Microplastics in the ocean, pieces of plastic less than 5mm in size, have shot to infamy in the last few years. Governments and businesses targeted microbeads in cosmetics, some were banned, and the world felt a little better.
Dealing with microbeads in cosmetics is a positive first step, but the reality is that they are just a drop in the ocean (less than a billionth of the world’s ocean).
Microplastics in soil may be a far greater problem. Norwegian research estimates that in Europe and North America, between 110,000 and 730,000 tonnes of microplastic are transferred to agricultural soils each year.
Here lies the issue: we know almost nothing about microplastics in global soils, and even less in Australian soils. In this article we take a look at what we do know, and some questions we need to answer.
How microplastics get into agricultural soil
Sewage sludge and plastic mulch are the two biggest known contributors of microplastics to agricultural soil. Australia produces about 320,000 dry tonnes of biosolids each year, 55% of which is applied to agricultural land. Biosolids, while controversial, are an excellent source of nutrients for farmland. Of the essential plant nutrients, we can only manufacture nitrogen. The rest we must either mine or recycle.
Sewage treatment plants receive water from households, industry, and stormwater, each adding to the load of plastics. Technical clothing such as sportswear and quick-dry fabrics often contain polyesters and polyamides that break off when clothes are washed. Tyre debris and plastic films wash in with the stormwater. Treatment plants filter microplastics out of the water, retaining them in the sludge that is then trucked away and spread over agricultural land.
In agriculture, plastic mulch suppresses weeds, keeps the soil warm and damp to assist germination, and improves yield. Over time, these mulches break down, and some fragment into smaller pieces.
Biodegradable bioplastic mulches are designed to break down into carbon dioxide, water, and various “natural substances”. Environmentally friendly plastics are often more expensive, raising the question of whether businesses will be able to afford them.
Other potential sources of plastics in agricultural soil include polymer sealants on fertilisers and pesticides, and industrial compost. Unsold food is often sent to the composting facility still in plastic packaging, and with plastic stickers on every apple and kiwi fruit.
The Australian Standard for composts tacitly recognises that microplastics are likely to be present in these products by having acceptable levels of “visible contamination”. Anyone who has bought compost or garden loam from a landscaping supplier may have noticed pieces of plastic in the mix.
In horticulture, particularly as green walls and green roofs grace more buildings, polystyrenes are used deliberately to make lightweight ‘soil’.
There might be other pathways we don’t know about yet.
What happens once microplastics are in the soil?
Here we stand at the edge of the cavernous knowledge gap, because we don’t know the effect of microplastics in our soil. The overarching question, physically and biologically, is where do microplastics go?
How plastics fragment and degrade in the soil depends on the type of plastic and soil conditions. Compostable, PET, and various degradable plastics will behave differently, having different effects on soil physics and biology.
Fragments could move through soil cracks and pores. Larger soil fauna might disperse fragments vertically and laterally, while agricultural practices such as tillage could push plastics deeper into the soil. Some fragmented plastics can absorb agrochemicals.
Soil microbes can break down some plastics, but what are the byproducts and what are their effects? Newer, biodegradable bioplastics theoretically have limited impact as they break down into inert substances. But how long do they take to break down in different soil and climatic conditions, and what proportion in the soil are non-degradable PET plastics?
Both the main form of carbon in soil and polythene (the most common type of plastic) are carbon-based polymers. Could the two integrate? If they did, would this prevent plastics from moving deeper into the soil, but would it also stop them breaking down?
Could plastics be a hidden source of soil carbon storage?
Bioaccumulation is when something builds up in a food chain.
Research into microplastic accumulation on land is sparse at best. A 2017 study in Mexico found microplastics in chicken gizzards. In the study area, waste management is poor and most plastics were ingested directly from the soil surface as opposed to having bioaccumulated.
Nematodes can take up polystyrene beads suggesting some potential for bioaccumulation, however earthworms have reduced growth rate and increased mortality when they ingest microbeads.
Larger microplastics are unlikely to cross plant cell membranes, but it’s possible that plants can absorb the chemicals formed when plastic degrades. Plants have natural mechanisms to keep contaminants out of their fruiting bodies – pieces of plastic in apples or berries is highly unlikely – but root vegetables and leafy greens are a different story.
