Sedum alfredii Hance has been identified as a new zinc (Zn) hyperaccumulating plant species. In this study, the effects of cadmium (Cd) supply levels (control, 12.5, 25, 50, 100, 200, 400, 800 μmol ...Cd L-1) on the growth and cadmium accumulation and Zn supply on Cd accumulation in S. alfredii Hance were studied. The results showed that no reduction in shoot and root dry matter yields were noted when the plants were grown at Cd supply levels up to 200 μmol L-1 in nutrient solution. Slight stimulation on shoot growth was noted at relatively low Cd levels (25 to 100 μmol L-1). Cadmium concentrations in leaves and stems increased with increasing Cd supply levels, and reached a maximum of approximately 9000 and 6500 mg kg-1 (DW) at 400 μmol Cd L-1, respectively. Root Cd concentration increased sharply only at relatively high Cd levels. Cadmium distribution in different parts of the plant was in the order: leaf > stem >> root. The amount of Cd accumulated in the shoots reached 2.9 and 3.2 mg plant-1 at external Cd levels of 200 and 400 μmol L-1, respectively. The shoot/root Cd ratios were greater than 2 and more than 95% of the total Cd taken up by S. alfredii was translocated to the shoots at the external Cd levels ≤200 μmol L-1. The concentrations of P, Ca, Mg, B, Fe, Mn, Cu, and in the shoots and roots were influenced differentially by Cd treatments. High Zn supply (500 μmol L-1) enhanced Cd concentrations in the leaves and stems at the Cd levels ≤100 μmol L-1, and root Cd concentration at the Cd levels ≤50 μmol L-1. These results indicate that S. alfredii has an extraordinary ability to tolerate and hyperaccumulate Cd and this is the first report of the new Cd hyperaccumulator S. alfredii Hance. The finding of Cd/Zn hyperaccumulation in S. alfredii Hance provides an important plant material for understanding the mechanisms of Cd/Zn co-hyperaccumulation and for phytoremediation of the heavy metal contaminated soils.
Cadmium (Cd) enters the food chain from polluted soils via contaminated cereals and vegetables; therefore, an understanding of Cd bioaccessibility, bioavailability, and toxicity in humans through ...rice grain is needed. This study assessed the Cd bioaccessibility, bioavailability, and toxicity to humans from rice grown on Cd-contaminated soils using an in vitro digestion method combined with a Caco-2/HL-7702 cell model. Cadmium bioaccessibility (18.45–30.41%) and bioavailability (4.04–8.62%) were found to be significantly higher in yellow soil (YS) rice than calcareous soil (CS) rice with the corresponding values of 6.89–11.43 and 1.77–2.25%, respectively. Toxicity assays showed an initial toxicity in YS rice at 6 mg kg–1 Cd, whereas CS rice did not show any significant change due to low Cd concentrations. The acidic soils of Cd-contaminated areas can contribute to a higher dietary intake of Cd. Therefore, it is imperative to monitor Cd concentration in rice to minimize human health risk.
Zinc (Zn) is an essential micronutrient for humans, and increasing Zn density in rice (Oryza sativa L.) grains is important for improving human nutrition. The characteristics of Zn translocation and ...remobilization were investigated in high Zn density genotype IR68144, in comparison with the low Zn density genotype IR64. Stable isotope tracer 68Zn was supplied at various growth stages, either to the roots in nutrient solution or to the flag leaves to investigate the contribution of 68Zn absorbed at different growth stages to grain accumulation and the remobilization ability of 68Zn within plants. Significant differences in 68Zn allocation were observed between the two rice genotypes. Much higher 68Zn concentrations were found in grains, stems, and leaves of IR68144 than in IR64, but higher 68Zn was found in roots of IR64. More than half of the Zn accumulated in the grains was remobilized before anthesis, accounting for 63 and 52% of the total Zn uptake for IR68144 and IR64, respectively. Without supply of external Zn, at vegetative or reproductive stages, more 68Zn was retranslocated from “old tissues” to “new tissues” in IR68144 than in IR64. Retranslocation of 68Zn from flag leaves to grains was twice as high in the former when 68Zn was applied to the flag leaves during booting or anthesis. These results indicate that Zn density in rice grains is closely associated with the ability to translocate Zn from old tissues to new tissues at both early and late growth stages and with phloem remobilization of Zn from leaves and stems to grains.
