The accumulation of elements in plants growing spontaneously on small heaps left by the historical Zn-Pb ore mining

Potentially harmful elements pollute soil and vegetation around the Atrevida mine (Tarragona, NE Spain)

Mining activity is one of the main sources to pollute soil, water and plants. An analysis of soil and plant samples around the Atrevida mining area in Catalonia (NE Spain) was preformed to determine potentially harmful elements (PHEs). Soil and plant samples were taken at eight locations around the mining area. The topsoil (0-15 cm) samples were analysed for physico-chemical properties by standard methods, by ICP-MS for Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn, and were microwave-digested. Plant, root and shoot samples were digested separately, and heavy metals were analysed by AAS. Translocation factor (TF), biological concentration factor (BCF) and biological accumulation factor (BAF) were determined to assess the tolerance strategies developed by native species and to evaluate their potential for phytoremediation purposes. Soil pH was generally acid (5.48-6.72), with high soil organic matter (SOM) content and a sandy loamy or loamy texture. According to the agricultural soil values in southern Europe, our PHEs concentrations exceeded the toxicity thresholds. The highest root content of the most studied PHEs appeared in Thymus vulgaris L. and Festuca ovina L., while Biscutella laevigata L. accumulated more PHEs in shoots. The TF values were > 1 in B. laevigata L., but BAF obtained < 1, except Pb. B. laevigata L., and can be considered potentially useful for phytoremediation for having the capacity to restrict the accumulation of large PHEs amounts in roots and Pb translocation to shoots.

The diversity of iron acquisition strategies of calcifuge plant species from dry acidic grasslands

Although the calcifuge plant species existing in dry acidic grasslands are believed to be prone to iron (Fe)-dependent limitations, little is known about their susceptibility and reaction to pH-dependent Fe starvation. Therefore, the present study examines the effects of contrasting soils (acidic Podzol vs alkaline Rendzina) and Fe supplementation (Fe-HBED) on alkaline substratum (5 and 25 μmol Fe-HBED kg^-1 soil). Five calcifuge dicotyledonous plant species (Alyssum montanum L., Antennaria dioica (L.) Gaertn., Hypochaeris radicata L., Jasione montana L. and Potentilla arenaria Borkh.) were tested in a pot experiment under field conditions. Chlorosis, chlorophyll content, growth and chlorophyll a fluorescence were measured. The elemental composition (contents of Ca, Mg, Fe, Mn, Zn and Cu) of the roots and shoots were analyzed, as well as their specialized metabolites. Two studied species (A. dioica d and J. montana) were susceptible to pH-dependent chlorosis, and this deficiency was successfully diminished by the application of Fe-HBED. Almost all the studied species (except A. montanum) preferred the acidic soil. Fe-HBED treatments were not sufficient for supporting the growth of H. radicata and J. montana in alkaline soil to the same degree as in acidic soil, which suggests additional non-Fe-dependent limitations. Both Fe starvation and Fe over-supplementation caused species-specific changes in chlorophyll a fluorescence. The disturbed Fe acquisition in the alkaline soil was not the sole source of the observed limitations, as the chlorosis-susceptible species demonstrated a complex interaction between Fe, Mn and Zn. The species resistant to lime chlorosis contained greater amounts of specialized metabolites than the susceptible plants. Our findings do not support hypothesis that all calcifuges are susceptible to Fe-dependent chlorosis: calcifuge plant species from dry acidic grasslands appear to have diverse Fe requirements and acquisition strategies.

Tolerance and Heavy Metal Accumulation Characteristics of Sasa argenteostriata (Regel) E.G. Camus under Zinc Single Stress and Combined Lead–Zinc Stress

Sasa argenteostriata (Regel) E.G. Camus is a gramineous plant with the potential for phytoremediation. In this study, we aimed to determine its tolerance to zinc stress and combined lead–zinc stress and the effect of zinc on its absorption and accumulation characteristics of lead. The results showed that S. argenteostriata had good tolerance to zinc stress, and S. argenteostriata was not significantly damaged when the zinc stress concentration was 600 mg/L. Under both zinc stress and combined lead–zinc stress, the root was the main organ that accumulated heavy metals in S. argenteostriata. The presence of zinc promoted the absorption of lead by the root of S. argenteostriata, and the lead content in the root under PZ1, PZ2, PZ3 and PZ4 treatments was 2.15, 4.31, 4.47 and 6.01 times that of PZ0 on the 20 days. In the combined lead–zinc stress treatments, the toxicity of heavy metals to S. argenteostriata was mainly caused by lead. Under high concentrations of combined lead–zinc stress (PZ4), the proportion of zinc in the leaf of S. argenteostriata on the 20 days increased, which was used as a tolerance strategy to alleviate the toxicity of lead.

