Using stable isotopes to assess the bioavailability of minerals in food-fortification programs

Food fortification with minerals is often undertaken without consideration of the bioavailability or nutrient-nutrient interactions related to its use. Stable isotopes provide a safe and accessible approach to providing direct evidence regarding these issues. Studies can be applied in all areas of the world and in all population groups. Mineral stable isotopes are safe and meet stringent ethical standards for use in children. Clinical studies in children allowing scientists, policy makers and the food industry to obtain data needed to understand how best to fortify foods to enhance the nutritional health of children of all ages. It is not necessary to have analytical mass spectrometry equipment available in each country where studies are performed. Rather, international collaborations can be developed to allow clinical studies to be performed in the field setting with analysis elsewhere if needed. The combination of isotope studies with field intervention trials may be beneficial.

[The influence of some trace elements on bioaccumulation in tissues and bioenergetic metabolism of the edible snail Helix aspersa maxima as determined by HPLC of purine derivatives]

The aim of this work was to determine the bioaccumulation of fluoride and some metals (Cu, Zn, Pb) in tissues of snails under strictly controlled conditions expecting with this approach to verify the hypothesis that snails are suitable for the monitoring of environmental hazards. Additionally, the toxicity of fluorides administered orally on the energy balance of the snail's foot was investigated basing on concentrations of nucleosides, nucleotides and their products measured with high-performance liquid chromatography (HPLC). Two parallel snail cultures were started. The effect of dose on tissue levels of fluoride and metals was studied in the first part of the experiment. The second part served to study the effects of fluoride on energy metabolism of foot muscle (Tab. 1). Quantitation of fluoride and metal levels was done in soft tissues (foot, hepatopancreas) and shells of snails. Qualitative and quantitative analysis of purine compounds was performed in slices of foot. Fluoride concentrations in pulverized shells were measured using an ion-selective electrode. Gas chromatography served to determine fluoride concentrations in soft tissues (hepatopancreas and foot). Concentrations of metals were determined spectrophotometrically. Fluoride and metal content was calculated basing on weight of the pulverized sample. Purines were measured in foot muscle slices with high-performance liquid chromatography (HPLC). Concentrations were adjusted for protein content of sample. Concentrations of the following nucleosides, nucleotides and their products were determined: ATP, ADP, AMP, Ado (adenosine), GTP, GDP, GMP, Guo (guanosine), Hyp (hypoxanthine), IMP, Ino (inosine), Xan (xanthine), Urd (uridine), UA (uric acid), NAD+, and NADP (Fig. 1.). Statistical analysis was done with non-parametric test of Kruskal-Wallis, Mann-Whitney U-test and Spearman Rank Correlation Coefficient.

CONCLUSIONS

1. Accumulation in the shell was significantly increased at the lowest concentration of fluoride, but levels remained below those in the foot or hepatopancreas. It can be inferred that due to low sensitivity, accumulation of fluoride in soft tissues is not a suitable indicator for biomonitoring purposes. Shells seem to be more suited for this aim. 2. Due to low sensitivity, accumulation of metals in soft tissues is not a suitable indicator for biomonitoring purposes. 3. Fluoride had a statistically significant effect on the energy metabolism in muscle, especially on the content of AMP and GMP (Fig. 3, 4). The content of adenylate derivatives was increased (Fig. 3, 4) and phosphorylation of ADP to ATP was inhibited (Fig. 2, 5). 4. An increase in TAN and AEC with 1330 mg F-/kg seems to result from inhibition by fluoride of energy-consuming processes (Fig. 5). 5. In cases of high levels of fluoride it seems reasonable to measure the content of AMP, GMP, Guo or the value of AEC which appear to serve as universal indicators of depressed metabolic function (Fig. 3, 4, 5, 6).

Nutritive metal uptake in teleost fish

Transition metals are essential for health, forming integral components of proteins involved in all aspects of biological function. However, in excess these metals are potentially toxic, and to maintain metal homeostasis organisms must tightly coordinate metal acquisition and excretion. The diet is the main source for essential metals, but in aquatic organisms an alternative uptake route is available from the water. This review will assess physiological, pharmacological and recent molecular evidence to outline possible uptake pathways in the gills and intestine of teleost fish involved in the acquisition of three of the most abundant transition metals necessary for life; iron, copper, and zinc.

