Bioavailability In Soil Research Articles

Effects of biochar on the dynamic immobilization of Cd and Cu and rice accumulation in soils with different acidity levels

The aim of this study was to investigate the effect of biochar on Cd and Cu immobilization and bioavailability in soils with different acidity levels. Four dosages (0, 20, 40 and 60 g kg−1; namely CK, C1, C2 and C3) of biochar produced from rice straw were applied into the soils with four acidity levels (pH 4.5, 5.0, 5.5 and 6.0; namely L1, L2, L3 and L4), the uptake and transport of Cd and Cu by rice and metal speciation dynamics in soil were investigated through the two-year pot experiment. The soil pH and organic matter under all the four acidity levels were significantly increased during the rice maturity stage in the second year after biochar application. Biochar mainly promoted the formation of oxidizable Cd, followed by reducible Cd, and decreased residual Cd content (except for the first-year in the jointing period) during the two consecutive years of rice growth. Biochar reduced the acid extractable Cu content (especially in L2 and L3), increased the oxidizable Cu content, and interconverted Cu between reducible and residual status. The content of Cd in different rice organs were reduced by biochar, and compared with CK, the two-year average reduction in brown rice was 38.12%, 58.07%, 50.99% and 36.45% under L1, L2, L3 and L4. The reduction effect of Cu content in brown rice by biochar was mainly reflected in the second year, which decreased by 17.52%, 20.17%, 20.63% and 9.74% respectively under the four acidity levels. Rice straw biochar can be used for Cd pollution control of rice grain in paddy soil with varied acidity levels. However, further studies are needed on how biochar promotes Cu transport from rice root to shoot.

Evaluation of Silicon Bioavailability in Soil with Different Chemical Extractants

Evaluation of Silicon Bioavailability in Soil with Different Chemical Extractants

Reduction of cadmium bioavailability in paddy soil and its accumulation in brown rice by FeCl3 washing combined with biochar: A field study

Cadmium (Cd) removal from paddy soil to reduce Cd accumulation in brown rice is essential for agroecology, food safety, and human health. In this study, we demonstrate that ferric chloride (FeCl3) washing combined with biochar treatment efficiently remediates Cd-contaminated paddy soil in field trials. Our results showed that 30.9 % of total Cd and 41.6 % of bioavailable Cd were removed by the addition of 0.03 M FeCl3 at a liquid/soil ratio of 1.5:1. The subsequent addition of 1 % biochar further reduced bioavailable Cd by 36.5 and 41.5 %, compared with FeCl3 washing or biochar treatment alone. The principal component regression analysis showed that the Cd content in brown rice was primarily affected by the bioavailable Cd in soil. The combined remediation contributed to the decreased Cd contents in brown rice by 45.5–62.5 %, as well as a 2.7–11.8 % increase in rice yield. The Cd contents in brown rice decreased to 0.12 and 0.04 mg kg−1 in two cultivars of rice (Zhuliangyou189 and Zhuliangyou929), lower than the national food safety standard limit value of China (0.2 mg kg−1). Meanwhile, the combined remediation promoted the restoration of soil pH and organic matter as well as the improvement of available nutrients. This finding suggests that the combination of FeCl3 washing and biochar is an effective remediation strategy to minimize Cd bioavailability in paddy soil, and improves soil quality, thus contributing to food safety.

The immobilization, plant uptake and translocation of cadmium in a soil-pakchoi (Brassica chinensis L.) system amended with various sugarcane bagasse-based materials

