Increasing Cd Concentration Research Articles

Environmental risk due to the accumulation of metals in Sedum alfredii under different intercropping patterns during phytoremediation

AbstractA field experiment was conducted to evaluate the environmental risk of phytoextraction of Cd, Cu, and Pb using Sedum alfredii Hance. with different intercropping patterns. Three receptors representing invertebrates (earthworms), avians (yellow‐feathered chickens), and small mammalian omnivores (Rattus losea) were selected as the potentially impacted environmental receptors. Soil deglutition and food ingestion are considered dominant pathways of metal exposure. Different planting patterns, including S. alfredii monoculture and S. alfredii intercropped (coordinate and malposed) with Cicer arietinum L., were used to evaluate the mobilization, absorption, and migration of Cd during phytoextraction. This study revealed that the intercropping systems, particularly the malposed intercropping patterns, significantly increased the Cd decontamination efficiency by 31.3% and enhanced the content of Cu and Pb in the aboveground tissues of the intercropped C. arietinum. Correspondingly, different planting patterns resulted in varying environmental risks. For the omnivores, which primarily consume earthworms and plant tissues, the hazard index was 0.096 for the S. alfredii monoculture, and the index decreased to 0.074 and 0.090 in the coordinate and malposed intercropping patterns, respectively. The environmental risk might be induced by the increased Cd concentrations in the roots and shoots of S. alfredii. When extrapolating the results of this treatment to the entire region, all the environmental hazard index values of the receptors were higher than 1.0. This study suggests that if a phytoextraction method is used for metal decontamination, corresponding prevention strategies should be established to prevent the diffusion of concentrated metals to higher trophic levels via the food chain.

Studying structural, molecular, morphological and electrical properties of Co0.2 Zn0.8 Fe2O4 doped with Cadmium

A series of (Co0.2 Zn0.8-xCdxFe2O4) with (x = 0, 0.3, 0.6) were prepared by flash auto combustion method and annealed at 800 ℃ for 2hrs and morphological and structural using XRD, FTIR, and SEM characterization were studied. The cubic spinel structure is affirmed by XRD analysis of the samples. The XRD peaks elucidate that all synthesized ferrites have Fd3m phase group. The FTIR spectra evidenced two intensive absorption bands (ν1 and ν2) in the 400 – 600 cm−1 range corresponding to A and B sites. Peaks in FTIR analysis shift towards lower wavenumber as Cd doping concentration increases. Cd doping is essential for crystal growth, as evidenced by SEM images. The AC resistivity decreases by rising temperature whereas it increases by increasing Cd content up to × = 0.3 and after that decreases. The magnetic manner of our samples was distinguished by Vibrating Sample Magnetometer (VSM). Eventually, the hysteresis loop is small; So Co0.2 Zn0.8-xCdxFe2O4 nanoparticles are soft magnetic materials.

Transcriptional memory of gene expression across generations participates in transgenerational plasticity of field pennycress in response to cadmium stress.

Transgenerational plasticity (TGP) occurs when maternal environments influence the expression of traits in offspring, and in some cases may increase fitness of offspring and have evolutionary significance. However, little is known about the extent of maternal environment influence on gene expression of offspring, and its relationship with trait variations across generations. In this study, we examined TGP in the traits and gene expression of field pennycress (Thlaspi arvense) in response to cadmium (Cd) stress. In the first generation, along with the increase of soil Cd concentration, the total biomass, individual height, and number of seeds significantly decreased, whereas time to flowering, superoxide dismutase (SOD) activity, and content of reduced glutathione significantly increased. Among these traits, only SOD activity showed a significant effect of TGP; the offspring of Cd-treated individuals maintained high SOD activity in the absence of Cd stress. According to the results of RNA sequencing and bioinformatic analysis, 10,028 transcripts were identified as Cd-responsive genes. Among them, only 401 were identified as transcriptional memory genes (TMGs) that maintained the same expression pattern under normal conditions in the second generation as in Cd-treated parents in the first generation. These genes mainly participated in Cd tolerance-related processes such as response to oxidative stress, cell wall biogenesis, and the abscisic acid signaling pathways. The results of weighted correlation network analysis showed that modules correlated with SOD activity recruited more TMGs than modules correlated with other traits. The SOD-coding gene CSD2 was found in one of the modules correlated with SOD activity. Furthermore, several TMGs co-expressed with CSD2 were hub genes that were highly connected to other nodes and critical to the network’s topology; therefore, recruitment of TMGs in offspring was potentially related to TGP. These findings indicated that, across generations, transcriptional memory of gene expression played an important role in TGP. Moreover, these results provided new insights into the trait evolution processes mediated by phenotypic plasticity.

