Toxic effects of lead in plants grown in brazilian soils

A Halloysite Nanotubes-based Probe for Efficient Fluorescence Detection and Adsorption Removal of Pb2+ in Water

The detection and removal of Pb2+ is of utmost importance for environmental protection and human health due to its toxicity, persistent pollution, and bioaccumulation effects. To address the limitations associated with organic small molecule-based fluorescence probes such as poor water solubility and single functionality in detecting Pb2+, a fluorescence probe based on halloysite nanotubes was developed. This probe not only enables specific, rapid, and reliable detection of Pb2+ but also facilitates efficient removal of it from water. The development of this bifunctional fluorescent probe provides a valuable insight for designing more advanced probes targeting heavy metal ions.

An analysis of differentially expressed and differentially m6A-modified transcripts in soybean roots treated with lead

Lead is one of the most common toxic heavy metal pollutants in nature, and exposure to lead can cause serious toxicity to many organisms. In this study, we collected root growth data from soybean plants exposed to lead for seven days and confirmed that lead significantly inhibited root growth. We performed a transcriptome-wide m6A methylation analysis to study the response of soybean RNA methylation groups to lead. The m6A modified regions were enriched near the 3'UTR region and stop codon, and m6A methylation was positively correlated with transcript abundance. In the presence of lead, the transcriptome range of m6A RNA methylation peaks increased, and we identified 1144 m6A modification peaks and 1094 differentially expressed genes. The integration of m6A methylation and transcriptomic results enabled us to identify 16 candidate genes whose transcripts were differentially methylated and differentially expressed under lead stress. Annotation results suggest that these genes may promote abiotic stress tolerance by impacting lead uptake, transport, and accumulation through ROS pathways, enzymes, transporters, and hormones. These results provide candidate genes for future studies of lead stress tolerance mechanisms in soybean roots and provide genetic resources for studying plant heavy metal stress in soybean breeding.

Ecological risk threshold for Pb in Chinese soils

Derivation of ecological risk threshold (the threshold concentration value that protect a certain proportion of species within the acceptable hazard level) of lead (Pb) is a yardstick and plays a key role in formulating soil protection policies, while the research about deducing soil Pb ecological risk threshold is still limited. In this study, toxicological data of Pb based on 30 different test endpoints was collected from our experiment and literature, and applied into interspecific extrapolation by species sensitivity distribution (SSD) method to derive the hazard concentration for 5% of species (HC₅, that can protect 95% of species), the prediction models according to different soil properties were established. The results showed that EC₁₀ (the effective concentrations of Pb that inhibit 10% of endpoint bioactivity) ranged from 205.6 to 1596.3 mg kg¹, and hormesis induced by Pb were up to 118%. Toxicity data were corrected by leaching and aging process before SSD curves fitting. HC₅ was then derived and prediction model was developed, as LogHC₅ = 0.134 pH + 0.315 LogOC + 0.324 LogCEC + 1.077. The prediction model was well verified in the field test, indicating that can correctly estimate Pb ecotoxicity thresholds in different soils. This study provides a scientific frame for deriving the ecological risk threshold of Pb and is of great significance for ecological species protection.

Potentially toxic elements in iron mine tailings: Effects of reducing soil pH on available concentrations of toxic elements

Tailings from iron mining are characterized by high concentrations of iron and manganese oxides, as well as high pH values. With these characteristics, most of the potentially toxic elements (PTE) contained in the tailings are somewhat unavailable. The aim of the present study was to evaluate how a reduction in the pH of iron mine tailings may affect PTE availabilities. The tailings were collected on the banks of the Gualaxo do Norte River (Mariana, MG, Brazil), one of the main areas impacted by the rupture of the Fundão Dam (Barragem de Fundão). A completely randomized experimental design was used, including five pH values (6.4, 5.4, 4.3, 3.7, and 3.4) and five replications. The concentrations of the PTE (Ba, Cr, Cd, Co, Cu, Fe, Mn, Pb, Ni, and Zn) were determined after extraction following different methodologies: USEPA 3051A, DTPA, Mehlich-1, Mehlich-3, and distilled water. A comparison of the available concentrations of the elements in the tailings with those in a soil not impacted by tailings shows that Cr, Cd, Cu, Fe, Mn, Ni, Ba, and Co were higher in the soil impacted by the tailings. The different methods used for evaluating the availability of PTE in the tailings at various pH exhibited the following decreasing order in relation to the quantity extracted: Mehlich-3 > Mehlich-1 > DTPA > distilled water. However, regarding sensitivity to change in pH, the order was DTPA > water > Mehlich-1 > Mehlich-3. The increases in the concentrations of PTE due to the reduction in the pH of the tailings did not lead to concentrations that exceed the limits of Brazilian regulations. The DTPA extractant exhibited higher coefficients of correlation between the PTE concentrations and the pH of the tailings, proving to be suitable for use in areas affected by the deposition of iron mine tailings.

