The influence of nutritional conditions on metal uptake by the mixotrophic dual symbiosis harboring vent mussel Bathymodiolus azoricus

The vent mussel Bathymodiolus azoricus, host thioautotrophic and methanotrophic bacteria, in their gills and complementary, is able to digest suspended organic matter. But the involvement of nutritional status in metal uptake and storage remains unclear. The influence of B. azoricus physiological condition on its response to the exposure of a mixture of metals in solution is addressed. Mussels from the Menez Gwen field were exposed to 50 μg L^− 1 Cd, plus 25 μg L^− 1 Cu and 100 μg L^− 1 Zn for 24 days. Four conditions were tested: (i) mussels harboring both bacteria but not feed, (ii) harboring only methanotrophic bacteria, (iii) without bacteria but fed during exposure and (iv) without bacteria during starvation. Unexposed mussels under the same conditions were used as controls. Eventual seasonal variations were assessed. Metal levels were quantified in subcellular fractions in gills and digestive gland. Metallothionein levels and condition indices were also quantified. Gill sections were used for fluorescence in situ hybridization (FISH) to assess the temporal distribution of symbiotic associations. Starvation damages metal homeostasis mechanisms and increase the intracellular Zn and MT levels function. There is a clear metallic competition for soluble and insoluble intracellular ligands at each condition. Seasonal variations were observed at metal uptake and storage.     

Effects of eutrophic water flooding on nitrate concentrations in mine wastes

Salt marshes near urban, industrial and mining areas are often affected both by heavy metals and by eutrophic water. The aim of this study was to assess and evaluate the main processes involved in the decrease of nitrate concentration in pore water of mine wastes flooded with eutrophic water, considering the presence or absence of plant rhizhosphere. Basic (pH ∼ 7.8) carbonated loam mine wastes and free-carbonated acidic (pH ∼ 6.2) sandy-loam mine wastes were collected from polluted coastal salt marshes of SE Spain which regularly receive nutrient-enriched water. The wastes were put in pots and flooded for 15 weeks with eutrophic water (dissolved organic carbon ∼26 mg L⁻¹, PO₄³⁻ ∼23 mg L⁻¹, NO₃⁻ ∼180 mg L⁻¹). Three treatments were assayed for each type of waste: pots with Sarcocornia fruticosa, pots with Phragmites australis and unvegetated pots. Soluble organic carbon, nitrate, soluble Cd, Pb and Zn, pH and Eh were monitored. But the 2nd day of flooding, nitrate concentrations had decreased between 70% and 90% (equivalent to 1.01-1.12 g N-NO₃⁻ m⁻² day⁻¹) with respect to the content in the water used for flooding, except in unvegetated pots with acidic wastes. Denitrification was the main mechanism associated with the removal of nitrate. The role of vegetation in improving the rhizospheric environment was relevant in the acidic wastes because higher sand content, lower pH and higher soluble metal concentrations might strongly hinder microbial activity Hence, revegetation of salt marshes polluted by acidic sandy mining wastes might improve the capacity of this type of environment to act as a green filter against excessive nitrate contents flowing through them.     

Accumulation of Indium and other heavy metals by Eleocharis acicularis: an option for phytoremediation and phytomining

Eleocharis acicularis was exposed to different concentrations of In, Ag, Pb, Cu, Cd, and Zn in the laboratory to assess its capability in accumulating these metals. After 15 days, 477 mg/kg dry wt. of In was accumulated by the roots; concentrations of Ag, Pb, Cu, Cd, and Zn in the shoots were 326, 1120, 575, 195, and 213 mg/kg dry wt., respectively. The results indicate that E. acicularis has the ability to accumulate these metals from water, making it a good candidate species for phytoremediation and phytomining.     

Effects of vegetation and fertilizer on metal and Sb plant uptake in a calcareous shooting range soil