Many organic materials have been used to decrease heavy-metal bioavailability in soil via in-situ remediation due to its high efficiency and easy operation; meanwhile, cheap materials have also been pursued to decrease the cost of remediation. Agricultural wastes exhibit their potential in remediation materials due to their low cost; however, raw agricultural wastes have a low ability to immobilize heavy metals in soil. Attempts have been made to modify agricultural wastes to improve the efficiency of heavy-metal passivation. In this study, novel agricultural waste-based materials, raw sugarcane bagasse (SB), citric acid modified (SSB) and citric-acid/Fe3O4 modified (MSB) sugarcane bagasse at 0.5% and 1% addition rates, were compared for their effectiveness in soil Cd passivation and Cd accumulations in pakchoi plants in a 30-day pot experiment. The addition of SB did not decrease soil bioavailable Cd effectively and slightly decreased Cd accumulation in plant roots and leaves. In comparison, SSB and MSB exhibited a great potential to decrease the transformation, translocation and accumulation of Cd with the decrease being greater at 1% than 0.5% rate in the soil-pakchoi system. For example, the addition of SSB and MSB at 0.5% decreased the concentration of Cd in leaves by 10%, and 16%, and at 1% decreased the concentration by 25% and 30%, respectively. High pH and abundant functional groups of three amendments played important roles in Cd immobilization. The enhanced microbial activities might also contribute to Cd passivation. However, plant growth was decreased in the amended treatments except SSB at 0.5% rate. The results suggest that citric-acid-modified sugarcane bagasse at addition rate of 0.5% has a potential to immobilize Cd in soil and decrease Cd accumulation in edible part of pakchoi effectively without decreasing vegetable growth.

Combined apatite, biochar, and organic fertilizer application for heavy metal co-contaminated soil remediation reduces heavy metal transport and alters soil microbial community structure

Soil amendments are used extensively to remediate soils contaminated with heavy metals. However, the effects of soil amendments on heavy metal bioavailability, plant yield, and bacterial community structure in tropical farmland soils remain largely unknown. In the present study, seaweed organic fertilizer (S), apatite (A), biochar (B), and seaweed organic fertilizer-apatite-biochar mixtures (SAB) were applied at different rates to assess their influence on cadmium (Cd), lead (Pb), and chromium (Cr) bioavailability in contaminated farmland soils, using different component ratios and doses in maize field plots, and maize yield. Effects on soil bacterial community structure were also evaluated based on high-throughput sequencing. Following addition of 2 % S + A + B combined amendment at a ratio of 1:0.5:1.5 (2%S1A0.5B1.5), soil pH and electrical conductivity (EC) were elevated, and bioavailable Cd, Pb, and Cr concentrations were reduced in potted soils, leading to higher heavy metal immobilization. Under field conditions, soil pH, EC, organic matter, ammonium‑nitrogen, available phosphorus, available potassium, and crop productivity were all increased considerably, whereas soil Cd and Cr bioavailability were lower in the combined amendment treatments than in the control treatments. Particularly, application of a 2.49 t·ha−1 combined amendment (0.83 t·ha−1 S + 0.41 t·ha−1A + 1.25 t·ha−1B,1:0.5:1.5) decreased Cd, Pb, and Cr concentrations in maize grain by 68.9 %, 68.9 %, and 65.7 %, respectively. Species abundance and evenness in bacterial communities increased in field soils subjected to combined amendments, with shifts in community structure and function mostly driven by changes in soil pH, organic matter content, and nutrient availability. Overall, the results suggest that 1.5%S1A0.5B1.5 is the optimal treatment for remediating heavy metal co-contaminated soil, and thereby, improving maize yield and quality. Combined organic and inorganic amendments achieve high remediation efficiency, mainly by improving chemical properties, reducing heavy metal bioavailability, and altering bacterial community structure and function in heavy metal contaminated farmland soils.

Chronic toxicity, bioavailability and bioaccumulation of Zn, Cu and Pb in Lactuca sativa exposed to waste from an abandoned gold mine

Abandoned mines with untreated waste cause environmental pollution. The complex mixture of mining waste includes high metal content, anthropogenic chemicals and sterile rocks. Adverse effects of contaminated soils have been widely assessed by the use of plants. The aim of this study was to assess the chronic toxicity of a contaminated soil by waste from an abandoned gold mine on Lactuca sativa and its relationship with the bioavailability and bioaccumulation of Zn, Cu and Pb. Soil samples were taken from the site of mining waste stacking and a reference site in La Planta (Argentina). Contamination indices were calculated and acute and chronic exposures on L. sativa were carried out. Phytotoxicity indices, morphological and biochemical parameters, and concentrations of Zn, Cu and Pb in pseudo total and bioavailable soil fractions and in plant tissue were determined. Concentration- and time-dependent toxicity effects were observed, especially on plant width, fresh aerial biomass, leaf area and percentage of plants with completely necrotic aerial biomass. High levels of Zn (1453.3 ± 220.3 μg g−1) were found in plant tissue compared to Pb (277.2 ± 18.0 μg g−1) and Cu (255.3 ± 25.6 μg g−1). Toxicological endpoints correlated with metal uptake and mining waste concentration. In addition, bioaccumulation factors correlated with mobilisable and water soluble fractions. The concentration of Pb in aerial biomass surpassed the permissible concentrations in leaf vegetables, even at the reference site, indicating that lettuce crop consumption could be risky for the local population's health. This study demonstrated a strong relationship between metal bioavailability, toxicity endpoints and bioaccumulation, contributing with novel information to future ecotoxicological risk assessments and remediation plans.