[Studies on the zinc bioavailability using stable isotope techniques]

Zinc is one of essential trace elements in humans. Zinc homeostasis is mainly regulated by the changes of intestinal absorption efficiency and endogenous excretion, namely the regulation of bioavailability. Studies on zinc bioavailability play an important role on a thorough understanding of zinc metabolism and reliable assessment on population zinc status. Stable isotopes are valuable tools for research on mineral bioavailability and metabolism. Zinc stable isotopes can be used for all population as tracers with no exposure to radiation. Since 1980s' many different stable isotope methods have been applied to the zinc metabolism research. However, limitations to these approaches and methodological problems remain to be resolved. In addition, the introduction and development of new analytical instruments not only make it possible to use zinc stable isotope, also greatly diminish the difficulty and cost on it. The paper is mainly focused on the zinc bioavailability and present a review of its development history, main research methods and analytical skills.

The respiration rate of the beet armyworm pupae (Spodoptera exigua) after multi-generation intoxication with cadmium and zinc

The beet armyworm (Spodoptera exigua) were fed on artificial food contaminated with zinc (200 mg kg(-1) dry mass) or cadmium (66 mg kg(-1) dry mass) for 15 generations. In 15th generation, O2 output and CO2 production of pupae were measured. Exposure to cadmium did not cause any effects whilst exposure to zinc led to a significant increase in the respiration rate of pupae. The average respiratory quotient (RQ) did not differ between treatments (ca. 0.7).

Variation of metal and metallothionein concentrations in a natural population of Ruditapes decussatus

The spatial and seasonal variation of total and subcellular distribution of Cd, Cu, and Zn was followed in different tissues (gills, digestive gland, and remaining tissues) of the clam Ruditapes decussatus collected along a metal contamination gradient in the Ria Formosa lagoon (southern Portugal) and compared with metallothionein (MT) concentrations.Total metal concentrations decreased according to the sequence digestive gland > gills > remaining tissues for Cd, digestive gland approximately gills > remaining tissues for Cu and gills > digestive gland > remaining tissues for Zn. MT concentrations in these tissues decreased according to the same sequence observed for Cd. In all the tissues, the highest subcellular concentration was in the cytosol for Cd and Cu and in the pellet for Zn. Among the three metals, Cd concentrations showed the most evident spatial variation. In all tissues, total and subcellular Cd concentrations decreased from the inner parts of the lagoon toward the ocean. However, no significant spatial or seasonal variation occurred in clam tissues for the other two metals, though marginal elevated Cu concentrations were observed in the inner parts of the lagoon. Therefore, Cu subcellular distribution in clam tissues was not significantly altered by Cu changes in the lagoon and are the baseline levels for normal metabolism of this clam population. The fact that total Zn concentrations remained unchanged both spatial and seasonal suggested that these clams regulate Zn in their tissues. In the three tissues, MT bind most significantly to Cd and Cu, while Zn, although binding to MT, is preferably bound to other ligands. MT concentrations showed the same spatial and seasonal variation of Cd and were significantly related with total and heat-treated cytosolic Cd in all tissues. For Cu a significant relationship between MT and total or cytosolic Cu was only observed in the remaining tissues. No relationship was observed between MT and total or cytosolic Zn concentrations. Metals and MT concentrations increased with the increase in the condition index for the gills and the digestive gland and decreased from the remaining tissues.Cd concentrations in the gills increased only in the heat-treated cytosolic fraction while Zn in this fraction decreased. Thus Cd concentrations in this tissue displaced Zn from the MT-fraction, leading to a modification of the soluble/insoluble Zn ratio once total Zn concentrations remained unchanged. This modification reflects a perturbation in the normal metabolism in this tissue due to the excess of Cd present. With the exception of the gills, Zn subcellular distribution in the other two tissues was similar among sites and season. The model that describes the relationship between MT, metals, and weight in the gills, digestive gland and remaining tissues also indicates that Cd was the only metal that influence MT synthesis significantly in all the tissues. The induced and/or existent MT was sufficient to bind free Cd ions present in the cells, preventing any damage to cellular metabolism in this clam population. Therefore, MT in the gills and digestive gland of R. decussatus can be used as an early warning signal for Cd exposure and are a useful biomarker to assess the toxicological status of this population in the Ria Formosa lagoon.

