Cadmium Fluxes Research Articles

Phosphorus and cadmium release and distribution characteristics in environmental microinterfaces of biochar based on DGT technology

ABSTRACT This study employs a soil-biochar-soil sandwich model to investigate phosphorus and cadmium transport mechanisms at the biochar-soil interface. Utilizing DGT-CID technology, we found phosphorus and cadmium exhibit gradient diffusion, with biochar as the diffusion center. Biochar significantly increased soil effective phosphorus concentration by 7-fold (p < 0.05) through sustained release. Cadmium concentration increased from 7.11 mg/L to 10.09 mg/L, with a concentration jump at the interface, indicating aggregation and transfer towards the biochar layer. Theoretical calculations show that the transport fluxes of phosphorus and cadmium at the interface were 0.94 mg/L and 0.75 mg/L, respectively. Our findings clarify the distribution and transport fluxes of these elements at the biochar-soil interface.

Arsenic and cadmium in the hydrological cycle and soil in a maquis broadleaved evergreen forest stand in Greece. Sources of some uncertainties

ABSTRACT The concentrations and fluxes of arsenic (As) and cadmium (Cd) were examined in the hydrological cycle, litterfall and soils in a maquis broadleaved evergreen forest stand in western Greece. The concentrations of the metals in the hydrological cycle ranged from 0.076 to 0.306 μg L−1 and 0.040–0.050 μg L−1 for As and Cd, respectively. It was found that the enrichment of As in the atmosphere was both due to suspended geogenic material and long range transfer, whereas for Cd the long range transfer was the predominant way for deposition. Two models were assessed to find the volumes of percolation water to compare the fluxes with the estimated ones derived from soil solution measurements. The daily deterministic forest-hydrological model (WBS3) was found to perform better than the physically based 1D semi-distributed soil-plant-atmosphere model (BROOK90). When calculating the total amounts of the heavy metals in soils, the statistical uncertainty derived from every soil layer has to be taken into account. The residence time of Cd in the forest floor (L + FH) of the soils was found 6.4 years, whereas that of As 36.3 years. This difference shows the mobility of Cd in comparison to As in the soils of the area.

Characterizing the remobilization flux of cadmium from pre-anthesis vegetative pools in rice during grain filling using an improved stable isotope labeling method

A clear understanding of the allocation of Cd to grains is essential to manage the level of Cd in cereal diets effectively. Yet, debate remains over whether and how the pre-anthesis pools contribute to grain Cd accumulation, resulting in uncertainty regarding the need to control plant Cd uptake during vegetative growth. To this end, rice seedlings were exposed to 111Cd labeled solution until tillering, transplanted to unlabeled soils, and grown under open-air conditions. The remobilization of Cd derived from pre-anthesis vegetative pools was studied through the fluxes of 111Cd-enriched label among organs during grain filling. The 111Cd label was continuously allocated to the grain after anthesis. The lower leaves remobilized the Cd label during the earlier stage of grain development, which was allocated almost equally to the grains and husks + rachis. During the final stage, the Cd label was strongly remobilized from the roots and, less importantly, the internodes, which was strongly allocated to the nodes and, to a less extent, the grains. The results show that the pre-anthesis vegetative pools are an important source of Cd in rice grains. The lower leaves, internodes, and roots are the source organs, whereas the husks + rachis and nodes are the sinks competing with the grain for the remobilized Cd. This study provides insight into understanding the ecophysiological mechanism of Cd remobilization and setting agronomic measures for lowering grain Cd levels.

Cadmium Transport in Maize Root Segments Using a Classical Physiological Approach: Evidence of Influx Largely Exceeding Efflux in Subapical Regions.