Impacts of Uptake and Accumulation of Cd on Double Rice-Paddy Soil by Silicon Fertilizer Continuous Application

The impacts of silicon (Si) fertilizers on cadmium (Cd) bioavailability in soil and Cd accumulation in paddy-rice plants were investigated in a field positioning test. The results indicated that the continuous application of 180 kg·hm-2 Si fertilizers improved soil bioavailable Si in paddy-rice fields by 108.1%-275.0% and improved pH values by 1.15-1.33 in soil. The difference in the contents of DTPA-Cd in soil by 12.3% and 15.9% was significant in early and late rice, respectively. The continuous application of silicon promoted the transformation of soil cadmium to a stable form and reduced the contents of exchangeable Cd and carbonate binding state Cd in the soil by 2.6%-5.1% and 8.6%-24.9%. The contents of ferric manganese oxide binding state Cd were increased significantly; meanwhile, the contents of organic binding state Cd and residue state Cd in soil were improved by 2.3%-12.8% and 2.3%-6.0%, respectively. The contents of Cd in the root, shoot, and rice were reduced by 38.4%, 49.7%, and 50.9% in early season rice and by 30.6%, 34.4%, and 39.2% in late season rice, respectively. The absorption factors and translocation factors were reduced significantly by 25.5%-49.6% and 13.5%-52.6%, and the average bioaccumulation factors were decreased by 6.0% and 8.0% in early and late season rice. The powder Si fertilizer had the best results overall. In conclusion, Si fertilizer could reduce the absorption and accumulation in rice; however, the continuous Cd reduction effect of continuous application Si fertilizer was not obvious.

Zinc application promotes nitrogen transformation in rice rhizosphere soil by modifying microbial communities and gene expression levels

Application of Zn fertilizers to agricultural field is a simple and effective way for farmers to manage Zn deficient stress in soils to avoid yield lose. Although a synergistic effect of Zn on N transformation in soil has been reported, the mechanism is not fully understood yet. In this study, we planted rice in soils with different combinations of Zn and N supply, and analyzed the plant growth and N uptake, the N transformation, microbial communities, enzyme activities and gene expression levels in rhizosphere soil to reveal the underlying mechanism. Results showed that Zn application promoted the rice growth and N uptake, increased the soil alkali-hydrolyzed N and NH4+, but decreased NO3− and inhibited NH3 volatilization from the rhizosphere soil under optimal N condition. Zn supply significantly increased the relative abundances of Sphingomonas, Gaiella, subgroup_6, and Gemmatimonas, but decreased nitrosifying bacteria Ellin6067; while increased saprophytic fungi Schizothecium and Mortierella, but decreased pathogenic fungi Gaeumannomyces, Acremonium, Curvularia, and Fusarium in the rhizosphere soil under optimal N condition. Meanwhile, Zn application elevated the activities of protease, cellulase and dehydrogenase, and up-regulated the expression levels of napA, nirS, cnorB, and qnorB genes involved in the denitrification process in rice rhizosphere soil under optimal N condition. These results indicated Zn application could facilitate the soil N transformation and improved its availability by modifying both bacterial and fungal communities, and altering the soil enzyme activities and functional gene expression levels, ultimately promoted the N uptake and biomass of rice plant. However, this synergistic effect of Zn on rice growth, N uptake and soil N transformation strongly depended on the external N conditions, as no significant changes were observed under high N condition. Our results indicated that Zn co-fertilized with appropriate application of N is a useful strategy to improve the N bioavailability in rice rhizosphere soil and enhance the N uptake in rice plant.

