Aluminum Retention Research Articles

Short-chain aldehydes increase aluminum retention and sensitivity by enhancing cell wall polysaccharide contents and pectin demethylation in wheat seedlings

Upon environmental stimuli, aldehydes are generated downstream of reactive oxygen species and thereby contribute to severe cell damage. In this study, using two wheat genotypes differing in aluminum (Al) tolerance, we investigated the effects of lipid peroxidation-derived aldehydes on cell wall composition and subsequent Al-binding capacities. The spatial accumulation of Al along wheat roots was found to the generation of reactive aldehydes, which are highly localized to the apical regions of roots. Elimination of aldehydes by carnosine significantly reduced Al contents in root tips, with a concomitant alleviation of root growth inhibition. In contrast, root growth and Al accumulation were exacerbated by application of the short-chain aldehyde (E)−2-hexenal. We further confirmed that cell wall binding capacity, rather than malate efflux or pH alteration strategies, is associated with the aldehyde-induced accumulation of Al. Scavenging of lipid-derived aldehydes reduced Al accumulation in the pectin and hemicellulose 1 (HC1) fractions of root cell walls, whereas exposure to (E)−2-hexenal promoted a further accumulation of Al, particularly in the cell wall HC1 fraction of the Al-sensitive genotype. Different strategies were introduced by pectin and HC1 to accumulate Al in response to aldehydes in wheat roots. Accumulation in pectin is based on a reduction of methylation levels in response to elevated pectin methylesterase activity and gene expression, whereas that in HC1 is associated with an increase in polysaccharide contents. These findings indicate that aldehydes exacerbate Al phytotoxicity by enhancing Al retention in cell wall polysaccharides.

Aluminium and manganese leaching and retention in two contrasting soils treated with aluminium-based sludge water in a column experiment

Liquid waste (sludge water (SW)) from treatment of drinking water contains impurities which pose disposal challenges. Irrigation with SW could be a solution for the Morton Jaffray Water Works. This study was conducted to determine the effects of SW dilution on aluminium (Al) and manganese (Mn) concentrations in (a) leachates from columns with either clay or a sandy loam soil and (b) different depths in the columns. The columns were leached with tap water (control) and 25, 50, 75 and 100% of the original SW concentration and the leachates were analysed for pH, electrical conductivity (EC), Al, and Mn. The sectioned soils (0–5, 5–10, 10–15 cm depths) were analysed for pH, exchangeable acidity, extractable Mn and total Al and Mn. Leaching with undiluted SW significantly increased EC and Al and Mn concentrations and lowered pH in leachates of the first four and two leaching events in the clay and sandy loam soils, respectively. The last two to four leaching events released additional Mn. Higher SW concentrations significantly increased retention of Mn, Al, extractable Mn and acidity, and lowered pH in the soils. In practice, irrigation with SW may retain the pollutants and acidify the soil, increasing Mn mobility, potentially causing leaching and phytotoxicity.

Improving the Performance of Composite Hollow Fiber Membranes with Magnetic Field Generated Convection Application on pH Correction.

The membranes and membrane processes have succeeded in the transition from major technological and biomedical applications to domestic applications: water recycling in washing machines, recycling of used cooking oil, recovery of gasoline vapors in the pumping stations or enrichment of air with oxygen. In this paper, the neutralization of condensation water and the retention of aluminum from thermal power plants is studied using ethylene propylene diene monomer sulfonated (EPDM-S) membranes containing magnetic particles impregnated in a microporous propylene hollow fiber (I-PPM) matrix. The obtained membranes were characterized from the morphological and structural points of view, using scanning electron microscopy (SEM), high resolution SEM (HR-SEM), energy dispersive spectroscopy analysis (EDAX) and thermal gravimetric analyzer. The process performances (flow, selectivity) were studied using a variable magnetic field generated by electric coils. The results show the possibility of correcting the pH and removing aluminum ions from the condensation water of heating plants, during a winter period, without the intervention of any operator for the maintenance of the process. The pH was raised from an acidic one (2–4), to a slightly basic one (8–8.5), and the concentration of aluminum ions was lowered to the level allowed for discharge. Magnetic convection of the permeation module improves the pH correction process, but especially prevents the deposition of aluminum hydroxide on hollow fibers membranes.

