The legacy of metallurgical atmospheric contamination in a mountainous catchment: A delayed response of Pb contamination.

Metal-rich fumes emitted during ore smelting contribute to widespread anthropogenic contamination. Environmental archives (such as lake sediments) record fallouts deposited on lake and terrestrial surfaces during ancient mining and smelting activities. However, very few is known about the potential buffering effect of soils upon which metal falls out, prior to be released through runoff and or/erosion, hence leading to pervasive contamination fluxes long after the ceasing of metallurgical activities. Here we aim at assessing this long-term remobilisation in a mountainous catchment area. Lake sediments and soils were collected 7 km upward a 200-year-old historic mine. The PbAg mine of Peisey-Nancroix was operated between the 17th and the 19th centuries with a documented smelting period of 80 years. In lake sediments, the total Pb content varies from 29 mg.kg-1 prior smelting to 148 mg.kg-1 during ore smelting. Pb isotopes in lake sediments and soils provide evidence of anthropogenic Pb from the local ore (206Pb/207Pb = 1.173; 208Pb/206Pb = 2.094) during and after smelting, suggesting anthropogenic Pb remobilisation for 200 years. The accumulation rates of anthropogenic Pb calculated in lake sediments after the smelting period confirm such a remobilisation. Despite a decrease in this accumulation rate through time, soils still contain significant stocks of anthropogenic Pb (54-89 % of PbANTH). The distribution of present-day anthropogenic Pb in the catchment area depends mainly on topographic characteristics. Coupling lake sediments and soils investigations is thus necessary to constrain the long-term persistence and remobilisation of a diffuse contamination related to mining activities.

Exploring a new approach for assessing the fate and behavior of the tailings released by the Brumadinho dam collapse (Minas Gerais, Brazil).

In 2019, the Brumadinho dam rupture released a massive amount of iron ore mining tailings into the Paraopeba River. Up to now, it remains a public health issue for the local and downstream populations. The present study aims to assess the behavior and fate of metal contamination following the disaster. Using new sampling strategies and up-to-date geochemistry tools, we show that the dissolved metal concentrations (< 0.22 µm cutoff filtration) remained low in the Paraopeba River. Although the tailings present high metal concentrations (Fe, Mn, Cd, and As), the high local background contents of metals and other previous anthropogenic contamination hamper tracing the sediment source based only on the geochemical signature. The Pb isotopic composition coupled with the metals enrichment factor of sediments and Suspended Particulate Matter (SPM) constitutes accurate proxies that trace the fate and dispersion of tailing particles downstream of the dam collapse. This approach shows that 1) The influence of the released tailing was restricted to the Paraopeba River and the Retiro Baixo reservoir, located upstream of the São Francisco River; 2) The tailings' contribution to particulate load ranged from 17 % to 88 % in the Paraopeba River; 3) Other regional anthropogenic activities also contribute to water and sediment contamination of the Paraopeba river.

New insights into metal(loid) dynamics in the Doce River estuary (Brazil) after a massive iron ore-processing tailing dam collapse.

The present study investigated metal and metalloid dynamics in the estuarine water of the Doce River (Brazil) after the collapse of an iron ore-processing tailing dam in 2015. Spectroscopic and isotopic techniques were applied to bring new insights into the effects of the dam failure on the dynamics and hazardousness of particulate and dissolved metal(loid) concentrations along the fluvial-estuarine continuum. Spectroscopic analysis showed that the suspended particulate matter (SPM) of the Doce River estuary consisted of a combination of soil-delivered particles and fine tailing mud particles with small amounts of coarse tailing mud Fe oxides (~150-µm width). Enrichment and contamination factors showed that the dam failure increased particulate Fe, Pb, Cd, and As, and dissolved Pb concentrations. Total concentrations of As (15 µg/L), Pb (30 µg/L), Cd (8 µg/L), and Cr (105 µg/L) increased up to values higher than quality and regulatory guidelines. Human health risk assessment showed that local communities are exposed to a potentially chronic Cr noncarcinogenic effects, although Cr high concentrations were not linked with the dam failure by this study. The particulate Pb isotope signatures reported herein (206/207Pb ratios of 1.214 ± 0.006 and 208/206Pb ratios of 2.025 ± 0.011) can be applied to constrain metal(loid) sources in the Doce River sediment plume and continental shelf. The river-ocean mixing zone caused abrupt changes metal(loid) partitioning (Zn, Pb, Cr, Cu, Cd, and As), controlling their fate in the estuary and the Brazilian southeast coastal.

