The planet’s prodigious poo problem

the uk’s cows produce 36m tonnes in waste every year
The UK’s cows produce 36m tonnes in waste every year. Composite: The Guardian Design Team

Each year, livestock produces billions of tonnes of excrement. It’s starting to poison the natural world. So what is to be dung?

How much poo is generated by the world’s farms?

Recent research has estimated that by 2030, the planet will be generating at least 5bn tonnes of poo each year, with the vast majority being deposited by livestock. With 80% of farms in the Netherlands already producing more cow dung than they can legally use as fertiliser, and China resorting to drastic measures to try to reduce the amount of manure being discharged into rivers, scientists say this is a major environment and health challenge.


“It’s a huge problem,” says Joe Brown, professor of environmental engineering at Georgia Institute of Technology. “Animal waste is going up because as populations and wealth increase, there’s a bigger demand for protein. But while we’ve seen lots of initiatives to safely manage human waste, nobody is talking about this.”

So let’s talk about it: how big is the problem in the UK?

Despite extensive Environmental Agency regulations, the UK’s dairy, poultry and pig farms were responsible for 424 incidents of serious pollution related to waste disposal between 2010 and 2016.

With the UK’s cows already producing 36m tonnes in waste every year – enough to fill the Shard 78 times over – and many dairy farmers feeling the pinch from tumbling milk prices, safely disposing of these mounds of toxic mess is a serious and expensive conundrum.

What are the knock-on environmental risks?

Because most first world farming systems are highly concentrated, industrial operations, this produces very concentrated streams of waste. Unless these are dealt with rapidly, they can pollute the air with large amounts of harmful gases such as ammonia, nitrous oxide and hydrogen sulphide.

Inhaling these toxic fumes can be lethal in large quantities, and studies have repeatedly shown that people who live near industrial farms have a much greater risk of chronic asthma, respiratory irritation, immune suppression, and even mood disorders.

Water pollution and climate change are also issues.

a young girl from niger carries animal dung on her head to sell at a local market
A young girl from Niger carries animal dung on her head to sell at a local market. Photograph: Plan International


Moreover, the greenhouse gas methane is produced in large quantities when waste is left to decay uncontrollably. Many scientists believe animal waste is already a vastly overlooked component of climate change. “When methane is first released, it’s around 80 times worse than CO2 at trapping heat, and that continues for 10-20 years until it becomes oxidised and its global warming potential is reduced,” says Philip Longhurst, a professor at Cranfield University’s centre for climate and environmental protection. “When you look at sources of methane emissions across Europe, agricultural waste is probably in the top three.”

In China, where production of animal protein increased nearly five-fold as part of its dramatic economic growth between 1980 and 2010, methane from animal waste is thought to be one of the main reasons why greenhouse gas emissions to the atmosphere doubled during the same period.

What about water pollution?

So far, it’s the impact of manure on waterways that has received the most attention. This either occurs through accidental spillages, flooding or farmers deliberately dumping excess waste into rivers. Investigations have found that the latter practice is still commonplace, despite being illegal in many countries.


The ecological consequences are typically drastic, with the high levels of nutrients such as phosphorus and nitrates in manure leading to the spread of waterborne pathogens, and the growth of harmful algal blooms. The latter can poison wildlife by releasing deadly neurotoxins, and if they become widespread in fresh and marine water, they can end up getting into the food chain and being consumed by humans.

As an example, in China, more than half the freshwater lakes have become polluted, which has led to the rise of diseases such as cholera in many rural communities. Unless more effective ways are found to deal with the increasing amounts of animal manure, some scientists predict that by 2050, large swathes of the country’s rivers will see a 100%-200% increase in phosphorus and nitrate pollution.

“Water pollution is a one of the biggest problems resulting from ineffective disposal of animal waste,” says Oene Oenema, a professor at Wageningen University, who has spent many years researching agricultural pollution across Asia. “When waste is being disposed of in rivers, and then transported to lakes and coastal zones, fish disappear, the water becomes dark and black, and there’s a high risk of infections being transmitted to humans. In parts of China, there are still discharges directly into service water.”

an indian woman arranges animal dung, to be used as fuel
An Indian woman arranges animal dung, to be used as fuel, to dry on the outskirts of New Delhi. Photograph: Prakash Singh/AFP/Getty Images


What are the risks to human health?

Some of the most direct health risks posed by increasing amounts of animal waste are likely to come in parts of the world such as Africa, India and much of south-east Asia where communities still live in close contact with their livestock. As these economies grow and become increasingly urbanised in decades to come, the demand for protein will rise sharply, as will the amount of dung.

“This issue will be most acute in places which see massive population increases, such as parts of eastern and southern Asia, and areas of sub-Saharan Africa,” Brown says.

While many sanitation initiatives across sub-Saharan Africa have focused solely on human waste, scientists fear they have overlooked a much greater problem. “There have been a number of studies in low-income countries, where human sanitation for people was improved, but outcomes like diarrhoea didn’t change,” says Jan-Willem Rosenboom, senior programme officer for sanitation and hygiene at the Gates Foundation. “This could be because there’s already so much animal waste in the environment, that merely improving human sanitation doesn’t have enough of an impact on health.”

While centralised farming systems, such as those in Europe and the US, mean that humans avoid direct exposure to animal poo, this is far more commonplace in many low and middle income countries, meaning that enteric infections are still a common cause of death, especially in children. Scientists suspect that many of these deadly infections are zoonotic – which means they can be transmitted directly from animals, or their waste, to humans – and in countries where farmers use high amounts of antibiotics in their livestock, many of these strains may be antibiotic resistant.

“A lot of the animals used in livestock production are reservoirs of zoonotic infections,” Brown says. “So we know, for example, that chickens can transmit salmonella, or hepatitis A, and cows are known to be a source of cryptosporidium exposure. These infections can have long-term outcomes such as malnutrition, anaemia and even cognitive problems.”

piglets at a farm in near buenos aires, argentina
Piglets at a farm in near Buenos Aires, Argentina, that captures methane emissions from pig manure and uses it to produce electricity or biogas. Photograph: Enrique Marcarian/Reuters


Exploiting animal poo to produce environmentally friendly energy through anaerobic digesters requires vast slurry stores to hold the manure, which are prone to either leaking or collapsing. Investigations have found that a store big enough to hold all the waste produced by 100 cows costs UK farmers tens of thousands of pounds, meaning that for many it’s more economically viable to pay a fine for illegally disposing waste than buying a new slurry store.

At the more exotic end of innovation, some companies are convinced they can take waste and turn it into furniture, paper and even clothing.

These are unlikely to make a big difference. A systemic approach to safe management of this waste is going to be needed.



cattle grazing at a gas power plant where cow manure is used to produce energy near pretoria, south africa
Cattle grazing at a gas power plant where cow manure is used to produce energy near Pretoria, South Africa. Photograph: Mujahid Safodien/AFP/Getty Images


by David Cox | The Guardian



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