Effect of Cadmium and Lead Stress on Seed Germination and Seedling Growth of Jatropha curcas L.

Heavy metal pollution in the biosphere has become a worldwide problem. Metal industry effluents, mining sites, municipal and agricultural waste are important sources of metal dispersion in environment. Heavy metal imposed phytotoxicity affects seed germination, seedling growth, photosynthesis and other physiological processes. Exposure of seeds to cadmium (Cd) and lead (Pb) has deleterious effects resulting into inhibition of germination, delayed germination time and retardation of seedling growth due to toxicity. The aim of this research is to investigate the toxic effects of Cd and Pb on seed germination and seedling growth of Jatropha curcas L. and evaluate its tolerance for heavy metal stress. The experimental treatments included exposure to five concentrations of cadmium nitrate and lead acetate (ranging from 25 to 125 µM/L), under which the germination and seedling growth parameters were determined periodically. The germination and growth of J. curcas L. was affected by cadmium and lead supplemented at different concentrations and the toxicity effects were found to be concentration dependent. Tolerance indices declined sharply with increasing concentrations of lead and cadmium treatments. Germination was inhibited upto 50% by 100 μmol/L of Cd, 125 μmol/L of Pb. Mean germination time and seedling vigour index also gradually decreased with increase in Cd and Pb concentration. Cadmium proved to be more toxic than lead in all considerations.

Effect of Cadmium and Lead Stress on Seed Germination and Seedling Growth of Jatropha curcas L.

Heavy metal pollution in the biosphere has become a worldwide problem. Metal industry effluents, mining sites, municipal and agricultural waste are important sources of metal dispersion in environment. Heavy metal imposed phytotoxicity affects seed germination, seedling growth, photosynthesis and other physiological processes. Exposure of seeds to cadmium (Cd) and lead (Pb) has deleterious effects resulting into inhibition of germination, delayed germination time and retardation of seedling growth due to toxicity. The aim of this research is to investigate the toxic effects of Cd and Pb on seed germination and seedling growth of Jatropha curcas L. and evaluate its tolerance for heavy metal stress. The experimental treatments included exposure to five concentrations of cadmium nitrate and lead acetate (ranging from 25 to 125 µM/L), under which the germination and seedling growth parameters were determined periodically. The germination and growth of J. curcas L. was affected by cadmium and lead supplemented at different concentrations and the toxicity effects were found to be concentration dependent. Tolerance indices declined sharply with increasing concentrations of lead and cadmium treatments. Germination was inhibited upto 50% by 100 μmol/L of Cd, 125 μmol/L of Pb. Mean germination time and seedling vigour index also gradually decreased with increase in Cd and Pb concentration. Cadmium proved to be more toxic than lead in all considerations.

Metabolome and transcriptome association analysis revealed key factors involved in melatonin mediated cadmium-stress tolerance in cotton.