Innovative combination of tracing methods to differentiate between legacy and contemporary PAH sources in the atmosphere-soil-river continuum in an urban catchment (Orge River, France).

Polycyclic aromatic hydrocarbons (PAH) have been released by human activities during more than a century, contaminating the entire atmosphere - soil - river continuum. Due to their ubiquity in the environment and their potential severe biological impacts, PAH became priority pollutants and were targeted by environmental public agencies. To better manage PAH pollution, it is necessary to identify unambiguously the sources and pathways of those compounds at the catchment scale, and to evaluate the persistence of historical PAH pollution in the environment especially in those urban contexts concentrating multiple PAH sources. Accordingly, the current research monitored the contamination in atmospheric fallout, soils and rivers of a 950-km2 catchment (Orge River) characterized by an increasing urban gradient in downstream direction, and located in the Seine River basin characterized by a high level of PAH legacy contamination. A combination of various approaches was used, including the widely used PAH diagnostic ratios, together with innovative methods such as PAH correlations and sediment fingerprinting using fallout radionuclides to clearly identify both the origin of PAH and their main PAH pathways to the river. The results demonstrated the persistence of legacy PAH contamination in the catchment, responsible for the signature of the suspended particulate matter currently transiting in the Orge River. They underlined the conservation of PAH through the soil - river continuum. Finally, urban runoff was demonstrated to provide the main PAH source to the river in the densely urbanized area by both PAH correlations and sediment fingerprinting. These results were used to model PAH concentrations in those particles supplied from urban areas to the river.

Impact of urban pressure on the spatial and temporal dynamics of PAH fluxes in an urban tributary of the Seine River (France).

Polycyclic aromatic hydrocarbons (PAHs) produced by numerous anthropogenic activities are ubiquitous in the environment and have become a priority concern due to their potential severe biological impacts. A better understanding of PAH transfer at the catchment scale is therefore necessary to improve the management of PAH contaminants and protect rivers. Furthermore, the impact of changes in hydrological regimes and land uses on PAH fluxes should be specifically investigated. Accordingly, the current research monitors the contamination in atmospheric fallout, soils and rivers in a 950-km2 catchment (Orge River) characterized by an increasing urban gradient in downstream direction. During an entire hydrological year, river water contamination was quantified through regular sampling of both particulate and dissolved material at four river-monitoring stations, reflecting the increasing urbanization gradient. The significant input of PAHs from urban areas in downstream river sections corresponded to a specific PAH flux that reached 23 g km-2 y-1 despite the low sediment yield. Moreover, the comparison with runoff-specific fluxes reported in the literature underlined the major impact of urban runoff on the Orge River water and sediment quality. Nevertheless, the annual PAH load exported by the river (21 kg y-1) remained lower than the PAH inputs from atmospheric fallout (173 kg y-1), demonstrating the continuous accumulation of PAH from atmospheric fallout in the catchment soils. Consequently, the notably large PAH stock (close to 1000 tons) resulting from historical contamination of this early-industrialized region continues to increase due to ongoing atmospheric inputs.

Tracing the sources of suspended sediment and particle-bound trace metal elements in an urban catchment coupling elemental and isotopic geochemistry, and fallout radionuclides.

The excessive supply of contaminants from urban areas to rivers during the last centuries has led to deleterious impacts on aquatic ecosystems. The sources, the behavior, and the dynamics of these contaminants must be better understood in order to reduce this excessive anthropogenic pollution. Accordingly, the current research investigated the particle-bound trace element (TE) contamination of the 900-km2 Orge River (Seine basin, France) and the potential sources of these particles (agricultural or forest soils, channel banks, road deposited sediments), through the analysis of multiple fallout radionuclides, elemental geochemistry, and lead isotopic composition on suspended particulate matter (SPM) collected during a hydrological year at four stations following an increasing urbanization gradient (300 to 5000 inhab.km-2). Fallout radionuclide measurements showed an increasing contribution of recently eroded particles from urban areas to the SPM in downstream direction. However, this contribution varied depending on hydrological conditions. A greater contribution of particles originating from urban areas was observed during low stage periods. On the contrary, the contribution of agricultural soils and channel banks that are less enriched in contaminants and fallout radionuclides was higher during seasonal floods, which explained the dilution of radionuclide contents in sediment transiting the river during those events. Trace element contamination of SPM in Cu, Zn, Pb, and Sb increased from moderate to significant levels with urban pressure in downstream direction (with corresponding enrichment factors raising from 2 to 6). In addition, Pb isotopic ratios indicated that the main source of Pb corresponded to the "urban" signature found in road deposited sediments. The low variations in lead isotope ratios found in the SPM for contrasting hydrological conditions demonstrated the occurrence of a single source of Pb contamination. These results demonstrate the need to better manage urban runoff during both flood and low precipitation events to prevent the supply of diffuse particle-bound contamination to rivers draining urban areas.

