Passive exposure to marijuana

[jaglady]

Since "Shattered" is one of my favorite CSI Miami episodes (My favorite IAB agent has more than one scene in this one), I've been bugged about the passive marijuana exposure thing.

My husband prosecuted a similar case several years ago. A soldier who came up hot on a random urinalysis claimed that he had hung around a buddy who had smoked marijuana, and he had simply breathed the secondhand smoke.

CID (The U.S. Army's version of NCIS), did an experiment to see just how much marijuana smoke would have caused a false positive.

For Delko to have popped positive from passive exposure, the air would have to have been so thick from marijuana smoke that the top two layers of his skin would have burned off. A good way to compare: Take the most smoke-filled room you've ever been in, and multiply it by ten.

Needless to say, this guy got kicked out of the Army.

[suzmicsoc]

Wow...I had always heard of passive exposure to marijuana showing up on a drug test...I guess there is no such thing then.

Thanks for the info JL

[ladytaz29]

Wow...like Suzy, I had always thought it was a legit excuse... I've never even tried it. Don't know anything about it either. I was 38 before I knew a roach wasn't a bug...

[mirium]

There seems to be some disagreement between studies, jaglady. There are certainly studies that say you can't get a false positive from passive exposure:

www.ncbi.nlm.nih.gov/pubmed/3386204

Some say you can:

www.ukcia.org/research/medline/4.htm

And some are mixed:

www.ncbi.nlm.nih.gov/pubmed/3037193 (I interpret "At the lower level of passive marijuana-smoke exposure, specimens tested positive only infrequently or were negative." to mean that false positives are rare but they do occur.)

I must admit that Eric's "passive exposure" explanation sounded unlikely to me. I am *ahem* aware of anecdotal evidence that a person sitting in a dorm room with about half a dozen active marijuana smokers for a period of several hours did not get high from passive exposure (and by the end of the jam session, you couldn't see across the room because of the smoke -- or so I was told. *ahem*). However, the same individual didn't feel any effects on another occasion when she actively smoked a joint, either, so that result could be due to high tolerance in one individual.

On the other hand, the sample size is awfully small in all the tests I found via Google -- usually less than half a dozen subjects in each. That's enough to find out what's usual, but not enough to spot rare effects -- say, 1 in 500.

Any idea how many subjects were tested in the CID studies? I'm just curious, personally I agree with you that this is another example of CSI:Miami using a factoid without understanding the science, and getting it wrong. (You should have read my rant on the CBS board after the "Triple Threat" episode, they messed up six ways from Sunday in that one!)

[jaglady]

Well, hubby came back with this. And if I'm wrong, I'm red-faced.

CID does urinalysis tests in two phases: preliminary screening and actual screening. If a sample contains 50 or more nanograms of THC per mL of urine, the sample is what's called "presumptive positive" and is screened again. If the sample is then 100 or more nanograms per mL, the person is positive.

I guess what they're saying is "it's possible."

And you're so right about scientific accuracy. I guess because I'm a purist, I try to look things up.

Hey, thanks for setting me straight on that.

[mirium]

Your face can stay its usual delightful color, jaglady. ;D

The "it's possible" studies I linked to gave "positive" thresholds of 6.8 and about 13 ng/ml in the urine assay, respectively, which is MUCH lower than the 50 or 100 ng/ml in CID study your hubby used. "Positives" in the "it's possible" studies would have been clear "negatives" in the CID study, both in the preliminary and the confirming test. The "it's possible" studies seem to have been investigating whether there would be any THC detected at all, rather than whether there would be enough to conclusively incriminate someone.

I don't remember if the CSIM episode said what threshold they used as "positive", do you? It still looks to me like CSIM was on very shaky ground scientifically, but not absolutely totally indisputably wrong. Pretty darn close, though. ;D

(BTW, I spent more than 10 years doing medical research, so I have some practice at evaluating experimental protocols and comparing experimental results -- stuff that normal people wouldn't know. Kudos for looking it up, that's much better than taking it on faith and 'way more than most folks do!)

Anyone know if the episode said how much THC was found in Eric's samples?

[suzmicsoc]

They did not state the levels of THC that were in Eric's samples...when asked if he had evidence that the exposure came from active use, Stetler stated, "there is really no way to tell..." ;D