Zinc is incorporated into cuticular "tools" after ecdysis: the time course of the zinc distribution in "tools" and whole bodies of an ant and a scorpion

An understanding of the developmental course of specialized accumulations in the cuticular "tools" of arthropods will give clues to the chemical form, function and biology of these accumulations as well as to their evolutionary history. Specimens from individuals representing a range of developmental stages were examined using MeV - Ion microscopy. We found that zinc, manganese, calcium and chlorine began to accumulate in the mandibular teeth of the ant Tapinoma sessile after pre-ecdysial tanning, and the zinc mostly after eclosion; peak measured zinc concentrations reached 16% of dry mass. Accumulations in the pedipalp teeth, tarsal claws, cheliceral teeth and sting (aculeus) of the scorpion Vaejovis spinigeris also began after pre-ecdysial tanning and more than 48 h after ecdysis of the second instars. Zinc may be deposited in the fully formed cuticle through a network of nanometer scale canals that we observed only in the metal bearing cuticle of both the ants and scorpions. In addition to the elemental analyses of cuticular "tools", quantitative distribution maps for whole ants were obtained. The zinc content of the mandibular teeth was a small fraction of, and independent of, the total body content of zinc. We did not find specialized storage sites that were depleted when zinc was incorporated into the mandibular teeth. The similarities in the time course of zinc, manganese and calcium deposition in the cuticular "tools" of the ant (a hexapod arthropod) and those of the scorpion (a chelicerate arthropod) contribute to the evidence suggesting that heavy metal-halogen fortification evolved before these groups diverged.

The changes in common carp blood after short-term zinc exposure

Blood zinc level, hematological parameters and blood cell morphology were evaluated in common carp immediately after 3 h exposure to 20 mg dm(-3) of zinc (Zn0), and in 24, 48 and 96 hours after the end of it (Zn24, Zn48, Zn96). Blood zinc level in the non-exposed fish was 8 mg dm(-3), reached a maximum of 20 mg dm(-3) in Zn48, while it dropped to 9 mg dm(-3) in Zn96. Zinc caused a stress reaction in fish indicated by an increase in hematocrit value in Zn0, and elevated plasma glucose level and trombocytosis which persisted until the end of the experiment. Zinc-exposed fish showed an increased frequency of abnormal erythrocytes, and a compensatory release of immature erythrocytes to the blood stream. In zinc-treated fish, leukocyte count initially increased and subsequently decreased significantly below the control level due to a drop in lymphocyte number. Lymphocyte viability was reduced, and abnormal lymphocytes appeared. A decreased count of juvenile neutrophiles, and reduced phagocyte activity also occurred. The results indicate possible zinc-induced disturbances in both specific and non-specific immune mechanisms.

Magnesium and trace elements in the elderly: intake, status and recommendations

Imbalances between mineral intakes and recommended amounts have been observed in different groups of elderly subjects. Nevertheless, assessment of the status of magnesium and trace elements in the elderly is difficult, even for iron because infection and inflammation increases ferritin. Mineral bioavailability may change due to ageing. Therefore, formulation of mineral recommendations is complex and individual recommendations are sometimes necessary. A number of surveys show magnesium, zinc, selenium and chromium intakes by old persons to be lower than the corresponding reference nutrient intakes. Contrarily, intakes of iron are generally adequate or higher than recommended, and it has been suggested that increased storage of iron in the elderly may be related with the development of age-related diseases through the increase in oxidative stress. Low iron status together with iron excess may be common in an elderly population. The same applies for zinc. Magnesium and selenium deficiencies among the elderly are also well documented, especially among the institutionalised and people with pathologies. Chromium deficiency is associated with type II diabetes mellitus. Recommended iron intake is lower for elderly women compared to young, because menstruation ceases after menopause, but in old men, it is similar to that of young men. Dietary Reference Values for the rest of the elements are similar to those of adults, although several suggestions have been made about the quantities. This review examines various aspects of the changes in mineral bioavailability due to ageing, of data published on mineral intakes and status, and finally the dietary recommendations for this vulnerable population group.

Bioavailability of zinc in fiber-enriched bread fortified with zinc sulphate

The present study aimed to reduce the caloric value of bread by substituting a part of wheat flour with artichoke bracts at levels of 5%, 10% and 15% without sacrificing taste, texture or acceptability. Moreover, considerable trials had been made to reduce zinc deficiency in wheat bread and fiber-enriched bread and also to study the effect of fiber on zinc bioavailability. Therefore, zinc sulphate was added to bread at levels of 40, 60, 80, 100 and 120 mg/100 g edible portion. The results from this study show that: (i) The addition of artichoke bracts to wheat flour increased the water absorption, arrival time, development time, and weakening of the dough as the level of artichoke bracts increased, while dough stability decreased. (ii) Mixing wheat flour with increasing amount of artichoke bracts increased the content of protein, fiber and total essential amino acids, also all essential amino acids increased in wheat bread and fiber-enriched bread after fortification with zinc sulphate at a level of 100 mg/100 g edible portion except methionine, threonine and tyrosine. (iii) The best level of zinc sulphate to give the best bioavailability for zinc is 100 mg/100 g edible portion. (iv) Evaluation of fortified wheat bread and fiber-enriched bread with zinc sulphate showed no significant difference by test panel.

