with the trichothecenes in humans and farm animals is currently unknown owing to the number of entities in this group and the difficulty of assaying for these compounds. The acute LD50s of the trichothecenes range from 0.5 to 70 mg/kg, and though there have been reports of possible chronic toxicity associated with certain