These “microplastics”, which are derived from petrochemicals extracted from oil and gas products, are settling in dust around the house.
Some of these particles are toxic to humans — they can carry carcinogenic or mutagenic chemicals, meaning they potentially cause cancer and/or damage our DNA.
We still don’t know the true impact of these microplastics on human health. But the good news is, having hard floors, using more natural fibres in clothing, furnishings and homewares, along with vacuuming at least weekly can reduce your exposure.
What are microplastics?
Microplastics are plastic particles less than five millimetres across. They come from a range of household and everyday items such as the clothes we wear, home furnishings, and food and beverage packaging.
We know microplastics are pervasive outdoors, reaching remote and inaccessible locations such as the Arctic, the Mariana Trench (the world’s deepest ocean trench), and the Italian Alps.
Our study demonstrates it’s an inescapable reality that we’re living in a sea of microplastics — they’re in our food and drinks, our oceans, and our homes.
While research has focused mainly on microplastics in the natural environment, a handful of studies have looked at how much we’re exposed to indoors.
People spend up to 90% of their time indoors and therefore the greatest risk of exposure to microplastics is in the home.
Our study is the first to examine how much microplastic we’re exposed to in Australian homes. We analysed dust deposited from indoor air in 32 homes across Sydney over a one-month period in 2019.
We asked membersof the public to collect dust in specially prepared glass dishes, which we then analysed.
Here’s how microplastics can be generated, suspended, ingested and inhaled inside a house. Monique Chilton, Author provided
We found 39% of the deposited dust particles were microplastics; 42% were natural fibres such as cotton, hair and wool; and 18% were transformed natural-based fibres such as viscose and cellophane. The remaining 1% were film and fragments consisting of various materials.
Between 22 and 6,169 microfibres were deposited as dust per square metre, each day.
Homes with carpet as the main floor covering had nearly double the number of petrochemical-based fibres (including polyethylene, polyamide and polyacrylic) than homes without carpeted floors.
Conversely, polyvinyl fibres (synthetic fibres made of vinyl chloride) were two times more prevalent in homes without carpet. This is because the coating applied to hard flooring degrades over time, producing polyvinyl fibres in house dust.
These chemicals can leach from the plastic surface once in the body, increasing the potential for toxic effects. Microplastics can have carcinogenic properties, meaning they potentially cause cancer. They can also be mutagenic, meaning they can damage DNA.
However, even though some of the microplastics measured in our study are composed of potentially carcinogenic and/or mutagenic compounds, the actual risk to human health is unclear.
Given the pervasiveness of microplastics not only in homes but in food and beverages, the crucial next step in this research area is to establish what, if any, are safe levels of exposure.
How much are we exposed to? And can this be minimised?
Roughly a quarter of all of the fibres we recorded were less than 250 micrometres in size, meaning they can be inhaled. This means we can be internally exposed to these microplastics and any contaminants attached to them.
Using human exposure models, we calculated that inhalation and ingestion rates were greatest in children under six years old. This is due to their lower relative body weight, smaller size, and higher breathing rate than adults. What’s more, young children typically have more contact with the floor, and tend to put their hands in their mouths more often than adults.
Microplastics are found not only in the sea, but in our food, beverages, and our homes. Shutterstock
Children under six inhale around three times more microplastics than the average — 18,000 fibres, or 0.3 milligrams per kilogram of body weight per year. They would also ingest on average 6.1 milligrams of microplastics in dust per kg of body weight per year.
For a five-year-old, this would be equivalent to eating a garden pea’s worth of microplastics over the course of a year. But for many of these plastics there is no established safe level of exposure.
Our study indicated there are effective ways to minimise exposure.
First is the choice of flooring, with hard surfaces, including polished wood floors, likely to have fewer microplastics than carpeted floors.
Also, how often you clean makes a difference. Vacuuming floors at least weekly was associated with less microplastics in dust than those that were less frequently cleaned. So get cleaning!
The Pacific Ocean is the deepest, largest ocean on Earth, covering about a third of the globe’s surface. An ocean that vast may seem invincible. Yet across its reach – from Antarctica in the south to the Arctic in the north, and from Asia to Australia to the Americas – the Pacific Ocean’s delicate ecology is under threat.