Chronic effects of clothianidin to non-target soil invertebrates: Ecological risk assessment using the species sensitivity distribution (SSD) approach

This study aimed to assess the chronic toxicity and risk of clothianidin in a seed dressing formulation to non-target soil invertebrates. The toxicity assays were performed with two oligochaetes (earthworms Eisenia andrei and enchytraeids Enchytraeus crypticus) and three collembolans (Folsomia candida, Proisotoma minuta and Sinella curviseta) species following ISO protocols. Risk assessment (via Hazard Quotient approach - HQ) was based on the hazardous concentrations for 95% of the species (HC₅), derived from chronic Species Sensitivity Distributions (SSD) for clothianidin, and on its predicted environmental concentrations (PEC). Four SSD scenarios were generated with literature and/or this study data, following different data selection criteria (i.e., general, only data from tests using similar formulations, similar soils, or identical soil/formulation). In our experiments, a higher clothianidin toxicity (EC₅₀-based) was found for collembolans (varying from 0.11 to 0.28 mg kg^-1 between species) followed by the earthworms (4.35 mg kg^-1), while the enchytraeids were the least sensitive (33.5 mg kg^-1). HQ indicated a significant risk of clothianidin to soil invertebrates because the estimated PEC were at least 16.6 times higher than HC₅ and are expected to affect the whole group of collembolans. Despite the criteria for data inclusion have influenced the HC₅ values, no substantial changes were observed for the risk outcomes. To our knowledge, this is the first study assessing the chronic ecological risk of clothianidin to beneficial soil fauna based on a probabilistic SSD approach. Data from this study can help to derive more reliable protection thresholds for clothianidin in soils.

Steel mill waste application in soil: dynamics of potentially toxic elements in rice and health risk perspectives

Potentially toxic elements (PTEs) are of great concern in steel mill wastes. Therefore, in order to use them as potential fertilizers in soil, risk assessments are needed. Three steel mill wastes were tested as possible amendments for soils at seven different doses (0, 0.5, 1, 2, 4, 8, 16 t ha^-1): phosphate mud (PM), metallurgical press residue (MPR), and filter press mud (FPM) during rice cultivation in a pot experiment in a Haplic Gleisol. Analysis on rice tissues, including roots, shoots, husk, and grains, were conducted and contents of Cu, Cd, Ni, Zn, Mn, and Pb were assessed. Translocation and bioaccumulation factors were calculated for each element. In general, PTEs are more accumulated in roots and greater contents of Zn and Mn were found, while the lowest ones were found for Pb, probably due to its lack of functional roles during plants development. Higher translocation was observed for Mn, which is associated to the redox conditions of rice cultivation and the high mobility of this element under this condition. Application of steel mill wastes can increase PTE bioavailability and translocation factors, especially PM, but all of the wastes reveal a high hazard index.

Lead acetate ecotoxicity in tropical soils

Lead acetate (AcPb) is an important raw material used in chemical industries worldwide. The potential toxicity of AcPb is generally attributed to the presence of Pb. However, the effect of AcPb on the environment as a whole is still poorly known. This study aimed to evaluate AcPb toxicity on three standard species of soil invertebrates and two plant species using ecotoxicology tests. Three tropical soils (Oxisol, Inceptisol, and Tropical Artificial Soil (TAS)) were contaminated with different concentrations of AcPb and one dose of K-acetate (positive control). These soils were used in tests with Eisenia andrei (earthworm), Folsomia candida (springtail), Enchytraeus crypticus (enchytraeid), Zea mays (maize), and Phaseolus vulgaris (common bean). Dose-response curves obtained in the laboratory tests were used to estimate the EC₅₀ values for each species. Among invertebrates, the highest sensitivity to AcPb was observed for E. crypticus in the TAS (EC₅₀ = 29.8 mg AcPb kg^-1), whereas for E. andrei and F. candida the highest sensitivity was observed in the Oxisol (EC₅₀ = 141.9 and 1835 mg AcPb kg^-1, respectively). Folsomia candida was the least sensitive invertebrate species to AcPb in all soils. Among plant species, Z. mays was less sensitive (EC₅₀ = 1527.5 mg AcPb kg^-1) than P. vulgaris (EC₅₀ = 560.5 mg AcPb kg^-1) in the Oxisol. The present study evidenced that the toxicity of AcPb should not be attributed uniquely to the presence of Pb, as the treatment containing uniquely Ac provoked the same toxicity as the highest dose of AcPb.

