How to test for microplastics in water
Microplastics – defined as small pieces of plastic usually smaller than 5 mm – are becoming ubiquitous in our daily lives: they can be found in everyday products, in our food, and have even been detected in blood. Despite their creeping presence on our planet, there’s currently very little known about the effects of microplastics on humans and the environment. But we do know that their levels are going to increase in the years to come. This makes research essential to understand the effects that exposure to microplastics will have on humans, animals, and the world around us.
Methods for detecting microplastics in water
The presence of microplastics in water is a particular area of interest, posing safety concerns not only for our drinking water but also for the harm they can cause to marine life. When it comes to identifying the presence and characteristics of microplastics in water, there are currently two main steps that are often employed.
First, filtration helps to extract the microplastics from the water. The chosen filter’s pore size will depend on the size of the microplastics of interest. By passing a specified volume of water through the filter, the plastics will be collected and ready for analysis.
Optical microscopy can then be used to image the particles and obtain sizing information, while vibrational spectroscopy techniques such as Raman spectroscopy can be used to identify the polymer type. Light scattering technologies, such as laser diffraction, can also support particle size analysis in suspension.
With both the size and the chemical identity of the particles, we can get a more complete picture of the microplastics present, where they may have come from, and where they might end up in our environment.
Why microplastic particle size matters
Microplastics are broadly categorized as particles ranging from 1 µm to 5 mm in size, becoming nanoplastics when the particle size is below 1 µm. These are then sorted into two main types. Primary microplastics are those that enter the environment in their original size, such as fibers washed from synthetic clothing. Secondary microplastics are formed by the fragmentation of larger plastic items, such as bags or bottles that have not been properly disposed of.
Both types contribute a substantial amount of microplastics to the environment, making it important to understand and minimize both points of entry. The size of the particle can also affect how it travels through the environment, such as in the air, or in the current when in water. When it reaches a human or animal, size can affect how likely they are to enter the organism and where in the body it may end up.
Comparing analysis techniques
There is currently a wide range of techniques available for microplastic analysis, which has resulted in a call for greater standardization between labs. At Malvern Panalytical, we see that the combination of optical microscopy with Raman spectroscopy offers a good understanding of the size and shape of particles, which can help when predicting their potential impact. Raman spectroscopy can identify the types of plastics present and thus distinguish between a mix of polymers, such as PET, PVC, and various polyolefins such as PP and PE.
While infrared spectroscopy and Raman spectroscopy are both widely used to characterize microplastics, Raman spectroscopy offers some advantages. For example, Fourier-transform infrared spectroscopy can typically analyze particle sizes down to 5-10 µm, while Raman spectroscopy is able to reach 1 µm, unlocking many more measurable particles. What’s more, Raman spectroscopy supports measurement in water.
Whichever technique you choose, there are some general precautions to take in the lab to maintain safety and prevent contamination. Analysts should avoid wearing synthetic clothing and using plastic equipment like beakers, filters, and pipettes. Depending on the origin of the water sample, it can also be necessary to carry out some pre-treatment steps to remove contaminants, such as organic matter.
Closing the knowledge gap
Malvern Panalytical is a member of the Netherlands based MOMENTUM project, which has brought together many areas of microplastics research and expertise. As a result, they have recently published a roadmap proposing solutions to minimize the health impacts of exposure to microplastics.
As part of this, the MOMENTUM project has looked to create “microplastic passports” for their samples used in toxicology studies. Malvern Panalytical has contributed by using laser diffraction with the Mastersizer 3000+ instrument to carry out rapid particle size distribution analysis on these samples. X-ray fluorescence (XRF) technology, using the Epsilon 4, has also been deployed to provide fast and accurate identification of the atomic composition of the samples.
Another powerful technology available is the Morphologi 4-ID, which combines automated image analysis with Raman spectroscopy to give particle size, shape and chemical identification information in one measurement. Morphologically-Directed Raman Spectroscopy (MDRS) provides information on both the individual microplastic particles and the sample as a whole.
These techniques and technologies are contributing to a greater understanding of how microplastics in water can impact human and environmental health. But there’s still plenty of work to do. If you’d like to explore the potential for microplastic analysis with Malvern Panalytical’s instruments, please contact our experts today.