In most cases, human activity is to blame. We have systematically pillaged the Pacific of fish. We have used it as a rubbish tip – garbage has been found even in the deepest point on Earth, in the Mariana Trench 11,000 metres below sea level.
And as we pump carbon dioxide into the atmosphere, the Pacific, like other oceans, is becoming more acidic. It means fish are losing their sense of sight and smell, and sea organisms are struggling to build their shells.
Oceans produce most of the oxygen we breathe. They regulate the weather, provide food, and give an income to millions of people. They are places of fun and recreation, solace and spiritual connection. So, healthy, vibrant oceans benefit us all. And by better understanding the threats to the precious Pacific, we can start the long road to protecting it.
The series opens with five profiles delving into ancient Indian Ocean trade networks, Pacific plastic pollution, Arctic light and life, Atlantic fisheries and the Southern Ocean’s impact on global climate. It’s brought to you by The Conversation’s international network.
The ocean plastic scourge
The problem of ocean plastic was scientifically recognised in the 1960s after two scientists saw albatross carcasses littering the beaches of the northwest Hawaiian Islands in the northern Pacific. Almost three in four albatross chicks, who died before they could fledge, had plastic in their stomachs.
Now, plastic debris is found in all major marine habitats around the world, in sizes ranging from nanometers to meters. A small portion of this accumulates into giant floating “garbage patches”, and the Pacific Ocean is famously home to the largest of them all.
Most plastic debris from land is transported into the ocean through rivers. Just 20 rivers contribute two-thirds of the global plastic input into the sea, and ten of these discharge into the northern Pacific Ocean. Each year, for example, the Yangtze River in China – which flows through Shanghai – sends about 1.5 million metric tonnes of debris into the Pacific’s Yellow Sea.
A wildlife killer
Plastic debris in the oceans presents innumerable hazards for marine life. Animals can get tangled in debris such as discarded fishing nets, causing them to be injured or drown.
Some organisms, such as microscopic algae and invertebrates, can also hitch a ride on floating debris, travelling large distances across the oceans. This means they can be dispersed out of their natural range, and can colonise other regions as invasive species.
And of course, wildlife can be badly harmed by ingesting debris, such as microplastics less than five millimetres in size. This plastic can obstruct an animal’s mouth or accumulate in its stomach. Often, the animal dies a slow, painful death.
Seabirds, in particular, often mistake floating plastics for food. A 2019 study found there was a 20% chance seabirds would die after ingesting a single item, rising to 100% after consuming 93 items.
Discarded fishing nets, or ‘ghost nets’ can entangle animals like turtles. Shutterstock
And since floating plastics in the open ocean are transported mainly by ocean surface currents and winds, plastic debris accumulates on island coastlines along their path. Kamilo Beach, on the south-eastern tip of Hawaii’s Big Island, is considered one of the world’s worst for plastic pollution. Up to 20 tonnes of debris wash onto the beach each year.
Similarly, on uninhabited Henderson Island, part of the Pitcairn Island chain in the south Pacific, 18 tonnes of plastic have accumulated on a beach just 2.5km long. Several thousand pieces of plastic wash up each day.
Kamilo Beach is referred to as the world’s dirtiest.
Subtropical garbage patches
Plastic waste can have different fates in the ocean: some sink, some wash up on beaches and some float on the ocean surface, transported by currents, wind and waves.
Around 1% of plastic waste accumulates in five subtropical “garbage patches” in the open ocean. They’re formed as a result of ocean circulation, driven by the changing wind fields and the Earth’s rotation.
There are two subtropical garbage patches in the Pacific: one in the northern and one in the southern hemisphere.
The northern accumulation region is separated into an eastern patch between California and Hawaii, and a western patch, which extends eastwards from Japan.
Locations of the five subtropical garbage patches. van der Mheen et al. (2019)
Our ocean garbage shame
First discovered by Captain Charles Moore in the early 2000s, the eastern patch is better known as the Great Pacific Garbage Patch because it’s the largest by both size (around 1.6 million square kilometers) and amount of plastic. By weight, this garbage patch can hold more than 100 kilograms per square kilometre.