Cadmium (Cd), a non-essential element for plant, is a ubiquitous and highly toxic heavy metal, seriously endangering agricultural production and human health. As a nonedible economic crop, cotton (Gossypium hirsutum L.) has great potential in remediation of Cd contaminated soil, but its underlying mechanism is still unknown. Melatonin (MT), as a plant growth regulator, is involved in alleviating Cd toxicity in some plants, but the molecular mechanisms of MT-mediated Cd detoxification in cotton are largely unknown. This study investigated the possible molecular mechanisms of the MT-mediated Cd detoxification in cotton seedlings by comparative transcriptomic and metabolomic analyses. The results showed that the cotton seedlings were dwarfed and the leaves were wilted and yellow under Cd stress. The application of 50 µmol L−1 MT significantly increased the superoxide dismutase (SOD) activity and malondialdehyde (MDA) content under Cd stress, but 100 µmol L−1 MT significantly decreased SOD activity, while increased ascorbate peroxidase (APX) activity significantly. The addition of 100 μmol L−1 MT significantly increased Cd concentration in the shoots and roots under Cd stress. RNA-seq analysis showed that 5573, 7105, 7253, 25, 198, 9 up-regulated and 6644, 7192, 7404, 9, 59, 0 down-regulated differentially expressed genes (DEGs) were identified in the comparisons of CK vs T1, CK vs T2, CK vs T3, T1 vs T2, T1 vs T3 and T2 vs T3, respectively. It was revealed that MT promoted the expression of certain related genes under Cd stress, and the effect of 100 µmol L−1 MT was better. Moreover, UPLC-MS/MS widely targeted metabolites analyses showed that 195, 150, 150, 12, 24, 59 up-regulated and 16, 11, 23, 38, 127, 66 down-regulated differentially accumulated metabolites (DAMs) were changed in the CK vs T1, CK vs T2, CK vs T3, T1 vs T2, T1 vs T3 and T2 vs T3, respectively. It was revealed that MT induced the synthesis of alkaloids and flavonoids, and inhibited or reduced the synthesis of lipids, amino acids and their derivatives. The comprehensive analyses of transcriptomic and metabolic data showed that 33 DEGs and 4 DAMs, 46 DEGs and 16 DAMs, and 1 DEGs and 1 DAMs were dominantly involved in the pathways of valine, leucine and isoleucine degradation, ABC transporter, alpha-linolenic acid metabolism, respectively. It was revealed that there were three major mechanisms involved in MT-mediated Cd detoxification in cotton, including the enhancement of antioxidant capacity regulated by APX, flavonoids and alkaloids; accumulation of secondary metabolites related to Cd chelation, such as amino acids and derivatives; and regulation of cadmium ion transportation, such as ABC transporter activation. In conclusion, this study provides new insights into the MT-mediated Cd stress response.

Accumulation and Elimination of Cadmium by the Nile Tilapia (Oreochromis niloticus) in differing Temperatures and Responses of Oxidative Stress Biomarkers.

The aims of this study were to investigate the accumulation (15 days) and elimination (15 and 30 days) of cadmium (Cd) in the liver, gill, kidney and muscle of Oreochromis niloticus following exposures to different concentrations (1 and 2mg/L) of Cd at different water temperatures (20, 25, 30 oC). Additionally, responses of oxidative stress biomarkers (superoxide dismutase, SOD; catalase CAT; glutathione peroxidase, GPx and malondialdehyde, MDA) of the liver were determined following Cd exposures. In accumulation period, Cd levels increased significantly in all the tissues at all temperatures and tissue accumulation order was kidney > liver > gill. All tissues, except the muscle, accumulated Cd in relation to exposure concentrations and water temperatures. There was no measurable level of Cd accumulation in the muscle, except in fish exposed to 2mg Cd/L at 30 oC. Likewise, elimination of Cd from the tissues also increased in depends on periods and water temperatures. The order of Cd elimination from the tissues was gill > liver > kidney. The oxidative stress biomarkers also responded to both Cd exposure and temperature increases. The activities of antioxidant enzymes such as SOD, CAT, GPx and MDA levels in the liver increased in relation to increases in Cd concentrations and water temperatures.

Time-Dependent Toxicity and Health Effects Mechanism of Cadmium to Three Green Algae.