Geochemistry of Cd, Cr, and Zn in highly contaminated sediments and its influences on assimilation by marine bivalves

We tested the controls of metal geochemistry in sediments collected from an extremely contaminated Chinese bay on metal assimilation by marine mussels and clams. Metal speciation in the contaminated sediments, quantified by the Tessier operational extraction method, was significantly dependent on metal concentrations in the sediments. The fractions of Cd in the easily exchangeable and carbonate phases increased, while the reducible and residue phases decreased with increasing Cd concentration. The majority (72-91%) of Cr was associated with the residue component with the remainder of Cr in the organic matter and reducible phases. Zn in carbonate phase increased, whereas in the organic matter and residue phases it decreased with increasing Zn concentration. The bioavailability of Cd, Cr, and Zn to marine green mussels (Perna viridis) and clams (Ruditapes philippinarum) was quantified using radiotracer spiked technique with concurrent measurements of speciation of spiked metals. There was a significant correlation between the Cd assimilation efficiency (AE) by both mussels and clams and Cd partitioning in the easily exchangeable and reducible phases. In contrast to previous studies, a negative correlation was found between the Cd AE and its total concentration in sediment, likely caused by the saturation of Cd binding sites in the gut or by its antagonistic interaction with a very high Zn concentration in these collected sediments. In contrast, there was no significant correlation between the AEs of Cr or Zn and any of their geochemical phases or their concentrations. The metal AEs were further quantified by experimentally manipulating different concentrations and ratios of acid volatile sulfide (AVS) and simultaneously extractable metals (SEM). There was no statistically significant relationship between the AEs of the three metals and the concentrations of AVS and SEM or [SEM-AVS]. Geochemical controls on metal assimilation from contaminated sediment are therefore only relatively apparent for Cd. The influences of metal speciation on metal bioavailability can be confounded by the degree to which sediments are contaminated with metals.

Bioavailability of minerals in legumes

The mineral content of legumes is generally high, but the bioavailability is poor due to the presence of phytate, which is a main inhibitor of Fe and Zn absorption. Some legumes also contain considerable amounts of Fe-binding polyphenols inhibiting Fe absorption. Furthermore, soya protein per se has an inhibiting effect on Fe absorption. Efficient removal of phytate, and probably also polyphenols, can be obtained by enzymatic degradation during food processing, either by increasing the activity of the naturally occurring plant phytases and polyphenol degrading enzymes, or by addition of enzyme preparations. Biological food processing techniques that increase the activity of the native enzymes are soaking, germination, hydrothermal treatment and fermentation. Food processing can be optimized towards highest phytate degradation provided that the optimal conditions for phytase activity in the plant is known. In contrast to cereals, some legumes have highest phytate degradation at neutral or alkaline pH. Addition of microbial enzyme preparations seems to be the most efficient for complete degradation during processing. Fe and Zn absorption have been shown to be low from legume-based diets. It has also been demonstrated that nutritional Fe deficiency reaches its greatest prevalence in populations subsisting on cereal- and legume-based diets. However, in a balanced diet containing animal protein a high intake of legumes is not considered a risk in terms of mineral supply. Furthermore, once phytate, and in certain legumes polyphenols, is degraded, legumes would become good sources of Fe and Zn as the content of these minerals is high.

Uptake and release of zinc by aquatic bryophytes (Fontinalis antipyretica L. ex. Hedw.)

