International audience | Amphibians are now recognized as the most endangered group. One of this decline causes is the degradation of their habitat through direct contamination of water, soil leaching, or runoff from surrounding contaminated soils and environments. In the North of France, the extensive industrial activities resulted in massive soil contamination by metal compounds. Mineral amendments were added to soils to decrease trace metal mobility. Because of the large areas to be treated, the use of inexpensive industrial by-products was favored. Two types of fly ashes were both tested in an experimental site with the plantation of trees in 2000. Aim of the present work was to investigate the effects of extracts from metal-contaminated soils treated or not for 10 years with fly ashes on Xenopus laevis oocyte using cell biology approaches. Indeed, our previous studies have shown that the Xenopus oocyte is a relevant model to study the metal ion toxicity. Survival and maturation of oocyte exposed to the soil extracts were evaluated by phenotypic approaches and electrophysiological recordings. An extract derived from a metal-contaminated soil treated for 10 years with sulfo-calcic ashes induced the largest effects. Membrane integrity appeared affected and ion fluxes in exposed oocytes were changed. Thus, it appeared that extracted elements from certain mineral amendments used to prevent the mobility of metals in the case of highly metal-contaminated soils could have a negative impact on X. laevis oocytes.

International audience | Amphibians are now recognized as the most endangered group. One of this decline causes is the degradation of their habitat through direct contamination of water, soil leaching, or runoff from surrounding contaminated soils and environments. In the North of France, the extensive industrial activities resulted in massive soil contamination by metal compounds. Mineral amendments were added to soils to decrease trace metal mobility. Because of the large areas to be treated, the use of inexpensive industrial by-products was favored. Two types of fly ashes were both tested in an experimental site with the plantation of trees in 2000. Aim of the present work was to investigate the effects of extracts from metal-contaminated soils treated or not for 10 years with fly ashes on Xenopus laevis oocyte using cell biology approaches. Indeed, our previous studies have shown that the Xenopus oocyte is a relevant model to study the metal ion toxicity. Survival and maturation of oocyte exposed to the soil extracts were evaluated by phenotypic approaches and electrophysiological recordings. An extract derived from a metal-contaminated soil treated for 10 years with sulfo-calcic ashes induced the largest effects. Membrane integrity appeared affected and ion fluxes in exposed oocytes were changed. Thus, it appeared that extracted elements from certain mineral amendments used to prevent the mobility of metals in the case of highly metal-contaminated soils could have a negative impact on X. laevis oocytes.

Fly ash (FA), a solid waste generated in thermal power plants, is considered an environmental pollutant. Therefore, measures must be taken to dispose of FA in an environmentally friendly manner. In this paper, an electrospinning technique was employed to incorporate FA particles onto zinc oxide nanofibers (ZnO NFs), and the product (FA/ZnO composite) was used for the removal of methylene blue (MB) from the water. Herein, ZnO NFs may serve as effective semiconductor photocatalysts and provide sufficient surface area for FA, while the FA particles serve as an effective adsorbent. The adsorption capacity and photocatalytic efficiency of the as-synthesized nanocomposite fibers were enhanced compared to those of the pristine ZnO NFs, and this result is attributed to the uniform distribution of FA on the surface of the ZnO NFs. The as-synthesized nanocomposite could have great significance in wastewater treatment.

A study was undertaken to test the hypothesis that the presence of fly ash and other artifactual materials (AMs) significantly increases the toxicity of urban soil and street dust. AMs were distinguished as artifacts (artificial particles > 2 mm in size), and particulate artifacts (≤2 mm in size); street dust was the <63 μm fraction of street sediments. Reference artifacts, street dusts, and topsoils representing different land use types in Detroit, Michigan were analyzed for miscellaneous radionuclides, trace elements, magnetic susceptibility (MS), and acetic acid-extractable (leachable) Pb. Background levels were established using native glacial sediments. Street sediments were found to have a roadside provenance, hence street dusts inherited their contamination primarily from local soils. All soils and dusts had radionuclide concentrations similar to background levels, and radiological hazard indices within the safe range. Artifacts, fly ash-impacted soils and street dusts contained elevated concentrations of toxic trace elements, which varied with land use type, but none produced a significant amount of leachable Pb. It is inferred that toxic elements in AMs are not bioavailable because they are occluded within highly insoluble materials. Hence, these results do not support our hypothesis. Rather, AMs contribute to artificially-elevated total concentrations leading to an overestimation of toxicity. MS increased with increasing total concentration, hence proximal sensing can be used to map contamination level, but the weak correlation between total and leachable Pb suggests that such maps do not necessarily indicate the associated biohazard. Home site soils with total Pb concentrations >500 mg kg−1 were sporadically toxic. Thus, these results argue against street dust as the local cause of seasonally elevated blood-Pb levels in children. Lead-bearing home site soil tracked directly indoors to form house dust is an alternative exposure pathway.