Lead-Immobilization, transformation, and induced toxicity alleviation in sunflower using nanoscale Fe°/BC: Experimental insights with Mechanistic validations

ABSTRACT Lead (Pb) is a biologically non-essential element in the soil that brutally affects plants and other living organisms in soil; hence, its removal has become a worldwide concern. In this work, a multifunctional nanoscale zerovalent-iron assisted biochar (nFe°/BC) was used to minimize the Pb bioavailability in soil with aim of alleviating the Pb-induced toxicity in sunflower. Results revealed that nFe°/BC treatment had significantly improved plant growth (58%), chlorophyll contents (66%), intracellular permeability (60%), and ratio factor (93%), while decreasing the Pb uptake (78%) in plants. The Pb-immobilization and transformation mechanisms were proposed, suggesting that the presence of organic functional groups over the nFe°/BC surface might induce the complex formation with Pb by the ions exchange process in soil solution. The XPS analysis confirmed that surface-active components (Fe+, O2−, O*, C═O) were the key factor for high Pb-immobilization within soil matrix. In addition, 87% of stable Pb species, including PbCO3, PbO, Pb (OH)2, and Pb-O-Fe were found in the soil surface. Current findings have exposed the diverse functions of nFe°/BC on plant health and established a phenomenon that nFe°/BC application could improve the plant agronomic attributes by regulating the homeostasis of antioxidants and Pb uptake.

Mechanistic insight into the release behavior of arsenic (As) based on its geochemical fractions in the contaminated soils around lead/zinc (Pb/Zn) smelters

Arsenic (As) was known as human carcinogen . It was therefore of great importance to better understanding the release behavior of arsenic in soils for managing and controlling the potential risks of smelter contaminated sites. The present work evaluated arsenic bioavailability and bioaccessibility, in combination with geochemical fractionation and valence analysis by X–ray photoelectron spectroscopy (XPS), and also investigated the release patterns of bioavailable and bioaccessible arsenic in soils. The present results showed that there was a significant variation in the bioavailable and bioaccessible fractions of arsenic, due to the great difference in soil properties, extractants types, and in vitro assays . Moreover, it was found that KH 2 PO 4 presented the relatively higher arsenic bioavailability with wide range of 9.89–25.5 %, which might better predict the arsenic bioavailability in soils than the other extractants. In addition, the relatively higher arsenic bioaccesibility was found in Solubility Bioaccessibility Research Consortium (SBRC) assay, ranging from 5.50 to 67.4 % for gastric phase (GP) and 3.85–18.8 % for gastrointestinal phase (GIP), respectively. In addition, the time–dependent release of bioavailable arsenic was controlled by the competitive desorption between phosphate and As (V) ions, while the time–dependent release of bioaccessible arsenic was dominated by the stable complexation of organic ligands and the strong affinity of Al, Mn and Fe–(hydr) oxides. According to the study results, a new insight into the arsenic behavior was provided to more scientifically evaluate its contamination risks. • The updated knowledge was provided for arsenic geochemical behavior in smelter soils. • KH 2 PO 4 was identified as the best extractant to assess the arsenic bioavailability. • SBRC showed the relatively higher arsenic bioaccessibility than PBET and IVG. • Arsenic desorption reaction was better explained by the pseudo second order model.

Trace Elements Uptake in Brassica rapa chinensis Cultivated in Ultrabasic (Oxisol) and Ultisol Soils, North Borneo

The study aims to investigate the soil physico-chemical properties and trace elements uptake of Brassica rapa chinensis plants cultivated in ultrabasic (oxisol) and ultisoil soil of Ranau, North Borneo, Malaysia by inductively coupled plasma-optical emission spectrometry (ICP-OES). This study can contribute to propose a more sustainable soil management practice. All selected trace elements bioavailability in ultrabasic soil was significantly higher than ultisols except for Ca and Cd. There was no significant amount of difference in soil pH (slightly acidic) and electrical conductivity (slightly saline) between these soil types. However, a significant amount of difference between the percentage of soil moisture and organic matter between ultrabasic and ultisol soils was observed. These might contribute to the uptake of elements into the studied plant. The B. rapa chinensis is a hyperaccumulator of Cd and Pb for both type of soils. The B. rapa chinensis is an accumulator of As when grown in ultrabasic soil, while an accumulator of Co when grown in ultisol soil. Although Pb was not detected in ultisol soil as compared to ultrabasic soil, the concentration of Pb in plants cultivated in ultisol soil had exceeded the maximum permissible limit of Malaysia Food Regulation 1985. Soil amendment in frequently use agriculture sites needs to be conducted such as the addition of organic matter to reduce transfers of trace elements from soil to plants that can pose toxicity risk.

