The increasing development of industries, resulting in a large volume of mining, smelting, and combustion wastes, and intense agricultural activities, due to demand for food and energy, have caused environmental hazards for food quality and ecosystems. This is a review on the contamination of the soil–groundwater–crop system and a potential reduction of the contamination by a gradual shift towards green economy within the European Union and on a worldwide scale. Available mineralogical and geochemical features from contaminated Neogene basins have shown a diversity in the contamination sources for soil and groundwater, and highlighted the need to define the contamination sources, hot spots, degree/extent of contamination, and provide ways to restrict the transfer of heavy metals/metalloids into the food chain, without the reduction of the agricultural and industrial production. Among harmful elements for human health and ecosystems, the contamination of groundwater (thousands of μg/L Cr(VI)) by industrial activities in many European countries is of particular attention. Although Cr(VI) can be reduced to Cr(III) and be completely attenuated in nature under appropriate pH and Eh conditions, the contamination by Cr(VI) of coastal groundwater affected by the intrusion of seawater often remains at the hundreds μg/L level. A positive trend between B and Cr(VI) may provide insights on the role of the borate [B(OH)₄]⁻ ions, a potential buffer, on the stability of Cr(VI) in coastal groundwater. Efforts are needed towards reducing toxic metal(loids) from the industrial wastewaters prior to their discharge into receptors, as well as the transformation of hazardous mining/industrial wastes to new products and applications to the optimization of agricultural management strategies.

The investigation of the contamination in soil, plants and groundwater revealed a spatial evolution, with an increasing trend in the Cr, Fe, Ni, Mn and Co contents in soils from the Assopos to Thiva basin, followed by C. Evia and Ni-laterite deposits, suggesting that the latter and their parent ophiolites are a potential source for these metals. In contrast, the contamination in groundwater by Cr(VI), ranging from 2 to 360 μg/L Cr, and a varying degree of salinization is probably due to both human activities and natural processes. A diverse source for the contamination of soil and groundwater in the Assopos-Thiva basins is consistent with the increasing trend of the Mg/Si ratio and Cr(VI) concentration in water. The use of deep karst-type aquifer instead of the shallow-Neogene one may provide a solution to the crucial environmental problem. The selective extraction by EDTA and alkaline solution showed that Cr and Fe are less available than Mn. The Cr contents in plants range from <1 to tens of mg/kg, due probably to the high resistance of chromite. However, the average Cr_total contents in plants/crops are higher than normal or sufficient values, whilst Cr_total accumulation [(% metals in plants × 100)/metal in soil] and Cr(VI) accumulation are relatively low. There is a very good positive correlation between accumulation factors for Cr and Fe (R² = 0.92), suggesting a similarity concerning their uptake.

As the global energy sector is expected to experience a gradual shift towards renewable energy sources, access to special metals in known resources is of growing concern within the EU and at a worldwide scale. This is a review on the Fe–Ni ± Co-laterite deposits in the Balkan Peninsula, which are characterized by multistage weathering/redeposition and intense tectonic activities. The ICP-MS analyses of those laterites indicated that they are major natural sources of Ni and Co, with ore grading from 0.21 to 3.5 wt% Ni and 0.03 to 0.31 wt% Co, as well as a significant Sc content (average 55 mg/kg). The SEM-EDS analyses revealed that fine Fe-, Ni-, Co-, and Mn-(hydr)oxides are dominant host minerals and that the enrichment in these elements is probably controlled by the post-formation evolution of initial ore redeposition. The paucity of rare earth element (REE) within the typical Fe–Ni laterite ore and the preferential occurrence of Co (up to 0.31 wt%), REE content (up to 6000 mg/kg ΣREE), and REE-minerals along with Ni, Co, and Mn (asbolane and silicates) towards the lowermost part of the Lokris (C. Greece) laterite ore suggest that their deposition is controlled by epigenetic processes. The platinum-group element (PGE) content in those Fe–Ni laterites, reaching up to 88 μg/kg Pt and 26 μg/kg Pd (up to 186 μg/kg Pd in one sample), which is higher than those in the majority of chromite deposits associated with ophiolites, may indicate important weathering and PGE supergene accumulation. Therefore, the mineralogical and geochemical features of Fe–Ni laterites from the Balkan Peninsula provide evidence for potential sources of certain critical metals and insights to suitable processing and metallurgical methods. In addition, the contamination of soil by heavy metals and irrigation groundwater by toxic Cr(VI), coupled with relatively high Cr(VI) concentrations in water leachates for laterite samples, altered ultramafic rocks and soils neighboring the mining areas and point to a potential human health risk and call for integrated water–soil–plant investigations in the basins surrounding laterite mines.