Shooting range soils frequently contain anomalous concentrations of metals (e.g. Pb, Zn, Mn) and Sb coming from bullets which may be released into the environment. In a pot experiment, we investigated metal and Sb uptake by three plant species (Plantago lanceolata, Lolium perenne and Triticum aestivum) growing on a calcareous shooting range soil (pH 7.8; 500 mg kg⁻¹ Pb, 21 mg kg⁻¹ Sb) and the uptake changes when an acidic fertilizer solution was applied to the soil. Metal and Sb solubility in the soil was determined by extraction with 0.1 M NaNO₃. In addition, we measured pH, electrical conductivity and dissolved organic carbon in drainage samples. The results showed significant increase over time of pH (from 7.8 to 8.3) and decrease of electrical conductivity and dissolved organic carbon (from 230 to ∼130 mg L⁻¹). Fertilizer application increased NaNO₃-extractable Pb and Sb and root:shoot biomass ratio but not plant metal uptake. In T. aestivum spikes accumulated more Zn, Ni and Cu than shoots and grains. Mn and Zb uptake was correlated in L. perenne shoots. P. lanceolata, a Sb-bioindicator, did not accumulate high amounts of Sb (<1 mg kg⁻¹).     

Effects of sediment-bound Cd, Pb, and Ni on the growth, feeding, and survival of Capitella sp. I

Anthropogenic metal pollutants bioaccumulated in benthic animals by means of feeding and osmotic diffusion. These metals may affect the physiology of the benthos. In this study, we exposed Capitella sp. I to three metals (Cd, Pb, and Ni), each in eight different concentrations, to determine the effects of metals on the animals. Growth rate, ingestion rate, and percent survival were estimated in three separated experiments. The growth and feeding of the worms were sensitive to even the lowest concentrations of each metal added to the sediments. The lowest observable adverse effect levels for Cd, Ni, and Pb were 0.03, 1.59, and 0.41 μmol g^− 1 sediment, respectively. Growth rates in the elevated metal contaminant treatments decreased drastically at slightly contaminated levels, lessened detrimental effects at moderately contaminated levels, and showed incompensable intoxication at heavily contaminated levels. The trends in ingestion rates were similar to those of growth rates. No significant difference in survivorship was found among the different contaminant levels for any of the three heavy metals. Capitella sp. I was most sensitive to Cd, followed by Ni and Pb, which had similar effects. The rapid physiological responses of Capitella sp. I allowed the animals to survive metal exposure. Sediment productivity remained unchanged at different contamination levels of Ni and Pb, but was drastically reduced at 4.75 μmol g^− 1 Cd in the sediment. This further demonstrated Capitella sp. I can adjust their ingestion rates to maintain constant sediment productivities in moderate pollution conditions; however, when threshold concentration was exceeded, homeostasis collapsed.     

Inoculation of Rhizobium (VR-1 and VA-1) induces an increasing growth and metal accumulation potential in Vigna radiata and Vigna angularis L. growing under fly-ash

Fly-ash-tolerant Rhizobium strains were isolated from plants grown in fly-ash-contaminated soil, axenically under laboratory conditions. Saplings of both plants were raised in N₂-free Jenson medium and inoculated with 2.6 × 10⁸ cell ml⁻¹ and 5.2 × 10⁸ cell ml⁻¹ of culture after 10 d of growth. Plants were transferred into 100% fly-ash under natural condition. Rhizobium-inoculated plants grown on 100% fly-ash showed marked increase in relation to root-shoot length, biomass yield, photosynthetic pigment, protein content and nodulation frequency compared to uninoculated plant grown in control (100% fly-ash). Inoculation of fly-ash-tolerant Rhizobium increased the accumulation of Fe, Zn, Cu Cd and Cr in different tissues vis-à-vis enhanced translocation of metals to the aboveground part of plant. Although inoculation of fly-ash-tolerant Rhizobium strains (VR-1 and VA-1) enhanced the translocation of more Fe to shoot parts, nevertheless, the amount of Rhizobium inoculants supplied to the plant was found to be very important since it has a positive role in increasing plant growth through increased N₂ supply via nitrogenase activity. Results suggest that an integrated approach employing biotechnological means and inoculation of plants with host-specific fly-ash-tolerant Rhizobium strain may prove a stimulus to a fly-ash management programme.     

