The researchers studied the levels of certain heavy metals in the mud of the Yangtze Estuary in China. They found that metals like copper, lead, and zinc were more concentrated in certain areas due to factors like sewage and sediment size. In summer, the levels of these metals were lower than in spring because of storms washing them away. Copper and lead levels were affected by the amount of organic matter in the sediment. Overall, the study showed that some areas had higher levels of heavy metals, but chromium pollution was not a major issue in the estuary.