Incineration has overtaken landfilling as the most important option for disposal of the increasing volumes of municipal solid waste (MSW) generated in China. Accordingly, disposal of the incineration fly ash, which is enriched with a range of heavy metals, has become a key challenge for the industry. This review analyzes the temporal and spatial trends in the distributions of As, Cd, Cr, Cu, Ni, Pb, Zn, and Hg in MSW incineration fly ash between 2003 and 2017, and estimates the inventories of heavy metals associated with the fly ash and the average levels of heavy metals in Chinese MSW based on their mass flow during MSW incineration. It was estimated that MSW incinerators in China released approximately 1.12 × 10², 2.96 × 10³, 1.82 × 10², 3.64 × 10⁴, 1.00 × 10², 7.32 × 10³, 2.42 × 10², and 1.47 × 10¹ tonnes of Cd, Pb, Cr, Zn, Ni, Cu, As, and Hg, respectively, with the fly ash in 2016. Due to the much greater fly ash generation rate, the incinerators based on circulating fluidized bed combustor (CFBC) technology released more heavy metals during incineration of MSW compared to those based on grate furnace combustor (GFC) technology. Results of mass-flow modeling indicate that the geometric mean contents of Cd, Pb, Cr, Zn, Ni, Cu, As, and Hg in Chinese MSW were 3.0, 109, 101, 877, 34, 241, 21, and 1.7 mg/kg, respectively, which are comparable to those in the MSW from other countries. To protect the environment from the significant potential ecological risk posed by heavy metals in the mismanaged fly ash, strict regulation enforcement and compliance monitoring are necessary to reduce the heavy metal pollution brought by improper disposal of MSW incineration fly ash, and more research and development efforts on advanced technologies for stabilization of heavy metals in fly ash and its environmentally sound reuse can help mitigate its environmental risk.

Red mud, which is from the aluminum industry, is a potentially under-utilized resource. Technological processes for using low-cost red mud as an alternative precursor for detoxifying metal pollutants urgently need to be developed. In this study, we systematically investigated the feasibility of using red mud to detoxify metal-containing wastes (e.g., fly ash) via the formation of preferable crystalline phases. To understand the mechanism of metal detoxification by red mud, CuO, NiO, and ZnO were blended with red mud at different weight ratios and the mixtures were then subjected to ceramic-sintering. After sintering, the X-ray diffraction results revealed that all of the metals (i.e., Cu, Ni, and Zn) were able to be crystallographically incorporated into spinel lattices. Sintering the red mud at 1100 °C for 3 h effectively converted the metals into spinels. The mixing weight ratios strongly affected the efficiency of the metal incorporation. The red mud was able to incorporate 15 wt% of metal oxides. The incorporation mechanisms mainly occurred between the metal oxide(s) and hematite. Modified TCLP tests were conducted to further evaluate the metal stabilization performance of the red mud, which demonstrated the leachabilities of ZnO and the sintered red mud + ZnO product. The concentration of leached metal was substantially reduced after the incorporation process, thus demonstrating that red mud can be successfully used to detoxify metals. The results of this study reveal that waste red mud can be feasibly reused as a promising waste-to-resource strategy for stabilizing heavy metal wastes.

Cement-solidification and chelator-stabilisation of municipal solid waste incineration fly ash (MSWI-FA) are two main treatment techniques to immobilise heavy metals. Differences in the long-term stabilities of those two methods of heavy-metal immobilisation were explored to aid in determining the better MSWI-FA treatment. However, few comparative studies have been conducted on 6-year-old cement-solidified FA (Ce-6-FA) and chelator-stabilised FA (Ch-6-FA). In this study, we compared the physicochemical and heavy metal leaching characteristics of Ce-6-FA and Ch-6-FA. The chemical speciation of heavy metals was modelled using geochemical software to assess long-term stability. The results showed weaker long-term stability in Pb immobilisation under the chelating system. The leaching concentrations of target heavy metals, acetic acid leaching tests, acid neutralising capacity, and pH-dependent leaching results indicated that Ce-6-FA had higher long-term stability than Ch-6-FA. A column experiment indicated that the cumulative release rates of Pb in Ce-6-FA and Ch-6-FA were 2.49% and 4.72%, respectively. The phase-controlled leaching of Pb in Ce-6-FA mainly occurred through Pb2(OH)3Cl and chloropyromorphite (Pb5(PO4)3Cl), whereas that in Ch-6-FA mainly occurred through Pb5(PO4)3Cl. The decomposition of heavy metal chelates in Ch-6-FA and salt generation in this process led to the release of Pb via the inorganic complex.

