More than 1,200 tonnes of microplastics are dumped into Aussie farmland every year from wastewater sludge


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Abbas Mohajerani, RMIT University

Every year, treated wastewater sludge called “biosolids” is recycled and spread over agricultural land. My recent research discovered this practice dumps thousands of tonnes of microplastics into farmlands around the world. In Australia, we estimate this amount as at least 1,241 tonnes per year.

Microplastics in soils can threaten land, freshwater and marine ecosystems by changing what they eat and their habitats. This causes some organisms to lose weight and have higher death rates.

But this is only the beginning of the problem. Microplastics are good at absorbing other pollutants – such as cadmium, lead and nickel – and can transfer these heavy metals to soils.

Wastewater treatment plants create biosolids, which are packed full of microplastics and toxic chemicals.
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And while microplastics alone is an enormous issue, other contaminants have also been found in biosolids used for agriculture. This includes pharmaceutical chemicals, personal care products, pesticides and herbicides, surfactants (chemicals used in detergents) and flame retardants.

We must stop using biosolids for farmlands immediately, especially when alternative ways to recycle wastewater sludge already exist.

Where do the microplastics come from?

Biosolids are mainly a mix of water and organic materials.

But many household items that contain microplastics – such as lotions, soaps, facial and body washes, and toothpaste – end up in wastewater, too. Other major sources of microplastics in wastewater are synthetic fibres from clothing, plastics in the manufacturing and processing industries, and the breakdown of larger plastic debris.

Before they’re taken to farmlands, wastewater collection systems carry all, or most, of these microplastics and other chemicals from residential, commercial and industrial sources to wastewater treatment plants.

To determine the weight of microplastics in Australia and other countries, my data analysis used the average minimum and maximum numbers of microplastics particles, per kilogram of biosolids samples, found in Germany, Ireland and the USA.




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Australia produced 371,000 tonnes of biosolids in 2019. And globally, we estimate between 50 to more than 100 million tonnes of biosolids are produced each year.

Why microplastics are harmful

Microplastics in soil can accumulate in the food web. This happens when organisms consume more microplastics than they lose. This means heavy metals attached to the microplastics in soil organisms can progress further up the food chain, increasing the risk of human exposure to toxic heavy metals.

When microplastics accumulate heavy metals, they transfer these contaminants to plants and crops, such as rice and grains, as biosolids are spread over farmland.




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After a storm, microplastics in Sydney’s Cooks River increased 40 fold


Over time, microplastics break down and become even tinier, creating nanoplastics. Crops have also been shown to absorb nanoplastics and move them to different plant tissues.

Our research results also show that after the wastewater treatment process, the absorption potential of microplastics for metals increases.

The metal cadmium, for example, is particularly susceptible to microplastics in biosolids and can be transported to plant cells. Research from 2018 showed microplastics in biosolids can absorb cadmium ten times more than virgin microplastics (new microplastics that haven’t gone through wastewater treatment).

Biosolids have a cocktail of nasty chemicals

It’s not just plastic – many industrial additives and chemicals have been found in wastewater and biosolids.

This means they may accumulate in soils and affect the equilibrium of biological systems, with negative effects on plant growth. For example, researchers have found pharmaceutical chemicals in particular can reduce plant growth and inhibit root elongation.




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Other chemical contaminants – such as PFCs, PFAS and BPA – have likewise been detected in biosolids.

The effects these chemicals have on plants may lead to problems further down the food chain, such as humans and other animals inadvertently consuming pharmaceuticals and harmful chemicals.

What can we do about it?

Given the cocktail of toxic chemicals, heavy metals and microplastics, using biosolids in agricultural soils must be stopped without delay.

The good news is there’s another way we can recycle the world’s biosolids: turning them into sustainable fired-clay bricks, called “bio-bricks”.

Bricks incorporated with biosolids are a sustainable solution to an environmental problem.
RMIT media, Author provided

My team’s research from last year found bio-bricks a sustainable solution for both the wastewater treatment and brick manufacturing industries.

If 7% of all fired-clay bricks were biosolids, it would redirect all biosolids produced and stockpiled worldwide annually, including the millions of tonnes that currently end up in farmland each year.




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We also found they’d be more energy efficient. The properties of these bio-bricks are very similar to standard bricks, but generally requires 12.5% less energy to make.

And generally, comprehensive life-cycle assessment has shown biosolid bricks are more environmentally friendly than conventional bricks. These bricks will reduce or eliminate a significant source of greenhouse gas emissions from biosolids stockpiles and will save some virgin resources, such as clay soil and water, for the brick industry.

Now, it’s up to the agriculture, wastewater and brick industries, and governments to make this important transition.The Conversation

Abbas Mohajerani, Associate Professor, School of Engineering, RMIT University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

After a storm, microplastics in Sydney’s Cooks River increased 40 fold



A litter trap in Cook’s River.
James HItchcock, Author provided

James Hitchcock, University of Canberra

Each year the ocean is inundated with 4.8 to 12.7 million tonnes of plastic washed in from land. A big proportion of this plastic is between 0.001 to 5 millimetres, and called “microplastic”.