Vegetation and Environmental Changes on Contaminated Soil Formed on Waste from an Historic Zn-Pb Ore-Washing Plant

Simple Summary

Remnants of former Zn-Pb mining in southern Poland are an important element of geographical space. Some of the post-mining areas have found new economic and residential functions. Many of them are undergoing ecological succession and constitute valuable natural habitats enriching biodiversity of the surrounding landscapes. There are places where we can observe and document various ecological and geochemical transformations in its historical and contemporary aspects. These changes provide a basis for observing and functioning of ecosystems developing in an area transformed under the influence of Zn-Pb mining.

Abstract

Post-mining waste from Zn-Pb ore exploitation undergoes processes of spontaneous succession and changes in soil chemical composition. The Zakawie area was industrially transformed by historical mining activity, ore enrichment, and the metallurgical processing of Zn-Pb ore. The subject of the study was to analyse the rate of vegetation succession (from 1999 to 2019), soil chemistry, and the relationships between them in an anthropogenic habitat with high concentrations of potentially toxic metals. Ecological and geochemical studies were carried out in an area contaminated with waste from a disused Zn-Pb ore-washing plant. Between 1999 and 2019, the transformation of grassland and meadow vegetation into scrub and forest–grassland communities was observed. This transformation led to a decrease in the area of Molinietum caeruleae meadow (from 25.8% in 1999 to 10.7% in 2019), whose place was taken by Prunus spinosa and Rhamnus cathartica. The community of xerothermic limestone grasslands completely disappeared, being replaced in favour of the Diantho-Armerietum and Prunus spinosa community. In this period, the share of lifeforms of plants and species composition (46 and 60, respectively) also changed. The Shannon and Simpson biodiversity index reached high values in the second investigation period, and it was 0.893 and 0.86, respectively. The anthrosols had a high content of Zn—85,360 mg kg⁻¹, Pb—28,300 mg kg⁻¹, Cd—340 mg kg⁻¹, and As—1200 mg kg⁻¹. Carbonates, clay minerals, and fe-oxides are predominant in the mineral composition of the rhizosphere; the metal-bearing phases are stable; and hardly soluble minerals include smithsonite, cerussite, monheimite, hemimorphite, and oxides of Fe and Fe-Mn. Mineralisation/crust processes formed on the epidermis, and their influences on root development were found. Scanning electron microscopy and energy-dispersive X-ray spectroscopy studies on rhizosphere soil components provide information on the type of minerals and their susceptibility to heavy metals release. The identification of some biotic and mineral structures in rhizospheres can be an interesting source of information on pedogenic processes identified in back-scattered electron images.

Saponaria officinalis L. and Achillea millefolium L. as possible indicators of trace elements pollution caused by mining and metallurgical activities in Bor, Serbia

This study evaluates bioaccumulation and translocation potentials of trace elements (TEs) by Saponaria officinalis L. (soapwort) and Achillea millefolium L. (yarrow) in order to select and optimize phytoremediation methods for the polluted environment of the city of Bor, Serbia. According to the enrichment factor for soil (i.e., 57.9-128.8 for Cd and As), pollution index (i.e., 6.6-84.7 for Cu), pollution load index (2.9-98.8), individual potential risk factors (11.5-5163), and potential ecological risk index values (260-6379), urban and rural soils from the city of Bor were classified as very contaminated with the investigated TEs. The results from all the indices and statistical analysis showed significant ecological risks of Cu, As, and Cd at the investigated sites and urge the need for remediation. The enrichment factor of the plants for As (566.3) and Cd (306.2) indicated a high enrichment level of the herb organs at all the sites. Since there are small differences in metal accumulation index values between the herbs and their parts (root, shoot), soapwort and yarrow can be considered as potential bioindicators. Based on the biological concentration and translocation factors, soapwort can be recommended as a suitable herb for phytoextraction purposes of Pb, As, and Cd polluted areas. Yarrow shows good characteristics for phytoextraction of Cu, Pb, and As from the contaminated soil. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) results indicate their similar origin from atmospheric deposition. Therefore, these herbs can be utilized as a bioindicator and phytoremediator in polluted areas influenced by metallurgical activities to detect possible levels of TEs.

