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International audience; Arsenate As(V) and arsenite As(III) are toxic forms of arsenic in waters. The risk of As toxicity is high in small tropical islands because tap water is often provided from surface water, and As contamination of surface water is rarely studied. For instance, the risk is high in New Caledonia because 61% of the water comes from surface water, and nickel mines induce the dispersal of large quantities of ultramafic rocks's alterites rich in iron oxide-hydroxide, which are known to be associated with arsenite and arsenate. Levels exceeding the World Health Organization standard of 10 µg L −1 have been detected in rivers downstream of Ni mines, yet there is a lack of systematic assessment. Here, we analyzed total and exchangeable As in alterites collected near three active mines. Arsenate and arsenite adsorption capacity was studied using batch experiments. The results show that alterite contains total As contents ranging from 0.20 to 5.14 mg kg −1 , yet the primary mineralogical source of As remains unknown. No exchangeable arsenite was detected. Exchangeable arsenate amounted to 0.16 mg kg −1 , thus meaning that 10.3% of the total As is easily mobile. The maximum adsorption capacity of arsenate and arsenite in mining sediments was 1.05 mg kg −1. Overall, our findings reveal that ultramafic rock alterites are a source of arsenic in surface water in the form of suspended particulate matter, 10.3% of which being easily soluble.

Pollution and climate change issues are calling for advanced techniques of pollutant sequestration to decrease toxicity, of coral and costal remediation, and of carbon sequestration to decrease atmospheric CO2 levels. For that, calcareous deposition appears as an overlooked, but potentially efficient technique. The calcareous deposit is a well-known precipitation by-product of cathodic protection in seawater. The deposit is made of a mixture of CaCO3 and Mg(OH)2. A calcareous deposit is formed electrochemically when a metal connected to an electrical power source is immersed in seawater. So far, electrochemical calcareous deposition has seldomly found applications, except for speedup of coral growth, prevention of shore erosion, reinforcement of artificial marine structures and remediation of polluted seawater. Here, we review the principles and mechanisms of electrochemical calcareous deposition. The growth, composition and mechanical properties of calcareous deposits are controlled by several factors such as 1) the impact of electrochemical parameters on the Ca/Mg ratio. For instance, CaCO3 formation is favoured at low cathodic potentials and low currents, whereas Mg(OH)2 precipitates preferentially at high cathodic potentials and high applied current; 2) the nature of the metallic electrode: although lime could be deposited onto any metallic surface at a fixed potential, electrochemical reactions and deposit composition are controlled by the metal nature. Moreover, the state of the electrode surface, e.g. with the presence of oxides or biofilms, modifies the kinetics of deposit formation; and 3) electrolyte composition, pH, temperature and stirring. For instance, in seawater, Ca2+ and Mg2+ concentrations control the allotropic variety of CaCO3 formed, e.g. Mg2+ inhibits the formation of calcite and vaterite. Hydrodynamic conditions near the electrode also influence the deposit composition since conditions regulate the mass transport at the electrode–solution interface. Below 10 °C, aragonite is not formed and the deposit stays thin. In the first stage of the deposit formation, an Mg-based compound is formed, followed by the growth of a Ca-based compound with time.

Covered by ultrabasic units for more than a third of its surface, the New Caledonia (South West Pacific) is one of the largest world producers of Ni-ore from lateritic deposits. Almost all outcrops of geological units and open mines contain serpentine and amphibole, also as asbestos varieties. In this geological context, in which weathering processes had a great contribution in the production and dispersion of mineral fibres into the environment, the development of a routinely analytical strategy, able to discriminate an asbestiform fibre from a non-harmful particle, is a pivotal requisite. However, the acquisition of all these parameters is necessary for determining the risk associated to fibres exposition. A multidisciplinary routinely approach, based on the use of complementary simply-to-use but reliable analytical methods is the only possible strategy. In addition, the instrumental apparatus must be easily transportable on the field, directly on the mining site. The employment of specialized tools such as Polarized Light Microscopy associated to Dispersion Staining method (PLM/DS) and portable Raman spectroscopy for identification of environmental asbestos, are proved extremely effective in the improvement of the performance and rapidity of data acquisition and interpretation. Both PLM/DS and handheld Raman devices confirmed to be discriminant in the detection and characterization of asbestos fibres for both serpentine and amphibole. Furthermore, these techniques proved extremely effective even in the presence of strongly fibrous and altered samples. Keywords: Asbestos, Fibrous antigorite, In situ monitoring, Dispersion staining, Portable Raman, New Caledonia