Metals can accumulate in leafy greens and the skin of root vegetables – could plastics or their byproducts do the same?
This is before we even get to nanoplastics, which are 1-100 nanometres wide. Can plant roots can absorb nanoplastics, and can they pass through an animal’s gut membrane?
Where to now?
The first step is to quantify how much plastic is currently in the soil, where it is, and how much more to expect. This is more difficult in land than water, as it’s easier to filter plastics out the ocean than to separate them from soil samples. The smaller the plastics are, the harder they’ll be to track and identify – which is why research must start now.
Research needs to address the different types of plastics, including beads and other synthetic fibres. Each is likely to act differently in the soil and terrestrial ecosystems.
Understanding how these plastics react will inform the next obvious questions: at what quantity do they become hazardous to soil, plant and animal life, and how can we mitigate this impact?
Plastics in soil represent artefacts of human civilisation. Soils are full of human artefacts; if this was not the case then there would be no field archaeology. However, the effects of microplastic may persist far longer than our own civilisation. We must fill in our knowledge gaps swiftly.
Alisa Bryce, Research Affiliate, University of Sydney; Alex McBratney, Professor of Digital Agriculture & Soil Science; Director, Sydney Institute of Agriculture, University of Sydney; Budiman Minasny, Professor in Soil-Landscape Modelling, University of Sydney; Damien Field, Associate professor, and Stephen Cattle, Associate professor, University of Sydney
Australia’s recycling crisis needs us to look into waste management options beyond just recycling and landfilling. Some of our waste, like paper or organic matter, can be composted. Some, like glass, metal and rigid plastics, can be recycled. But we have no immediate solution for non-recyclable plastic waste except landfill.
At a meeting last month, federal and state environment ministers endorsed an ambitious target to make all Australian packaging recyclable, compostable or reusable by 2025. But the ministers also showed support for processes to turn our waste into energy, although they did not specifically discuss plastic waste as an energy source.
The 100% goal could easily be achieved if all packaging were made of paper or wood-based materials. But realistically, plastic will continue to dominate our packaging, especially for food, because it is moisture-proof, airtight, and hygienic.
Most rigid plastic products can only be recycled a few times before they lose their original properties and become non-recyclable. Even in European countries with strict waste management strategies, only 31% of plastic waste is recycled.
Worldwide plastic production is predicted to increase by 3.8% every year until 2030. Flexible, non-recyclable plastic materials are used in an increasing range of applications like packaging, 3D printing, and construction.
We need to expand our range of options for keeping this plastic waste out of landfill. One potential approach is “plastic to energy”, which unlocks the chemical energy stored in waste plastic and uses it to create fuel.
How plastic to energy works
Plastic is made from refined crude oil. Its price and production are dictated by the petrochemical industry and the availability of oil. As oil is a finite natural resource, the most sustainable option would be to reduce crude-oil consumption by recycling the plastic and recovering as much of the raw material as possible.
There are two types of recycling: mechanical and chemical. Mechanical recycling involves sorting, cleaning and shredding plastic to make pellets, which can then be fashioned into other products. This approach works very well if plastic wastes are sorted according to their chemical composition.
Gasification involves heating the waste plastic with air or steam, to produce a valuable industrial gas mixtures called “synthesis gas”, or syngas. This can then be used to produce diesel and petrol, or burned directly in boilers to generate electricity.
In pyrolysis, plastic waste is heated in the absence of oxygen, which produces mixture of oil similar to crude oil. This can be further refined into transportation fuels.
Gasification and pyrolysis are completely different processes to simply incinerating the plastic. The main goal of incineration is simply to destroy the waste, thus keeping it out of landfill. The heat released from incineration might be used to produce steam to drive a turbine and generate electricity, but this is only a by-product.
Gasification and pyrolysis can produce electricity or fuels, and provide more flexible ways of storing energy than incineration. They also have much lower emissions of sulfur and nitrogen oxides than incineration.
Currently, incineration plants are viewed as an alternative energy supply source and a modern way of driving a circular economy, particularly in Japan, South Korea and China, where land is valuable and energy resources are scarce. In other countries, although waste incineration is common practice, the debate around human health impacts, supply issues and fuel trade incentives remains unresolved.
