The weed-killing chemical involved in a Monsanto lawsuit was found in Cheerios and Quaker Oat bars. Here's how worried you should be.

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Cheerios' Oat Crunch Cinnamon flavor was deemed particularly hazardous by the report.

• A new round of tests from the Environmental Working Group shows the presence of a weed-killer in children's breakfast foods like Cheerios and Lucky Charms.
• The chemical in question, known as glyphosate, has been tentatively linked to cancer, though many scientists argue the evidence isn't there yet.
• All but two of the 28 samples in the report showed "harmful" levels of glyphosate, but this safety threshold is far more stringent than the EPA standard.
• As the scientific community awaits further research, consumers are left to decide whether the products pose a risk.

Ten weeks after the Environmental Working Group published a report revealing the presence of weed-killer in children's breakfast foods, a new round of tests is likely to generate additional concerns.

In August, the EWG discovered traces of glyphosate - the most widely used agricultural pesticide in the world - in dozens of Quaker, Kellogg's, and General Mills products, including beloved cereals like Cheerios and Lucky Charms.

The timing of the report aligned closely with a $289 million lawsuit against Monsanto (recently acquired by Bayer), which uses glyphosate as the active ingredient in its popular herbicide, Roundup. Earlier this week, a judge denied the company's motion for a new trial after the court ruled that Monsanto knew its product was "dangerous" and could potentially lead to cancer.

In its August report, EWG tested the levels of glyphosate in 45 samples of conventionally grown oats, before determining that 31 samples fell below their safety criteria. Their latest study adds another 28 samples to the mix, focusing exclusively on Cheerios and Quaker oat products. This time, all but two of the samples showed "harmful" levels of glyphosate (at least according to EWG's measures).

But there's a catch: We don't yet know whether glyphosate is actually linked to cancer. As it stands, the majority of published research finds that glyphosate isn't a health threat at the low levels at which consumers are exposed.

Does glyphosate cause cancer?

Certain scientific groups have defended the link between glyphosate and cancer, but others aren't convinced. Organizations such as the Environmental Protection Agency, European Commission, Canadian Pest Management Regulatory Agency, and the WHO International Programme on Chemical Safety have all determined that glyphosate does not present a public health concern.

Much of the argument surrounding glyphosate boils down to a report published by WHO's International Agency for Research on Cancer (IARC), which said the herbicide was "probably carcinogenic in humans." But an extensive review of the material found that the IARC had edited parts of the document that didn't align with its conclusion.

While some scientists have backed away from the IARC findings, others are doubling down. According to Alex Lu, an associate professor of environmental exposure biology at Harvard, the IARC is a "world renowned and reputable" institution whose findings have benefitted global cancer researchers.

Having conducted his own research of pesticides in children's diets, Lu believes the EWG's safety measures to be relatively conservative. "In my opinion, EWG's [threshold] is too high," he said. "This is especially true for parents buying breakfast cereals for their infants and children." Lu is not affiliated with EWG, though they've covered his findings in the past.

According to the EWG, any cereal with a glyphosate level of more than 160 ppb, or parts per billion, is considered unsafe. The legal limit outlined by the Environmental Protection Agency is 5 parts per million - or 5,000 parts per billion - for adults. That makes the EWG's threshold a whopping 31 times more stringent than the EPA regulations, though it's common to enforce stricter limits for children.

"Since children have an increased susceptibility to cancer-causing substances, it's standard scientific practice to include a tenfold margin of safety," said Tasha Stoiber, a senior scientist at the EWG.

Are Cheerios safe to eat?

In the wake of the EWG's findings, both General Mills and Quaker have insisted that their products are safe. In August, the companies released statements to Fast Company, citing their compliance with EPA standards.

"Our products are safe and without question they meet regulatory safety levels," General Mills stated.

"Once the oats are transported to us, we put them through our rigorous process that thoroughly cleanses them," Quaker wrote in a statement. "Any levels of glyphosate that may remain are significantly below any regulatory limits."

But it still warrants the question: Are the EPA's standards up to par?

A 2017 study published in the Journal of Epidemiology and Public Health argued that it could be time to reassess our criteria. The report found enough evidence to suggest that the current EPA standard for glyphosate is "outdated and may fail to protect public health or the environment."

According to the EWG report, "the EPA's standards for pesticides and other chemicals are also heavily influenced by lobbying from industry."

Despite these claims, there's still not enough data to determine a risk. For this reason, Lu said, people might want to limit their exposure to glyphosate as a precautionary measure.

Those worried about the safety of their breakfast should consider what the EWG has to say about individual foods. Of the 28 new samples, Quaker Oatmeal Squares showed the highest levels of glyphosate - nearly 18 times higher than the group's safety threshold. Other foods that stood out as particularly hazardous by the report's standards include Quaker Overnight Oats and Cheerios' Oat Crunch Cinnamon flavor. But even these foods wouldn't be considered unsafe by the EPA.

As with any scientific study, it's possible that new research could shed light on the EWG's warnings. Even studies that once seemed definitive have been called into question: A zero-calorie sweetener called saccharin was recently determined not to cause cancer after decades of being labeled a carcinogen.

It's also possible that scientists could uncover new safety concerns for crops like wheat, barley, beans, and chickpeas, which are exposed to glyphosate during pre-harvest.

With the majority of research still to come, it's up to consumers to decide whether their breakfast foods are safe to eat.