The study looked at how earthworms can help reduce cobalt and lead levels in sewage sludge when mixed with different types of animal dung during vermicomposting. They found that the combination of cow and horse dung with sewage sludge led to the biggest decrease in cobalt and lead levels in the final compost. Earthworms also absorbed some of these metals, but overall, the levels in the compost decreased due to the earthworms' accumulation of the metals in their bodies.