Alkiviadis Stamatakis

Heavy metal contamination poses a major threat to soil quality and agricultural sustainability, particularly in Mediterranean regions affected by both anthropogenic activities and naturally metal-rich parent materials. This study evaluated the potential of iron oxide nanomaterials (Fe₃O₄) as a soil amendment for reducing heavy metal mobility in three agricultural soils from Western Macedonia, Greece, representing contamination from (i) lignite-fired power plant emissions, (ii) mining activities, and (iii) geogenic enrichment associated with ultramafic (ophiolitic) parent material. Fe₃O₄ nanomaterials were applied at rates of 0.5 and 1.0% (w/w), followed by a 45-day laboratory incubation alongside untreated controls. The application of Fe₃O₄ nanomaterials modified selected soil physicochemical properties, with the strongest response observed in the acidic mining soil, where soil pH increased from 5.80 ± 0.08 to 6.02 ± 0.07 and cation exchange capacity increased by approximately 10%, indicating more favorable conditions for metal retention. Changes in metal mobility and fractionation, assessed using calcium chloride (CaCl₂) and diethylenetriaminepentaacetic acid (DTPA) extractions and the Community Bureau of Reference (BCR) sequential extraction procedure, showed a marked reduction in the most readily extractable metal fractions, although the magnitude of the response varied according to soil properties, initial metal mobility, and geochemical distribution. The strongest immobilization response was observed in the mining soil, where the 1.0% rate reduced CaCl₂-extractable Cu, Zn, Cd and Pb by approximately 50, 40, 47 and 68% relative to the untreated control, whereas the changes in the geogenic soil were small. Metals lost from the exchangeable and acid-soluble fraction were recovered mainly in the reducible fraction, indicating redistribution among soil fractions rather than removal from the soil. Overall, Fe₃O₄ nanomaterials effectively immobilized potentially toxic metals under the conditions examined, although their efficiency depended on soil properties, contamination source, initial metal mobility, and geochemical distribution. These findings indicate that remediation performance cannot be predicted solely from pseudo-total metal concentrations and highlight the need to adapt Fe₃O₄ application strategies to site-specific soil characteristics and contaminant fractionation. As these results derive from a 45-day laboratory incubation, longer-term and field-scale evaluation is required before wider agricultural application can be recommended.

Microplastics are an increasingly pervasive contaminant of agricultural soils, where they frequently co-occur with heavy metals such as nickel (Ni), an element still catalogued mainly as a pollutant yet now recognised as an essential plant micronutrient and the cofactor of urease. A pot experiment assessed how three of the most common microplastics—polyethylene (PE), poly(ethylene terephthalate) (PET) and polystyrene (PS), added at 2% v/v—affect nickel behaviour in two calcareous agricultural soils differing chiefly in texture (Soil 1, a clay loam; Soil 2, a silty clay), cropped with industrial hemp (Cannabis sativa L., cv. Fedora 17) and tobacco (Nicotiana tabacum L., cv. Burley). Forty-eight pots (2 soils × 4 treatments × 2 crops × 3 replicates) were analysed for pseudo-total (aqua regia), bioavailable (DTPA-extractable) and plant-tissue Ni. Pseudo-total Ni was unchanged across all treatments (15.1–15.4 mg kg⁻¹), confirming that microplastics are modifiers and not sources of the metal. DTPA-extractable Ni rose significantly under PE and PS in the coarser-textured Soil 1 (1.87 and 1.80 versus 1.69 mg kg⁻¹) but not in the finer-textured Soil 2. Tissue Ni nevertheless declined under every polymer, in the order control > PE > PS > PET, and was consistently lower on Soil 2. The Bioavailability Factor and the soil-referenced transfer indices (BAF, TC) followed the same pattern, whereas the internal root-to-shoot Transfer Factor remained close to unity, indicating that microplastics restrict the acquisition of nickel rather than its internal distribution. Neither crop showed visible symptoms of phytotoxicity and both completed their full growth cycle; because biomass was not quantified, no conclusion regarding yield is drawn. Chemically measured availability therefore ceases to predict plant uptake under microplastic amendment, with implications both for the expected efficiency of Ni phytoextraction and for the supply of an essential micronutrient on calcareous soils.

