Glycinebetaine: a versatile protectant to improve rice performance against aluminium stress by regulating aluminium uptake and translocation

Glycinebetaine alleviates the detrimental effects of aluminium stress by regulating aluminium uptake and translocation, maintaining PSII activity, and activating the oxidative defence, thereby maintaining the growth and development of rice. Aluminium (Al) toxicity is one of the primary growth-limiting factors that limits plant growth and crop productivity in acidic soils. Rice (Oryza sativa L.) plants are susceptible to Al stress and do not naturally accumulate glycinebetaine (GB), one of the most effective protectants. Therefore, the objective of this study was to investigate whether exogenous GB can ameliorate the detrimental effects of Al stress on rice plants. Our results showed that the growth, development and biomass of rice were clearly inhibited under Al stress. However, exogenous GB application increased rice shoot growth and photosynthetic pigments contents, maintained photosystem II (PSII) activity, and activated the antioxidant defence system under Al stress. More importantly, GB may mediate the expression of Al uptake- and translocation-related genes, including OsALS1, OsNrat1, OsSTAR1 and OsSTAR2, and the galacturonic acid contents in rice roots under Al stress. Therefore, our findings highlight exogenous GB application is a valid approach to effectively combat Al toxicity by regulating physiological and biochemical processes in crops.

Endocrine disruption caused by the aquatic exposure to aluminum and manganese in Astyanax altiparanae (Teleostei: Characidae) females during the final ovarian maturation

Aluminum (Al) and manganese (Mn) can be toxic to aquatic biota and cause endocrine disruption in fish, affecting reproduction. This study evaluates the physiological responses of the ray-finned teleost fish Astyanax altiparanae vitellogenic females after acute exposure (96 h) to Al and Mn (alone and combined) in acid pH followed by the same period of exposure to metal-free water in neutral pH. The aim of this second period of exposure was to assess the recovery capacity from the toxic effects these metals. Five experimental groups were established: a control in neutral pH (Ctrl), and acidic pH (Ac), aluminum (Al), manganese (Mn), and Al + Mn groups, maintaining the acidic pH in the groups to which metals were added. The following biological parameters were evaluated: metal tissue concentration, relative fecundity (RF: absolute fecundity/body mass). Plasma levels of cortisol (proxy for stress) and 17α hydroxyprogesterone (17α-OHP), and gene expression of pituitary lhβ mRNA (proxies for final maturation) were measured to evaluate endocrine disruption. In the synchronic exposure, the presence of Mn potentiated the accumulation of Al in gills. The females from acidic pH and Al groups showed a reduced RF. Exposure to Al and Mn triggered an endocrine disruption response, evidenced by a decrease in the plasma concentration of 17α-OHP and cortisol. Despite this anti-steroidogenic effect, no changes occurred in the pituitary gene expression of lhβ. The endocrine changes and the metal accumulation were temporary, while the impacts on RF under the experimental conditions suggest permanent impairment in the reproduction of this species.

Dehydrin MsDHN1 improves aluminum tolerance of alfalfa (Medicago sativa L.) by affecting oxalate exudation from root tips

A SK3 -type dehydrin MsDHN1 was cloned from alfalfa (Medicago sativa L.). Its function and gene regulatory pathways were studied via overexpression and suppression of MsDHN1 in alfalfa seedlings or hairy roots. The results showed that MsDHN1 is a typical intrinsically disordered protein that exists in the form of monomers and homodimers in alfalfa. The plant growth rates increased as a result of MsDHN1 overexpression (MsDHN1-OE) and decreased upon MsDHN1 suppression (MsDHN1-RNAi) in seedlings or hairy roots of alfalfa compared with the wild-type or the vector line under Al stress. MsDHN1 interacting with aquaporin (AQP) MsPIP2;1 and MsTIP1;1 positively affected oxalate secretion from root tips and Al accumulation in root tips. MsABF2 was proven to be an upstream transcription factor of MsDHN1 and activated MsDHN1 expression by binding to the ABRE element of the MsDHN1 promoter. The transcriptional regulation of MsABF2 on MsDHN1 was dependent on the abscisic acid signaling pathway. These results indicate that MsDHN1 can increase alfalfa tolerance to Al stress via increasing oxalate secretion from root tips, which may involve in the interaction of MsDHN1 with two AQP.

Aluminum Enters Mammalian Cells and Destabilizes Chromosome Structure and Number

Chromosome instability (CIN) consists of high rates of structural and numerical chromosome abnormalities and is a well-known hallmark of cancer. Aluminum is added to many industrial products of frequent use. Yet, it has no known physiological role and is a suspected human carcinogen. Here, we show that V79 cells, a well-established model for the evaluation of candidate chemical carcinogens in regulatory toxicology, when cultured in presence of aluminum—in the form of aluminum chloride (AlCl₃) and at concentrations in the range of those measured in human tissues—incorporate the metal in a dose-dependent manner, predominantly accumulating it in the perinuclear region. Intracellular aluminum accumulation rapidly leads to a dose-dependent increase in DNA double strand breaks (DSB), in chromosome numerical abnormalities (aneuploidy) and to proliferation arrest in the G2/M phase of the cell cycle. During mitosis, V79 cells exposed to aluminum assemble abnormal multipolar mitotic spindles and appear to cluster supernumerary centrosomes, possibly explaining why they accumulate chromosome segregation errors and damage. We postulate that chronic aluminum absorption favors CIN in mammalian cells, thus promoting carcinogenesis.

Arabidopsis casein kinase 2 triggers stem cell exhaustion under Al toxicity and phosphate deficiency through activating the DNA damage response pathway

Aluminum (Al) toxicity and inorganic phosphate (Pi) limitation are widespread chronic abiotic and mutually enhancing stresses that profoundly affect crop yield. Both stresses strongly inhibit root growth, resulting from a progressive exhaustion of the stem cell niche. Here, we report on a casein kinase 2 (CK2) inhibitor identified by its capability to maintain a functional root stem cell niche in Arabidopsis thaliana under Al toxic conditions. CK2 operates through phosphorylation of the cell cycle checkpoint activator SUPPRESSOR OF GAMMA RADIATION1 (SOG1), priming its activity under DNA-damaging conditions. In addition to yielding Al tolerance, CK2 and SOG1 inactivation prevents meristem exhaustion under Pi starvation, revealing the existence of a low Pi-induced cell cycle checkpoint that depends on the DNA damage activator ATAXIA-TELANGIECTASIA MUTATED (ATM). Overall, our data reveal an important physiological role for the plant DNA damage response pathway under agriculturally limiting growth conditions, opening new avenues to cope with Pi limitation.

The bioavailability of ingested 26Al-labelled aluminium and aluminium compounds in the rat

The fractional uptake of ingested aluminium and aluminium compounds (aluminium citrate, aluminium nitrate, aluminium chloride, aluminium sulphate, aluminium hydroxide, aluminium oxide, aluminium metal, powdered aluminium pot electrolyte, acidic sodium aluminium phosphate (SALP), basic sodium aluminium phosphate (Kasal), sodium aluminium silicate and FD&C red 40 aluminium lake) from the gastro-intestinal tract of adult female rats was measured. This was determined by comparing retained body burden of 26Al at seven days post-admistration of an i.v. injection of 26Al-labelled aluminium citrate with that retained following the gastric admistration of 26Al-labelled test compounds as either solutions or suspended solid. The calculated percentage uptake of 26Al for all the aluminium solutions was similar: aluminium citrate 0.08%, aluminium chloride 0.05%, aluminium nitrate 0.05% and aluminium sulphate 0.21%. The uptake of 26Al administered as insoluble particulates was lower: 0.03% for aluminium hydroxide; 0.02% for aluminium oxide; 0.04% for powdered pot electrolyte; 0.12% for sodium aluminium silicate; and 0.09% for FD&C red 40 aluminium lake. For aluminium metal, SALP and Kasal the amount of 26Al present in the rats was insufficient to determine uptake and was less than 0.03%. The results produced for aluminium citrate, aluminium hydroxide and aluminium sulphate are close to those published for man.

