Source: Canadian Food Inspection Agency, L.L. Charmley and H.L. Trenholm, AgReTech
Mycotoxins are secondary metabolites produced by a variety of moulds on several agricultural commodities under specific environmental conditions. It has been estimated that at least 25% of the grain produced each year worldwide is contaminated with mycotoxins. In temperate climates such as Canada, the mycotoxins of major concern are the trichothecenes (including deoxynivalenol (DON), nivalenol (NIV), T-2 toxin and HT-2 toxin), zearalenone (ZEN), the fumonisins (FB) predominantly fumonisin B1 (FB1), the ochratoxins, predominantly ochratoxin A (OA), and ergot. However, aflatoxins (AF) are of concern in food and feedstuffs imported from warmer tropical and subtropical regions. Canada’s indigenous mycotoxins occur mainly in cereal grains and corn, although occasionally there have been reports of contamination of other crops such as alfalfa and oilseeds, and foods such as coffee, cocoa, rice, beer and wine. As analytical techniques evolve to become more sensitive and widely available, the documentation of widespread contamination in a variety of commodities and of new mycotoxins no doubt, will increase.
Toxic Effects on Humans and Animals
Most toxicity studies deal with ingestion of contaminated food and feeds, but inhalation and skin exposure may also cause signs of toxicity.
The toxicology of many mycotoxins, particularly those commonly encountered, has been well documented for several animal species including humans. The signs of the many mycotoxicoses are diverse, numerous and often dependent on species, sex, age, stress, reproductive and health status of the animal. They include: feed refusal and vomitingDON (DON); impaired reproductive function and reduced fertility (ZEN, DON, T-2 toxin); nephrotoxicosis (OA, FB); neurotoxicosis (FB); lung disease (FB); hepatotoxicosis (FB); cancer (AF, OA, FB), and death (AF, T-2 toxin, FB, OA). Research has demonstrated subtle effects of mycotoxin contamination, including reduced immune function with compromised resistance to infection and disease (DON, AF, OA), and reduced animal performance (DON, AF, T-2 toxin, OA). The former condition increases the likelihood of transmission of pathogens such as Salmonella into the food chain. Recently FB was found to inhibit sphingolipid biosynthesis, which is thought to be a sensitive indicator of exposure to dietary FB contamination.
If a livestock species that is tolerant to a particular mycotoxin is fed a contaminated diet, there is a potential for the “carry-over” of toxin into animal products, such as milk or meat, destined for human consumption. In addition, the by-products of certain food processes, have the potential for being highly contaminated with certain mycotoxins and may cause severe adverse effects if subsequently fed to a species particularly sensitive to the contaminating mycotoxin or toxins. In both these cases a certain degree of care and monitoring is required to ensure the safety of humans and animals.
Under natural field conditions, it is unlikely that mycotoxins occur in isolation and more commonly a combination of contaminants will be found. In addition, the combining of several commodities in the manufacture of feeds for livestock may result in the concomitant combining of different mycotoxins, and so exacerbate this problem. Some mycotoxins when combined elicit a synergistic effect and some have an additive action, on an animal’s health or performance. The type of interaction incurred is determined not only by the particular mycotoxin combination, but also the animal species involved. Moreover, an animal’s response to mycotoxin-contaminated feed can be adversely affected by other factors such as nutrient availability, or deficiency, or environmental stressors (temperature, crowdingetc.).
Some management practices help to minimize mycotoxin contamination. These include:
- Limiting bird and insect damage, because moulds tend to invade damaged kernels more easily than intact ones.
- Harvesting grain as soon as possible. Fusarium mould grows readily under damp conditions.
- Adequate drying and storage of grain to prevent mould growth and mycotoxin production post-harvest.
- With high moisture corn, ensuring that ensiling conditions remain anaerobic to limit mould growth and mycotoxin contamination. Moulds cannot grow under truly anaerobic conditions.
- Using crop rotation to minimize the carry-over of moulds from one year to the next.
- Avoiding planting crops that may be susceptible to mould infestation in adjacent fields where the disease may spread from one crop to the other.
- When contamination does occur, mould spores and mycotoxins are often concentrated in the fines and dust of grains. Use of masks to avoid inhalation and ingestion of dust by grain handlers is recommended,
A preeminent strategy for eliminating or reducing mycotoxin contamination is the development of pre-harvest host plant resistance to mould infestation and mycotoxin production in crops. Advances in this regard have been made to identify resistance to Aspergillus infestation and AF contamination, in corn, Fusarium infestation and DONcontamination in wheat, and Fusarium infestation and FB contamination in corn. Genetic engineering strategies and the selection of hybrids naturally resistant to mould infestation and mycotoxin contamination are being studied in this regard. Promising results indicate that under some conditions, genetic engineering for insect and mould and mycotoxin resistance may enhance the safety of commodities such as corn, for animal and human consumption.
Under the Canadian National Feed Inspection Program, approximately 300 samples are analyzed annually for DON,FB1, T-2, HT-2, diacetoxyscirpenol (DAS), ZEN, and OA. In addition, AF (mycotoxins never detected in Canadian crops) are monitored in corn imported from warmer, drier climates such as the southern USA. There is also a mycotoxin trace back program which is used to investigate mycotoxin outbreaks.
A comprehensive survey of worldwide regulations and guidelines, as they existed on several mycotoxins in various countries was published by the FAO (FAO Food and Nutrition Paper 81, 2003). Regulations and guidelines for recommended tolerances for several mycotoxins (Canada and USA only) are shown in Tables 1 and 2.
Canada has established regulations for AF levels in food and feeds, and guidelines for DON, and HT-2 toxin (see Table 1). Moreover, although, many countries have established regulations or guidelines to protect consumers from the harmful effects of AF in foods and feedstuffs, the maximum permissible levels vary greatly among countries as do the guidelines and/or regulations or lack thereof regarding other mycotoxins.
