Colorado's legal marijuana is three times stronger than it was a generation ago and is often contaminated with heavy metals, pesticides, fungus and bacteria, a startling chemical analysis of 600 samples has found. Additionally, modern pot has very low levels of cannabidiol, or CBD, the compound that medical marijuana advocates say gives the drug its healing properties. In most samples, the CBD levels were so small they were undetectable. The findings come from Andy LaFrate, a Ph.D. chemist and the founder of Colorado testing firm Charas Scientific. LaFrate will present the results of his research today at the national meeting of the American Chemical Society in Denver. Scroll down for video . Andy LaFrate, the founder of Charas Scientific, knows that most people think it's a joke when he says he tested 600 samples of Colorado's legal pot . In fact, LaFrate used highly accurate liquid chromatography to isolate all of the compounds within the marijuana samples - and got some surprising results . LaFrate's survey of Colorado's marijuana casts doubt on claims that by legalizing the drug for recreational use in 2012, it would make it safer to consume. 'It's pretty startling just how dirty a lot of this stuff is,' he told Smithsonian.com. Also alarming is the fact that people using marijuana for its reported medicinal properties usually have no way of knowing how much CBD is actually in their products. Colorado only requires marijuana dispensaries to test and advertise the levels of THC - the compound in pot that gets user 'high.' CBD and contaminant levels are not tested. 'I've heard a lot of complaints from medical patients because somebody claims that a product has a high level of CBD, and it turns out that it actually doesn't,' LaFrate says. Children who are given marijuana to control epilepsy can actually be worse off because they're being given strains of the drug with virtually no CBD and high levels of THC, which can trigger seizures, he added. LaFrate's tests used liquid chromatography, a highly accurate method of chemical analysis that separates out the component parts of a substance. LaFrate says more testing is needed on the effects of contaminants on people who consume marijuana . He found that Colorado's legal marijuana has THC levels of 18 to 20percent. Sometimes THC is as high as 30percent. Marijuana from the 1980s usually had THC levels of less than 10percent - meaning modern pot is two to three times stronger than it was a generation ago. It's no coincidence that Colorado's marijuana is dramatically stronger and has dramatically lower CBD levels than the pot of yesteryear. Growers responded to a demand from consumers for more potent pot by breeding varieties with higher levels of THC and less CBD. LaFrate says he found very small levels of genetic variation between 'strains' of marijuana. This means, the claims of pot with exotic names - 'Skunkberry,' 'Ghost Train Haze,' 'Girl Scout Cookies' - are usually just slick marketing ploys. Additionally, much of Colorado's marijuana is contaminated with high levels of fungus spores and bacteria. It's not known what levels of those microorganisms are safe for marijuana and more study on the subject is needed, LaFrate says. Many samples also contained traces of cancer-causing heavy metals, which come from the plants growing in contaminated soil. Others had high levels of pesticides. LaFrate warned that the marijuana growing industry is getting by on it's hippy reputation and that many consumers believe the plants are grown naturally using organic methods - when in fact, that usually is not the case at all. Even more troubling were the 200 samples of marijuana concentrates - or pot extract - that LaFrate tested. These are used to make edibles and can contain up to 90percent THC. Because they are concentrated doses, they can also contain very high levels of heavy metals and pesticides - as the THC level is dialed up, so are the levels of background contaminants. The solvents used like alcohol and heptane to make the concentrates also contribute startling levels of contaminants, LaFrate warned.
Modern pot also has very low levels of cannabidiol, or CBD, the compound that advocates say gives marijuana its medicinal properties . Colorado weed has THC levels of 18 to 20percent - sometime as high as 30percent . Marijuana 30 years ago had THC levels of less than 10percent . Findings come from Dr Andy LaFrate, who tested 600 marijuana samples with liquid chromatography . Also found high levels of fungus, bacteria, heavy metals, pesticides and other contaminants in much of the pot .