The bidirectional fluxes of cadmium and calcium across the plasma membrane were assessed and compared in subapical maize root segments. This homogeneous material provides a simplified system for investigating ion fluxes in whole organs. The kinetic profile of cadmium influx was characterized by a combination of a saturable rectangular hyperbola (Km = 30.15) and a straight line (k = 0.0013 L h-1 g-1 fresh weight), indicating the presence of multiple transport systems. In contrast, the influx of calcium was described by a simple Michaelis-Menten function (Km = 26.57 µM). The addition of calcium to the medium reduced cadmium influx into the root segments, suggesting a competition between the two ions for the same transport system(s). The efflux of calcium from the root segments was found to be significantly higher than that of cadmium, which was extremely low under the experimental conditions used. This was further confirmed by comparing cadmium and calcium fluxes across the plasma membrane of inside-out vesicles purified from maize root cortical cells. The inability of the root cortical cells to extrude cadmium may have driven the evolution of metal chelators for detoxifying intracellular cadmium ions.

Land use change increases contaminant sequestration in blue carbon sediments

Coastal blue carbon habitats perform many important environmental functions, including long-term carbon and anthropogenic contaminant storage. Here, we analysed twenty-five 210Pb-dated mangrove, saltmarsh, and seagrass sediment cores from six estuaries across a land-use gradient to determine metal, metalloid, and phosphorous sedimentary fluxes. Cadmium, arsenic, iron, and manganese had linear to exponential positive correlations between concentrations, sediment flux, geoaccumulation index, and catchment development. Increases in anthropogenic development (agricultural or urban land uses) from >30 % of the total catchment area enhanced mean concentrations of arsenic, copper, iron, manganese, and zinc between 1.5 and 4.3-fold. A ~ 30 % anthropogenic land-use was the threshold in which blue carbon sediment quality begins to be detrimentally impacted on an entire estuary scale. Fluxes of phosphorous, cadmium, lead, and aluminium responded similarly, increasing 1.2 to 2.5-fold when anthropogenic land-use increased by at least 5 %. Exponential increases in phosphorus flux to estuary sediments seem to precede eutrophication as observed in more developed estuaries. Overall, multiple lines of evidence revealed how catchment development drives blue carbon sediment quality across a regional scale.

Integrated assessment of land-to-river Cd fluxes and riverine Cd loads using SWAT-HM to guide management strategies

In 2011, China invested US$9.8 billion to combat the severe heavy metal pollution in the Xiang River basin (XRB), aiming to reduce 50% of the 2008 industrial metal emissions by 2015. However, river pollution mitigation requires a holistic accounting of both point and diffuse sources, yet the detailed land-to-river metal fluxes in the XRB remain unclear. Here, by combining emissions inventories with the SWAT-HM model, we quantified the land-to-river cadmium (Cd) fluxes and riverine Cd loads across the XRB from 2000 to 2015. The model was validated against long-term historical observations of monthly streamflow and sediment load and Cd concentrations at 42, 11, and 10 gauges, respectively. The analysis of the simulation results showed that the soil erosion flux dominated the Cd exports (23.56–80.14 Mg yr−1). The industrial point flux decreased by 85.5% from 20.84 Mg in 2000 to 3.02 Mg in 2015. Of all the Cd inputs, approximately 54.9% (37.40 Mg yr−1) was finally drained into Dongting Lake; the remaining 45.1% (30.79 Mg yr−1) was deposited within the XRB, increasing the Cd concentration in riverbed sediment. Furthermore, in XRB's 5-order river network, the Cd concentrations in small streams (1st order and 2nd order) showed larger variability due to their low dilution capacity and intense Cd inputs. Our findings highlight the need for multi-path transport modeling to guide future management strategies and better monitoring schemes to restore the small polluted streams.

Machine learning method for predicting cadmium concentrations in rice near an active copper smelter based on chemical mass balance

Identification the sources of heavy metals can effectively control and prevent agricultural soil pollution. Here we performed a three-year mass balance study along a gradient of soil pollution near a smelter to quantify the potential contribution and net cadmium (Cd) fluxes and predict Cd concentration in rice grains by multiple regression (MR) and back propagation (BP) neural network. The Cd inputs were mainly from the irrigation water (54.6–60.8%) in the moderately polluted and background sites but from atmospheric deposition (90.9%) in the highly polluted site. The Cd outputs were mainly from the surface runoff (55.8–59.5%) in the moderately polluted and background sites, but from Sedum plumbizincicola phytoextraction (83.6%) in the highly polluted site. The soil Cd concentrations, the annual fluxes of atmospheric deposition, pesticides and fertilizers, irrigation water, surface runoff, and leaching water were selected as the dependent factors to predict Cd concentrations in rice grains. The genetic algorithms (GA)-BP neural network model gives the best prediction accuracy compared to the BP neural network model and multivariate regression analysis. The major implication is that the health risks through the consumption of rice can be rapidly assessed based on the Cd concentrations in rice grains predicted by the model.