Aluminum phosphate as active matrix of fluid catalytic cracking catalysts: Y zeolite stabilization

The development of new matrices can improve the hydrothermal stability of fluid catalytic cracking catalysts and provide better selectivity to cracking products. Amorphous, mesoporous and stoichiometric aluminum phosphate (AlPO4) was investigated as active matrix to achieve these purposes. In its gel form, the material was initially added to ultra-stabilized Y zeolite to generate composites with mass ratio of about 1:1. The interaction between AlPO4 and Y zeolite avoided AlPO4 crystallization during steaming and increased framework aluminum retention, preserving more Brönsted acid sites. A spray-dried catalyst containing AlPO4 was steam deactivated and tested by vacuum gas oil cracking, being compared with an alumina-containing catalyst and a reference without active matrix. AlPO4-containing catalyst presented tolerance to contaminant metals, higher selectivity to naphtha yields and exhibited a higher hydrogen transfer reaction rate, leading to the increase in isoparaffins and aromatics yields and the increase in the motor octane number in the cracked naphtha.

Acute exposure and chronic retention of aluminum in three vaccine schedules and effects of genetic and environmental variation

Like the mechanisms of action as adjuvants, the pharmacodynamics of injected forms of aluminum commonly used in vaccines are not well-characterized, particularly with respect to how differences in schedules impact accumulation and how factors such as genetics and environmental influences on detoxification influence clearance. Previous modeling efforts are based on very little empirical data, with the model by Priest based on whole-body clearance rates estimated from a study involving a single human subject. In this analysis, we explore the expected acute exposures and longer-term whole-body accumulation/clearance across three vaccination schedules: the current US Centers for Disease Control and Prevention (CDC) schedule, the current CDC schedule using low aluminum or no aluminum vaccines, and Dr. Paul Thomas’ “Vaccine Friendly Plan” schedule. We then study the effects of an implicit assumption of the Priest model on whether clearance dynamics from successive doses are influenced by the current level of aluminum or modeled by the assumption that a new dose has its own whole-body dynamics “reset” on the day of injection. We model two additional factors: variation (deficiency) in aluminum detoxification, and a factor added to the Priest equation to model the potential impact of aluminum itself on cellular and whole-body detoxification. These explorations are compared to a previously estimated pediatric dose limit (PDL) of whole-body aluminum exposure and provide a new statistic: %alumTox, the (expected) percentage of days (or weeks) an infant is in aluminum toxicity, reflecting chronic toxicity. We show that among three schedules, the CDC schedule results in the highest %alumTox regardless of model assumptions, and the Vaccine Friendly Plan schedule, which avoids >1 ACV per office visit results in the lowest (expected) %alumTox. These results are conservative, as the MSL is derived from data used by FDA to estimate safety of aluminum in adult humans. These results demonstrate high potential utility of modeling variation in patient responses to aluminum. More empirical data from individuals who are suspected of being intolerant of aluminum from vaccines, evidenced by high aluminum retention, neurodevelopmental disorders and/or a myriad of chronic illnesses would help answer questions on whether the model predictions can be used to estimate parameter values tied to genetic factors including genomic sequence variation and family history of chronic illnesses tied to aluminum exposure.

