Science - USA (2022-02-18)

INSIGHTS | PERSPECTIVES

GRAPHIC: N. CARY/

SCIENCE

systems, where the layers are rotated as they
are stacked, and with the trilayer rhombo-
hedral graphene ( 2 ). Some of those showed
similar robustness of superconductivity to
magnetic fields ( 2 , 6 ). However, the bilayer
graphene of Zhou et al. is arguably the sim-
plest graphene system where superconduc-
tivity has been observed. Hence, it works as
an ideal candidate for further experimenting
with graphene superconductivity.
One remaining question is the underly-
ing mechanism for electron pairing in gra-
phene. A common idea is that extraordinary
superconductivity requires an extraordinary
pairing mechanism ( 7 ). However, it may be
possible to explain the phenomenon with a
conventional mechanism, where electron
pairing is mediated by lattice vibrations
( 8 – 11 ). In this case, the exotic nature of the
superconductivity of graphene seems to orig-
inate from its special band structure. Other
open questions are related to the interplay
of magnetism and superconductivity, com-
petition of the spin-singlet and spin-triplet
forms of superconductivity, and the precise
nature of excitations in the triplet state. The
experimental challenge comes from optimiz-
ing the conditions for superconductivity with
a maximal operating temperature.
Before the gold rush of superconductiv-
ity studies on graphene, there were claims
of superconductivity in graphite ( 12 ). Those
findings reported much higher critical tem-
peratures than those measured in few-layer
graphene ( 1 , 2 , 6 ), but they were not widely
accepted by the field because of strong sam-
ple-to-sample variations and difficulty repro-
ducing the results. However, based on the
findings of Zhou et al., superconductivity of
graphene-based systems seems more com-
monplace than what was previously thought.
This may open new possibilities for gra-
phene-based, ultrasmall electronics. Perhaps
in the future, ordinary graphene will be used
for extraordinary applications. j

REFERENCES AND NOTES

1. Y. Cao et al., Nature 556 , 43 (2018).


2. H. Zhou, T. Xie, T. Taniguchi, K. Watanabe, A. F. Young,
   Nature 598 , 434 (2021).


3. H. Zhou et al., Science 375 , 774 (2022).


4. Y. Zhang et al., Nature 459 , 820 (2009).


5. Y.-T. Hsu, Nature 595 , 495 (2021).


6. J. M. Park, Y. Cao, K. Watanabe, T. Taniguchi, P. Jarillo-
   Herrero, Nature 590 , 249 (2021).


7. A. Ghazaryan, T. Holder, M. Serbyn, E. Berg, Phys. Rev.
   Lett. 127 , 247001 (2021).


8. R. Ojajärvi, T. Hyart, M. A. Silaev, T. T. Heikkilä, Phys. Rev.
   B 98 , 054515 (2018).


9. T. J. Peltonen, R. Ojajärvi, T. T. Heikkilä, Phys. Rev. B 98 ,
   220504 (2018).


10. Y.-Z. Chou, F. Wu, J. D. Sau, S. Das Sarma, Phys. Rev. Lett.
    127 , 187001 (2021).


11. Y.-Z. Chou, F. Wu, J. D. Sau, S. Das Sarma, https://arxiv.
    org/abs/2110.12303 (2021).


12. P. Esquinazi, Pap. Phys. 5 , 050007 (2013).

ACKNOWLEDGMENTS
I thank R. Ojajärvi, Y. Lu, and T. Hyart for illuminating discussions.

10.1126/science.abn9631

ENVIRONMENTAL HEALTH

H uman health effects of

chemical mixtures

Child neurodevelopment can be adversely affected

by endocrine-disrupting chemicals

By Zeyan Liew1,2 and Pengfei Guo1,2

H

uman populations are exposed to a

large and diverse set of endocrine-

disrupting chemicals (EDCs), exog-

enous chemicals that can interfere

with hormone activity and the en-

docrine system ( 1 ). Toxicological and

epidemiological studies have relied on a

one-chemical-at-a-time approach to investi-

gate possible human health effects of EDC

exposure. It has been suggested that this

approach provides inadequate protection

against human exposure to EDCs because

it fails to consider the mixture effects of

exposure to multiple chemicals simultane-

ously. Indeed, adverse health effects from

EDC exposure arise at regulation-compliant

concentrations, raising the possibility that

mixtures manifest additive effects at lower

doses than the regulatory thresholds for sin-

gle chemicals. A robust and evidence-based

approach for regulating exposure to chemi-

cal mixtures has been lacking. On page 735

of this issue, Caporale et al. ( 2 ) demonstrate

a mixture-centered risk assessment strategy

and identify a prenatal EDC-mixture con-

centration that could increase risks of child

language delay.

Humans are exposed to multiple classes of

EDCs through their encounters with polluted

air, water, food, and consumer products.

Caporale et al. investigated simultaneous

exposure to three classes of synthetic com-

pounds widely used in commercial applica-

tions, including perfluoroalkyl substances

(PFASs), phthalates, and phenols. PFASs are

extremely persistent, with a biological half-

life of up to 4 to 8 years in the human body

( 3 ). Phthalates and phenols are less persis-

tent, but humans are repeatedly and con-

stantly exposed to them, for example, from

personal care products. Exposure to these

EDCs has been linked to several major health

conditions ( 4 , 5 ) (see the figure).

To what extent long-term developmental

consequences can be caused by these wide-

spread EDCs is not fully understood. The

fetus or infant is exposed to various EDCs

through placental and lactational transfer

from the mother ( 6 ). Fetal and infant de-

velopment are sensitive periods that can be

adversely affected by EDCs. For example,

disruption of central nervous system devel-

Pesticides

Heavy metals

Polychlorinated biphenyls and

polybrominated diphenyl ethers

Bisphenol A and phthalates

Perfluoroalkyl substances

EDC exposure

Polycyclic aromatic hydrocarbons

Language impairment

EDCs contaminate food

and drink, as well as air.

Cognitive decits

Autism spectrum disorder

Behavioral and social communication problems

Motor coordination disorder

Attention-decit/hyperactivity disorder

Depression and/or anxiety

Potential outcomes of EDC exposure

!

Effects of

EDC exposure

Hormonal

dysregulation

Inflammation

Oxidative

stress

Metabolic

alterations

Epigenetic

modications

Microbiome

alterations

science.org SCIENCE

Early life exposure to endocrine-disrupting chemicals

Endocrine-disrupting chemicals (EDCs) are widespread and can migrate into the air, water, and food.

Maternal exposure to EDCs can transfer them to the fetus through the placenta and to infants through

breastfeeding, potentially leading to a range of neurodevelopmental disorders in offspring.

720 18 FEBRUARY 2022 • VOL 375 ISSUE 6582