Soil microbes and associated extracellular enzymes largely impact nutrient bioavailability in acidic and nutrient poor grassland ecosystem soils

Understanding the role of soil microbes and their associated extracellular enzymes in long-term grassland experiments presents an opportunity for testing relevant ecological questions on grassland nutrient dynamics and functioning. Veld fertilizer trials initiated in 1951 in South Africa were used to assess soil functional microbial diversity and their metabolic activities in the nutrient-poor grassland soils. Phosphorus and liming trials used for this specific study comprised of superphosphate (336 kg ha−1) and dolomitic lime (2250 kg ha−1) (P + L), superphosphate (336 kg ha−1) (+ P) and control trials. These soils were analyzed for their nutrient concentrations, pH, total cations and exchange acidity, microflora and extracellular enzyme activities. The analysed soil characteristics showed significant differences except nitrogen (N) and organic carbon (C) concentrations showing no significant differences. P-solubilizing, N-cycling and N-fixing microbial diversity varied among the different soil treatments. β-glucosaminidase enzyme activity was high in control soils compared to P-fertilized and limed soils. Alkaline phosphatase showed increased activity in P-fertilized soils, whereas acid phosphatase showed increased activity in control soils. Therefore, the application of superphosphate and liming influences the relative abundance of bacterial communities with nutrient cycling and fixing functions which account for nutrient bioavailability in acidic and nutrient stressed grassland ecosystem soils.

Effect of Nanoscale Zero-Valent Iron on Arsenic Bioaccessibility and Bioavailability in Soil.

Hand-to-mouth activity is considered to be the main way for children to come into contact with contaminated soil, and bioavailability is an important factor affecting their health risk. To reduce soil As risk to humans by oral exposure, nanoscale zero-valent iron (nZVI) has been extensively studied for immobilizing As-contaminated soil, but its efficiency has not been investigated using in vitro assay and its influence on As-RBA. In this study, two contaminated soil samples (A and B) were amended with 1% and 2% (w/w) nZVI for 56 days to study its effect on As fraction by sequence extraction, As bioaccessibility by SBRC assay, and As relative bioavailability (RBA) by the mouse liver and kidney model. Based on the sequence extraction, the As associated with the E1 (exchangeable fraction) and C2 (carbonate fraction) fractions were decreased from 3.00% to 1.68% for soil A and from 21.6% to 7.86% for soil B after being treated with 2% nZVI for 56 days. When assessing As bioaccessibility in all soils treated with nZVI by SBRC assay, it was found that As bioaccessibility was significantly higher in the gastric phase (GP) and lower in the intestinal phase (IP) (p < 0.05), and the bioaccessible Fe concentration decreased significantly from the gastric to intestinal phase at the same time. Based on the mouse liver–kidney model, the As-RBA in soil A increased from 21.6% to 22.3% and 39.9%, but in soil B decreased from 73.0% to 55.3% and 68.9%, respectively. In addition, there was a significant difference between As bioaccessibility based on GP or IP of SBRC assay and As-RBA in two soils after being treated with nZVI for 56 days. To more accurately assess the effects of nZVI human arsenic exposure, As-RBA should be considered in concert with secondary evidence provided through fraction and bioaccessibility assessments. In addition, it is necessary to develop a suitable in vitro assay to predict As-RBA in nZVI-amended soils.