Phosphorus recovery in an acidic environment using layer-by-layer modified membranes

Phosphorus (P) is a limited natural resource and essential for global food supply, particularly given our ever-growing world population. However, natural P deposits are restricted to just a few countries and the quality of exploited primary sources is declining. Phosphorus recovery from sewage sludge or sewage sludge ash leached by acids is hence gaining importance. During P recovery the removal of impurities is a challenge that can be addressed by nanofiltration retaining e. g. multivalent metals and allowing phosphoric acid to pass. However, currently available membranes show low permeability and limit this process option economically. Layer-by-layer (LbL) membrane synthesis is a technology that allows membrane performance to be tailored to individual filtration tasks. Little is known for such membranes with respect to acid resistance, acid permeability and impurity rejection. We show that LBL membranes based on PDADMAC/PSS show the desired passage of phosphoric acid with retentions values below 10%, aluminum retention was always above 95%. Permeabilities up to 4 L/(m2 h bar) were reached even up to a phosphorous recovery of 75%. Overall permeabilities were 16 times higher than a commercial benchmark membrane. Initial stability tests and upscaling into a larger module show the viability of the proposed modification approach.

Prenatal Exposure to Aluminum and Status of Selected Essential Trace Elements in Rural South African Women at Delivery.

This study sought to evaluate the in utero exposure to aluminum and status of selected trace elements in South African women at delivery since aluminum is known to be toxic in all developmental stages even at low concentrations. Serum aluminum was negatively correlated with aluminum in urine, both uncorrected and corrected for creatinine, which suggests the retention of aluminum in body stores. Serum copper and zinc levels were found to be high in this study population. Serum copper levels were negatively correlated with aluminum in serum (β = −0.095; p = 0.05). There was a marginal negative correlation between aluminum levels in serum and manganese levels in whole blood (β = −0.087; p = 0.08). Copper levels in maternal serum were negatively correlated with birth weight and the length of neonates. There were a number of positive correlations between maternal characteristics and birth outcomes. Mothers who consumed root vegetables frequently appeared to be protected from aluminum retention and increased body burden since their serum aluminum levels were found to be significantly lower. The findings of the current study can be used as a baseline for further research on aluminum exposure and its associated interactions and outcomes in vulnerable populations.

Correlated Effects on Forming and Retention of Al Doping in HfO2-Based RRAM

Editor’s note: Retention time is one of the key parameters of emerging memories, which define the time duration the data can be retained when the power supply is removed. In this work, the authors investigate the forming voltage and the data retention of aluminum (Al)-doped HfO2-based RRAM devices and suggest a way to improve the device’s data retention time. ——Yiran Chen, Duke University

Elevation of arginine decarboxylase-dependent putrescine production enhances aluminum tolerance by decreasing aluminum retention in root cell walls of wheat

Aluminum (Al) stress induces putrescine (Put) accumulation in several plants and this response is proposed to alleviate Al toxicity. However, the mechanisms underlying this alleviation remain largely unknown. Here, we show that exposure to Al clearly increases Put accumulation in the roots of wheat plants (Triticum aestivum L. ‘Xi Aimai-1’) and that this was accompanied by significant increase in the activity of arginine decarboxylase (ADC), a Put producing enzyme. Application of an ADC inhibitor (d-arginine) terminated the Al-induced Put accumulation, indicating that increased ADC activity may be responsible for the increase in Put accumulation in response to Al. The d-arginine treatment also increased the Al-induced accumulation of cell wall polysaccharides and the degree of pectin demethylation in wheat roots. Thus, it elevated Al retention in cell walls and exacerbated Al accumulation in roots, both of which aggravate Al toxicity in wheat plants. The opposite effects were true for exogenous Put application. These results suggest that ADC-dependent Put accumulation plays important roles in providing protection against Al toxicity in wheat plants through decreasing cell wall polysaccharides and increasing the degree of pectin methylation, thus decreasing Al retention in the cell walls.