Dysfunction of the 4-coumarate:coenzyme A ligase 4CL4 impacts aluminum resistance and lignin accumulation in rice

The root cell wall is the first and primary target of aluminum (Al) toxicity. Monocots such as rice (Oryza sativa) can accumulate appreciable levels of hydroxycinnamic acids (HCAs) to modify and cross-link hemicellulose and/or lignin of the cell wall. Nevertheless, it is unclear whether this HCA-mediated modification of the cell wall is important for Al accumulation and resistance. We previously isolated and characterized a rice ral1 (resistance to aluminum 1) mutant that shows enhanced Al resistance. In this study, we cloned RAL1 and found that it encodes the 4-coumarate:coenzyme A ligase 4CL4, an enzyme putatively involved in lignin biosynthesis. Mutation of RAL1/4CL4 reduces lignin content and increases the accumulation of its substrates 4-coumaric acid (PA) and ferulic acid (FA). We demonstrate that altered lignin accumulation is not required for the enhanced Al resistance in ral1/4cl4 mutants. We found that the increased accumulation of PA and FA can reduce Al binding to hemicellulose and consequently enhance Al resistance in ral1/4cl4 mutants. Al stress is able to trigger PA and FA accumulation, which is likely caused by the repression of the expression of RAL1/4CL4 and its homologous genes. Our results thus reveal that Al-induced PA and FA accumulation is actively and positively involved in Al resistance in rice through the modification of the cell wall and thereby the reduced Al binding to the cell wall.

Biochar increases nitrogen use efficiency of maize by relieving aluminum toxicity and improving soil quality in acidic soil

The low nitrogen use efficiency (NUE) of fertilizers and aluminum toxicity are major limiting factors for crop development in red soil (acidic soil) of China. Biochar is a promising material for improving soil quality, alleviating aluminum and acidic toxicity. The present study was conducted on maize to evaluate the effects of biochar on NUE and soil quality under different applications of nitrogen fertilizer. Biochar was used in the following five levels in each pot; C0 (0 g), C1 (7.5 g), C2 (15 g), C3 (30 g), C4 (45 g), in combination with δ¹⁵N at two N levels: N0 (0 g kg^-1) and N1 (0.2 g kg^-1). The biochar increased soil nutrients, exchangeable cation, and SOM. Compared with C0, the K⁺, Ca²⁺, and Mg²⁺ were increased by 31.58%, 95.87%, and 463.75% while total Al³⁺ content of C4 treatment was decreased by 91.98%-93.30% in soil, respectively. X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) showed that Al₂SiO₅ was adsorbed on the surface of biochar in the soil due to the special physical structure of biochar. Besides, the results showed that root and shoot biomass increased by 44.5% and 89.6%, respectively under biochar treatment. The nitrogen utilization rate of the plant was increased by 11.08% after the amendment of biochar to soil. The δ¹⁵N content was increased from 11.97 to 21.32 for root and from 50.84 to 82.33 mg kg^-1 for the shoot. The use of biochar with N fertilizer showed a more positive effect on improving NUE of maize and facilitating soil quality. Our results suggest that biochar could be used to improve soil available nutrients, alleviate aluminum toxicity and acidic toxicity. Therefore, biochar could also increase the NUE of maize by adjusting soil quality.

Aggregated aluminium exposure: risk assessment for the general population

Aluminium is one of the most abundant elements in earth's crust and its manifold uses result in an exposure of the population from many sources. Developmental toxicity, effects on the urinary tract and neurotoxicity are known effects of aluminium and its compounds. Here, we assessed the health risks resulting from total consumer exposure towards aluminium and various aluminium compounds, including contributions from foodstuffs, food additives, food contact materials (FCM), and cosmetic products. For the estimation of aluminium contents in foodstuff, data from the German "Pilot-Total-Diet-Study" were used, which was conducted as part of the European TDS-Exposure project. These were combined with consumption data from the German National Consumption Survey II to yield aluminium exposure via food for adults. It was found that the average weekly aluminium exposure resulting from food intake amounts to approx. 50% of the tolerable weekly intake (TWI) of 1 mg/kg body weight (bw)/week, derived by the European Food Safety Authority (EFSA). For children, data from the French "Infant Total Diet Study" and the "Second French Total Diet Study" were used to estimate aluminium exposure via food. As a result, the TWI can be exhausted or slightly exceeded-particularly for infants who are not exclusively breastfed and young children relying on specially adapted diets (e.g. soy-based, lactose free, hypoallergenic). When taking into account the overall aluminium exposure from foods, cosmetic products (cosmetics), pharmaceuticals and FCM from uncoated aluminium, a significant exceedance of the EFSA-derived TWI and even the PTWI of 2 mg/kg bw/week, derived by the Joint FAO/WHO Expert Committee on Food Additives, may occur. Specifically, high exposure levels were found for adolescents aged 11-14 years. Although exposure data were collected with special regard to the German population, it is also representative for European and comparable to international consumers. From a toxicological point of view, regular exceedance of the lifetime tolerable aluminium intake (TWI/PTWI) is undesirable, since this results in an increased risk for health impairments. Consequently, recommendations on how to reduce overall aluminium exposure are given.

Boron supply maintains efficient antioxidant system, cell wall components and reduces aluminum concentration in roots of trifoliate orange

Aluminum (Al) toxicity in the acid soils (pH ≤ 5) is the major limiting abiotic factor affecting the productivity of crops. Boron (B) has been reported to alleviate Al toxicity. In spite of recent advances, it is not clear how B relieves Al toxicity. Results demonstrated that Al toxicity hampered the root elongation. Moreover, lumogallion fluorescent molecular probe unequivocally localized mostly bound Al to the periphery of the cell wall (CW) and to the nuclei. Additionally, Al toxicity induced variations in the CW components through the accumulation of pectin and hemicellulose. Nevertheless, B supply reduced callose deposition, increased root growth and reduced changes in the CW components under Al toxicity. Moreover, B supply reduced the un-methylated pectin while increased the degree of methyl esterification of pectin. These results imply that B due to its role in the CW formation could reduce aluminum-induced negative effects on plant growth by attenuating apoplastic Al³⁺ and changes in the CW components which ultimately results in the improved root growth.

Assessment of Dermal Absorption of Aluminum from a Representative Antiperspirant Formulation Using a 26 Al Microtracer Approach

A clinical pharmacokinetic study was performed in 12 healthy women to evaluate systemic exposure to aluminum following topical application of a representative antiperspirant formulation under real-life use conditions. A simple roll-on formulation containing an extremely rare isotope of aluminum (26 Al) chlorohydrate (ACH) was prepared to commercial specifications. A 26 Al radio-microtracer was used to distinguish dosed aluminum from natural background, using accelerated mass spectroscopy. The 26 Al citrate was administered intravenously (i.v.) to estimate fraction absorbed (Fabs ) following topical delivery. In blood samples after i.v. administration, 26 Al was readily detected (mean area under the curve (AUC) = 1,273 ± 466 hours×fg/mL). Conversely, all blood samples following topical application were below the lower limit of quantitation (LLOQ; 0.12 fg/mL), except two samples (0.13 and 0.14 fg/mL); a maximal AUC was based on LLOQs. The aluminum was above the LLOQ (61 ag/mL) in 31% of urine samples. From the urinary excretion data, a conservative estimated range for dermal Fabs of 0.002-0.06% was calculated, with a mean estimate of 0.0094%.

