When Todd Gullion of Orange County was suffering with back pain last year, he decided to try medical marijuana, thinking it was a safer alternative than prescription drugs. But Gullion says after using the pot, he ended up in the emergency room with serious neurological symptoms.

"My hands go numb, my arms go numb, my feet go numb," Gullion told NBC4. "I feel like I was poisoned."

Gullion was worried that the pot had poisoned him. So he had the product tested at a nationally-known lab. The lab found high levels of toxic pesticides in it--chemicals that scientists say could cause serious health problems.

An NBC4 I-Team investigation found evidence suggesting that pesticides could be present in a lot of the marijuana legally sold in California. And, some scientists are especially concerned about those pesticides being inhaled when people smoke or vape marijuana.

"It's really like injecting that pesticide right into your bloodstream," said former USC Chemistry professor Dr. Jeff Raber, who now runs another prestigious cannabis testing lab.

Dr. Raber co-authored a peer-reviewed study in The Journal of Toxicology about the dangers of smoking marijuana with pesticides on it.

"It could cause damage to your kidneys, to your liver, or other organs," Dr. Raber told the I-Team.

That's because the body doesn't filter the pesticides when inhaled like it does when you eat something with the same chemicals on it.

"You are running a great risk by introducing some of these things which we know have known toxicity with them," said Dr. Raber.

To get a better sense of how widespread pesticide use on California's marijuana products may be, the I-Team obtained 44 samples of marijuana products from 15 dispensaries in Los Angeles, Orange, Riverside, and San Bernardino counties.

At each dispensary, we bought flower marijuana often used for smoking and cannabis cartridges used for vaping. Cartridges are now one of the most popular forms of marijuana consumption. The cartridges contain concentrated cannabis oil and they slip into a "pen" that heats up the marijuana. The marijuana vapors can then be inhaled.

Almost every salesperson at the dispensaries we visited told us their products were pesticide-free.

So the I-Team had the 44 marijuana products tested for 16 pesticides at Steep Hill Labs in Berkeley, one of the nation’s largest cannabis testing labs.

Steep Hill Labs found 41 out of 44 samples, 93 percent, tested positive for pesticides, at levels high enough that those products would've been banned for sale in some other states that currently regulate the use of pesticides in marijuana products.

"It appears pesticides are very widely used" on California's marijuana crops, said Dr. Don Land, a UC Davis chemistry professor who is Steep Hill’s chief scientist. "It was surprising that so many (samples) had so much contamination."

Dr. Land said one possible reason is that California has no laws or regulations banning use of pesticides on marijuana crops, unlike many other states and there are no federally approved pesticides for cannabis

Twenty-six states have laws allowing the sale of marijuana for medical or recreational use.

States like Massachusetts ban use of non-organic pesticides on pot altogether. Other states, like Nevada, Oregon, and Washington have strict limits on how much pesticide residue is allowed on marijuana that's sold. Those states require testing pot products before they go on sale. But California does not.

Dr. Land said some pesticides become more dangerous when they're heated up or burned, like Myclobutanil, a fungicide Steep Hill Labs found in 23 of the samples we sent.

According to the manufacturer, Myclobutanil can turn into hydrogen cyanide when it's heated up. Hydrogen cyanide has been used in gas chambers to kill people.

Even at low doses, Dr. Land said "hydrogen cyanide is very toxic." And someone smoking or vaping pot with Myclobutanil in it "could become ill immediately," Land said.

Although Todd Gullion's doctors have not linked his pot use to his symptoms, Gullion believes pesticides are causing his symptoms.

"It's affecting my balance a bit, my vision, my hearing literally shuts off," said Gullion.

He said he began experiencing those symptoms for the first time after inhaling marijuana from cartridges from a well-known company called Bhang. Bhang says on its website that its products are lab tested for the absence of pesticides.

But Gullion said when he sent one of his partially-used Bhang cartridges to Steep Hills Labs, they found 355 times the amount of myclobutanil allowed on pot in some other states. He said he's stopped using marijuana.

The I-Team bought two other Bhang cartridges and had them tested by Steep Hill. They also tested positive for multiple pesticides including myclobutanil.

"This is terrible for us," said Marco Rullo, a Bhang executive.

He said because of the I-Team's findings, the company is recalling all cartridges from stores that match the lot numbers of those purchased by NBC4.

Rullo said Bhang has all its products tested for pesticides by another lab, which found them to be clean of pesticides. Rullo and others said it's not unusual for different labs to come up with different results when testing cannabis products, because California still has no regulations for testing marijuana.

Rullo told the I-Team that Bhang is going to "take a closer look at the testing we've done and see if there’s a better way to guarantee a pure product."

People who work in the legal marijuana industry say California needs regulations severely limiting and prohibiting use of pesticides on pot and ensure a safe legal marijuana supply.

"I'm seriously concerned about the potential problems of pesticides," said Dr. Jeff Raber. "You're more susceptible when you're doing things by inhalation."

Regulations might not be far off. Proposition 64, passed by voters last November, legalizes recreational marijuana in California in 2018. Prop 64 also requires the state to "establish standards for marijuana products."

The Chief of California's Bureau of Medical Cannabis Regulation, Lori Ajax, told NBC4 they are currently drawing up regulations for pesticide use on pot crops and they should be in effect in 2018.

"All cannabis will need to be tested before it is passed on to the dispensary to be sold," Ajax said.

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