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Mycotoxins: Deoxynivalenol and Other Trichothecenes
MYCOTOXINS
Deoxynivalenol and Other Trichothecenes JI Pitt, CSIRO Animal, Food and Health Sciences, North Ryde, NSW, Australia r 2014 Elsevier Inc. All rights reserved.
Glossary Apoptosis Programed cell death that is a normal component of the development and health of multicellular organisms. Conidium (pl. conidia) Microscopic asexual spores produced by molds (filamentous fungi with small fruiting bodies); the main means of propagating many species.
Chemical Characterization Deoxynivalenol (DON) belongs to the family of chemicals known as the trichothecenes, sesquiterpenoid compounds characterized by an epoxy ring at the C-12,13 position. At least 100 trichothecene molecules are known, differentiated by hydroxy or acetyl groups and side chains. DON, still sometimes known as vomitoxin in the USA, is 12,13-epoxy-3,7,15trihydroxy-trichothec-9-en-8-one, CAS number 51481-10-8 (Figure 1). It is the most commonly produced trichothecene in foodstuffs. Nivalenol (NIV), less commonly produced but more toxic, differs from DON by the substitution of a hydroxy group for the hydrogen atom at the C-4 position (Figure 1). The most toxic trichothecene is known as T-2 toxin. It differs from DON in several positions: at C-4, an acetyl ester in place of H; at C-7, H in place of OH; at C-8 an isovalerate ester in place of O; and at C-15, an acetyl ester in place of OH.
Fungal Sources, Physiology, and Ecology DON and NIV are produced by Fusarium graminearum (often listed as Gibberella zeae, its sexual stage), Fusarium culmorum, and some related species. H O
H
H
H
O OH
O
O HO
O H
Deoxynivalenol
OH O
O HO
O H Nivalenol
Figure 1 Structures of deoxynivalenol and nivalenol.
Encyclopedia of Food Safety, Volume 2
O H
Macroconidium (pl. macroconidia) The larger of the two conidial types produced by Fusarium species, and characteristic of the genus. Microconidium (pl. microconidia) The smaller of the two types produced by some Fusarium species, but also produced by a number of other related genera.
Fusarium graminearum grows rapidly on any standard mycological medium including Czapek yeast extract agar (CYA), malt extract agar (MEA), potato dextrose agar (PDA), and dichloran chloramphenicol peptide agar (DCPA). Colonies on CYA and MEA are colored grayish rose, grayish yellow or paler, with reverses orange red to yellowish brown. On PDA, colonies are colored yellowish brown to reddish brown, sometimes with a central mass of red brown to orange areas bearing macroconidia, with the reverse dark red (Figure 2). Characteristic Fusarium conidia, macroconidia, are produced on DCPA or other specialist medium, usually with 5 septa, thick walled, straight to moderately curved, with the basal cell distinctly foot-shaped; microconidia are not produced. Colonies of F. culmorum are similar to those of F. graminearum, but colored pale red to pastel red on CYA, MEA, and PDA, the reverse on CYA and PDA is pastel red to deep red, and on MEA brown to reddish brown. Macroconidia are relatively short, wide, and only slightly curved, with 4–5 septa, 30–45 mm long, with basal cells with a slight to definite notch. Microconidia are not produced. Fusarium graminearum grows from below 5 1C to approximately 35 1C, and optimally at 25 1C. Growth occurs down to 0.90 water activity. Fusarium culmorum has a minimum temperature for growth near 0 1C, a maximum approximately 33 1C, and an optimum near 30 1C. It is capable of growth down to 0.87 water activity, lower than most other Fusarium species that have been studied. Fusarium graminearum occurs in maize, and both F. graminearum and F. culmorum in small grains, especially wheat and barley. These species are rank pathogens, invading plants and grains by causing diseases, known as Gibberella ear rot in maize and Fusarium head blight in wheat, barley, and triticale. Epidemics of Gibberella ear rot require the congruence of three factors: airborne or insectborne spores, inoculation at the susceptible time, and appropriate moisture and temperature. This disease is
doi:10.1016/B978-0-12-378612-8.00193-1
295
296
Mycotoxins: Deoxynivalenol and Other Trichothecenes
(a)
(b)
(c)
Figure 2 Fusarium graminearum. (a) Colonies on PDA and dichloran chloramphenicol peptone agar (DCPA), 7 days, 25 1C; (b) Gibberella zeae perithecium and ascospores, bar ¼25 mm; (c) macroconidia, bar¼ 10 mm.
