Research reveals how linear alkylbenzene sulfonate (LAS) in detergents interferes with microplastic removal during water treatment
Imagine washing synthetic clothing, and with every rinse, thousands of invisible plastic fibers flow down the drain. Along with them goes linear alkylbenzene sulfonate (LAS), the active ingredient in many household detergents.
Recent scientific research reveals a troubling interaction: the very detergent designed to clean our clothes may be complicating the removal of dangerous microplastic pollution from our water.
Global plastic production annually, with significant portion degrading into microplastics9
LAS surfactant used worldwide each year in detergents and cleaning products7
When these two substances converge in wastewater, they create a complex challenge for water treatment facilities striving to provide clean, safe water.
Tiny plastic particles smaller than 5mm that persist in the environment and resist natural settling in water.
The active ingredient in most laundry detergents with both hydrophilic and hydrophobic components7 .
Water treatment process that destabilizes suspended particles to form removable flocs9 .
Did you know? "Aged" microplastics studied in research have been exposed to environmental stressors like UV radiation, which changes their surface properties and makes them more likely to attract and transport other contaminants1 .
To understand exactly how LAS affects microplastic removal, researchers conducted a carefully designed experiment using jar test methods—the standard approach for evaluating coagulation effectiveness1 .
Researchers first created environmentally relevant microplastics by exposing polyethylene spheres to UVB radiation and hydrogen peroxide for 96 hours, simulating natural aging processes1 8 .
Through preliminary testing, scientists determined the optimal coagulation parameters for removing aged microplastics without LAS present: a pH of 5.0 and an aluminum sulfate coagulant concentration of 4.25 mg/L1 .
Researchers added LAS at concentrations ranging from 20 mg/L to 300 mg/L—spanning typical levels found in domestic wastewater1 .
Using turbidity measurements (which quantify water cloudiness), the team assessed microplastic removal efficiency by comparing the clarity of water before and after coagulation treatment1 .
The results demonstrated a clear dose-dependent relationship between LAS concentration and reduced coagulation efficiency. As LAS concentrations increased, microplastic removal rates dropped significantly, revealing the surfactant's disruptive influence on the treatment process.
| LAS Concentration (mg/L) | Removal Efficiency (%) | Reduction from Baseline |
|---|---|---|
| 0 (Baseline) | 94.79% | - |
| 20 | 89.50% | -5.59% |
| 100 | 82.15% | -13.33% |
| 200 | 77.80% | -17.91% |
| 300 | 76.50% | -19.28% |
Research confirmation: The interference pattern wasn't limited to polyethylene microplastics. Similar studies examining the effect of LAS on zinc oxide nanoparticle removal found parallel results, with efficiency dropping to below 5% at LAS concentrations of 300 mg/L5 .
The interference mechanism stems from LAS's fundamental properties as a surfactant. The same characteristics that make it effective for cleaning also allow it to disrupt the coagulation process.
LAS molecules can adsorb onto both microplastic surfaces and coagulant particles, potentially modifying the charge interactions essential for effective coagulation9 .
LAS may compete with coagulants for binding sites on microplastic surfaces, effectively "blocking" the coagulant from performing its job1 .
LAS can form complexes with coagulant hydrolysates, reducing the availability of these species for microplastic destabilization5 .
By modifying particle surfaces, LAS may increase the stability of microplastic suspensions, making them more resistant to aggregation and settling1 .
Visualization of LAS Interference with Coagulation
LAS molecules (purple) surround microplastics (dark blue) preventing coagulant (light blue) from forming flocs
The implications of these findings extend far beyond the laboratory. With microplastics now detected in human organs, including concerning concentrations in brain tissue where they may be linked to neurological conditions6 , ensuring effective removal during water treatment becomes increasingly urgent.
Recent discoveries show alarming accumulations of microplastics in human brains6 , highlighting the urgent need for effective water treatment solutions.
The interaction between LAS and microplastic coagulation represents a classic environmental challenge—solutions in one area (effective cleaning with LAS) creating unintended consequences in another (microplastic pollution management).
As research continues to unravel these complex interactions, what becomes clear is that addressing our plastic pollution crisis will require integrated approaches that consider the entire lifecycle of products—from their design and use to their eventual disposal and treatment.
The next time you do laundry, consider that the journey of those microplastic fibers and detergent surfactants is far from over once they disappear down the drain. Through continued scientific investigation and technological innovation, we can work toward ensuring that journey ends with effective removal rather than environmental contamination.