The zinc uptake and posterior release by an aquatic bryophyte-Fontinalis antipyretica L. Ex Hedw.--was experimentally studied in laboratory exposing the plants to different zinc concentrations in the range, 1.0-5.0 mg 1(-1), for a 144 h contamination period, and then exposed to metal-free water for a 120 h decontamination period. The experiments were carried out in perfectly mixed contactors at controlled illumination, using mosses picked out in February 1997, with a background initial zinc concentration of 263 mg g(-1) (dry wt.). A first-order mass transfer kinetic model was fitted to the experimental data to determine the uptake and release constants, k1 and k2, the zinc concentration in mosses at the end of the uptake period, C(mu), and at the equilibrium, for the contamination and decontamination stages, C(me) and C(mr), respectively. A bioconcentration factor, BCF = k1 /k2 (zinc concentration in the plant, dry wt./zinc concentration in the water) was determined. A biological elimination factor defined as BEF = 1 - C(mr)/C(mu) was also calculated. BCF decreases from about 4500 to 2950 as Zn concentration in water increases from 1.05 to 3.80mg 1(-1). BEF is approximately constant and equal to 0.80. Comparing Zn and Cu accumulation by Fontinalis antipyretica, it was concluded that the uptake rate for Zn (145 h(-1)) is much lower than for Cu (628 h(-1)) and the amount retained by the plant decreased by a factor of about seven.

Interclonal variation of heavy metal interactions in Salix viminalis

In the complex chemistry of soil, interactions between metals can be expected and these affect the uptake of the metals by the plants. The role of the metal-metal interaction may vary between different plants. This study was performed to investigate if variations exist in the interactions between Cd, Cu, and Zn on toxicity and accumulation of these metals in different clones of Salix viminalis. Two studies were performed. First, to study interaction at uptake, 10 clones with high or low accumulation capacity of Cd, Cu, and Zn, respectively, were treated with 0.3 microM Cd, 0.1 microM Cu, and 3 microM Zn (all three metals at the same time or separately). Second, to study the effect of one of the metals on the sensitivity of the plant to the other metals, three clones with high or low sensitivity to each of the three metals were used in a modified Weibull analysis. Examination of the results shows that interclonal variation exists in effects of metal interaction on metal accumulation and sensitivity exists. The uptake experiment showed that accumulation of Cu was decreased by the other metals, but only in clones with high Cu-accumulating properties because of decreased net uptake of Cu. The accumulation of Zn in roots was increased two- to threefold in all clones in the presence of the other metals because of a decreased translocation of Zn to the shoot. The accumulation of Cd was not changed by the presence of the other metals in any of the clones. The second experiment showed that the effect of interactions between the different metals on metal toxicity was present in all clones but appeared most frequently in the clone with high Zn resistance. Synergistic effects between Cu and Zn in the Zn-resistant clone suggested that this clone had evolved an additional site of toxic action that was absent in the other clones.

Linking biokinetics and consumer-resource dynamics of zinc accumulation in pond abalone Haliotis diversicolor supertexta

A dynamic model that links biokinetics and consumer-resource dynamics for describing zinc (Zn) accumulation in abalone Haliotis diversicolor supertexta has been developed and then applied to Zn data from real abalone farms. The biokinetic parameters used in this study, uptake and depuration rate constants of abalone and their food source, red alga Gracilaria tenuistipitata var. liui, were obtained from a laboratory 14-d exposure experiment. We carried out a sensitivity analysis of the model by using the fractional factorial design technique, taking into account the influence of consumer-resource-related parameters such as growth and death rates and biomass and biokinetic parameters characterized by bioconcentration factor. Results indicate that the response time of biomagnification dynamics of Zn accumulation in abalone was influenced mainly by the growth rate of algae and biomass and the death rate of abalone and by interactions algae biomass and abalone death rate and abalone and algae biomass. New algae production results in substantially higher values of biomagnification factor. The linked model was then applied to field observations from a real-life situation of variable Zn concentrations occurring in abalone farms. Simulation results show that the predicted values are within a factor of 2 of the measured values (% errors range from 5.3 +/- 4% to 44.1+/- 8%). Both model analysis and model application to the abalone farms suggest that the linking influences between biokinetics and consumer-resource dynamics support Zn accumulation in H. diversicolor supertexta and in G. tenuistipitata var. liui as functions of Zn concentration in water and abundance of food occurring in abalone farms.

Accumulation and regulation of zinc in Daphnia magna: links with homeostasis and toxicity

Zinc accumulation in Daphnia magna was investigated, and the results were linked to the previously established optimal concentration range for zinc and D. magna. It was observed that organisms cultured in this optimal range (300-600 microg Zn/L) contained 212 +/- 57 to 254 +/- 79 microg Zn/g dry weight. Lower and higher zinc contents were obtained after acclimation to previously established culture concentrations inducing deficiency and toxicity, respectively. The calculation of bioconcentration factors indicated that zinc was actively regulated, at least up to a concentration of 600 microg Zn/L. Zinc uptake and elimination are rapid processes; major increases and decreases in body content occurred within 1 day. Zinc concentrations in daphnids exposed to 600 microg Zn/L fluctuated with 2- to 3-day intervals, suggesting a role of molting in the regulation and elimination of zinc.