prevalent in north temperate climates especially in wet years, but is much less common in the tropics. Fusarium head blight affects all commercial cultivars of wheat and barley. Fusarium culmorum always produces DON, but whether DON or NIV is produced by F. graminearum depends on the geographical origin of the fungal strain. T-2 toxin is produced mainly by Fusarium sporotrichioides. This species grows rapidly on CYA, MEA, and PDA, producing white to pale pink mycelium, with reverse pale on CYA, violet brown on MEA and PDA. Macroconidia are similar to those of F. graminearum, but, unlike that species, abundant microconidia are also produced. Fusarium sporotrichioides grows under similar conditions to F. graminearum, except that its minimum temperature is 2 1C. T-2 toxin is produced on grains, but occurs only under cool conditions.
History Before 1950, feed refusal in pigs in the US and human toxicoses in Japan and the USSR were separately found to be associated with consumption of small grains. In the USA, pigs became sick and sometimes died. Feeding trials soon established the source as blighted wheat grains and the source of toxicity as F. graminearum. This was confirmed by experimental
inoculation and feeding. In Japan, it soon became clear the suspect grain – wheat, barley, and rice – was infected with Fusarium species, and that the disease, known as Akakabibyo, had been occurring sporadically for half a century or more. The disease was characterized by nausea, vomiting, diarrhea, and sometimes other symptoms, but was rarely fatal. In the USSR, however, the disease called alimentary toxic aleukia, from the consumption of rye grain that had overwintered in the field due to wartime labor scarcity, killed several hundred thousand people, with symptoms like radiation poisoning. Identification of the toxin or toxins involved in each of these outbreaks had to wait for improvements in chemical techniques. In the 1970s, the isolation and structural characterization of several trichothecene toxins took place in the USA and Japan. In the USA, DON, then termed vomitoxin, was shown unequivocally to be the cause of the pig disease, whereas in Japan, both DON and NIV were seen as the likely causes of Akakabi-byo. The USSR outbreak was eventually attributed to T-2 toxin produced mainly by F. sporotrichioides. By the turn of the twenty-first century, more than 100 trichothecene molecules were known to occur naturally, produced by a number of plant pathogenic fungal genera. Of these genera, Fusarium is by far the most important trichothecene source. At this time, production of DON and
Mycotoxins: Deoxynivalenol and Other Trichothecenes
sometimes NIV by F. graminearum and F. culmorum are the main sources of trichothecenes in foods and feeds, and the main causes for concern.
Hazard Identification Trichothecenes are potent inhibitors of protein synthesis. DON and other trichothecenes bind to ribosomes, interfering with normal ribosomal function by causing dysregulation of various proteins related to immune function and sometimes apoptosis. Toxicity of the particular molecule varies with conformation that depends on the particular side groups in the molecule. NIV is much more toxic than DON, but is produced in much lower quantities in grains, and so is much less important. T-2 toxin is the most toxic of these compounds when tested in cell lines, and equal to NIV by intraperitoneal injection. T-2 toxin is more than 10 times as toxic as DON by injection, and 70 times as toxic to cell lines. Early studies of DON toxicity used naturally toxic grain. This always included other naturally occurring compounds, providing erroneous results that indicated that DON was more toxic than has been established by assays using the pure compound. Nonetheless, DON is a significant mycotoxin because of its widespread occurrence in cereals and products derived from cereals. The most obvious syndrome in animals caused by DON is feed refusal in pigs, accompanied by decreased weight gain, gastroenteritis, and effects on heart function and the immune system. DON may cause acute gastroenteritis in humans, where the main symptoms are nausea, vomiting, abdominal pain, diarrhea, and fever. Symptoms can develop within 30 min of exposure and are difficult to distinguish from effects due to bacteria, such as the emetic toxins from Bacillus cereus. Recovery is usually complete. In 2001, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) reviewed the safety of DON and on the basis of a 2-year feeding study in mice concluded that DON was not carcinogenic.