The garbage patch in the southern Pacific is located off Valparaiso, Chile, extending to the west. It has lower concentrations compared to its giant counterpart in the northeast.
Discarded fishing nets make up around 45% of the total plastic weight in the Great Pacific Garbage Patch. Waste from the 2011 Japan tsunami is also a major contributor, making up an estimated 20% of the patch.
With time, larger plastic debris degrades into microplastics. Microplastics form only 8% of the total weight of plastic waste in the Great Pacific Garbage Patch, but make up 94% of the estimated 1.8 trillion pieces of plastic there. In high concentrations, they can make the water “cloudy”.
Each year, up to 15 million tonnes of plastic waste are estimated to make their way into the ocean from coastlines and rivers. This amount is expected to double by 2025 as plastic production continues to increase.
We must act urgently to stem the flow. This includes developing plans to collect and remove the plastics and, vitally, stop producing so much in the first place.
Divers releasing a whale shark from a fishing net.
Fisheries on the verge of collapse
As the largest and deepest sea on Earth, the Pacific supports some of the world’s biggest fisheries. For thousands of years, people have relied on these fisheries for their food and livelihoods.
But, around the world, including in the Pacific, fishing operations are depleting fish populations faster than they can recover. This overfishing is considered one of the most serious threats to the world’s oceans.
Humans take about 80 million tonnes of wildlife from the sea each year. In 2019, the world’s leading scientists said of all threats to marine biodiversity over the past 50 years, fishing has caused the most harm. They said 33% of fish species were overexploited, 60% were being fished to the maximum level, and just 7% were underfished.
The decline in fish populations is not just a problem for humans. Fish play an important role in marine ecosystems and are a crucial link in the ocean’s complex food webs.
Overfishing is stripping the Pacific Ocean of marine life. Shutterstock
Not plenty of fish in the sea
Overfishing happens when humans extract fish resources beyond the maximum level, known as the “maximum sustainable yield”. Fishing beyond this causes global fish stocks to decline, disrupts food chains, degrades habitats, and creates food scarcity for humans.
The Pacific Ocean is home to huge tuna fisheries, which provide almost 65% of the global tuna catch each year. But the long-term survival of many tuna populations is at risk.
For example, a study released in 2013 found numbers of bluefin tuna – a prized fish used to make sushi – had declined by more than 96% in the Northern Pacific Ocean.
Developing countries, including Indonesia and China, are major overfishers, but so too are developing nations.
Along Canada’s west coast, Pacific salmon populations have declined rapidly since the early 1990s, partly due to overfishing. And Japan was recently heavily criticised for a proposal to increase quotas on Pacific bluefin tuna, a species reportedly at just 4.5% of its historic population size.
Experts say overfishing is also a problem in Australia. For example, research in 2018 showed large fish species were rapidly declining around the nation due to excessive fishing pressure. In areas open to fishing, exploited populations fell by an average of 33% in the decade to 2015.
Stocks of fish used to make sushi have declined in number. Shutterstock
So what’s driving overfishing?
There are many reasons why overfishing occurs and why it is goes unchecked. The evidence points to:
fishing subsidies that enable large fishing fleets to travel to the waters of developing countries and compete with small-scale fishers and keep ailing industries going
Let’s take Indonesia as an example. Indonesia lies between the Pacific and Indian oceans and is the world’s third-biggest producer of wild-capture fish after China and Peru. Some 60% of the catch is made by small-scale fishers. Many hail from poor coastal communities.
Overfishing was first reported in Indonesia in the 1970s. It prompted a presidential decree in 1980, banning trawling off the islands of Java and Sumatra. But overfishing continued into the 1990s, and it persists today. Target species include reef fishes, lobster, prawn, crab, and squid.
Indonesia’s experience shows how there is no easy fix to the overfishing problem. In 2017, the Indonesian government issued a decree that was supposed to keep fishing to a sustainable level – 12.5 million tonnes per year. Yet, in may places, the practice continued – largely because the rules were not clear and local enforcement was inadequate.