Cadmium pollution of environment by the use of solar cells: a systemic review of the problem

Use of solar cells contributes to ecologization of the energy sector of economy, but also requires taking into account various influences on environment. Particularly, many of them utilize cadmium (as cadmium telluride), which triggers concerns of possible pollution by this toxic heavy metal. This article summarizes and systematizes a significant amount of information, which allows evaluating such a pollution. Methodologically, this work is based on bibliographical survey and examination of the content of articles in the leading domestic and foreign editions on the considered problematic. It is established that the problem of cadmium pollution of environment by the use of solar cells has generally been formulated in the contemporary science, but as hypothetical to significant degree, and its treatment is distinguished by remarkable incompleteness. The authors show that in the light of the earlier conducted research, pollution of environment (also industrial) can take place together with cadmium extraction, production of solar cells, their use and utilization, the facts of which are known. The scale of this problem is currently difficult to establish, but its under-study itself creates risks of its large-scale appearance in the nearest future. Sometimes, scientists raise the question of replacing cadmium-bearing materials by those ecologically more “clean”. In this regard, a question is posed about whether such a replacement would diminish interest to correct utilization of already used cells, mass accumulation of which as waste makes pollution inevitable. The attention is also paid to the fact that even if solar energetic itself diminishes cadmium flux to environment via replacement of “traditional” sources of energy, changes in the geography of production of the latter is able to extend the appearance of the considered problem.

Annual net input fluxes of cadmium in paddy soils in karst and non-karst areas of Guangxi, China

In recent years, the problems of high cadmium content and low Cd mobility in karst areas compared with non-karst areas have attracted extensive attention. Identifying the difference between the net Cd flux in karst and non-karst areas is crucial for sustainable land management. Basically, rock weathering is a natural source of Cd. While Cd accumulation in soil has increased due to both anthropogenic and natural sources, the contributions of anthropogenic input and rock weathering to soil Cd concentration in karst and non-karst areas remain unclear. In this study, the input (e.g., atmospheric deposition, fertilizer and irrigation) and output fluxes (e.g., leaching and early and later rice harvest) of Cd in farmland soils in karst and non-karst areas of Guangxi from 2017 to 2018 were monitored. The results showed no significant difference (P = 0.289) in the contributions of various input pathways between karst area and non-karst area, and atmospheric deposition (64–55 %) played an important role in the input fluxes. Nevertheless, the low soil pH value and high rainfall in non-karst areas increase Cd mobility and plant availability in soil, causing the output flux in non-karst areas (5.30 g/ha/y) to be greater than that in karst areas (3.17 g/ha/y). According to the national standard, the exceedance rate of Cd in rice grains in non-karst area (17 %) was higher than that in karst area (15 %). Therefore, ecological risk assessment in non-karst areas with high Cd bioavailability should be prioritized. Furthermore, the annual increase rate of Cd concentration in topsoil of karst and non-karst areas was −0.27 μg/kg/y and −1.23 μg/kg/y, respectively. However, the soil Cd concentration in karst and some non-karst areas still exceeded the guideline value. Given that the net input flux of Cd was negative, the accumulation of Cd in soil may be determined by rock weathering.

Trace metal concentrations, fluxes, and potential human health risks in West Africa rivers: a case study on the Bia, Tanoé, and Comoé rivers (Cote d'Ivoire).