297
8 mg kg1 bodyweight for DON and its acetylated derivatives using the lowest lower limit on the benchmark dose for a 10% response of 0.21 mg per kg bodyweight per day for emesis in pigs. Limited data from human case reports indicated that dietary exposures to DON up to 50 mg per kg bodyweight per day are not likely to induce emesis.
Exposure Assessment DON occurs worldwide in maize, wheat, and sometimes other small grains due to growth of F. graminearum and related species. JECFA has estimated that the total intake of DON in micrograms per kilogram of bodyweight per day to be 0.78 from the African diet, 1.2 from the Latin American diet, 1.4 from the European diet, 1.6 from the Far Eastern diet, and 2.4 from the Middle Eastern diet. The main source of intake in Europe, Latin America, and the Middle East is wheat (64–88% of total intake), whereas the sources in the other two regions are more varied: wheat, rice, and maize in the African region and wheat and rice in the Far East.
Risk Characterization The main risk from DON is from chronic exposure, which has been estimated to exceed the PMTDI in many areas of the world. However, the reduction in exposure levels due to processing was not taken into account. For wheat, such reductions can be significant. Regarding acute exposure, the sporadic occurrence of outbreaks of acute gastroenteritis is of public health concern. A potential risk to farm workers exists from DON inhalation. Grain dusts may contain quite high concentrations of DON. Air samples from Canadian grain elevators contained up to 2.6 mg m3 of DON. Airborne dust from the same sources contained up to 5.8 mg kg1 of DON, plus smaller amounts of T-2 toxin. Some evidence has been reported that grain farming may be associated with midterm pregnancy deliveries in northern Europe.
Hazard Characterization Chemical Analysis JECFA also evaluated other long-term effects from the same 2year mice feeding study. Although the mean bodyweight of animals at the lowest dose was lower than that of controls, the difference was considered not to be biologically significant, and no toxicological changes were observed at this dose. JECFA established a provisional maximum tolerable daily intake (PMTDI) of 1 mg kg1 bodyweight on the basis of the no effect level of 100 mg per kg bodyweight per day in this study and a safety factor of 100. The committee concluded that intake at this level would not result in effects of DON on the immune system, growth, or reproduction. Consumption of maize containing excessive levels of DON has been associated with numerous incidents of intoxication in China and India. Tens of thousands of people have sometimes been affected. In one episode in India, DON levels in wheat ranged from 0.4 to 8.4 mg kg1, whereas in China, intoxication was linked to wheat contaminated with 0.3 to 100 mg kg1 DON. In 2010, JECFA derived a group acute reference dose of
Analysis for DON usually requires gas chromatography and mass spectroscopy. Modified DON, in the form of the 3-glucoside, is a problem because it is not assayed by the usual techniques. Extraction may use chloroform – ethyl acetate or 70% methanol, and cleanup is accomplished by filtering through a C18 or silica gel column.
Levels in Foods DON is found in maize and small grains in all areas where these crops are grown, and particularly in wheat, the crop most commonly invaded by F. graminearum. It is especially prevalent in cooler areas where rainfall is higher, such as Canada, Europe, and Argentina, but less commonly occurs in drier, hotter areas such as Australia. Levels of DON and other related trichothecenes are usually lower than 1 mg kg1 in
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Mycotoxins: Deoxynivalenol and Other Trichothecenes
foods, but can be much higher, potentially causing intoxication (see Section ‘Risk Characterization’). A number of studies have shown that fungal infection rates are higher in crops planted in fields previously planted with maize, particularly when residues from those crops were left in the field. Once grains begin to dry, with the water activity reduced to o0.9, increases in levels of Fusarium mycotoxins rarely occur. Favorable weather conditions are critical for infection to occur in wheat heads. Field observations have confirmed that temperature and moist conditions during anthesis and heading are the major factors of importance.
