Climate change is expected to increase the frequency and magnitude of river floods1. Floods not only cause damage by inundation and loss of life2,3 but also jeopardize infrastructure because of bank failure and riverbed erosion processes that are poorly understood. Common flood safety programmes include dyke reinforcement and river widening4-9. The 2021 flood in the Meuse Basin caused 43 fatalities and billions of dollars of damage to infrastructure10. Here, on the basis of analysis of the Meuse flood, we show how uneven widening of the river and heterogeneity of sediment deposits under the river can cause massive erosion. A recent flood safety programme widened the river11, but created bottlenecks where widening was either prevented by infrastructure or not yet implemented. Riverbed erosion was exacerbated by tectonic uplift that had produced a thin top gravel layer above fine-grained sediment. Greatly enhanced flow velocities produced underwater dunes with troughs that broke through the gravel armour in the bottlenecks, exposing easily erodible sands, resulting in extreme scour holes, one more than 15 m deep. Our investigation highlights the challenges of re-engineering rivers in the face of climate change, increased flood risks and competition for river widening space, and calls for a better understanding of the subsurface.

Fine particulate matter (particulate matter with a diameter of 2.5 μm or less; PM2.5) causes millions of premature deaths globally1, but not all particles are equally harmful2-4. Current air-pollution control strategies, prioritizing PM2.5 mass reduction, have provided considerable health benefits but further refinements based on differences in the toxicity of various emission sources may provide greater benefits5-7. Here we integrated field measurements with air-quality modelling to assess the unequal toxicities of PM2.5 from various anthropogenic sources. Our findings revealed that the toxicity per unit of PM2.5 mass differed substantially between major sources, differing by up to two orders of magnitude. PM2.5 from solid fuel combustion in residential stoves had the highest toxicity, followed by those from the metallurgy industry, brake wear, diesel vehicles, petrol vehicles, the cement industry and power plants. We further analysed the source contributions of toxicity-adjusted PM2.5 emissions and population exposures in China. From 2005 to 2021, both the PM2.5 mass and relative-potency-adjusted emissions substantially decreased. Although industrial sources contributed 57.5% to the reduction in PM2.5 mass emissions, the reduction in relative potency-adjusted emissions was driven by residential combustion (approximately 80%). Clean-air policies should consider the differing toxicities of PM2.5 when formulating source-specific emission control regulations. This study proposes a cellular toxicity-based framework for PM2.5 reduction that could address the specific health risks in diverse regions, but further epidemiological studies will be required to confirm their relevance to human health outcomes and their application to public policy.

When two monolayer materials are stacked with a relative twist, an effective moiré translation symmetry emerges, leading to fundamentally different properties in the resulting heterostructure. As such, moiré materials have recently provided highly tunable platforms for exploring strongly correlated systems1,2. However, previous studies have focused almost exclusively on monolayers with triangular lattices and low-energy states near the Γ (refs. 3,4) or K (refs. 5-9) points of the Brillouin zone (BZ). Here we introduce a new class of moiré systems based on monolayers with triangular lattices but low-energy states at the M points of the BZ. These M-point moiré materials feature three time-reversal-preserving valleys related by threefold rotational symmetry. We propose twisted bilayers of exfoliable 1T-SnSe2 and 1T-ZrS2 as realizations of this new class. Using extensive ab initio simulations, we identify twist angles that yield flat conduction bands, provide accurate continuum models, analyse their topology and charge density and explore the platform's rich physics. Notably, the M-point moiré Hamiltonians exhibit emergent momentum-space non-symmorphic symmetries and a kagome plane-wave lattice structure. This represents, to our knowledge, the first experimentally viable realization of projective representations of crystalline space groups in a non-magnetic system. With interactions, these systems act as six-flavour Hubbard simulators with Mott physics. Moreover, the presence of a momentum-space non-symmorphic in-plane mirror symmetry renders some of the M-point moiré Hamiltonians quasi-one-dimensional in each valley, suggesting the possibility of realizing Luttinger-liquid physics.

Plastic pollution is a pervasive and growing global problem1-4. Chemicals in plastics are often not sufficiently considered in the overall strategy to prevent and mitigate the impacts of plastics on human health, the environment and circular economy5-7. Here we present an inventory of 16,325 known plastic chemicals with a focus on their properties, presence in plastic and hazards. We find that diverse chemical structures serve a small set of functions, including 5,776 additives, 3,498 processing aids, 1,975 starting substances and 1,788 non-intentionally added substances. Using a hazard-based approach, we identify more than 4,200 chemicals of concern, which are persistent, bioaccumulative, mobile or toxic. We also determine 15 priority groups of chemicals, for which more than 40% of their members are of concern. Finally, we examine data gaps regarding the basic properties, hazards, uses and exposure potential of plastic chemicals. Our work maps the chemical landscape of plastics and contributes to setting the baseline for a transition towards safer and more sustainable materials and products. We propose that removing known chemicals of concern, disclosing the chemical composition and simplifying the formulation of plastics can provide pathways towards this goal.