Downstream water pollution resulting from anthropogenic pressures on upstream water can cause conflicts, especially in transboundary rivers basins. This study assessed trace metals cadmium, lead, copper, and iron total concentrations, fluxes, and the potential human health risks through ingestion or dermal contact of waters at the mouth of three West African transboundary rivers: the Comoé, Bia, and Tanoé rivers. The results showed highest total concentrations during the months of May and October and statistically comparable concentrations in the rivers. The fluxes discharged to the Atlantic Ocean through the Aby and Ebrie Lagoons are as high as average values found elsewhere in the World. Trace metals lead, copper, and iron fluxes were highest during the month of October in the Bia, Tanoé, and Comoé rivers. The cadmium flux was highest during the month of October in the Bia and Comoé rivers, and during the months of February and December in the Tanoé River, indicating that contamination came mainly from upstream waters and the draining of the river basins. The Pearson correlation analysis showed that the trace metals were mainly from anthropogenic sources including gold mining and agriculture. The total concentrations were lower than international guidelines set by the World Health Organization (WHO). However, the potential human health risk assessment results suggest a significant likelihood of community exposure to harmful effects but not to cancers through water ingestion. This work recommends including small rivers when assessing global river metal fluxes to the ocean and also reducing upstream inputs from human activities to mitigate downstream river water pollution.

Sedimentary cycling and benthic fluxes of manganese, cobalt, nickel, copper, zinc and cadmium in the Peruvian oxygen minimum zone

Marine sediments are an important source and sink of bio-essential trace metals to the ocean. However, the different mechanisms leading to trace metal release or burial are not fully understood and the associated fluxes are not well quantified. Here, we present sediment, pore water, sequential extraction and benthic flux data of Mn, Co, Ni, Cu, Zn and Cd along a latitudinal depth transect across the Peruvian oxygen minimum zone at 12°S. Sediments are depleted in Mn and Co compared to the lithogenic background. Diffusive Mn fluxes from the sediments into the bottom water (−26 to −550 μmol m−2 y−1) are largely consistent with the rate of Mn loss from the solid phase (−100 to −1160 μmol m−2 yr−1) suggesting that 50% or more of the sedimentary Mn depletion is attributed to benthic efflux. In contrast, benthic Co fluxes (~ −3 μmol m−2 yr−1) are lower than the rate of Co loss from the solid phase (up to −120 μmol m−2 yr−1), implying Co dissolution in the water column. The trace metals Ni, Cu, Zn and Cd are enriched within the sediments with respect to the lithogenic background. Uptake of Ni by phytoplankton in the photic zone and delivery with organic matter to the sediment surface can account for up to 100% of the excess Ni accumulation (87 to 180 μmol m−2 y−1) in shelf sediments near the coast, whereas at greater water depth additional scavenging by Mn- and Fe-oxides may contribute to Ni accumulation. Up to 20% of excess Cu (33 to 590 μmol m−2 y−1) and generally less than 20% of excess Zn (58 to 2170 μmol m−2 y−1) and Cd (6 to 260 μmol m−2 y−1) can be explained by delivery with fresh organic matter. Sequential extraction data suggest that the discrepancies between the known sources of Cd (and Cu) and their excess accumulation may be driven by the delivery of allochthonous sulphide minerals precipitated from the water column. Additionally, Cu may be scavenged by downward sinking organic material. In contrast, precipitation of Zn sulphide chiefly takes place in the sediment. Diffusive Zn fluxes into the sediment (21 to 1990 μmol m−2 y−1) match the excess Zn accumulation suggesting that Zn delivery is mediated by molecular diffusion from bottom waters. Considering the diverse behavioural pattern of trace metals observed in this study, we argue that declining oxygen and increasing hydrogen sulphide concentrations in a future ocean will modify trace metal fluxes at the seafloor and the trace metal stoichiometry of seawater.

Integrated spatial approaches for long-term monitoring of cadmium contamination caused by rainfall erosion: A case study of overland sediment in Mae Sot, Thailand

Mae Tao basin, Thailand has been reported as a remote cadmium (Cd) - contaminated area from 2002 to 2016 and a declaration on the contaminant source has not been accomplished. Howbeit, the determination of contaminant sources transmitted by overland flow is generally limited by various kinds of factors, data insufficiency in particular. In this study, the integrated spatial technology between remote sensing, digital mapping, GIS, and RUSLE were used to conduct the approach in deciding the source of contamination in the basin. According to the results, the significant anthropogenic activity which can release the highest cadmium's level was determined as the cornfield in the upstream. With the potential cadmium flux from erosion ranged from 279.86 to 703.73 t/ha/year and 0.77 correlation factor to the cadmium contamination level in the creeks, the soil surface and corn collected from the upstream were investigated using FAAS and Micro XRF for validation. The cadmium transported by upstream soil surface may not affect the Cd contamination in the downstream so that the contamination's source be from other anthropogenic activities. As a result, this integrated method demonstrates a capability in applying this set of applications to monitoring, investigating and managing contaminant sources in a remote area.