Activity and Diversity of Microorganisms in Root Zone of Plant Species Spontaneously Inhabiting Smelter Waste Piles

The aim was to assess plant driven changes in the activity and diversity of microorganisms in the top layer of the zinc and lead smelter waste piles. The study sites comprised two types (flotation waste—FW and slag waste—SW) of smelter waste deposits in Piekary Slaskie, Poland. Cadmium, zinc, lead, and arsenic contents in these technosols were extremely high. The root zone of 8 spontaneous plant species (FW—Thymus serpyllum, Silene vulgaris, Solidago virgaurea, Echium vulgare, and Rumex acetosa; and SW—Verbascum thapsus; Solidago gigantea, Eupatorium cannabinum) and barren areas of each waste deposit were sampled. We observed a significant difference in microbial characteristics attributed to different plant species. The enzymatic activity was mostly driven by plant-microbial interactions and it was significantly greater in soil affected by plants than in bulk soil. Furthermore, as it was revealed by BIOLOG Ecoplate analysis, microorganisms inhabiting barren areas of the waste piles rely on significantly different sources of carbon than those found in the zone affected by spontaneous plants. Among phyla, Actinobacteriota were the most abundant, contributing to at least 25% of the total abundance. Bacteria belonging to Blastococcus genera were the most abundant with the substantial contribution of Nocardioides and Pseudonocardia, especially in the root zone. The contribution of unclassified bacteria was high—up to 38% of the total abundance. This demonstrates the unique character of bacterial communities in the smelter waste.

Metal Homeostasis and Gas Exchange Dynamics in Pisum sativum L. Exposed to Cerium Oxide Nanoparticles

Cerium dioxide nanoparticles are pollutants of emerging concern. They are rarely immobilized in the environment. This study extends our work on Pisum sativum L. as a model plant, cultivated worldwide, and is well suited for investigating additive interactions induced by nanoceria. Hydroponic cultivation, which prompts accurate plant growth control and three levels of CeO2 supplementation, were applied, namely, 100, 200, and 500 mg (Ce)/L. Phytotoxicity was estimated by fresh weights and photosynthesis parameters. Additionally, Ce, Cu, Zn, Mn, Fe, Ca, and Mg contents were analyzed by high-resolution continuum source atomic absorption and inductively coupled plasma optical emission techniques. Analysis of variance has proved that CeO2 nanoparticles affected metals uptake. In the roots, it decreased for Cu, Zn, Mn, Fe, and Mg, while a reversed process was observed for Ca. The latter is absorbed more intensively, but translocation to above-ground parts is hampered. At the same time, nanoparticulate CeO2 reduced Cu, Zn, Mn, Fe, and Ca accumulation in pea shoots. The lowest Ce concentration boosted the photosynthesis rate, while the remaining treatments did not induce significant changes. Plant growth stimulation was observed only for the 100 mg/L. To our knowledge, this is the first study that demonstrates the effect of nanoceria on photosynthesis-related parameters in peas.

Metal Mobility in Afforested Sites of an Abandoned Zn-Pb Ore Mining Area

Heaps of waste material constitute a serious environmental problem in regions where the historical exploitation and processing of metal ores has taken place. The presented paper describes the trace metal distribution in selected heaps in the lead-zinc mining area of an abandoned mine in Poland, as well as the soil horizons beneath. The study aims at the estimation of the metal remobilization rate in vertical profiles in the spontaneously afforested area in the context of the potential danger it poses to the local groundwater. Individual samples were taken from profiles dug in heaps found in deciduous and coniferous forests. The bulk density, pH, organic matter and carbonate content, as well as the concentration and chemical forms of metals were analysed. Buffer properties and the mineralogical composition were also determined for the selected samples. The investigation indicates excessive cadmium, zinc and lead concentrations in the analysed heap material and the significant secondary enrichment of former soil horizons. A large percentage of these metals occur in potentially mobile forms. It suggests that, despite the high pH of the heap material and the good buffer properties of soil, cadmium and to a lesser extent, zinc, has migrated downwards to depths of at least several dozen centimetres over a period of about 200 years. This is related to soil acidity, particularly in profiles abundant in organic matter resulting from the encroachment of forest communities, particularly of coniferous forest. Spontaneous afforestation forming the litter cover contribute to the stabilization of the heap material and limiting groundwater pollution. Even though specific remediation measures are not needed in this area, it requires long-term monitoring.

