Microplastics, Biosolids and What We Don't Know

Some thoughts based on recent microplastics research and microplastice-in-biosolids as a soil contaminant

Scott Dunham

11/2/20266 min read

Why some recent scientific discoveries raise important questions about turning sewage sludge into fertiliser.

Most of us have heard about microplastics. Tiny fragments of plastic are now found almost everywhere, from oceans and rivers to agricultural soils and even inside living organisms.

What we don't hear so much about is how they get there, what happens to them over time, and what effects they might have on the environment.

Recent scientific research is beginning to reveal some surprising answers. And some of those findings are particularly relevant to the proposed biosolids-to-fertiliser operation at Glan Devon.

From our drains to our paddocks

Every day, wastewater treatment plants receive tiny plastic particles from clothing, household products, industrial waste and countless other sources.

Modern sewage treatment removes much of this plastic from the water. That's good news for our rivers and waterways, but there's a catch. A lot of the plastic ends up in the sewage sludge.

This sludge, known as biosolids once suitably treated, contains nutrients and organic matter that can be useful for agriculture. Rather than disposing of it, the material can be processed and spread on farmland as a fertiliser or soil conditioner.

Unfortunately, any microplastics that survive treatment can go along for the ride.

This isn't speculation. A 2024 Australian study examined biosolids from 13 wastewater treatment plants and found between 11 and 150 microplastic particles per gram of dry material.

Another study examined agricultural soils in Queensland where biosolids had been applied. Researchers found an average of 1,137 microplastic particles per kilogram of soil, compared with just 36 at reference sites.

So we know that biosolids can carry microplastics into agricultural soils. The more difficult question is what happens next.

A surprising new discovery

In October 2026, researchers published a study in the prestigious scientific journal Nature that may change how we think about microplastics.

They discovered that several common plastics can produce highly reactive chemicals called hydroxyl radicals simply through contact with water.

These belong to a group known as reactive oxygen species, or ROS. They can damage living cells, including their proteins, membranes and genetic material.

Until now, much of the concern about microplastics has centred on their physical presence and the chemicals they contain or collect from their surroundings.

This research suggests that the surface of the plastic itself may be chemically active.

And that introduces an interesting problem.

Imagine breaking a plastic object into thousands or millions of tiny pieces. You haven't increased the amount of plastic, but you've enormously increased its total surface area.

For the same mass of plastic, reducing particle diameter from one millimetre to one micrometre increases the total surface area by roughly 1,000 times, assuming similarly shaped particles.

If chemical reactions occur on those surfaces, fragmentation could make the material more active even though the amount of plastic hasn't changed.

There are complications. Weathering, oxidation and the materials coating a plastic particle can change its behaviour, sometimes reducing particular reactions. But that is part of the problem. Plastic particles don't simply remain unchanged after entering the environment.

This is early research, conducted under laboratory conditions. We don't yet know how significant the newly discovered chemical mechanism is in ordinary soils and waterways.

Nevertheless, it opens up an important new area of investigation.

What about the living environment?

Perhaps the most interesting implications concern microorganisms.

Bacteria, fungi and countless other microscopic organisms are fundamental to healthy soils. They break down organic matter, recycle nutrients and help maintain the biological systems on which agriculture depends.

Recent research has shown that microplastics can change the composition and behaviour of these microbial communities. Some organisms become less abundant while others may benefit.

Researchers have also found that microplastics can encourage bacterial biofilm formation and, under certain experimental conditions, increase antibiotic resistance or the movement of resistance genes between bacteria.

This is particularly interesting because sewage sludge can already contain bacteria, antibiotic resistance genes and genetic material released from dead organisms.

The possibility that microplastics might influence which organisms survive, reproduce or exchange genetic material deserves attention.

We should not jump to conclusions. Laboratory experiments do not establish that biosolids-derived fertilisers are creating dangerous new pathogens in agricultural soils.

But the research does suggest that microplastics may influence biological systems in ways we are only beginning to understand.

And an important ecological effect need not involve killing large numbers of organisms. Changing the balance between different microorganisms could alter how a soil functions, with consequences that might only become apparent over time.

