The Los Angeles Times reported Tuesday that researchers have found high levels of radiation in giant clams near the Central Pacific site where the United States “entombed waste from nuclear testing almost four decades ago.”

The finding is “raising concerns the contamination is spreading from the dump site’s tainted groundwater into the ocean and the food chain.”

The radioactive shellfish were found near Runit Dome on Enewetak Atoll, a giant concrete structure called “The Tomb.” In the late 1970s, waste and debris from islands in the atoll were stored in the dome, which fills a blast crater from a 1958 nuclear test.

The radiation “is either leaking from the waste site — which U.S. officials reject — or that authorities did not adequately clean up radiation left behind from past weapons testing, as some in the Marshall Islands claim.”

It’s unclear whether the shellfish were poisoned by radioactive material from the dome, or from “residue” from previous tests. The U.S. conducted 67 nuclear tests in the Marshall Islands in the 1940s and 1950.

The Times report comes a week after The Washington Post reported that the dome is cracking and there are concerns that radioactive material is leaking into the lagoon.

Read Civil Beat’s 2016 story of the struggle of American workers who were exposed to the radioactive soil and debris to obtain adequate health care from the U.S. government.