In recent months, national media has detailed how ‘forever chemicals’ – whether in carpets, makeup, clothing, or breast milk – pose an assortment of health issues including liver disease, decreased immunity, and cancer.
A common fertiliser, and the food grown from it, could be added to that list too.
Sludge, or ‘biosolids’, is sewage waste treated and often applied on farmland as a fertiliser. It’s a combination of, importantly, human excrement, but also other waste – some flushed down the loo, some drained off our roads. Some 170,000 truckloads of sludge (87 per cent of what we produce) are applied to UK farmland each year.
Returning so-called ‘organic matter’ to the land in this way has many benefits. It increases the water retention levels of carbon in the soil, builds soil fertility, and in theory, returning human excreta to the land could help farmers move away from intensively manufactured artificial fertilisers, which have high carbon footprints.
A 2020 Portuguese study, over the course of two years, demonstrated how sludge can outperform mineral fertiliser by increasing levels of nutrients such as nitrogen, potassium, and phosphorus in the soils they’re applied to. In some cases, by two or three times that of mineral fertiliser.
It is, also, resourceful – if sludge wasn’t returned to the land, it would get incinerated, or disposed into landfill. The Environment Agency claims the most sustainable option is to recycle sludge to agricultural land as organic manure.
But it’s not all positive. Sludge may be causing more harm to us than good, some studies have suggested, due to contamination from heavy metals and newer threats like microplastics.
A study at the University of California this year concluded that microplastics were more common in sludge than first thought, with some tests showing plastic particles were 25 times more present than expected. What’s worse, microplastics absorb heavy metals, potentially rendering soils toxic at high concentrations.
The Soil Association recognises that biosolids, even when regulated, could introduce toxins to plants and therefore the human body, and their organic regulations “strictly prohibit” human-based waste, such as sewage sludge.
Dr Alfonso Lag-Brotons, a senior research associate at Lancaster University, whose focus includes soil protection and waste management, says that while “certain sewage sludge streams will contain pollutants or substances with potential to alter natural [biological] cycles or cause harm,” he does not consider the problem to be widespread, as pollutants are generally restricted to the areas in which they originate.
“The key point is whether regulations are keeping up with the pace at which waste treatment processes change. And at which new threats are being identified – for example, antibiotic resistance, microplastics, etcetera,” he adds.
Even if not widespread, the risks to human health, even if regulated, make for alarming reading. Last year, a Greenpeace report found sludge destined for some UK fields was full of salmonella, e-coli, and weedkiller. And this was after the sludge had been treated. Meanwhile, a study in North Carolina showed that three quarters of people living near farmland spread with sludge suffered reactions such as nausea, vomiting, rashes, and boils.
But before our waste is flushed away as a fertiliser solution once and for all, there is a way human waste can be added to the land in a more sustainable way: with a smaller and more localised approach.
‘Humanure’, as some call it, is distinct from sewage sludge or biosolids in that it does not contain chemical waste or heavy metals, as it is not part of the sewage network, deriving from compost toilets, like the sort found at festivals and campsites.
Visitors to Cordelia Rowlatt’s campsite at Vallis Veg in Somerset use the compost loos onsite, and the resulting human excreta is kept in containers for two years to kill any pathogens, then left to earthworms to break it down over another year or so. At this point, the compost is ready for Rowlatt’s garden beds. But not, due to time and money associated with required tests, the farm’s food.
“It would be safe to put on the veg,” she says, “but you need to do a lot of tests – rightly – to put anything back onto agricultural land. Not so much because of the pathogens, but the heavy metals.”
That said, Rowlatt believes that generally, “it would be better to use sewage sludge than not.” Heavy metals, much of which wash into the water system from roads, are in her view the biggest risk to our health. “But [water treatment systems] are getting better and better at keeping the wastewater stream separate from the sewage stream, and if you do that, you have less of a problem with heavy metals.”
At its worst, sludge is a toxic concoction poisoning soils, food, and us. But, when managed properly, or even better, approved for carefully monitored small-scale local systems, human excreta returned to the land can provide the kind of cheap, organic, nutrient-cycling fertiliser needed to replenish our soils.