Management In 2010, the US Food and Drug Administration issued revised guidelines for DON in foods and feeds as follows: for finished wheat products that may be consumed by humans, 1 mg kg1; for grains and byproducts for feedlot and dairy cattle, 10 mg kg1, except that for dairy cattle, the total DON content in feed should not exceed 5 mg kg1; in feed for pigs, 5 mg kg1, but not exceeding 20% of the total diet; and for all other animals, 5 mg kg1, not exceeding 40% of the total diet. Some success has been achieved in controlling DON formation in wheat by the use of azole fungicides at anthesis. Forecasting systems to advice farmers of the likelihood of DON formation have been developed in Canada and Europe. Otherwise, control relies on reducing levels of Fusarium species in the field by good management and crop rotation.
Further Reading Fungal Sources Leslie JF and Summerell BA (2006) The Fusarium Laboratory Manual. Ames, IA: Blackwell Publishing. Pitt JI and Hocking AD (2009) Fungi and Food Spoilage, 3rd edn. New York: Elsevier.
History Beardall JM and Miller JD (1994) Diseases in humans with mycotoxins as possible causes. In: Miller JD and Trenholm HL (eds.) Mycotoxins in Grain, pp. 487–540. St. Paul, MN: Eagan Press.
Dejardins AE (2006) Fusarium Mycotoxins: Chemistry, Genetics, Biology. S.t Paul, MN: APS Press. Miller JD, ApSimon JW, Blackwell BA, Greenhalgh R, and Taylor A (2001) Deoxynivalenol: A 25 year perspective on a trichothecene of agricultural importance. In: Summerell BA, Leslie JF, Backhouse D, Bryden WL, and Burgess LW (eds.) Fusarium: Paul E. Nelson Memorial Symposium, pp. 310–320. St. Paul, MN: APS Press.
Toxicology Feinberg B and MacLaughlin CS (1989) Biochemical mechanism of action of trichothecene mycotoxins. In: Beasley VR (ed.) Trichothecene Mycotoxins: Pathophysiological Effects, vol. 1, pp. 27–36. Boca Raton, FL: CRC Press. Pestka JJ (2008) Mechanisms of deoxynivalenol-induced gene expression and apoptosis. Food Additives and Contaminants, Part A 25: 1128–1140. Sudakin DL (2003) Trichothecenes in the environment: Relevance to human health. Toxicology Letters 143: 97–107.
Chemical Analysis AOAC (Association of Official Analytical Chemists) (2005) AOAC Official Methods of Analysis, 18th edn. Gaithersburg, MD: AOAC International. Sasanya JJ, Hall C, and Wolf-Hall C (2008) Analysis of deoxynivalenol, masked deoxynivalenol, and Fusarium graminearum pigment in wheat samples, using liquid chromatography-UV mass spectrometry. Journal of Food Protection 71: 1205–1213.
Occurrence and Prevention Beardall J and Miller JD (1994) Natural occurrence of mycotoxins other than aflatoxin in Africa, Asia and Souths America. Mycotoxin Research 10: 21–40. Gourdain E, Piraux F, and Barrier-Guillot B (2011) A model combining agronomic and weather factors to predict occurrence of deoxynivalenol in durum wheat kernels. World Mycotoxin Journal 4: 129–139. Hooker DC, Schaafsma AW, and Tamburic-Ilincic L (2002) Using weather variables pre- and post-heading to predict deoxynivalenol in winter wheat. Plant Disease 88: 611–619. Paul PA, Lipps PE, Hershman DE, McMullen MP, Draper MA, and Madden LV (2008) Efficacy of triazole-based fungicides for Fusarium head blight and deoxynivalenol control in wheat: A multivariate meta-analysis. Phytopathology 98: 999–1011. Schaafsma AW, Tanburic-Ilinic L, Miller JD, and Hooker DC (2001) Agronomic considerations for reducing deoxynivalenol in wheat grain. Canadian Journal of Plant Pathology 23: 279–285.