Boron Alleviates Aluminum Toxicity by Promoting Root Alkalization in Transition Zone via Polar Auxin Transport

Boron (B) alleviates aluminum (Al) toxicity in higher plants; however, the underlying mechanisms behind this phenomenon remain unknown. Here, we used bromocresol green pH indicator, noninvasive microtest, and microelectrode ion flux estimation techniques to demonstrate that B promotes root surface pH gradients in pea (Pisum sativum) roots, leading to alkalization in the root transition zone and acidification in the elongation zone, while Al inhibits these pH gradients. B significantly decreased Al accumulation in the transition zone (∼1.0-2.5 mm from the apex) of lateral roots, thereby alleviating Al-induced inhibition of root elongation. Net indole acetic acid (IAA) efflux detected by an IAA-sensitive platinum microelectrode showed that polar auxin transport, which peaked in the root transition zone, was inhibited by Al toxicity, while it was partially recovered by B. Electrophysiological experiments using the Arabidopsis (Arabidopsis thaliana) auxin transporter mutants (auxin resistant1-7; pin-formed2 [pin2]) and the specific polar auxin transporter inhibitor1-naphthylphthalamic acid showed that PIN2-based polar auxin transport is involved in root surface alkalization in the transition zone. Our results suggest that B promotes polar auxin transport driven by the auxin efflux transporter PIN2 and leads to the downstream regulation of the plasma membrane-H+-ATPase, resulting in elevated root surface pH, which is essential to decrease Al accumulation in this Al-targeted apical root zone. These findings provide a mechanistic explanation for the role of exogenous B in alleviation of Al accumulation and toxicity in plants.

Sorptive equilibrium profile of fluoride onto aluminum olivine [(FexMg1-x)2SiO4] composite (AOC): Physicochemical insights and isotherm modeling by non-linear least squares regression and a novel neural-network-based method

A novel aluminum/olivine composite (AOC) was prepared by wet impregnation followed by calcination and was introduced as an efficient adsorbent for defluoridation. The adsorption of fluoride was modeled with one-, two- and three-parameter isotherm equations by non-linear regression to demonstrate the adsorption equilibrium. The FI was the best-fitted model among the two-parameter isotherms with a R² value of 0.995. The three-parameter models were found to have better performance with low values of the error functions and high F values. The neural-network-based model was applied for the first time in the isotherm study. The optimized model was framed with eight neurons in hidden layer with a mean square of error of 0.0481 and correlation coefficient greater than 0.999. The neural-based model has the better predictability with a higher F value of 9484 and R² value of 0.998 compared to regression models, exhibiting the F value and the R² in the range of 86-3572 and 0.835-0.995, respectively. The material characterization established the formation of the aluminum oxide, silicate, etc. onto the olivine which is conducive of the removal of fluoride by the formation of aluminum fluoride compounds, such as AlF₃ in the spent material after defluoridation.

Halloysite nanotubes-induced Al accumulation and oxidative damage in liver of mice after 30-day repeated oral administration

Halloysite (Al₂ Si₂ O₅ (OH)₄ ·nH₂ O) nanotubes (HNTs) are natural clay materials and widely applied in many fields due to their natural hollow tubular structures. Many in vitro studies indicate that HNTs exhibit a high level of biocompatibility, however the in vivo toxicity of HNTs remains unclear. The objective of this study was to assess the hepatic toxicity of the purified HNTs in mice via oral route. The purified HNTs were orally administered to mice at 5, 50, and 300 mg/kg body weight (BW) every day for 30 days. Oral administration of HNTs stimulated the growth of the mice at the low dose (5 mg/kg BW) with no liver toxicity, but inhibited the growth of the mice at the middle (50 mg/kg BW) and high (300 mg/kg BW) doses. In addition, oral administration of HNTs at the high dose caused Al accumulation in the liver but had no marked effect on the Si content in the organ. The Al accumulation caused significant oxidative stress in the liver, which induced hepatic dysfunction and histopathologic changes. These findings demonstrated that Al accumulation-induced oxidative stress played an important role in the oral HNTs-caused liver injury.

Changes in the fractionation profile of Al, Ni, and Mo during bioleaching of spent hydroprocessing catalysts with Acidithiobacillus ferrooxidans

Spent hydroprocessing catalysts are known to contain a variety of potentially toxic metals and therefore studies on the bioavailability and mobility of these metals are critical for understanding the possible environmental risks of the spent catalysts. This study evaluates the different chemical fractions/forms of aluminium (Al), nickel (Ni), and molybdenum (Mo) in spent hydroprocessing catalyst and the changes they undergo during bioleaching with Acidithiobacillus ferrooxidans. In the spent catalyst (prior to bioleaching), Al was primarily present in its residual form, suggesting its low environmental mobility. However, Ni comprised mainly an exchangeable fraction, indicating its high environmental mobility. Molybdenum was mainly in the oxidizable form (47.1%), which indicated that highly oxidizing conditions were required to liberate it from the spent catalyst. During bioleaching the exchangeable, reducible and oxidizable fractions of all the metals were leached, whereas the residual fractions remained largely unaffected. At the end of bioleaching process, the metals remaining in the bioleached sample were predominantly in the residual fraction (98.3-99.5%). The 'risk assessment code' (RAC) and I_R analysis also demonstrated that the environmental risks of the bioleached residue were significantly lower compared to the untreated spent catalyst. The results of this study suggest that bioleaching is an effective method in removing the metals from spent catalysts and the bioleached residue poses little environmental risk.

The therapeutic protection of a living and dead Lactobacillus strain against aluminum-induced brain and liver injuries in C57BL/6 mice

Our previous study found that Lactobacillus plantarum CCFM639 had the ability to alleviate acute aluminum (Al) toxicity when the strain was introduced simultaneously with Al exposure. This research was designed to elucidate the therapeutic effects of living and dead L. plantarum CCFM639 against chronic Al toxicity and to gain insight into the protection modes of this strain. Animals were assigned into control, Al only, Al + living CCFM639, and Al + dead CCFM639 groups. The Al exposure model was established by drinking water for the first 4 weeks. The strain was given after Al exposure by oral gavage at 109 colony-forming units once per day for 12 weeks. The results show that the Al binding ability of dead CCFM639 was similar to that of living CCFM639 in vitro. The ingestion of living or dead CCFM639 has similar effects on levels of Al and trace element in tissues, but living strains led to more significant amelioration of oxidative stress and improvement of memory deficits in Al-exposed mice. In conclusion, in addition to intestinal Al sequestration, CCFM639 treatment offers direct protection against chronic Al toxicity by alleviation of oxidative stress. Therefore, L. plantarum CCFM639 has a potential as dietary supplement ingredient that provides protection against Al-induced injury.

Jasmonic Acid Enhances Al-Induced Root Growth Inhibition

Phytohormones such as ethylene and auxin are involved in the regulation of the aluminum (Al)-induced root growth inhibition. Although jasmonate (JA) has been reported to play a crucial role in the regulation of root growth and development in response to environmental stresses through interplay with ethylene and auxin, its role in the regulation of root growth response to Al stress is not yet known. In an attempt to elucidate the role of JA, we found that exogenous application of JA enhanced the Al-induced root growth inhibition. Furthermore, phenotype analysis with mutants defective in either JA biosynthesis or signaling suggests that JA is involved in the regulation of Al-induced root growth inhibition. The expression of the JA receptor CORONATINE INSENSITIVE1 (COI1) and the key JA signaling regulator MYC2 was up-regulated in response to Al stress in the root tips. This process together with COI1-mediated Al-induced root growth inhibition under Al stress was controlled by ethylene but not auxin. Transcriptomic analysis revealed that many responsive genes under Al stress were regulated by JA signaling. The differential responsive of microtubule organization-related genes between the wild-type and coi1-2 mutant is consistent with the changed depolymerization of cortical microtubules in coi1 under Al stress. In addition, ALMT-mediated malate exudation and thus Al exclusion from roots in response to Al stress was also regulated by COI1-mediated JA signaling. Together, this study suggests that root growth inhibition is regulated by COI1-mediated JA signaling independent from auxin signaling and provides novel insights into the phytohormone-mediated root growth inhibition in response to Al stress.

Spatial-temporal analysis of polyethylene glycol-reduced aluminium accumulation and xyloglucan endotransglucosylase action in root tips of common bean (Phaseolus vulgaris)

BACKGROUND AND AIMS

Aluminium (Al) toxicity and drought are two major limiting factors for common bean (Phaseolus vulgaris) production on tropical acid soils. Polyethylene glycol (PEG 6000)-induced osmotic stress (OS) simulating drought stress reduces Al accumulation in the entire root tips of common bean by alteration of cell-wall (CW) porosity, which might be regulated by two genes encoding xyloglucan endotransglucosylase/hydrolase, PvXTH9 and PvXTHb The aim of this research was to understand the spatial and temporal regulation of both XTH genes in PEG-mediated Al accumulation in the root tips.

