This study describes the role of zinc oxide nanoparticles (ZnO NPs) in alleviating arsenic (As) stress in rice (
Oryza sativa
) germination and early seedling growth. Seeds of rice were primed with ...different concentrations (10, 20, 50, 100, and 200 mg L
−1
) of ZnO NPs and As (0, and 2 mg L
−1
) for 12 days in petri dishes. Two milligrams per liter of As treatment represented a stress condition, which was evidenced by germination rate, seedling length, seedling dry weight, chlorophyll, superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) content of rice shoot. ZnO NPs amendment (10–100 mg L
−1
) increased the germination rate (2.3–8.9%), shoot weight (18.2–42.4%), root weight (5.2–23.9%), and chlorophyll content (3.5–40.1%), while elevated the SOD (2.2–22.8%) and CAT (7.2–60.7%) activities and reduced the MDA content (17.5–30.8%). As concentrations were significantly decreased by 8.4–72.3% and 10.2–56.6%, respectively, in rice roots and shoots with ZnO NPs amendment (10–200 mg L
−1
) by the As adsorption of ZnO NPs and promoted biomass of rice. All the amendments improved the Zn concentrations in rice shoots and roots. Overall, ZnO NPs provide effective resistance to arsenic toxicity by increasing germination, biomass, and nutrients of Zn and decreasing As uptake in rice.
Soil contamination in urban environment by trace metals is of public concerns. For better risk assessment, it is important to determine their background concentrations in urban soils. For this study, ...we determined the background concentrations of 9 trace metals including As, Ba, Cd, Co, Cu, Ni, Pb, Se, and Zn in 214 urban soils in Florida from two large cities (Orlando and Tampa) and 4 small cities (Clay County, Ocala, Pensacola and West Palm Beach). The objectives were to determine: 1) total concentrations of trace metals in urban soils in cities of different size; 2) compare background concentrations to Florida Soil Cleanup Target Levels (FSCTLs); and 3) determine their distribution and variability in urban soils via multivariate statistical analysis. Elemental concentrations in urban soils were variable, with Pb being the highest in 5 cities (165–552 mg kg−1) and Zn being the highest concentration in Tampa (1,000 mg kg−1). Besides, the As and Pb concentrations in some soils exceeded the FSCTL for residential sites at 2.1 mg kg−1 As and 400 mg kg−1 Pb. Among the cities, Clay County and Orlando had the lowest concentrations for most elements, with Cd, Co, and As being the lowest while Ba, Pb and Zn being the highest. Among all values, geometric means were the lowest while 95th percentile was the highest for all metals. Most 95th percentile values were 2–3 folds higher than the GM data, with Pb presenting the greatest difference, being 4 times greater than GM value (58.9 vs. 13.6 mg kg−1). Still they were lower than FSCTL, with As exceeding FSCTL for residential sites at 2.1 mg kg−1. In addition, the linear discriminate analysis showed distinct separation among the cities: Ocala (Ba & Ni) and Pensacola (As & Pb) were distinctly different from each other and from other cities with higher metal concentrations. The large variations among elemental concentrations showed the importance to establish proper background concentrations of trace metals in urban soils.
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•Background concentrations of 9 trace elements in 214 urban soils were determined.•Arithmetic and geometric mean, 95th percentile and upper confidence level were calculated.•Regardless city size, human activities had similar impacts on elemental concentrations.•As, Ba, Cr and Pb levels exceeded Florida Soil Cleanup Target Levels for residential sites.•Among all values, GM was the lowest while 95th percentile was the highest.
Large concentration variations showed the importance to establish proper background concentrations of trace metals in urban soils.
Rice is particularly effective, compared to other cereals, at accumulating arsenic (As), a nonthreshold, class 1 human carcinogen in shoot and grain. Nano-zinc oxide is gradually used in agricultural ...production due to its adsorption capacity and as a nutrient element. An experiment was performed to explore the effects of zinc oxide nanoparticles (nZnO) on arsenic (As) toxicity and bioaccumulation in rice. Rice seedlings were treated with different levels of nZnO (0, 10, 20, 50, 100 mg/L) and As (0, and 2 mg/L) for 7 days.
