Mycotoxins in stored cereals from rural households in central northern Namibia

Abstract

Cereal contamination by mycotoxins is a significant food safety concern globally. To date, the spectrum of mycotoxins in stored cereals in Namibia was not yet studied. Therefore, this study aimed to gather data on grain storage practices and mycotoxin awareness using validated questionnaires as well as determine by LC-MS/MS analysis the types and levels of mycotoxins present in 100 samples of stored cereal flour in rural households in two regions (Oshana and Oshikoto) of central northern Namibia. In both regions, cereal grains were predominantly stored in traditional silos and for longer periods of more than 12 months under poorly aerated conditions. One hundred and ninety-four metabolites of fungal, bacterial and plant origins, including 30 regulated and emerging mycotoxins, were positively identified in at least one sample. About 42% of all samples were contaminated with aflatoxins, and 14% and 9% samples exceeded the European Union's maximum acceptable limit of 2 μg/kg AFB1 and 4 μg/kg total aflatoxin limit, respectively. Only five emerging mycotoxins (moniliformin, alternariolmethylether, tenuazonic acid, 3-nitropropionic acid (3-NPA) and enniatin B) contaminated at least 50% of all samples. 3-NPA had the highest concentration in all flour samples (max: 54,400 μg/kg; mean: 5420 μg/kg). In view of the consumption of the flour by children and adults, the extremely high levels of 3-NPA and evident co-contamination by different toxin classes, urgent mitigation interventions that include educational awareness campaigns and provision of better storage facilities are required to minimize mycotoxin contamination in the staple cereals in central northern Namibia.