"We need to quantify the microplastics in sewage sludge so that we can [determine] where the hot spots are and start managing it," says Wilson. In places with high levels of microplastics, sewage sludge could be incinerated to generate energy instead of used as fertiliser, she suggests. One way to prevent the contamination of farmland is to recover fats, oil and grease (which contain high levels of microplastics) at wastewater treatment plants and use this "surface scum" as biofuel, instead of mixing it with sludge, Wilson and her colleagues say.