Deoxynivalenol and Other Trichothecenes JI Pitt, CSIRO Animal, Food and Health Sciences, North Ryde, NSW, Australia r 2014 Elsevier Inc. All rights reserved.
Glossary Apoptosis Programed cell death that is a normal component of the development and health of multicellular organisms. Conidium (pl. conidia) Microscopic asexual spores produced by molds (filamentous fungi with small fruiting bodies); the main means of propagating many species.
Chemical Characterization Deoxynivalenol (DON) belongs to the family of chemicals known as the trichothecenes, sesquiterpenoid compounds characterized by an epoxy ring at the C-12,13 position. At least 100 trichothecene molecules are known, differentiated by hydroxy or acetyl groups and side chains. DON, still sometimes known as vomitoxin in the USA, is 12,13-epoxy-3,7,15trihydroxy-trichothec-9-en-8-one, CAS number 51481-10-8 (Figure 1). It is the most commonly produced trichothecene in foodstuffs. Nivalenol (NIV), less commonly produced but more toxic, differs from DON by the substitution of a hydroxy group for the hydrogen atom at the C-4 position (Figure 1). The most toxic trichothecene is known as T-2 toxin. It differs from DON in several positions: at C-4, an acetyl ester in place of H; at C-7, H in place of OH; at C-8 an isovalerate ester in place of O; and at C-15, an acetyl ester in place of OH.
Fungal Sources, Physiology, and Ecology DON and NIV are produced by Fusarium graminearum (often listed as Gibberella zeae, its sexual stage), Fusarium culmorum, and some related species. H O
H
H
H
O OH
O
O HO
O H
Deoxynivalenol
OH O
O HO
O H Nivalenol
Figure 1 Structures of deoxynivalenol and nivalenol.
Encyclopedia of Food Safety, Volume 2
O H
Macroconidium (pl. macroconidia) The larger of the two conidial types produced by Fusarium species, and characteristic of the genus. Microconidium (pl. microconidia) The smaller of the two types produced by some Fusarium species, but also produced by a number of other related genera.
Fusarium graminearum grows rapidly on any standard mycological medium including Czapek yeast extract agar (CYA), malt extract agar (MEA), potato dextrose agar (PDA), and dichloran chloramphenicol peptide agar (DCPA). Colonies on CYA and MEA are colored grayish rose, grayish yellow or paler, with reverses orange red to yellowish brown. On PDA, colonies are colored yellowish brown to reddish brown, sometimes with a central mass of red brown to orange areas bearing macroconidia, with the reverse dark red (Figure 2). Characteristic Fusarium conidia, macroconidia, are produced on DCPA or other specialist medium, usually with 5 septa, thick walled, straight to moderately curved, with the basal cell distinctly foot-shaped; microconidia are not produced. Colonies of F. culmorum are similar to those of F. graminearum, but colored pale red to pastel red on CYA, MEA, and PDA, the reverse on CYA and PDA is pastel red to deep red, and on MEA brown to reddish brown. Macroconidia are relatively short, wide, and only slightly curved, with 4–5 septa, 30–45 mm long, with basal cells with a slight to definite notch. Microconidia are not produced. Fusarium graminearum grows from below 5 1C to approximately 35 1C, and optimally at 25 1C. Growth occurs down to 0.90 water activity. Fusarium culmorum has a minimum temperature for growth near 0 1C, a maximum approximately 33 1C, and an optimum near 30 1C. It is capable of growth down to 0.87 water activity, lower than most other Fusarium species that have been studied. Fusarium graminearum occurs in maize, and both F. graminearum and F. culmorum in small grains, especially wheat and barley. These species are rank pathogens, invading plants and grains by causing diseases, known as Gibberella ear rot in maize and Fusarium head blight in wheat, barley, and triticale. Epidemics of Gibberella ear rot require the congruence of three factors: airborne or insectborne spores, inoculation at the susceptible time, and appropriate moisture and temperature. This disease is
doi:10.1016/B978-0-12-378612-8.00193-1
295
296
Mycotoxins: Deoxynivalenol and Other Trichothecenes
(a)
(b)
(c)
Figure 2 Fusarium graminearum. (a) Colonies on PDA and dichloran chloramphenicol peptone agar (DCPA), 7 days, 25 1C; (b) Gibberella zeae perithecium and ascospores, bar ¼25 mm; (c) macroconidia, bar¼ 10 mm.