Seasonal courses of nutrients and heavy metals in water,sediment and above- and below-ground Typha domingensis biomass in Lake Burullus (Egypt): Perspectives for phytoremediation

The present study was carried out in natural stands of Typha domingensis in Lake Burullus, Egypt, to investigate (1) nutrient dynamics and heavy metals accumulation in its organs, (2) the phytoextractive potential of its organs and (3) the amount of nutrients and heavy metals released back into the water after decomposition of the dead tissues. Nitrogen concentrations were higher in the shoot than in the root and rhizome, while P, Ca, Cu, Fe, Zn and ash concentrations were higher in the root than in the rhizome and shoot. Significant differences in the concentrations of Mg, Cd, Cu and ash were assessed during the growing season of T. domingensis. The content of most nutrients and heavy metals in the shoot increased rapidly during the early growing season in February, reached maximal values in July and then decreased again. The nutrient and heavy metal contents in the below-ground portion of the plant showed an opposite trend compared to the shoot; they decreased sharply during the spring, when they were translocated, supporting the heterotrophic phase of shoot growth. However, they increased slightly from July to September and then decreased again. The transfer factors of all nutrients and heavy metals from the sediment to the below-ground organs were greater than unity. The higher translocation ratio of N in T. domingensis shoots makes it suitable for N phytoextraction from water and sediment, while the lower translocation ratios for Cd, Cu, Fe, Pb and Zn make it suitable for metal ion phytostabilisation. The dead shoot biomass of the stands at the end of 2010 amounted to 1950 g DM m⁻², when the seasonal decomposition process began. With a decay rate of 0.0049 day⁻¹, 1624 g DM m⁻² is decomposed in the lake in a year. This is equivalent to releasing the following nutrient and heavy metals into the surrounding water (in g m⁻²): 23.4 N, 0.8 P, 19.2 Ca, 1.8 Mg, 5.6 Na, 32.8 K, 0.01 Cd, 0.01 Cu, 0.84 Fe, 0.12 Pb and 0.03 Zn.     

Bioaccumulation du Cd et du Zn chez les plants de tomates (Lycopersicon esculentum L.)

This work aims at evaluating the accumulation of cadmium (Cd) and zinc (Zn) (trace elements) in the organs of young tomato plants (Lycopersicon esculentum L. var. Rio Grande) and their effects on the rate of chlorophyll and enzyme activities involved in the antioxidant system: catalase (CAT), glutathion-S-transferase (GST) and peroxysase ascorbate (APX). Plants previously grown on a basic nutrient solution were undergoing treatment for 7 days, either by increasing concentrations of CdCl₂ or ZnSO₄ (0, 50, 100, 250, 500 μM) or by the combined concentrations of Cd and Zn (100/50, 100/100, 100/250, 100/500 μM). The results concerning the determination of metals in the various compartments of tomato plants as a function of increasing concentrations of Cd or Zn, suggest a greater accumulation of Cd and Zn in the roots compared to leaves. The combined treatment (Cd/Zn) interferes with the absorption of the two elements according to their concentrations in the culture medium. The presence of Zn at low concentrations (50 μM of Zn/100 μM Cd) has little influence on the accumulation of Cd in the roots and leaves, while the absorption of these two elements in the leaves increases and decreases in roots when their concentrations are equivalent (100/100 μM) compared to treatment alone. When the concentration of Zn is higher than that of Cd (500 μM of Zn/100 μM Cd) absorption of the latter is inhibited in the roots while increasing their translocation to the leaves. Meanwhile, the dosage of chlorophylls shows that they tend to decrease in a dose-dependent for both treatments (Cd or Cd/Zn), however, treatment with low concentrations of Zn (50 and 100 μM) stimulates chlorophyll synthesis. However, treatment with different concentrations of Cd seems to induce the activity of the enzymes studied (CAT, APX, GST). It is the same for treatment with different concentrations of Zn and this particularly for the highest concentrations. Finally, the combined treatment (Zn/Cd) also appears to cause enzyme inductions: CAT, APX and GST.     

Structural and thermodynamic characterization of metal ion binding in Streptococcus suis Dpr

The use of protein cages for the creation of novel inorganic nanomaterials has attracted considerable attention in recent years. Ferritins are among the most commonly used protein cages in nanoscience. Accordingly, the binding of various metals to ferritins has been studied extensively. Dps (DNA-binding protein from starved cells)-like proteins belong to the ferritin superfamily. In contrast to ferritins, Dps-like proteins form 12-mers instead of 24-mers, have a different ferroxidase center, and are able to store a smaller amount of iron atoms in a hollow cavity (up to ∼ 500, instead of the ∼ 4500 iron atoms found in ferritins). With the exception of iron, the binding of other metal cations to Dps proteins has not been studied in detail. Here, the binding of six divalent metal ions (Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺, Cu²⁺, and Mg²⁺) to Streptococcus suisDps-like peroxide resistance protein (SsDpr) was characterized by X-ray crystallography and isothermal titration calorimetry (ITC). All metal cations, except for Mg²⁺, were found to bind to the ferroxidase center similarly to Fe²⁺, with moderate affinity (binding constants between 0.1 × 10⁵ M^− 1 and 5 × 10⁵ M^− 1). The stoichiometry of binding, as deduced by ITC data, suggested the presence of a dication ferroxidase site. No other metal binding sites were identified in the protein. The results presented here demonstrate the ability of SsDpr to bind various metals as substitutes for iron and will help in better understanding protein-metal interactions in the Dps family of proteins as potential metal nanocontainers.     

