For thousands of years, human urine has had real value.
After our bodies absorb nutrients from our food, they excrete the rest – mainly via urine. An adult produces about 500 litres a year. This liquid gold is very rich in nitrogen, phosphorus and potassium, three compounds vital for plant growth.
Ancient civilisations from Greece to China to Rome used it as fertiliser for crops, alongside faeces.
Synthetic fertilisers have largely replaced natural fertilisers such as urine. Half the world’s population now relies on food grown using synthetic fertilisers. Urine is still used as fertiliser by smallholder farmers who cannot afford synthetic fertilisers or want a sustainable alternative.
This year, the Iran war has made synthetic fertilisers more expensive. If the era of cheap fertilisers is ending, urine-based fertilisers could make a comeback. Call it “peecycling”.
Human urine and faeces have long been used as fertiliser. Pictured: agricultural workers spreading nightsoil in Szechuan province, China, in 1960.Sovfoto/Getty
Of chamber pots and nightsoil
Before modern toilets, humans were a lot more intimately acquainted with the waste they produced. Peasants and smallholders would store their collective waste in cesspits. In cities, people used privies or chamberpots.
As cities grew, so did the volume of waste. While people slept, nightsoil workers would go door-to-door collecting human waste. Often, it would be transported for use on farms.
In the 19th century, modern central sewage greatly improved sanitation and cut rates of infectious diseases. But it also changed how we thought about pee and poo from resource – to waste.
From guano to synthetic fertilisers
During the 19th century, nations competed to gain access to a new source of fertiliser – guano, the compressed, nitrogen-rich droppings of seabirds. But the resource was limited. Guano islands were progressively mined out.
In the early 20th century, chemists invented synthetic fertilisers as an alternative.
These fertilisers boosted crop yields. But they also created new social and environmental problems.
Synthetic nitrogen fertilisers are produced using the industrial Haber-Bosch process. It uses lots of energy and relies on natural gas, a potent fossil fuel.
Synthetic phosphorus fertilisers are made by treating phosphate rock, a finite resource mined in only a few places. One of the largest reserves is in Western Sahara, a disputed territory long occupied by Morocco.
Guano was mined intensively, especially on Peruvian islands. The industry has largely vanished bar small-scale extraction on places like Santa Island.Ernesto Benavides/Getty
Fertiliser shocks
Australian soils are heavily weathered and nutrient-poor in most places.
To produce as much food as it does, Australia has to import 3.5-4 million tonnes of synthetic fertilisers every year. Almost no fertilisers are produced locally.
Once mixed with wastewater, these nutrients are much harder to access.
To get enough urine to make fertiliser would involve using separate plumbing in homes, public toilets and at events. Urinals are an existing source.
When mixed with wastewater, the nitrogen in urine can turn into nitrous oxide, a potent greenhouse gas, or ammonia. Wastewater plants release the greenhouse gas emissions equivalent of the global aviation industry.
If urine is diverted from wastewater, authorities could save on wastewater treatment – and cut emissions.
If urine is diverted from wastewater, it would save authorities money on treatment.Bilanol/Getty
How do we capture urine?
At a small scale, raw urine can be captured using specialised urine-diverting toilets or urinals. Urine can be applied directly to your home garden, as long as sensible guidelines are followed.
These can be managed with the right treatments and governance.
Urine nations?
Urine fertilisers have gained popularity in recent years.
In the United States, the Rich Earth Institute has lead community peecycling programs for over a decade. In Europe, Swiss startup VunaNexus uses diverted urine to make a sustainable fertiliser.
One of the biggest barriers to scaling up urine-based fertilisers is the ick factor. Some people find the idea gross.
Fortunately, this can change. Researchers have been testing ways to challenge the stigma around urine. Our new podcast examines how rethinking the humble toilet can turn waste into fertiliser.
For centuries, people saw urine as the vital resource it is. The fact we can help grow crops using something from our bodies is remarkable. In an increasingly uncertain world, it might well be necessary.
Jordan Roods receives funding through the Australian Research Council Research Hub for Nutrients in a Circular Economy.
Kerry Tozer receives funding from the UTS Institute for Sustainable Futures and in connection with the Australian Research Council Research Hub for Nutrients in a Circular Economy.
Cleaner engine standards and a gradual uptake of electric vehicles have been credited with helping improve Auckland’s air quality over recent years.
But for policymakers working to tackle city traffic pollution, another problem remains: not all of it comes from vehicle exhaust pipes.
