Absorption and disposition of aluminum in the rat

Review: Vaccine Myth-Buster - Cleaning Up With Prejudices and Dangerous Misinformation

Although vaccines have already saved and will continue to save millions of lives, they are under attack. Vaccine safety is the main target of criticism. The rapid distribution of false information, or even conspiracy theories on the internet has tremendously favored vaccine hesitancy. The World Health Organization (WHO) named vaccine hesitancy one of the top ten threats to global health in 2019. Parents and patients have several concerns about vaccine safety, of which the ubiquitous anxieties include inactivating agents, adjuvants, preservatives, or new technologies such as genetic vaccines. In general, increasing doubts concerning side effects have been observed, which may lead to an increasing mistrust of scientific results and thus, the scientific method. Hence, this review targets five topics concerning vaccines and reviews current scientific publications in order to summarize the available information refuting conspiracy theories and myths about vaccination. The topics have been selected based on the author's personal perception of the most frequently occurring safety controversies: the inactivation agent formaldehyde, the adjuvant aluminum, the preservative mercury, the mistakenly-drawn correlation between vaccines and autism and genetic vaccines. The scientific literature shows that vaccine safety is constantly studied. Furthermore, the literature does not support the allegations that vaccines may cause a serious threat to general human life. The author suggests that more researchers explaining their research ideas, methods and results publicly could strengthen the general confidence in science. In general, vaccines present one of the safest and most cost-effective medications and none of the targeted topics raised serious health concerns.

Aluminum reproductive toxicity: a summary and interpretation of scientific reports

Publications addressing aluminum (Al)-induced reproductive toxicity were reviewed. Key details were compiled in summary tables. Approximate systemic Al exposure, a measure of bioavailability, was calculated for each exposure, based on the Al percentage in the dosed Al species, Al bioavailability, and absorption time course reports for the exposure route. This was limited to laboratory animal studies because no controlled-exposure human studies were found. Intended Al exposure was compared to unintended dietary Al exposure. The considerable and variable Al content of laboratory animal diets creates uncertainty about reproductive function in the absence of Al. Aluminum-induced reproductive toxicity in female mice and rats was evident after exposure to ≥25-fold the amount of Al consumed in the diet. Generally, the additional daily Al systemic exposure of studies that reported statistically significant results was greater than 100-fold above the typical human daily Al dietary consumption equivalent. Male reproductive endpoints were significantly affected after exposure to lower levels of Al than females. Increased Al intake increased fetus, placenta, and testes Al concentrations, to a greater extent in the placenta than fetus, and, in some cases, more in the testes than placenta. An adverse outcome pathway (AOP) was constructed for males based on the results of the reviewed studies. The proposed AOP includes oxidative stress as the molecular initiating event and increased malondialdehyde, DNA and spermatozoal damage, and decreased blood testosterone and sperm count as subsequent key events. Recommendations for the design of future studies of reproductive outcomes following exposure to Al are provided.

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.

Al and Si: their speciation, distribution, and toxicity

OBJECTIVES

In dialysis patients both aluminum (AI) and silicon (Si) may accumulate. Whereas the toxic effects of AI within this population are clearly established, little is known on the role of Si in the development/protection of particular dialysis-related diseases. A clear insight in the protein binding and speciation of trace elements is important to better understand the mechanisms underlying their toxicity/essentiality. Research in this field however is complex and often prone to analytical difficulties and inaccuracies.

DESIGN AND METHODS

In the first part of this review techniques used for speciation studies of AI and Si in biological fluids are discussed. Notwithstanding recent technical advances (a) extraneous metal contamination, (b) unrecognized aspecific binding of metals to proteins, and (c) unwanted interactions with separation equipment such as chromatography columns and ultrafiltration membranes remain important pitfalls and often lead to erroneous conclusions. The factors that determine the speciation of AI and Si and their ultimate tissue distribution and toxicity are dealt with in the second part. Here, experimental data obtained with various speciation techniques are linked to in vivo data on the tissue distribution, localization/toxicity of both elements.