Updated aluminum pharmacokinetics following infant exposures through diet and vaccination

Aluminum is a ubiquitous element that is released naturally into the environment via volcanic activity and the breakdown of rocks on the earth's surface. Exposure of the general population to aluminum occurs primarily through the consumption of food, antacids, and buffered analgesics. Exposure to aluminum in the general population can also occur through vaccination, since vaccines often contain aluminum salts (frequently aluminum hydroxide or aluminum phosphate) as adjuvants. Because concerns have been expressed by the public that aluminum in vaccines may pose a risk to infants, we developed an up-to-date analysis of the safety of aluminum adjuvants. Keith et al. [1] previously analyzed the pharmacokinetics of aluminum for infant dietary and vaccine exposures and compared the resulting body burdens to those based on the minimal risk levels (MRLs) established by the Agency for Toxic Substances and Disease Registry. We updated the analysis of Keith et al. [1] with a current pediatric vaccination schedule [2]; baseline aluminum levels at birth; an aluminum retention function that reflects changing glomerular filtration rates in infants; an adjustment for the kinetics of aluminum efflux at the site of injection; contemporaneous MRLs; and the most recent infant body weight data for children 0-60 months of age [3]. Using these updated parameters we found that the body burden of aluminum from vaccines and diet throughout an infant's first year of life is significantly less than the corresponding safe body burden of aluminum modeled using the regulatory MRL. We conclude that episodic exposures to vaccines that contain aluminum adjuvant continue to be extremely low risk to infants and that the benefits of using vaccines containing aluminum adjuvant outweigh any theoretical concerns.

Tissue Response to a Supplement High in Aluminum and Silicon

The objective was to determine the effects of sodium zeolite A (SZA) on mineral metabolism and tissue mineral composition in calves. Twenty calves were placed on study at 3 days of age and were placed into one of two groups: SS, which received 0.05% BW SZA added to their milk replacer, and CO, which received only milk replacer. Blood samples were taken on days 0, 30, and 60 for mineral analysis. Urine and feces were collected on day 30 for mineral metabolism, and on day 60, the calves were euthanized, and samples were taken from numerous organs for mineral analyses. Aluminum retention was increased in the SS calves (p = 0.001). Silicon concentrations were increased in the aorta, spleen, lung, muscle, and kidney of the SS calves, and aluminum was increased in all SS tissues (p < 0.05). Calcium concentrations were increased in aorta, liver, muscle, and tendon; phosphorus concentrations were increased in aorta, but decreased in plasma; magnesium concentrations were increased in aorta, heart, kidney, liver, and pancreas, but decreased in plasma; and iron concentrations were decreased in kidney and liver (p < 0.05). The accumulation of tissue aluminum and therefore potential adverse consequences may preclude any benefits of using SZA as a dietary supplement.

Converting reactive iron, reactive aluminium, and phosphorus retention index (PRI) to the phosphorus buffering index (PBI) for sandy soils of south-western Australia

The recently developed phosphorus (P) buffering index (PBI) is now the national single-point P sorption index to rank the capacity of soil to sorb P. However, before PBI was developed, P sorption was routinely measured by 2 simple procedures in Western Australia: (i) since the mid 1970s, reactive iron (Fe), which is the concentration of Fe extracted from soil by ammonium oxalate; and (ii) since the mid 1980s, the P retention index (PRI), a single-point P sorption index. Both reactive Fe and aluminium (Al) extracted from soil by ammonium oxalalate (reactive Al) have been measured in experiments conducted in Western Australia. Because PBI is now routinely measured in Western Australia there is the need to convert historical reactive Fe, reactive Al, and PRI values to PBI values. In this study we used soil samples collected from 2 field studies and a study of 96 paddocks, all on sandy soil types common in the region, to measure PBI, reactive Fe, reactive Al (not measured in the paddock study), and PRI. We related PBI (dimensionless), as the dependent (y-axis), to reactive Fe (mg/kg), reactive Al (mg/kg), or PRI (mL/g), as the independent (x-axis). The relationships for all data were good for reactive Al (47 data points from the 2 field studies) and PRI (133 data points for the 2 field studies and the paddock study): --&gt; However, the relationships was poor for reactive Fe (133 data points) and differed for each of the 2 field studies and the paddock study, so no consistent, reliable approach for converting reactive Fe to PBI values could be determined. We recommend that reactive Fe is no longer used in the region, and that only PBI is used to estimate P sorption.