Cadmium (Cd) content in cacao beans above a critical level (0.6 mg kg(-1)) has raised concerns in the consumption of cacao-based chocolate. Little is available regarding Cd concentration in soil and ...cacao in Ecuador. The aim of this study was to determine the status of Cd in both, soils and cacao plants, in southern Ecuador. Soil samples were collected from 19 farms at 0-5, 5-15, 15-30, and 30-50 cm depths, whereas plant samples were taken from four nearby trees. Total recoverable and extractable Cd were measured at the different soil depths. Total recoverable Cd ranged from 0.88 to 2.45 and 0.06 to 2.59, averaged 1.54 and 0.85 mg kg(-1), respectively in the surface and subsurface soils whereas the corresponding values for M3-extractable Cd were 0.08 to 1.27 and 0.02 to 0.33 with mean values of 0.40 and 0.10 mg kg(-1). Surface soil in all sampling sites had total recoverable Cd above the USEPA critical level for agricultural soils (0.43 mg kg(-1)), indicating that Cd pollution occurs. Since both total recoverable and M3-extractable Cd significantly decreased depth wise, anthropogenic activities are more likely the source of contamination. Cadmium in cacao tissues decreased in the order of beans>shell>>leaves. Cadmium content in cacao beans ranged from 0.02 to 3.00, averaged 0.94 mg kg(-1), and 12 out of 19 sites had bean Cd content above the critical level. Bean Cd concentration was highly correlated with M3- or HCl-extractable Cd at both the 0-5 and 5-15 cm depths (r=0.80 and 0.82 for M3, and r=0.78 and 0.82 for HCl; P<0.01). These results indicate that accumulation of Cd in surface layers results in excessive Cd in cacao beans and M3- or HCl-extractable Cd are suitable methods for predicting available Cd in the studied soils.
Elevated concentration of cadmium (Cd) in cacao beans has raised serious concerns about the chocolate consumption on human health. Accumulation of Cd in cacao bean in southern Ecuador has been ...related to soil contamination. In this study, soil fractionation approach was used to identify available Cd pools in the soils and to correlate these Cd pools with bean Cd concentration and soil test indexes. The distribution of soil Cd fractions decreased in the order: oxidizable > acid-soluble > residual > reducible >> water-soluble (+exchangeable). Oxidizable and acid-soluble fractions accounted for 59 and 68% of the total recoverable Cd for the 0–5 and 5–15 cm soil depth, respectively. Acid-soluble fraction was closely related to bean-Cd, with correlation coefficients (r) of 0.70 and 0.81 (P < 0.01) for the 0–5 and 5–15 cm soil depth, respectively. Acid-soluble Cd was significantly correlated with 0.01 M HCl- (r = 0.99, P < 0.01) or Mehlich 3- extractable Cd (r = 0.97, P < 0.01). These results indicate that acid-soluble Cd fraction is an important part of available Cd pool. Since approximately 60% of Cd in the cacao-growing soils is related to the acid-soluble fraction and bound to organic matter, remediation of the contaminated soils should consider to the dynamics of soil pH and organic matter content.
•Soil Cd fractionation was performed to identify available Cd pools.•Oxidizable and acid soluble Cd account for >60% of total recoverable Cd.•Acid-soluble Cd is correlated with extractable soil Cd, or cacao bean Cd.
Activation of low-grade phosphate rocks such as dolomite phosphate rock (DPR) with organic molecules of humic acid (HA) and sodium lignosulfonate (SLS) holds promise for developing slow release P ...fertilizers. Consequently, activated DPR fertilizers also contains multiple essential plant elements, including P, Ca, Mg, Zn, and Fe, while minimizing leaching losses of nutrients and heavy metals. Greenhouse experiments were conducted to examine the availability of Ca, Mg, and trace metals in soils applied with activated DPR fertilizers and subsequent response of lettuce (Lactuca Sativa L.) as compared with original DPR and water-soluble P fertilizers including superphosphates (SP) and diammonium phosphates (DAP). Application of activated DPR fertilizers stimulated the uptake of Ca, Mg, Zn, Fe, B by lettuce plants relative to original DPR and DAP. Potential toxic elements such as Cr, Cd, Ni, Pb, and Cu were mostly immobilized in soil without uptake by lettuce when applied with activated DPRs primarily due to increased soil pH, as compared with water soluble fertilizers such as DAP and SPs. Apparently, the activated DPR fertilizers offer advantages over original DPR materials and water-soluble P fertilizers in providing multiple nutrients with minimal adverse effects on soil and environmental quality.
• Wastewater affects nutrient in plants as follow: B
>
Zn
>
Mn
=
Ca
>
Cu
>
Mg
>
P
>
K. • Wastewater rendered macro-nutrients in plants closer to their optimum levels. • Imbalanced nutrients in ...wastewater cause micro-nutrients excess in plants. • Eleven years of irrigation with wastewater has no influence on fruit yield.