CONCLUSIONS

A model in which the AI tissue distribution/toxicity is mediated by either its citrate or transferrin bound form is proposed.

Kinetics of aluminum disposition after ingestion of low to moderate pharmacological doses of aluminum

We assessed the kinetics of aluminum uptake and elimination by tissues of Sprague Dawley rats following a single gavage dose of 0, 0.25, 0.5, or 1 mmol Al/kg body weight (b.w.) in 1 ml of 16% citrate (equivalent to 0-650 mg Al to a 70-kg human). Serum, liver, kidney, and tibia aluminum concentrations were measured 15, 30, 60, 120, 270, and 360 min after dosing. Serum aluminum concentrations were proportional to dose in rats dosed with 0.25 or 0.5 mmol Al/kg b.w. but were not proportional to dose for rats dosed with 1 mmol Al/kg b.w. Elimination half-lives of serum aluminum were similar for all treatments (102-119 min) which suggests that the non-linear aluminum kinetics in serum reflected a difference in absorption of the highest dose. Although fasted rats dosed with 0.25 or 1 mmol Al/kg b.w. with citrate absorbed aluminum with similar efficiency (4.2% of dose), the length of the absorptive period was prolonged in the rats given the highest does. Total absorbed aluminum mass in rats dosed with 0.25 and 0.5 mmol vs. 1 mmol Al/kg b.w. reached a plateau at 120 vs. 270 min after dosing, respectively. The kinetics of aluminum in liver, bone, and kidney were generally dose-independent. Elimination half-lives of liver aluminum were similar for all aluminum treatments (267-465 min); elimination half-lives could not be estimated in bone and kidney because of turnover exceeded the 6 h collection period.

Aluminum exposure and metabolism

Aluminum (Al) is a nonessential, toxic metal to which humans are frequently exposed. Oral exposure to aluminum occurs through ingestion of aluminum-containing pharmaceuticals and to a lesser extent foods and water. Parenteral exposure to aluminum can occur via contaminated total parenteral nutrition (TPN), intravenous (i.v.) solutions, or contaminated dialysates. Inhalation exposure may be important in some occupational settings. The gut is the most effective organ in preventing tissue aluminum accumulation after oral exposure. Typically gastrointestinal absorption of aluminum from diets is < 1%. Although the mechanisms of aluminum absorption have not been elucidated, both passive and active transcellular processes and paracellular transport are believed to occur. Aluminum and calcium may share some absorptive pathways. Aluminum absorption is also affected by the speciation of aluminum and a variety of other substances, including citrate, in the gut milieu. Not all absorbed or parenterally delivered aluminum is excreted in urine. Low glomerular filtration of aluminum reflects that most aluminum in plasma is nonfiltrable because of complexation to proteins, predominantly transferrin. The importance of biliary secretion of aluminum is debatable and the mechanism(s) is poorly understood and appears to be saturable by fairly low oral doses of aluminum.

Biological indicators of exposure to total and respirable aluminium dust fractions in a primary aluminium smelter

OBJECTIVES

The study attempts to define biological indicators of aluminium uptake and excretion in workers exposed to airborne aluminium compounds in a primary aluminium smelter. Also, this study defines the total and respirable aluminium dust fractions in two different potrooms, and correlates their concentrations with biological indicators in this group of workers.

METHODS

Air was sampled at defined work sites. Non-destructive and conventional techniques were used to find total and respirable aluminium content of the dust. Blood and urine was collected from 84 volunteers employed at various work stations throughout the smelter and from two different cohorts of controls matched for sex, age, and socioeconomic status. Aluminium in serum samples and urine specimens was measured by flameless atomic absorption with a PE 4100 ZL spectrometer.