Can Australia embrace plastic to waste?
Gasification of plastic waste needs significant initial financing. It requires pre-treatment, cleanup facilities, gas separation units, and advanced control systems. Pyrolysis units, on the other hand, can be modular and be installed to process as little as 10,000 tonnes per year – a relatively small amount in waste management terms. Plastic pyrolysis plants have already been built in the UK, Japan and the United States.
As pyrolysis and gasification technologies can only process plastics, many councils do not see major advantages in using them. But by taking only a specific waste stream, they encourage better waste sorting and help to reduce the flow of mixed waste and plastic litter.
Australia has invested a serious amount of funding into research, particularly in waste conversion. It has a solid industrialised infrastructure and a highly skilled workforce. The current recycling crisis offers an opportunity to explore some innovative ways of turning our waste into valuable products.
There are direct job opportunities in plastic conversion plants, and indirect jobs around installation, maintenance and distribution of energy and fuels. We might even see jobs in R&D to explore other waste conversion technologies.
Shopping can be confusing at the best of times, and trying to find environmentally friendly options makes it even more difficult. Our Sustainable Shopping series asks experts to provide easy eco-friendly guides to purchases big and small. Send us your suggestions for future articles here.
We have many options when it comes to how we drink water, given the large range of consumer products available, and Australia’s high standards of tap water.
But which option is the smartest choice from an environmental perspective?
According to the waste management hierarchy, the best option is one that avoids waste altogether. Recyclable options are less preferable, and landfill disposal the worst of all.
For water bottles, this suggests that keeping and reusing the same bottle is always best. It’s certainly preferable to single-use bottles, even if these are recyclable.
Of course, it’s hardly revolutionary to point out that single-use plastic bottles are a bad way to drink water on environmental grounds. Ditching bottled water in favour of tap water is a very straightforward decision.
However, choosing what reusable bottle to drink it out of is a far more complex question. This requires us to consider the whole “life cycle” of the bottle.
Cycle of life
Life-cycle assessment is a method that aims to identify all of the potential environmental impacts of a product, from manufacture, to use, to disposal.
A 2012 Italian life-cycle study confirmed that reusable glass or plastic bottles are usually more eco-friendly than single-use PET plastic bottles.
However, it also found that heavy glass bottles have higher environmental impacts than single-use PET bottles if the distance to refill them was more than 150km.
Granted, you’re unlikely ever to find yourself more than 150km from the nearest drinking tap. But this highlights the importance of considering how a product will be used, as well as what it is made of.
What are the reusable options?
In 2011, we investigated and compared the life cycles of typical aluminium, steel and polypropylene plastic reusable bottles.
Steel and aluminium options shared the highest environmental impacts from materials and production, due to material and production intensity, combined with the higher mass of the metal bottles, for the same number of uses among the options. The polypropylene bottle performed the best.
Polypropylene bottles are also arguably better suited to our lifestyles. They are lighter and more flexible than glass or metal, making them easier to take to the gym, the office, or out and about.
The flip side of this, however, is that metal and glass bottles may be more robust and last longer, so their impacts may be diluted with prolonged use – as long as you don’t lose them or replace them too soon.
Health considerations are an important factor for many people too, especially in light of new research about the presence of plastic particles in drinking water.
Other considerations aside, is may even be best to simply buy a single-use PET plastic water bottle and then reuse it a bunch of times. They are lighter than most purpose-designed reusable bottles, but still long-lasting. And when they do come to the end of their useful life, they are more easily recycled than many other types of plastic.
Sure, you won’t look very aspirational, but depending on how many uses you get (as you approach the same number of uses as other options), you could be doing your bit for the environment.
Maintaining reusable options
There are a few things to bear in mind to ensure that reusable bottles produce as little waste as possible.
Refill from the tap, as opposed to using water coolers or other bottled water that can come from many kilometres away, requiring packaging and distribution. Unsurprisingly, tap water has the lowest environmental impacts of all the options.
Clean your bottle thoroughly, to keep it hygienic for longer and avoid having to replace grotty bottles. While cleaning does add to the environmental impact, this effect is minor in comparison to the material impacts of buying new bottles – as we have confirmed in the case of reusable coffee cups.