METHODS

In this study the spatial and temporal expression patterns of Al-inhibited root elongation, Al accumulation, XTH gene expression and xyloglucan endotransglucosylase (XET) enzyme action in the root tips were analysed under PEG-induced OS by a combination of physiological and molecular approaches such as quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and in situ fluorescence detection of XET in root tips.

KEY RESULTS

The results showed that Al accumulation, expression of XTH genes and XET action were distinctly reduced in the apical 0-2, 2-7 and 7-12 mm zones under OS, implying a potential regulatory role of XTH genes and XET enzyme in CW Al accumulation in these zones.

CONCLUSIONS

The results provide novel insights into the physiological and molecular mechanisms of CW structure modification as a response of plant roots to OS, which will contribute to mitigate Al and drought stresses, severely limiting crop yields on acid soils.

Aluminum as a toxicant

Although aluminum is the most abundant metal in nature, it has no known biological function. However, it is known that there is a causal role for aluminum in dialysis encephalopathy, microcytic anemia, and osteomalacia. Aluminum has also been proposed to play a role in the pathogenesis of Alzheimer’s disease (AD) even though this issue is controversial. The exact mechanism of aluminum toxicity is not known but accumulating evidence suggests that the metal can potentiate oxidative and inflammatory events, eventually leading to tissue damage. This review encompasses the general toxicology of aluminum with emphasis on the potential mechanisms by which it may accelerate the progression of chronic age-related neurodegenerative disorders.

Aluminium and the human breast

The human population is exposed to aluminium (Al) from diet, antacids and vaccine adjuvants, but frequent application of Al-based salts to the underarm as antiperspirant adds a high additional exposure directly to the local area of the human breast. Coincidentally the upper outer quadrant of the breast is where there is also a disproportionately high incidence of breast cysts and breast cancer. Al has been measured in human breast tissues/fluids at higher levels than in blood, and experimental evidence suggests that at physiologically relevant concentrations, Al can adversely impact on human breast epithelial cell biology. Gross cystic breast disease is the most common benign disorder of the breast and evidence is presented that Al may be a causative factor in formation of breast cysts. Evidence is also reviewed that Al can enable the development of multiple hallmarks associated with cancer in breast cells, in particular that it can cause genomic instability and inappropriate proliferation in human breast epithelial cells, and can increase migration and invasion of human breast cancer cells. In addition, Al is a metalloestrogen and oestrogen is a risk factor for breast cancer known to influence multiple hallmarks. The microenvironment is established as another determinant of breast cancer development and Al has been shown to cause adverse alterations to the breast microenvironment. If current usage patterns of Al-based antiperspirant salts contribute to causation of breast cysts and breast cancer, then reduction in exposure would offer a strategy for prevention, and regulatory review is now justified.

Rapid activation of catalase followed by citrate efflux effectively improves aluminum tolerance in the roots of chick pea (Cicer arietinum)

The present study demonstrates the comparative response of two contrasting genotypes (aluminum (Al) tolerant and Al sensitive) of chick pea (Cicer arietinum) against Al stress. The Al-tolerant genotype (RSG 974) showed lesser inhibition of root growth as well as lower oxidative damages, measured in terms of the accumulation of H2O2 and lipid peroxidation compared to the Al-sensitive genotype (RSG 945). The accumulation of Al by roots of both genotypes was almost equal at 96 and 144 h after Al treatment; however, it was higher in Al-tolerant than Al-sensitive genotype at 48 h after Al treatment. Further, the Al-mediated induction of superoxide dismutase (SOD) activity was significantly higher in Al-tolerant than Al-sensitive genotype. Ascorbate peroxidase (APX) activity was almost similar in both genotypes. Al treatment promptly activated catalase activity in Al-tolerant genotype, and it was remarkably higher than that of Al-sensitive genotype. As another important Al detoxification mechanism, citrate efflux was almost equal in both genotypes except at 1000 μM Al treatment for 96 and 144 h. Further, citrate carrier and anion channel inhibitor experiment confirmed the contribution of citrate efflux in conferring Al tolerance in Al-tolerant genotype. Based on the available data, the present study concludes that rapid activation of catalase (also SOD) activity followed by citrate efflux effectively improves Al tolerance in chick pea.

Bioaccumulation of Metals in Tissues of Seahorses Collected from Coastal China

Seahorses, which have been used in Chinese traditional medicine, are poor swimmers and easily affected by regional ecological conditions. In this study, we investigated the bioaccumulation of nine metals in different tissues of four seahorse species (Hippocampus trimaculatus, H. histrix, H. kelloggi, and H. kuda) from six locations along the Chinese coast. The present study found relatively low concentrations of metals in the seahorses compared with those in other marine fishes. There was a location-dependent variation in metal concentrations in the seahorses, especially between developed and less developed cities. Results also showed metal concentrations varied among different seahorse species and tissues, with H. kelloggi having higher bioaccumulation ability compared with H. trimaculatus and higher metal levels were found in visceral mass, muscle, and skin tissues than those in brain, lips gill, endoskeleton, and exoskeleton tissues in the seahorses. Among different metals, Mg had the highest tissue concentrations in all the seahorses, followed by Al and Mn.

The impact of aluminum, fluoride, and aluminum-fluoride complexes in drinking water on chronic kidney disease

It is suspected that drinking water containing fluoride and aluminum results in negative health effects especially on brain, liver, and kidney. In this investigation, the effect of F, Al, and AlFx complex on chronic kidney disease (CKD) was investigated. Mice were treated either with WHO recommended or slightly higher F and Al levels in drinking water. Treatment solutions contained 0.05-10.0 mg/L of F, 0.08-10.0 mg/L of Al, or 0.07-15 mg/L of AlFx, and the treatment period was 42 weeks. Blood urea level and creatinine levels were investigated as a measure of malfunction of kidneys. Histopathological evaluations of kidney tissues were carried out to assess the extent of damage that F, Al, and AlFx complex could cause. It was demonstrated that the treated drinking water containing F and Al with par with WHO or moderately above the WHO levels or AlFx in low level (0.07-15 mg/L) does not lead to CKD in mice.

Aluminium uptake and translocation in Al hyperaccumulator Rumex obtusifolius is affected by low-molecular-weight organic acids content and soil pH

BACKGROUND AND AIMS

High Al resistance of Rumex obtusifolius together with its ability to accumulate Al has never been studied in weakly acidic conditions (pH > 5.8) and is not sufficiently described in real soil conditions. The potential elucidation of the role of organic acids in plant can explain the Al tolerance mechanism.

METHODS

We established a pot experiment with R. obtusifolius planted in slightly acidic and alkaline soils. For the manipulation of Al availability, both soils were untreated and treated by lime and superphosphate. We determined mobile Al concentrations in soils and concentrations of Al and organic acids in organs.

RESULTS

Al availability correlated positively to the extraction of organic acids (citric acid < oxalic acid) in soils. Monovalent Al cations were the most abundant mobile Al forms with positive charge in soils. Liming and superphosphate application were ambiguous measures for changing Al mobility in soils. Elevated transport of total Al from belowground organs into leaves was recorded in both lime-treated soils and in superphosphate-treated alkaline soil as a result of sufficient amount of Ca available from soil solution as well as from superphosphate that can probably modify distribution of total Al in R. obtusifolius as a representative of "oxalate plants." The highest concentrations of Al and organic acids were recorded in the leaves, followed by the stem and belowground organ infusions.

CONCLUSIONS

In alkaline soil, R. obtusifolius is an Al-hyperaccumulator with the highest concentrations of oxalate in leaves, of malate in stems, and of citrate in belowground organs. These organic acids form strong complexes with Al that can play a key role in internal Al tolerance but the used methods did not allow us to distinguish the proportion of total Al-organic complexes to the free organic acids.

Aluminum contamination in parenteral products

PURPOSE OF REVIEW

In 1986, the US Food and Drug Administration issued an aluminum mandate in hopes of minimizing patient exposure to aluminum contaminates contained in parenteral nutrition additives. The purpose of this article is to revisit the status of aluminum contamination as it relates to parenteral nutrition and to survey the recent literature to determine if any new findings have emerged. A special emphasis will be placed on the complications associated with aluminum toxicity.

