Detecting secondhand exposure to marijuana


A new urine test that quantifies very low biomarkers of marijuana smoke can help assess how much children are being passively exposed.

Reviewed by Binnian Wei, PHD; Benjamin C Blount, PHD; Karen Wilson, MD, MPH

A new, highly sensitive analytical test method provides a way to detect and quantify smaller levels than ever before of the analytes associated with marijuana, levels on the order of those produced by secondhand exposure to the psychoactive substance.

Related: Talking to teenagers about marijuana

“Our study is the first [to show] that we can measure marijuana-specific chemicals in people passively exposed to secondhand marijuana smoke,” explains Binnian Wei, PhD, lead author of the study and research scientist in the Tobacco and Volatiles Branch, Division of Laboratory Sciences, of the Centers for Disease Control and Prevention (CDC) National Center for Environmental Health, Atlanta, Georgia. The method is detailed in a study recently published in the journal Analytical Chemistry.1

Wei explains that currently available methods can detect larger amounts of cannabinoids and their metabolites, including urinary delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), and cannibinol (CBN), and 2 major metabolites of THC, 11-nor-9-carboxy-THC (COOH-THC) and 11-hydroxy-THC (OH-THC), which allows analysis of the health effects of primary marijuana use. Limits of detection for these analytes in presently available methods range from 0.2 to 5.0 nanograms per milliliter (ng/mL).

Quantifying marijuana biomarkers

However, persons smoking marijuana can expose other people passively. Such exposure is characterized by very low biomarker levels. The new test method is about 10 to 100 times more sensitive than currently available approaches, with limits of detection ranging from 0.002 to 0.008 ng/mL for “free” (unconjugated forms) and 0.005 to 0.017 ng/mL for “total” (unconjugated plus conjugated forms) measurements, making it possible to study the health effects of secondhand marijuana smoke (SHMS).

NEXT: Clinical utility of new test


The method described in the study uses ultrahigh-pressure liquid chromatography-electrospray ionization combined with tandem mass spectrometry. Wei explains that in addition to using new, top-of-the-line instrumentation, the method owes its increased sensitivity to modifications in sample preparation procedures.

More: Where's the evidence base for medical marijuana?

Benjamin C. Blount, PhD, coauthor of the study and branch chief of the Tobacco and Volatiles Branch, Division of Laboratory Sciences of the CDC National Center for Environmental Health, says that many laboratories have instrumentation similar to what was used in the analysis. “I do think that a number of labs would be interested in bringing this method to their facility,” Blount comments. With the increased legalization and recreational, as well as medicinal, use of marijuana, more people are asking questions about secondhand exposure to marijuana smoke. “With the new method, these questions will be answered based on gold standard scientific analysis with quantitative measurements,” he adds.

According to the study, validation results indicate that the method is accurate (average inter-/intraday bias, <10%), precise (inter-/intraday imprecision, <10%), and fast, with a runtime of about 6 minutes. In addition, improved sample preparation throughput using an automation liquid-handling system makes the test method ideal for potential large-scale population studies. “Large-scale population studies might have several thousand samples, so it is important for us to have a fast method to run samples in a short time,” explains Wei.

Clinical utility of the new test

Asked if the new test method has clinical utility, Karen Wilson, MD, MPH, associate professor of Pediatrics, University of Colorado School of Medicine, Denver, and section head, Pediatric Hospital Medicine, Children’s Hospital Colorado, Aurora, replied, “The short answer is ‘probably,’” although immediate use likely is limited to the research realm.

“The best analogy that we have is tobacco smoke exposure and the use of high-sensitivity testing to monitor that, but unlike tobacco smoke exposure, we have almost no direct data on the effects of secondhand marijuana smoke exposure in children,” Wilson states. “Being able to measure very low levels will give us the ability to look at which children are exposed and then look at their outcomes to see whether marijuana smoke exposure has the same impact as secondhand tobacco smoke exposure,” she says. “If we don’t know what the effects are, it’s hard to say we should be testing.”

NEXT: The importance of connecting exposure with adverse health outcomes


Research shows that children exposed to secondhand tobacco smoke have certain negative health effects, including increased frequency of lower respiratory illnesses and respiratory symptoms, an increased incidence of asthma and number of asthma attacks in those who have asthma, and an increased incidence of middle ear disease and infections, compared with children not exposed to secondhand tobacco.2

Research also shows that there are negative health effects of primary marijuana use. According to the American Academy of Pediatrics, for adolescents, regular use of marijuana can impair memory and concentration and interfere with learning, and it is linked to a lower probability of completing high school or obtaining a college degree. Marijuana use also can alter motor control, coordination, and judgment, potentially contributing to unintentional deaths and injuries, and it is linked to psychological problems, poorer lung function, and a higher likelihood of drug dependence in adulthood.3

Regarding SHMS, Wilson says, “Although we don’t have the studies to say that it has an impact, the likelihood that it does is extraordinarily high, and I wouldn’t use the lack of evidence as tacit approval for parents to go ahead and smoke around their kids,” she says.

Next: Why AAP opposes marijuana use and legalization

“We think that screening, whether by a question or by a biological measure, is a reasonable way to assess how much children are being exposed, so that we can give some advice to their parents about how to reduce that exposure, just like we would with lead. Now that marijuana has become legal in places like my state, we have to council families about not exposing their children to marijuana smoke with no data behind it because we haven’t actually looked at it yet,” Wilson concludes.

“The bottom line,” says Blount, “is that the new method allows us to characterize individuals exposed to secondhand marijuana smoke in a quantifiable way and . . . connect those exposures to potential health effects, if any exist.”



1. Wei B, Wang L, Blount BC. Analysis of cannabinoids and their metabolites in human urine. Anal Chem. 2015;87(20):10183-10187.

2. US Department of Health and Human Services. The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. Atlanta, GA: US Department of Health and Human Services, Centers for Disease Control and Prevention, Coordinating Center for Health Promotion, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health; 2006.

3. Ammerman S, Ryan S, Adelman WP; Committee on Substance Abuse, the Committee on Adolescence. The impact of marijuana policies on youth: clinical, research, and legal update. Pediatrics. 2015;135(3):e769-e785.

Ms Hack is a freelance medical writer and editor in northern New Jersey who has more than 30 years of medical editorial experience. The author has nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article.

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