PART III PROCESS SAFETY
3. Occurrence of Mycotoxins and their Geographical Distribution
was probably the cause of “alimentary toxic aleukia” which affected thousands of people in Siberia during the Second World War. It is responsible for haemor- rhagic disease in animals and is associated with the formation of oral lesions and neurotoxic effects in poultry. However the most significant effect of this and other trichothecenes is the immunosuppressive activity, which is probably linked to the inhibitory effect on the biosynthesis of macromolecules (e.g., DNA, proteins).
Fumonisins are a group of very closely related compounds (fumonisin B1, B2and B3), produced predominately in maize by F. verticillioides (F. moniliforme).
Another important Fusarium toxin is zearalenone (ZEA), which has oestrogenic properties.
3. Occurrence of Mycotoxins and their Geographical
– humans are less exposed in developed countries than developing; and
– the major problem in developed countries is animal health as feeds are more likely to contain toxins.
3.1. Aflatoxins
Aflatoxin (Figure 1) producing fungi have a worldwide distribution in sub/tropi- cal and tropical climates (CAST, 2003). The toxins are especially common on edible nuts, oilseeds, and cereals. Many other foods and feeds are susceptible.
They can be produced before and after harvest. There is a high incidence in Southeast Asian countries (Thailand, Indonesia, and the Philippines). However, they are not necessarily the most severely affected countries. They are detected also in the USA, South America, and Africa.
3.2. Ochratoxin A
A. ochraceus and P. verrucosum are associated with cereal products, and are the primary producers of OTA. The chemical structure of OTA is provided in Figure 1.
P. verrucosum is more prevalent in regions with temperate, and A. ochraceus with tropical climates. A third species, A. carbonarius is associated with grape prod- ucts and is the main species responsible for the presence of OTA in grapes and products. OTA is found in corn, wheat, sorghum, oats, rice, wine, beer, and green coffee. OTA in coffee (Paterson et al., 2001), corn, grapes, dried fruits and wheat is generally below 500 µg kg−1. In contrast, barley and oats in Denmark and Scandinavian have high levels of OTA. Animal feeds in Canada and Europe can be highly contaminated with more than 5000 µg kg−1 having been recorded.
Highest levels have been detected in barley, oats, wheat and corn in (a) Northern Europe, i.e., UK, Denmark, Sweden and in the Balkans (former Yugoslavia) and (b) India (CAST, 2003). In these examples concentrations approach the mg kg−1 range. Levels are much lower in the USA. OTA appears to occur mainly in wheat and barley growing areas in the temperate zones of the northern hemisphere. High levels have been recorded in Canadian wheat, and UK barley and wheat. It is also in maize, rice, peas, beans and cowpeas. Developing country origins include Brazil, Chile, Egypt, India, Indonesia, Senegal and Tunisia. Pork is a significant dietary source and OTA has been found in the blood and milk of people in Bulgaria, Denmark, France, Germany, Italy, Poland, Sweden, and the former Yugoslavia (CAST, 2003).
3.3. Fumonisins, trichothecenes and zearalenone
After aflatoxin, the Fusarium toxins are the most frequently reported in raw agri- cultural commodities in US; DON (Figure 1) may be the most widely occurring Fusarium toxin. Grain containing DON is detected frequently. In Japan, there are high levels of DON in corn, wheat and barley. North America, Japan, and Europe are susceptible to low concentrations of DON in grains, whereas higher levels may
occur intermittently in developing countries. Other vulnerable countries include China and India. There are high levels of the related compound NIV in barley, corn, and wheat in Japan. T-2 toxin is produced on cereals in many parts of the world, and is associated with prolonged wet weather at harvest (CAST, 2003).
ZEA mainly occurs in maize in low concentration in Europe, Japan and North America. High concentrations have been detected in developing countries, espe- cially in the more temperate Highland regions (CAST, 2003). ZEA is frequently found in corn, wheat, barley and grain sorghum from the USA.
Low levels of fumonisins are extremely common throughout the world (CAST, 2003). However, in some cases more than 5 mg kg−1is observed. They are pro- duced by the fungus F. verticillioides which occurs worldwide and is found fre- quently on maize. It is prevalent in the USA, Canada, Brazil, South Africa, Austria, Italy, and France. Fumonisins especially occur when maize is grown under warm dry conditions. These compounds are associated with oesophageal cancer in southern Africa, and China.
3.4. Patulin
Occurrence of patulin (Figure 1) is likely to be more frequent than is generally realised as numerous fungi produce this compound and in a wider range of fruits and vegetables (Paterson, 2004a). The toxin is associated with P. expansum blue rot of apples and grapes. Anywhere that fruit products such as juice are manu- factured will have a potential problem. Patulin producing fungi are isolated fre- quently from vegetables and so products are likely to be contaminated in some cases, and similarly for silage and malt. The presence of patulin has been reported from many EU countries in relation to the recent regulations imposed by the EU.
It occurs frequently in the USA where the FDA operates mandatory action levels in apple juice. It is a problem in parts of South America (see case study below), in South Africa and in Portugal (Smith and Solomons, 1994).
3.5. Co-occurrence of mycotoxins
Fusarium toxins often co-occur with aflatoxins but not with OTA. Production of aflatoxins in stored grain is enhanced by the presence of trichothecenes.
Synergistic effects enhance the toxicity of naturally occurring trichothecenes: the effect of DON is enhanced by T-2 toxin; potent synergism of DON with non-toxic Fusarium metabolites has been reported. In Japan, ZEA sometimes occurs as a co-contaminant when there are high levels of either DON or NIV in corn, wheat, and barley (CAST, 2003). More information is required generally about this important area.
3.6. Biocontrol agents (BCAs)
Natural pathogens of certain pests and diseases are being considered as alternatives to synthetic chemical pesticides with potential benefits in terms of
environmental contamination and resistance of target organisms. However, a possible source of mycotoxins is from fungal BCAs. These may produce toxins and are sprayed onto crops pre- and (potentially) post-harvest. Metarrhizium anisopliae is one such and produces the highly toxic cytochalasins amongst other things (Paterson, 2004b). These compounds have been detected in agricul- tural commodities (CAST 2003) indicating the need to carefully regulate the use and production of these products. In addition, enniatins and beauvaricins are metabolites of insect and plant pathogens and have been detected in wheat and maize infected with Fusarium with negative implications for using the insect pathogens as biological control agents. The fact that BCAs are often for use in developing countries compounds the disproportionate mycotoxin problem that already exists.
3.7. Warfare
There are reports of mycotoxins having been used as biochemical weapons.
Recent events have indicated that they are still actively being considered. CAST (2003) recommends that assessments are required of mycotoxins as biological weapons. Obviously, levels of mycotoxins in the environment used for this pur- pose will be at higher concentrations than occur naturally. Drinking water is an obvious target (Paterson and Lima, 2005).