Does drying solve the problem?

This brings us to Glan Devon.

BYV Organics' previous development application proposed using a Xetrov incinerator to burn non-recyclable waste and generate heat. That heat would be used in a separate process to dry sewage sludge before blending and pelletising it into fertiliser.

It's an important distinction.

The Xetrov incinerator was proposed to burn waste plastics, including high-density polyethylene (HDPE), as fuel. But the biosolids intended for fertiliser would go through a dryer, not the incinerator.

In other words, the operation proposed to deliberately burn plastic in one part of the process, while potentially allowing microplastics in the separately processed biosolids to end up in fertiliser spread on agricultural land.

And drying doesn't necessarily solve the problem.

A 2023 scientific study found that thermal drying of sewage sludge increased the number of detectable microplastic particles by around ten times, largely because existing particles fragmented into smaller pieces.

That doesn't mean BYV's proposed dryer would do the same thing. We don't have the evidence to establish that.

But there's another complication. Laboratory tests cannot necessarily detect every particle, particularly the very smallest ones.

A test that can't see the smallest particles could make dried fertiliser look cleaner than the sludge it came from, even if drying had broken the plastic into far more pieces.

That's an important consideration when assessing the finished product. The amount of plastic might not have increased at all, but its particle sizes, surface area and potential biological effects could have changed considerably.

Here's the real problem: we aren't routinely measuring them

There is another difficulty, and it's a substantial one.

Queensland has established requirements for testing biosolids before they can be used as a resource. These include limits and monitoring requirements for various metals, chemicals, pathogens and, more recently, PFAS.

Microplastics aren't on that regulatory testing list.

Queensland's current End of Waste Code for Biosolids, updated in May 2026, contains no specific requirement to measure microplastic concentrations or particle sizes.

The Queensland Government has identified microplastics as an emerging environmental issue, but testing methods are still developing.

Part of the difficulty is that microplastics aren't a single chemical. They include many different plastics in different shapes and sizes, from visible fragments down to particles too small for conventional microscopes.

Different laboratories and methods can produce very different results. In fact, the Australian and New Zealand Biosolids Partnership has acknowledged that two Australian research projects produced particle counts differing by approximately an order of magnitude.

The Partnership also identified problems with analytical consistency, cost and contamination of samples.

So we have a rather awkward situation.

We know microplastics occur in sewage sludge. We know they can enter agricultural soils. We have evidence that processing can change their characteristics, and an expanding body of research suggests they can affect chemical and biological processes.

Yet we generally don't measure them as part of routine biosolids regulation, and we don't have a sufficiently developed understanding of their effects to establish reliable environmental limits.

How do we confidently assess the environmental risk of something when we don't routinely measure how much is present, and we're still discovering what it does?

What does this mean for Glan Devon?

The point isn't that BYV's proposed fertiliser has been demonstrated to be dangerous. It hasn't.

Nor does this research prove that every use of biosolids in agriculture is unacceptable. Recycling nutrients and organic matter can provide genuine benefits.

The issue is that the benefits need to be considered alongside the contaminants that may accompany the material.

For Glan Devon, some fairly straightforward questions arise. How much microplastic is present in the incoming sewage sludge? What happens to those particles during drying and pelletising? How much remains in the finished fertiliser? And what happens when that fertiliser is repeatedly applied to agricultural land?

Those questions need evidence, not assumptions.

The difficulty is that even good measurements won't answer every question while the science of long-term biological effects continues to develop.

That brings us to the broader issue of environmental risk and uncertainty.

Scientific research rarely provides every answer we would like. But when we're dealing with persistent materials that can be spread widely across agricultural land, uncertainty matters. Once those materials are in the soil, removing them may be practically impossible.

There is a reasonable argument for taking a conservative approach, particularly where the quantities, characteristics and long-term consequences of the contaminants have not been adequately established.

The absence of a regulatory limit doesn't mean the absence of a problem. Sometimes it means the science and the regulations haven't caught up with one another.

And with microplastics, that's increasingly looking like an important distinction.