prevalent in north temperate climates especially in wet years, but is much less common in the tropics. Fusarium head blight affects all commercial cultivars of wheat and barley. Fusarium culmorum always produces DON, but whether DON or NIV is produced by F. graminearum depends on the geographical origin of the fungal strain. T-2 toxin is produced mainly by Fusarium sporotrichioides. This species grows rapidly on CYA, MEA, and PDA, producing white to pale pink mycelium, with reverse pale on CYA, violet brown on MEA and PDA. Macroconidia are similar to those of F. graminearum, but, unlike that species, abundant microconidia are also produced. Fusarium sporotrichioides grows under similar conditions to F. graminearum, except that its minimum temperature is 2 1C. T-2 toxin is produced on grains, but occurs only under cool conditions.
History Before 1950, feed refusal in pigs in the US and human toxicoses in Japan and the USSR were separately found to be associated with consumption of small grains. In the USA, pigs became sick and sometimes died. Feeding trials soon established the source as blighted wheat grains and the source of toxicity as F. graminearum. This was confirmed by experimental
inoculation and feeding. In Japan, it soon became clear the suspect grain – wheat, barley, and rice – was infected with Fusarium species, and that the disease, known as Akakabibyo, had been occurring sporadically for half a century or more. The disease was characterized by nausea, vomiting, diarrhea, and sometimes other symptoms, but was rarely fatal. In the USSR, however, the disease called alimentary toxic aleukia, from the consumption of rye grain that had overwintered in the field due to wartime labor scarcity, killed several hundred thousand people, with symptoms like radiation poisoning. Identification of the toxin or toxins involved in each of these outbreaks had to wait for improvements in chemical techniques. In the 1970s, the isolation and structural characterization of several trichothecene toxins took place in the USA and Japan. In the USA, DON, then termed vomitoxin, was shown unequivocally to be the cause of the pig disease, whereas in Japan, both DON and NIV were seen as the likely causes of Akakabi-byo. The USSR outbreak was eventually attributed to T-2 toxin produced mainly by F. sporotrichioides. By the turn of the twenty-first century, more than 100 trichothecene molecules were known to occur naturally, produced by a number of plant pathogenic fungal genera. Of these genera, Fusarium is by far the most important trichothecene source. At this time, production of DON and
Mycotoxins: Deoxynivalenol and Other Trichothecenes
sometimes NIV by F. graminearum and F. culmorum are the main sources of trichothecenes in foods and feeds, and the main causes for concern.
Hazard Identification Trichothecenes are potent inhibitors of protein synthesis. DON and other trichothecenes bind to ribosomes, interfering with normal ribosomal function by causing dysregulation of various proteins related to immune function and sometimes apoptosis. Toxicity of the particular molecule varies with conformation that depends on the particular side groups in the molecule. NIV is much more toxic than DON, but is produced in much lower quantities in grains, and so is much less important. T-2 toxin is the most toxic of these compounds when tested in cell lines, and equal to NIV by intraperitoneal injection. T-2 toxin is more than 10 times as toxic as DON by injection, and 70 times as toxic to cell lines. Early studies of DON toxicity used naturally toxic grain. This always included other naturally occurring compounds, providing erroneous results that indicated that DON was more toxic than has been established by assays using the pure compound. Nonetheless, DON is a significant mycotoxin because of its widespread occurrence in cereals and products derived from cereals. The most obvious syndrome in animals caused by DON is feed refusal in pigs, accompanied by decreased weight gain, gastroenteritis, and effects on heart function and the immune system. DON may cause acute gastroenteritis in humans, where the main symptoms are nausea, vomiting, abdominal pain, diarrhea, and fever. Symptoms can develop within 30 min of exposure and are difficult to distinguish from effects due to bacteria, such as the emetic toxins from Bacillus cereus. Recovery is usually complete. In 2001, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) reviewed the safety of DON and on the basis of a 2-year feeding study in mice concluded that DON was not carcinogenic.
