Philadelphia’s first Roundup trial kicked off Tuesday in front of a packed courtroom, with plaintiffs counsel advancing a new claim that has started to emerge in recent litigation over the weedkiller.

Thomas Kline of Kline & Specter, making his opening statement for the plaintiff, asserted that Roundup’s alleged cancer-causing properties are rooted in more than just its active ingredient, glyphosate. He called another ingredient, surfactant, “a problem chemical,” and said it was one of multiple harmful substances in Roundup that were not listed on the product’s packaging.