Ecophysiological responses of the mangrove Avicennia marina to trace metal contamination

Growth responses of Avicennia marina seedlings to contamination by different concentrations of two essential (Cu, Zn) and two non-essential (Pb, Hg) trace metals were studied under glasshouse conditions. We tested the hypothesis that soil retention and root ultrafiltration would exclude most of the trace metals, and that those that are absorbed and translocated to the shoots would interfere with plant performance and be excreted via leaf salt glands. One-month-old seedlings were subjected to Cu, Zn, Pb and Hg at concentrations of 0, 40, 80, 120 and 160 μg g⁻¹ sediment for 12 months in a randomized complete block design (n = 6). Photosynthesis was measured at the end of 12 months of trace metal exposure with a portable gas exchange system and chlorophyll fluorescence with a pulse-modulated fluorometer. After morphometric measurements, plants were harvested and analyzed for Cu, Zn, Pb and Hg by atomic absorption spectroscopy. Total dry biomass decreased with increasing trace metal concentration for all metals. In the 160 μg g⁻¹ Cu, Zn, Hg and Pb treatments, total biomass was significantly lower than the control value by 43%, 37%, 42% and 40%, respectively. Decreases in plant height and number of leaves followed trends similar to those for total biomass and ranged from 37% to 60%, compared to the controls. Decreases in chlorophyll content in the trace metal treatments ranged from 50% to 58% compared to the control. Carbon dioxide exchange, quantum yield of photosystem II (PSII), electron transport rate (ETR) through PSII and photosynthetic efficiency of PSII (F_v/F_m) were highest in the control treatment and decreased with increasing trace metal concentrations. Decreases in CO₂ exchange in the 160 μg g⁻¹ treatments for all trace metals ranged from 50% to 60%. Concentrations of all trace metals in plant organs increased with increasing metal concentrations and were higher in roots than in shoots, with concentrations of Cu and Zn being considerably higher than those of Hg and Pb. Qualitative elemental analyses and X-ray mapping of crystalline deposits over the glands at the leaf surfaces indicated that Cu and Zn were excreted from the salt glands, while Hg and Pb were absent, at least being below the limits of detection. These results demonstrate that growth processes are sensitive to trace metals and therefore can be considered as a cost of metal tolerance, but salt glands of this mangrove species do contribute eliminating at least part of physiologically essential trace metals if taken up in excess.     

The brown alga Lobophora variegata, a bioindicator species for surveying metal contamination in tropical marine environments

Uptake and depuration kinetics of Cd, Co, Cr, Mn, Ni and Zn were determined in the brown alga Lobophora variegata exposed to realistic concentrations of these metals, using highly sensitive radiotracer techniques. The experiments were designed to assess the possible influence of varying dissolved metal concentrations on the capacity of metal bioconcentration and retention in the alga. Results indicate that the alga takes up Cd, Co, Cr, Ni, and Zn in direct proportion to their ambient dissolved concentrations over the entire range of concentrations tested (three orders of magnitude). In contrast, Mn was taken up in proportion to its dissolved concentration only over a concentration range of 2 orders of magnitude (up to 250 ng Mn L^− 1, i.e. 4.55 nM), then at higher concentrations its accumulation efficiency slightly decreased. Overall, L. variegata appears to be a reliable bioindicator species that shows a rapid response time in metal uptake (uptake rate constants ranging from 60 to 1,023 d^− 1) and has a suitable potential to furnish valuable information on the bioavailable contamination levels occurring in New Caledonian areas affected by land-based mining activities. Furthermore, due to its wide geographical distribution, L. variegata could be considered as a useful bioindicator species for surveying metal contamination in many other tropical areas.     