RECENT FINDINGS

In addition to metabolic bone disease, patients with aluminum toxicity are also prone to other complications such as neurodevelopmental delays and cholestasis. Other potentially serious consequences, including osteoporosis, growth failure, and dementia, can arise years after the initial exposure to aluminum, showing that preventing toxicity is imperative.

SUMMARY

Unlike the rapid response to eliminating aluminum toxicity in the dialysis patient population, similar successes have not been realized in patients receiving parenteral nutrition solutions. Product formulation changes have been slow to emerge from manufacturers. It remains the responsibility of healthcare practitioners to recognize the patient populations at risk for toxicity and act accordingly. Monitoring aluminum status and purchasing products known to possess the least amount of aluminum are two such approaches.

Monitoring impacts of air pollution: PIXE analysis and histopathological modalities in evaluating relative risks of elemental contamination

Environmental toxicants invariably affect all biological organisms resulting to sufferings ranging from subclinical to debilitating clinical conditions. This novel research aimed to determine the toxic burdens of increased environmental elements in some vital organs/tissues of the wild animals (starling, owl, crow and pigeon), exposed to air polluted environment were assessed using particle induced X-ray emission and histopathological approaches. The presence of significantly elevated amounts of elemental toxicants namely: Aluminum (Al), Chlorine (Cl), Iron (Fe), Potassium (K), Magnesium (Mg), Manganese (Mn), Silicon (Si) and Vanadium (V) from the skin, muscle, lungs, liver and kidney of sampled animals were in concurrence with the observed histopathological changes. The skin of sampled starling, owl, pigeon and crow spotlighted highly significant increase (P < 0.001) in Al, Cl, Mg and Si. Muscle samples with myodegenerative lesions and mineral depositions highlighted substantial augmentation (P < 0.001) in the amount of Al, Fe, Mn, Si and V. The lungs of starling, owl, and pigeon were severely intoxicated (P < 0.001) with increased amount of Al, Fe, K, Mn and Si producing pulmonary lesions of congestion, edema, pneumonitis and mineral debris depositions. Liver samples revealed that the sampled animals were laden with Cl, Fe, Mg, Mn and V with histopathological profound degenerative changes and hepatic necrosis. Kidney sections presented severe tubular degenerative and necrotic changes that may be attributed to increased amounts of Cl and Fe. These current findings implied that the environmental/elemental toxicants and the accompanying lesions that were discerned in the organs/tissues of sampled birds may as well be afflicting people living within the polluted area. Further assessment to more conclusively demonstrate correlations of current findings to those of the populace within the area is encouraged.

Assessing human exposure to aluminium, chromium and vanadium through outdoor dust ingestion in the Bassin Minier de Provence, France

The Western part of the "Bassin Minier de Provence", a former coal mining area, is still occupied by old polluting industries such as a coal-fired power plant and an alumina factory. The identified pollution sources that raise more concern in the population are the emission of gases and dusts, as well as the storage of raw and transformed materials. In 2011, a preliminary survey was carried out in the area as the first step to an exposure and health risk-assessment study. This first survey intends to assess human exposure through ingestion and health risk associated with potentially harmful elements (PHEs) in ground-level dusts collected in recreational areas used by children. Dust samples were taken at 19 sites distributed across the study area, depending on the location of public parks, public gardens, playgrounds and schools. Pseudo-total concentrations of 53 elements were determined by ICP-MS. Bioaccessible concentrations were estimated using the unified bioaccessibility method. This study presents the results obtained for Al, V and Cr, which seem to be related with industry and show similar distribution patterns. PHEs presumably related to traffic or other urban pollution sources are not discussed in this study. The highest total concentrations occur in dusts near the alumina plant that have significant amounts of Al mineral phases (gibbsite and alumina). However, in these dusts only small fractions of the elements under study are in bioaccessible forms. The highest bioaccessible fractions occur in dusts collected near the coal-fired power plant. Further investigation is required to assess potential pathways of exposure and health risk in this area.

Localization of fluoride and aluminum in subcellular fractions of tea leaves and roots

The tea plant is a fluoride (F) and aluminum (Al) hyperaccumulator. High concentrations of F and Al have always been found in tea leaves without symptoms of toxicity, which may be related to the special localization of F and Al in tea leaves. In this study, we for the first time determined the subcellular localization of F and Al in tea roots and leaves and provided evidence of the detoxification mechanisms of high concentrations of F and Al in tea plants. Results revealed that 52.3 and 71.8% of the total F accumulated in the soluble fraction of tea roots and leaves, and vacuoles contained 98.1% of the total F measured in the protoplasts of tea leaves. Cell walls contained 69.8 and 75.2% of the total Al detected in the tea roots and leaves, respectively, and 73.2% of Al sequestered in cell walls was immobilized by pectin and hemicellulose components. Meanwhile, 88.3% of the Al measured in protoplasts was stored in the vacuoles of tea leaves. Our results suggested that the subcellular distributions of F and Al in tea plants play two important roles in the detoxification of F and Al toxicities. First, most of the F and Al was sequestered in the vacuole fractions in tea leaves, which could reduce their toxicities to organelles. Second, Al can be immobilized in the pectin and hemicellulose components of cell walls, which could suppress the uptake of Al by tea roots.

[Experimental evaluation of combined effects caused by stress and metals (cadmium and aluminium) in reproductivity of male rats]

To investigate combined effects of stress and metal (aluminium, cadmium) on reproductivity, male rats twice per week received intraperitoneal injections of aluminium (3.8 mg Al3+ per kg of body weight) or cadmium (0.3 mg Cd2+ per kg of body weight) and were subjected to stress via short-term immobilization during spermatogenic cycle (54 +/- 3 days). Findings are cumulation of both cadmium and aluminium in genitals and brain, increasing under stress. When acting separately to the laboratory animals, the three factors (aluminium/cadmium/stress) increase serum corticosterone level, change testosterone level, increase number of aberrant mitoses of spermatogenic epithelium cells, increased sperm count with fragmented DNA, lower percentage of the impregnated females. If the exposure combined with stress, spermatogenesis disorders are more marked, and preimplantation death rate of intact females' offspirngs becomes statistically significant.

Human exposure to aluminium

Human activities have circumvented the efficient geochemical cycling of aluminium within the lithosphere and therewith opened a door, which was previously only ajar, onto the biotic cycle to instigate and promote the accumulation of aluminium in biota and especially humans. Neither these relatively recent activities nor the entry of aluminium into the living cycle are showing any signs of abating and it is thus now imperative that we understand as fully as possible how humans are exposed to aluminium and the future consequences of a burgeoning exposure and body burden. The aluminium age is upon us and there is now an urgent need to understand how to live safely and effectively with aluminium.

Coordination between apoplastic and symplastic detoxification confers plant aluminum resistance

Whether aluminum toxicity is an apoplastic or symplastic phenomenon is still a matter of debate. Here, we found that three auxin overproducing mutants, yucca, the recessive mutant superroot2, and superroot1 had increased aluminum sensitivity, while a transfer DNA insertion mutant, xyloglucan endotransglucosylase/hydrolases15 (xth15), showed enhanced aluminum resistance, accompanied by low endogenous indole-3-acetic acid levels, implying that auxin may be involved in plant responses to aluminum stress. We used yucca and xth15 mutants for further study. The two mutants accumulated similar total aluminum in roots and had significantly reduced cell wall aluminum and increased symplastic aluminum content relative to the wild-type ecotype Columbia, indicating that altered aluminum levels in the symplast or cell wall cannot fully explain the differential aluminum resistance of these two mutants. The expression of Al sensitive1 (ALS1), a gene that functions in aluminum redistribution between the cytoplasm and vacuole and contributes to symplastic aluminum detoxification, was less abundant in yucca and more abundant in xth15 than the wild type, consistent with possible ALS1 function conferring altered aluminum sensitivity in the two mutants. Consistent with the idea that xth15 can tolerate more symplastic aluminum because of possible ALS1 targeting to the vacuole, morin staining of yucca root tip sections showed more aluminum accumulation in the cytosol than in the wild type, and xth15 showed reduced morin staining of cytosolic aluminum, even though yucca and xth15 had similar overall symplastic aluminum content. Exogenous application of an active auxin analog, naphthylacetic acid, to the wild type mimicked the aluminum sensitivity and distribution phenotypes of yucca, verifying that auxin may regulate aluminum distribution in cells. Together, these data demonstrate that auxin negatively regulates aluminum tolerance through altering ALS1 expression and aluminum distribution within plant cells, and plants must coordinate exclusion and internal detoxification to reduce aluminum toxicity effectively.