Microbes adapted to acid mine drainage as source for strains active in retention of aluminum or uranium

The use of microorganisms for the extraction of contaminants like solved metals from drainage or surface waters was investigated using strains adapted to a polluted environment at a former uranium mining site near Kauern, Eastern Thuringia, Germany. Soil respiration data showed increasing variation indicating stress response and hence need for adaptation. Thus, isolation of single strains was performed for more detailed analyses. Of the isolated fungi and bacteria (single-celled bacteria as well as filamentous actinobacteria), 15 were grown in mine drainage waters in order to test their capacity to retain (heavy) metals including rare earth elements and radioisotopes. Out of the 15 strains (respectively 5 single-celled bacteria, actinobacteria and fungi), 11 strains could grow in media containing acid mine drainage waters diluted by half which is representative of the conditions a few meters downstream of the entry point of the acid mine drainage. Two strains showed promising capacity for aluminum or uranium retention. Using rare earth elements as tracers, selective biosorption or uptake of heavy rare earth elements was prominent in one sample, a fungal isolate. The actinobacterial strains also showed capacity for bioremediation of contaminated seepage waters. Different reactions to single elements varying between all isolates indicate biologically controlled transport processes because such strong fractionation would not be expected from physico-chemical adsorption processes.

Brain uptake, retention, and efflux of aluminum and manganese.

My colleagues and I investigated the sites and mechanisms of aluminum (Al) and manganese (Mn) distribution through the blood-brain barrier (BBB). Microdialysis was used to sample non-protein-bound Al in the extracellular fluid (ECF) of blood (plasma) and brain. Brain ECF Al appearance after intravenous Al citrate injection was too rapid to attribute to diffusion or to transferrin-receptor-mediated endocytosis, suggesting another carrier-mediated process. The brain:blood ECF Al concentration ratio was 0.15 at constant blood and brain ECF Al concentrations, suggesting carrier-mediated brain Al efflux. Pharmacological manipulations suggested the efflux carrier might be a monocarboxylate transporter (MCT). However, the lack of Al (14)C-citrate uptake into rat erythrocytes suggested it is not a good substrate for isoform MCT1 or for the band 3 anion exchanger. Al (14)C-citrate uptake into murine-derived brain endothelial cells appeared to be carrier mediated, Na independent, pH independent, and energy dependent. Uptake was inhibited by substrate/inhibitors of the MCT and organic anion transporter families. Determination of (26)Al in rat brain at various times after intravenous (26)Al suggested a prolonged brain (26)Al half-life. It appears that Al transferrin and Al citrate cross the BBB by different mechanisms, that much of the Al entering brain ECF is rapidly effluxed, probably as Al citrate, but that some Al is retained for quite some time. Brain influx of the Mn(2+) ion and Mn citrate, determined with the in situ brain perfusion technique, was greater than that attributable to diffusion, suggesting carrier-mediated uptake. Mn citrate uptake was approximately 3-fold greater than the Mn(2+) ion, suggesting it is a primary Mn species entering the brain. After Mn(2+) ion, Mn citrate, or Mn transferrin injection into the brain, brain Mn efflux was not more rapid than that predicted from diffusion. The BBB permeation of Al and Mn is mediated by carriers that may help regulate their brain concentrations.

Aluminum accumulation and membrane fluidity alteration in synaptosomes isolated from rat brain cortex following aluminum ingestion: effect of cholesterol.

