The study looked at how earthworms can show us what elements are in the soil. They found that earthworms can accumulate certain elements like Cd, Co, Hg, and Zn from the soil. The researchers used radioactive tracers to track this. They also looked at how sewage sludge affects the levels of these elements in earthworms. They found that Cd, Cu, and Zn levels in earthworms increased with more sludge, while Se levels decreased. The study showed that earthworms can efficiently accumulate Cd, with levels increasing significantly in affected samples.