RESULTS

The correlation of aluminium concentrations in serum and urine samples with the degree of exposure was assessed for three arbitrary exposure categories; low (0.036 mg Al/m3), medium (0.35 mg Al/m3) and high (1.47 mg Al/m3) as found in different areas of the smelter. At medium and high exposure, the ratio of respirable to total aluminium in the dust samples varied significantly. At high exposure, serum aluminium, although significantly raised, was still within the normal range of an unexposed population. The workers with low exposure excreted aluminium in urine at levels significantly higher than the controls, but still within the normal range of the population. However, potroom workers with medium and high exposure had significantly higher urinary aluminium than the normal range.

CONCLUSIONS

It is concluded that only urinary aluminium constitutes a practical index of occupational exposure at or above 0.35 mg Al/m3, and that the respirable fraction of the dust may play a major role in the biological response to exposure to aluminium in a smelter environment.

Tissue aluminium distribution in growing, mature and ageing rats: relationship to changes in gut, kidney and bone metabolism

The purpose of this study was to determine whether accumulation and turnover of aluminium differed among growing (2 month old), mature (8 month old) and ageing (19 month old) rats and assess whether these differences could be ascribed to physiological changes with age. One day after a large oral dose (0.8 mmol Al in 0.75 M citrate) growing rats had the highest concentrations of aluminium in tibias, whereas ageing rats had the highest concentrations of aluminium in kidneys. The half-life of aluminium in tibias (38 v. 58 v. 173 days in growing, mature and ageing rats, respectively) and kidneys (9 v. 12 v. 16 days) lengthened with age. According to stepwise multiple regression analysis, 73% variation in tibia aluminium concentrations was explained by final body weight of rats, length of time after dosing, tibia weights, haematocrits, urinary hydroxyproline excretion, ulna calcium concentrations, and urinary creatinine excretion but 57% variation in kidney aluminium concentrations was explained by length of time after dosing and feed intake. Although age, per se, was a significant predictor of spleen and liver aluminium concentrations, the measured changes in gut, kidney, bone and mineral metabolism were less predictive of aluminium concentrations in livers and spleens than in bone.

Single-dose toxicokinetics of aluminum in the rat

The toxicokinetics of aluminum (Al) in male Wistar rats was studied after single intragastric (IG) doses of 1000 and 12,000 micrograms Al/kg and intravenous (IV) doses of 10, 100, 1000, and 12,000 micrograms Al/kg. Serial blood samples, daily samples of urine and feces as well as brain, liver, kidney, spleen, quadriceps muscle, and femur samples were collected. Al was measured by atomic absorption spectrometry. Al blood profiles after IV doses were adequately described by a two-compartment open model. Al toxicokinetics was dose dependent and appeared to plateau at 12,000 micrograms/kg. At IV doses between 10 and 1000 micrograms/kg the terminal half-life of elimination from whole blood (t1/2 beta) increased from 29.9 +/- 7.8 to 209.3 +/- 32.6 min, and the total body clearance (CL) decreased from 2.45 +/- 0.64 to 0.28 +/- 0.03 ml min-1 kg-1. Following an IV bolus of 10 and 100 micrograms/kg the administered Al was recovered completely from urine (94.4% +/- 9.9% and 98.5% +/- 3.2%). Twenty-nine days after the IV dose of 1000 micrograms/kg daily renal excretion decreased to baseline values while only 55.1% +/- 8.0% of the dose was excreted. Nineteen days after the single IV dose of 1000 micrograms/kg Al accumulated in liver (28.1 +/- 7.7 versus 1.7 +/- 0.5 micrograms/g of control rats) and spleen (72.5 +/- 21.1 versus < 0.4 microgram/g). After the single 1000 micrograms/kg IG dose no absorption of Al was detectable. The IG dose of 12,000 micrograms/kg resulted in a maximum blood Al level of 47.9 +/- 12.4 micrograms/l after 50 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of aluminum in rats. III: Effect of route of administration