In the present work, we studied the effect of cholesterol/phospholipid (CH/PL) molar ratio on aluminum accumulation and aluminum-induced alteration of membrane fluidity in rat brain cortex synaptosomes. We observed that sub-acute (daily supply of 1.00 g of AlCl(3) during 10 days) and chronic (daily supply of 0.03 g of AlCl(3) during 4 months) exposure to dietary aluminum leads to a synaptosomal aluminum enrichment of 45 and 59%, respectively. During chronic exposure to AlCl(3), the enhancement of aluminum content was prevented by administration of colestipol (0.31 g/day), which decreased the synaptosomal membrane CH/PL molar ratio (nmol/nmol) from 1.2 to 0.4. Fluorescence anisotropy analysis, using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene (TMA-DPH), showed that after treatment with colestipol a decrease in membrane order occurs at the level of hydrophilic lipid-water surface and deeper hydrophobic region of the synaptosomal membrane. When the rats were exposed to aluminum, it was observed a significant enhancement of membrane fluidity, which was more pronounced at the level of the membrane hydrophilic regions. Meanwhile, when chronic exposure to dietary AlCl(3) was accompanied by treatment with colestipol, the aluminum-induced decrease in membrane order was negligible when compared to TMA-DPH and DPH anisotropy values measured upon colestipol treatment. In contrast, in vitro incubation of synaptosomes (isolated from control rats) with AlCl(3) induced a concentration-dependent rigidification of this more hydrophilic membrane region. The opposite action of aluminum on synaptosomal membrane fluidity, during in vivo and in vitro experiments, appears to be explained by alteration of synaptosomal CH/PL molar ratio, since a significant reduction (approximately 80%) of this parameter occurs during in vivo exposure to aluminum. In conclusion, during in vivo exposure to aluminum, fluidification of hydrophilic regions and reduction of CH/PL molar ratio of presynaptic membranes accompany the accumulation of this cation, which appear to restrict aluminum retention in brain cortex nerve terminals.

Aluminum toxicokinetics regarding infant diet and vaccinations

Some vaccines contain aluminum adjuvants to enhance the immunological response, and it has been postulated that this aluminum could contribute to adverse health effects, especially in children who receive a vaccination series starting at birth. The pharmacokinetic properties and end-point toxicities of aluminum are presented. In assessing the relevance of dietary and medical aluminum exposure to public health, we estimated infant body burdens during the first year of life for breast milk and formula diets and for a standard vaccination schedule. We then compared those body burdens with that expected for intake at a level considered safe for intermediate-duration exposure. The methodology blends intake values and uptake fractions with an aluminum retention function derived from a human injection study using radioactive 26Al. The calculated body burden of aluminum from vaccinations exceeds that from dietary sources, however, it is below the minimal risk level equivalent curve after the brief period following injection.

Studies on interactions between aluminum compounds and cellulosic fibers in water by means of27Al-NMR

Interactions between pulp fibers and aluminum compounds in pulp suspensions were studied using fibrous cellulose (FC) and fibrous carboxymethylcellulose (FCMC) powders as models of pulp fibers by X-ray fluorescence analysis and27Al nuclear magnetic resonance. When deionized water was used at pH 4–5, water-soluble cationic aluminum species (Al3+, aluminum oligomer, and polyaluminum species) were adsorbed on the solid FCMC, forming carboxylic acid aluminum salts by cation exchange. The formation of these nondissociated pulp-COOAl type structures in paper sheets may contribute to some decreases in hydrophilic property. On the other hand, the water-soluble cationic aluminum species had nearly no interactions with hydroxyl groups of solid cellulose in the suspensions at pH 4–5. When tap water was used at pH 5–7, some aluminum components were retained on not only FCMC but also the FC sample. Probably, water-insoluble Al(OH)3 flocs are formed in the suspensions at pH 5–7 and retained on the FC sample by simple filtration effect. Therefore, two mechanisms of the aluminum retention (i.e., electrostatic interactions and a simple filtration effect) may exist between pulp fibers and aluminum components in the practical papermaking process.

Effects of acute and chronic coingestion of AlCl3 with citrate or polyphenolic acids on tissue retention and distribution of aluminum in rats.

