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 . 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 . 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
- 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.
- 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].
- 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].
While it is unclear what contamination is actually in the Hugo water supply, it is unlikely to be THC, based on the spurious nature of the DL test and the poor water solubility of THC itself. Further testing is underway to resolve the question and results should be released tomorrow by the Department of Health.
1. Tetrahydrocannabinol, in Wikipedia. 2016, Wikipedia.
2. Cannabis sativa, in Wikipedia. 2016.
3. Trofin I, D.G., Vaireanu D, Filipescu L, The Influence of Long-term Storage Conditions on the Stability of Cannabinoids derived from Cannabis Resin. Revista de Chimie (Bucharest), 2012. 63(4): p. 422-427.
4. Duquenois–Levine reagent, in Wikipedia. 2016: Internet.
5. O'Neal, Validation of twelve chemical spot tests for the detection of drugs of abuse. Forensic Science International, 2000. 109: p. 189-201.
6. Kelly, The Non-Specificity of the Duquenois-Levine Field Test for Marijuana. The Open Forensic Science Journal, 2012. 5: p. 4-8.
7. Jacobs, Detection of the Duquenois-Levine Chromophore in a Marijuana Sample. Forensic Science International, 2014. 239: p. 1-5.
8. Rubiano, The effect of benzene ring substituents on the mechanism of Duquenois Levine (DL) test for cannabinoid detection. Journal of Chemical and Pharmaceutical Research,, 2014. 6(6): p. 1261-1264.
9. Zaglul, J., An Analysis of Froehde’s and Duquenois-Levine Colorimetric Tests, in Biological Sciences. 2013, Wilkes Honors College of Florida Atlantic University. p. 23.
10. Kovar, Chemistry and reaction mechanisms of rapid tests for drugs of abuse and precursors chemicals, in UN Scientific and Technical Notes. 1989, The United Nations. p. 1-19.
11. Kelly, J., False Positives Equal False Justice. 2008: p. 1-44.