Soil chemistry of toxic metalloids and metals differs, making their simultaneous removal difficult. Soil contaminated with As, Pb, Zn and Cd was washed with oxalic acid, Na-dithionite and EDTA solution. Toxic elements were removed from the washing solution by alkalinisation with CaO to a pH 12.5: As was co-precipitated with Fe from Fe-EDTA chelate formed after the soil washing. The toxic metals precipitated after substitution of their EDTA chelates with Ca. The novel method was scaled up on the ReSoil® platform. On average, 60, 76, 29, and 53% of As, Pb, Zn, and Cd were removed, no wastewater was generated and EDTA was recycled. Addition of zero-valent iron reduced the toxic elements' leachability. Remediation was most effective for As: phytoaccessibility (CaCl₂ extraction), mobility (NH₄NO₃), and accessibility from human gastric and gastrointestinal phases were reduced 22, 104, 6, and 51 times, respectively. Remediation increased pH but had no effect on soil functioning assessed by fluorescein diacetate hydrolysis, dehydrogenase, β-glucosidase, urease, acid and alkaline phosphatase activities. Brassica napus produced 1.9 times more biomass on remediated soil, accumulated no As and 5.0, 2.6, and 9.0 times less Pb, Zn and Cd, respectively. We demonstrated the novel remediation technology as cost-efficient (material cost = 41.86 € t^-1) and sustainable.

Sewage sludge (SS) is a potential resource for P and other nutrients, but often contaminated with metals. SS containing Pb-102, Zn-968, Cu-267, Cr-101, Mn-222, and Fe-8374 mg kg^-1 was washed in a batch process for 1 h with a recycled washing solution containing 50 mmol L^-1 of recycled EDTA and 50 mmol L^-1 H₂SO₄, solid/liquid ratio 1/7 (w/V). After solid/liquid separation, the washed SS was further rinsed 3-times with cleansed recycled solutions. EDTA and process solutions were recycled/cleansed in a pH gradient of 12.5-2.0 imposed by addition of CaO and H₂SO₄ (the ReSoil® method). EDTA, recycled as ineffective Ca-EDTA, was activated by capturing Ca with H₂SO₄. The process was closed-looped, no wastewater was generated, solid waste was centrifuged away. 10 consecutive SS washing batches preserved the quality of the process solutions. Metals were mainly removed from the SS organic fraction, the average removal was Pb-35, Zn-59, Cu-60, Cr-19, Mn-25, and Fe-1%. Washing reduced the leachability of Cu and Cr from SS by 13.4 and 3.5 times, but increased the leachability of Pb, Zn, Mn, and Fe by 2.5, 3.8, 1.9, and 1.6 times, respectively. Metal concentrations in the leachates were below the limits stipulated as hazardous. The content of accessible P and K in washed SS decreased by 24 and 45%, and the total N decreased by 10%. Overall, the results prove the feasibility of the novel SS washing process.

Contamination with toxic metals prevents the use of sewage sludge (SS) as a soil fertilizer. Hydrodynamic cavitation, thermal microwaving, microwave-assisted alkaline, and acid hydrolysis coupled with ethylenediaminetetraacetate (EDTA) washing were tested as a method to remove toxic metals from SS. Acid hydrolysis coupled with EDTA washing was most effective and was used in a closed-loop process based on ReSoil technology. EDTA and process solutions were recycled at a pH gradient of 12.5–2, which was imposed by the addition of quicklime (CaO) and H₂SO₄. An average of 78%-Pb, 76%-Zn, 1%-Cu, and 17%-Cr were removed from SS in five consecutive batches. No wastewater was generated, only solid waste (40%). The EDTA lost in the process (42%) was resupplied in each batch. In a series of batches, the process solutions retained metal removal efficiency and quality. The treatment removed 70% and 23% of P and N, respectively, from SS and increased the leachability of Zn, Cu, Mn, and Fe in the washed SS by 11.7, 6.8, 1.4, and 5.2 times, respectively. Acid hydrolysis coupled with EDTA washing proved to be a technically feasible, closed-loop process but needs further development to reduce reagent, material, and nutrient loss and to reduce toxic emissions from the washed sludge.

Los suelos varían ampliamente en la Amazonia mostrando gran diversidad, diferentes características morfológicas y propiedades físico-químicas del suelo. Las investigaciones llevadas a cabo en relación a las propiedades del suelo en estas áreas ayudan al conocimiento general de los suelos nativos e inexplorados y proporcionan muestras de control para el estudio del suelo. En la literatura existen importantes investigaciones que estudian los bosques amazónicos en un entorno heterogéneo en relación con el suelo y la topografía. En el estudio actual se recolectaron muestras de suelo de 3 profundidades, 9 localidades y altitudes diferentes en la selva amazónica; y proporciona la visión sobre los efectos de la profundidad del suelo así como las variaciones altitudinales sobre el contenido de Fe y la acidez intercambiable (intercambio iónico H-al). Los resultados indicaron que la altitud, en comparación con la profundidad del suelo, puede desempeñar un papel importante en el contenido de Fe y la acidez intercambiable.

