8
NEWS
December 2025 ESRFnews
Tuna might be less toxic than
previously thought
ESRF absorption spectroscopy with
high energy resolution has revealed,
in unprecedented chemical detail,
how Atlantic Bluefin tuna convert
toxic methylmercury into less harmful
forms. The findings could help inform
how seafood safety should be assessed.
Mercury in seafood is a global
concern. Because its presence is
amplified up the food chain, long-
lived predators such as tuna are
particularly in the spotlight. A team
led by ESRF scientist Alain Manceau
used the ESRF’s ID26 beamline
to track mercury species inside the
Atlantic Bluefin tuna’s organs and
muscle. The data allowed them to
identify a detoxification route that
hinges on selenium and culminates
in the formation of inert mercury
selenide.
“When evaluating the level of
toxicity, we should do so by measuring
the concentration of methylmercury
– which can be done routinely today
– instead of total mercury,” says
Manceau. “Otherwise, we include
forms of mercury that are sometimes
present in fish but are harmless to
the human body.”
The work shows that, unlike
toothed whales and apex seabirds,
which detoxify mercury in the liver,
Atlantic Bluefin tuna primarily
detoxify mercury in the spleen
– including the mercury in the tuna’s
edible muscle, which is partly present
as a tetraselenolate complex.
Sampling focused on large tuna
caught along the Norwegian coast.
“Samples of such large individuals,
which can weigh up to 300 kg, are
difficult to get, but being high trophic
predators, they make key model
organisms to study,” says coauthor
Martin Wiech of the Institute of
Marine Research in Norway.
The authors stress that the
conclusions do not extend to lower-
trophic tuna – albacore or skipjack,
for instance, which are commonly
found in cans – because their mercury
burdens and speciation differ.
Nevertheless, they report that up to a
quarter of mercury in the edible muscle
of Atlantic Bluefin tuna is present
in less harmful forms (Environ. Sci.
Technol. 59 20332).
Part of the 2025 Nobel Prize in
Chemistry has been awarded to a
previous ESRF user, Omar Yaghi, for
his pioneering work on metal–organic
frameworks (MOFs). Based at the
University of California, Berkeley, in
the US, Yaghi was the main author
of a beamtime proposal to study
high-porosity MOF glasses using
X-ray absorption spectroscopy at
the ESRF’s BM23 beamline. The
experiments were conducted locally
by ESRF scientist Kirill Lomachenko
and postdoc Cesare Atzori, with
remote participation from Yaghi and
his US collaborators, and culminated
in a paper in Angewandte Chemie.
“I’m grateful to have had the
chance to collaborate and co-author a
publication with Professor Yaghi,” says
Lomachenko. “It started when I gave a
talk at his lab in Berkeley about ESRF
capabilities. That led him and his team
to apply for beamtime, which eventually
grew into a fruitful collaboration.”
Alexandr Chumakov, an ESRF senior
scientist, has received the IBAME
Science Award “in recognition of
his seminal contributions to nuclear
inelastic scattering of synchrotron
radiation applied to glass dynamics.”
Over three decades, Chumakov has
been a leading figure in nuclear inelastic
scattering (NIS), shaping its theory and
practice and driving the development
of the synchrotron Mössbauer source
(SMS). His studies on glass dynamics
including resolving the debated
boson peak have set international
benchmarks
At the ESRF he guided the design
of the new ID14 beamline combining
SMS with advanced time and energy
domain techniques submicron
focusing and ultrahigh resolution
These unique capabilities enable micro
Mössbauer studies under extreme
conditions and are opening new
directions across materials science
geoscience and magnetism
Levels of
methylmercury,
not total mercury,
should officially
dictate the toxicity
of Atlantic Bluefin
tuna, says Alain
Manceau.
S H U T T E R S T O C K/J U R G A L P H O T O G R A P H E R
Chumakov receives award
B R I T T A N Y H O S E A-S M A L L, U C B E R K E L E Y
Nobel Prize for ESRF user