Aluminum (Al) is toxic to certain biological systems and has been implicated as a neurotoxic agent in the pathogenesis of Alzheimer's disease. Intestinal absorption of Al is very low (0.1%), but many organic dietary components are potential chelators of Al and may enhance its absorption and tissue distribution. We examined the effects of acute and chronic coingestion of AlCl3 with different polyphenolic acids on Al retention and compared to citrate in rats. In experiment 1, animals fasted for 14 h were dosed orally with demineralized water, Al chloride, Al chloride plus sodium citrate, or Al chloride plus a polyphenol acid. Blood samples were taken before and 2 h after the gavage and animals were killed 6 h later. In experiment 2, the rats were adapted on a purified diet for 1 wk and received the following for 4 wk in their experimental diets: AlCl3, except group 1, plus citrate or a polyphenol acid, except groups 1 and 2. Animals were killed and blood and tissues were sampled. In experiment 1, citrate highly enhanced Al absorption and its tissue retention. Gallic and chlorogenic acids significantly increased tibia and kidney Al levels compared to the Al group. In experiment 2, Al levels in the urine were significantly increased in all the Al groups compared to the control group. Significantly higher Al levels in the tibia, kidney, and brain were observed in the citrate group and a significant increase in brain Al level was also noted in the chlorogenic acid group compared to AlCl3 group. This may suggest a possible relation structure-activity of polyphenol acids. However, further studies are necessary to better understand the influence of polyphenol acids on Al metabolism, in particular that of chlorogenic acid.

CLEARANCE AND TRANSLOCATION OF ALUMINUM OXIDE (ALUMINA) FROM THE LUNGS

Significant respiratory-tract exposure to insoluble aluminum compounds, such as alumina (aluminum oxide, Al2O3), can occur in occupational settings, yet little is known about the temporal pattern of pulmonary clearance of these materials from the lungs with repeated exposures, and potential subsequent translocation to other organs. This study evaluated the clearance pattern of alumina from the lungs of rats, and burdens in selected extrapulmonary organs (brain, bone, liver, spleen, kidney). Rats were instilled with alumina once weekly for 20 wk. Quantification of retention was performed by measuring aluminum burdens in the lungs and extrapulmonary organs during the exposure period, and then weekly for an additional 19 wk after the exposures ended. Lung burdens of aluminum were found to steadily increase during exposure. Clearance of the material following the end of the exposure regime was extremely slow; only approximately 9% of the amount in the lungs following the 20 weekly exposures was cleared by the end of the postexposure period. This study supports the concept of gradual accumulation and long-term retention of aluminum within the respiratory tract of individuals repeatedly exposed to alumina in occupational settings.

Bioavailability and intestinal absorption of aluminum in rats: effects of aluminum compounds and some dietary constituents.

In the present investigation, the deposition of aluminum in intestinal fragment and the appearance in blood were studied in a perfused rat intestine in situ for 1 h with several aluminum forms (16 mM). We observed that aluminum absorption was positively correlated with the theoretic affinity of aluminum and the functional groups of the chelating agent. The absorption of aluminum after ingestion of organic compounds is more important than after ingestion of mineral compounds, with the following order: Al citrate > Al tartrate, Al gluconate, Al lactate > Al glutamate, Al chloride, Al sulfate, Al nitrate. Absorption depends on the nature of the ligands associated with the Al3+ ion in the gastrointestinal fluid. The higher the aluminum retention in intestinal fragment, the lower the absorption and appearance in blood. However, the higher aluminum concentration is always in the jejunal fragment because of the influence of pH variation on this fragment. Another objective of the present study was to determine the influence of several parameters on aluminum citrate absorption: with or without 0.1 mmol dinitrophenol/L, with aluminum concentration from 3.2, 16, 32, and 48, to 64 mmol/L, media containing 0, 3, or 6 mmol Ca/L, with or without phosphorus or glucose. It is concluded that aluminum is absorbed from the gastrointestinal tract by (1) a paracellular energy independent and nonsaturable route, mainly used for high aluminum concentration, which is modified by extracellular calcium, and (2) a transcellular and saturable route, the aluminum level was not modified with enhancement of aluminum quantity in intestinal lumen. This pathway can be similar with calcium transfer through the intestine and is energy dependent because of a decrease of aluminum absorption that follows the removal of glucose and phosphorus.