Metal accumulation in wild nine-banded armadillos

Nine-banded armadillos (Dasypus novemcinctus) are widespread and abundant New World mammals with a lifestyle that entails prolonged, intimate contact with soils. Thus, armadillos would seem a promising candidate as a sentinel species to monitor chemical contamination in terrestrial ecosystems. Surprisingly, there have been virtually no toxicology studies on armadillos. Here, we provide the first analysis of metal contaminants for wild armadillos. Liver tissues were obtained from 302 armadillos collected at 6 sites in Georgia and Florida, USA that varied in their extent of human disturbance, from rural pine plantations to highly modified military/space installations. Data were stratified by age (juvenile and adult), sex, and site. Temporal (yearly) variation was examined at two of the sites that were sampled over three consecutive years. Concentrations of aluminum, cadmium, copper, nickel, lead, and zinc were measured in liver samples from each site. Although reference levels are not available for armadillos, accumulated metal concentrations were comparable to those reported for other mammals. We found no evidence of sex or age differences in the concentrations of any metal, except for Cd (age) and Pb (sex and age). However, concentrations of most metals varied substantially across sites and over time. Finally, concentrations of many metals were positively correlated with one another, suggesting that they likely co-occurred in some areas. Collectively, this study indicates the utility of armadillos as a sentinel species for studies of metal contamination in terrestrial systems, and highlights the need for further studies of other toxicants in these animals.

Sublethal effects in Atlantic salmon (Salmo salar) exposed to mixtures of copper, aluminium and gamma radiation

The present study was designed to investigate the effects in presmolt of Atlantic salmon (Salmo salar) exposed to copper (Cu), aluminium (Al) and gamma radiation, individually or in combination. Fish were exposed for 48 h to metals added to lake water; 10, 40 and 80 μg Cu/L, 250 μg Al/L and a combination of 40 μg Cu/L and 250 μg Al/L. In addition, gamma radiation (4-70 mGy delivered over 48 h) was added as an additional exposure stressor. Selected endpoints were chosen to reveal different toxic mechanisms and included Cu and Al accumulation on gills, blood chemistry and haematological variables (plasma sodium and chloride, haematocrit, glucose), hepatic levels of reduced and oxidised glutathione (GSH and GSSG) and hepatic transcriptional response of glutathione peroxidase (GPx), gamma-glutamylcysteine synthetase (GCS), metallothionein (MT) and ubiquitin. Exposure to Cu alone resulted in gill accumulation of Cu, reduction of plasma ions and increased transcriptional response of GPx, MT and ubiquitin. Exposure to Al alone reduced plasma ion levels but did not affect any of the hepatic biomarkers except for ubiquitin. The combined metal exposure (Cu + Al) altered the GSH levels, however GPx and MT were not affected suggesting a different mode of detoxification in the combined exposure. Gamma radiation appeared to influence GSH and ubiquitin levels. The observed effects seemed to be both stressor and concentration dependent.

Salicylic acid alleviates aluminum toxicity in rice seedlings better than magnesium and calcium by reducing aluminum uptake, suppressing oxidative damage and increasing antioxidative defense

Aluminum toxicity is a major constraint to crop production in acid soils. The present study was undertaken to examine the comparative ameliorating effects of salicylic acid, Ca and Mg on Al toxicity in rice (Oryza sativa L.) seedlings grown in hydroponics. Al treatment (0.5 mM AlCl3) caused decrease in plant vigour, loss of root plasma membrane integrity, increased contents of O 2 (∙-) , H2O2, lipid peroxidation, protein carbonyls and decline in the level of protein thiol. Al treatment caused significant changes in activity of antioxidative enzymes in rice seedlings. Exogenously added salicylic acid (60 μM), Ca (1 mM) and Mg (0.25 mM) significantly alleviated Al toxicity effects in the seedlings marked by restoration of growth, suppression of Al uptake, restoration of root plasma membrane integrity and decline in O 2 (∙-) , H2O2, lipid peroxidation and protein carbonyl contents. Salicylic acid, Ca and Mg suppressed Al-induced increase in SOD, GPX and APX activities while it elevated Al-induced decline in CAT activity. By histochemical staining of O 2 (∙-) using NBT and H2O2 using DAB, it was further confirmed that added salicylic acid, Ca or Mg decreased Al-induced accumulation of O 2 (∙-) and H2O2 in the leaf tissues. Results indicate that exogenously added salicylic acid, Ca or Mg alleviates Al toxicity in rice seedlings by suppressing Al uptake, restoring root membrane integrity, reducing ROS level and ROS induced oxidative damage and regulating the level of antioxidative enzyme activities. Further salicylic appears to be superior to Mg and Ca in alleviating Al toxicity effects in rice plants.

Responses of earthworm to aluminum toxicity in latosol

Excess aluminum (Al) in soils due to acid rain leaching is toxic to water resources and harmful to soil organisms and plants. This study investigated adverse impacts of Al levels upon earthworms (Eisenia fetida) from the latosol (acidic red soil). Laboratory experiments were performed to examine the survival and avoidance of earthworms from high Al concentrations and investigate the response of earthworms upon Al toxicity at seven different Al concentrations that ranged from 0 to 300 mg kg(-1) over a 28-day period. Our study showed that the rate of the earthworm survival was 100 % within the first 7 days and decreased as time elapsed, especially for the Al concentrations at 200 and 300 mg kg(-1). A very good linear correlation existed between the earthworm avoidance and the soil Al concentration. There was no Al toxicity to earthworms with the Al concentration ≤ 50 mg kg(-1), and the toxicity started with the Al concentration ≥ 100 mg kg(-1). Low Al concentration (i.e., <50 mg kg(-1)) enhanced the growth of the earthworms, while high Al concentration (>100 mg kg(-1)) retarded the growth of the earthworms. The weight of earthworms and the uptake of Al by earthworms increased with the Al concentrations from 0 to 50 mg kg(-1) and decreased with the Al concentrations from 50 to 300 mg kg(-1). The protein content in the earthworms decreased with the Al concentrations from 0 to 100 mg kg(-1) and increased from 100 to 300 mg kg(-1). In contrast, the catalase (CAT) and superoxide dismutase (SOD) activities in the earthworms increased with the Al concentrations from 0 to 100 mg kg(-1) and decreased from 100 to 300 mg kg(-1). The highest CAT and SOD activities and lowest protein content were found at the Al concentration of 100 mg kg(-1). Results suggest that a high level of Al content in latosol was harmful to earthworms.

Evaluating the potential role of pomegranate peel in aluminum-induced oxidative stress and histopathological alterations in brain of female rats

Studies have shown that pomegranate, Punica granatum Linn. (Lythraceae), has remarkable biological and medicinal properties. However, the effects of pomegranate peel methanolic extract (PPME) on the aluminum-induced oxidative stress and histopathological change have not been reported yet. To determine the effect of PPME (200 mg/kg bwt) on the aluminum chloride (AlCl₃; 34 mg/kg bwt)-induced neurotoxicity, aluminum accumulation in brain and oxidant/antioxidant status were determined. The change of brain structure was investigated with hematoxylin and eosin, and anti-apoptosis effects of PPME were analyzed by immunohistochemistry. The present study showed an indication of carcinogenicity in the AlCl₃-treated group representing an increase in tissue tumor markers such as tumor necrosis factor-α and angiogenin and inflammation by inducing an increase in prostaglandin E2 and prostaglandin F2α. PPME protected brain through decreasing the aluminum accumulation and stimulating antioxidant activities and anti-apoptotic proteins namely Bcl-2. Therefore, these results indicated that pomegranate peel methanolic extract could inhibit aluminum-induced oxidative stress and histopathological alternations in brain of female rats, and these effects may be related to anti-apoptotic and antioxidants activities.