As algae are extremely sensitive to heavy-metal ions and can be critical biological indicators in the heavy-metal toxicity analyses conducted by environmental health researchers, this paper explores the sensitivity to temporal toxicity of three species of green algae: Scenedesmus obliquus, Chlorella pyrenoidosa, and Selenastrum capricornutum. The method of time-dependent microplate toxicity analysis was used to systematically investigate the changes in the toxicities of the three green-algae species induced by different concentrations of cadmium (Cd). The chlorophyll a content, antioxidant enzyme activity, and malondialdehyde (MDA) content in the algae were analyzed to explore the mechanism of Cd toxicity after 96 h of exposure. The results showed that the toxic effects of Cd on the three algae species were time-dependent. By comparing the toxic effect of Cd, indicated by pEC50 (the negative logarithm of EC50), on the algae species at four durations of exposure (24, 48, 72, and 96 h), this study found that the indicator organisms had different sensitivities to Cd. The order of sensitivity was C. pyrenoidosa > S. obliquus > S. capricornutum. Cd exposure had significant effects on the chlorophyll a and MDA content and on the enzyme activity of superoxide dismutase (SOD) and catalase (CAT) in the algae species. The chlorophyll a content in the cells of the algae decreased with increasing Cd concentration. The enzyme activity of CAT and content of MDA increased with increasing Cd concentration, which indicated that Cd had an oxidative stress effect on the three algae species.

Chalcogens reduce grain Cd accumulation by enhancing Cd root efflux and upper organ retention in wheat (Triticum aestivum L.)

A seedling-stage sand culture experiment and whole growth period pot experiment were conducted together to investigate the effects of chalcogenide elements (S, Se, Te) on the morphology, photosynthesis, Cd absorption, Cd and mineral nutrient transport, and transporter gene expression of wheat under Cd stress. Compared with S, Se and Te can alleviate wheat Cd toxicity and reduce Cd accumulation more efficiently. Compared with control conditions, S reduced the root Cd concentration by about 20 %, while SeIV and TeIV reduced the root Cd concentration by more than 60 % and the shoot Cd concentration by about 30 %. Chalcogens reduced Cd uptake by increasing root diameter (by about 50 %) and inhibiting lateral root formation under SeIV and TeIV treatments compared to Cd treatment alone. Moreover, chalcogens accelerated Cd efflux by up-regulating TaTM20 , thereby reducing Cd accumulation. Meanwhile, chalcogens enhanced Cd isolation in the cell wall and vacuole, reduced the active Cd proportion by increasing synthesis of chelates, and improved wheat Cd tolerance. Spraying Se and Te increased both the photosynthetic rate and yield, while also improving mineral nutrient contents (including magnesium, calcium, zinc, iron, manganese, copper, and molybdenum contents) in wheat grains. Selenomethionine (SeMet) was more effective in reducing upper organ Cd reactivation and inhibiting Cd transport from upper organs to grains, which was able to reduce grain Cd content by 27 % in the 5 mg/kg Cd treatment. Additionally, SeIV and TeIV reduced grain Cd content by 14 % and 16 %, respectively; while SeVI increased Cd content by 11 %. The current study reveals the mechanism by which chalcogens alleviate Cd toxicity and reduce grain Cd accumulation, which provides valuable insights for safe wheat production despite Cd soil contamination. • Se and Te alleviate Cd toxicity and increase wheat yield. • Chalcogens decrease Cd uptake by increasing root diameter and inhibiting lateral root growth. • Chalcogens reduce Cd accumulation by increasing root Cd efflux. • Increases in PC S -Cd complexes and up-regulation of HMA2 expression promote Cd transport to shoots. • SeMet reduces Cd transport to grains by reducing Cd reactivation in stem, leaf, and glume tissues.

Response of Castor Seedling Roots to Combined Pollution of Cd and Zn in Soils

Castors are used to remediate heavy-metal-polluted soils due to their good ability to accumulate heavy metals. However, only limited studies addressed the interaction between heavy metals and castor seedling roots. In this study, the physiological response of castor seedling roots to Cd and Zn stress, and the change in trace elements in rhizosphere and non-rhizosphere soils were investigated. The results showed that, with an increase in Cd concentration, the accumulation of Zn in roots decreased by 20%, indicating a competition between Cd and Zn accumulation. The increase in Cd content enlarged the difference in nutrient contents at different depths: the amounts of P, Fe, and Mn were more in rhizosphere soils than in non-rhizosphere soils, while the amount of K showed an opposite trend. The addition of Cd and Zn stimulated root growth, but root activity was reduced. The addition of Cd and Zn affected the root cell morphology, including increases in the root cortex thickness and the root xylem area. The contents of the enzymes SOD, POD, and MDA increased with the addition of Cd and Zn, while the activity of CAT first increased and then decreased. There was no significant change in the soluble protein content. The decrease in IAA oxidase content, from 40.1% to 72.7%, was conducive to plant growth. To sum up, high contents of Cd and Zn in soils not only affect the root morphology and increase the gap in the contents of K, P, Fe, and Mn between rhizosphere and non-rhizosphere soils but also change the SOD, POD, MDA, and IAA contents in the root, so as to reduce the amount of root damage caused by the external environment.