Implementation was complicated by the fact that almost all Indonesia’s smaller fishing boats come under the control of provincial governments. This reveals the need for better cooperation between levels of government in cracking down on overfishing.
Globally, compliance and enforcement of fishing limits is often poor. Shutterstock
What else can we do?
To prevent overfishing, governments should address the issue of poverty and poor education in small fishing communities. This may involve finding them a new source of income. For example in the town of Oslob in the Philippines, former fishermen and women have turned to tourism – feeding whale sharks tiny amounts of krill to draw them closer to shore so tourists can snorkel or dive with them.
Tackling overfishing in the Pacific will also require cooperation among nations to monitor fishing practices and enforce the rules.
And the world’s network of marine protected areas should be expanded and strengthened to conserve marine life. Currently, less than 3% of the world’s oceans are highly protected “no take” zones. In Australia, many marine reserves are small and located in areas of little value to commercial fishers.
The collapse of fisheries around the world shows just how vulnerable our marine life is. It’s clear that humans are exploiting the oceans beyond sustainable levels. Billions of people rely on seafood for protein and for their livelihoods. But by allowing overfishing to continue, we harm not just the oceans, but ourselves.
Providing fishers with an alternative income can help prevent overfishing. Shutterstock
The tropical and subtropical waters of the Pacific Ocean are home to more than 75% of the world’s coral reefs. These include the Great Barrier Reef and more remote reefs in the Coral Triangle, such as those in Indonesia and Papua New Guinea.
Coral reefs are bearing the brunt of climate change. We hear a lot about how coral bleaching is damaging coral ecosystems. But another insidious process, ocean acidification, is also threatening reef survival.
Ocean acidification particularly affects shallow waters, and the subarctic Pacific region is particularly vulnerable.
Coral reefs cover less than 0.5% of Earth’s surface, but house an estimated 25% of all marine species. Due to ocean acidification and other threats, these incredibly diverse “underwater rainforests” are among the most threatened ecosystems on the planet.
A chemical reaction
Ocean acidification involves a decrease in the pH of seawater as it absorbs carbon dioxide (CO₂) from the atmosphere.
Each year, humans emit 35 billion tonnes of CO₂ through activities such as burning of fossil fuels and deforestation.
Oceans absorb up to 30% of atmospheric CO₂, setting off a chemical reaction in which concentrations of carbonate ions fall, and hydrogen ion concentrations increase. That change makes the seawater more acidic.
Each year, humans emit 35 billion tonnes of CO₂. Shutterstock
Why is ocean acidification harmful?
Carbonate ions are the building blocks for coral structures and organisms that build shells. So a fall in the concentrations of carbonate ions can spell bad news for marine life.
Ocean acidification is also a problem for the fishes. Many studies have revealed elevated CO₂ can disrupt their sense of smell, vision and hearing. It can also impair survival traits, such as a fish’s ability to learn, avoid predators, and select suitable habitat.
However, ocean acidification does not affect all marine species in the same way, and the effects can vary over the organism’s lifetime. So, more research to predict the future winners and losers is crucial.
This can be done by identifying inherited traits that can increase an organism’s survival and reproductive success under more acidic conditions. Winner populations may start to adapt, while loser populations should be targets for conservation and management.
One such winner may be the epaulette shark, a shallow water reef species endemic to the Great Barrier Reef. Research suggests simulated ocean acidification conditions do not impact early growth, development, and survival of embryos and neonates, nor do they affect foraging behaviours or metabolic performance of adults.
But ocean acidification is also likely to create losers on the Great Barrier Reef. For example, researchers studying the orange clownfish – a species made famous by Disney’s animated Nemo character – found they suffered multiple sensory impairments under simulated ocean acidification conditions. These ranged from difficulties smelling and hearing their way home, to distinguishing friend from foe.
