Microplastics in water: Understanding the risks

Tiny pieces of plastics or polymers were found in the ocean in the 70s, however the term Microplastics (also known as MP) was introduced in the early 2000s. MPs refer to plastics or polymer pieces that are small in their physical dimensions.  According to the U.S. Environmental Protection Agency (U.S. EPA), MPs are plastic particles ranging in size from 5 millimeters (mm) to 1 nanometer (nm).  Within this general range, MPs with the size ranging from 1nm to 1000nm are further defined as Nanoplastics (NP).  There are two major sources of MPs: primary and secondary.  Primary MPs are used in certain products such as personal care products, cosmetics, and industrial nurdles. Secondary MPs, on the other hand, refer to the plastics pieces coming from the degradation of larger pieces of plastic such as bulk plastics sheets, textiles, films, pipes, etc.

Due to the ubiquitous nature and the small size of MPs, it is estimated that on average humans are consuming about 5 grams of plastics (a plastic credit card) every week¹. While the impact of MPs on human health is still under investigation, several potential health risks have been identified. For example, ingested MP can accumulate in the gastrointestinal tract and potentially lead to physical irritation, inflammation, or damage to the intestinal lining. The inhalation of airborne MP is another concern, especially in urban areas. Once inhaled, these particles could lead to respiratory problems. In a 2024 Harvard health paper², it has been pointed that people with MPs in the plaque clogging their neck arteries were far more likely to have a heart attack or stroke than people with MP free plaque. All these acute health impacts are a call to action.

Both primary and secondary MPs once released into the environment will undergo complex environmental-induced degradation and depending on the types of plastics and their chemical make-up, additional toxic species such as phthalates, catalysts residues, and additives can be leached into the environment. In addition, MPs and NPs can serve as carriers for other toxic contaminants, such as heavy metals and endocrine-disrupting chemicals. Further, certain PFAS such as perfluorooctanesulfonamide (FOSA) has a higher affinity toward hydrophobic polyethylene (PE), a very common source for MPs and NPs. Lastly, plastics are widely used in household plumbing, piping, and membrane treatment processes, all of which degrade over time. If we do not carefully consider the impacts of material selection, we risk introducing more MPs into our water systems, creating additional problems. It is therefore crucial to evaluate material choices meticulously to avoid contributing to the generation of microplastics.

Due to their small size, the detection and measurement of MPs is a challenging task. This is especially true for measuring MPs in water. For example, due to their low concentrations (can be a few particles per 1000 liter), MPs must first be concentrated using a concentrating means to accumulate enough quantity for further characterization. Once enough samples are collected, microscopy and spectroscopy means will be employed to measure and quantify the samples. All these are extremely labor-intensive endeavors. In addition, the presence of co-contaminants on the MPs remains a challenging task.
 
Management of MPs in wastewater and drinking water is an emerging field. The relatively good news here is that it has been demonstrated that the conventional wastewater and drinking water processes can remove most of the MPs (>1 micrometer). For example, in the wastewater treatment process, the primary treatment can remove up to 98% MPs, whereas secondary treatment can remove up to 99% of MPs³. In the drinking water treatment process, the removal of MPs can be as high as 80% using a combination of coagulation/flocculation, sedimentation and filtration⁴. However, the removal efficiency of NPs remains unknown due to the limitation in testing and evaluation. To note, in addition to the existing water treatment technologies, emerging technologies such as dynamic membrane filtration⁵, coagulation⁶, and microbial degradation⁷ are also being evaluated to actively remove MPs from the water. It is also worth noting that as a common by-product for WWTP and DWTP, sludge and biosolids have been shown to carry high levels of MPs. The MPs in the sludge and biosolids can lead to MP pollution when land applied. As such, the understanding of the fate and transport of MPs and ways to retard or destroy MPs warrants further analysis.

The management of MPs and NPs is a complex task which requires the characterization of these fine plastics pieces, assessing the toxicity of MPs/NPs, their health and environmental related impacts as well as their co- contaminants, addressing the interaction of MPs/NPs with existing water treatment technologies, and the understanding of the fate and transport of MPs/NPs in the environment. Much of this requires the expertise ranging from environmental science, materials science, chemistry, geology, modeling and simulation among others that GHD can offer.

Should you have any questions on these topics, please reach out to us!

 

References:

1. Plastic ingestion by people could be equating to a credit card a week / Featured News / Newsroom / The University of Newcastle, Australia. [Plastic ingestion by people could be equating to a credit card a week / Featured News / Newsroom / The University of Newcastle, Australia]
2. Microplastics in arteries linked to heart disease risk - Harvard Health.
3. Carr, S.A., Liu, J., Tesoro, A.G., 2016. Transport and fate of microplastic particles in wastewater treatment plants. Water Res. 91, 174–182. doi: 10.1016/j.watres.2016.01.002.
4. Pivokonsky, M., Cermakova, L., Novotna, K., Peer, P., Cajthaml, T., Janda, V., 2018. Occurrence of microplastics in raw and treated drinking water. Sci. Total Environ. 643, 1644–1651. doi: 10.1016/j.scitotenv.2018.08.102.
5. Li, L., Liu, D., Song, K., Zhou, Y., 2020. Performance evaluation of MBR in treating microplastics polyvinylchloride contaminated polluted surface water. Mar. Pollut. Bull. 150, 110–724.
6. Rajala, K., Grönfors, O., Hesampour, M., Mikola, A., 2020. Removal of microplastics from secondary wastewater treatment plant effluent by coagulation/flocculation with iron, aluminum and polyamine-based chemicals. Water Res. 183, 116045.
7. Chuah, L.F., Mokhtar, K., Abu Bakar, A., Othman, M.R., Osman, N.H., Bokhari, A., Mubashir, M., Abdullah, M.A., Hasan, M., 2022a. Marine environment and maritime safety assessment using Port State Control database. Chemosphere 304, 135245. [http://dx.doi.org/10.1016/j.chemosphere.2022.135245](http://dx.doi.org/10.1016/j.chemosphere.2022.135245).