But now, amid good sampling results, environmental advisers and advocates have largely turned their attention to the next possible ecological challenge, Dennison said.

“At this point, the attention has turned mostly to the sediments,” he said.

Ungrounding the ship’s bow, which is lodged in the mud, and lifting the fallen bridge from the river bottom is certain to kick up plenty of sediment, Dennison said. And as officials clear the channels for ships, it’s possible they will need to dredge.

And buried within that sediment are legacy contaminants from Baltimore’s industrial past.

To the west of the bridge site sits Wagner’s Point, Curtis Bay and Hawkins Point, which host numerous industrial sites, from coal piers to incinerators and chemical plants. To the east lies the Port of Baltimore’s Seagirt Marine Terminal. And just southeast is Sparrows Point, land heavily polluted by more than a century of steelmaking.

One site on Bear Creek, near the bridge site, had sediments so polluted with heavy metals that the EPA designated it a Superfund site, adding it to a list of the most polluted locations in the nation. Earlier this year, EPA unveiled careful dredging plans for the area, involving sediment screens, booms and treatment technology.

“In a typical dredge operation, there are mitigation efforts they can deploy,” Volpitta said. “They can use things like dredge curtains to reduce the amount of sediment that’s kicked up … The problem is, those types of measures may not be suitable to use, like specifically around the salvage efforts, because those curtains can get wrapped up in the debris, things like that.”

After initial rounds of river sampling screened for fuel and hazardous materials aboard the ship, such as battery acid, the Maryland Department of the Environment has expanded its testing to include metals, “to assess whether any of the activities might be causing contaminants in the river bed to be resuspended,” said spokesman Jay Apperson in a statement.

“Based on the results, which include a showing that levels are slightly higher upriver of the bridge, there is no indication that the activities are affecting those levels,” Apperson said.

Typically, dredging occurs only during the winter, to avoid interfering with underwater plants and wildlife as temperatures warm. But given the timing of the collapse, dredging could be needed during warm weather, Dennison said.

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