Microplastics and Leachables
20. July 2025
Microplastics and Theory of Change
24. July 2025
Water-soluble polymers:
An invisible threat to our freshwater ecosystems
Water-soluble polymers have become an indispensable part of modern life. We encounter them every day in detergents, cosmetics, paints, and industrial processes. But while these synthetic macromolecules make our lives easier, they pose a growing and often overlooked threat to aquatic ecosystems—especially the sensitive freshwater organisms in our lakes, rivers, and streams.
What are water-soluble polymers?
Water-soluble polymers are large molecules composed of repeating subunits that can completely dissolve in water. Conventional plastics, known as microplastics if they are smaller than 5 mm, remain visible in the environment. Water-soluble polymers, in contrast, seemingly disappear without a trace in the water.
The most common examples include:
- Polyethylene glycol (PEG) – used in cosmetics and pharmaceuticals
- Polyvinyl alcohol (PVA) – the main ingredient in detergent pods
- Polyacrylic acid – used in detergents as a water softener
- Carboxymethylcellulose – a thickener in food and cosmetics
Many laundry detergents contain water-soluble polymers. They are often used to label a product as "microplastic-free," but polymers are still used. © Freepik (licensed)
These substances enter our waterways via wastewater, industrial discharges, and agricultural runoff.
The invisible entry into the environment
The problem with water-soluble polymers lies, paradoxically, in their main property: their water solubility. While conventional plastics are at least partially retained by wastewater treatment plants or can be retained with innovative technologies such as Wasser 3.0 PE-X®, water-soluble polymers pass through these barriers almost unhindered. Studies show that conventional wastewater treatment plants can only remove approximately 20-60% of these substances, although the actual removal rates can vary considerably depending on the polymer type, wastewater treatment plant technology, and operation.
The use of PVA in detergent pods is particularly problematic. Although these dissolve completely in the washing machine, the polymer enters the environment directly via wastewater. Estimates suggest that in Europe alone, several thousand tons of PVA are released into waterways annually via this route.
Effects on Freshwater Organisms
Direct Toxic Effects
Although water-soluble polymers are often advertised as "biologically inert," recent research paints a different picture. Harmful effects have already been demonstrated in various freshwater organisms:
Daphnia (water fleas): These important filter feeders are particularly sensitive to water-soluble polymers. Impaired reproduction and growth are evident even at concentrations of 10–100 mg/L. Since daphnia play a key role in the aquatic food web, these effects can impact the entire ecosystem.
Algae: Various algae species exhibit reduced photosynthetic performance and slowed growth when exposed to PEG and PVA. This is particularly concerning because algae form the basis of the aquatic food chain.
Fish: Developmental toxic effects have been observed in zebrafish when exposed to water-soluble polymers. Embryos showed malformations and delayed development.
The effects of water-soluble polymers on flora and fauna, as well as human health, are still the subject of intensive research, but for years there have been no recommendations for action or prevention strategies. However, we already know that these substances, which are not of natural origin, harm the environment. © Freepik (licensed)
Indirect Ecological Impacts
In addition to direct toxic effects, water-soluble polymers can also indirectly affect the ecosystem:
- Changes in water properties: Polymers can alter the viscosity and surface tension of water, which can impair oxygen uptake and gas exchange.
- Bioaccumulation: Although water-soluble, some polymers can accumulate in organisms and be passed through the food chain.
- Complex formation: Polymers can form complexes with other pollutants, altering their availability and toxicity.
Challenges in Assessing (Eco)toxicity
Assessing the environmental impacts of water-soluble polymers presents us, as well as many other scientists, with particular challenges:
- Analytical difficulties: The detection and quantification of water-soluble polymers in environmental samples is technically demanding and cost-intensive. We have already developed manuals in the UPSTREAM project that enable this detection (quantitative and qualitative).
- Diversity of substances: The large number of different water-soluble polymers with different properties makes a comprehensive risk assessment complex.
- Long-term effects: Since these polymers have only been used in large quantities for a few decades, their long-term effects are not yet fully understood.
Solutions and Alternatives – Different Requirement Profiles: New Paths
The removal of polyvinyl alcohol from wastewater presents a particular challenge due to the complex molecular structure and high biological resistance of these water-soluble plastics. In the INVEST BW project, we are researching new processes for reducing PVA contamination from highly contaminated industrial wastewater. This is a collaborative project with abcr GmbH.
In the UPSTREAM project, we are shifting the issue to the context of municipal wastewater treatment plants. The focus here is on researching new technology combinations for the removal of microplastics, PVA, and PFAS. In both cases, we are using hybrid silica gel mixtures that, in combination with other technologies, are capable of delivering targeted removal efficiencies of over 80% in the municipal sector and more than 90% in the industrial sector.
Regulatory measures are also gaining momentum – but lagging behind the need for action. These include:
- Extended registration requirements: Tightening requirements for the environmental assessment of water-soluble polymers prior to market launch.
- Discharge limits: Establishing specific limits for water-soluble polymers in industrial and municipal wastewater.
- Consumer responsibility
- Conscious product choice: Consumers can contribute by choosing polymer-free or low-polymer products.
- Correct dosage: Avoid overdosing with detergents and other polymer-containing products.
It's not too late, but things shouldn't get worse either! It's time to act.
Water-soluble polymers may be invisible, but their impacts on freshwater ecosystems are real and potentially far-reaching. Evidence so far clearly shows that these substances are not as harmless as long assumed.
A concerted effort by science, industry, regulators, and consumers is needed to address this challenge. Only through early action can we prevent water-soluble polymers from becoming another invisible environmental problem that permanently damages our precious freshwater ecosystems.
Nature knows no invisible pollutants – everything we release into the environment has consequences. It's time for us to act according to the precautionary principle with water-soluble polymers and develop sustainable alternatives before it's too late.
You, too, can support our research and educational work and become an impact accelerator. With donations and sponsorships, we can act much more and faster. Sounds exciting?
