The marine ecosystem of the lower Penobscot River in Maine has long suffered from mercury poisoning caused by the Orrington-based HoltraChem Manufacturing Company (owned by the Mallinckrodt Corporation), which in 1967 began releasing the toxin into the air and directly into the Penobscot. Studies show that 6 to 12 tons of mercury were dumped in the river through 1972, lying in bottom sediments and working its way through the food chain to contaminate fish, birds, shellfish, mammals and, in some cases, humans who consume these animals.

In 2022, a consent decree was issued requiring Mallinckrodt to fund $187 million in mercury remediation measures to accelerate recovery of the lower Penobscot marine ecosystem, long-term contamination monitoring, and “beneficial projects.”

The remediation effort may include placing a layer of clean bottom sediment over the contaminated sediments, a process known as “capping.” Capping is designed to prevent the mercury-contaminated sediment from spreading, and also kills the tiny benthic organisms and vegetation that first assimilate the mercury. This would theoretically prevent mercury from accumulating in the animals that eat them. Over time, the clean sediment would be repopulated by a new generation of benthic plants and animals.

If permits are approved, a pilot study will blanket six acres of Orrington Reach’s East Cove 3 with four to six inches of clean sand, perhaps as early as September 2025. The site would then be monitored to see if the capping was successful and that the cap layer is not swept away by the river’s currents.