Turtles hold post-WW2 nuclear history in their shells

Scientists show uranium signatures persist in turtles and tortoises, even decades after World War Two nuclear activities.
Sade Agard
Close up portrait of a tortoise.
Close up portrait of a tortoise.


Imagine if the stories of our past were etched onto our bodies, visible for all to see. For turtles, tortoises, and sea turtles, this is their reality. That is, these creatures literally carry their history on their shells. 

Now, in a new study published in PNAS Nexus on August 22, their shells reveal an astonishing deep connection to our 20th-century nuclear past and its impact on the environment that still resonates today.

Shells and uranium signatures, USA

Cyler Conrad from the Pacific Northwest National Laboratory and his colleagues explored chelonian shells – the sturdy armor that shields these creatures – to understand their interactions with human-made uranium. 

This radioactive element is associated with nuclear fallout and waste, marking a haunting reminder of humanity's nuclear endeavors.

The team examined shells from five different specimens in areas linked to uranium accumulation from nuclear events. Like the rings of a tree, the shells preserved a timeline of exposure to these atomic materials. 

Turtles hold post-WW2 nuclear history in their shells
Scute growth sequence from the eastern box turtle collected from Oak Ridge National Laboratory in 1962.

One such discovery unfolded in the shell of a green sea turtle found in Enewetak Atoll, part of the Republic of the Marshall Islands. The atoll, once a nuclear testing ground, yielded a surprising uranium signature even decades after testing ceased. 

The researchers speculate that either cleanup efforts stirred up contaminated sediment or residual contamination from the testing era persisted.

A desert tortoise from southwestern Utah, near the Nevada National Security Site – formerly known as the Nevada Test Site – shared a similar narrative. 

Its shell also had a uranium signature, a testament to the historical nuclear activities in the region. Similarly, a river cooter from the Savannah River Site in South Carolina and a box turtle from Oak Ridge, Tennessee, told their tales of uranium interaction. 

Oak Ridge, once a hub of nuclear weapons research post-World War Two, left its mark on the shells, hinting at the enduring effects of nuclear pursuits.

One intriguing revelation emerged from the box turtle's shell layers. Samples taken from various layers disclosed a chronicle of uranium exposure. 

The turtle's birth shell was the most contaminated layer, implying even higher contamination levels in its mother – a stark reminder of the reach of nuclear influence.

Nuclear activity and the natural world

The implications of these findings are profound. The shells, serving as unwitting environmental monitors, offer a chance to comprehend the lingering footprints of nuclear history. 

They tell a silent but crucial story of our past actions and their ramifications. This study underscores the persistence of nuclear legacy and its intertwining with the natural world, transcending generations and species.

As we look to the future, these chelonian sentinels beckon us to reflect on our responsibility towards the environment and the consequences of our scientific advancements. 

The silent witnesses of history remind us that our choices resonate far beyond our immediate time, underscoring the importance of mindful stewardship for the world we share with creatures that have stood the test of time.

The complete study was published in PNAS Nexus on August 22 and can be found here.

Study abstract:

Chelonians (turtles, tortoises, and sea turtles) grow scute keratin in sequential layers over time. Once formed, scute keratin acts as an inert reservoir of environmental information. For chelonians inhabiting areas with legacy or modern nuclear activities, their scute has the potential to act as a time-stamped record of radionuclide contamination in the environment. Here, we measure bulk (i.e. homogenized scute) and sequential samples of chelonian scute from the Republic of the Marshall Islands and throughout the United States of America, including at the Barry M. Goldwater Air Force Range, southwestern Utah, the Savannah River Site, and the Oak Ridge Reservation. We identify legacy uranium (235U and 236U) contamination in bulk and sequential chelonian scute that matches known nuclear histories at these locations during the 20th century. Our results confirm that chelonians bioaccumulate uranium radionuclides and do so sequentially over time. This technique provides both a time series approach for reconstructing nuclear histories from significant past and present contexts throughout the world and the ability to use chelonians for long-term environmental monitoring programs (e.g. sea turtles at Enewetok and Bikini Atolls in the Republic of the Marshall Islands and in Japan near the Fukushima Daiichi reactors).

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