But what happens during a storm, when lashings of rain funnel even more water from urban land into waterways? To date, no one has studied just how important storm events may be in polluting waterways with microplastics.




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So to find out, I studied my local waterway in Sydney, the Cooks River estuary. I headed out daily to measure how many microplastics were in the water, before, during, and after a major storm event in October, 2018.

The results, published on Wednesday, were startling. Microplastic particles in the river had increased more than 40 fold from the storm.

Particles of plastic found in rivers. They may be tiny, but they’re devastating to wildlife in waterways.
Author provided

To inner west Sydneysiders, the Cooks River is known to be particularly polluted. But it’s largely similar to many urban catchments around the world.

If the relationship between storm events and microplastic I found in the Cooks River holds for other urban rivers, then the concentrations of microplastics we’re exposing aquatic animals to is far higher than previously thought.

14 million plastic particles

They may be tiny, but microplastics are a major concern for aquatic life and food webs. Animals such as small fish and zooplankton directly consume the particles, and ingesting microplastics has the potential to slow growth, interfere with reproduction, and cause death.

Determining exactly how much microplastic enters rivers during storms required the rather unglamorous task of standing in the rain to collect water samples, while watching streams of unwanted debris float by (highlights included a fire extinguisher, a two-piece suit, and a litany of tennis balls).

Back in the laboratory, a multi-stage process is used to separate microplastics. This includes floating, filtering, and using strong chemical solutions to dissolve non-plastic items, before identification and counting with specialised microscopes.

Litter caught in a trap in Cooks River. These traps aren’t effective at catching microplastic.
Author provided

In the days before the October 2018 storm, there were 0.4 particles of microplastic per litre of water in the Cooks River. That jumped to 17.4 microplastics per litre after the storm.

Overall, that number averages to a total of 13.8 million microplastic particles floating around in the Cooks River estuary in the days after the storm.




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In other urban waterways around the world scientists have found similarly high numbers of microplastic.

For example in China’s Pearl River, microplastic averages 19.9 particles per litre. In the Mississippi River in the US, microplastic ranges from 28 to 60 particles per litre.

Where do microplastics come from?

We know runoff during storms is one of the main ways pollutants such as sediments and heavy metals end up in waterways. But not much is known about how microplastic gets there.

However think about your street. Wherever you see litter, there are also probably microplastics you cannot see that will eventually work their way into waterways when it rains.




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Many other sources of microplastics are less obvious. Car tyres, for example, which typically contain more plastic than rubber, are a major source of microplastics in our waterways. When your tyres lose tread over time, microscopic tyre fragments are left on roads.

Did you know your car tyres can be a major source of microplastic pollution?
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Microplastics may even build up on roads and rooftops from atmospheric deposition. Everyday, lightweight microplastics such as microfibres from synthetic clothing are carried in the wind, settling and accumulating before they’re washed into rivers and streams.

What’s more, during storms wastewater systems may overflow, contaminating waterways. Along with sewage, this can include high concentrations of synthetic microfibers from household washing machines.

And in regional areas, microplastics may be washing in from agricultural soils. Sewage sludge is often applied to soils as it is rich in nutrients, but the same sludge is also rich in microplastics.

What can be done?

There are many ways to mitigate the negative effects of stormwater on waterways.

Screens, traps, and booms can be fitted to outlets and rivers and catch large pieces of litter such as bottles and packaging. But how useful these approaches are for microplastics is unknown.

Raingardens and retention ponds are used to catch and slow stormwater down, allowing pollutants to drop to bottom rather than being transported into rivers. Artificial wetlands work in similar ways, diverting stormwater to allow natural processes to remove toxins from the water.

Almost 14 million plastic particles were floating in Cooks River after a storm two years ago.
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But while mitigating the effects of stormwater carrying microplastics is important, the only way we’ll truly stop this pollution is to reduce our reliance on plastic. We must develop policies to reduce and regulate how much plastic material is produced and sold.

Plastic is ubiquitous, and its production around the world hasn’t slowed, reaching 359 million tonnes each year. Many countries now have or plan to introduce laws regulating the sale or production of some items such as plastic bags, single-use plastics and microbeads in cleaning products.




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We have no idea how much microplastic is in Australia’s soil (but it could be a lot)


In Australia, most state governments have committed to banning plastic bags, but there are still no laws banning the use of microplastics in cleaning or cosmetic products, or single-use plastics.

We’ve made a good start, but we’ll need deeper changes to what we produce and consume to stem the tide of microplastics in our waterways.The Conversation

James Hitchcock, Post-Doctoral Research Fellow, University of Canberra

This article is republished from The Conversation under a Creative Commons license. Read the original article.