Fly ash generated from coal-fired power plants is a source of potential pollutants, but can be used as a soil ameliorant to increase plant biomass and yield in agriculture. However, the effects of fly ash soil application on plant biomass and the accumulation of both nutrient and toxic elements in plants remain unclear. Based on 85 articles, we conducted a comprehensive meta-analysis to evaluate changes in plant biomass and concentrations of 21 elements in plants in response to fly ash application. These elements included macro-nutrients (N, P, K, Ca, and S), micro-nutrients (B, Co, Cu, Fe, Mn, Mo, Ni, and Zn), and metal(loid)s (Al, As, Cd, Cr, Pb, and Se). Overall, fly ash application decreased plant biomass by 15.2%. However, plant biomass was enhanced by fly ash application by 11.6–29.2% at lower application rates (i.e. <25% of soil mass), and decreased by 45.8% at higher application rates (i.e. 50–100%). Belowground biomass was significantly reduced while yield was enhanced by fly ash application. Most of the element concentrations in plants were enhanced by fly ash application, and followed a descending order with metal(loid)s > micro-nutrients > macro-nutrients. Concentrations of elements tended to increase with an increase in fly ash application rate. Our syntheses indicated that fly ash should be applied at less than 25% in order to enhance plant biomass and yield but avoid high accumulations of metal(loid)s.

Apportioning sources of environmental pollutants is key to controlling pollution. In this study, the sources of heavy metals to 234 agricultural soils from the Jianghan Plain (JHP) (∼22454 km2) in central China were discriminated between using Cd and Pb isotope compositions and multivariate statistical analyses. Concentrations of some metals in JHP soils (0.48 ± 0.2, 48.2 ± 15.9, 0.12 ± 0.23, 48.8 ± 16.4, 36.5 ± 9.8, and 96.8 ± 42.2 mg kg−1 for Cd, Cu, Hg, Ni, Pb, and Zn, respectively) were higher than background concentrations in Chinese soil. The Cd isotope compositions for the JHP soils (δ114/110Cd values −0.76‰ to −0.25‰) were similar to Cd isotope compositions found for smelter dust and incinerator fly ash, indicating Cd was supplied to the JHP soils by ore smelting and/or refining processes. The Pb isotope compositions for the JHP soils (206Pb/207Pb 1.182–1.195 and 208Pb/206Pb 2.078–2.124) were between the Pb isotope compositions found for Chinese coal and natural sources, which a binary isotope mixing model indicated contributed 52% and 48%, respectively, of the Pb in JHP soils. Cluster analysis and positive matrix factorization indicated that the sources of heavy metals in JHP soils may consist of smelting and/or refining activities, coal combustion, agricultural activities, and natural sources (including Han River sediment and soil parent materials). The isotope fingerprints and multivariate statistical analyses together indicated that coal combustion and smelting and/or refining activities were the main anthropogenic sources of heavy metals polluting JHP soils.

A soil column migration trough was used to study the leaching behavior and geochemical partitioning of fifteen elements Al, As, Cr, Cu, Fe, Mg, Sn, Sb, Zn, V, Co, Mn, Pb, Ni and Cd in simulated ash reclaimed soil. According to the results of cluster analysis for the sampling stations, there were three clusters: Cluster 1 of 7 wells with relative good groundwater quality originated from the background control area, Cluster 2 of 9 wells with worst groundwater quality in the downstream parts of the simulated ash reclaimed soil, and Cluster 3 of 2 wells with representative of samples influenced by the combined effect of injection of leaching solution and the main current. Statistical analysis identified five factor types that accounted for 83.055% of the total variance, which declined in the order: ash-soil rate > leaching intensity > water depths > flow velocity > leaching time. As, Sb, Cd, Pb and Ni were the dominant contaminants. The water around ash reclaimed soil was unsuitable for drinking. As, Mn, Cd, Sb, Co and V were the largest contributors to health risks. Soils reclaimed with fly ash can consequently be a long-time source for the transfer of toxic elements into groundwater.