The research showed that 2 mg/L of As treatment represented a stress condition, which was evidenced by phenotypic images, seedling dry weight, chlorophyll, and antioxidant enzyme activity of rice shoot. The addition of nZnO (10-100 mg/L) enhanced the growth and photosynthesis of rice seedlings. As concentrations in the shoots and roots were decreased by a maximum of 40.7 and 31.6% compared to the control, respectively. Arsenite As (III) was the main species in both roots (98.5-99.5%) and shoots (95.0-99.6%) when exposed to different treatments. Phytochelatins (PCs) content up-regulated in the roots induced more As (III)-PC to be complexed and reduced As (III) mobility for transport to shoots by nZnO addition.
The results confirmed that nZnO could improve rice growth and decrease As accumulation in shoots, and it performs best at a concentration of 100 mg/L.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Zeolite-supported nanoscale zero-valent iron (Z-NZVI) has great potential for metal(loid) removal, but its encapsulation mechanisms and ecological risks in real soil systems are not completely clear. ...We conducted long-term incubation experiments to gain new insights into the interactions between metal(loid)s (Cd, Pb, As) and Z-NZVI in naturally contaminated farmland soils, as well as the alteration of indigenous bacterial communities during soil remediation. With the pH-adjusting and adsorption capacities, 30 g kg−1 Z-NZVI amendment significantly decreased the available metal(loid) concentrations by 10.2–96.8% and transformed them into strongly-bound fractions in acidic and alkaline soils after 180 d. An innovative magnetic separation of Z-NZVI from soils followed by XRD and XPS characterizations revealed that B-type ternary complexation, heterogeneous coprecipitation, and/or concurrent redox reactions of metal(loid)s, especially the formation of Cd3(AsO4)2, PbFe2(AsO4)2(OH)2, and As0, occurred only under specific soil conditions. Sequencing of 16S rDNA using Illumina MiSeq platform indicated that temporary shifts in iron-resistant/sensitive, pH-sensitive, denitrifying, and metal-resistant bacteria after Z-NZVI addition were ultimately eliminated because soil characteristics drove the re-establishment of indigenous bacterial community. Meanwhile, Z-NZVI recovered the basic activities of bacterial DNA replication and denitrification functions in soils. These results confirm that Z-NZVI is promising for the long-term remediation of metal(loid)s contaminated farmland soil without significant ecotoxicity.
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•Z-NZVI combined the advantages of pH adjustment and adsorption.•Z-NZVI decreased available Cd, Pb, and As by 10.21–96.79% in acid and alkaline soils.•B-type ternary complexation, heterogeneous coprecipitation, and redox occurred.•The dynamic impacts of Z-NZVI on indigenous bacterial communities were discussed.•The secondary mineralization of Z-NZVI bonded metal(loid)s and improved soil quality.
The encapsulation mechanisms and microbial responses of Z-NZVI were investigated.
•As(III) can be effectively removed by ball milled, sulfidated ZVI (S-mZVIbm).•As(III) was removed primarily through As4S4 formation under anoxic conditions.•As(III) was removed through adsorption ...onto corrosion product under oxic conditions.•S-mZVIbm/sand column rapidly reduces As(III) in a groundwater from 300 to 10 µg/L.•S-mZVIbm in sand column treats >750 BV groundwater with a capacity of 12.2 mg/g.
The interaction of As(III) with micron-sized, mechanochemically sulfidated zero-valent iron (S-mZVIbm) has been studied under both anoxic and oxic conditions. The As(III) removal capacity varied with the increase of S/Fe molar ratio under anoxic conditions, while it continuously decreased under oxic conditions. A series of sequential extractions, X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy analyses were used to investigate As(III) removal mechanisms. In the absence of oxygen, As(III) was removed from solution primarily through the formation of As4S4 with less than half of the removal resulting from the adsorption of As(III)/As(V) and FeAsS precipitation. Under oxic conditions, adsorption onto iron (oxyhydr)oxides was the dominant mechanism of As(III) removal. Increasing sulfidation decreased particle Fe(0) content, which resulted in less production of iron (oxyhydr)oxides and therefore lower As(III) removal capacities. Column experiments showed that less than 2 wt% of S-mZVIbm in sand was able to rapidly reduce the As(III) concentration in a real groundwater from 300 to 10 µg/L, the Chinese drinking water standard, for up to 750 BV with an EBCT of 2.54 min. This study demonstrates that S-mZVIbm is an efficient and cost-effective material in treating As-contaminated water to ensure water safety.
