Liquid gold: Urine passes test as safe eco-fertiliser that won’t make us all sick

22 Jan 2020

Image: © Татьяна Белова/

Researchers are flush with excitement after finding aged urine can be safely used as a fertiliser without passing on antibiotic resistance to the land.

While bodily waste – whether human or animal – has been used as fertiliser for centuries, our wee could be about to make the transition to a large-scale, eco-friendly kick-start for plant growth.

Researchers from the University of Michigan have published a paper to Environmental Science and Technology showing that aged human urine can be safely used in soil with minimal risk of transferring antibiotic resistant DNA to the environment.

It’s hoped that our liquid waste could be an alternative to widely used fertilisers that contribute greatly to water pollution. The high levels of nitrogen and phosphorus in these fertilisers can spur the growth of algae, which can threaten our sources of drinking water.

Also, synthetic fertiliser is expensive and energy intensive to produce. By comparison, urine contains nitrogen, phosphorus and potassium – key nutrients that plants need to grow.

‘Our current agricultural system is not sustainable, and the way we address nutrients in our wastewater can be much more efficient’

In this new study, the researchers found that aged samples sealed in containers deactivate 99pc of antibiotic resistant genes that were present in the bacteria in the urine.

“Based on our results, we think that microorganisms in the urine break down the extracellular DNA in the urine very quickly,” said Krista Wigginton, environmental engineering professor at University of Michigan and corresponding author of the study.

The researchers collected urine from more than 100 men and women and stored it for between 12 and 16 months. During that time, ammonia levels increased, lowering acidity levels in the urine and killing most of the bacteria.

When the ammonia kills the bacteria, they dump their DNA into the solution. It’s these extracellular snippets of DNA that the researchers studied to see how quickly they would break down.

“There are two main reasons we think urine fertiliser is the way of the future,” Wigginton said. “Our current agricultural system is not sustainable, and the way we address nutrients in our wastewater can be much more efficient.”

So far, the researchers said, field experiments have been “quite promising” and they see it being an effective, sustainable fertiliser for food crops and other plants, such as flowers.

Colm Gorey was a senior journalist with Silicon Republic