Alleviation of aluminum toxicity by hydrogen sulfide is related to elevated ATPase, and suppressed aluminum uptake and oxidative stress in barley

Greenhouse hydroponic experiments were performed to evaluate potential role of H(2)S on Al toxicity in barley seedlings. Seedlings pretreated with 200 μM NaHS as a donor of H(2)S for 24h and subsequently exposed to 100 μM AlCl(3) for 24h had significantly longer roots than those without NaHS. The promoted root elongation was correlated with a substantial decrease in Al-induced overproduction of lipid peroxidation, electrolyte leakage and Al accumulation in roots, and a marked increase in Al-induced depress activities of Na(+)K(+)-ATPase and H(+)-ATPase. The alleviating role of H(2)S on Al-induced toxicity was also found in a time- and dose-dependent experiment. Addition of 200 and 400 μM NaHS to 100 μM AlCl(3) effectively alleviated Al-toxicity, markedly diminished Al-induced MDA accumulation, and increased chlorophyll content, net photosynthetic rate (Pn) and maximal photochemical efficiency (Fv/Fm) compared with Al alone. Exogenous H(2)S significantly elevated depressed CAT activities, and further improved root POD activity. Moreover, NaHS decreased Al accumulation, but elevated concentrations of S, P, Ca, Mg and Fe in plants. These data suggest that H(2)S-induced alleviation in Al toxicity is attributed to reduced Al uptake and MDA accumulation, improved uptake of P, Ca, Mg and Fe, and elevated ATPase and photosynthetic performance.

Assessment of sacrificial anode impact by aluminum accumulation in mussel Mytilus edulis: a large-scale laboratory test

Since the early 1960s, the application of aluminum alloy sacrificial anodes to mitigate marine corrosion has been well known. The aim of this work was to study aluminum bioconcentration in Mytilus edulis by an in vitro test performed in two tanks: the first containing non-contaminated water (NCW) and the second containing aluminum-contaminated water (CW) (530 μg L(-1)) released by sacrificial anode. The mussels were collected and examined over a period of 8 weeks. A comparison between the aluminum concentrations in the digestive glands of mussels from the CW and NCW tanks shows that the highest value (1700 mg/kg d.w.) was found in the CW mussels collected after 13 days. In NCW, the mean aluminum concentration in digestive glands during the test was 281 mg/kg d.w. The rapid concentration decrease in digestive glands is probably due to the inhibition of filtering activity due to valve closure at the high concentration as well as the induction of the detoxification response.

Toxicity of aluminium in natural waters controlled by type rather than quantity of natural organic matter

Extension of the conditions under which Al toxicity is tested is required. Environmentally representative preparation of waters is used in investigating roles of alginate (AA) and humic acids (HA) in partitioning of Al (0.5 mg L(-1)), subsequent uptake and accumulation by and toxicity to Lymnaea stagnalis. HA and AA did not alter precipitation of Al(OH)3, but altered subsequent behaviour of Al. High (40 mg L(-1)) HA concentrations, and to a lesser extent AA, prevented settling and availability for benthic grazing but made deposited Al more likely to be ingested. HA detoxified but AA increased toxicity relative to Al alone. Low concentration (4 mg L(-1)) AA and HA do not change partitioning but increase uptake; they both detoxify, but AA less than HA. The study shows OC:Al ratio is critical in predicting Al behaviour in natural waters, also uptake is mediated by snail behaviour, not solely a function of concentration and form of Al. Therefore, predicting Al behaviour will be subject to errors in determining relevant water composition and response of biota to the new speciation. However, with respect to toxicity, rather than other aspects of Al behaviour, different ratios of HA and Al are insignificant compared to whether AA is present rather than HA.

Accumulation and toxicity of aluminium-contaminated food in the freshwater crayfish, Pacifastacus leniusculus

The accumulation and toxicity of aluminium in freshwater organisms have primarily been examined following aqueous exposure. This study investigated the uptake, excretion and toxicity of aluminium when presented as aluminium-contaminated food. Adult Pacifastacus leniusculus were fed control (3 μg aluminium/g) or aluminium-spiked pellets (420 μg aluminium/g) over 28 days. Half the crayfish in each group were then killed and the remainder fed control pellets for a further 10 days (clearance period). Concentrations of aluminium plus the essential metals calcium, copper, potassium and sodium were measured in the gill, hepatopancreas, flexor muscle, antennal gland (kidney) and haemolymph. Histopathological analysis of tissue damage and sub-cellular distribution of aluminium were examined in the hepatopancreas. Haemocyte number and protein concentration in the haemolymph were analysed as indicators of toxicity. The hepatopancreas of aluminium-fed crayfish contained significantly more aluminium than controls on days 28 and 38, and this amount was positively correlated with the amount ingested. More than 50% of the aluminium in the hepatopancreas of aluminium-fed crayfish was located in sub-cellular fractions thought to be involved in metal detoxification. Aluminium concentrations were also high in the antennal glands of aluminium-fed crayfish suggesting that some of the aluminium lost from the hepatopancreas is excreted. Aluminium exposure via contaminated food caused inflammation in the hepatopancreas but did not affect the number of circulating haemocytes, haemolymph ion concentrations or protein levels. In conclusion, crayfish accumulate, store and excrete aluminium from contaminated food with only localised toxicity.

Molecular and physiological strategies to increase aluminum resistance in plants

Aluminum (Al) toxicity is a primary limitation to plant growth on acid soils. Root meristems are the first site for toxic Al accumulation, and therefore inhibition of root elongation is the most evident physiological manifestation of Al toxicity. Plants may resist Al toxicity by avoidance (Al exclusion) and/or tolerance mechanisms (detoxification of Al inside the cells). The Al exclusion involves the exudation of organic acid anions from the root apices, whereas tolerance mechanisms comprise internal Al detoxification by organic acid anions and enhanced scavenging of free oxygen radicals. One of the most important advances in understanding the molecular events associated with the Al exclusion mechanism was the identification of the ALMT1 gene (Al-activated malate transporter) in Triticum aestivum root cells, which codes for a plasma membrane anion channel that allows efflux of organic acid anions, such as malate, citrate or oxalate. On the other hand, the scavenging of free radicals is dependent on the expression of genes involved in antioxidant defenses, such as peroxidases (e.g. in Arabidopsis thaliana and Nicotiana tabacum), catalases (e.g. in Capsicum annuum), and the gene WMnSOD1 from T. aestivum. However, other recent findings show that reactive oxygen species (ROS) induced stress may be due to acidic (low pH) conditions rather than to Al stress. In this review, we summarize recent findings regarding molecular and physiological mechanisms of Al toxicity and resistance in higher plants. Advances have been made in understanding some of the underlying strategies that plants use to cope with Al toxicity. Furthermore, we discuss the physiological and molecular responses to Al toxicity, including genes involved in Al resistance that have been identified and characterized in several plant species. The better understanding of these strategies and mechanisms is essential for improving plant performance in acidic, Al-toxic soils.

Dynamic analysis of exposure to aluminum and an acidic condition on bone formation in young growing rats

The toxic effects of exposure to aluminum (Al) in an acidic condition on bone formation in young growing rats were studied. Wistar rats were divided randomly into Al-treated group (100mg Al(3+)/L; pH 5.6) and control group (distilled water). Al-treated rats showed lower body weight, lower serum pH, higher accumulation of Al, in addition to disordered metabolism of calcium and phosphorus compared with control rats. The levels of parathyroid hormone, calcitonin, osteocalcin, procollagen carboxy-terminal propeptide and bone alkaline phosphatase were significantly lower in the Al-treated group than in the control group from days 90, 30, 60, 60 and 90, respectively. The bone mineral density of the distal and proximal femoral metaphysis was significantly lower in the Al-treated group than in the control group on days 120 and 150. These findings suggest that long-term Al exposure in an acidic condition inhibits bone formation and induces bone loss in young growing animals.