Assessment of the Quality of Polluted Areas in Northwest Romania Based on the Content of Elements in Different Organs of Grapevine (Vitis vinifera L.)

The purpose of this study was to evaluate the environmental quality of polluted areas near the Baia Mare Mining and Smelting Complex for future improvements the quality of the environment in polluted areas, such as the city of Baia Mare and its surroundings. Samples of soil and organs of grapevine (Vitis vinifera L.) were collected from Baia Mare, Baia Sprie and surrounding areas (Simleul Silvaniei) and their content of Cu, Zn, Pb, Cd, Ni, Co, As, Cr, Hg were analyzed. Most soil and plant samples showed higher metal concentrations in Baia Mare and Baia Sprie areas compared to Simleul Silvaniei, exceeding the normal values. The results obtained from the translocation factors, mobility ratio, as well as from Pearson correlation study confirmed that very useful information is recorded in plant organs: root, canes, leaves and fruit. Results also indicated that Vitis vinifera L. has some highly effective strategies to tolerate heavy metal-induced stress, may also be useful as a vegetation protection barrier from considerable atmospheric pollution. At the same time, berries are safe for consumption to a large degree, which is a great advantage of this species.

Soil organic matter prevails over heavy metal pollution and vegetation as a factor shaping soil microbial communities at historical Zn-Pb mining sites

This study examined the effects of soil heavy metals, macronutrients, texture and pH as well as plant species richness and composition on soil respiration, enzymatic activity, microbial biomass, metabolic quotient (qCO₂) and arbuscular mycorrhizal fungi (AMF) at sites of historical Zn-Pb mining. The study was conducted both on a large scale (65 heaps scattered over the area of 750 km²) and on a small scale (25 plots along two 48 m transects extending from heaps to adjacent fallow fields). Total concentrations of metals exceeded 400 (Cd), 20,000 (Pb) and 80,000 (Zn) mg kg^-1 at the most polluted sites. Although they decreased along the heap-fallow direction, they still remained above environmental standards in fallow soils. In contrast, some soluble metal forms increased with the increasing distance from heaps. Soil organic matter had the strongest positive effect on most microbial parameters. Total and/or available heavy metals exhibited significant negative effects on microbial biomass, enzymatic activity and AMF, and a positive effect on qCO₂. Organic matter alleviated negative effects of heavy metals on microorganisms; they were not observed where the increase in the contamination was accompanied by the increase in organic matter content. Plant species richness affected positively enzymatic activity and mycorrhization level. Plant species composition possibly contributed to the formation of soil microbial communities, but its effect was entangled in that of heavy metals as plant communities changed along pollution gradients (from metal-tolerant grasslands dominated by Festuca ovina to calcareous grasslands and ruderal communities at less polluted sites).

Solidago canadensis as a bioaccumulator and phytoremediator of Pb and Zn

Canadian goldenrod (Solidago canadensis L.) is a plant that grows in a variety of environmental conditions. It shows high capability to spread in various habitats, including fallow lands and brownfield land. The research aimed at analyzing the content of Pb and Zn in the underground (roots, rhizomes) and aboveground parts (stems, leaves, inflorences) of Solidago canadensis (SC) originating from two locations that are clearly different in terms of metal content in soil. Statistically significant differences were determined in the content of Pb and Zn in soil and particular morphological parts of the plant, depending on the sampling location. It has been shown that in the conditions of increased (compared with natural) Pb and Zn content in the soil, SC may serve as a bioaccumulator of these metals. It was determined that SC can be used as a phytostabilizer of Pb and Zn in soils heavily contaminated with these elements. The content of Zn in the aboveground parts of SC indicates that this plant can also be used for phytoextraction of soils contaminated with this metal.