Lunar mare basalts illuminate the nature of the Moon's mantle, the lunar compositional asymmetry and the early lunar magma ocean (LMO)1-3. However, the characteristics of the mantle beneath the vast South Pole-Aitken (SPA) basin on the lunar farside remain a mystery. Here we present the petrology and geochemistry of basalt fragments from Chang'e-6 (CE6), the first returned lunar farside samples from the SPA basin4-7. These 2.8-billion-year-old CE6 basalts8 share similar major element compositions with the most evolved Apollo 12 ilmenite basalts. They exhibit extreme Sr-Nd depletion, with initial 87Sr/86Sr ratios of 0.699237 to 0.699329 and εNd(t) values (a measure of the neodymium isotopic composition) of 15.80 to 16.13. These characteristics indicate an ultra-depleted mantle, resulting from LMO crystallization and/or later depletion by melt extraction. The former scenario implies that the nearside and farside may possess an isotopically analogous depleted mantle endmember. The latter is probably related to the SPA impact, indicating that post-accretion massive impacts could have potentially triggered large-scale melt extraction of the underlying mantle. Either way, originating during the LMO or later melt extraction, the ultra-depleted mantle beneath the SPA basin offers a deep observational window into early lunar crust-mantle differentiation.

Plastic pollution of the marine realm is widespread, with most scientific attention given to macroplastics and microplastics1,2. By contrast, ocean nanoplastics (<1 μm) remain largely unquantified, leaving gaps in our understanding of the mass budget of this plastic size class3-5. Here we measure nanoplastic concentrations on an ocean-basin scale along a transect crossing the North Atlantic from the subtropical gyre to the northern European shelf. We find approximately 1.5-32.0 mg m-3 of polyethylene terephthalate (PET), polystyrene (PS) and polyvinyl chloride (PVC) nanoplastics throughout the entire water column. On average, we observe a 1.4-fold higher concentration of nanoplastics in the mixed layer when compared with intermediate water depth, with highest mixed-layer nanoplastic concentrations near the European continent. Nanoplastic concentrations at intermediate water depth are 1.8-fold higher in the subtropical gyre compared with the open North Atlantic outside the gyre. The lowest nanoplastic concentrations, with about 5.5 mg m-3 on average and predominantly composed of PET, are present in bottom waters. For the mixed layer of the temperate to subtropical North Atlantic, we estimate that the mass of nanoplastic may amount to 27 million tonnes (Mt). This is in the same range or exceeding previous budget estimates of macroplastics/microplastics for the entire Atlantic6,7 or the global ocean1,8. Our findings suggest that nanoplastics comprise the dominant fraction of marine plastic pollution.

In the past decade, ancient protein sequences have emerged as a valuable source of data for deep-time phylogenetic inference1-4. Still, even though ancient proteins have been reported from the Middle-Late Miocene5,6, the recovery of protein sequences providing subordinal-level phylogenetic insights does not exceed 3.7 million years ago (Pliocene)1. Here, we push this boundary back to 21-24 million years ago (Early Miocene) by retrieving enamel protein sequences of a rhinocerotid (Epiaceratherium sp.; CMNFV59632) from Canada's High Arctic. We recover partial sequences of seven enamel proteins and more than 1,000 peptide-spectrum matches, spanning at least 251 amino acids. Endogeneity is in line with thermal age estimates and is supported by indicators of protein damage, including several spontaneous and irreversible chemical modifications accumulated during prolonged diagenesis. Bayesian tip-dating places the divergence time of CMNFV59632 in the Middle Eocene-Oligocene, coinciding with a phase of high rhinocerotid diversification7. This analysis identifies a later Oligocene divergence for Elasmotheriinae, weakening alternative models suggesting a deep basal split between Elasmotheriinae and Rhinocerotinae8,9. The findings are consistent with hypotheses on the origin of the enigmatic fauna of the Haughton Crater, which, in spite of considerable endemism, has similarity to distant Eurasian faunas10,11. Our findings demonstrate the potential of palaeoproteomics in obtaining phylogenetic information from a specimen that is approximately ten times older than any sample from which endogenous DNA has been obtained so far.

Spontaneous two-photon emission (STPE) is a second-order quantum radiation process with implications in astrophysics1, atomic physics2 and quantum technology3. In particular, on-demand STPE from single quantum emitters has long been predicted to revolutionize photonic quantum science and technology4,5. Here we report STPE with brightness comparable to that of competing single-photon radiation from a single semiconductor quantum dot deterministically coupled to a high-quality micropillar cavity. This is because of strong vacuum fluctuations in the microcavity, which drive a biexciton directly to the ground state. We show the quantum nature associated with STPE in the cavity quantum electrodynamics regime using photon statistics measurements. Furthermore, STPE is exploited to build unconventional entangled quantum light sources that can simultaneously achieve near-unity entanglement fidelity for spontaneous parametric down-conversion sources and on-demand photon emission for atomic quantum emitters. Our work provides insights into the two-photon process in the quantum regime, which could empower photonic quantum technology with nonlinear quantum radiation.