Cars, trucks, vans and buses all generate and stir up dust and tiny particles as they move along roads and motorways, regardless of what powers them.
As exhaust emissions slowly decline, these other sources of traffic pollution – particularly road dust – are becoming increasingly important to understand.
Our new research suggests they’re also likely to require a different set of solutions.
What we found on Auckland’s roads
Traffic creates tiny particles as tyres and brakes wear down, road surfaces erode and passing vehicles kick dust back into the air. As some EVs and SUVs are heavier than conventional cars, this can increase wear on tyres and roads.
This all creates what are known as non-exhaust emissions – and they don’t disappear when petrol and diesel cars are replaced by EVs. But relatively little has been known about the scale of this type of pollution in Auckland.
To investigate, we analysed data from 2006 to 2019 to measure the contribution of road dust to PM?? – the technical abbreviation for airborne particles with a diameter of 10 micrometres or less.
Our study covered three monitoring sites: Queen Street in the central city, Khyber Pass on a major arterial route, and Penrose near a key motorway corridor. We then combined this air-quality data with information on traffic and weather conditions.
Even after accounting for factors such as rainfall, wind, temperature and traffic, road dust was more strongly linked to PM?? levels than pollution from vehicle exhausts.
Perhaps surprisingly for a relatively wet city, road dust remained a major contributor to Auckland’s particulate pollution.
Heavy vehicles – those weighing more than 3.5 tonnes – also stood out. While accounting for just 4% of traffic in our dataset, a higher proportion of heavy vehicles was associated with increased PM?? levels.
Our modelling suggests part of that effect may come from heavy vehicles disturbing soil and other loose material, which can then become road dust.
Weather also influenced the picture. Stronger winds were associated with higher PM10 levels when road dust concentrations were elevated, while rainfall had no statistically significant effect in the relevant model.
Overall, the findings suggest what makes up Auckland’s traffic can matter as much as how much traffic there is.
Why road dust is a regulatory headache
For regulators, exhaust pollution is relatively straightforward to tackle. It comes from a clear source and vehicle-emission standards can be designed to reduce it.
Road dust is much harder to deal with. It comes from multiple sources, can be stirred up repeatedly by traffic, and falls largely outside conventional vehicle-emission standards.
All the same, this pollution can have serious health effects. Non-exhaust emissions have been linked to cardiovascular and respiratory problems, including increased hospital admissions in New Zealand.
Reducing those risks will require a better understanding of where road dust builds up, what sends it back into the air and who is most exposed.
Possible policy responses include better containment of soil and loose material near roads, improved management of road dust, and targeted controls on heavy-vehicle movements at pollution hotspots.
Reducing traffic volumes could help, too. Better public transport and infrastructure for walking and cycling would mean fewer vehicle movements generating and stirring up particles.
There is still much more to learn.
Our study covers only three Auckland sites, over a 13-year period up to 2019. Wider and more recent monitoring could show how newer vehicle technology, heavier vehicles and changing travel patterns are affecting non-exhaust pollution.
But the broader challenge is already apparent. As tailpipe emissions decline, transport and air-quality policies will increasingly need to account for the pollution generated simply by vehicles moving on roads.
Otherwise, a significant source of Auckland’s particulate pollution risks remaining overlooked.
The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
A total of six people apprehended as clean-up of rubbish stacked 10 metres high cost about £6m
Two men have been arrested after fly-tippers dumped a “mountain of illegal waste”, stacked 10 metres high, in Oxfordshire.
Hundreds of tonnes of rubbish appeared in a field between the River Cherwell and the A34 near Kidlington in November last year. The waste tip was so large that removing it could cost more than the local council’s annual budget, the area’s MP said.
More than 140 clubs breached licences, with a third caught taking water illegally, analysis shows – but no fines issued
More than 140 golf clubs in England have breached their water extraction licences in the past five years, according to data analysis by the Guardian.
More than a third of these clubs were caught taking water illegally from the environment, either by taking more than permitted or by removing it outside the permitted period.
Feral horses, also known as brumbies, are descendants of domesticated horses that now live and breed independently in the wild. For some people, these horses are a cherished part of Australia’s cultural heritage. For others, they represent a major threat to the environments they inhabit.
Yuraygir National Park, on the coast of northern New South Wales on Yaegl and Gumbaynggirr Country, is a stunning landscape where you can see coastal emus and spot migrating whales from the shore.
It is also home to a small feral horse population that is now at the centre of a legal dispute. The final hearing, taking place on Wednesday, could have repercussions far beyond feral horses.
