A review on the relation between soil and mycotoxins: Effect of aflatoxin on field, food and finance

Soil phytopathogenic fungi are principally associated with crop diseases; however, the effects of fungal infection may extend beyond the field to human and animal consumers putting their health at risk. Mycotoxigenic fungi can produce secondary metabolites known as mycotoxins, which are considered to be toxic when present in human food and animal feed. Mycotoxins are characterized as odourless and tasteless compounds, thus their identification in food is difficult. Furthermore, mycotoxins are heat resistant and tolerate a wide range of pH, making them hard to breakdown. In this review we follow the fates of mycotoxins from the ecology of their producers in the soil to pre-harvest occurrence in host plants, postharvest in storage and their effect on human well-being, focusing on aflatoxin as a case study. Aflatoxin production begins in the soil, the natural habitat of toxin-producing fungi of the Aspergillus spp., and its production is influenced by agricultural practices, environmental conditions and fungal interaction with the plant. The fungi are further dispersed during storage, which leads to a vast increase in toxin concentration during the storage period. Aflatoxin may then be consumed by humans or animals in raw or processed foods and feeds, respectively. Animal consumption of the toxin might carry over to humans in animal food products, such as milk. Once consumed, various forms of aflatoxin are recognized as human carcinogens and exposure is mainly associated with the development of hepatocellular carcinoma. The presence of mycotoxins in foods also carries severe economic implications because of the loss of crops, the cost of analysis and enforcement of a regulatory system. This review provides a critical analysis of each of these stages and highlights the importance of understanding soil-fungal-plant interactions as key steps in the development of successful strategies to minimize mycotoxin exposure. Highlights Mycotoxins are produced by soil-borne fungi during pre- and post-harvest stages. Mycotoxins reach human diet directly by contamination of foods or indirectly through animal feeds. Chronic and acute exposure to mycotoxins is a major health hazard. Economic impact from mycotoxin contamination exceeds US$1 billion.