For most volatile organic compound analysis a 14 day holding time is common.

FORBES: Responsible Investing: Is Pall 'Leading' in Water Filtration? (Governor Snyder's Hometown has a 1,4 Dioxane Problem)

The new study has attempted to address some of the criticisms by limiting analysis to "truly" organic systems.

CNN: Study: Organic yields 25% lower than conventional farming

So on the face of it, this latest analysis is a vote for conventional methods above organic.

BBC: Food: Organic growth?