Hygienic quality of soil in the Gemer region (Slovakia) and the impact of risk elements contamination on cultivated agricultural products

The Gemer region (Slovakia) belongs to areas with a high concentration of risk elements. The contents of Cu, Ni, Pb, Cd, Hg and Mn were determined in soils and cultivated agricultural production from lands in three cadastres of the Gemer region (Henckovce (48.713845, 20.426189) and Nižná Slaná (48.717373, 20.4208423), cultivated crop—spring triticale; Gemerská Poloma (48.704523, 20.487645), cultivated crop—maize). Bioavailable forms of Pb (0.306–0.532 mg/kg) and Cd (0.104–0.154 mg/kg), pseudototal forms of Cd (3.07–3.98 mg/kg) and Hg (0.484–2.18 mg/kg) represented the highest risk in soils. The highest contents of Pb (Cd, Hg) were in maize from Gemerská Poloma: 0.898 (0.081, 0.399) mg/kg DM. Soils were classified based on several indicators of soil contamination. The highest values of indicators are: Contamination factor (C_f 29.1—Hg), Degree of contamination (C_deg 51.5), Potential ecological risk factor (E_r 1163—Hg), Potential ecological risk index (RI 1,520), Pollution load index (PLI 4.76), Geo-accumulation index (I_geo 5.60—Hg). All indicators concerned the lands of Henckovce and Gemerská Poloma, RI also concerned the land of Nižná Slaná. Bioaccumulation factor (BAF) was calculated to assess the plant's ability to absorb the risk element. For both crops and all risk elements, BAF values were < 1. Obtained results indicate heavy metal contamination of soils, therefore monitoring of soils in investigated area is necessary.

Steel mill waste effects on rice growth: comparison of chemical extractants on lead and zinc availability

Zinc deficiency is widespread in cultivated soils, limiting the grain crop production and the adequate human nutrition. Several wastes from metallurgical activity can be used as Zn source, but these materials generally also have other potentially toxic elements, such as Pb, that can be highly toxic for plants and humans. This study aimed to evaluate the efficiency of five chemical extractors (water, citric acid, DTPA, Mehlich 1, and USEPA 3051A) in better correlating with the bioavailable contents of Zn and Pb in soils treated with steel mill wastes (metallurgic press residue (MPR), filter press mud (FPM), and phosphate mud (PM)). Rice plants were cultivated in pots with 4 kg of a Haplic Eutrophic Gleisol and steel mill wastes were applied in soil at increasing doses (0, 0.5, 1, 2, 4, 8, and 16 t ha^-1). The availability of the potentially toxic elements Zn and Pb was assessed as total contents in rice shoots, grains, husks, and roots. The results showed that the USEPA 3051A method extracted greater contents of Zn and Pb from soil compared with other extractants. Due to their greater natural Pb and Zn contents, MPR and PM promoted higher contents of these elements in soils, respectively. Doses of PM influenced Zn contents in grains. After adding 16 t ha^-1 of PM, Zn content in rice grains was 0.1 mg kg^-1. However, at doses 0.5, 1, 2, and 4 t ha^-1, the average concentration of Zn in the grains was 40 mg kg^-1. The wastes MPR and FPM at 16 t ha^-1 promoted Zn concentration in grains of 42 and 45 mg kg^-1, respectively. The greatest contents of Pb in grains were found after addition of FPM at doses 0.5, 1, and 2 t ha^-1: 6.67, 4.96, and 0.45 mg kg^-1, respectively, and above 4 t ha^-1 (4, 8, and 16 t ha^-1); Pb content in grains was less than 0.3 mg kg^-1. The content of Pb in roots at 16 t ha^-1 of PM, MPR, and FPM was 18, 25, and 155 mg kg^-1, respectively, and for Zn, under the same conditions, 100, 255, and 813 mg kg^-1 for MPR, FPM, and PM, respectively. USEPA 3051A can be used to assess Pb and Zn available contents, and positive correlations with bioavailable contents of these elements in roots prove its feasibility. Further studies are necessary to state the safety of using steel mill application, including the use of other crop species, but PM is a promising waste for soil Zn fertilization.

Biosolid compost with wood shavings and yard trimmings alleviates stress and improves grain quality in soybean grown in lead polluted soils

Heavy metals induce stress in plants, thereby affecting growth, crop quality, and food security. Most studies addressing the mitigation of these effects by soil amendment have focused on metals in soils and plant uptake, with there still being a great deal of uncertainty about how amendment application in polluted soils can modify plant stress response and, consequently, yield and food safety. Thus, the aim of this study was to evaluate the effect of biosolid compost amendment on stress response, growth, and lead accumulation in Glycine max, when applied to lead polluted agricultural soils. Soybean was grown in lead polluted soils with 0%, 5%, or 10% (w/w) biosolid compost amendment under controlled conditions in a greenhouse, and the stress response indicators chlorophylls, proteins, sugars, malondialdehyde, glutathione S-transferase activity, carotenes, and the ferric reducing antioxidant power were investigated. In addition, the biomass and lead accumulation in different organs were determined and evaluated with respect to the plant stress. Our results revealed that the addition of 10% biosolid compost improved the grain biomass and appeared to reduce the amount of defective grains, which was related to higher Pb concentrations. Furthermore, 10% compost treatment reduced the stress in plants, leading to a better performance of the photosynthetic system, and with the antioxidant response being positively correlated to Pb accumulation. Lead uptake in plants was decreased by between 35 and 57% after this treatment in comparison with unamended soils. These results indicate that biosolid compost amendment may be an effective way to alleviate Pb uptake and metal stress in soybeans.