When Ralf Reski read the latest paper from controversial French biologist Gilles-Eric Séralini, he quickly decided he wanted nothing to do with it. Séralini’s report in BioMed Research International describes how pesticides kill cultured human cells, with the hair-raising conclusion that pesticides may be vastly more toxic than assumed by regulatory authorities. Some scientists are criticizing the findings as neither surprising nor significant—but they have touched off a firestorm, with environmental groups calling for changes in how pesticides are regulated. That was too much for Reski. Within hours of reading the paper last week, the plant scientist at the University of Freiburg in Germany resigned as an editor of the journal and asked for his name to be removed from its website. "I do not want to be connected to a journal that provides [Séralini] a forum for such kind of agitation," he wrote in his resignation e-mail to the publisher, Hindawi Publishing Corporation.

To many backers of genetically modified (GM) foods, Séralini is already a bête noire. The scientist at the University of Caen in France made headlines in 2012 with a paper in Food and Chemical Toxicology purporting to show that rats fed a maize variety engineered to resist the herbicide glyphosate were more likely to develop cancer than rats fed non-GM maize. The paper has been widely touted by GM opponents as evidence that GM crops are dangerous. But it hasn’t held up to scrutiny. Scientists slammed the report and in a November 2012 review, the European Food Safety Authority called it "inadequately designed, analysed and reported." The journal retracted the paper a year later, stating that "the results presented (while not incorrect) are inconclusive" due to the type of lab animal and small number used. Séralini counters that those reasons "are unscientific and stupid" and contends that the journal bowed to industry pressure. Some researchers have criticized the decision to retract a paper because it is inconclusive.

In the new work in BioMed Research International, Séralini and three co-authors affiliated with the University of Caen and a private organization founded by Séralini, the Committee for Research and Independent Information on Genetic Engineering, examine the effects of nine pesticides on three human cell lines. Eight of the nine “were several hundred times more toxic than their active principle," the authors write. For example, they found that the herbicide Roundup was 125 times more toxic to cells than its principle active ingredient, glyphosate. "Our results challenge the relevance of the Acceptable Daily Intake for pesticides because this norm is calculated from the toxicity of the active principle alone," the authors write.

Toxicologists have reservations about the study. "There are issues in terms of its design and execution, as well as its overall tone," writes Michael Coleman, a toxicologist at Aston University in Birmingham, U.K., in an e-mail to ScienceInsider. "Anything is toxic in high concentration, the question is whether the toxicity is relevant to the levels of the agents we are ingesting. This paper does not seem to address this issue at all." Martin van den Berg, a toxicologist at Utrecht University in the Netherlands, says the paper deserved to be reviewed. But he, too, questions the experimental design. "The endpoints observed are so general that we could probably find the same kind of toxicity with lemon juice or grapefruit extract," he says. "It's not new or shocking. It is what I would have expected at the level he is giving this to the cells." Séralini dismisses the criticisms as biased. "I recognize the remarks of industry in that," he tells ScienceInsider.

Reski says that while he cannot judge the new paper's scientific merits, he argues that any article by Séralini should be vetted with extra care and that the timing alone was enough to make him suspicious. "It took just 6 weeks for this paper to be accepted, and I think that's inadequate," he says. Paul Peters, chief strategy officer at Hindawi, says the review time was within the normal range for the journal and that the paper "underwent the normal peer review process, which included external review by three independent peer reviewers."

Some say that while they view Séralini’s study as flawed, the central questions it addresses are important. How adjuvants, the compounds mixed with the main pesticide, affect a formulation’s toxicity "is a justifiable angle to explore," Coleman writes. "I do welcome research in this area." Roland Solecki, a toxicologist at the Federal Institute for Risk Assessment in Berlin, agrees that there is a knowledge gap. It’s standard to test acute toxicity of adjuvants used in pesticides in combination with the principle active ingredient, he says. But if there is no indication of an elevated risk, he says, the effects of exposing animals to such a combination repeatedly are not studied, in part to reduce the numbers of animals used in testing. Solecki says that his institute is taking Séralini's study “very seriously” and is assessing it “carefully.”