Toxicity and bioaccumulation of copper in the oribatid mite Oppia nitens (Acari: Oribatida)

To determine the toxicity and bioaccumulation of copper, adult oribatid soil mites Oppia nitens were exposed for 28 days to LUFA 2.2 soil spiked at concentrations of 0–6400 mg Cu kg−1 dry soil. Effects on survival and reproduction were related to total and available (0.01 M CaCl2 extractable and pore water) concentrations in the soil and concentrations in the animals. The mites showed a concentration-dependent uptake of copper, which, however, decreased at toxic concentrations. Overall bioaccumulation factors were low, suggesting a low tendency for copper bioaccumulation. The estimated median lethal concentration (LC50) values were 3251 mg Cu kg−1 dry soil, 1130 mg Cu kg−1 dry soil, 1977 mg Cu L−1 pore water, and 592 mg Cu kg−1 dry body weight, and the estimated 50 % effective concentrations (EC50) for effects of copper on reproduction were 589 mg Cu kg−1 dry soil, 116 mg Cu kg−1 dry soil, 78.5 mg Cu L−1 pore water, and 413 mg Cu kg−1 dry body weight, based on measured soil total concentrations, 0.01 M CaCl2 extractable, porewater, and internal concentrations, respectively. The results show that the mite O. nitens is a suitable test organism for measuring metal bioavailability and toxicity in soil.

Effect of slow-released biomass alkaline amendments oyster shell on microecology in acidic heavy metal contaminated paddy soils

Soil ecosystem functions and microbial community structure were severely impaired with long-term cadmium (Cd) contamination and acidification. To investigate the effect of amendments on soil physiochemical parameters and soil micro-ecology in acidic Cd contaminated soil, this study was conducted in a pot experiment with the application of calcium amendments, oyster shell powders (OS) and limestone (LM). Each amendment applied at ratios of 1.0%, 3.0%, and 5.0% (w/w), respectively. The results showed that the application of amendments increased the soil pH by 2.10–2.88, the bioavailable Cd decreased by 12.49%–19.48%, and un-bioavailable Cd increased by 96.57%–200.7%. The OS increased the richness index (Chao and Ace increased by 13.23%–16.20% and 7.13%–47.63%), and LM increased the microbial diversity index (Shannon increased by 1.14%–8.72% and Simpson indexes decreased by 28.00%–63.61%). In LM groups, soil microbial communities were significantly altered with increasing application concentrations, the relative abundance of phylum Proteobacteria, Bacteroidota and Gemmatimonadota increased, while Firmicute, Actinobacteria, Chloroflexi decreased. In OS treatments, the soil microbial community structure was basically unchanged. The correlation analysis showed that pH, TN, TP, CEC, OM were the dominant factors affecting the microbial community. This study has shown that application of amendments could effectively reduce the Cd bioavailability in soil, but LM altered the soil microbial community structure, while OS maintained the soil microbiological structure.

Mechanisms and influencing factors of yttrium sorption on paddy soil: Experiments and modeling

High-technology rare earth elements (REEs) as emerging contaminants have potentially hazardous risks for human health and the environment. Investigating the sorption of REEs on soils is crucial for understanding their migration and transformation. This study evaluated the sorption mechanisms and influencing factors of the rare earth element yttrium (Y) on paddy soil via integrated batch sorption experiments and theoretical modeling analysis. Site energy distribution theory (SEDT) combined with kinetics, thermodynamics, and isotherm sorption models were applied to illustrate the sorption mechanism. In addition, the effects of phosphorus (P), solution pH, particle size of soil microaggregates, and initial Y content on the sorption processes were evaluated by self-organizing map (SOM) and Boruta algorithm. The sorption kinetic behavior of Y on paddy soil was more consistent with the pseudo-second-order model. Thermodynamic results showed that the Y sorption was a spontaneous endothermic reaction. The generalized Langmuir model well described the isotherm data of Y sorption on heterogeneous paddy soil and soil microaggregates surface. The maximum sorption capacity of Y decreased with increasing soil particle size, which may be related to the number of sorption sites for Y on paddy soil and soil microaggregates, as confirmed by SEDT. The heterogeneity of sorption site energy for Y was the highest in the original paddy soil compared with the separated soil microaggregates. The SOM technique and Boruta algorithm highlighted that the initial concentration of Y and coexisting phosphorus played essential roles in the sorption process of Y, indicating that the addition of phosphate fertilizer may be an effective way to reduce the Y bioavailability in paddy soil in practice. These results can provide a scientific basis for the sustainable management of soil REEs and a theoretical foundation for the remediation of REEs-contaminated soils.