EDTA-assisted phytoextraction of heavy metals by turfgrass from municipal solid waste compost using permeable barriers and associated potential leaching risk

A column experiment with horizontal permeable barriers was conducted to investigate phytoextraction of heavy metals by Lolium perenne L. from municipal solid waste compost following EDTA application, as well as to study the effects of L. perenne and permeable barriers on preventing metal from leaching. In columns with barriers, EDTA addition yielded maximum concentrations of Cu, Zn and Pb of 155, 541 and 33.5 mg kg⁻¹ in shoot, respectively. This led to 4.2, 2.1 and 7.4 times higher concentrations of Cu, Zn and Pb compared to treatment with no chelating agent, respectively. In treatments with 10 mmol kg⁻¹ EDTA, the barriers reduced leaching of Cu, Zn and Pb by approximately three times, respectively, resulting in leaching of total initial Cu, Zn and Pb by 27.3%, 25.2% and 28.8%, respectively, after four times’ irrigation. These results indicate that L. perenne and permeable barriers are effective to reduce leaching of heavy metals and minimize the risk of contaminating groundwater in EDTA-enhanced phytoremediation. Thus these findings highlight that turfgrass and permeable barriers can effectively prevent metal leaching.     

Cadmium accumulation in Atriplex halimus subsp. schweinfurthii and its influence on growth,proline, root hydraulic conductivity and nutrient uptake

Atriplex halimus subsp. schweinfurthii is a newly found cadmium (Cd)-hyperaccumulator, but there have been no detailed studies on its physiological responses when Cd is hyperaccumulated. A. halimus was grown in hydroponic conditions to investigate the effect of cadmium chloride (CdCl₂) on growth, water status, leaf chlorophyll concentration, proline and Cd accumulation. Treatments were prepared by adding 0, 50, 100, 200 and 400 μM CdCl₂ to the nutrient medium. Plant growth was significantly affected at high-Cd treatments. Increased CdCl₂ decreased chlorophyll concentration, transpiration and root hydraulic conductivity (L₀). Hence water flux had only a little effect on the uptake of Cd in A. halimus seedlings. In contrast, proline content increased with increasing CdCl₂ concentration. Plants accumulated substantial amount of Cd in different plant parts (shoot and root). Most of the Cd taken up was retained in roots (606.51 μg g⁻¹DW after 15 d at 400 μM CdCl₂). The addition of Cd in the culture medium affected calcium (Ca) and potassium (K) nutrition in both shoot and root. A. halimus provides a new plant resource for exploring the mechanism of Cd hyperaccumulation and has potential for use in the phytostabilization of Cd-contaminated salt soils.     

Cost-effective production of Bacillus thuringiensis biopesticides by solid-state fermentation using wastewater sludge: effects of heavy metals

This study demonstrated the feasibility to produce Bacillus thuringiensis subsp. kurstaki (Btk) based biopesticides using wastewater sludge as raw materials under solid-state fermentation (SSF). More than 10¹⁰ CFU/g viable cells of Btk were obtained using sludge or its mixture with agricultural wastes. This study well considered the effect of heavy metals on Btk growth and their changes of chemical speciation caused by SSF. The IC₅₀ (concentration causing 50% inhibition in total cell biomass) for Pb(II), Cu(II), Cd(II) and Cr(III) on Btk were determined to be 227, 82, 15 and 263 mg/L, respectively. Exposure to 150 mg/L of Cu(II) severely reduced the amount and size of toxin crystals, which decreased the endotoxin synthesis and entomotoxicity potency of Btk cells. Using Tessier’s sequential extraction procedure, the exchangeable heavy metals in sludge were shown to be transformed into residual fractions after SSF, and thus significantly reduced their bioavailability and potential environmental risks.     

Biomarkers response to zinc exposure in the symbiont-bearing foraminifer Amphistegina lessonii (Amphisteginidae, Foraminifera)

