Pork accounts for at least 60% of all meat eaten in China, but its popularity exacts a heavy toll on the environment that has proven tricky to resolve until now.

A new study by Chinese and Australian researchers has identified a sustainable solution to mitigating excessive amounts of copper found in the 3.8 billion tons of pig manure turned into organic fertiliser to increase crop yields.

Although an essential nutrient in small doses, high concentrations of copper – added to pig feed to promote growth – is toxic to plants, soil, water and humans.

Researchers from China’s Fujian Normal University and the University of South Australia have demonstrated that adding green-synthesised iron nanoparticles (G-nFe) to pig manure neutralises the amount of bioavailable copper in piggery effluent, reducing the environmental risks.

China has regulations limiting the amount of copper allowed in pig feed, but the scale of livestock farming keeps increasing to feed a population of 1.4 billion people, making it difficult to control the huge amount of manure and sewage released into the environment.

Experiments undertaken by researchers showed that adding G-nFe to pig manure compost reduced exchangeable cooper by 66.8%, carbonate-bound copper by 47.5%, and iron-manganese oxide-bound copper by 15.4%.

“This process was able to convert free copper into a less bioavailable form, reducing the potential for uptake by plants,” according to UniSA environmental chemist, Associate Professor Gary Owens, who was part of the study.

Residual copper levels initially increased by a third in the first five days before declining by over 60.9% over the full composting period.

The study findings have recently been published in the journal Science of the Total Environment.

China processes approximately 628 million pigs annually, making it the world’s largest pork producer.

Nearly half of the 3.8 billion tons of the resulting pig manure is inadequately treated, researchers say, and the heavy metal and organic pollutants are causing widespread environmental contamination.

While pig manure has traditionally been valued as an inexpensive organic fertiliser for Chinese farmers, it is increasingly posing a serious problem due to the heavy metal contamination, posing a challenge for both government and researchers seeking economically viable solutions.

Green synthesised iron nanoparticles have been widely used to remediate water and soil contamination due to its cost-effectiveness, low toxicity, and strong absorption rates.

However, this is the first study to explore its use in organic compost to remediate heavy metal pollution.

“This research presents a significant step forward in addressing heavy metal contamination in agricultural waste,” according to Assoc Prof Owens.

“By using green-synthesised iron nanoparticles, we can not only improve the safety of composted pig manure, but also contribute to more sustainable farming practices.”

The researchers plan to test G-nFe’s efficiency in larger composting systems using fresh pig manure, hoping to encourage stakeholders in the livestock and composting sectors to adopt the process.

A video explaining the research is available at https://youtu.be/CoEz82qlSq8

Notes for editors

“Enhanced Copper Passivation in Pig Manure Composting through Iron Nanoparticle Amendment” is authored by researchers from Fujian Polytechnic Normal University, Fujian Key Laboratory of Pollution Control & Resource Reuse, and the University of South Australia. DOI: 10.1016/j.scitotenv.2024.177950