August FrankTalk​
The topic of August's FrankTalk (date and venue TBD) will be the conversion of CBD to THC, and the legal and medical implications of this little-known phenomenon. I'll update blog with more details and source references in the coming week, but for now, here's the summary:

tl; dr
Cannabidiol (CBD) and tetrahydrocannabinol (THC) are nearly identical, but whereas THC is psychoactive, CBD is not. The two compounds differ only slightly in chemical structure - CBD is bicyclic ("two-ring") and THC is tricyclic ("three-ring"). The carbon and oxygen molecules in the partial central ring of CBD will rearrange under various natural and artificial conditions to form THC. The rate of conversion is influenced by many factors, including length of storage time, exposure to light and air, ambient temperature, acidity, and the presence of protic solvents such as ethanol or methanol (alcohols). 

​http://www.9news.com/news/local/hugo-water-tests-negative-for-thc/280096515
The Colorado Bureau of Investigation (CBI) has ruled out the presence of THC [1] in the water supply of Hugo, CO [2], but the identity of the contaminating compound has not yet been resolved or disclosed. I have a few thoughts though, which I will post later today.  

Side note: Incident Management
Due to the nature of the suspected contaminant (the unlikelihood of THC), there has been some tacit criticism on social media about how this situation was handled by local officials. As mentioned in a previous post, the Duquenois–Levine test creates spurious results, but this is also not widely known. In my opinion, the Hugo water incident was handled very effectively, and with the utmost regard for the well-being of the town's residents.  In just 48 hours:

1. The physical origin of the contamination and possible cause were identified;
2. The community was immediately notified and steps were taken to minimize possible harm;
3. Further analysis was ordered and undertaken;
4. The situation was effectively concluded by this morning

If you require an example of how water contamination issues should *not* be handled, please read about Flint, MI [3]. In Hugo, the coordinated efforts of the Department of Public Works, Dr. John Fox of the Lincoln Community Hospital and Care Center, and Captain Michael Yowell of Lincoln County Sheriff's Office, were nothing short of commendable.

References
1.            Healy, J., A Colorado Town Tests Positive for Marijuana (in Its Water), in The New York Times. 2016.
2.            Villanueva, R., Hugo water tests negative for THC. 2016, Channel 9 News, KUSA.
3.            Graham, D.A., What Did the Governor Know About Flint's Water, and When Did He Know It?, in The Atlantic. 2016.

​Water Contamination in Hugo, Colorado
On 21-July-2016, Officials in Hugo, Colorado reported that they had detected Δ9-tetrahydrocannabinol (THC), the psychoactive compound derived from Cannabis sativa [1, 2], in the town's water supply, and have issued a health advisory warning residents not to bathe or drink municipal water until further notice.

Legal and Pharmacological Threshold of THC
While there is no regulatory limit for THC in water that I'm aware of, there is a widely accepted threshold for THC in industrial hemp-derived products intended for human consumption. Products containing no more than 0.3% THC w/w (3000 ppm) are legal (even by the Federal government) and not considered psychoactive. By application of the same standard, 3000 ppm or lower in drinking water would produce no clinically relevant symptoms or noticeable effects.   

Solubility and Stability of THC
THC is a non-polar compound (i.e. fat-soluble) and does not dissolve or mix well with water [1]. It is also susceptible to degradation by various environmental factors, and upon exposure to light, oxygen, or elevated ambient temperature, rapidly breaks down into inert compounds [3]. In other words, THC would not travel far in groundwater, and wouldn't survive very long even if it did.

The Duquenois–Levine Marijuana Field Test
The water supply in Hugo was evaluated using a color-change assay called the modified Duquenois–Levine Marijuana Field Test (DL test). As the name implies, the DL test is used to screen suspected contraband for the presence of THC and other cannabinoids. Despite its frequent use as a screening tool, it is not widely known that the modified Duquenois–Levine (DL) test reacts with numerous non-cannabinoid compounds [4-8]. For example, the DL test will produce a false positive THC result if used to test sage, cypress, or eucalyptus plant material [5, 6, 9] or over-the-counter sore throat lozenges [5, 6].  
How It Works - Duquenois–Levine Marijuana Field Test (DL test)

How It Works

1. Suspected marijuana sample (Ex. tap water, from Hugo, CO) is added to a vial or pouch containing the DL reagent in liquid form.  No visible reaction occurs and liquid should remain clear or pale yellow in color.
2. Hydrochloric acid is used to activate the mixture, and a visible color change occurs upon reaction of the activated DL reagent with resorcinol [5, 10]. The degree of change and actual color is highly variable and depends on the type of resorcinol in the sample [5, 7, 8].  
3. Chloroform is added to separate water-soluble from fat-soluble resorcinols, with fat-soluble compounds accumulating in the bottom of the sample vial (bottom color layer). [5, 7].