Effects of cadmium and flooding on the formation of iron plaques, the rhizosphere bacterial community structure, and root exudates in Kandelia obovata seedlings

In the rhizosphere, plant root exudates (REs) serve as a bridge between plant and soil functional microorganisms, which play a key role in the redox cycle of iron (Fe). This study examined the effects of periodic flooding and cadmium (Cd) on plant REs, the rhizosphere bacterial community structure, and the formation of root Fe plaques in the typical mangrove plant Kandelia obovata, as well as the relationship between REs and Fe redox cycling bacteria. Based on two-way analysis of variance, flooding and Cd had a considerable effect on the REs of K. obovata. DOC, NH4+-N, NO3−-N, dissolved inorganic phosphorus, acetic acid, and malonic acid concentrations in REs of K. obovata increased considerably with the increase of Cd concentration under 5 and 10 h flooding conditions. Fe plaque development in the plant root was stimulated by flooding and Cd, although flooding was more effective. After Cd treatment, the ways in which Fe-oxidizing bacteria (FeOB) and Fe-reducing bacteria (FeRB) were enriched in the rhizosphere and rhizoplane of plants were different. Thiobacillus and Sideroxydans (dominant FeOB) were more abundant in the plant rhizosphere, whereas Acinetobacter (dominant FeRB) was more abundant in the rhizoplane. Cd considerably decreased the relative abundance of unclassified_f_Gallionellaceae in the rhizosphere and rhizoplane but dramatically enhanced the relative abundance of Thiobacillus, Shewanella, and unclassified_f_Geobacteraceae. Unclassified_f_Geobacteraceae and Thiobacillus exhibited substantial positive correlations with citric acid and DOC in REs in the rhizosphere and rhizoplane but strong negative correlations with Sideroxydans. The findings indicate that Cd and flooding treatments may play a role in the production and breakdown of Fe plaque in K. obovata roots by affecting the relative abundance of Fe redox cycling bacteria in the rhizosphere and rhizoplane.

Effects of subacute cadmium exposure and subsequent deferiprone treatment on cadmium accumulation and on the homeostasis of essential elements in the mouse brain

IntroductionCadmium (Cd) is а hazardous multi-organ toxin. In this study, we provide the first results about the effect of oral administration of deferiprone (DFP) on Cd accumulation and on the homeostasis of essential elements in the brain of Cd-exposed mice. MethodsAdult Institute of Cancer Research (ICR) male mice were randomized into four experimental groups: untreated controls – administered distilled water for 28 days; Cd-exposed group – exposed to 18 mg/kg body weight (b.w.) Cd(II) acetate for 14 days followed by the administration of distilled water for two weeks; Cd + DFP (low dose) – Cd-intoxicated mice subsequently treated with 19 mg/kg b.w. DFP for two weeks; and Cd + DFP (high dose) – Cd-exposed mice administered high-dose DFP (135 mg/kg b.w.) for 14 days. Brains were subjected to inductively coupled plasma-mass spectrometry (ICP-MS) and histological analysis. ResultsThe results revealed that exposure of mice to Cd for 14 days significantly increased Cd concentration and significantly decreased magnesium (Mg), phosphorus (P), and zinc (Zn) contents in the brain compared to untreated controls. This effect was accompanied by necrotic-degenerative changes in both the cerebrum and cerebellum. Oral administration of low-dose DFP to Cd-exposed mice decreased the concentration of the toxic metal in the brain by 16.37% and restored the concentration of the essential elements to normal control values. Histological analysis revealed substantially improved cerebral and cerebellar histoarchitectures. In contrast, oral administration of high-dose DFP increased Cd content and significantly decreased selenium (Se) concentration in the brain. Necrotic neurons and Purkinje cells were still observed in the cerebral and cerebellar cortices. ConclusionThe results demonstrated that oral administration of DFP at low doses has a better therapeutic potential for the treatment of Cd-induced brain damage compared to high doses.

