Other brands, including Burt's Bees, Desert Essence and EO, are not certified to meet organic food standards but still contained no 1,4-dioxane in the tests.
Method, a San Francisco-based company whose products are sold at Target, intentionally does not call its products "natural," said co-founder Adam Lowry. Instead, the labels say "naturally derived" because the plant oils have been processed with ethylene oxide to make them better cleansers.
Three of its products were tested, and two -- its ultra-concentrated dish soap and a hand soap -- contained 1,4-dioxane.
"For us there are no alternatives that are still effective," Lowry said. "Unless you can have a high-performance product, if you have a green product or a natural product, then what's the point of having one that doesn't work?"
Method's creamy hand soap, which had 7 parts per million of 1,4-dioxane in the tests, has been reformulated and now contains none, Lowry said.
"We 100% believe that our products are completely safe and there's zero risk," he said.
Whole Foods on Thursday declined to say whether the test results would prompt any changes in products sold at its stores. Three of four products tested in Whole Foods' own product line, 365 Everyday Value, contained 1,4-dioxane.
Dishwashing liquids are particularly hard to keep free of 1,4-dioxane because they require surfactants that are powerful grease cutters.
Seventh Generation uses coconut oil in its dish soaps, which although it is processed with a petrochemical and vacuum-stripped, still contains almost 2 parts per million of 1,4-dioxane. Wolf said the only way to remove all traces would be to use another surfactant that irritates skin, which the Burlington, Vt.-based company considers unacceptable.
Seventh Generation is "working with several surfactant manufacturers to look for alternatives to this process to modify coconut oil," Wolf said. "We're not there yet. We have more work to do."