Soil salinization affects more than 424 million hectares of topsoil worldwide and is associated with yield losses of 18–43% in drylands, yet its long-term dynamics have rarely been compared across regions on a common basis. This work synthesizes nine case studies from a systematic, PRISMA-guided search, selected purposively to maximize variation in climate, scale and method. ECe (dS/m) and total salt content (g/kg) have no general conversion, so the eight ECe-based studies are compared class by class using their own figures; the single g/kg study contributes direction only, and no values are pooled. The largest transfers occur between the intermediate and higher classes, while the non-saline class changes little in most settings; intensification of already salt-affected land therefore predominates over conversion of new land, though the latter also occurs (Bachu County). The drivers reported by the source studies are irrigation expansion, inadequate drainage, and shallow saline groundwater, with rising evaporative demand and reduced leaching as amplifiers; since no study partitions the change between climatic and management causes, this ordering is descriptive, not a causal attribution. The synthesis is hypothesis-generating; its main product is a direction-of-change summary table separating observed trends from projections.

Microplastics are emerging as ubiquitous contaminants in agricultural soils, while nickel (Ni), although catalogued as a potentially toxic element, is an essential micronutrient and a cofactor of urease. In a pot experiment, this study examined how three microplastics (polyethylene, PE; poly(ethylene terephthalate), PET; and polystyrene, PS) affect nickel availability and the properties of two calcareous agricultural soils from central Greece. The microplastics were applied at two levels (1.5 and 3.0% by weight), and the samples were analysed at four time points (3, 6, 9, and 12 months, n = 3). Total (aqua regia) and available (DTPA) nickel, pH, electrical conductivity, organic matter, bulk density (BD), water-holding capacity (WHC), and microbial respiration (qCO₂) were measured, and the data were evaluated by one-way ANOVA with Tukey HSD tests. Total nickel remained stable (about 15.1–15.4 mg/kg; non-significant), whereas the available fraction changed systematically. In Soil 1 (12 months, 1.5%), PE raised DTPA-Ni by +24.9%, PET by +19.8% and PS by −1.7%, while at 3.0% the increases reached +39.8% and +31.7%. In parallel, PE lowered bulk density by up to −16.1%, PET raised water holding capacity by up to +28.9%, and PS raised microbial respiration by up to +38.3%, producing distinct, polymer-specific responses. The changes intensified with time and dose and were milder in the more strongly buffered Soil 2. Microplastics redistribute the biologically active, rather than the total, pool of nickel, a finding that supports reappraising Ni as a nutritional micronutrient and monitoring its available fraction. Because no plants were grown, the nutritional interpretation is advanced as a hypothesis for future testing rather than as a demonstrated agronomic benefit, and the applied microplastic doses (1.5–3.0% w/w) exceed most reported field levels and were chosen to resolve mechanisms under accelerated conditions.

Per- and polyfluoroalkyl substances (PFASs) are persistent, surface-active contaminants for which soil represents the largest terrestrial reservoir. This review synthesizes a rapidly expanding but fragmented body of literature in order to reframe PFAS not merely as a groundwater transport problem but as a systemic stressor of soil health, drawing together their reported effects on the chemical, physical and biological properties of soils and giving particular attention to the calcareous, alkaline, carbon-poor and seasonally dry soils of the Mediterranean. The reviewed evidence suggests that, chemically, PFASs perturb the coupled carbon and nitrogen cycles rather than the bulk soil reaction, transiently stimulating and then depressing organic carbon turnover, drawing down the dissolved organic carbon pool and disturbing nitrification, while their retention and bioavailability are governed chiefly by organic carbon, chain length and pH. Physically, the surfactant character that defines these molecules lowers the surface tension of soil water and concentrates PFASs at the air–water interface, so that in unsaturated and drought-prone soils much of the burden is retained and then released episodically, most clearly on rewetting after dry periods. Biologically, the literature consistently reports dose-dependent declines in microbial viability, diversity and enzyme activity, alongside toxicity to earthworms and other soil fauna, with sensitivity strongly modulated by soil texture and organic matter. Across all three domains, the Mediterranean emerges as both potentially vulnerable and conspicuously understudied, the available data being clustered in a few western countries and effectively absent for much of the eastern and southern basin, so that the regional assessment offered here rests largely on mechanistic inference rather than on direct observation. The review argues that these coupled mechanistic and geographic gaps define an urgent, region-specific research agenda for the protection of soil health.

