Surreal illustration of soil pollution and the complex effects of surfactants on plant growth.

Soil SOS: Can 'Cleaning Agents' Actually Hinder Pollution Cleanup?

Samir D’Costa in Climate & Environment August 2025 • 4 min read.

"The Surprising Twist in Soil Remediation: Why Some Surfactants Backfire & What It Means for a Greener Future"

Polycyclic aromatic hydrocarbons (PAHs) are stubborn pollutants lurking in soils worldwide, posing significant risks due to their carcinogenic properties. Bioremediation, the process of using living organisms to clean up contaminated soil, is often used, but its effectiveness is hampered by the fact that PAHs don't dissolve easily in water and tend to stick strongly to soil particles.

To combat this, scientists often turn to surfactants—substances that act like detergents, helping to loosen PAHs from the soil and make them more accessible to the microbes that break them down. Both synthetic surfactants and biosurfactants (naturally produced by microorganisms) have been explored for their ability to accelerate PAH degradation.

However, recent research has uncovered a concerning trend: some surfactants, particularly certain biosurfactants, may actually inhibit the breakdown of PAHs in soil. This article explores these surprising findings, shedding light on why some soil 'cleaning agents' backfire and what it means for a more sustainable approach to soil remediation.

The Biosurfactant Paradox: When 'Natural' Doesn't Mean 'Better'

Surreal illustration of soil pollution and the complex effects of surfactants on plant growth.

A recent study investigated the impact of two types of surfactants on the breakdown of pyrene, a common PAH, in soil: a synthetic surfactant called Brij-35 and a biosurfactant known as rhamnolipid. The researchers tested these surfactants in both natural soils and soils enhanced with Mycobacterium vanbaalenii PYR-1, a bacterium known for its ability to degrade PAHs.

The results revealed a stark contrast in performance. While Brij-35 generally boosted pyrene degradation, rhamnolipid had the opposite effect, especially at higher concentrations. In fact, soils treated with rhamnolipid exhibited a longer lag period before pyrene breakdown began, suggesting that the microbes were preferentially consuming the surfactant instead of the PAH.

Brij-35: Generally enhances PAH degradation, increasing bioavailability.
Rhamnolipid: May inhibit PAH degradation, acting as a more desirable food source for soil microbes.
Bioaugmentation: Adding PAH-degrading bacteria can improve results, but surfactant choice remains critical.

This phenomenon, known as 'diauxie,' occurs when microorganisms consume the most readily available carbon source first, delaying the breakdown of other compounds. In this case, the rhamnolipid biosurfactant appeared to be a more attractive meal for the soil microbes than the pyrene, effectively slowing down the cleanup process.

Rethinking Our Approach to Soil Remediation

These findings underscore the complexity of soil remediation and highlight the importance of carefully selecting surfactants for specific situations. While biosurfactants are often touted as environmentally friendly alternatives to synthetic surfactants, their impact on PAH degradation can be unpredictable.

The key takeaway is that simply adding a 'cleaning agent' to soil doesn't guarantee successful pollution removal. Factors like surfactant type, concentration, soil composition, and the presence of specific microorganisms all play a crucial role in the outcome.

Moving forward, a more nuanced approach is needed, one that involves thorough site assessments, careful surfactant selection, and a focus on stimulating the activity of PAH-degrading microbes. By understanding the intricate interactions within the soil ecosystem, we can develop more effective and sustainable strategies for cleaning up contaminated land and protecting our environment.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.envpol.2018.10.031, Alternate LINK

Title: Influence Of Rhamnolipid Biosurfactant And Brij-35 Synthetic Surfactant On 14C-Pyrene Mineralization In Soil

Subject: Health, Toxicology and Mutagenesis

Journal: Environmental Pollution

Publisher: Elsevier BV

Authors: D.C. Wolf, J. Gan

Published: 2018-12-01

Everything You Need To Know

What are polycyclic aromatic hydrocarbons (PAHs) and why are they a concern in soil?

Polycyclic aromatic hydrocarbons, or PAHs, are hazardous pollutants found in soils. These compounds are carcinogenic and persist in the environment. Bioremediation, using living organisms, is often employed to address PAH contamination, but their low water solubility makes them difficult to remove from soil.

What role do surfactants play in the bioremediation of soil contaminated with PAHs?

Surfactants are substances that help to detach PAHs from soil particles, making them more accessible for microbial breakdown during bioremediation. Both synthetic surfactants, like Brij-35, and biosurfactants, such as rhamnolipid, are used for this purpose, although their effectiveness varies.

How do different types of surfactants, such as Brij-35 and rhamnolipid, affect the breakdown of PAHs in soil?

A recent study showed that while the synthetic surfactant Brij-35 generally enhanced the degradation of pyrene, a common PAH, the biosurfactant rhamnolipid sometimes inhibited it, especially at higher concentrations. This is because soil microbes sometimes prefer to consume rhamnolipid over the PAH, delaying the breakdown of the pollutant. This phenomenon is known as 'diauxie'.

What is 'diauxie,' and how does it impact the effectiveness of biosurfactants in soil remediation?

Diauxie refers to the preferential consumption of one carbon source over another by microorganisms. In the context of soil remediation, microbes might consume the biosurfactant rhamnolipid more readily than the target pollutant, pyrene, slowing down the overall cleanup process. This highlights the importance of understanding microbial preferences when designing remediation strategies.

What are the implications of these findings for choosing soil 'cleaning agents,' and what alternative strategies, like bioaugmentation, should be considered?

The choice of surfactant significantly impacts the efficiency of soil remediation. While biosurfactants are often considered environmentally friendly, their effect on PAH degradation can be unpredictable. Bioaugmentation, which involves adding PAH-degrading bacteria like Mycobacterium vanbaalenii PYR-1, can improve outcomes, but selecting the right surfactant remains critical to ensure that the introduced microbes effectively target the pollutants rather than consuming the surfactant itself. Therefore, a careful assessment of both surfactant type and soil microbial ecology is crucial for successful bioremediation.