Forests are major sinks for atmospheric mercury (Hg) due to the efficiency of stomatal uptake and litter deposition. Tropical forests, highly productive ecosystems, remain understudied despite their pronounced climatic and phenological variability. We investigated whether seasonal rainfall regimes and associated tree adaptations regulate the Hg dynamics – its uptake by leaves, deposition through litter, and storage in soils– in secondary tropical moist broadleaf (TMBF) and tropical dry broadleaf (TDBF) forests from Costa Rica. Seasonality strongly controlled Hg sequestration in TDBF. Deciduous trees showed 4.7 times higher foliar Hg concentration in the wet season, when leaves were mature, compared to the dry season, when newly flushed leaves emerged after leaf shedding. Evergreen trees in TDBF demonstrated 2.3 times lower foliar Hg concentrations in the dry season than in the wet season (23 vs. 53 µg kg^-1), likely due to various associated physiological processes (e.g., leaf flushing). However, the primary mechanism remains unclear given the complex and unexplored Hg dynamics in TDBF. TMBF showed no clear seasonal variation in foliar Hg in either deciduous (dry: 48; wet: 54 µg kg^-1) or evergreen trees (dry: 57; wet: 53 µg kg^-1), likely due to longer leaf lifespan sustaining year-round transpiration and stomatal Hg uptake under high humidity. Atmospheric Hg concentrations in TDBF were two times higher than in TMBF (1.2 vs. 0.6 ng m^-3) across both seasons, likely reflecting greater Hg capture per unit area in TMBF due to denser vegetation and enhanced wet deposition via rainfall. Foliar Hg was not correlated with stomatal density or specific leaf area in either forest type. Soil Hg concentrations, however, were correlated with litter-derived inputs, supporting litter as the dominant Hg transfer pathway. Higher seasonally averaged Hg inputs via litter (34 μg m^-2) in TMBF than in the TDBF (19 μg m^-2) resulted in 3.4 times higher soil Hg concentrations (0–30 cm) in TMBF (115 µg kg^-1) than in TDBF (34 µg kg^-1). Soil Hg stocks were 2.6 times lower at a previously deforested TMBF site, indicating persistent disturbance effects despite almost three decades of reforestation. Overall, seasonality regulated Hg sequestration in TDBF, yet both TDBF and TMBF serve as important global Hg sinks with contrasting dynamics that are potentially sensitive to climate change.

Forests are major sinks for atmospheric mercury (Hg) due to the efficiency of stomatal uptake and litter deposition. Tropical forests, highly productive ecosystems, remain understudied despite their pronounced climatic and phenological variability. We investigated whether seasonal rainfall regimes and associated tree adaptations regulate the Hg dynamics – its uptake by leaves, deposition through litter, and storage in soils– in secondary tropical moist broadleaf (TMBF) and tropical dry broadleaf (TDBF) forests from Costa Rica. Seasonality strongly controlled Hg sequestration in TDBF. Deciduous trees showed 4.7 times higher foliar Hg concentration in the wet season, when leaves were mature, compared to the dry season, when newly flushed leaves emerged after leaf shedding. Evergreen trees in TDBF demonstrated 2.3 times lower foliar Hg concentrations in the dry season than in the wet season (23 vs. 53 µg kg^-1), likely due to various associated physiological processes (e.g., leaf flushing). However, the primary mechanism remains unclear given the complex and unexplored Hg dynamics in TDBF. TMBF showed no clear seasonal variation in foliar Hg in either deciduous (dry: 48; wet: 54 µg kg^-1) or evergreen trees (dry: 57; wet: 53 µg kg^-1), likely due to longer leaf lifespan sustaining year-round transpiration and stomatal Hg uptake under high humidity. Atmospheric Hg concentrations in TDBF were two times higher than in TMBF (1.2 vs. 0.6 ng m^-3) across both seasons, likely reflecting greater Hg capture per unit area in TMBF due to denser vegetation and enhanced wet deposition via rainfall. Foliar Hg was not correlated with stomatal density or specific leaf area in either forest type. Soil Hg concentrations, however, were correlated with litter-derived inputs, supporting litter as the dominant Hg transfer pathway. Higher seasonally averaged Hg inputs via litter (34 μg m^-2) in TMBF than in the TDBF (19 μg m^-2) resulted in 3.4 times higher soil Hg concentrations (0–30 cm) in TMBF (115 µg kg^-1) than in TDBF (34 µg kg^-1). Soil Hg stocks were 2.6 times lower at a previously deforested TMBF site, indicating persistent disturbance effects despite almost three decades of reforestation. Overall, seasonality regulated Hg sequestration in TDBF, yet both TDBF and TMBF serve as important global Hg sinks with contrasting dynamics that are potentially sensitive to climate change.