International audience; The ultramafic massifs of New Caledonia are mainly composed of regolites with lateritic soils rich in metals such as Co, Fe, Mg and Ni. The nickeliferous ore is exploited by opencast mines. After rainfalls, erosion and particle runoff cause the mobilization of metals and metalloids in surface waters. The objective of this study is (i) to determine the geochemical background of metals and metalloids in surface waters draining a mining ultramafic massif, (ii) to identify the geochemical markers influenced by the mining of nickeliferous ore (iii) and to define discriminant values of the mining impact. Hydrochemical monitoring was carried out on five streams draining the Koniambo massif over a 15-years period. Twenty-four elements were analyzed for their total concentration and 18 for their dissolved concentration (

Lichen biomonitoring and air mass trajectories were used to study the influence of mining activities in the atmospheric dispersion of metallic elements to assess the exposure of the population to dust emitted by mining activities. A map of forward trajectory densities from open mine surfaces throughout New Caledonia was computed and allowed to identify three preferred wind directions (trade wind, bent trade winds and oceanic winds) that could arise in mining particles dispersion all over New Caledonia. Areas where an air quality monitoring would be advisable to evaluate the exposure of the population to the Nickel dusts have been identified. Lichens collected around the industrial mining site KNS and in North Provence of New Caledonia were analysed for their Ni, Co, Cr, Zn and Ti contents. Backward trajectories were simulated from the lichen sampling point using FLEXTRA fed with ECMWF meteorological data, and densities of trajectories having overflown a mine were calculated. Ratio metal/Ti was then plotted as a function of air mass trajectory densities having overflown open pits. A positive correlation between trajectory densities and titanium-normalized metal in lichen for Ni, Co, Cr was highlighted, indicating that mining is a source of dispersion of these metals. For Zn, which is a tracer of fossil fuel or biomass (wood) combustion activity, no correlation was found. Graphical abstract.

Cultivation of salt-tolerant crops help to face to irreversible global salinization of freshwater and soils. In New-Caledonia, three halophytes are candidates for saline crops, Salsola australis R.Br., Suaeda maritima (L.) Dumort and Enchylaena tomentosa R.Br. Their success and quality depend yet on availabilities of salinity and essential nutrients in agrosystems. So, we investigated effects of three salinities, i.e., control moderate and high, and five nitrogen ratios, i.e., 100:0, 75:25, 50:50, 25:75 or 0:100 NO3−-N:NH4+-N ratio on their growth and functional value for fatty acids and antioxidants. Results show that the leaf fatty acid and antioxidant profiles of species, emphasize their good potential to become functional crop products, based on comparison with other functional plants, dietetic recommendation, or functional indices. However, their total phenolic compounds (TPC) content can be influenced by N-ratio (Suaeda maritima and Enchylaena tomentosa) and their antioxidant activity index (AAI) can be influenced by salinity (Suaeda maritima), N-ratio (Salsola australis) or both (Enchylaenatomentosa). Their quantitative and/or qualitative fatty acid profiles can also be influenced by salinity (Enchylaena tomentosa), N-ratio (Suaeda maritima), or both (Salsola australis). Regarding these variations, involving salt tolerance and nitrogen nutrition mechanisms, we recommend suitable treatments to maintain or optimize the growth and the functional quality of leaves in the three species.