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In situ immobilization of heavy metals in contaminated soils using industrial by-products is an attractive remediation technique. In this work, titanium gypsum (TG) was applied at two levels (TG-L: ...0.15% and TG-H: 0.30%) to simultaneously reduce the uptake of cadmium (Cd), lead (Pb) and arsenic (As) in rice grown in heavy metal contaminated paddy soils. The results showed that the addition of TG significantly decreased the pH and dissolved organic carbon (DOC) in the bulk soil. TG addition significantly improved the rice plants growth and reduced the bioavailability of Cd, Pb and As. Particularly, bioavailable Cd, Pb and As decreased by 35.2%, 38.1% and 38.0% in TG-H treatment during the tillering stage, respectively. Moreover, TG application significantly reduced the accumulation of Cd, Pb and As in brown rice. Real-time PCR analysis demonstrated that the relative abundance of sulfate-reducing bacteria increased with the TG application, but not for the iron-reducing bacteria. In addition, 16S rRNA sequencing analysis revealed that the relative abundances of heavy metal-resistant bacteria such as Bacillus, Sulfuritalea, Clostridium, Sulfuricella, Geobacter, Nocardioides and Sulfuricurvum at the genus level significantly increased with the TG addition. In conclusion, the present study implied that TG is a potential and effective amendment to immobilize metal(loid)s in soil and thereby reduce the exposure risk of metal(loid)s associated with rice consumption.
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•Titanium gypsum addition decreased the bioavailability of Cd, Pb and As in soil.•Titanium gypsum addition reduced the accumulation of Cd, Pb and As in brown rice.•Titanium gypsum addition enhanced the abundance of sulfate-reducing bacteria and metal-resistant bacteria in soil.•Titanium gypsum is a potential and effective amendment to immobilize metals in soil.
Titanium gypsum is a potential and effective amendment to immobilize Cd, Pb and As in paddy soils.
Most studies of the effects of manure amendment on the occurrence of antibiotics and antibiotic resistance genes (ARGs) in soil employ the investigation of grab samples or short-term laboratory ...studies. However, the effects of long-term manure applications on antibiotics, ARGs and their vertical distribution in paddy soil in field experiments are lacking. We assessed the concentrations of antibiotics, ARGs and their vertical distribution in paddy soil receiving long-term manure applications in four field experiments. High concentrations of tetracyclines were detected in most manured soils, while sulfonamides were not detectable. Long-term manure amendments generally increased the antibiotic concentrations and ARGs abundances in the paddy soil over decades. However, in some sites such significant trends of ARGs could not be observed. The abundance of ARGs was statistically correlated with antibiotics and soil properties including pH and soil organic matter (SOM), indicating their importance in the selection of resistance genes. Tetracyclines could be detected in soil at different depths and the concentrations of tetracyclines and abundance of ARGs generally decreased with increasing soil depths.
•The occurrence of antibiotics and ARGs in soil affected by manure applications at known rates in field sites was investigated.•High concentrations of tetracyclines were detected in long-term manured soils.•Long-term manure applications did not always increase the abundance of ARGs in soil.•The abundance of ARGs correlated well with antibiotics and soil properties.•The concentrations of tetracyclines and abundance of ARGs generally decreased with increasing soil depths.
Cadmium is a highly persistent and toxic heavy metal that poses severe health risks to humans. Diet is the primary source of human exposure to cadmium, especially in China. Soil, as the main medium ...that transfers cadmium to rice, can be used as a helpful indicator to predict human exposure to cadmium in soils. There is, however, very little work that links a soil-rice transfer model with a biokinetic model to assess health risks. In this work, we introduce a multi-medium chain model based upon a soil-rice-human continuum to address this issue. The model consists of three basic steps: (i) development and validation of a soil-rice transfer model for cadmium based on 189 pairs of measured data in Wenling of Zhejiang province in Southeast China; (ii) calculation of weekly exposure based on the nationwide monitoring and survey results; (iii) linking the exposure model with a modified biokinetic model proposed with a classic biokinetic model to predict urinary cadmium, which is a biomarker to assess the health risks. Results indicated that the developed soil-rice-human transfer model predicted well the urinary cadmium levels in humans subjected to age and exposure uncertainties. We observed a maximum of 0.71 μg g−1 creatinine in males and 1.53 μg g−1 creatinine in females at 70 years old under median cadmium exposure, which was consistent with previous studies. Sensitive analysis was also conducted to detect the sensitive parameters that have the most significant influences on the output of the model. The new risk assessment strategy proposed in this work is beneficial for predicting the cumulative cadmium levels in various exposed populations so that we can quickly identify the critical areas from basic soil properties.