Male Fischer rats received 0.1 mg/kg (bolus) of elemental aluminum as the sulfate salt via the portal (n = 4) or systemic (n = 4) route of administration. Blood and bile were serially sampled over an 8-h period, postadministration. Aluminum was determined by flameless atomic absorption spectrophotometry. Blood aluminum concentrations declined in a monoexponential fashion, with half-lives of 0.7 h (portal) and 1.08 h (systemic) (p less than 0.05). The corresponding systemic clearances were 48.9 +/- 10.6 and 35.1 +/- 3.64 mL/(h.kg) (p less than 0.05). The systemic availability following portal administration was 0.66, indicating a significant "first-pass" effect. Biliary aluminum recovery (% dose) was negligible following both routes [0.83 +/- 0.062% (portal) versus 1.3 +/- 0.22% (systemic), p less than 0.05]. Bile flow decreased approximately 40% (p less than 0.05) immediately upon injection of aluminum via the portal route only; flow remained suppressed throughout the study. This decrease in bile flow was most likely responsible for the lower biliary recovery with this route. In contrast, liver recovery of aluminum at 8-h postadministration was higher with the portal route (65.4 +/- 4.1 versus 39.4 +/- 2.52%). These results show that reported values for oral "bioavailability" of aluminum, often calculated by the standard AUC ratio method, underestimate the true extent of absorption. One mechanism of aluminum-related jaundice observed clinically may be due to cholestasis.

Kinetics of aluminum in rats. II: Dose-dependent urinary and biliary excretion

Previous iv studies from our laboratories have shown that the disappearance half-life of blood aluminum increased with dose. Experiments were initiated to determine if saturation of biliary and/or urinary excretion could be responsible for this dose-dependent behavior. Biliary aluminum excretion (0-12 h) accounted for less than 1% of the injected amount at 0.1- and 1.0-mg/kg doses. During the same interval, urinary excretion accounted for 16.7 +/- 2.66 and 8.85 +/- 2.2% of administered dose at the low and high doses, respectively (p less than 0.05); corresponding long term (0 to 13 or 22 days) urinary recoveries were 37.6 +/- 3.67 and 28.4 +/- 1.88% of the injected dose (p less than 0.05), with most (66-70%) of the excretion occurring in the first 24 h. This is consistent with many previous reports showing that urinary excretion is one major elimination pathway for aluminum. Both biliary and urinary clearances decreased with increasing blood aluminum concentration; the biliary and urinary clearance values at low concentrations (500-900 ng/mL) were approximately four- and threefold higher than the corresponding values at higher concentrations (10,000-12,000 ng/mL), respectively. It appears that this apparent saturability of biliary clearance may be due to concentration-dependent of transfer from blood to liver, rather than from liver to bile. In vitro ultrafiltration studies support the hypothesis that decreases in urinary clearance were due to decreased filterability of aluminum at the glomerulus as its blood concentration was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum transfer as glutamate complex through blood-brain barrier. Possible implication in dialysis encephalopathy

In vitro distribution of aluminium between plasma and erythrocytes has been studied in the presence of variable amounts of sodium L-glutamate. With a red blood cell suspension in isotonic sodium chloride, aluminium remains confined in erythrocytes even when the sodium L-glutamate concentration increases in the medium. Aluminium initially present in plasma penetrates red blood cells when sodium L-glutamate increases in whole blood, showing that this metal is able in vitro to cross the erythrocyte membrane as glutamate complex. In vivo experiments with male Wistar rats prove that aluminium is also able to pass the blood--brain barrier as glutamate complex and deposit in the brain cortex.