Heavy metal contamination of soils represents a persistent environmental challenge, for which in situ immobilization has emerged as a cost-effective and technically viable alternative to conventional invasive remediation technologies. This review comparatively evaluates three distinct categories of soil amendments—biochar, zeolite and attapulgite—within a unified analytical framework integrating extractable fractions (TCLP, DTPA, and CaCl₂) and geochemical fractionation approaches (BCR and Tessier). The novelty of this study lies in the systematic assessment of the dominant immobilization mechanisms associated with each amendment in relation to soil properties and the chemical speciation of the target metal, as well as in distinguishing between an apparent reduction in metal extractability and a genuine shift toward more stable geochemical fractions. The findings identify ion exchange as the primary immobilization mechanism in zeolites (NaA zeolite, 1–5% w/w, 96% reduction in TCLP-extractable Pb and 91% reduction in TCLP-extractable Cd), the synergistic action of adsorption, complexation, and precipitation in biochar systems (manure-derived biochar, 0–5% w/w, 97.4% reduction in the exchangeable Pb fraction according to the Tessier scheme), and the critical role of surface modification in attapulgite-based amendments (C-ATP, 4% w/w, 95.1% and 74.3% reductions in TCLP-extractable Pb and Cd, respectively). Because these efficiencies were obtained using different extraction protocols, they are not directly comparable. At the same time, cases of adverse responses were identified, including increased As extractability following the application of phosphate-modified biochar and the redistribution of Pb and Cd after amendment with natural zeolite in industrially contaminated soil. These observations highlight that amendment performance is not an intrinsic property of the material itself, but rather the outcome of specific geochemical interactions occurring within the soil system. Increased soil pH emerged as the principal common factor promoting metal stabilization across all amendment categories, whereas substantial variability in amendment dosage, incubation period, and analytical methodology limited direct quantitative comparisons among studies. Consequently, the selection of an appropriate soil amendment should be based on the integrated evaluation of soil physicochemical properties, contaminant speciation, and the intended scale of application, supported by long-term monitoring under field conditions.

Floods and wildfires are two extreme environmental events with significant yet different impacts on soil health and on two particularly important soil pollutants, heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs), which are directly associated with ishytoxic properties and their ability to enter the food chain. The present study includes a methodological approach that was based on a literature review of published studies conducted worldwide regarding these two phenomena. The main forms of both pollutants, their possible sources and inevitable deposition onto the soil surface, along with their behavior–transport–mobility, and their residence time in soil were investigated. Furthermore, the changes that both HMs and PAHs induce in the physicochemical properties of post-flood and post-fire soils (in soil pH, Cation Exchange Capacity (CEC), organic matter content, porosity, mineralogical alterations, etc.), are investigated after a literature review of various case studies. Wildfires, in contrast to floods, can more easily remove large quantities of heavy metals into the soil ecosystem, most likely due to the intense erosion they cause. At the same time, floods appear to significantly burden soils with PAHs. In wildfires, the largest mean increases were observed for Mn (386%), Zn (300%), and Cu (202%). In floods, Pb showed the highest mean increase (534%), with Cd also rising substantially (236%). Regarding total PAHs, mean post-event concentrations reached 482.3 μg/kg after wildfires, compared to 4384 μg/kg after floods. Changes in the structure and chemical composition of flooded and burned soils may also affect the mobility and bioavailability of the pollutants under study. Overall, these two phenomena significantly alter soil quality, affecting both ecological processes and potential health impacts.