The study looked at the levels of heavy metals in the sediment of the Yangtze estuary and nearby areas in 2006. By using a method called the Hakanson ecological risk index, the researchers assessed the contamination and potential ecological risk of these metals. They found that the sediment quality was good overall, with arsenic, chromium, and cadmium being the most common contaminants. The potential ecological risk was low, with cadmium posing the highest risk. The areas with the highest contamination and risk were outside Hangzhou bay and southeast of the estuary. Overall, the levels of heavy metals and ecological risk did not change significantly compared to data from 2003.