What are mycotoxins and why do they matter?

In any given season, 25 percent of the global food supply is at risk from an elusive and persistent threat. It comes in several different forms, some more dangerous than others, can cause serious short and long term health effects and can create severe economic problems. We’re talking about mycotoxins.  

So, what exactly are mycotoxins? Like many food safety hazards, mycotoxins’ inability to be seen with the naked eye makes them a challenge both to understand and to address. Mycotoxins form through nature’s constant competition for resources. As fungi in the soil and in plant material vie for survival, they produce a diverse set of chemicals called secondary metabolites that help them compete, grow and thrive. Some of these chemicals are toxic to humans and animals and can accumulate to extremely high levels in food and feed – these are mycotoxins. While mycotoxins are a problem from Siberia to South Africa, they can pose a particular challenge in the tropics, subtropics and the southern United States. One of the most dangerous and common mycotoxins is aflatoxin (produced by certain Aspergillus fungal species). Aflatoxin can have serious negative health effects when consumed in large or continuous quantities – high levels of acute ingestion can cause death, but perhaps more perniciously, long-term consumption can cause cancer and has been associated with negative birth outcomes, stunting children’s development and blocking nutrient uptake.

Prevalent in common crops such as maize (corn), groundnut (peanut) and wheat, mycotoxins present a complex global challenge. Contamination can occur at multiple places along the production chain. Aflatoxin contamination, for example, can be affected by climatic conditions in the environment before and after harvest, especially when good agricultural practices are not implemented. In the field, stressed crop plants can more easily succumb to fungal invasion and toxin accumulation. This includes crops that lack sufficient nutrients due to poor soils and insufficient fertilizer application, or are drought stressed due to dry spells in rain-fed farming systems and to planting mal-adapted or unimproved seeds. Improper harvest, drying and storage practices can further exacerbate already established contamination, or even introduce the fungus anew, creating conditions for deadly levels of mycotoxin accumulation.

In the United States, losses due to aflatoxin contamination could reach $1.68 billion in a bad season for corn alone. While large agricultural economies like the U.S. have the capabilities and systems in place to protect the food supply against mycotoxin contamination, developing countries often do not have such protections. As developed and developing countries alike work to address this menace to the food supply, they face challenging decisions, such as condemning entire harvests, particularly where contaminated crops are an essential staple food. As public awareness increases, responsibly and proactively addressing the threat of mycotoxins demands that research for development formulate integrated, locally appropriate, and scalable surveillance and mitigation options. The Feed the Future Innovation Lab for the Reduction of Post-Harvest Loss (PHLIL), funded by the United States Agency for International Development and based at Kansas State University, is working with a range of committed partners to address this challenging problem in multiple commodities and across three continents.

A multi-food problem

Some of PHLIL’s most recent efforts took place in Nepal, where the Lab conducted a large-scale survey to assess levels of aflatoxin in particularly susceptible crops. The assessment was conducted in 20 districts within the Feed the Future Zone of Influence. The PHLIL Nepal project team collected samples from eight different commodities, as well as surveying households and markets about their pre- and post-harvest agricultural practices, including storage, cleaning, sorting and storage practices.

Initial analysis produced some expected results and some that were a bit more surprising. As could be expected, high levels of aflatoxin contamination were found in some collected maize and groundnut samples. More surprising were the results for dried chilies – a cornerstone spice in Nepali diets – and soyballs, a soy-based extruded product common in Nepali dishes (especially for low-income families). Prior to PHLIL’s analysis, these were not foods suspected of significant aflatoxin contamination. However, our analysis found moderate levels of contamination, with some collected samples falling above the maximum allowable limit. In good news that can be used to address this problem more immediately and within current dietary preferences, rice and wheat-based weaning food was found to have consistently low levels of aflatoxin, below the maximum allowable limit. These findings emphasize how widespread mycotoxin contamination can be, how vulnerable our food system is to this threat and how an evidence base revealing where and why the contamination occurs in the food system can be invaluable to guide mitigation strategies.

In collaboration with the Nutrition Innovation Lab, this research is providing an agriculture and nutrition evidence base to inform Nepal’s national multi-sectorial response on improving nutrition, including food safety.

Lack of dietary diversity increases risk

Specific instances of mycotoxin exposure, such as consuming food from a single contaminated bag of grain or a meal purchased from a roadside vendor, is not the only reason to be concerned; consistent exposure to levels below the maximum allowable limit can still add up to chronic health problems over time. Total mycotoxin exposure accounts for contamination in the food, but also how much of that food is consumed. The PHLIL Guatemala team’s maize analysis found that many samples were under the legal regulatory limit; however, because maize is such a staple of the diet (daily adult consumption of corn can surpass 500g), the amount consumed daily in conjunction with the levels found signaled a real health concern. This research finding led the PHLIL Guatemala team to promote nutritional diversity in communities in the highlands in combination with improved practices that reduce post-harvest loss issues, including mycotoxin accumulation.