Clownfish struggled to tell friend from foe when exposed to ocean acidification. Shutterstock
It’s not too late
More than half a billion people depend on coral reefs for food, income, and protection from storms and coastal erosion. Reefs provide jobs – such as in tourism and fishing – and places for recreation. Globally, coral reefs represent an industry worth US$11.9 trillion per year. And importantly, they’re a place of deep cultural and spiritual connection for Indigenous people around the world.
Ocean acidification is not the only threat to coral reefs. Under climate change, the rate of ocean warming has doubled since the 1990s. The Great Barrier Reef, for example, has warmed by 0.8℃ since the Industrial Revolution. Over the past five years this has caused devastating back-to-back coral bleaching events. The effects of warmer seas are magnified by ocean acidification.
Cutting greenhouse gas emissions must become a global mission. COVID-19 has slowed our movements across the planet, showing it’s possible to radically slash our production of CO₂. If the world meets the most ambitious goals of the Paris Agreement and keeps global temperature increases below 1.5℃, the Pacific will experience far less severe decreases in oceanic pH.
We will, however, have to curb emissions by a lot more – 45% over the next decade – to keep global warming below 1.5℃. This would give some hope that coral reefs in the Pacific, and worldwide, are not completely lost.
Clearly, the decisions we make today will affect what our oceans look like tomorrow.
Our decisions today will determine the fate of tomorrow’s oceans. Shutterstock
Freshwater ecosystems are a priority for environmental scientists because they affect the health of animals and plants on land too – as well as people. They provide food, water, transport and flood control. Freshwater ecosystems also keep nutrients moving among organisms and support diverse forms of life.
Freshwater systems make a big difference to the quality of life in any human society. But they are under great pressure. Freshwater biodiversity is declining faster than terrestrial biodiversity.
Among the three major types of habitats – terrestrial, freshwater and marine – freshwater accounts for less than 1% of the earth’s surface. Yet these habitats support more species per unit area and account for about 6% of the world’s biodiversity.
One of the biggest stresses on freshwater ecosystems is the presence of plastics. Some microplastics – tiny pieces of plastic that have broken down from bigger pieces – get into water from various sources. Some are introduced from industrial sources like cosmetics, toothpaste and shaving cream. Another major source is dumping of plastic waste like bags and bottles.
In Nigeria, an important source is the plastic sachets that contain drinking water. Over 60 million of these are consumed in a day.
Ultimately all these types of plastic waste find their way to the aquatic environment. There they stay in the water column, settle on river beds or are ingested by aquatic animals.
My research group set out to assess the load and chemical nature of microplastics in two important rivers and Gulf of Guinea tributaries in Nigeria. We looked for the presence of microplastics in aquatic insects since they often dominate aquatic animal life. Most also spend their adult stage in the terrestrial environment, once they emerge from their larvae. We found that microplastics were present in large quantities in the insect larvae. The insects are part of a food chain and could transfer the harmful effects of microplastics throughout the chain.
This further reinforces the urgent need for Nigeria to go ahead with measures to reduce the use of plastic bags and single-use plastics.
The research findings
We used three of the rivers’ aquatic insect species as bio-indicators and found that all three had ingested microplastics from the two rivers. The ingested microplastics include styrene-ethylene-butylene-styrene, acrylonitrile butadiene styrene, chlorinated polyethylene, polypropylene, and polyester. The quantity of microplastics ingested by the insects was fairly high, especially in the Chironomus sp. which is a riverbed dweller recorded in the Ogun River.
The diversity of plastic polymers recorded in these insects suggests a wide range of applications of plastics in Nigeria.
The three insect species spend their larval stages in the water and later migrate to land in the adult phase. The concern is that the insect larvae could serve as a link for microplastics’ transfer to higher trophic levels in the aquatic environment. Also, the adults serve in the same capacity in the terrestrial environment. A trophic level is the group of organisms within an ecosystem which occupy the same level in a food chain.
Dragonfly larvae in the water are eaten by fish, salamanders, turtles, birds and beetles. Adult dragonflies on land are also eaten by birds and other insects.
Other research elsewhere has shown the link between microplastics and human health.
Through feeding, the transfer of microplastics in the environment could go as far as people – who caused the plastic pollution in the first place.