International audience

The aim of this study was to determine the mobilization capability of Ni, Co, and Mn contained in New Caledonian ultramafic soils. Two series of soils were sampled: bare-surface mining soils in a Ni-mining context (n = 10), and forest soils, either in the vicinity of mine-working areas (n = 3) or far away from any known mining activity (n = 2). We focused on the

There are few efficient, rapid and cheap methods to remove toxic metals from contaminated waters. Here we hypothesised that cathodic protection, an existing method used to control the corrosion of metallic structures, may trap toxic metals. Indeed, in seawater, the application of a cathodic current on a metallic structure induces the precipitation of limestone (CaCO3) and magnesium dihydroxyde (Mg(OH)2), thus forming a calcareous deposit on the metal surface. We therefore presumed that such calcareous deposit may trap metals dissolved in waters. Actually calcareous deposit formation has never been studied in the presence of dissolved metallic contaminants such as nickel. Here we tested ionic nickel (Ni2+) precipitation in calcareous deposit with a galvanized steel electrode by spiking artificial seawater with a NiCl2 salt during 7 days of applied current. We analysed deposit surface and cross section by µ-Raman spectroscopy and scanning electron microscopy (SEM) with X-ray microanalysis. Ni concentration in the deposit was quantified by inductively coupled plasma analysis, after deposit dissolution in 60% HNO3. Results show that in 7 days up to 24% of nickel can be trapped in the calcareous deposit. Scanning electron microscopy reveals that Ni is trapped under a pure CaCO3 layer of aragonite. Raman spectra show that nickel is incorporated as nickel dihydroxyde (Ni(OH)2), as evidence by vibration bands at 446 and 510 cm−1. Overall our findings disclose a new and efficient method, calcareous electrochemical precipitation, which has potential applications to remove toxic metals from contaminated waters.

14 pages; International audience; The aim of this study is to explore the use of lichens as biomonitors of the impact of nickel mining and ore treatment on the atmosphere in the New Caledonian archipelago (South Pacific Ocean); both activities emitting also Co, Cr and possibly Fe. Metal contents were analysed in thirty-four epiphytic lichens, collected in the vicinity of the potential sources, and in places free from known historical mining. The highest Ni, Co, and Cr concentrations were, as expected, observed in lichens collected near ore deposits or treatment areas. The elemental composition in the lichens was explored by multivariate analysis, after appropriately transforming the variables (i.e. using compositional data analysis). The sample score of the first principal component (PC1) makes the largest (positive) multiplicative contribution to the log-ratios of metals originating from mining activities (Ni, Cr, Co) divided by Ti. The PC1 scores are used here as a surrogate of pollution levels related to mining and metallurgical activity. They can be viewed as synthetic indicators mapped to provide valuable information for the management and protection of ecosystems or, as a first step, to select locations where air filtration units could be installed, in the future, for air quality monitoring. However, as this approach drastically simplifies the problem, supplying a broadly efficient picture but little detail, recognizing the different sources of contamination may be difficult, more particularly when their chemical differences are subtle. It conveys only relative information: about ratios, not levels, and is therefore recommended as a preliminary step, in combination with close examination of raw concentration levels of lichens. Further validation using conventional air-monitoring by filter units should also prove beneficial.

International audience; A simple new device for dry separation of fine particulate matter from bulk soil samples is presented here. It consists of a stainless steel tube along which a nitrogen flow is imposed, resulting in the displacement of particles. Taking into account particle transport, fluid mechanics, and soil sample composition, a tube 6-m long, with a 0.04-m diameter, was found best adapted for PM10 separation. The device rapidly produced several milligrams of particulate matter, on which chemical extractions with EDTA were subsequently performed to study the kinetic parameters of extractable metals. New Caledonian mining soils were chosen here, as a case-study. Although the easily extracted metal pool represents only 0.5-6.4 % of the total metal content for the elements studied (Ni, Co, Mn), the total concentrations are extremely high. This pool is therefore far from negligible, and can be troublesome in the environment. This dry technique for fine particle separation from bulk parent soil eliminates the metal-leaching risks inherent in wet filtration and should therefore ensure safe assessment of environmental quality in fine-textured, metal-contaminated soils.