297
8 mg kg1 bodyweight for DON and its acetylated derivatives using the lowest lower limit on the benchmark dose for a 10% response of 0.21 mg per kg bodyweight per day for emesis in pigs. Limited data from human case reports indicated that dietary exposures to DON up to 50 mg per kg bodyweight per day are not likely to induce emesis.
Exposure Assessment DON occurs worldwide in maize, wheat, and sometimes other small grains due to growth of F. graminearum and related species. JECFA has estimated that the total intake of DON in micrograms per kilogram of bodyweight per day to be 0.78 from the African diet, 1.2 from the Latin American diet, 1.4 from the European diet, 1.6 from the Far Eastern diet, and 2.4 from the Middle Eastern diet. The main source of intake in Europe, Latin America, and the Middle East is wheat (64–88% of total intake), whereas the sources in the other two regions are more varied: wheat, rice, and maize in the African region and wheat and rice in the Far East.
Risk Characterization The main risk from DON is from chronic exposure, which has been estimated to exceed the PMTDI in many areas of the world. However, the reduction in exposure levels due to processing was not taken into account. For wheat, such reductions can be significant. Regarding acute exposure, the sporadic occurrence of outbreaks of acute gastroenteritis is of public health concern. A potential risk to farm workers exists from DON inhalation. Grain dusts may contain quite high concentrations of DON. Air samples from Canadian grain elevators contained up to 2.6 mg m3 of DON. Airborne dust from the same sources contained up to 5.8 mg kg1 of DON, plus smaller amounts of T-2 toxin. Some evidence has been reported that grain farming may be associated with midterm pregnancy deliveries in northern Europe.
Hazard Characterization Chemical Analysis JECFA also evaluated other long-term effects from the same 2year mice feeding study. Although the mean bodyweight of animals at the lowest dose was lower than that of controls, the difference was considered not to be biologically significant, and no toxicological changes were observed at this dose. JECFA established a provisional maximum tolerable daily intake (PMTDI) of 1 mg kg1 bodyweight on the basis of the no effect level of 100 mg per kg bodyweight per day in this study and a safety factor of 100. The committee concluded that intake at this level would not result in effects of DON on the immune system, growth, or reproduction. Consumption of maize containing excessive levels of DON has been associated with numerous incidents of intoxication in China and India. Tens of thousands of people have sometimes been affected. In one episode in India, DON levels in wheat ranged from 0.4 to 8.4 mg kg1, whereas in China, intoxication was linked to wheat contaminated with 0.3 to 100 mg kg1 DON. In 2010, JECFA derived a group acute reference dose of
Analysis for DON usually requires gas chromatography and mass spectroscopy. Modified DON, in the form of the 3-glucoside, is a problem because it is not assayed by the usual techniques. Extraction may use chloroform – ethyl acetate or 70% methanol, and cleanup is accomplished by filtering through a C18 or silica gel column.
Levels in Foods DON is found in maize and small grains in all areas where these crops are grown, and particularly in wheat, the crop most commonly invaded by F. graminearum. It is especially prevalent in cooler areas where rainfall is higher, such as Canada, Europe, and Argentina, but less commonly occurs in drier, hotter areas such as Australia. Levels of DON and other related trichothecenes are usually lower than 1 mg kg1 in
298
Mycotoxins: Deoxynivalenol and Other Trichothecenes
foods, but can be much higher, potentially causing intoxication (see Section ‘Risk Characterization’). A number of studies have shown that fungal infection rates are higher in crops planted in fields previously planted with maize, particularly when residues from those crops were left in the field. Once grains begin to dry, with the water activity reduced to o0.9, increases in levels of Fusarium mycotoxins rarely occur. Favorable weather conditions are critical for infection to occur in wheat heads. Field observations have confirmed that temperature and moist conditions during anthesis and heading are the major factors of importance.