Effect of Cadmium on Macro and Micronutrient Uptake and Translocation by Leucaena leucocephala.

Environmental contamination with Cadmium (Cd) is of great concern due to its hazardous effects on living organisms.Query In the present research, Leucaena leucocephala plants were exposed to Cd concentrations of 5, 10, and 15mg/L to determine their potential use in Cd remediation. Different parameters including Cd uptake, macro/micronutrient content, chlorophyl, and catalase production were determined. Results indicated that Cd uptake by L. leucocephala roots did not show a significant difference between treatments. However, a significant increase in Cd content (Tukey´s HSD) was observed in stems as Cd levels in the media augmented. The highest Cd content (830 ± 20mg/kg) was determined in stems of plants exposed to 15mg/L Cd, and no Cd was detected in leaves. Data showed that as Cd concentration increased in the media, Ca, Mg, K, Zn, and Mn decreased. Moreover, while the presence of Cd reduced catalase activity in roots, chlorophyll production was not affected.

Evaluation of Cadmium Effects on Six Solanum melongena L. Cultivars from the Mediterranean Basin

Cadmium (Cd) contamination is a severe problem in the environment and produces detrimental effects on crop productivity and quality. Characterization of crop performance at different Cd concentrations is crucial to identify pollution-safe cultivars with low translocation efficiency to aboveground organs to be used for food safety. Here, we estimated germination, survival, growth, photosynthetic pigments, Cd bioaccumulation, among-organs translocation, and ionic balance in six Solanum melongena L. (eggplant) cultivars from the central Mediterranean basin. On two cultivars, we also analyzed expression of genes involved in Cd uptake, i.e., heavy metal ATPases (HMAs) and metal tolerance proteins (MTPs). We found that Cd has a negative effect on all the investigated parameters but with relevant among-cultivar differences. Cd-treated plants showed a decrease in germination rate and survival. Photosynthetic pigments showed opposite trends, i.e., with increasing Cd contents, we observed a decrease in chlorophylls and an increase in carotenoids. The investigated cultivars showed high ability of sequestrating Cd in roots but a low translocation efficiency to the aboveground organs, suggesting a good potential for food safety. The response of plants to Cd was mediated by a different expression of the MTP and HMA gene families. Our study represents the first comprehensive investigation of Cd tolerance in eggplant varieties from the Mediterranean basin and highlights the importance of comparative studies to identify Cd-tolerant cultivars.

Responses of soil fungal taxonomic attributes and enzyme activities to copper and cadmium co-contamination in paddy soils

Excess heavy metals, especially copper (Cu) and cadmium (Cd), are common in paddy soils in the red soil hilly areas of southern China. Microorganisms are regulators of soil organic matter accumulation and pollutant transformation. Clarifying the effects of Cu and Cd accumulation on microbial community composition and function is a prerequisite for bioremediation of paddy soil contamination. However, it remains unclear how Cu and Cd contamination affects soil fungal taxonomic attributes and microbial-mediated biogeochemical processes in paddy soils. Here, soil heavy metals, fungal community composition, and soil enzyme activities were determined in paddy fields downstream of a typical mining area in southern China, and the effects of Cu and Cd co-contamination on fungal community diversity and co-occurrence networks, as well as the associations between them were assessed. The concentrations of Cu and Cd in paddy soils decreased from upstream to downstream of the river, and were positively correlated with the Shannon index of fungal communities. Soil Cu and Cd concentrations exhibited a greater impact on the structure and assembly of fungal communities than soil general properties. Increases in soil Cu and Cd concentrations were correlated with drastic changes in the cumulative relative abundance of ecological clusters in fungal co-occurrence networks. Soil Cu and Cd concentrations were positively correlated with the relative abundances of Eurotiomycetes, Pezizomycetes, Ustilaginomycetes, and Kickxellomycetes, respectively, whereas negatively correlated with hydrolase activities related to carbon, nitrogen, and phosphorus cycles. These results confirmed in the field that long-term Cu and Cd enrichment significantly altered the structure and diversity of fungal communities in the subtropical paddy soils, thereby affecting soil nutrient transformation and organic matter accumulation. This can also provide a basis for the bioremediation of heavy metal pollution in paddy soils.

