Medical marijuana is legal in 20 states and in Washington, D. C., but safety regulations vary. In states such as Washington and Colorado, where pot is now sold openly in stores, legislators are for the first time putting more rigid testing requirements in place.
Since the legalization of limited amounts of medical marijuana in Colorado in 2000, the state has had no requirements for testing -- it was all voluntary, according to Genifer Murray, CEO of Cannlabs, a private testing company.
"The only reasons for testing have been to market [marijuana] -- to say you have a high THC plant," Murray told ABCNews.com.
She said that in addition to microbes, such as e-coli and salmonella, testers have found resident solvents in hashish, which is made from the resin and other fragments of cannabis.
"When you take the flower of the plant to make hash you need to use a solvent – it can be water, CO2 or alcohol," she said. "All those are safe. But then you have hydrocarbons like butanes and propane."
When Colorado voters approved legalization of marijuana for recreational use in 2012, labs were required to test for residual solvents and perform microbe testing for molds, mildew, salmonella and e-coli, she said. Pesticide testing will be required in 2014.
But so far, the law applies only to marijuana sold in stores to those over the age of 21, not to medical marijuana.
"Since there has been no regulation, there have been a lot of backseat labs and mobile labs with no chemistry who don't know what they are doing," Murray said.
"To be honest – it's absolutely awful," said Murray. "Only about 7 percent of the market is tested. It's very expensive and no one wants to pay for it. But now, it is going to be mandated and they are adding other tests."
Colorado only allows marijuana to be grown in the state, mostly in large warehouses and greenhouses. "Colorado has some of the best genetics in the country," she said.
But even so, mold can grow in hot summer temperatures if air conditioning fails, or if the plants are transported to dispensaries in containers that are humid.
"The last thing we want to do is preach it won't kill you, and then have someone die of contaminated cannabis," said Murray.
Researcher Coyle said that the federal government already had the technology to test agricultural products for potentially dangerous contaminants.
"The food industry has had it for a long time for salmonella outbreaks on eggs and lettuce," she said. "If states are going to allow [marijuana], they should have controlled facilities and monitor those facilities and report to the federal government so there is some measure of safety."