Microplastics regulation is gaining momentum. What should utilities do now?

Microplastics are everywhere. They have been detected worldwide in water bodies, treated water, soil, biosolids and other environmental media, but questions remain about how they should be defined, measured, assessed and managed. Nanoplastics, particles smaller than 1,000 nm or 1 μm, add further uncertainty because their size makes them more likely to interact with cell membranes and more challenging to detect and characterise. As definitions, analytical methods, risk thresholds and regulatory expectations continue to evolve, utilities have growing evidence of a problem but limited certainty about how to respond.

Regulators are beginning to act despite these uncertainties. The European Commission has adopted a harmonised methodology for measuring microplastics in drinking water, creating a common basis for monitoring and reporting across Member States. In the US, the EPA included microplastics on its draft Sixth Contaminant Candidate List (CCL6) in April 2026. However, the current Unregulated Contaminant Monitoring Rule (UCMR6) proposal does not include microplastics monitoring, reflecting technical challenges, such as the lack of a health-based definition and well-established test methodologies. While jurisdictions may be moving at different speeds, regulatory attention continues to build.

Utilities should act before requirements are settled, building the evidence needed to respond as expectations change.

A useful baseline starts with clarity about what the data represents. With no universally accepted definition or methodology for microplastics detection, results can vary depending on how samples are collected, analysed and reported, limiting comparability across studies and laboratories. Sampling scope, detection limits and analytical methods therefore need to be clearly documented.

Standards are beginning to provide more structure. ISO 24187:2023 establishes common principles for sampling and laboratory analysis, while ASTM standards (such as D8332, D8333 and D8401) cover stages from sample collection and preparation to particle identification, quantification and characterisation. California has taken a similar structured approach, combining a common definition, testing methods and laboratory accreditation with a four-year, two-step monitoring program to generate consistent data.

Monitoring locations and scope should reflect the operational, environmental or risk-management question and the parts of the system being assessed. This creates a repeatable baseline that can expand as methods and requirements develop.

Detecting microplastics does not, on its own, establish a human health or environmental risk. Potential impacts depend on particle size, chemical composition, particle concentration, exposure pathway and associated chemicals. Experimental studies have identified possible human health effects including gastrointestinal inflammation, generation of oxidative stress and cellular damage, while studies have also reported plastic particles in human organ tissues and placentas. Their relevance to real-world exposure through drinking water largely remains uncertain.

Due to their surface chemistry and high specific surface area, microplastics can act as vectors for a wide range of co-contaminants, including per- and polyfluoroalkyl substances (PFAS), heavy metals, pharmaceuticals and personal care products (PPCPs) and microbial pathogens. The surface characteristics of microplastics, combined with environmental weathering and ageing, can change how these contaminants move through the environment and interact with living systems, adding further complexity to environmental risk assessment.

Conventional drinking water and wastewater treatment processes can remove some microplastics, particularly larger particles, with reported wastewater removal efficiencies ranging from 57 percent to 99 percent. However, these figures depend on analytical capabilities. For example, laser-directed infrared spectroscopy (LDIR) typically measures particles down to approximately 20 μm and may overlook particles less than 20 μm that could pose greater health risks.

The removal efficacy of microplastics also varies with the particle morphology, surface chemistry, and treatment process. Membrane filtration, such as reverse osmosis (RO) may improve removal but can introduce fouling, higher energy demand and costs. Full-scale performance remains under investigation.

Before changing operations or investing in infrastructure, utilities need to understand what their treatment trains remove and what remains. Future treatment decisions, including technologies adopted for PFAS, should also consider potential implications for microplastics management.

Removing microplastics from water does not necessarily remove them from the environment. Treatment can transfer particles into sludge, biosolids, filter backwash and other residual streams. Wastewater treatment, for example, can concentrate microplastics into sewage sludge, creating the potential for re-entry into soils or waterways through disposal or reuse.

Once widely dispersed, microplastics become harder to detect and remove as they fragment and spread. Modelling suggests that even an 80 percent reduction in plastic pollution sources would stabilise, but not reduce, ocean plastic debris by 2040 because legacy plastics would continue to fragment for decades. This strengthens the case for prevention, source control and interception while particles remain concentrated and manageable.

Water utilities should use what they learn through monitoring to identify likely sources, pathways and accumulation points and guide action. Existing processes, such as coagulation, filtration, backwashing and flushing can be assessed and optimised before major infrastructure changes are considered.

Where pathways overlap, monitoring can be coordinated with existing emerging-contaminant programs. Results can inform treatment upgrades, pilots and infrastructure renewal.

In the near term, two developments are likely to shape the field: standardised methods for microplastics sampling and characterisation and a more health-based definition reflecting characteristics relevant to human and ecological effects. These advances should support more consistent data and better-informed regulatory decisions.

Research will increasingly focus on smaller particles, particularly nanoplastics, contaminant interactions and airborne microplastics and inhalation exposure. Artificial intelligence, machine learning and predictive modeling may also improve particle identification, integrate laboratory and field data and strengthen fate and transport predictions.

The next decade will move the field beyond asking whether microplastics are present toward understanding where they go, what risks they pose and what action is needed.

Microplastics will remain an evolving challenge for water utilities and environmental remediation. Progress will depend on building a defensible evidence base, understanding how particles move and concentrate across systems and translating that knowledge into practical action before contamination becomes more fragmented, dispersed and difficult to manage.