Cadmium Caused Different Toxicity to Photosystem I and Photosystem II of Freshwater Unicellular Algae Chlorella pyrenoidosa (Chlorophyta)

Heavy metals such as Cd pose environmental problems and threats to a variety of organisms. The effects of cadmium (Cd) on the growth and activities of photosystem I (PSI) and photosystem II (PSII) of Chlorella pyrenoidosa were studied. The growth rate of cells treated with 25 and 100 µM of Cd for longer than 48 h were significantly lower than the control, accompanying with the inhibition of photosynthesis. The result of quantum yields and electron transport rates (ETRs) in PSI and PSII showed that Cd had a more serious inhibition on PSII than on PSI. Cd decreased the efficiency of PSII to use the energy under high light with increasing Cd concentration. In contrast, the quantum yield of PSI did not show a significant difference among different Cd treatments. The activation of cyclic electron flow (CEF) and the inhibition of linear electron flow (LEF) due to Cd treatment were observed. The photochemical quantum yield of PSI and the tolerance of ETR of PSI to Cd treatments were due to the activation of CEF around PSI. The activation of CEF also played an important role in induction of non-photochemical quenching (NPQ). The binding features of Cd ions and photosystem particles showed that Cd was easier to combine with PSII than PSI, which may explain the different toxicity of Cd on PSII and PSI.

Effects of Phosphorus Sufficiency and Deficiency on Cadmium Uptake and Transportation by Rice

Phosphorus (P) is an essential nutrient element for crop growth. The effects of P surplus or deficit on Cd absorption and transport in rice in Cd-polluted farmland is not clear. The effects of P deficiency and P sufficiency on Cd uptake, transport, and accumulation in rice under Cd stress were investigated by applying different levels of phosphorus (NaH2PO4) in a hydroponic experiment. The results showed that:① with the increase in ρ(P) (1.5-48.0 mg·L-1), the biomass in all parts of the rice plants had no obvious change, and the contents of photosynthetic pigment (chlorophyll a, chlorophyll b, and carotenoid) firstly ascended and then descended; high concentrations of P inhibited the synthesis of photosynthetic pigments. ② Under Cd stress, when the P was deficient (1.5-6.0 mg·L-1) or sufficient (12.0-48.0 mg·L-1), the Cd content in different parts of the rice increased with the increase in P addition level, and the maximum increase in Cd content in brown rice was 132.1% and 191.2%, respectively. ③ The P/Cd of brown rice showed a piecewise decreasing rule under P deficiency and P sufficiency, and the Cd content in brown rice was significantly negatively correlated with P/Cd (P<0.01). These results indicated that elevating phosphorus concentration when rice was under both the conditions of P deficiency and P sufficiency could promote the uptake and transport of Cd by rice roots under Cd stress, thus increasing the accumulation of Cd in aboveground parts and the risk of excessive Cd in rice.

Insoluble dietary fiber (non-starch polysaccharides) from rice bran attenuates cadmium-induced toxicity in mice by modulating the gut microbiota and alleviating liver and kidney injury