[Intestinal and hepatic subcellular localization of aluminium and indium administered orally to rat]

Aluminium and indium are two elements used in industrial and medical fields. The purpose of this work was to study the subcellular localization of these elements, after their single and simultaneous oral administration to rats. 2h after the administration of these two elements, the small intestine and the liver were removed.Ultrastructural study showed the presence of electron dense deposits in the lysosomes of apical parts of duodenal enterocytes. When the minerals were administered simultaneously, deposits were observed in lysosomes of duodenal and jejunal enterocytes. No deposits were seen in the hepatic tissue of treated and control rats. Microanalysis identification showed that the deposits are constituted of aluminium, indium as well as phosphorus. Our results suggested that the elements are concentrated, in lysosomes, under the form of insoluble phosphate salts and it seemed that there are no specific lysosomes for the concentration of minerals since the two elements were concentrated in the same lysosome when they are administered simultaneously.

Effect of water treatment residuals on soil phosphorus, copper and aluminium availability and toxicity

Water treatment residuals (WTRs) are produced by the treatment of potable water with coagulating agents. Beneficial recycling in agriculture is hampered by the fact that WTRs contain potentially toxic contaminants (e.g. copper and aluminium) and they bind phosphorus strongly. These issues were investigated using a plant bioassay (Lactuca sativa), chemical extractions and an isotopic dilution technique. Two WTRs were applied to an acidic and a neutral pH soil at six rates. Reductions in plant growth in amended soils were due to WTR-induced P deficiency, rather than Al or Cu toxicity. The release of potentially toxic Al from WTRs was found to be mitigated by their alkaline nature and pH buffering capacity. However, acidification of WTRs was shown to release more soluble Al than soil naturally high in Al. Copper availability was relatively low in all treatments. However, the lability of WTR-Cu increased when the WTR was applied to the soil.

Physiology-based modelling in radiation research: the biokinetics of plutonium

For many years, the biokinetics of radioactive substances was calculated on the basis of mathematical criteria only. Biokinetic compartments in most cases did not correspond to anatomically defined distribution areas in an organism but were operational values. However, the quality of the resulting models depends on how accurately their assumptions reflect reality. Ideally, a biokinetic model develops which reproduces reality. In the past few years, this need has resulted increasingly in physiological operational sequences being modelled in realistic anatomical structures of the body along with physicochemical parameters. In this study, an estimate of the biokinetic operational sequence after an incorporation of plutonium is made similar to the pharmacokinetics of a substance showing comparable chemical and physiological behaviours in the body. These behaviours are found for metals, iron and aluminium. Thus, comparison of the biokinetics of plutonium with the pharmacokinetics of aluminium results in some commonalities and some differences. A new model with physiological compartments for plutonium is presented on the basis of the biokinetics of aluminium.

Fatty acids increase paracellular absorption of aluminium across Caco-2 cell monolayers

Passive paracellular absorption, regulated by tight junctions (TJs), is the main route for absorption of poorly absorbed hydrophilic substances. Surface active substances, such as fatty acids, may enhance absorption of these substances by affecting the integrity of TJ and increasing the permeability. It has been suggested that aluminium (Al) absorption occurs mainly by the paracellular route. Herein, we investigated if physiologically relevant exposures of fully differentiated Caco-2 cell monolayers to oleic acid and docosahexaenoic acid (DHA), which are fatty acids common in food, increase absorption of Al and the paracellular marker mannitol. In an Al toxicity test, mannitol and Al absorption through Caco-2 cell monolayers were similarly modulated by Al concentrations between 1 and 30mM, suggesting that absorption of the two compounds occurred via the same pathways. Exposure of Caco-2 cell monolayers to non-toxic concentrations of Al (2mM) and (14)C-mannitol in fatty acid emulsions (15 and 30mM oleic acid, 5 and 10mM DHA) caused a decreased transepithelial electrical resistance (TEER). Concomitantly, fractional absorption of Al and mannitol, expressed as percentage of apical Al and mannitol retrieved at the basolateral side, increased with increasing dose of fatty acids. Transmission electron microscopy was applied to assess the effect of oleic acid on the morphology of TJ. It was shown that oleic acid caused a less structured morphology of TJ in Caco-2 cell monolayers. Taken together our findings indicate that fatty acids common in food increase the paracellular intestinal absorption of Al. These findings may influence future risk assessment of human Al exposure.

Effects of co-application of biosolids and water treatment residuals on corn growth and bioavailable phosphorus and aluminum in alkaline soils in egypt

The co-application of biosolids and water treatment residuals (WTRs) has been previously trialed to reduce excessive bioavailable P in the soil treated with biosolids. However, uncertainty still exists regarding the environmental consequences of the co-application of biosolids and WTRs, especially in alkaline soils in Egypt or the Middle East region. A greenhouse pot study was conducted with Egyptian alkaline soils to (i) quantify the effects of co-application of biosolids and drinking WTRs on biomass production of corn (Zea mays L. cultivar single hybrid 10), (ii) determine the co-application effects on Olsen-P and KCl-extractable Al in relation to their accumulation in plant tissues, and (iii) optimize the co-application ratio of biosolids to WTRs for the best yield and effective reduction of soil bioavailable P. The results show that, among the studied soils treated with 1% biosolids along with various rates of WTRs, the corn yield increased significantly (P < 0.01) with increasing WTR application rate from 0 to 3% (w/w), but decreased at 4% application rate. The corn yield also significantly correlated with soil water holding capacity that increased with the addition of WTRs. Phosphorus uptake by plants significantly (P < 0.01) increased when the biosolid application rate was increased from 1 to 3% in the three studied soils that were treated with 1, 2, or 3% WTRs. The application of 4% WTRs in the biosolid-amended soils resulted in a significant reduction in soil Olsen-P values, but without having observable phytotoxicity of metals (such as Al) to corn during the growth period. The effective co-application ratio of biosolids to WTRs, for increasing corn yield and minimizing the potential for bioavailable P in runoff, was approximately 1:1 at the application rate of 3% biosolids and 4% WTRs in the alkaline soils.

Tissue accumulation of aluminium is not a predictor of toxicity in the freshwater snail, Lymnaea stagnalis

The amount of toxic metal accumulated by an organism is often taken as an indicator of potential toxicity. We investigated this relationship in the freshwater snail, Lymnaea stagnalis, exposed to 500 microg l(-1) Al over 30 days, either alone or in the presence of phosphate (500 microg l(-1) P) or a fulvic acid surrogate (FAS; 10 mg l(-1) C). Behavioural activity was assessed and tissue accumulation of Al quantified. Lability of Al within the water column was a good predictor of toxicity. FAS increased both Al lability and behavioural dysfunction, whereas phosphate reduced Al lability, and completely abolished Al-induced behavioural toxicity. Tissue accumulation of Al was not linked to toxicity. Higher levels of Al were accumulated in snails exposed to Al + P, compared to those exposed to Al alone, whereas FAS reduced Al accumulation. These findings demonstrate that the degree of tissue accumulation of a metal can be independent of toxicity.

Accumulation, tolerance and impact of aluminium, copper and zinc on growth and nitrate reductase activity of Ceratophyllum demersum (Hornwort)

Ceratophyllum demersum (homwort) was subjected to toxic concentrations of Al (3 and 9 mg l(-1)), Zn (3 and 9 mg l(-1)) and Cu (2.5 and 7 mg l(-1)) in culture solutions for 15 days. The higher dose of Al enhanced the chlorophyll content significantly (p<0.05) in the first 6 days of treatment while other treatments caused marked reductions. Nitrate reductase activity (NRA) was significantly reduced (p<0.05) byAl, Cu and Zn toxicity and ceased completely in plants treated with Cu by the 6th day of treatment. Dry biomass and relative growth rate were reduced significantly (p<0.05) by metal treatment. Tolerance index of the plant was low for Cu (21.62 and 13.43% at low and high doses, respectively) and moderate for Zn (63.74 and 54.85%) and Al (72.83 and 68.79%). Accumulation ofAl, Zn and Cu was threefold at higher doses compared with the lower doses but the bioconcentration factors (BCF) were very low indicating that this plant is not a hyper accumulator of these metals.