Microplastics are tiny pieces (less than 5 mm in diameter) of plastic that end up in the environment from sources such as cosmetics, synthetic textiles, car tires, industrial processes, and the breakdown of larger plastics. Growing regulatory and scientific concern about microplastic pollution in lakes, oceans, and drinking water is increasing the demand for laboratory analyses to measure microplastic concentrations in water samples.
This article summarizes the current state of the art for analyzing microplastics in different types of water, covering analytical methods, sample pretreatment, sampling considerations, testing standards, and typical reasons to perform testing.
Analytical methods
The three most common methods for detecting and quantifying microplastic concentrations in water are micro-FTIR spectroscopy (µFTIR), micro-Raman spectroscopy (µRaman), and pyrolysis-GC/MS (py-GC/MS). µFTIR and µRaman determine the number of microplastic particles by plastic type and size range, whereas py-GC/MS quantifies mass concentrations of specific types of microplastics in mg/l. The key strengths and limitations of these methods when used for water testing are summarized in Table 1.
Table 1: Comparison of common microplastic analysis methods for water samples
Method | Particle size range / detection limit | Ideal use cases | Advantages & limitations |
µFTIR | From 10 µm to ~2,000 µm | Routine, cost-effective particle size-based analysis of clean water and wastewater | + Fast, high-throughput method + Little interference from inorganic compounds and pigments - Lower spatial resolution than µRaman - Possible interference from water |
µRaman | From 1 µm to ~2,000 µm | Analysis of small microplastics (<10 µm) in clean water samples | + Better spatial resolution than µFTIR + Lower interference from water - Lower throughput - Interference from inorganic compounds and pigments |
py-GC/MS | ~100 nm* Down to nanograms per plastic type | Mass-based quantification of microplastics in a wide range of water samples | + Robust identification & quantification + Good sensitivity - No particle size information - More limited range of quantifiable polymers than µFTIR and µRaman |
* py-GC/MS does not provide particle size information directly. However, the sample can be passed through a series of filters with decreasing mesh sizes before analysis, allowing the mass concentration of microplastics within specific size ranges to be quantified.
The specific water matrix influences method selection, as different methods are susceptible to different sources of interference. As a general rule, µFTIR is better-suited than µRaman for water matrices that contain a significant amount of suspended solids, as it is less susceptible to fluorescence interference from inorganic particles, organic matter, and pigments often present in turbid water samples.
Pyrolysis-GC/MS can be used for both clean and less clean water when the mass concentration of plastic particles rather than the particle count is of interest. It is also the only method that can, at least in theory, be used to study nanoplastics (<1 µm diameter particles). However, the mass of particles—obtained through cascade filtering—within the nanoplastic size range can be so small that it falls below the detection limit of the method.
For a more detailed comparison of these methods, see our webinar on analytical techniques for microplastic analysis.
Sample preparation
Clean water samples, such as drinking water and ultrapure water, are the most straightforward matrix for microplastics testing, as extensive pretreatment is not needed to separate the plastic particles from the sample. The sample can simply be passed through a filter with an appropriate mesh size to capture the particles of interest, after which the filter is analyzed directly with a FTIR or Raman microscope, or the material retained on the filter is transferred to the py-GC/MS system for analysis.
Lake, river, and seawater, wastewater, process water, and other more complex samples require a digestion step to separate the plastic particles from other solid residue before analysis can be performed. Hydrogen peroxide (H2O2) is used most often, as it leaves the plastic particles largely intact while effectively dissolving other solid residue.
Sampling considerations
As microplastic concentrations in water samples can be very low—particularly in clean water—contamination during sampling or shipping can seriously compromise result integrity. To minimize sources of contamination, glass containers should be used, and cosmetics and synthetic textiles should be avoided during sampling. A strictly plastic-free environment should also be maintained in the laboratory, and blanks should be run alongside the actual samples to control for background contamination.
Microplastic testing standards for water samples
While microplastic analysis is a relatively new testing field, standardization efforts have moved forward over the past few years. There are now several internationally recognized testing standards for water samples:
ISO 16094-2 outlines a testing procedure for measuring microplastic particle counts by polymer type and size range in clean water samples, such as drinking water and ultrapure water, using µFTIR and µRaman.
ISO 16094-3 is in the final draft stage and awaits publication. It focuses on testing clean water samples with thermoanalytical methods (py-GC/MS and TED-GC/MS).
ISO 24187 outlines general guidelines for analyzing microplastics in water samples rather than a specific method. It also contains a classification table that can be used to estimate the mass of plastic particles based on their count and size range, or vice versa. This can help compare results obtained with microspectroscopy and thermoanalytical methods.
ISO 4484-2 focuses specifically on microplastic quantification in textiles and wastewater from the textile production process.
In addition to the above standards, Commission Delegated Decision (EU) 2024/1441 specifies a harmonized methodology for measuring microplastics in drinking water with vibrational microspectrocopy methods, including µFTIR and µRaman.1 The method is intended for monitoring microplastic concentrations under the Drinking Water Directive (EU) 2020/2184, once microplastics are added to the watch list of substances of concern referred to in the directive.2
When and why should water samples be tested for microplastics?
The regulatory environment around microplastics testing is evolving rapidly in the EU. In addition to their planned inclusion on the Drinking Water Directive watch list, the Urban Wastewater Treatment Directive (EU) 2024/3019 requires authorities to monitor microplastic concentrations at the inlets and outlets of large urban wastewater treatment plants.3 However, neither directive currently specifies a maximum permissible level of microplastic pollution.
While actionable regulatory limits are pending, companies and research organizations already have many reasons to test water samples for microplastics. These include:
Assessing and improving filtration efficacy in wastewater treatment, shipping, and the textile industry
Investigating the presence and sources of microplastics in bottled water to reduce contamination
Monitoring microplastic pollution levels in natural bodies of water to plan remediation efforts
One partner for all your microplastics testing needs
Measurlabs offers microplastics testing for various water matrices using both spectroscopic and thermoanalytical methods:
Testing is also available for a range of additional matrices, including food, cosmetics, blood, and other biological samples. Use the form below to ask our experts for more information or a quote.
References:
1 Commission Delegated Decision (EU) 2024/1441 laying down a methodology to measure microplastics in water intended for human consumption
2 Article 13(8) of the Drinking Water Directive (EU) 2020/2184 outlines the Commission’s intention to “establish and update” a watch list of substances of concern, specifically mentioning microplastics as an example of the types of substances that will be added to the list.
3 Article 21(3) of the Urban Wastewater Treatment Directive (EU) 2024/3019 obliges competent authorities to monitor microplastics and other pollutants at the inlets and outlets of treatment plants that handle a wastewater load of at least 10,000 population equivalents.