Respiratory Exposure to Mycotoxins and Farming

By Ginger D Fenton and Adriana Murillo-Williams

Airborne exposures are a significant risk to farmers. In some cases, the resulting effects can be immediate and severe. Recently, almost everyone has experienced a heightened awareness of respiratory exposures with an increased emphasis on protective measures. It is an opportune time to review and reassess potential exposures in the farm environment. Potential hazards on the farm including dust, fungi, pathogens, animal dander, chemicals such as cleaners and fumigants, and gases from exhaust, decay of plant matter, mycotoxins, and manure storage. Potential exposure can vary by season and the type of task being performed. The severity of body’s response may be related to the toxin and the length or frequency of exposure.

In a study published several years ago, farmers and their spouses were reported to have a lower risk of respiratory diseases when compared to the general population; however, the authors noted that farmers had different exposures and a higher prevalence of self-reported symptoms due to irritations (Hoppin et al., 2014). In another article, the collective results of many studies were reviewed with the authors reporting an elevated risk of exposure to aflatoxin for those working in agriculture including managing contaminated grains along with processing and handling animal feed (Nabwire Wangia et al., 2019).

Aflatoxin is part of a larger group of toxins referred to as mycotoxins, commonly found in cereal crops. For farmers, exposure to aflatoxin can occur through various routes including ingestion which is most common, topically through skin and mucosa, and through inhalation. As harvest approaches, the risk of inhalational exposures increases, while long-term exposure due to the nature of agricultural work also is of concern. Aflatoxin is a hazard because it is linked to organ damage with the liver as a target and is carcinogenic (FDA, 2012). Farmers may encounter or be familiar with many mycotoxins as they monitor the quality of their grains and animal feed.

The most economically important mycotoxins in crops include aflatoxins, ochratoxin A, deoxynivalenol (DON), T-2 and HT-2 toxin, zearalenone (ZEA), and fumonisins (FBs). Agricultural products commonly contaminated with mycotoxins include corn, wheat, barley, oats, rye, peanut, and cottonseed. Each type of mycotoxin can be produced by different fungal species, and different fungal species can produce a wide range of mycotoxins. In addition, many fungal species may occur simultaneously in the crop either as pathogens or saprophytes which feed on decaying matter. Therefore, multiple mycotoxin contamination of food crops occurs more frequently than contamination with a single mycotoxin.

Aflatoxins are produced mainly by the fungus Aspergillus flavus (A. flavus), which is the cause of Aspergillus ear rot of corn. Infection of A. flavus in corn will occur in the field, along with the potential for aflatoxin contamination. Once mycotoxin contamination occurs, the drying process will not degrade the mycotoxins in grain. In addition, if corn is stored at a high moisture content, field fungi will resume growth and may further contaminate corn with mycotoxins. Under these circumstances, the growth of additional fungal species present in the storage facility or grain bin also will be promoted and will contribute to aerial contamination with spores and mycotoxins.

In humans, A. flavus can cause infections including sinusitis, cutaneous infections, otitis, keratitis, and pulmonary infections (Hedayati et al., 2007). Aspergillus flavus and aflatoxins have been detected in dust samples from grain processing facilities (Ghosh et al., 1997), however, current research shows that incidence of A. flavus and aflatoxins can be quite variable. For example, toxigenic A. flavus was the most frequently recovered fungus from the environment in Croatian grain mills (Jakšić et al., 2019). The fungus was also found in suspended dust and air at animal feed factories in Egypt, however, other microorganisms were predominant in suspended dust and feed materials (Hameed et al., 2003). In a more recent study, Szulc and collaborators (2020) analyzed dust and air samples in cattle barns in Poland. They indicated that samples were mainly contaminated with bacteria, and no aflatoxins were detected. 

The effect of mycotoxins on the respiratory system has been studied in cell cultures under laboratory conditions. Lee and collaborators (2016) demonstrated that aflatoxins can impair ciliary beat frequency, thus, impairing respiratory physical defenses against inhaled pathogens and potentially enhancing A. flavus ability to cause disease. More recent studies indicate that aflatoxins in occupational environments could lead to epithelial damage in airways, which would also contribute to respiratory disease severity (Jakšić et al., 2019).

The diverse and dynamic composition of bioaerosols pose a challenge for evaluating the health risk of mycotoxins via inhalation. However, since the toxicity of mycotoxins via ingestion has been well documented, farmers should be proactive and take all precautionary measurements when working in areas or with tasks where exposure to dust is high. Additionally, cleaning equipment, storage areas, and other areas where dust accumulates is critical, since dust could represent a source of mycotoxin contamination, and harbor other potential hazards.