The acute effects of zinc (Zn) were evaluated in the symbiont-bearing foraminifer Amphistegina lessonii from the Fernando de Noronha Archipelago (Northeastern Brazil). Foraminifers were acutely (48 h) exposed to dissolved Zn concentrations ranging from 9.5 to 93.4 μg Zn/l. Endpoints analyzed included mortality, visual alterations (white spots and dark-brown areas in the test), oxidative stress biomarkers (reactive oxygen species generation, lipid peroxidation and total superoxide dismutase activity), and concentration of metallothionein-like proteins in whole individuals after Zn exposure. No significant mortality was observed during the 48-h exposure period to waterborne Zn. However, a significant percentage of individuals showed visual alterations (white spots and/or dark-brown areas in the test) after 24 and 48 h of Zn exposure. In fact, a significant positive correlation between this endpoint and dissolved Zn concentrations was observed for both times of exposure. Based on this endpoint, the 24-h and 48-h EC₅₀ values and their corresponding 95% confidence intervals for total measured Zn concentrations were calculated as 112.2 (86.5 - 199.5) and 43.6 (34.9 - 57.3) μg Zn/l, respectively. Based on the dissolved Zn concentrations, they were 100.7 (75.3 - 175.9) and 38.2 (29.7 - 49.4) μg Zn/l, respectively. Therefore, a significant increase in Zn toxicity was observed with increasing time of exposure. After 48 h of Zn exposure, whole body antioxidant capacity was lower in normal-appearing individuals than in those at the initial stage of bleaching. Increases in lipid peroxidation, metallothionein-like protein concentration and total SOD activity was observed at a greater extent in pale/partly-bleached individuals associated with an increased Zn toxicity measured as visual alterations. These findings suggest that an activation of some components of the antioxidant system occurred in A. lessonii to counteract the oxidative stress induced by Zn exposure, and consequently avoid a possible complete loss of the symbiont.     

Rat primary hepatocyte cultures are a good model for examining metallothionein-induced tolerance to cadmium toxicity

Summary The effect of Zn-induced metallothionein (MT) on the toxicity, uptake, and subcellular distribution of cadmium (Cd) was examined in rat primary hepatocyte cultures and compared to results obtained earlier in this laboratory from intact animals. Hepatocytes were isolated and grown in monolayer culture for 22 h and subsequently treated with ZnCl₂ (100 μM) for 24 h, which increased MT concentration about 15-fold. After Zn pretreatment, hepatocytes were exposed to Cd for 24 h. Cytotoxicity was assessed by enzyme leakage, intracellular potassium loss, and cellular glutathione content. The toxicity of Cd was much less in Zn-pretreated cells than in control cells, similar to that previously demonstrated in the intact animal. Zn pretreatment had no appreciable effect on the hepatocellular uptake of¹⁰⁹Cd, but markedly altered its subcellular distribution, with more Cd accumulating in the cytosol and less in the nuclear, mitochondrial, and microsomal fractions. In the cytosol of Zn-pretreated cells, Cd was associated mainly with MT; in contrast, cytosolic Cd in control cells was mainly associated with non-MT macromolecules. Zn-induced changes in the subcellular distribution of Cd in vitro are identical to those observed in vivo in Zn-pretreated rats challenged with Cd. In summary, Zn pretreatment of rat primary hepatocyte cultures protects cells against Cd toxicity. Protection seems to be due to MT-promotes sequestration of Cd and reduction of the amount of Cd associated with critical organelles and proteins. These observations are similar to those noted in the whole animal. These results indicate that cultured hepatocytes are an ideal model for examining MT-induced tolerance to Cd hepatotoxicity. This work was supported by grant ES-01142, and WCK was supported by training grant ES-07079, both from the Public Health Service, Department of Health and Human Services.     

Gastro-intestinal transport of calcium and cadmium in fresh water and seawater acclimated trout (Oncorhynchus mykiss)

Transport of calcium (Ca) and cadmium (Cd) was examined along the gastro-intestinal tract (GIT) of freshwater and seawater Oncorhynchus mykiss irideus (FWT and SWTies respectively) using in vitro and in vivo experiments. Based on known physiological differences between FWT and SWT which aid in regulating ion levels and osmolarity, we hypothesized that SWT would have lower rates of Ca uptake. Also, we predicted that Cd rates would also be lower because Cd is known to share a common transport mechanism with Ca. Kinetics of Ca and Cd transport were determined using mucosal salines of varying concentrations [1, 10, 30, 60, and 100 (mmol L^− 1 for Ca, μmol L^− 1 for Cd)]. Linear and saturating relationships were found for Ca for FWT and SWT, but overall SWT had lower rates. Linear and/or saturating relationships were also found for Cd uptake, but rates varied little between fish types. Elevated Ca had no inhibitory effect on Cd transport, and Ca channel blockers nifedipine and verapamil had little effect on Ca or Cd uptake. However, lanthanum reduced Ca transport into some compartments. A 21 day in vivo feeding experiment was also performed where FWT and SWT were exposed to control diets or Cd-spiked diets (552 μg Cd g^− 1 food). Whole body Cd uptake between fish types was similar, but the majority of Cd in SWT remained in the posterior intestine tissue, while FWT transported more Cd through their gut wall. Overall it appears that large differences in Ca and Cd uptake between FWT and SWT exist, with SWT generally having lower rates.     