Management In 2010, the US Food and Drug Administration issued revised guidelines for DON in foods and feeds as follows: for finished wheat products that may be consumed by humans, 1 mg kg1; for grains and byproducts for feedlot and dairy cattle, 10 mg kg1, except that for dairy cattle, the total DON content in feed should not exceed 5 mg kg1; in feed for pigs, 5 mg kg1, but not exceeding 20% of the total diet; and for all other animals, 5 mg kg1, not exceeding 40% of the total diet. Some success has been achieved in controlling DON formation in wheat by the use of azole fungicides at anthesis. Forecasting systems to advice farmers of the likelihood of DON formation have been developed in Canada and Europe. Otherwise, control relies on reducing levels of Fusarium species in the field by good management and crop rotation.
Further Reading Fungal Sources Leslie JF and Summerell BA (2006) The Fusarium Laboratory Manual. Ames, IA: Blackwell Publishing. Pitt JI and Hocking AD (2009) Fungi and Food Spoilage, 3rd edn. New York: Elsevier.
History Beardall JM and Miller JD (1994) Diseases in humans with mycotoxins as possible causes. In: Miller JD and Trenholm HL (eds.) Mycotoxins in Grain, pp. 487–540. St. Paul, MN: Eagan Press.
Dejardins AE (2006) Fusarium Mycotoxins: Chemistry, Genetics, Biology. S.t Paul, MN: APS Press. Miller JD, ApSimon JW, Blackwell BA, Greenhalgh R, and Taylor A (2001) Deoxynivalenol: A 25 year perspective on a trichothecene of agricultural importance. In: Summerell BA, Leslie JF, Backhouse D, Bryden WL, and Burgess LW (eds.) Fusarium: Paul E. Nelson Memorial Symposium, pp. 310–320. St. Paul, MN: APS Press.
Toxicology Feinberg B and MacLaughlin CS (1989) Biochemical mechanism of action of trichothecene mycotoxins. In: Beasley VR (ed.) Trichothecene Mycotoxins: Pathophysiological Effects, vol. 1, pp. 27–36. Boca Raton, FL: CRC Press. Pestka JJ (2008) Mechanisms of deoxynivalenol-induced gene expression and apoptosis. Food Additives and Contaminants, Part A 25: 1128–1140. Sudakin DL (2003) Trichothecenes in the environment: Relevance to human health. Toxicology Letters 143: 97–107.
Chemical Analysis AOAC (Association of Official Analytical Chemists) (2005) AOAC Official Methods of Analysis, 18th edn. Gaithersburg, MD: AOAC International. Sasanya JJ, Hall C, and Wolf-Hall C (2008) Analysis of deoxynivalenol, masked deoxynivalenol, and Fusarium graminearum pigment in wheat samples, using liquid chromatography-UV mass spectrometry. Journal of Food Protection 71: 1205–1213.
Occurrence and Prevention Beardall J and Miller JD (1994) Natural occurrence of mycotoxins other than aflatoxin in Africa, Asia and Souths America. Mycotoxin Research 10: 21–40. Gourdain E, Piraux F, and Barrier-Guillot B (2011) A model combining agronomic and weather factors to predict occurrence of deoxynivalenol in durum wheat kernels. World Mycotoxin Journal 4: 129–139. Hooker DC, Schaafsma AW, and Tamburic-Ilincic L (2002) Using weather variables pre- and post-heading to predict deoxynivalenol in winter wheat. Plant Disease 88: 611–619. Paul PA, Lipps PE, Hershman DE, McMullen MP, Draper MA, and Madden LV (2008) Efficacy of triazole-based fungicides for Fusarium head blight and deoxynivalenol control in wheat: A multivariate meta-analysis. Phytopathology 98: 999–1011. Schaafsma AW, Tanburic-Ilinic L, Miller JD, and Hooker DC (2001) Agronomic considerations for reducing deoxynivalenol in wheat grain. Canadian Journal of Plant Pathology 23: 279–285.