Synergistic Interaction between Symbiotic N2 Fixing Bacteria and Bacillus strains to Improve Growth, Physiological Parameters, Antioxidant Enzymes and Ni Accumulation in Faba Bean Plants (Vicia faba) under Nickel Stress.

Several activities in the agriculture sector lead to the accumulation of Nickel (Ni) in soil. Therefore, effective and economical ways to reduce soil bioavailability of Ni must be identified. Five isolates of Rhizobium leguminosarum biovar Viceae (ICARDA 441, ICARDA 36, ICARDA 39, TAL–1148, and ARC–207) and three bacterial strains (Bacillus subtilis, B. circulance, and B. coagulans) were evaluated for tolerance and biosorption of different levels of Ni (0, 20, 40, 60, and 80 mg L−1). Pot experiments were conducted during the 2019/2020 and 2020/2021 seasons using four inoculation treatments (inoculation with the most tolerant Rhizobium (TAL–1148), inoculation with the most tolerant Rhizobium (TAL–1148) + B. subtilis, inoculation with the most tolerant Rhizobium (TAL–1148) + B. circulance, and inoculation with the most tolerant Rhizobium (TAL–1148) + B. coagulans) under different levels of Ni (0, 200, 400, and 600 mg kg−1), and their effects on growth, physiological characteristics, antioxidant enzymes, and Ni accumulation in faba bean plants (Vicia faba C.V. Nobaria 1) were determined. The results showed that Rhizobium (TAL–1148) and B. subtilis were the most tolerant of Ni. In pot trials, inoculation with the most tolerant Rhizobium TAL–1148 + B. subtilis treatment was shown to be more effective in terms of growth parameters (dry weight of plant, plant height, number of nodules, and N2 content), and this was reflected in physiological characteristics and antioxidant enzymes under 600 mg kg−1 Ni compared to the other treatments in the 2019/2020 season. In the second season, 2020/2021, a similar pattern was observed. Additionally, lower concentrations of Ni were found in faba bean plants (roots and shoots). Therefore, a combination of the most tolerant Rhizobium (TAL–1148) + B. subtilis treatment might be used to reduce Ni toxicity.

Effects of Soil Application of Chitosan and Foliar Melatonin on Growth, Photosynthesis, and Heavy Metals Accumulation in Wheat Growing on Wastewater Polluted Soil

Due to freshwater scarcity in developing countries, irrigating the arable land with wastewater poses potential ecological risks to the environment and food quality. Using cheap soil amendments and foliar application of a newly discovered molecule “melatonin” (ML) can alleviate these effects. The objectives of this pot study were to evaluate the effectiveness of the sole addition of chitosan (CH) and sugar beet factory lime (SBL) in wastewater impacted soil, foliar application of ML, and combining each soil amendment with ML on the heavy metals (HMs) accumulation, growth, nutritional quality and photosynthesis in wheat. Results showed that CH was more effective than SBL for reducing HMs bioavailability in soil, HMs distribution in plants, improving photosynthesis, nutritional quality, and growth. ML application also influenced plant parameters but less than CH and SBL. The CH+ML treatment was the most effective for influencing plant parameters and reducing HMs bioavailability in the soil. Compared to control, CH+ML significantly reduced the concentrations of Pb, Cd, Cr, Ni, Cu, and Co in roots, shoots, and grain up to 89%. We conclude that adding CH+ML in wastewater impacted soils can remediate the soil; reduce HMs concentrations in plants; and improve their photosynthesis, plant growth, grain yield, and nutrition.

