Agriculture, Aflatoxins and Aspergillus

Abstract

Human activities affect both the size and SD1IClurc of fungal populations. ConsttUCtion. war, recreation, and agricuilure disrupt large expanses of vegellltion and soil; disruption causes redistribution of fungal propagules and makes nutrients available to fungi. Many fungi, including the aspergilJi. exploit these human engineered resources. This re.'iuhs in the association of large fungal populations with various human activities. especially agriculture. When crops are grown or animals raised. fungi are also grown. From a human perspective. most fungi associated with cultivation increase inadvenently. Human activity, bowever. partly dictates which and how many fungi occur and the fungi, both direclly and lhrough fungal products. influence human activities. domestic animals, and even humans lhemselves. During wann. dry periods. several of the aspergilli increase rapidly in association with crops. These include aspergilli in the Aspergillus flavur group. Prior to 1960, interest in the A. flavur group resulted both from the use of certain strains in processing of agriculturnJ. products in Europe and the Orient (Beuchat, 1978). and from the ability of some strains to parasitize insects. In the early 1960's fungi in the A. flavur group were implicated as the producers of aflatOxins (~d.spergillus..D!!vur toxins"), the toxins which poisoned thousands of poultry, pigs and trout; in trout these factors were associated with liver cancer (Goldblan and 51010ff. 1983). It soon became apparent that aflatoxin! also occurred in the human diet and that aflatoxins could pass from foed to milk with only slight modification (Goldblaa and 510108'. 1983). The most common aflatoxin, aflatoxin B • . was found to be a potent hepalD-careinogen in rats and trout carcinomas were induced at flltes below Ipgkg" body weight (Robens and Richard, 1992). Aflatoxin content of foods and feeds was eventually regulated in many countries (Stoloff et at.. 1991). In some products. such as milk or infant foods, aflatoxin levels below 0.02 pgkg··are mandated. Thus, for many, the focus of interest in this diverse and important fungal group became the production of aflatoxins. There clearly are interactions between agriculture, and both aflatoxins and lhe fungi in the A. flavus group. Some consequences of these interactions are obvious. others are virtually unexplored. The relationship of crop contamination cycles to the life strategies of no Gmar~. EdiIed. by Kcilb A. Powen d '"'~ Pta.aI Pl'es.s. N_ Yoft. 19'J.t A. flavus group fungi is uncertain. The role agriculture plays in structuring A. flavus populations and their tOldgenic potential is also uncenain. This chapter will address some aspects of the intemctions of A. /Iavus with humans and human activities: it includes suggestions on how these interactions may be altered to reduce human exposure to aflaloxins and other deuimental fungal trail~.