Seasonality impacts

Mycotoxin contamination can vary significantly by season as well. Weather and environmental factors, especially crop drought stress during grain development and high moisture near and after harvest, can drastically increase the risk of contamination for a given season. PHLIL research conducted in Ghana indicated that aflatoxin levels in maize in the major season (Oct.-Dec.) were detected at significantly higher levels than in the minor season (Jan.-Apr.). One of the potential causes for the increased levels of aflatoxin in the major season is the increased grain moisture content, likely a result of higher rainfall during major season harvesting. Harvest in the minor season overlaps with the dry season, giving farmers a drier environment to harvest and store their grain. These conditions during the grain drying process discourage the growth of the toxin-producing fungi, lowering the presence of aflatoxin. A further insight revealed that heaping – stacking harvested maize for prolonged periods before drying – additionally increased levels of aflatoxin contamination; current PHLIL research is exploring interventions to mitigate increased aflatoxin contamination from this practice.

Tools for prevention

So what can we do to address this threat to our food system? One of the most effective and practicable ways to reduce mycotoxin contamination is to properly dry and store commodities at harvest. Across the seven countries in which PHLIL has worked on mycotoxins, we have developed and validated a diverse set of tools and technologies to improve post-harvest practices.

Ensuring proper dryness before storing is a critical practice to limit mycotoxin contamination; even small variances in moisture content can make a big difference when it comes to mycotoxin contamination in stored commodities. With this in mind, PHLIL researcher Paul Armstrong from the USDA Agricultural Research Service, developed an Equilibrium Moisture Content moisture meter to provide a lower-cost, easy to use and very accurate tool for moisture measurement. After extensive field-testing, the GrainMate moisture meter is now being produced, marketed and distributed in Ghana by Sesi Technologies, a startup led by a young Ghanaian entrepreneur.

Once the grain is dry enough, it also needs to be properly stored to keep mycotoxins at bay, especially in high humidity environments. Hermetic storage is a proven technology to keep grain safe and maintain quality, but cost of hermetic bags remains a challenge for the lowest income farmers. PHLIL has partnered with Vestergaard to develop and establish distribution networks for the ZeroFly® hermetic bag. Vestergaard’s new “combi bag” reduces the bag’s plastic from three layers to one, making the bag cheaper and more environmentally-friendly, without losing efficacy.

Even simple changes to drying and storing practices can make a considerable difference in reducing mycotoxin accumulation in stored products. This makes providing education that is accessible for low-literate learners critical. In Guatemala, PHLIL worked with a local illustrator to produce educational materials that are simple, culturally appropriate and in tune with critical gender roles and perceptions in the post-harvest space. PHLIL has also partnered with Scientific Animations Without Borders to develop educational videos on mycotoxins and post-harvest practices that are available in many different languages.

Predicting risk

Because mycotoxins can vary from season to season and be affected by multiple factors, including temperature and rainfall, PHLIL is also developing methods to predict where aflatoxin contamination may be an emerging problem as harvest approaches within a given season. In Nepal we are combining survey data with additional environmental data to build a risk map that can help identify where aflatoxin hotspots might pop up in a given season, based on weather factors and past incidence. This mapping is being led by Dr. Ross Darnell at the Commonwealth Scientific and Industrial Research Organisation in Australia. Using the PHLIL aflatoxin survey data, combined with weather data provided by the Government of Nepal Department of Hydrology and Meteorology, Dr. Darnell was able to build a preliminary risk map, which he hopes to refine with future work and added data. Such risk maps could play a transformational role as decision-support tools to determine the most effective routine intervention strategies for a given geographic area and as surveillance to target further on the ground testing and more intensive post-harvest interventions to areas with highest contamination risk at and after harvest.

Capacity building for stronger national systems

The work that we do at PHLIL does not just seek to identify the problem or prescribe solutions. We work hand in hand with trusted in-country research leaders to build national research system capacity to monitor and address the threat of mycotoxins over the long term. USAID Missions provide invaluable guidance and linkages as we seek to catalyze these partnerships and extend project findings into broader programming and policy consideration. PHLIL worked in Nepal and Honduras to establish fully operational mycotoxin analysis laboratories. This included intensive and sustained training of technical staff, back in the U.S. and in situ in the country labs. Laboratory capacity has been enhanced through PHLIL programs in Bangladesh, Ethiopia, Ghana and Guatemala as well. These efforts position our in-country research teams to convene and lead the development and execution of ambitious and realistic strategic plans. In August 2019, a large and intensive national stakeholder workshop was held in Nepal that brought together professionals in the Ministries of Agriculture, Health, and National Planning, as well as several civil society organizations to collectively discuss policy approaches to addressing mycotoxins. Over four days, stakeholders considered evidence and possible interventions from Nepal and globally and formulated priorities to address this challenge in Nepal over the short-, medium- and long-term. Following the 2017-2019 PHLIL Nepal project, the Nepal Academy of Science and Technology agreed to continue funding the laboratory on an ongoing annual basis from core institutional funds, to continue building evidence and serving as a national resource to address mycotoxins in the Nepali food supply. This type of local investment is critical to realizing sustainable impact on research and policy that addresses mycotoxins and other post-harvest issues.

Conclusion

Mycotoxins are an elusive menace that are difficult to detect, and for which solutions must be locally appropriate at each level of the value chain. Alongside others in the Innovation Lab and agricultural research community, the Post-Harvest Loss Innovation Lab is undertaking aggressive and robust research to identify the scope of the challenge, develop means to address it and equip national research systems in Feed the Future countries with the tools to establish a sustainable and consistent testing and mitigation strategy to better safeguard our food from the destructive impacts of mycotoxin contamination.

To learn more about PHLIL’s work visit ksu.edu/phl. A full list of our partners can be found here.