Pesticides in French wine? Sacre bleu! But it’s true.

Bordeaux-based Excell Laboratory tested more than 300 French wines, looking for a range of treatments including pesticides and fungicides. Of the wines Excell tested, 90 percent had some trace of pesticide, though all the wines contained levels below legal limits. (It’s unclear whether or not the study was published in a peer-reviewed journal, however).

Limits for pesticide levels in the European Union vary depending on the agent, but they’re generally very small – for example, wine grapes can only contain a maximum 1 milligram per kilogram of the fungicide myclobutanil, and 0.2 mg/kg of the fungicide penconazole.

But “even though the individual molecules were below threshold levels of toxicity,” Excell head Pascal Chatonnet told the wine magazine Decanter, “there is a worrying lack of research into the accumulation effect, and how the molecules interact with each other.”

Some of the wines tested by Excell contained traces of nine types of pesticides, raising fears that small amounts of chemicals could add up. Data on a supposed "synergistic effect" of pesticides, where combinations of one or more chemicals adds up to something even more toxic than the effects of each individual pesticide’s effects – the chemical equivalent of adding two and two and getting five – has been documented in other settings.

For example, research from the National Oceanic and Atmospheric Agency in 2008 found that a mixture of the agricultural pesticides diazinon and malathion, which are common in streams in the Northwestern U.S., could kill salmon at extremely low concentrations, and dispatched the fish much more effectively than the pesticides taken singly. Mixtures of other pesticides commonly found in the salmon’s habitat also displayed synergistic effects.

But there’s less data available on the interactions between various pesticides and the wine-making process.

“Some molecules will break down during the process of fermentation, and we need more research into what they synthesize into, and more traceability in place,” Chatonnet told Decanter. “But we should not forget that it is not the consumers who are most impacted by this, it is the vineyard workers who are applying the treatments.”

About one-fifth of the pesticides used in France are sprayed onto vineyards, even though wine grapes are grown on just 5 percent of the total land used for crops nationally, according to the Telegraph.

Dozens of French grape farmers have been struck by illnesses that have been traced back to the pesticides they used. One farmer named Yannick Chenet died in 2011, seven years after he accidentally inhaled toxic fumes from his spraying machine. Other farmers have suffered Parkinson’s disease and various types of cancer. Studies have shown that farmers and laborers on vineyards in France tend to die from brain cancer at higher rates than the general population, and also are more likely to develop dementia.

France’s agricultural health agency suspects that the chemical benzene may play a big role, according to the Telegraph.

The EU has been placing more restrictions on pesticide use in recent years, and may tighten them even further. In January, the European Commission called for restricting the use of pesticides with neonicotinoid chemicals, which are believed to be harmful to bees. Farmers should only use such sprays on crops that do not attract these insects, the Commission said.