Mass balance approach to assess the impact of cadmium decrease in mineral phosphate fertilizers on health risk: The case-study of French agricultural soils

Cadmium is a ubiquitous and highly toxic contaminant that can cause serious adverse effects. The European Food Safety Authority (EFSA) and the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) have shown that the risk related to food contamination by cadmium cannot be ruled out in Europe and France. Fertilizing material is one of the main sources of cadmium contamination in the food chain on which regulators can play to reduce cadmium exposure in the population. The aim of this work was to develop a mass-balance approach integrating the various environmental sources of cadmium to estimate the effects of a decrease in cadmium concentrations in crop fertilizers on dietary exposure and on the health risk. This approach led to a predictive model that can be used as a decision-making tool. Representative and protective fertilization scenarios associated with controlled cadmium levels in mineral phosphate fertilizers were simulated and converted into cadmium fluxes. Cadmium inputs from industrial mineral phosphate fertilizers were then compared with cadmium brought by the application of manure, sewage sludge and farm anaerobic digest, at the levels typical of French agricultural practices. Regardless of the fertilizer and scenario used, a flux lower than 2 g Cd.ha−1.year−1 reduces both the accumulation in soils and the transfer of cadmium in the food chain. It corresponds to a cadmium content of 20 mg.kg P2O5−1 or less in mineral phosphate fertilizers. Modelling the transfer of cadmium from the soil to consumed food made it possible to propose cadmium limits in fertilizers applied in France. In a global context of ecological transition to promote human health, this research will help risk managers and public authorities in the regulatory decision-making process for the reduction of environmental cadmium contamination and human exposure.

The control of hydrogen sulfide on benthic iron and cadmium fluxes in the oxygen minimum zone off Peru

Abstract. Sediments in oxygen-depleted marine environments can be an important sink or source of bio-essential trace metals in the ocean. However, the key mechanisms controlling the release from or burial of trace metals in sediments are not exactly understood. Here, we investigate the benthic biogeochemical cycling of iron (Fe) and cadmium (Cd) in the oxygen minimum zone off Peru. We combine bottom water and pore water concentrations, as well as benthic fluxes determined from pore water profiles and from in situ benthic chamber incubations, along a depth transect at 12∘ S. In agreement with previous studies, both concentration–depth profiles and in situ benthic fluxes indicate a release of Fe from sediments to the bottom water. Diffusive Fe fluxes and Fe fluxes from benthic chamber incubations (−0.3 to −17.5 mmol m−2 yr−1) are broadly consistent at stations within the oxygen minimum zone, where the flux magnitude is highest, indicating that diffusion is the main transport mechanism of dissolved Fe across the sediment–water interface. The occurrence of mats of sulfur-oxidizing bacteria on the seafloor represents an important control on the spatial distribution of Fe fluxes by regulating hydrogen sulfide (H2S) concentrations and, potentially, Fe sulfide precipitation within the surface sediment. Rapid removal of dissolved Fe after its release to anoxic bottom waters hints at oxidative removal by nitrite and interactions with particles in the near-bottom water column. Benthic flux estimates of Cd suggest a flux into the sediment within the oxygen minimum zone. Fluxes from benthic chamber incubations (up to 22.6 µmol m−2 yr−1) exceed diffusive fluxes (&lt;1 µmol m−2 yr−1) by a factor of more than 25, indicating that downward diffusion of Cd across the sediment–water interface is of subordinate importance for Cd removal from benthic chambers. As Cd removal in benthic chambers covaries with H2S concentrations in the pore water of surface sediments, we argue that Cd removal is mediated by precipitation of cadmium sulfide (CdS) within the chamber water or directly at the sediment–water interface. A mass balance approach, taking the contributions of diffusive and chamber fluxes as well as Cd delivery with organic material into account, suggests that CdS precipitation in the near-bottom water could make an important contribution to the overall Cd mass accumulation in the sediment solid phase. According to our results, the solubility of trace metal sulfide minerals (Cd ≪ Fe) is a key factor controlling trace metal removal and, consequently, the magnitude and the temporal and spatial heterogeneity of sedimentary fluxes. We argue that, depending on their sulfide solubility, sedimentary source or sink fluxes of trace metals will change differentially as a result of declining oxygen concentrations and the associated expansion of sulfidic surface sediments. Such a trend could cause a change in the trace metal stoichiometry of upwelling water masses with potential consequences for marine ecosystems in the surface ocean.