Dual Role of Metallic Trace Elements in Stress Biology-From Negative to Beneficial Impact on Plants

Heavy metals are an interesting group of trace elements (TEs). Some of them are minutely required for normal plant growth and development, while others have unknown biological actions. They may cause injury when they are applied in an elevated concentration, regardless of the importance for the plant functioning. On the other hand, their application may help to alleviate various abiotic stresses. In this review, both the deleterious and beneficial effects of metallic trace elements from their uptake by roots and leaves, through toxicity, up to the regulation of physiological and molecular mechanisms that are associated with plant protection against stress conditions have been briefly discussed. We have highlighted the involvement of metallic ions in mitigating oxidative stress by the activation of various antioxidant enzymes and emphasized the phenomenon of low-dose stimulation that is caused by non-essential, potentially poisonous elements called hormesis, which is recently one of the most studied issues. Finally, we have described the evolutionary consequences of long-term exposure to metallic elements, resulting in the development of unique assemblages of vegetation, classified as metallophytes, which constitute excellent model systems for research on metal accumulation and tolerance. Taken together, the paper can provide a novel insight into the toxicity concept, since both dose- and genotype-dependent response to the presence of metallic trace elements has been comprehensively explained.

Differential Metal Tolerance and Accumulation Patterns of Cd, Cu, Pb and Zn in the Liverwort Marchantia polymorpha L

In this study, we investigated the bioaccumulation, tissue distribution and physiological responses to different metal concentration (0.2 and 2 mM) and time of exposure of 1, 2 and 3 weeks with cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) using the model liverwort Marchantia polymorpha. Our data showed, on one hand, a significant enrichment and tissue translocation of Cu, Zn, and specially Cd, reaching concentrations of 1800 µg g^- 1 in 3 weeks. On the other hand, Pb exhibited the lowest concentration values (50 µg g^- 1), and 90% of the total concentration in the rhizoids. We could observe a positive correlation between tissue concentration, metal translocation and an enhanced toxic response. The results obtained in this study might contribute not only in the application of this species in environmental studies with heavy metals but also as a starting point to study the evolution of metal tolerance in land plants.

Use of native aquatic macrophytes in the reduction of organic matter from dairy effluents

Considering the diversity and the unexplored potential of regional aquatic flora, this study aimed to identify and analyze the potential of native aquatic macrophytes to reduce the organic matter of dairy wastewater (DW) using experimental constructed wetlands. The dairy wastewater (DW) had an average chemical oxygen demand (COD) of 7414.63 mg/L and then was diluted to 3133.16 mg/L (D1) and to 2506.53 mg/L (D2). Total solids, COD, temperature, and pH analyses were performed, and the biochemical oxygen demand (BOD) was estimated from the COD values. The best performance in the reduction of the organic matter was observed for Polygonum sp. (87.5% COD and 79.6% BOD) and Eichhornia paniculata (90% COD and 83.7% BOD) at dilution D1, on the 8th day of the experiment. However, the highest total solids removal was observed for Polygonum sp. (32.2%), on the 4th day, at dilution D2. The total solid (TS) concentration has also increased starting from the 8th day of the experiment was observed which may have been due to the development of mosquito larvae and their mechanical removal by sieving, thus changing the steady state of the experimental systems. The macrophytes Polygonum sp. and E. paniculata were considered suitable for the reduction of organic matter of DW using constructed wetlands.

Effect of lead on physiological and antioxidant responses in two Vigna unguiculata cultivars differing in Pb-accumulation

Lead (Pb) is one of the most toxic anthropogenic pollutants, occurring widely in both terrestrial and aquatic ecosystems, where it impairs plant growth and development. In this work, the effect of 0.5 mM EDTA-Pb was evaluated in two Vigna unguiculata cultivars (SV and SET), with the aim of detecting genotype/cultivar dependent changes in the physiological and anti-oxidant responses (CAT and APX) of a leguminous plant. The data showed that SV accumulated more Pb in roots while SET accumulated more in leaves, indicating differential regulation in Pb-translocation/accumulation. Lead affected the growth of SV less severely than SET, mainly associated with reduced inhibition in photosynthetic parameters. Furthermore, CAT and APX activities increased or were sustained at elevated levels in both cultivars in response to lead. However, gene expression analyses revealed that CAT1 was the main lead responsive gene in SET while CAT2 was more responsive in SV. APX1 was higher expressed in tissues with higher Pb-accumulation while APX2 was ubiquitously responsive to lead in both cultivars. Taken together, these results reveal differential ability of V. unguiculata cultivars in Pb-accumulation in different tissues affecting distinctly physiological and anti-oxidant responses. In addition, the existence of cultivars with predominant Pb-accumulation in aerial tissues invokes a need for studies to identify pollution-safe cultivars of leguminous plants to ensure food safety.