A 2018 map of mercury found in the sediment of the Penobscot River and parts of upper Penobscot Bay that is part of the Penobscot River Mercury Study shows that the greatest concentrations of elevated levels of mercury are found in Orrington, where the chlor-alkali plant was located, Bucksport, Verona Island and Mendall Marsh in Frankfort.

On the map, dots indicating the presence of mercury travel upriver from the now-defunct Holtra-Chem site all the way to Eddington.

The factory, which had several owners from 1967 to 2000, supplied paper mills with chlorine and other chemicals. A court-ordered scientific study found that 6 to 12 tons of mercury were discharged from the chemical factory into Penobscot River between 1967 and the early 1970s.

Last fall, a report filed by an environmental engineering firm estimated that remediation of the Penobscot River estuary would cost between $246 million and $333 million.

In the upper portions of Penobscot Bay, higher concentrations of mercury have been found in the area stretching from Cape Jellison in Stockton Springs to Perkins Point in Castine. The state has closed a total of 12.5 square miles to lobster and crab fishing in the upper portion of the bay because of mercury contamination found in lobsters, although in 2016 state officials pointed out that the amount of mercury found in crustaceans in the southern portion of the closed area is less than the amount found in a can of tuna.

The dots on the mercury map dissipate as the bay widens out, and although there are several dots east of Belfast, they are the blues and greens that indicate smaller concentrations of the heavy metal, not the angrier-looking reds, oranges and yellows indicating larger concentrations that are more prevalent upriver. A Maine state official who is familiar with the Penobscot Mercury Study said last week that scientists who have worked on the two court-ordered reports focused their research efforts more on the river than on the bay.

While the map shows higher concentrations of mercury in the sediments near the proposed Whole Oceans’ RAS facility in Bucksport, the Sierra Club Maine chapter — which opposes the construction of a land-based fish farm in Belfast — is not as concerned about that.

“We haven’t really heard from people about Whole Oceans,” Alice Elliott, the Maine chapter director, said last week. “We haven’t had members in that area advocating for that.”