The city of Denver has ordered a hold on some marijuana plants from six grow facilities after the discovery that pesticides may have been improperly used.

The Denver Fire Department noticed the violations during routine inspections and passed along concerns to the city’s Department of Environmental Health, according to city spokesman Dan Rowland.

“There (is) clear language on the labels to guide their usage, saying it’s not for indoor use, or that the product isn’t intended to be used on items grown for human consumption — like marijuana,” Rowland said.

Rowland said the hold affects only part of the grow effort at the six facilities, adding that those plants can still be maintained and harvested but can’t be marketed at this time.

The plants are being tested by the Colorado Department of Agriculture, with the results expected in about a week. Rowland said that if the results are negative, the plants could be released from the hold.

The facilities can also have the plants tested independently and provide documentation to Environmental Health.

Rowland said the holds represent a small percentage of the city’s 371 grow facilities, but added that it’s possible others could be impacted.