Occurrence and toxicity of aflatoxins

In Eastern and Southern Africa, as in most developing countries, aflatoxins are the most important mycotoxins from the point of view of occurrence, toxicity and economy. The aflatoxins are produced primarily by strains of Aspergillus flavus and Aspergillus parasiticus. The four major aflatoxins commonly reported in foods are aflatoxin B1, B2, G1, and G2. In grains, aflatoxins are primarily a problem in maize although other grains such as sorghum, millet, and wheat also may be contaminated (Table 1). Other products such as peanuts, peanut butter, figs, dried fruits, cottonseed, spices, milk, and opaque beer also may be contaminated. However, it is not so much the type of food contaminated, as it is the amount of food ingested and its level of contamination that may lead to toxicity.

In Southern Africa, aflatoxins are not a major contaminant of maize and levels usually are < 20 ng/g. Several surveys of commercial maize in South Africa have found very low incidence of aflatoxins in maize (Viljoen et al, 1993). Similar low levels of aflatoxins in commercial maize in Botswana and Swaziland have been reported (Table 1), although higher levels have been found in some maize products from Zambia (Lovelace and Nyathi, 1977). Peanut and peanut butter samples from Southern Africa usually are more heavily contaminated with aflatoxins than maize, and levels > 20 ng/g are common (Table 1). In an analysis of peanuts and peanut butter for sale in Botswana supermarkets, the total aflatoxin concentration ranged from 3-64 ng/g (Mphande et al, 2004). In South Africa, a recent survey of peanut butter used in a national feeding scheme for school children found that 42% of the samples were contaminated with aflatoxins at levels as high as 470 ng/g (National Monitoring Programme, 2004).

Aflatoxins also have been reported in food samples from Eastern Africa at extremely high levels (Table 1). For example, aflatoxins levels of 1,700 ng/g were reported in cassava from Uganda and levels as high as 46,000 ng/g were reported in maize from Kenya (Lewis et al, 2005). Aflatoxin levels ranging between 100 and 525 ng/g also have been reported in red pepper and mixed legumes from Ethiopia (Fufa and Urga, 1996).

Aflatoxins are lethal when consumed in large doses and fatalities have been reported in Uganda and Kenya. In Uganda, a 15-year old boy died two days after hospitalization with a subsequent examination of foodstuffs in the boy's home finding moldy cassava containing aflatoxins at up to 1,700 ng/g (Alpert et al., 1971). An outbreak of aflatoxicosis was reported in 1982 in Kenya where 12 people died after consuming maize samples contaminated with aflatoxin Bi at levels ranging between 3,200 and 12,000 ng/g (Ngindu et al., 1982). In a more recent outbreak of aflatoxicosis in Kenya, over 100 people died after consuming maize contaminated with aflatoxins at up to 46,000 ng/g (Lewis et al., 2005).

Aflatoxins are potent carcinogens and mutagens. Naturally occurring mixtures of afla-toxins are classified as Class 1 human carcinogens (IARC, 1993). There is a correlation between the incidence of liver cancer in humans in some areas of Africa and dietary exposure to aflatoxins. Studies in Kenya, Mozambique, Swaziland, and South Africa have found that aflatoxin levels in the diet and the incidence of primary liver cancer are correlated (Groopman et al, 1988). Aflatoxin consumption also has been implicated in some infant diseases such as kwashiorkor, a form of protein malnutrition (Hendrickse, 1984), and protein-deficient diets may increase aflatoxin toxicity (Hendrickse et al., 1982).

The aflatoxin problem is not only a health risk but also can result in monetary losses to farmers when contaminated produce is rejected by export markets (Wu, 2004). The marketability of the contaminated produce, particularly in international trade also is considerably reduced due to stringent limits set by importing countries. In many developing countries, there is little, if any, regulation of aflatoxin contamination in foods at the local level, hence the population is always at risk. The Codex Alimentarius Commission, supported by FAO and WHO, set a standard of 15 ng/g total aflatoxins in unprocessed peanuts. However, in 1998, the European Union (EU) set a tolerance level of 2 ng/g for aflatoxin B1 and 4 ng/g for total aflatoxins in nuts and cereals meant for human consumption (Dimanche, 2001). To take advantage of the growing export market, farmers must use good agricultural practices and innovative methods, e.g., forming farmers' association and using low-cost technology

Table 1. Occurrence of aflatoxins (as aflatoxin B1) in food commodities reported from several countries from Eastern and Southern Africa.



Conc. Range (ng/g)




Not Detected

Siame et al., 1998

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