Non-invasive microelectrode cadmium flux measurements reveal the decrease of cadmium uptake by zinc supply in pakchoi root (Brassica chinensis L.)

Zinc (Zn) possesses similar properties to cadmium (Cd) and inhibits Cd uptake in plants. To get more detailed mechanisms of Zn-inhibited Cd uptake in pakchoi, a hydroponic experiment was conducted to investigate the effects of various Zn levels on Cd concentrations, real time flux of Cd, expressions of genes related to Cd uptake under Cd exposure. The results showed that the Cd concentrations and Cd accumulations in pakchoi root decreased with increasing Zn levels, which were coincident with that real time Cd influx and net Cd influx of pakchoi root decreased with increasing Zn levels by non-invasive micro-test technology (NMT). Additionally, the expressions of Cd-related transporters including BcNRAMP5, BcIRT1 and BcMGT1 decreased with the increase of Zn levels under Cd exposure, especially BcIRT1 with the highest decreased rates. Furthermore, the expressions of these genes decreased gradually with the prolongation of Zn treated time under Cd toxicity. The results indicate that Zn inhibits Cd uptake by inhibition of the expressions of Cd-related transporters, especially BcIRT1 in pakchoi root.

Isotope Tracing of Long-Term Cadmium Fluxes in an Agricultural Soil.

Globally widespread phosphate fertilizer applications have resulted in long-term increases in the concentration of cadmium (Cd) in soils. The accumulation of this biotoxic, and bioaccumulative metal presents problems for the management of soil-plant-animal systems, because the magnitude and direction of removal fluxes (e.g., crop uptake, leaching) have been difficult to estimate. Here, Cd isotopic compositions (δ114/110Cd) of archived fertilizer and soil samples from a 66 year-long agricultural field trial in Winchmore, New Zealand, were used to constrain the Cd soil mass balance between 1959 and 2015 AD, informing future soil Cd accumulation trajectories. The isotopic partitioning of soil Cd sources in this system was aided by a change in phosphate source rocks in 1998 AD, and a corresponding shift in fertilizer isotope composition. The dominant influence of mixing between isotopically distinct Cd end-members was confirmed by a Bayesian modeling approach. Furthermore, isotope mass balance modeling revealed that Cd removal processes most likely increased in magnitude substantially between 2000 and 2015 AD, implying an increase in Cd bioaccumulation and/or leaching over that interval. Natural-abundance stable isotopes are introduced here as a powerful tool for tracing the fate of Cd in agricultural soils, and potentially the wider environment.

Subsurface cadmium loss from a stony soil-effect of cow urine application.