Several international agencies currently strive to achieve universal standardization of regulatory limits for mycotoxins. This is an extremely difficult task because many factors have to be considered when deciding on regulatory standards. In addition to scientific factors, such as risk assessment (exposure and toxicological data), and analytical accuracy, economical and political factors, such as the commercial interests of each country, and the constant necessity of a sufficient food supply also play a role in the decision-making process. The whole process is further complicated by the fact that action levels pertain to single mycotoxin contamination, but in reality, several mycotoxins often co-occur in a contaminated commodity which may necessitate different (lower) action levels. Measuring the toxicological effects of a variety of different mycotoxin combinations, as they occur in nature, is an enormous and probably impossible task, especially considering that there may be mycotoxins present that have not been elucidated as yet. In addition, nutritional, management, environmental, and species effects all play a contributory role in determining the effect of a combination of mycotoxins on animal and human health.
Nevertheless, despite these obstacles most countries within the European Union have come to a common agreement on a standardized policy for regulation of AF levels in different feedstuffs and feedstuff ingredients (FAO Nutrition Paper 81, 2003).
A universal standard for total AF in foodstuffs of 15 µg/kg was suggested. However, countries with more stringent controls, based on the carcinogenic potential of these toxins, would be unlikely to agree with this level. Difficulties associated with enacting such legislation stem from analytical inadequacies regarding reproducibility of results, homogeneous and representative sampling and laboratory expertise.
The ideal goal is to eliminate mycotoxins from the food chain. However, on the practical level, this is not possible. The tolerance levels summarized in Tables 1 and 2 offer guidelines, based mainly on studies of individual toxins. Further research into the interactions of mycotoxins with each other and with other environmental and nutritional factors will enable validation and modification of these guidelines.
Mycotoxin contamination may be higher in grain dust and the lighter, shrivelled kernels. Thus, contamination may be reduced by density segregation to remove dust and the lighter, more highly contaminated kernels. Soaking, dehulling, or high velocity air cleaning of kernels can be used to remove surface contamination. Roasting may reduce mycotoxin contamination by burning surface contaminants and removing volatile, heat labile toxins and other mould metabolites.
Other approaches to reducing mycotoxin concentrations and effects on the animal are: improving the nutrient density of the feed; avoiding feeding contaminated commodities to sensitive animal species.
|Deoxynivalenol (mg/kg)||Uncleaned soft wheat for human consumption||2||Finished wheat products||1|
|Deoxynivalenol (mg/kg)||Diets for cattle & poultry||5||Grains and grain by-products destined for ruminating beef and feedlot cattle older than 4 months and chickens (not exceeding 50% of the cattle or chicken total diet)||10|
|Deoxynivalenol (mg/kg)||Diets for swine, young calves, & lactating dairy animals||1||Grains and grain by-products (not exceeding 40% of the diet)||5|
|Deoxynivalenol (mg/kg)||Grains and grain by-products destined for swine (not exceeding 20% of the diet)||5|
|HT-2 toxinmg/kg (ppm)||Diets for cattle & poultry||0.1|
|HT-2 toxinmg/kg (ppm)||Diets for dairy animals||0.025|
|Aflatoxinsµg/kg(ppb)||Nut products for human consumption||15||All foods||20|
|Aflatoxinsµg/kg(ppb)||Animal feeding stuffs||20||Dairy products (AFM1)||0.5|
|Aflatoxinsµg/kg(ppb)||Cottonseed meal intended for beef cattle, swine or mature poultry (regardless of age or breeding status)||300|
|Aflatoxinsµg/kg(ppb)||Corn and peanut products intended for breeding beef cattle, swine or mature poultry||100|
|Aflatoxinsµg/kg(ppb)||Corn and peanut products intended for finishing swine of 100 lbs or more||200|
|Aflatoxinsµg/kg(ppb)||Corn and peanut products intended for finishing beef cattle||300|
|Mycotoxin||Canada: Recommended tolerance levels||United States Guidelines|
|Diacetoxyscirpenol (DAS)||Swine feed <2
Poultry feed < 1
|T-2 toxin||Swine and poultry feed < 1|
|Zearalenone (ZEN)||Gilt diets < 1 – 3
Cow diets 10 (1.5 if other toxins present)
Swine industry has voiced concern over levels of 0.25 – 5 in diets for sheep and pigs.
|Ochratoxin A (OA)||Swine diets (kidney damage) 0.2
Swine diets (reduced weight gain) 2
Poultry diets 2
|Ergot||Maximum alkaloid content in feed of:
Cattle, sheep, horses 2-3
Swine 4 – 6
Chicks 6 – 9
|Fumonisin||Animal FeedsTable note 1
Total ration in feed for horses and rabbits, 1
Total ration for pigs, 10
Total ration for cattle, sheep and goats more than 3 months old, 30
Total ration for ruminant and poultry breeding stock, 15
Total ration for poultry fed for slaughter, 50
Human FoodsTable note 2
Degermed dry-milled corn products, 2
Dry milled corn bran, 4
Cleaned corn, for masa, 4
Cleaned corn for popcorn, 3
- Table note 1
- From Center for Veterinary Medicine/Food and Drug Administration Draft report, February 24, 2000.
- Table note 2
- From Center for Food Safety and Applied Nutrition/Center for Veterinary Medicine, Food and Drug Administration, November 9, 2001.
Canadian Food Inspection Agency
59 Camelot Drive
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Charmley, L.L. and Prelusky, D.B. 1994. In: Mycotoxins in Grain. Compounds Other than Aflatoxin. Miller, J.D., and Trenholm, H.L. (Eds) Eagan Press, St. Paul, MN, USA pages 421-435.
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