To reduce your environmental impacts of a drink of water, reusing a bottle, whether a designer bottle or a single-use bottle you use time and again, makes the most sense from a life-cycle, waste and litter perspective.
The maintenance of your reusable container is also key, to make sure you get as many uses as you can out of it, even if you create minor additional environmental impacts to do so.
Ultimately, drinking directly from a tap or water fountain is an even better shout, if you have that option. Apart from the benefit of staying hydrated, you will reduce your impacts on our planet.
Plastic waste in the ocean is a global problem; some eight million metric tonnes of plastic ends up in the ocean every year.
One possible solution – paying a small amount for returned drink containers – has been consistently opposed by the beverage industry for many years. But for the first time our research, published in Marine Policy, has found that container deposits reduce the amount of beverage containers on the coasts of both the United States and Australia by 40%.
What’s more, the reduction is even more pronounced in areas of lower socio-economic status, where plastic waste is most common.
Plastic not so fantastic
There have been many suggestions for how to reduce marine debris. Some promote reducing plastic packaging, re-purposing plastic debris], or cleaning beaches. There has been a push to get rid of plastic straws, and even Queen Elizabeth II has banned single use plastics from Royal Estates! All of these contribute to the reduction of plastics, and are important options to consider.
Legislation and policy are another way to address the problems of plastic pollution. Recent legislation includes plastic bag bans and microbead bans. Economic incentives, such as container deposits, have attracted substantial attention in countries around the world.
Several Australian jusrisdictions, including South Australia, the Northern Territory, and New South Wales), already have container deposit laws, with Western Australia and Queensland set to start in 2019. In the United States, 10 states have implemented container deposit schemes.
But how effective is a cash for containers program? While there is evidence to suggest that container deposits increase return rates and decrease litter, until now there has been no study asking whether they also reduce the sources of debris entering the oceans.
In Australia, we analysed data from litter surveys by Keep South Australia Beautiful, and Keep Australia Beautiful. In the US, we accessed data from the Ocean Conservancy’s International Coastal Cleanup.
We compared coastline surveys in states with a container deposit scheme to those without. In both Australia and the US, the proportion of beverage containers in states without a deposit scheme was about 1.6 times higher than their neighbours. Based on estimates of debris loading on US beaches that we conducted previously, if all coastal states in the United States implemented deposit schemes, there would be 6.6 million fewer containers on the shoreline each year.
Keep your lid on
But how do we know that this difference is caused by the deposit scheme? Maybe people in states with container deposit schemes simply drink fewer bottled beverages than people states without them, and so there are fewer containers in the litter stream?
To answer that question, we measured the ratio of lids to containers from the same surveys. Lids are manufactured in equal proportion to containers, and arrive to the consumer on the containers, but do not attract a deposit in either country.
If deposit schemes cause a decrease in containers in the environment, it is unlikely to cause a similar decrease in littered lids. So, if a cashback incentive is responsible for the significantly lower containers on the shorelines, we would expect to see a higher ratio of lids to containers in states with these programs, as compared to states without.
That’s exactly what we found.
We were also interested in whether other factors also influenced the amount of containers in the environment. We tested whether the socio-economic status of the area (as defined by data from the Australian census) was related to more containers in the environment. Generally, we found fewer containers in the environment in wealthier communities. However, the presence of a container deposit reduced the container load more in poorer communities.
This is possibly because a relatively small reward of 10 cents per bottle may make a bigger difference to less affluent people than to more wealthy consumers. This pattern is very positive, as it means that cashback programs have a stronger impact in areas of lower economic advantage, which are also the places with the biggest litter problems.
Ultimately, our best hope of addressing the plastic pollution problem will be through a range of approaches. These will include bottom-up grassroots governance, state and federal legislation, and both hard and soft law.
Along with these strategies, we must see a shift in the type of we products use and their design. Both consumers and manufacturers are responsibility for shifting from a make, use, dispose culture to a make, reuse, repurpose, and recycle culture, also known as a circular economy.
Qamar Schuyler, Research Scientist, Oceans and Atmospheres, CSIRO; Britta Denise Hardesty, Principal Research Scientist, Oceans and Atmosphere Flagship, CSIRO, and Chris Wilcox, Senior Research Scientist, CSIRO