Cadmium and zinc uptake by volunteer willow species and elder rooting in polluted dredged sediment disposal sites

Salix species and Sambucus nigra L. (elder) naturally invade dredged sediment landfills and are commonly encountered on substrates contaminated with heavy metals. Foliar concentrations of Cd and Zn in four Salix species and elder were explored in the field. Metal contents in dredged sediment derived soils were elevated compared to baseline concentration levels reported for Flanders. To evaluate foliar concentrations, reference data were compiled from observations in nurseries, young plantations and unpolluted sites with volunteer willow vegetation. Willows grown on polluted dredged sediment landfills showed elevated foliar Cd and Zn concentrations (>6.6 mg Cd/kg DW and >700 mg Zn/kg DW). This was not the case for elder. For willow, a significant relation was found between soil total Zn or Cd and foliar Zn or Cd, regardless of age, species, or clone. Willows proved to be useful bioindicators. Results indicated a possible threat in long-term habitat development of willow brushwood from transfer of Cd and Zn to the food web.

Kinetic uptake of bioavailable cadmium, selenium, and zinc by Daphnia magna

Kinetic uptake of Cd, Se(IV), and Zn by Daphnia magna from the dissolved phase was determined using radiotracer techniques in moderately hard water. The metal influx rate and distribution in the soft tissue and the exoskeleton of the daphnids as influenced by metal concentration, inorganic ligands including pH, Ca2+ and SO4(2-), and body size were quantified. When the metal concentrations were <180 nM for Cd and <769 nM for Zn, the concentration factor in daphnids increased linearly within the 12 h of exposure. At a higher concentration, apparent steady state was reached after 3 h of exposure. Cadmium and Zn distribution in the soft tissues was not affected by the total ambient concentrations, whereas Se distribution in the soft tissue decreased by 7 to 10% with increasing Se concentration from 16 to 643 nM. A linear positive power relationship was found between the influx rates of the metals and the ambient concentrations. The concentration factor for Se, however, decreased significantly with increasing Se concentration in water. The influx rate of metals was inversely related to the body size in a power function. When the pH in ambient water increased from 5.0 to 7.0, the influx rate of Cd, Se, and Zn increased by 2.9, 16.6, and 4.1 times, respectively. The influx rates of Cd, Se, and Zn decreased by 6.9, 8.7, and 4.4 times, respectively, with an increase in Ca2+ concentration from 0.6 to 5.1 mM. In contrast, the uptake rates of all three metals were not significantly affected by the SO4(2-) concentration. The majority of accumulated Se was distributed in the soft tissues after 12 h of exposure, whereas Cd and Zn were about evenly distributed in the soft tissue and exoskeleton. Any changes in pH, Ca2+, and SO4(2-) concentrations did not apparently affect their distributions in the daphnids. Our study provides important kinetic data necessary for delineating the exposure routes and for further development of the biotic ligand model in Daphnia. Using a bioenergetic-based kinetic model, we showed that the dissolved uptake is dominant for Zn accumulation (>50%). For Cd and Se, dietary exposure is dominant when the bioconcentration factors of these metals in phytoplankton are at the high end.

Genetic variability in sublethal tolerance to mixtures of cadmium and zinc in clones of Daphnia magna Straus

To date, studies on genetic variability in the tolerance of aquatic biota to chemicals have focused on exposure to single chemicals. In the field, metals occur as elemental mixtures, and thus it is essential to study whether the genetic consequences of exposure to such mixtures differs from response to single chemicals. This study determined the feeding responses of three Daphnia magna Straus clones exposed to Cd and Zn, both individually and as mixtures. Tolerance to mixtures of Cd and Zn was expressed as the proportional feeding depression of D. magna to Cd at increasing zinc concentrations. A quantitative genetic analysis revealed that genotype and genotype x environmental factors governed population responses to mixtures of both metals. More specifically, genetic variation in tolerance to sublethal levels of Cd decreased at those Zn concentrations where there were no effects on feeding, and increased again at Zn concentrations that affected feeding. The existence of genotype x environmental interactions indicated that the genetic consequences of exposing D. magna to mixtures of Cd and Zn cannot be predicted from the animals' response to single metals alone. Therefore, current ecological risk assessment methodologies for predicting the effects of chemical mixtures may wish to incorporate the concept of genetic variability. Furthermore, exposure to low and moderate concentrations of Zn increased the sublethal tolerance to Cd. This induction of tolerance to Cd by Zn was also observed for D. magna fed algae pre-loaded with both metals. Furthermore, in only one clone, physiological acclimatization to zinc also induced tolerance to cadmium. These results suggest that the feeding responses of D. magna may be related to gut poisoning induced by the release of metals from algae under low pH conditions. In particular, both induction of metallothionein synthesis by Zn and competition between Zn and Cd ions for uptake at target sites on the gut wall may be involved in determining sublethal responses to mixtures of both metals.

