Hidden contamination: Almost half of the wheat harvested in Europe is infected by the Fusarium fungus and therefore contains traces of toxic mycotoxins, a study reveals. In the decade before the pandemic, this rendered 75 million tons of wheat unfit for human consumption.

However, there is a concern: Even the permitted wheat still contains toxin residues, which can lead to chronic, gradual health problems. In addition, not all Fusarium toxins are recorded in the controls.

Wheat is one of our most important staple foods. In Europe, we eat an average of around 66 kilograms of wheat per capita and year – mostly as bread or pasta. But the grain does not have it easy: Wheat is susceptible to drought and heat, which is why particularly dry, hot summers like 2018 lead to severe crop failures. In warm and humid weather, on the other hand, the wheat is often attacked by Fusarium fungi. These plant parasites inhibit grain growth and grain formation and produce toxic metabolites.

However, the Fusarium toxins are toxic to humans and animals. Some of these fungal toxins such as deoxynivalenol (DON) disrupt protein synthesis, can cause growth retardation and, in the case of acute poisoning, nausea and vomiting. Others, including zearalenone (ZEA), disrupt hormone balance and may promote certain forms of cancer. “Grain contaminated with Fusarium toxins can pose a significant threat to our health, particularly as we are only partially aware of their impact on our well-being,” said senior author Neil Brown of the University of Bath.

In the EU, wheat may no longer be used for food from a contamination level of 1,250 micrograms DON per kilogram, and from 750 micrograms it is no longer permitted for direct consumption – for example in cereals. The contaminated grain is then mostly used as animal feed. To determine the extent of contamination in food and feed wheat, Brown and his team analyzed data from two European regulatory authorities on national toxin levels from 2010 to 2019, creating the most complete to date.

The result: “The Fusarium toxin DON was detected in wheat from all European countries,” the researchers report. On average, 47 percent of the grain was contaminated with the fungal toxin. Almost half of the wheat harvested in Europe contains at least traces of fungal toxins. The proportion of contaminated samples was highest in northern Europe and Great Britain, where 69 to 93 percent of the food wheat had increased Fusarium values.

In most cases, however, the exposure was below the EU limit values, and the samples contained an average of 358 micrograms per kilogram. But there were also outliers with more than 14,500 micrograms of DON per kilogram. “We estimate that around five percent of wheat in Europe has exceeded the permitted limit, which corresponds to around 75 million tons over the ten years,” reports lead author Louise Johns from the University of Bath. “The downgrading of this wheat to animal feed means a loss of three billion euros.”

Unsurprisingly, the toxin levels in the wheat fed to animals were significantly higher than in the food wheat. On average, the samples contained 858 micrograms of DON per kilogram, but maximum values ​​ranged up to 49,000 micrograms per kilogram. “This is of concern for animal health, but also shows how high the contamination of our food wheat would be without the limit values,” says Johns.

The problem, however, is that even if food wheat only contains traces of Fusarium toxins, this can be unhealthy in the long term. “There are serious concerns that chronic dietary exposure to these mycotoxins is detrimental to human health,” Brown says. The European food control authority estimates that chronic exposure to the fungal toxin DON already exceeds the tolerable daily amounts for children.

In addition, a large part of the wheat is contaminated with several Fusarium toxins. “25 percent of the food wheat and 45 percent of the feed wheat contained at least one other mycotoxin in addition to DON,” the researchers report. The number of unreported cases is probably much higher because most routine tests do not detect these other Fusarium toxins. “We don’t yet know the health consequences of exposure to multiple mycotoxins at the same time,” Brown says. “However, the increasing proportion of such co-contaminations gives cause for concern, also because of possible synergy effects between the fungal toxins.”

The researchers are also concerned that the Fusarium contamination in southern Europe has increased significantly in recent years. The outbreaks of 2018 and 2019 even reached record levels in the Mediterranean region. “We don’t know what’s causing this increase in mycotoxins, so we need more research here,” says Johns. “But we suspect that the warmer climate, coupled with changing farming practices, is playing an important role.”

According to the scientists, there is an urgent need for better monitoring and research into the problem of Fusarium contamination. “We need to know more about how Fusarium infestations develop in fields and which areas are most at risk in the future,” says co-author Dan Bebber from the University of Exeter. “Especially in the course of climate change, this is becoming increasingly important.” (Nature Food, 2022; doi: 10.1038/s43016-022-00655-z)

Quelle: University of Bath

This article was written by Nadja Podbregar

The original to this post “Half of the wheat is contaminated with fungal toxin” comes from scinexx.