Mineral nutrition and heterotrophy in the water conservative holoparasite Hydnora Thunb. (Hydnoraceae)

There are large gaps in our understanding of parasite–host nutrient relationships. Our goal was to evaluate transdermal water loss, parasite–host mineral relationships, and heterotrophy in the holoparasitic genus Hydnora. We estimated in situ transdermal water loss in Hydnora and measured nutrient profiles and δ¹³C and δ¹⁵N signatures for Hydnora and hosts in southern Africa and Madagascar. For comparison we also measured δ¹³C and δ¹⁵N for aerial hemiparasites at the same sites. Transdermal water loss in Hydnora ranged from 0.14 ± 0.02 to 0.38 ± 0.04 mg cm⁻² h⁻¹ and was comparable to transpiration rates for water conservative xerophytes. Concentrations of P and K were higher in Hydnora relative to CAM hosts; other mineral concentrations were significantly lower in the parasite or were not different. δ¹³C signatures of holoparasites and hemiparasites relative to their hosts reflected host metabolism and differences in commitment to heterotrophic C gain. Holoparasite δ¹³C values were significantly enriched (by 0.55‰ ± 0.23) compared to host shoot and depleted compared to host root tissues (by −0.97‰ ± 0.12). Holoparasite δ¹³C values were not significantly different compared to the estimated whole host δ¹³C value. δ¹⁵N values for holoparasites and hemiparasites were significantly correlated with hosts. The water conservative nature of Hydnora spp. combined with parasite–host mineral nutrition profiles are suggestive of active processes of solute uptake. Stable isotope fractionation in host tissues dictated significant differences between parasite and host (shoot and root) δ¹³C signatures. The confirmation of complete heterotrophy and the lack of a confounding transpiration stream may make Hydnora a promising model organism for the examination of parasite solute uptake.     

The impact of fish spawning on metal and protein levels in gastrointestinal cytosol of indigenous European chub

The study presented here reports for the first time cytosolic metal and protein levels in the gastrointestinal tissue of field-collected European chub (Squalius cephalus), living in low metal-contaminated river section. In two sub-cellular fractions (untreated cytosol and heat-treated cytosol), isolated from the whole gastrointestinal tract of indigenous chubs collected during spawning (April/May 2006) and post-spawning period (September 2006), seasonal or gender related differences of trace metals and proteins were determined. In both fractions, cytosol and heat-treated cytosol, metal levels decrease as follows: Zn > Fe > Cu > Mn > Cd and are significantly higher during the spawning period. Besides that, the level of heat-sensitive proteins (metalloenzymes) in cytosolic fractions is also significantly higher during the spawning period in both male and female specimens. Higher condition indices of chubs in the spawning period imply higher feeding activity, energy reserves and recent growth of indigenous chubs. Metallothionein levels, determined in the heat-treated cytosol, are comparable in gastrointestinal tract of feral chubs collected in both seasons and confine the background metallothionein levels, on average 3 mg g⁻¹ wet tissue. Chub spawning has been identified as a confounding factor, having an impact on cytosolic metal and protein levels, presumably due to enhanced food supply (higher condition indices) and fish spawning (higher gonadosomatic indices in some male specimens).     

Phytoaccumulation of cadmium through Azolla from aqueous solution

Azolla, which is an aquatic fern, has proved to be effective in the uptake and accumulation of metals from polluted waters. Azolla spp., namely A. microphylla cv. MH3 and A. caroliniana Willd, were chosen as model plants so that Cd(II) could be accumulated from aqueous solution. An increase in uptake time and the concentration of Cd(II) in aqueous solution resulted in more Cd(II) accumulation in both species. Modified Michaelis-Menten equation was employed to describe the concentration-dependent kinetics of Cd(II) uptake through the roots of A. microphylla cv. MH3, and the values of K_m and V_max were found to be 0.23 mg/L and 16.49 μg/(g.f.wt.h), respectively. Cd(II) uptake by A. microphylla cv. MH3 occurs partly through Ca(II) channels and has the potential to be mediated by Zn(II) transporters.