Cofortification of iron-fortified flour with zinc sulfate, but not zinc oxide, decreases iron absorption in Indonesian children

BACKGROUND

Iron deficiency is a major nutritional concern in developing countries, and food fortification is a common strategy to treat it. In Indonesia wheat flour is fortified with 60 mg Fe/kg, but because of increasing concerns about marginal zinc status in at-risk populations, consideration is being given to cofortifying flour with zinc. However, little is known about the effect of zinc fortification of flour on iron bioavailability or about the optimum form of zinc supplementation.

OBJECTIVE

We measured iron and zinc bioavailability from wheat-flour dumplings containing 25 g flour fortified with 60 mg Fe/kg, either alone or with 60 mg Zn/kg as zinc oxide or as zinc sulfate.

DESIGN

Ninety children aged 4-8 y were recruited and assigned randomly to the 3 groups; 86 completed the study. Iron and zinc absorption were measured with established stable-isotope methods.

RESULTS

Iron absorption from the flour fortified with iron only was good (15.9 +/- 6.8%), but when corrections were made for hemoglobin concentrations, it was significantly lower from the flour cofortified with zinc sulfate (11.5 +/- 4.9%; P < 0.05) but not from the flour cofortified with zinc oxide (14.0 +/- 8.9%). Zinc absorption was not significantly different between the zinc oxide and zinc sulfate cofortified flours (24.1 +/- 8.2% compared with 23.7 +/- 11.2%; P = 0.87).

CONCLUSIONS

Iron and zinc appear to be highly bioavailable from foods made from fortified flour, but zinc sulfate cofortification may have a detrimental effect on iron absorption.

Coupling toxicokinetics and pharmacodynamics for predicting survival of abalone (Haliotis diversicolor supertexta) exposed to waterborne zinc

We developed a mortality model, by coupling an acute toxicity model and a pharmacodynamic model, to predict survival of abalone (Haliotis diversicolor supertexta) exposed to waterborne zinc (Zn). We conducted a laboratory 14-day exposure experiment to obtain biokinetic parameters of depuration rate constant (k(2)) and bioconcentration factor (BCF). A one-compartment uptake-depuration model was used to fit the exposure data to estimate BCF and k(2) values. The acute toxicity model was developed based on the receptor theory and was verified with LC(50)(t) data obtained from a 7-day acute toxicity test. A highly significant correlation (r(2) = 0.98) was found between predictions and LC(50)(t) data for the acute toxicity model, indicating a successful description of 7-day LC(50)(t) data of Zn in abalone. The predicted time course of lethal body burden of Zn in abalone was compared with measured data, showing that the average percent error was 14.04 +/- 3.02%. A refined pharmacodynamic model was expressed as the Hill equation, which in terms of waterborne Zn and LC(50)(t) data was used to fit observed mortality percentages to determine the Hill coefficient (r(2) = 0.98). The proposed mortality model in terms of whole body burden and lethal body burden at site of action was then employed to predict the time-varying mortality of abalone exposed to various Zn concentrations in pond water. Our results demonstrate that 96-h LC(50) and incipient LC(50) for H. diversicolor supertexta exposed to Zn are 1.1 and 1.05 mg L(-1), respectively. Our predictions also demonstrate that equilibrium lethal body burden at site of action is about 198 microg g(-1), whereas the mortalities never reach 50% when H. diversicolor supertexta exposed to Zn is < or = 1 mg L(-1).