Yuraygir is home to the largest population of coastal emus left in Australia.David Watson
What is this dispute about?
In late August, feral horse advocates began urgent proceedings in the NSW Land and Environment Court. They argued the National Parks and Wildlife Service does not have the legal authority to kill feral horses in Yuraygir.
The National Parks and Wildlife Service had been using aerial shooting, ground shooting and trapping to manage feral horses, as well as feral pigs, deer and foxes. It has now agreed to suspend activities until the final hearing on September 9.
To date, the court has not ruled the proposed operations are unlawful. Rather, the current suspension gives the NSW Department of Climate Change, Energy, the Environment and Water time to ensure necessary approvals are in place so staff can continue working towards the goals of the Yuraygir management plan. These include controlling feral animals and restoring native vegetation.
A herd of feral horses, also known as brumbies.Skitzpix/Getty
A controversial topic
Feral horse control has long been a source of heated debate. For many people, it is more controversial than the management of other invasive species, such as deer and foxes, because horses are more culturally cherished. Lethal control is also associated with animal welfare concerns, including stress during pursuit and the possible risk of non-fatal wounding.
However, there is a strong ecological case for controlling feral horses. As large, hard-hooved, introduced grazing animals, feral horses can inflict significant damage to Australian ecosystems. They trample plants, compact soils, erode stream banks and disturb wetlands. This endangers many native species that rely on these fragile habitats, some of which live nowhere else. So feral horses must be managed with the same planning and urgency as other invasive animals.
Evidence suggests aerial shooting by professionals under strict protocols does not affect the welfare of feral horses. For example, independent veterinary assessments of recent operations in Kosciuszko National Park uncovered no welfare-related incidents.
A park worth protecting
Yuraygir National Park encompasses an extensive network of coastal lagoons, freshwater wetlands, saltmarshes and wet heaths that support an array of threatened animals. This includes the green and golden bell frog (Litoria aurea), the wallum froglet (Crinia tinnula) and the Olongburra frog (Litoria olongburensis).
However, these environments are among those most vulnerable to grazing and trampling. This is because their soft, often waterlogged soils and delicate vegetation are easily damaged by hard hooves. Feral horses can compact and churn up soil, increase erosion and muddy water, while destroying the shallow pools and vegetation that frogs use for shelter and breeding.
Beyond frogs, feral horses trample the nesting grounds of threatened shorebirds, such as the little tern (Sternula albifrons), pied oystercatcher (Haematopus longirostris) and critically endangered beach stone-curlew (Esacus magnirostris). Because these birds nest in shallow scrapes on the ground, horses could crush eggs or chicks and disturb nesting adults. Grazing and trampling may also reduce the dense vegetation relied on by species such as the eastern ground parrot (Pezoporus wallicus wallicus).
The current shooting suspension also delays control of pigs, deer and foxes, other invasive species that damage wetlands and native vegetation or prey on native wildlife. Yuraygir’s management plan identifies fox control as vital to protecting little terns, beach stone-curlews and coastal emu chicks.
So this legal dispute, while focused on feral horses, may have much broader ecological costs.
Yuraygir National Park is home to the endangered green and golden bell frog.Gerald Corsi/Getty
Early action is key
Control may seem unnecessary given there are relatively few horses in Yuraygir. However, research suggests the opposite is true.
Studies consistently show it’s often easier and cheaper to control small, localised populations of invasive species than larger, widespread populations. Delaying action gives animals time to reproduce, establish new populations and expand their geographical range. Management then becomes more difficult and expensive. It is also more likely to require repeated killing.
Kosciuszko is a case in point. Since late 2023, when aerial shooting was reintroduced to Kosciuszko National Park, thousands of feral horses have been removed. However, population numbers have stayed high and ecological damage remains widespread. This is partly because horses can breed quickly and move into controlled areas from surrounding land, particularly when management pauses.
There is still time to stop this happening at Yuraygir. For now, we await a decision from the NSW Land and Environment Court. But to safeguard this sacred landscape, we must protect it from the hard hooves and hungry mouths of feral horses.
Patt is the director for early career ecology at the Ecological Society of Australia, the Early Career Coordinator at the Australasian Wildlife Management Society, and a council member for the Royal Zoological Society of NSW. He receives funding from the Australian Research Council.
David M Watson receives funding from the Australian Research Council, the Department of Agriculture, Fisheries and Forestry and the Department of Climate Change, Energy, the Environment and Water. He also serves as a board member for the Great Eastern Ranges and the Holbrook Landcare Network.
