THE CHALLENGE OF ‘NON-DETECTS’ – INTERPRETING AND VALIDATING LOW-LEVEL PFAS DATA

Understanding what a “Non-Detect” Means

At the 2026 Battelle Chlorinated Conference, ddms Senior Environmental Chemist Virginia Clauser took on a frequently asked question: what does a “non-detect” tell you?

Labs can measure PFAS at smaller and smaller concentrations every year, which sounds like good news until you remember that “didn’t detect” and “it isn’t there” aren’t the same thing. Detection limits, background contamination, and how a lab chooses to report results all shape what shows up (or doesn’t) on your final report.

As you can tell on the poster below, non-detect doesn’t mean zero. It means “not above this threshold, under these conditions.” That’s a meaningful difference when regulators, risk assessors, and your own team are making decisions based on that number.

The fix isn’t complicated, but it does take discipline, solid QA/QC, and a careful second look at the data before anyone draws a conclusion from it.

With PFAS, what you don’t see can matter just as much as what you do — as long as you know how to read itWhen it comes to PFAS, “non-detect” sounds like good news — nothing there, nothing to worry about. But at the low concentrations where PFAS matters most, a non-detect (ND) is really just a claim. And like any claim, it needs to be validated. 

Virginia Clauser recently presented this topic in a talk called, “The Challenge of Non Detects — Interpreting and Validating Low-Level PFAS Data” at the July 2026 Department of War Environmental Monitoring Data Quality (EMDQ) webinar. 

The webinar used laboratory-scale validation exercises to examine how field and laboratory quality-control results — including blanks, surrogate recoveries, laboratory control samples, and matrix spikes — were evaluated when interpreting PFAS data. It highlighted how factors such as blank contamination, reporting limits, rounding conventions, and data-qualification decisions could influence whether a result was reported or interpreted as detected or non-detected, particularly at very low concentrations. 

For risk assessors, project chemists, and decision-makers, this isn’t academic. A misclassified ND can shift a risk assessment, close out a site too early, or underestimate exposure for a community that’s counting on your data being right. 

Ultimately, ND does not equal zero — validation provides the context necessary for confident PFAS decision-making. 

You can watch the full webinar here.