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•This is the first soil-rice-human chain model to evaluate cumulative cadmium risks in humans.•Cadmium transfer from soil to rice is validated using measured data from the rice paddies.•Urinary cadmium excretion is predicted subject to age and exposure uncertainties.•Global sensitive analysis (GSA) is applied to determine influential parameters.
First chain model through soil-plant-human continuum to calculate the potential cumulative cadmium levels in various exposed populations.
•Organic amendments were more effective to reduce Pb availability and uptake.•Organic amendments greatly increased the Fe–Mn oxides fractions.•Fe, Mn, Cu and Zn was not significantly affected in soil ...and plants.•The organic amendments have the potential to remediate Pb-contaminated soil in situ.
A greenhouse study was conducted to investigate the effects of inorganic (phosphate rock, single superphosphate and calcium magnesium phosphate) and organic amendments (peat, straw manure and pig manure) on the uptake of lead (Pb) and trace elements by Chinese Cabbage (Brassica chinensis) grown in an acidic red soil. The application of all organic amendments increased the soil pH while inorganic amendments such as single superphosphate did not. Both inorganic and organic amendments decreased the availability and uptake of Pb while the organic amendments were superior to the inorganic (phosphate) amendments in reducing the availability of the more labile (soluble and exchangeable Pb) forms of soil Pb. More Pb was taken up by roots than shoots with all soil amendments. Among the organic amendments, straw manure and pig manure caused the largest decrease in Pb availability at 456.5 and 457.3mgkg−1, respectively, when a high level of 30g organic amendments kg−1 was applied. The organic amendments greatly increased the fraction D targeted to Fe–Mn oxides bound Pb, and decreased the fraction A (water-soluble), B (exchangeable), and C (carbonate-bound), thereby decreasing the solubility and mobility of Pb in soil. The organic amendments also significantly improved the concentrations of Fe, Mn, Cu and Zn in the soil and shoots (except Fe in shoots and/or roots), which are essential for plant nutrition. The organic amendments of straw and pig manure lowered the availability and uptake of Pb but not that of other trace metals. Thus, these amendments have the potential to remediate Pb-contaminated soils in situ.
Microbial transformation of arsenic (As) plays a key role in As biogeochemical cycling and affects the mobility, bioavailability, and toxicity of As. This study aims to investigate the accumulation ...of As in marine sediments at different water depths in the East China Sea and reveal the abundance and diversity of the aioA, arrA, arsC, and arsM genes through quantitative real-time polymerase chain reaction (qPCR) and high-throughput sequencing. Results showed that the As content in sediments ranged from 5.53 mg kg−1 to 17.70 mg kg−1, which decreased with water depth. Abundant As biotransformation genes with low diversity were identified in these sediments, of which arsM and arrA were the most abundant. Significant positive correlation exists between the arsM and arrA gene abundance and between arsC and aioA, indicating the co-occurrence of the As biotransformation genes in microbes in marine sediments. Metagenomics analysis revealed that arsM gene was mainly distributed in Alphaproteobacteria, Solibacteres, Deltaproteobacteria, Clostridia, and Bacilli in these sediments. Among the sediment properties, total N, total S, C/N, and TOC were important factors that shaped the abundance profile of the genes involved in As transformation. This study provides a picture of As biotransformation genes in marine sediments from the East China Sea, which may affect As transformation and the ultimate fate of As in a marine environment.
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•As content in marine sediments from the East China Sea decreased with water depth.•As biotransformation genes were analyzed by metagenomics in marine sediments.•arsM and arrA were abundant and co-existed in marine sediments.•α-, δ-Proteobacteria, Solibacteres, Clostridia, were main microbes carrying arsM.•Total N, S, C/N and TOC were important factors shaping the diversity of these genes.
This study depicts the As distribution and its biotransformation genes in marine sediments from the East China Sea.
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