Oral bioaccessibility of inorganic contaminants in waste dusts generated by laterite Ni ore smelting.

The laterite Ni ore smelting operations in Niquelândia and Barro Alto (Goiás State, Brazil) have produced large amounts of fine-grained smelting wastes, which have been stockpiled on dumps and in settling ponds. We investigated granulated slag dusts (n = 5) and fly ash samples (n = 4) with a special focus on their leaching behaviour in deionised water and on the in vitro bioaccessibility in a simulated gastric fluid, to assess the potential exposure risk for humans. Bulk chemical analyses indicated that both wastes contained significant amounts of contaminants: up to 2.6 wt% Ni, 7580 mg/kg Cr, and 508 mg/kg Co. In only one fly ash sample, after 24 h of leaching in deionised water, the concentrations of leached Ni exceeded the limit for hazardous waste according to EU legislation, whereas the other dusts were classified as inert wastes. Bioaccessible fractions (BAF) of the major contaminants (Ni, Co, and Cr) were quite low for the slag dusts and accounted for less than 2 % of total concentrations. In contrast, BAF values were significantly higher for fly ash materials, which reached 13 % for Ni and 19 % for Co. Daily intakes via oral exposure, calculated for an adult (70 kg, dust ingestion rate of 50 mg/day), exceeded neither the tolerable daily intake (TDI) nor the background exposure limits for all of the studied contaminants. Only if a higher ingestion rate is assumed (e.g. 100 mg dust per day for workers in the smelter), the TDI limit for Ni recently defined by European Food Safety Authority (196 µg/day) was exceeded (324 µg/day) for one fly ash sample. Our data indicate that there is only a limited risk to human health related to the ingestion of dust materials generated by laterite Ni ore smelting operations if appropriate safety measures are adopted at the waste disposal sites and within the smelter facility.

Zinc speciation in the suspended particulate matter of an urban river (Orge, France): influence of seasonality and urbanization gradient.

Among trace metal pollutants, zinc is the major one in the rivers from the Paris urban area, such as the Orge River, where Zn concentration in the suspended particulate matter (SPM) can reach 2000 mg/kg in the most urbanized areas. In order to better understand Zn cycling in such urban rivers, we have determined Zn speciation in SPM as a function of both the seasonal water flow variations and the urbanization gradient along the Orge River. Using TEM/SEM-EDX and linear combination fitting (LCF) of EXAFS data at the Zn K-edge, we show that Zn mainly occurs as tetrahedrally coordinated Zn(2+) sorbed to ferrihydrite (37-46%), calcite (0-37%), amorphous SiO2 (0-21%), and organic-P (0-30%) and as octahedrally coordinated Zn(2+) in the octahedral layer of phyllosilicates (18-25%). Moreover, the Zn speciation pattern depends on the river flow rate. At low water flow, Zn speciation changes along the urbanization gradient: geogenic forms of Zn inherited from soil erosion decrease relative to Zn bound to organic-phosphates and amorphous SiO2. At high water flow, Zn speciation is dominated by soil-borne forms of Zn regardless the degree of urbanization, indicating that erosion of Zn-bearing minerals dominates the Zn contribution to SPM under such conditions.

Ion activity and distribution of heavy metals in acid mine drainage polluted subtropical soils.

The oxidative dissolution of mine wastes gives rise to acidic, metal-enriched mine drainage (AMD) and has typically posed an additional risk to the environment. The poly-metallic mine Dabaoshan in South China is an excellent test site to understand the processes affecting the surrounding polluted agricultural fields. Our objectives were firstly to investigate metal ion activity in soil solution, distribution in solid constituents, and spatial distribution in samples, secondly to determine dominant environment factors controlling metal activity in the long-term AMD-polluted subtropical soils. Soil Column Donnan Membrane Technology (SC-DMT) combined with sequential extraction shows that unusually large proportion of the metal ions are present as free ion in the soil solutions. The narrow range of low pH values prevents any pH effects during the binding onto oxides or organic matter. The differences in speciation of the soil solutions may explain the different soil degradation observed between paddy and non-paddy soils.