Detecting Microplastics is hard

Microplastics are now infamous for being everywhere; they have been detected in pristine glacier ice and in deepsea caves. But even though they have dominated environmental news since their discovery in 2004, over 20 years later environmental analytical scientists are still debating on the best methods for their detection.

There are multiple challenges that make microplastics detection difficult including their small size and how to differentiate them from other small particles in water or other samples. Multiple different methods have been applied towards microplastics detection, providing environmental scientists with a range of tools and possibilities for their analysis. The downside of this, is that different methods will have different "limits of detection," which refers to how small plastic particles can be before the method stops detecting them. The limits of detection for each lab will depend on both the pre-processing of the samples (for example, whether water is filtered or density separation employed) and the detection technique used. Many detection techniques rely on optical microscopy, meaning that the limits of detection can only go as small as ~1 micron. This means that nanoplastic particles smaller than 1 micron will often go undetected. This is critical, as smaller particles typically pose greater health risks than larger ones.

An example of how different detection methods lead to different results can be found in studies reporting on the microplastics levels in bottled water. In the image below we show plots from three recent investigations, all from 2024, estimating the number of microplastic/nanoplastic particles detected from commercial bottled waters. Estimates range from 1 to 250,000 particles per liter. The study finding over 250,000 particles/L has received some scrutiny from the scientific community, with some arguing that blank contamination contributed to the high detection rate and that true values are lower. Our unpublished work in this area detected between 1,000-9,000 counts of plastic particles per liter. Our technique using fluorescent microscopy is also subject to controversy; as some would argue that fluorescent methods give rise to too many false positives even when "quenching" methods are used to decrease the signal from non-plastic organics.

Figure: The lower limits of detection (LLOD) and specific method used for micro/nanoplastic detection leads to a huge range in estimated particles counts in commercial bottled water across different investigations from 2024.

This controversy in the field of microplastics detection means that we still don't have a complete picture of how risky bottled water is for human health. One thing that all studies agree on, though, is that tap water has significantly lower plastics concentrations compared to plastic bottled water. Thus, reducing reliance on single-use plastics (and aluminum cans, see results for Liquid Death in the third figure!) is one of the best ways to limit your exposure to micro and nano-plastics.