Cadmium (Cd) losses in subsurface flow from stony soils that have received cow urine are potentially important, but poorly understood. This study investigated Cd loss from a soil under a winter dairy-grazed forage crop that was grazed either conventionally (24h) or with restricted grazing (6h). This provided an opportunity to test the hypothesis that urine inputs could increase Cd concentrations in drainage. It was thought this would be a result of cow urine either (i) enhancing dissolved organic carbon (DOC) concentrations via an increase in soil pH, resulting in the formation of soluble Cd-organic carbon complexes and, or (ii) greater inputs of chloride (Cl) via cow urine, promoting the formation of soluble Cd-Cl complexes. Cadmium concentrations in subsurface flow were generally low, with a spike above the water quality guidelines for a month after the 24-h grazing. Cadmium fluxes were on average 0.30gCdha-1year-1 (0.27-0.32gCdha-1year-1), in line with previous estimates for agricultural soils. The mean Cd concentration in drainage from the 24-h grazed plots was significantly higher (P<0.05) than 6-h plots. No increase in DOC concentrations between the treatments was found. However, Cl concentrations in drainage were significantly higher (P<0.001) from the 24-h than the 6-h grazed treatment plots, and positively correlated with Cd concentrations, and therefore, a possible mechanism increasing Cd mobility in soil. Further study is warranted to confirm the mechanisms involved and quantities of Cd lost from other systems.

Net cadmium flux and gene expression in relation to differences in cadmium accumulation and translocation in four apple rootstocks

In order to investigate the variations in Cd uptake, translocation and tolerance among four apple rootstocks, seedlings were exposed to either 0 or 50μM CdCl2 for 50 days. Net Cd2+ influxes in the rhizosphere were greatest at 600μm in root meristematic zone of all apple rootstocks. There were large variations in net Cd2+ influxes among different apple rootstocks and the lowest Cd2+ influxes into roots and leaf petiole vascular bundles were observed in Malus baccata (Mb). Net Cd2+ influxes into roots of all apple rootstocks were significantly decreased after the treatment with metabolic inhibitors and channel blockers, such as vanadate, verapamil and N-ethylmaleimide. Moreover, net Cd2+ influxes into roots were also affected by exogenous Fe3+ concentrations. Cd exposure caused decline in photosynthesis and biomass increment in all apple rootstocks except in M. baccata (Mb). Among four apple rootstocks, M. baccata (Mb) displayed the lowest Cd concentrations and amounts in tissues, and the smallest bio-concentration factor (BCF) and translocation factor (Tf) under Cd exposure. Gene expression levels regarding Cd uptake, transport and detoxification were in line with the tendencies of Cd absorption, transport and tolerance, respectively. M. baccata (Mb) had lower transcript levels of genes related to Cd uptake and translocation but stronger gene expression for Cd detoxification. On the basis of this experiment, it is concluded that M. baccata (Mb) is superior to other three apple rootstocks to be used as rootstock in Cd contaminated soil.

Effect of supporting membrane on removal of cadmium by the hybrid liquid membrane process

A hybrid liquid membrane process was used to remove cadmium cation from a solution using bis-(2-ethylhexyl) phosphoric acid as the carrier for the first time. Different polyethersulphone supporting membranes were prepared by a phase inversion technique. The prepared membrane could be efficiently used as the supporting membranes for the proposed process. The effects of porosity and pore size of the supporting membrane on removal efficiency were investigated. In addition, the effects of various operating parameters such as carrier concentration in organic phase, pH of feed phase, acid concentration, and temperature on the performance of the process were also investigated. It was found that the maximum flux of cadmium is obtained using the supporting membrane with 84.5% porosity and the pore size of 132 nm. The optimum carrier concentration is 0.2 M, the optimum pH of the feed phase is 6, and the optimum concentration of acid in the stripping phase is 0.6 M.

Estimation of potential cadmium contamination using an integrated RUSLE, GIS and remote sensing technique in a remote watershed area: a case study of the Mae Tao Basin, Thailand

The Mae Tao Basin in Mae Sot district, Thailand, is a cadmium contaminated area, where the dominant carrier of the contaminant is sediment leached into the water resources by surface runoff. The Revised Universal Soil Loss Equation incorporated with remote sensing and geographic information system software were applied to calculate the potential erosion that can occur in the Mae Tao Basin. The erosion potential was combined with the cadmium concentration profile, obtained using secondary data from the Land Development Department, Royal Thai Survey Department and Meteorological Department of Thailand, to calculate the potential cadmium flux due to erosion. The results indicate that maximum value of potential cadmium flux due to erosion occurred in the mining production area of the Mae Tao Basin. In addition, there is significant evidence that the upstream area of the basin has the potential to release cadmium during incidents of erosion.