Kinetics of zinc transport in vitro in rat small intestine and colon: interaction with copper

The present study was planned to investigate the kinetic transport of zinc, in the intact intestine of the rat, in order to establish if more than one transporter is involved as well as the existence of a preferent sector in the cation uptake. Using an in vitro technique, the influx of zinc across the brush border membrane in three sectors of the small intestine (proximal, mid and distal) and in the colon of the rat was measured at six different concentrations (from 0.0007 to 11 mM). The kinetic study showed that intestinal transport of zinc occurs by a saturable process in the small intestine. The K(m) value obtained in the proximal segment (10.78+/-4.40 mM) is clearly higher than those obtained in the mid and distal segments (1.94+/-0.39 and 3.04+/-0.44 mM, respectively). The same occurs with the J(max) values. These results seem to indicate that more than one transporter may be implicated in zinc transport. In colon the most probable mechanism is non-saturable diffusion, the diffusive permeability, P, being 2.95.10(-7)+/-0.43.10(-7) cm/h. The statistical comparison of the fluxes indicated that, on the whole, there is not a well defined preferent sector in zinc transport. Additionally, the influence of copper on zinc transport, in three sectors of the small intestine, has been evaluated quantifying the influx of zinc at 0.037 mM in the absence and presence of three different concentrations of copper. The results showed that copper significantly reduced the influx of zinc, in the three sectors studied, in a concentration-dependent manner.

The influence of diet on comparative trace metal cadmium, copper and zinc accumulation in Thais clavigera (Gastropoda: Muricidae) preying on intertidal barnacles or mussels

The influence of diet on comparative metal accumulation was investigated using a predatory muricid gastropod Thais clavigera. Individuals were fed for up to 56 days on either barnacles, i.e., Tetraclita squamosa, or mussels, i.e., Perna viridis, collected from metal-contaminated and clean sites. Barnacles and mussels have contrasting metal handling strategies and, therefore, different body concentrations, intracellular distributions and detoxification systems. Field collection of prey items that accumulated body metal concentrations over a lifetime of exposure allowed bioavailability to the predator, T. clavigera, to be assessed naturally, which may not be the case for prey exposed to metals for a short time in the laboratory. T. clavigera that was fed cadmium- and copper-contaminated barnacles or mussels ingested significantly greater amounts compared to those fed conspecifics collected from clean locations. T. clavigera body cadmium and copper concentrations were not, however, significantly different between individuals fed either contaminated or clean prey. Amount of zinc ingested was similar in mussels collected from clean and contaminated environments but much less when compared to the barnacle prey. The body concentrations of zinc in T. clavigera fed mussels collected from both sites fell. In contrast, the amount of zinc ingested from barnacle prey was significantly greater from those collected from the metal-contaminated site as compared to the clean one. This was reflected as significantly greater body zinc concentrations in T. clavigera fed contaminated barnacles compared to those fed clean individuals. Copper and zinc accumulation from prey was, therefore, complex. It varied between metal and between prey type, but appeared to be related to the amount ingested and the metal handling strategy of the prey.

Maternal smoking effects on infant growth

The influence of maternal smoking the nutrient content of breastmilk and impact on infant longitudinal growth rate is unknown. From birth, 23 smoking (S), (7.1 +/- 4.4 cigarettes/day) and 23 non-smoking (NS) mother-infant pairs were followed. The breastmilk volume by deuterium dilution, zinc (Zn), copper (Cu), and iron (Fe) in breastmilk and hair by atomic absorption (AAS) and cotinine levels by radio-immuno-analysis (RIA) were evaluated. Birthweight was similar in contrast to height, and infants grew normally. Height and height-for-age (ZHA) were significantly lower in S infants and weight-for-height (ZWH) was higher in S infants in the third month, caused by slower height growth. Cotinine was 19 times greater in the S mothers and six times higher in their infants, as compared to NS group. Breastmilk volume was 743 +/- 119 g/day (S) and 742 +/- 111 g/day (NS), with no difference in zinc, copper, iron contents, except for cadmium (Cd). In infant's hair, all minerals were higher in the S group. Smoking affected infant's height during breastfeeding, attributed to an eventual impaired bioavailability of essential nutrients.

Zinc concentration effect at the organismal, cellular and subcellular levels in the eastern oyster

The purpose of this research was to demonstrate a concentration effect of zinc exposure at organismal, cellular and sub-cellular levels in the eastern oyster and to find associated protein expression signatures (PES) for each concentration of zinc. Oysters were exposed to six concentrations of zinc for 48 h in a controlled environment. At the organismal level, fecal material was observed as a measure of physiological health during metal exposures. At the cellular level, lysosomal destabilization was measured using hemolymph. This cellular response was significant only at the highest concentration, when the fecal index was lowest. Protein responses were monitored in the oyster following exposure to zinc. Gill tissue was excised and homogenized, and then analyzed using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and digital image analysis. Protein expression signatures were found to be specific to each concentration. The protein responses were linked to the other biological parameters measured, each of which followed a concentration gradient of zinc.