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 March 25, 2019
The planet's prodigious poo problem

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

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."

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.

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."

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."

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.

What next?

In 2006, the UN published a landmark report, titled Livestock's Long Shadow, highlighting the serious environmental and health problems posed by the growing amounts of animal waste, and calling for urgent action. However, little progress is being made.

China has attempted to lead the way, announcing strict regulations for the disposal of livestock waste in 2015, emphasising the need for farmers to recycle manure as a replacement for synthetic fertilisers. However, despite the threat of severe fines, critics still question whether these laws will prove effective.

Small-scale projects are under way, such as the efforts of a team of scientists from the University of Vienna who are partnering with various farms across Europe and helping them convert animal poo into paper. But while the potential of new revenue streams could spur more farmers worldwide into taking action to deal with waste, there remains a dire need for new policies, initiatives and conferences to discuss how to deal with the impending problem on a large scale.

In 2016, the Environmental Journal castigated "governmental apathy" surrounding the problem. Three years on, little has changed. "There's a massive policy gap around the world on how to safely manage animal waste, despite all the risks it presents," Brown says. "It's a huge missing piece, and it's been overlooked for so long. In the US, there's very little regulation at all on how to deal with animal waste. That's the same around the world. There's no systematic approach to the safe management and reuse of this waste, even though it does end up getting into the environment and leads to downstream exposures to people."

Solutions to a crappy problem

By 2030, world's total faecal output is likely to contain 100m tonnes of phosphorus, 30m tonnes of potassium, and 18m tonnes of calcium. These are all valuable minerals which if tapped, could be recycled back into the global agriculture system.

In addition, waste emissions such as methane can be converted into electricity through biogas generators, as recently highlighted by a British inventor who built a street lamp powered entirely by dog poo. "Methane is a very versatile fuel," Longhurst says. "It can be used to generate electrical power, domestic and industrial heating, and even in transport. In the coming years there's going to be increased pressure for countries across Europe and beyond, who are concerned about climate change, to control methane emissions from animal waste and make greater use of it."

Waste could also be seen as a valuable asset, though whether it can be exploited by the majority of farmers remains to be seen. "If you're living in an urban environment, you may not have the space to install a generator and it could seem easier to let your waste wash away," says Eric Fevre, professor of veterinary infectious diseases at the University of Liverpool. "It also requires access to financing to invest in a generator. And it requires time and labour to use that waste. But the hope is that the cost benefit is greater than the initial expenditure, and so it starts to happen on a larger scale."

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.