Evidence suggests that microplastics reduce the physiological fitness of animals. This comes through decreased food consumption, weight loss, decreased growth rate, energy depletion and susceptibility to other harmful substances. Human health could similarly be at risk on account of microplastic ingestion.
Microplastics can be retained for a longer time at the higher trophic levels where humans belong, thereby predisposing humans to serious health hazards.
Case for a plastic bags ban
A ban on plastic bags would curb the plastic pollution in Nigeria. There are alternatives to the use of plastic bags, for instance, bags made from banana stalks, coconut, palm leaf, cassava flour and chicken feathers. Unlike plastic bags, which could persist in the environments for over a century, bags made from these organic materials decompose readily in a manner that does not pose a health risk to the environment.
For a long while, the call to mitigate plastic pollution was not heeded in Nigeria. Recently, the House of Representatives passed a bill banning plastic bags. But this is yet to be implemented as the president has not assented to it.
A study in the European Union indicates that a ban on single-use plastics could reduce marine plastic pollution by about 5.5%.
It is about time Nigeria treated plastic pollution as a national emergency, considering its implications for human health and the ecological integrity of aquatic ecosystems. An approach that puts people at the centre of the issue has been suggested as one way to convince local communities to preserve the integrity of the environment.
Perhaps this approach could help restore plastic-laden aquatic ecosystems and preserve the pristine ones.
But the problem goes much deeper than this. Much plastic pollution is in the form of microplastics, tiny fragments less than five micrometres in size and invisible to the naked eye. Our new research shows that these microplastics are even getting into tiny flying insects such as mosquitoes. And this means the plastic can eventually contaminate animals in a more unlikely environment: the air.
Microplastics can come from larger plastic items as they break down, but are also released directly into waste water in their millions in the form of tiny beads found in many cosmetic products including face wash and toothpaste (though these are now banned in many countries). Many tiny animals can’t tell the difference between their food and microplastics so end up eating them. Once inside an animal, the plastic can transfer via the food chain into fish and other creatures and eventually become a potential health problem for humans.
By studying mosquitoes, we have found a previously unknown way for plastic to pollute the environment and contaminate the food chain. Our new paper, published in Biology Letters, shows for the first time that microplastics can be kept inside a water-dwelling animal as they grow from one life stage to another.
Although most microplastic research has focused on the sea, plastic pollution is also a serious problem in freshwater, including rivers and lakes. Much of the freshwater research has concentrated on animals that live in the water throughout their life. But freshwater insects such as mosquitoes start their lives (as eggs) in water and, after several stages, eventually fly away when they grow up.
Testing the mosquitoes
It occurred to us that aquatic insects might carry plastics out of the water if they were able to keep the plastics in their body through their development. We tested this possibility by feeding microplastics to mosquito larvae in a laboratory setting. We fed the aquatic young in their third larvae stage food with or without microplastic beads.
We then took samples of the animals when the larvae shed their skin to become larger fourth-stage larvae, when they transformed into a non-feeding stage called a pupa, and when they emerged from the water as a flying adult. We found the beads in all the life stages, although the numbers went down as the animals developed.
We were able to locate and count the microplastic beads because they were fluorescent. We found beads in the gut and in the mosquito version of the kidney, an organ that we know survives the development process intact. This shows that not only do aquatic insects such as mosquitoes eat both sizes of microplastics, they can keep them in their gut and kidney as they develop from a feeding juvenile larva up to a flying adult.
In this way, any flying insect that spends part of its life in water can become a carrier of plastic pollution. And flying insects are eaten in their thousands by predatory insects in the air such as dragonflies as well as by birds and bats.
Our results have important implications since any aquatic insect that can eat microplastics in the water could potentially carry them in their body to their flying stage where they can move the plastics into new food chains. As a result, freshwater plastic pollution is a problem that has implications far beyond those of water quality and eventual marine pollution.
Clearly these results raise a number of questions, including what effect microplastics have on the survival and development of mosquitoes through their life stages. And we still need to examine the effect of different types and sizes of plastics on more species to see how widespread an issue this could become.
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).
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?
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.
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.
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.
Kevin's Walk on the Wild Side 