The effects of irrigation with reclaimed wastewater (RWW) were compared with well water (WW) on citrus (
Citrus paradisi Macfad. X
Citrus aurantium L.) nutrition. The deviation from the optimum percentage (DOP) index of macro- and micro-nutrients were used to evaluate the nutritional status: optimal (DOP
=
0), deficiency (DOP
<
0) or excess (DOP
>
0). After 11 years of RWW irrigation the influence on nutrient concentration in plants decreased in the order: B
>
Zn
>
Mn
=
Ca
>
Cu
>
Mg
>
P
>
K. Reclaimed wastewater irritation positively affected citrus nutrition as it rendered the concentration of macro-nutrients, i.e. P, Ca, and K. closer to their optimum levels (ΣDOP
macro
=
7). However micro-nutrients tended to be excessive in plants (ΣDOP
micro
=
753) due to imbalanced supply of these elements in the RWW, particularly, for B and Cu. Citrus groves with long-term RWW irrigation may exercised caution in monitoring concentrations of B and Cu to avoid plant toxicity and soil quality degradation.
Environmental pollution affects the quality ofpedosphere, hydrosphere, atmosphere, lithosphere and biosphere. Great efforts have been made in the last two decades to reduce pollution sources and ...remedy the polluted soil and water resources. Phytoremediation, being more cost-effective and fewer side effects than physical and chemical approaches, has gained increasing popularity in both academic and practical circles. More than 400 plant species have been identified to have potential for soil and water remediation. Among them, Thlaspi, Brassica, Sedum alfredii H., and Arabidopsis species have been mostly studied. It is also expected that recent advances in biotechnology will play a promising role in the development of new hyperaccumulators by transferring metal hyperaccumulating genes from low biomass wild species to the higher biomass producing cultivated species in the times to come. This paper attempted to provide a brief review on recent progresses in research and practical applications of phytoremediation for soil and water resources.
The desorption characteristics of lead in two variable charge soils (one developed from Arenaceous rock (RAR) and the other derived from Quaternary red earths (REQ)) were studied, and the effects of ...pH value, organic acid, and competitive ions were examined. Desorption of Pb
2+ decreased from nearly 100.0 to 20.0% within pH 1.0–4.0 in both soils, and then the decrease diminished at pH
>
4.0. Organic ligands at relatively low concentrations (≤10
−3
mol
L
−1) slightly inhibited Pb
2+ desorption, but enhanced Pb
2+ desorption at higher concentrations. In this study, citric acid or acetic acid at higher concentrations (>10
−3
mol
L
−1) had the greatest improvement of Pb
2+ desorption, followed by malic acid; and the smallest was oxalic acid. Desorption of the adsorbed Pb
2+ increased greatly with increasing concentrations of added Cu
2+ or Zn
2+. Applied Cu
2+ increased Pb
2+ desorption more than Zn
2+ at the same loading.
The adsorption–desorption process is a basic and important reaction in soils controlling Pb
2+ mobility and bioavailability.
Trace elements mean elements present at low concentrations (mg
kg
−1 or less) in agroecosystems. Some trace elements, including copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), molybdenum (Mo), and ...boron (B) are essential to plant growth and are called micronutrients. Except for B, these elements are also heavy metals, and are toxic to plants at high concentrations. Some trace elements, such as cobalt (Co) and selenium (Se), are not essential to plant growth but are required by animals and human beings. Other trace elements such as cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), mercury (Hg), and arsenic (As) have toxic effects on living organisms and are often considered as contaminants. Trace elements in an agroecosystem are either inherited from soil parent materials or inputs through human activities. Soil contamination with heavy metals and toxic elements due to parent materials or point sources often occurs in a limited area and is easy to identify. Repeated use of metal-enriched chemicals, fertilizers, and organic amendments such as sewage sludge as well as wastewater may cause contamination at a large scale. A good example is the increased concentration of Cu and Zn in soils under long-term production of citrus and other fruit crops.
Many chemical processes are involved in the transformation of trace elements in soils, but precipitation–dissolution, adsorption–desorption, and complexation are the most important processes controlling bioavailability and mobility of trace elements in soils. Both deficiency and toxicity of trace elements occur in agroecosystems. Application of trace elements in fertilizers is effective in correcting micronutrient deficiencies for crop production, whereas remediation of soils contaminated with metals is still costly and difficult although phytoremediation appears promising as a cost-effective approach. Soil microorganisms are the first living organisms subjected to the impacts of metal contamination. Being responsive and sensitive, changes in microbial biomass, activity, and community structure as a result of increased metal concentration in soil may be used as indicators of soil contamination or soil environmental quality. Future research needs to focus on the balance of trace elements in an agroecosystem, elaboration of soil chemical and biochemical parameters that can be used to diagnose soil contamination with or deficiency in trace elements, and quantification of trace metal transport from an agroecosystem to the environment.
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