Physical and chemical soil properties are affected by wildfires. Post-wildfire runoff may contain nutrient loads and particulate matter that negatively impact soil, surface water, and groundwater. According to data from the Copernicus Emergency Management Service, devastating wildfires on Northern Euboea Island, Greece, in August 2021 destroyed more than 50,910 ha. Coniferous and broad-leaved forests mostly covered the affected area, according to CORINE. Topsoil and subsoil samples were collected from burned areas and analyzed for physicochemical parameters: pH, electrical conductivity, and organic carbon. After digestion with aqua regia, the Pb, Zn, Cd, Cu, Mn, Fe, Cr, Ni, Co, and As ‘pseudo total’ contents were determined. Leaching experiments were conducted to evaluate the levels of potentially toxic elements leaching from soils and the impact of environmental conditions. The leachates were analyzed for Pb, Zn, Cd, Cu, Mn, Fe, Cr, Ni, Co, As, Ca, Mg, Na, and K. Overall, most of the concentrations of the studied elements were higher in fire-affected soils than in unburned ones. Similar findings for element concentrations have been confirmed between topsoils and subsoils, with the latter exhibiting lower values. The increased ‘pseudo total’ values of Cr, Ni, Fe, Co, and Mn in all the soil samples, along with the medium to high positive correlations between them, indicate that geogenic factors play a major role in controlling element enrichment. High concentrations of Mn, Ni, and As in soil leachates exceeded the EU maximum permissible limits, indicating a potential ecological risk to natural water quality and, subsequently, to human health. The correlation coefficients between elements in fire-affected and unburned soils suggested that their geogenic origins were mainly associated with the ultramafic rocks and related ores of the study area. The elements’ concentrations in the leachates were significantly lower than their ‘pseudo total’ contents in soil, with no correlation between them. The reducing order of elements leachability did not coincide with the decreasing order of elements ‘pseudo total’ median values in soils. The decreasing order of element abundance in soil leachates coincides with their relative extractability and differs from the decreasing order of their ‘pseudo total’ median values in soils. Neutral to alkaline, soil pH conditions and organic carbon content, which substantially influence the retention and mobility of elements, presented different patterns among the studied elements, with only Mn, Cr, and Co showing correlations. The increased content of organic matter in fire-affected soils suggests that the combustion of vegetation was incomplete.

The Philippi peatland is considered the biggest peat deposit in the Balkan Peninsula and one of the deepest in the world. The purpose of this study was to access the impact of eight potentially toxic elements (PTEs), i.e., As, Se, Pb, Cr, Ni, Zn, Mn and Cu, on the local environment. PTE content was determined in corn grains and surface soil samples collected from 16 sites in the peatland, and pollution indices were calculated to evaluate the environmental risks. Soil organic matter ranged between 93 and 557 g kg⁻¹ soil, whereas the soil pH was >7, classifying the soils as neutral to slightly alkaline. Mean PTE contents in soil samples were 24.6 mg kg⁻¹ soil for As, 1.68 mg kg⁻¹ soil for Se, 113 mg kg⁻¹ soil for Pb, 32 mg kg⁻¹ soil for Cr, 36.3 mg kg⁻¹ soil for Ni, 141.4 mg kg⁻¹ soil for Zn, 35.5 mg kg⁻¹ soil for Cu and 845 mg kg⁻¹ soil for Mn. In corn grain samples, 0.06 mg kg⁻¹ grain for As, 0.14 mg kg⁻¹ grain for Se, 1.34 mg kg⁻¹ grain for Cr, 0.69 mg kg⁻¹ grain for Ni, 27 for Zn, 8.4 mg kg⁻¹ grain for Cu and 3.2 mg kg⁻¹ grain for Mn were recorded. No Pb was detected in the corn grains. The bioaccumulation factor (BF) was high for Cu, Zn and Se, indicating increased mobility of these elements in the soils and preferential plant uptake. For most soil samples, the geoaccumulation index (Igeo) and single pollution index (PI) showed low to moderate contamination. However, Igeo and PI values of Se in many sampling sites and of Pb and Zn in few were substantially increased, pointing to heavily contaminated soils. According to potential ecological risk (RI), the PTE content in the peat soils of Philippi imposes low to moderate risk on the environment.

The occurrence of very-high-grade bauxite ores of karst-type deposits resulting from Fe-leaching is of particular importance, because they are widespread in the Mediterranean metallogenetic province and result in the natural beneficiation of the ore quality. The present study focuses on mineral transformations and variations of major and trace elements, including platinum-group elements (PGE) and mineral chemistry along a bauxite profile from the Parnassos-Ghiona deposit, Greece underlying a fault. The most salient feature of the multicolor ores (grey–whitish, yellowish, deep red, deep grey to brown-red color, from top to bottom) is their association with fossilized and present-day microorganisms, which, by their reducing and/or oxidizing activity, catalyze redox reactions and provide nucleation sites for the precipitation of secondary minerals. Texture relationships between mineral and variations in the mineral chemistry, suggesting the sequence in their formation, indicate a multistage evolution. The recorded compositional variations show that the Al enrichment is accompanied by increase in the TOC, As, Pd and U, and chondrite-normalized REE patterns exhibit a similar trend and positive Ce anomalies. A lower (Pt + Pd) content and higher Pd/Pt ratio, ranging from 1.0 to 5.5 in the bauxite profile compared to those in Fe-Ni laterite deposits with the Pd/Pt ratio ranging from 0.1 to 0.68, reflect the higher solubility and mobility of Pd compared to that of Pt, and differences in their origin and genesis. A positive correlation between Pd and As and the elevated As content (up to 960 mg/kg) in multicolor ores compared to brown-red samples (average 10 mg/kg As) confirms their mobilization and redeposition.