International audience; In small Polynesian islands, family pig breeding is usually conducted without recovery of pig slurry. Raw pig slur-ry is spread onto the soil without any treatment. So far, most of the studies were carried out in temperate climate and for industrial digested pig slurry applications on agricultural lands. In the present case study, conducted in Uvéa Island, the aim is to determine if long term application of raw pig slurry on tropical soils, naturally rich in heavy metals has a significant influence on elements concentrations and mobility. Two types of tropical soils and two pig breeding systems, pig enclosure on small concrete pens or pig enclosure in large land pens, were investigated. Here we demonstrate that raw pig slurry inputs on soils can lead to an increase of total nitrogen and phosphorus content with high Contamination Factors. The Pollution Load Index values (1.3; 5.3; 2.5; 2.3) were indicative of multi-heavy metals pollution (Fe, Mn, Al, Cu, Zn, Cr and Ni) in mixed calcareous soils of the coastal area and they are exchangeable while they are immobilized or less mobile in inland pure ferralitic soils. For mixed calcareous soils of the coastal area, family pig breeding represents a drainage risk of soluble species (phosphorus, inorganic nitrogen, Fe, Mn, Al, Cu, Zn, Cr and Ni). For inland ferralitic soils, family pig breeding is more compatible with a sustainable management of the environment in Uvéa Island and by extension in volcanic tropical islands with respect to the investigated chemical elements.

International audience; Mining sediments are excavated from nickel ore exploitation in New Caledonia. In those sediments, chromium (Cr) occurs as Cr(III), but Cr(III) can be oxidized to the toxic Cr(VI) under oxic conditions, for instance in overlying water. Here, we aimed to determine whether mining sediments could release available Cr(VI) in surface waters. Water samples were collected in a mine and in the village downstream, and then were analysed for Cr. Batch leaching experiments were performed on mining sediments in order to determine their exchangeable and their water-soluble Cr content as a function of pH. Results show that mine waters contain high concentrations of total dissolved Cr, of up to 0.73 mg/L. Moreover, Cr(VI) concentration in village waters increases with the rainfall rate upto 0.34 mg/L. Cr is released from sediments solely as Cr(VI). Desorption of chromate complexes is the main process involved in Cr release. We conclude that drainage of sediments mobilized by opencast Ni mines is a source of toxic Cr(VI) for surface waters.

Under specific conditions (pH, concentrations), trace metals may form, with environmental inorganic ligands, neutral complexes which, in principle, might diffuse passively through biological membranes or influence the response of (bio)analytical sensors for trace metals based on permeation liquid membrane (PLM). In this study, metal (Cu, Cd, Pb) transport through the planar PLM device was evaluated in the presence of major environmental inorganic ligands such as sulfate, carbonate and chloride under conditions where neutral complexes may be formed (up to 73% of neutral metal complex in the solution). In the presence of sulfate, comparison of predicted and experimental PLM fluxes of Cu, Pb and Cd, suggests that passive transport of neutral sulfate-metal complexes does not occur. This was confirmed by comparing fluxes in the presence and absence of carrier. In the presence of carbonate (for Cd, Cu and Pb) and chloride (for Pb and Cd), however, experimental PLM fluxes were greater than predicted (up to 4 and 25 times in the presence of carbonate and chloride, respectively), but experiments in the absence of carrier in the membrane revealed that no passive transport of neutral complexes (MCl(2) or MCO(3)) occurs through PLM. A possible mechanism is discussed. In parallel to the experiments with PLM, the influence of carbonate on the internalization fluxes of Cu(II) and Pb(II) by the freshwater algae, Chlamydomonas reinhardtii, was assessed. Similarly to the results of PLM, the fluxes of these two metals were larger than expected (based on the free metal ion activity model). Thus, even though PLM and bioaccumulation mechanisms are certainly different, similar unexpected behaviours occur for the metal transport through the PLM and biological membrane of C. reinhardtii, in the presence of carbonate.

Metal toxicity is not related to the total metal ion concentration, but to those of some specific Cu(II) species. The Permeation Liquid Membrane technique is based on the carrier-mediated transport of the test metal across a hydrophobic membrane and enables discrimination between various trace metal species in solution. The present work shows how the labile and inert Cu(II) complexes can be determined selectively, by varying the flow-rate of the test solution, in a flow-through cell. A mathematical model of metal flux through the PLM, based on diffusion-limited transport under steady-state conditions, is described. The model and the performance of the technique were studied in well-defined synthetic solutions containing simple organic hydrophilic ligands forming either inert (nitrilotriacetic acid), or labile complexes with Cu(II) (tartaric acid, malonic acid). The results were compared with theoretical predictions of thermodynamic species distribution in solution. Uncertainties on stability constants for copper speciation calculation were taken into account. The detection limits of the device are discussed. This work demonstrates that the flow-through cell is a reliable tool for copper speciation measurements in natural waters.