Occurrence and distribution of aflatoxin contamination in groundnuts (Arachis hypogaea L) and population density of Aflatoxigenic Aspergilli in Malawi

Abstract

Groundnut (Arachis hypogaea L.) is susceptible to pre- and post-harvest infections by Aspergillus spp. Aflatoxin B1 (AFB1), is the contaminant produced by the fungus in infected grains posing a threat to human and animal health. This paper reports of a study undertaken in Malawi to determine the occurrence and distribution of Aflatoxigenic Aspergilli in the soil and AFB1 contamination in groundnuts. A total of 1397 groundnut samples collected from farm homesteads, local markets, warehouses and shops in 2008 and 2009 were analyzed for AFB1 contamination using the enzyme linked immunosorbent assay (ELISA), and A. Aspergilli population densities in 1053 soil samples collected from the same sites were estimated using serial dilutions plated on A. Aspergilli medium. Farmer socio-economic profile information was also collected to determine relationships to AFB1 contamination. The results revealed 46% and 23% of the total samples, from 2008 to 2009, respectively, had AFB1 contamination levels greater than 4 ppb, and those above 20 ppb were 21% for 2008 and 8% for 2009, respectively. Fitted smooth curve relationships show that there is a clear increase in the chance of groundnut contamination when the population density of A. Aspergilli in the soil increased beyond 3000 (log (cfu) > 8). The measured level of A. Aspergilli in soil varied by location, as well as ecologies within location. Low-altitude ecologies, which were warmer and experienced low precipitation levels, had the highest densities of A. Aspergilli, whereas cooler high-altitude ecologies had the lowest density of these fungi. Similarly high AFB1 contamination, was recorded across the country with 11–28% of all samples collected from the warm low to mid-altitude ecologies recording contamination ≥20 ppb and low contamination (2–10% of samples) in the mid to high altitude cool ecologies. From a crop management perspective, this study also suggests that both less experienced and older farmers were more likely to produce groundnuts contaminated with aflatoxin. These findings have implications in the design of intervention strategies to avoid short- and long-term human health effects from aflatoxin exposure.