Mysterious mycotoxins

Grain storage management is critical to control.
Amy Petherick
October 16, 2014
By Amy Petherick

Spores can be present in storage bins, but the fungus will never generate without the right conditions, so best management practices are key.

As a child, the scariest thing about the Boogeyman was that he was hiding so close by that he could attack at any minute but couldn’t be seen. Until recent discoveries by researchers, some mycotoxins had escalated to the same mythical proportions for almost the exact same reasons.

Playing the role of the monster-under-the-bed in this case is a mycotoxin known as ochratoxin A, and any farm with grain storage could be producing it, according to Dr. Art Schaafsma, a researcher at the University of Guelph’s Ridgetown Campus. Schaafsma is working with Victor Limay-Rios to complete a four-year study of the known carcinogen in Ontario grain storage, which has had him analyzing 30 to 40 grain bins a year in the province. He says that when he started looking for spores, indicating the presence of the penicillin relative that produces the toxin, he found spoilage fungus in abundance.

“You can find that inoculum everywhere, but originally, it came from the soil so there are places where we find more of it,” Schaafsma explains. “Manholes, doors, openings where there are air leaks and water getting in – that’s where the spore load is higher.” He says they also found that grain that has not touched the soil and was standing at harvest did not the have inoculum on it. “We did find a lot more inoculum on grain coming from heads in lodged crops or when the wheat field had been sprayed during heading and crop was tramped,” he adds. Basically, any wheat that has touched the ground will be loaded with spores.

Fortunately, Schaafsma has also found out that although spores can be present, the fungus will never generate without the right conditions. “Oddly enough, we’ve found ochratoxin in two of the many bins we’ve looked in, in the last three years,” he says. “So we’ve had six hits in three years . . . out of a whole pile of bins.”

With such sparse results, a budget-conscious researcher like Schaafsma ought to have concluded his study years ago. To understand why the study is still ongoing, he says, consider what instigated the research in the first place.

The ochratoxin hazard
In December 2009, Heinz Canada voluntarily recalled a baby cereal product after the Canadian Food Inspection Agency found elevated levels of ochratoxin A. Parents were simultaneously urged to inspect their pantry carefully, discard product lots immediately, and not worry if the cereal had already been fed to their child. As confusing as that may have been for consumers, it was downright bewildering to the food processing industry. “Raw cereal grains in Ontario were fingered,” Schaafsma recalls, “but most of the grain in this infant food production is coming from the west.” Wheat suppliers faced accusations but Schaafsma says that made little sense when oats posed the biggest ochratoxin concerns, by far.

Academics and international regulators, like Dr. David Miller, couldn’t find much common ground amongst themselves either, Schaafsma adds. Miller is a toxicologist who works at Carleton University in Ottawa and is one of those individuals that world health associations call on for expertise when it comes to mycotoxins. He says the problem with ochratoxin, unlike a mycotoxin like deoxynivalenol (DON), is twofold. “Ergot, vomitoxin, aflatoxin and zeralanone were all discovered because they made humans sick,” he says. “But ochratoxin suffers from the fact that we don’t know as much about it as we would like.” 

Currently, risk assessment evidence can only suggest the toxin has carcinogenic potential rather than confirm whether it is a known or even probable cancer-causing agent. Some countries, particularly those in Europe, have decided to treat the mycotoxin with extreme caution anyway and have established import restrictions Schaafsma says can get as low as 0.5-1 part per billion (ppb). Following the Heinz recall, Health Canada made the unpopular decision to venture into discussions about implementing similar regulations. “The European approach to regulating ochratoxin is not universally accepted,” he says. “This would be the first time a toxin is regulated that we don’t have any sure link to human disease.”

Miller adds that the logistics of finding it present the other side of the ochratoxin hazard. “It’s a one-in-5,000-kernel problem,” he says – not to mention the fact that one kernel is visibly undetectable. But he says the good news, as Schaafsma is confirming, is that all surveillance efforts across the country have been proving that Canada produces really great grain on the whole. Which has put an end to regulation discussions for now. “The question is though, are there little failures here and there that really need to be prevented on the farm? The answer is yes,” says Miller, “and that’s what Art’s work is about.”

Establishing best management practices
Miller believes the great opportunity that has emerged from Schaafsma’s research is a much better understanding of the details farmers can take care of in their storage that will improve the already extremely good quality of the grain that exists in Canada. Schaafsma says this is because they’ve been able to correlate physical indicators directly with the presence of the toxin. “Basically we’re very confident it has to do with moisture during storage,” he says. “It doesn’t have to be in a warm period, most often it’s a freeze-thaw thing.”

During a cold snap of -10 C temperatures over several days, for example, a farmer will ventilate like crazy to cool a grain pile down. Since the pile cools from the bottom up, this creates warm, moist air that has to get out somewhere. Schaafsma says he has found bin downspouts act like a chimney at the top of the bin, and the wet grain he’s finding toxin in is coming from where water condenses then drips down into the centre of the pile.

Alternatively, if there’s a bolt missing in the bin where a lot of snow and ice can get in, these can form hot spots too. Schaafsma says if farmers eliminate these hot spots, they eliminate the chances ochratoxin ever forms in the first place.

“Sampling and analysis is already bad enough for vomitoxin, which you’re trying to manage at a one parts per million,” he says, adding that much like the Boogeyman, once rational thinking, best management practices and good science shed light on this situation, the worry becomes manageable.

 

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