Evaluating the mouse model for estimation of arsenic bioavailability: Comparison of estimates of absolute bioavailability of inorganic arsenic in mouse, humans, and other species

ABSTRACT Accurate assessment of adverse health effects attributable to ingestion of inorganic arsenic (As) present in contaminated soils requires determination of the internal dose of metal provided by ingested soil. This calculation requires estimation of the oral bioavailability of soil-borne (As). Animal models to assess the bioavailability of soil (As) are frequently used as surrogates for determination of this variable in humans. A mouse assay has been widely applied to estimate the bioavailability of As in soils at sites impacted by mining, smelting, and pesticides. In the mouse assay, the relative bioavailability (RBA) of soil (As) is determined as the ratio of the fraction of the ingested arsenic dose excreted in urine after consumption of diets containing a test soil or the soluble reference compound, sodium arsenate. The aim of the current study was to compare (As) bioavailability measured in the mouse assay with reported estimates in humans. Here, a pharmacokinetic model based on excretion of arsenic in urine and feces was used to estimate the absolute bioavailability (ABA) of As in mice that received an oral dose of sodium arsenate. Based upon this analysis, in mice that consumed diet amended with sodium arsenate, the ABA was 85%. This estimate of arsenic ABA for the mouse is comparable to estimates in humans who consumed (As) in drinking water and diet, and to estimates of ABA in monkeys and swine exposed to sodium arsenate. The concordance of estimates for ABA in mice and humans provides further support for use of the mouse model in human health risk assessment. Sodium arsenate ABA also provides a basis for estimating soil arsenic ABA from RBA estimates obtained in the mouse model.

Risk Assessment of the Insecticide/Acaricide Milbeknock with the Active Substance Milbemectin

Milbeknock is a new insecticide/acaricide containing the new active substance milbemectin, which is a microbial fermentation product of Streptomyces. It is applied for control of mites and leafminers. The intended use is as a foliar spray in fruits (apples/pears), strawberries (only after harvest) and in ornamental plants growing in greenhouse and outdoors. The risk assessment was finalized at a meeting November 24, 2011, by VKM’s Scientific Panel on plant protection products (Panel 2). Panel 2 is in particular asked by the Norwegian Food Safety Authority to look at the following: 1) The human health risk for operators related to the properties of the active substance and the product. 2) The degree of oral absorption. 3) Acute toxicity. 4) The reproduction and developmental toxicity. 5) Establishment of reference values (ADI, AOEL and ARfD). 6) The fate and behaviour in the environment and environmental risk with regard to the properties of Milbeknock and milbemectin. 7) Bioavailability of milbemectin. 8) The microcosm study. &#x0D; VKM Panel 2’s conclusion is as follows: &#x0D; Health: Panel 2 proposes to set the absorption to 50%, which is in agreement with the EU DAR report (propose 47%). For acute toxicicity, Panel 2 concludes that milbemectin probably has a LD50 for dogs between 100 and 200 mg/kg body weight (bw)/day. Dogs seem to be the most sensitive experimental species and should be considered for hazard classification purposes. With respect to reproduction and developmental toxicity, Panel 2 concludes that the documentation of the role of the P-glycoprotein transporter is not convincing, and that the CF1 mice study cannot be used to support the argumentation of no developmental toxicity put forward by the applicant. The following reference values have been estimated: ADI of 0.03 mg/kg bw/day; AOEL of 0.015 mg/kg bw/day and ARfD of 0.067 mg/kg bw/day for milbemectin. Provided that personal protection equipment is used, the AOEL for operators is not exceeded. &#x0D; Environment: With respect to environmental fate, the opinion of the Panel is that the relatively rapid degradation in soil indicates a significant bioavailability in both soil and water-sediment systems. Further it concludes that 0.058µg/L should be regarded as NOECpopulation for the microcosm study. Panel 2 concludes that there is a medium risk of toxic effects on aquatic organisms due to exposure of milbemectin sprayed in fruits with the proposed application regime, provided that a buffer zone of 30 meters to surface water is applied. There are minimal risks of toxic effects on aquatic organisms with sufficient buffer zones in other applied crops. Panel 2 further considers the risk for foliage dwelling non-target predators and parasitoids to be high, and the risk to earthworms to be medium. &#x0D; The strong sorption to soil suggests that the bioavailability in soil may be limited. However, the opinion of the Panel is that the relatively rapid degradation in soil indicates a significant bioavailability. Also, for a substance with such a high log Kow the reported water solubility is relatively high, which will contribute to the availability for biological uptake. The toxicity observed in the microcosm study indicates high bioavailability also in a water/sediment system.