Cadmium (Cd) is a toxic heavy metal and leads to various altered physiological functions, which are harmful to health. This study aimed to evaluate the protective effect of insoluble dietary fiber from rice bran (RBIDF, non-starch polysaccharides) against Cd-induced toxicity in mice. The results showed that Cd exposure caused a significant decrease in body weight and that RBIDF recovered the body weight gain of mice (P < 0.05). Moreover, RBIDF reversed the decrease of liver and kidney weight, and the increase of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine (CREA) and urea (UREA) levels. The histopathological results showed that RBIDF alleviated severe liver damage induced by Cd exposure, and improved liver cell injury and glomerulus destruction. RBIDF also decreased the Cd accumulation in the intestine and Cd absorption and increased Cd content in mouse feces (P < 0.05). In addition, at phylum level, RBIDF increased Bacteroidetes abundance, while decreased Firmicutes and Proteobacteria abundances. At genus level, it increased Lactobacillus abundance as well. It could be seen that RBIDF ameliorated the Cd-induced decrease in gut microbiota disorders. The results indicated that RBIDF was an effective component in the daily diet against Cd toxicity.

Lithologic controls on the mobility of Cd in mining-impacted watersheds revealed by stable Cd isotopes

Cd-rich wastes from open-pit mining can be transported into rivers, which are often followed by deposition in river sediments and/or further transfer into agricultural soils. The lithology of bedrock exerts a huge effect on physicochemical properties (e.g., buffering capacities, metal species, mineral phases, etc.) of the river system, thereby potentially impacting the Cd mobility in watersheds. However, to date, little is known about the microscopic processes (e.g., dissolution, adsorption, and precipitation) controlling the migration of Cd from mines to varied watersheds. This study, therefore, aims to determine the controlling factors on Cd mobilization in two mining-impacted watersheds with contrasting bedrock lithology using both Cd and Pb isotopes. The Pb isotope ratios of sediments and soils in both watersheds fall into a binary mixing model with two isotopically distinct sources, i.e., mining wastes and bedrock. These results indicate that mining activities are the main sources of Cd in sediments and soils. However, the Cd isotope ratios reveal different Cd migration processes between the two watersheds. In the siliceous watershed, the δ114/110Cd values of sediments decrease from -0.116‰ in the upper reach to -0.712‰ in the lower reach, with a concomitant increase in Cd concentration, which may result from Cd adsorption by goethite due to the increased pH. In contrast, in the calcareous watershed, the Cd isotope compositions of sediments (-0.345 to -0.276‰) and the pH of river water are nearly invariable, suggesting that the adsorption and release of Cd in sediments are limited. This may result from the strong pH buffering effect due to the presence of carbonate rocks. This study highlights the different fates of Cd in siliceous and calcareous watersheds and suggests that the development of Cd pollution control policies must consider regional lithology.

Controlling electrical and optical properties of wurtzite CdxZn1−xO with high Cd contents via native defects manipulation by low-temperature annealing

Bandgap energies in wurtzite (WZ) structured CdxZn1−xO alloys are known to decrease with increasing Cd content (x). Our previous work demonstrated that WZ-CdxZn1−xO alloys with a high Cd content of x ∼ 0.6 and a low gap of 2 eV can be stabilized by oxygen interstitials when grown in an O-rich environment. However, such O-rich WZ-CdxZn1−xO alloys have poor electrical properties due to compensating native defects. In this work, we synthesized pure WZ phase CdxZn1−xO thin films with different Cd contents by magnetron sputtering in an oxygen-rich environment. Changes in structural, electrical, and optical properties of these O-rich wurtzite CdxZn1−xO after rapid thermal annealing were investigated. While alloys with a low Cd composition of 0.2 can maintain a pure wurtzite structure up to 500 °C, phase separation occurs at a lower annealing temperature of ∼400 °C for Cd-rich (x = 0.6) films. Isochronal and isothermal annealing studies reveal the kinetics of native defects in these alloys. Highly mobile hydrogen interstitial donor defects, oxygen interstitials, and more stable cation vacancies outdiffuse sequentially as the annealing temperature increases from &amp;lt;300 to &amp;gt;400 °C. By exploiting the difference in the energy barrier between acceptor defects removal and phase separation, a pure wurtzite phase alloy with a low bandgap of 2 eV and decent electrical properties was realized by annealing O-rich WZ-Cd0.6Zn0.4O at 300 °C with an extended annealing duration of &amp;gt;100 s. These results demonstrate a practical way to obtain low-gap oxide semiconductors with strong optical absorption and controllable electrical conductivities.