Illegal marijuana vape pens in California were found to be tainted with potentially dangerous additives, state officials said Monday.

A random sampling of more than 10,000 seized devices from unlicensed cannabis retailers in Los Angeles last month found the products contained undisclosed additives and significantly lower amounts of THC than indicated on the label, according to California’s Bureau of Cannabis Control.

The agency is urging consumers to scan QR codes to determine whether they are purchasing from licensed businesses.

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“The prevalence of dirty and dangerous vape pens at unlicensed cannabis stores demonstrate how important it is for consumers to purchase cannabis goods from licensed retailers, which are required to sell products that meet state testing and labeling standards,” bureau Chief Lori Ajax said in a statement.

Officials said they seized more than two tons of cannabis and cannabis products worth more than $10 million, in addition to 11 illegal firearms. The operation also resulted in 125 arrests, according to the agency.

A California Department of Public Health test found that 75 percent of the tested samples contained undisclosed additives, including cutting agents such as vitamin E, vitamin E acetate, propylene glycol, polyethylene glycol and medium chain triglycerides.

THC content was also incorrectly labeled on nearly all the samples, and some contained as little as 18 percent THC, the cannabis control bureau said.