Plants as biomonitors for volcanic emissions

Biomonitoring techniques have been widely used in environmental studies to monitor anthropogenic pollutant. Recently such techniques have been applied also to ascertain the impact of contaminants naturally released by volcanic activity. In the present study a biomonitoring surveys has been performed in many different active volcanic systems: Mt. Etna and Vulcano (Italy), Nisyros (Greece), Nyiragongo (DRC), Masaya (Nicaragua), Gorely (Kamchatka, Russia). We sampled leaves of different species Betulla aethnensis, Pinus nigra, Populus tremula, Senecio aethnensis and Rumex aethnensis on Etna, Cistus creticus and salvifolius on Vulcano and Nisyros, Senecio ssp. on Nyiragongo, a Fern on Masaya and Salix arctica at Gorely. All samples were analyzed by ICP-MS and ICP-OES for 49 elements after acid digestion with a microwave oven (HNO3 + H2O2). Major constituents in leaves are K, Ca, Mg, Na, Si, Al and Fe ranging from about 10 3 to 105 ppm. Manganesium, Sr, Rb, Ba, Zn, B, Cu show also relatively high concentrations (100-103 ppm) while the remaining elements (As, Bi, Cd, Ce, Co, Cr, Cs, Ga, Li, Mo, Ni, Pb, Sb, Sc, Se, Th, Tl, U, V, Y and lanthanide series) display much lower values (10-4-101 ppm). Nearly all investigated elements show their highest concentrations in the samples collected closest to the main degassing vents (open craters, fumarolic fields). Increased concentrations are also found in the samples collected in the downwind direction where volcanic emissions are prevailingly dispersed. Leaves collected along radial transects from the active vents, highlight that the levels of metals decrease from one to two orders of magnitude with increasing distance from the source. The decrease is stronger for volatile elements, which are highly enriched in volcanic emissions, (As, Bi, Cd, Cs, Pb, Sb, Tl) than for more refractory elements (Al, Ba, Sc, Si, Sr, Th, U). The different species of plants show significant differences in the bioaccumulation processes for most of the analyzed elements, in particular lanthanides, which are systematically enriched in Rumex leaves. Needles of pine (non-deciduous tree) represent a good tool for biomonitoring investigation because they are important tracers of accumulation with time. The high concentrations of many toxic elements in the leaves allow us to consider some of these plants as highly tolerant species to the volcanic emissions, and suitable for biomonitoring researches further confirming their strong potential in tracing the impact and geographic distribution of these natural contaminants

A gravitational-wave standard siren measurement of the Hubble constant

On 17 August 2017, the Advanced LIGO(1) and Virgo(2) detectors observed the gravitational-wave event GW170817-a strong signal from the merger of a binary neutron-star system(3). Less than two seconds after the merger, a gamma-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO-Virgo-derived location of the gravitational-wave source(4-6). This sky region was subsequently observed by optical astronomy facilities(7), resulting in the identification(8-13) of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first ''multi-messenger'' astronomical observation. Such observations enable GW170817 to be used as a ''standard siren''(14-18) (meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic ''distance ladder''(19): the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements(20,21), while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision