Behavior of trace metals during composting of mixed sewage sludge and tropical green waste: a combined EDTA kinetic and BCR sequential extraction study in New Caledonia.

The aim of the study was to assess the impact of composting on the release dynamics and partitioning of geogenic nickel (Ni), chromium (Cr) and anthropogenic copper (Cu) and zinc (Zn) in a mixture of sewage sludge and green waste in New Caledonia. In contrast to Cu and Zn, total concentrations of Ni and Cr were very high, tenfold the French regulation, due to their sourcing from Ni and Cr enriched ultramafic soils. The novel method used to assess the behavior of trace metals during composting involved combining EDTA kinetic extraction and BCR sequential extraction. BCR extraction revealed marked mobility of Cu and Zn: more than 30% of the total concentration of these trace metals was found in the mobile fractions (F1 + F2) whereas Ni and Cr were mainly found in the residual fraction (F4). Composting increased the proportion of the stable fractions (F3 + F4) of all four trace metals studied. Interestingly, only EDTA kinetic extraction was able to identify the increase in Cr mobility during composting, Cr mobility being driven by the more labile pool (Q1). However, the total mobilizable pool (Q1 + Q2) of Cr remained very low, < 1% of total Cr content. Among the four trace metals studied, only Ni showed significant mobility, the (Q1 + Q2) pool represented almost half the value given in the regulatory guidelines. This suggests possible environmental and ecological risks associated with spreading our type of compost that require further investigation. Beyond New Caledonia, our results also raise the question of the risks in other Ni-rich soils worldwide.

International Analysis of Sources and Human Health Risk Associated with Trace Metal Contaminants in Residential Indoor Dust.

People spend increasing amounts of time at home, yet the indoor home environment remains understudied in terms of potential exposure to toxic trace metals. We evaluated trace metal (and metalloid) concentrations (As, Cu, Cr, Mn, Ni, Pb, and Zn) and health risks in indoor dust from homes from 35 countries, along with a suite of potentially contributory residential characteristics. The objective was to determine trace metal source inputs and home environment conditions associated with increasing exposure risk across a range of international communities. For all countries, enrichments compared to global crustal values were Zn > Pb > Cu > As > Cr > Ni; with the greatest health risk from Cr, followed by As > Pb > Mn > Cu > Ni > Zn. Three main indoor dust sources were identified, with a Pb-Zn-As factor related to legacy Pb sources, a Zn-Cu factor reflecting building materials, and a Mn factor indicative of natural soil sources. Increasing home age was associated with greater Pb and As concentrations (5.0 and 0.48 mg/kg per year of home age, respectively), as were peeling paint and garden access. Therefore, these factors form important considerations for the development of evidence-based management strategies to reduce potential risks posed by indoor house dust. Recent findings indicate neurocognitive effects from low concentrations of metal exposures; hence, an understanding of the home exposome is vital.

Mobility of Ni, Co, and Mn in ultramafic mining soils of New Caledonia, assessed by kinetic EDTA extractions.

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 < 100 µm soil fraction, because of its sensitivity to wind erosion, and its possible dissemination toward urbanized areas. In order to assess maximum potential metal mobility, EDTA kinetic extractions were performed over 24 h. Extraction curves were modeled as the sum of two first-order reactions. The first EDTA extracted pool corresponds to "quickly" released metals, while the second pool corresponds to "slowly" released metals. The remaining fraction is the EDTA non-extractable pool. Extractable Ni, Co, and Mn were always low in relation to total concentrations (< 5% for Ni, and 5-35% for Co and Mn). The extraction rate of the less labile pool was significantly higher for forest soils than for mining soils, whatever the metal. Despite the greater extractability potential in forest surface soils, mining soils represent a bigger environmental risk, because of their high metal content and, above all, because of their predisposition to surface runoff and eolian deflation.

Predictive modeling of indoor dust lead concentrations: Sources, risks, and benefits of intervention.

Lead (Pb) contamination continues to contribute to world-wide morbidity in all countries, particularly low- and middle-income countries. Despite its continued widespread adverse effects on global populations, particularly children, accurate prediction of elevated household dust Pb and the potential implications of simple, low-cost household interventions at national and global scales have been lacking. A global dataset (∼40 countries, n = 1951) of community sourced household dust samples were used to predict whether indoor dust was elevated in Pb, expanding on recent work in the United States (U.S.). Binned housing age category alone was a significant (p < 0.01) predictor of elevated dust Pb, but only generated effective predictive accuracy for England and Australia (sensitivity of ∼80%), similar to previous results in the U.S. This likely reflects comparable Pb pollution legacies between these three countries, particularly with residential Pb paint. The heterogeneity associated with Pb pollution at a global scale complicates the predictive accuracy of our model, which is lower for countries outside England, the U.S., and Australia. This is likely due to differing environmental Pb regulations, sources, and the paucity of dust samples available outside of these three countries. In England, the U.S., and Australia, simple, low-cost household intervention strategies such as vacuuming and wet mopping could conservatively save 70 billion USD within a four-year period based on our model. Globally, up to 1.68 trillion USD could be saved with improved predictive modeling and primary intervention to reduce harmful exposure to Pb dust sources.

Is halophyte species growing in the vicinity of the shrimp ponds a promising agri-aquaculture system for shrimp ponds remediation in New Caledonia?

Plant culture integration within aquaculture activities is a topic of recent interest with economic and environmental benefits. Shrimp farming activities generate nutrient-rich waste trapped in the sediments of farming ponds or release in the mangrove area. Thus, we investigate if the halophytes species naturally growing around the pond can use nitrogen and carbon from shrimp farming for remediation purposes. Halophyte biomasses and sediments influenced by shrimp farm effluents, were collected in two farms in New-Caledonia. All samples were analyzed for their C and N stable isotopic composition and N content. Higher δ15N values were found in plants influenced by shrimp farm water thus evidenced their abilities to take nutrient derived from shrimp farming. Deep root species Chenopodium murale, Atriplex jubata, Suaeda australis and Enchylaena tomentosa appears more efficient for shrimp pond remediation. This work demonstrates that halophytes cultivation in shrimp ponds with sediments, could be effective for the pond's remediation.

Impact of nickel mining in New Caledonia on marbled eels Anguilla marmorata.

New Caledonia is particularly affected by nickel open pit mining activities because of the presence of ultramafic soils rich in metals. The particles dispersed by atmospheric transport and soil erosion during the excavation of nickel end up by deposition or leaching in rivers where they may be bioaccumulated by organisms living downstream the mines. Despite alarming freshwater metals concentrations, no study investigated the level of their bioaccumulation in eels, and if high bioaccumulation levels occur, the potential consequences on their health. The aim of this study was to determine how eels Anguilla marmorata are impacted in situ by metals issued from mining activity by measuring: morphometric parameters; metal concentrations in tissues and organs and transcription levels of target genes encoding proteins involved in several metabolic key functions. Among organs, liver was found to be the most affected by mining with average nickel concentrations of 5.14 mg/kg versus 1.63 mg/kg for eels away from mines leading to dysregulation of numerous genes involved in oxidative stress, DNA repair, apoptosis, reproduction and both lipid and mitochondrial metabolisms. This study should allow us to define in an integrated way if metals released by mining activities influence metals bioaccumulation in eels and induce biological effects.

Nickel spreading assessment in New Caledonia by lichen biomonitoring coupled to air mass history.

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.

Laboratory and in-situ investigations for trapping Pb and Ni with an unusual electrochemical device, the calcareous deposit in seawater.

In seawater, the application of a cathodic current in a metallic structure induces the formation of a calcareous deposit formed by co-precipitation of CaCO3 and Mg(OH)2 on the metal surface. A previous study proved that this electrochemical technique is convincing as a remediation tool for dissolved nickel in seawater and that it is trapped as nickel hydroxide in the deposit. Here, the precipitation of a carbonate form with lead is studied. Pb2+ precipitation in calcareous deposit was investigated with a galvanized steel electrode by doping artificial seawater with PbCl2. Results show for the first time the presence of Pb incorporated in its carbonate form in the calcareous deposit. Trapped Pb content increased with initial Pb content in seawater. Simultaneous doping with Ni and Pb revealed that Ni trapping was favoured by higher current densities while Pb trapping was favoured by lower current densities. Finally, preliminary in situ experiments were performed in an industrial bay and validated the incorporation in real conditions of contaminants by precipitation with the calcareous deposit The present work demonstrates that co-precipitation of contaminants under their hydroxide or carbonate form in a calcareous deposit is a promising clean-up device for remediation of contaminated seawater.

Speciation of Cu(II) with a flow-through permeation liquid membrane: discrimination between free copper, labile and inert Cu(II) complexes, under natural water conditions.

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.

Impact of nickel mining in New Caledonia assessed by compositional data analysis of lichens.

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.

Alternative dry separation of PM10 from soils for characterization by kinetic extraction: example of new Caledonian mining soils.

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.

Influence of inorganic complexes on the transport of trace metals through permeation liquid membrane.

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.