Renal aluminum excretion

Urinary aluminum (Al) excretion was studied in humans with normal and impaired renal function. Al was measured by atomic absorption spectrometry. In healthy volunteers (n = 50), renal Al excretion was 12.2 +/- 8.5 micrograms/24 h. Two patients on plasma exchange therapy with normal renal function and an inadvertent load of 870 and 388 micrograms Al/treatment showed a 23 and 14% positive balance until next treatment. The renal pathway of excretion was shown to be important in 6 chronic renal failure patients on continuous peritoneal dialysis with residual renal function who eliminated in 24 h 51.4 +/- 24.0 micrograms Al by urine and only 27.2 +/- 18.4 micrograms Al across the peritoneum following a daily oral application of 342 mg Al. Studies with the isolated perfused rat kidney confirmed the limited renal capacity to eliminate Al. Al clearance declined from 0.75 to less than 0.08 mL/min when the kidney was perfused with 0.04-12.4 micrograms Al/mL medium. Al content of the kidney increased in a dose-dependent manner from less than 0.05 to 4.4 micrograms/kidney and reached saturation at 5 micrograms Al/mL medium.

Elevated aluminum persists in serum and tissues of rabbits after a six-hour infusion

The half-life of aluminum was estimated in selected tissues and fluids in a representative mammal, the rabbit. After a single iv aluminum infusion, half-lives were determined by serial killing of rabbits and aluminum quantitation in selected tissues and fluids by electrothermal atomic absorption spectroscopy. Tissues and fluids demonstrating a significant increase 4 hr after the 200 mumol/kg aluminum dose were the bile, kidney, liver, lung, serum, and spleen. Aluminum concentration did not significantly increase above control in the adrenal gland, bone, heart, muscle, testis, thyroid gland, or selected central nervous system regions. Biliary aluminum concentration returned to control within 12 hr after infusion. Estimated half-lives were 113 days in spleen, 74 days in liver, 44 days in lung, 42 days in serum, 4.2 days in kidney cortex, and 2.3 days in kidney medulla. The kidney also demonstrated another half-life greatly exceeding 100 days. The results demonstrate that aluminum persists in various tissues and fluids for different lengths of time. The calculated half-life of aluminum in these tissues is substantially longer than previously estimated half-lives based on serum aluminum determination. The persistence of aluminum in the liver and other tissues may serve as a source of continuous aluminum exposure for sensitive target organs such as the brain. These calculated half-lives establish the normal rate of aluminum elimination from tissues. Future studies could determine the influence of factors such as uremia or chelation therapy on the rate of aluminum elimination from storage sites as well as serum.

Kinetics of aluminum in rats I: Dose-dependent elimination from blood after intravenous administration

Aluminum (Al) kinetics after intravenous bolus administration were studied in the rat. The animals received either 0.1 or 1.0 mg/kg (n = 6 at each dose) of elemental Al as the sulfate salt. The Al content of serial blood samples was determined by flameless atomic absorption spectrophotometry. Blood and plasma Al-time profiles after both doses were monoexponential in most cases. Increasing the administered dose increased the elimination half-life (mean +/- SD) from 1.20 +/- 0.25 to 2.41 +/- 0.26 h. A corresponding decrease in systemic clearance was observed (49.6 +/- 11.0 to 18.4 +/- 4.6 mL/kg.h). Both changes were significant (p less than 0.05). Significant differences were also observed in the volume of distribution, the values of which were 78.3 +/- 17.2 and 58.9 +/- 8.5 mL/kg at the low and high doses, respectively. At both doses, blood:plasma ratios ranged from 0.8 to 1.0, indicating considerable uptake/binding of the element by blood cells.

Renal clearance of aluminium: studies in the isolated perfused rat kidney

The model of isolated rat kidney was used to study the renal handling of aluminium (Al). The kidney function remained unchanged at perfusate concentrations of Al in a range of 0.04-12.4 micrograms/ml during a perfusion period of 60 min. The clearance values of Al decreased with increasing concentrations of Al in the perfusate. The fractional Al clearance was reduced from 70% at the lowest Al concentration in the perfusate to 8.2% at the highest Al concentration. The Al content of the kidneys increased dose-dependently and reached a maximum value of 4 micrograms Al per kidney at a perfusate concentration of 5 micrograms Al/ml. Protein-binding studies with Al confirmed the suggestion that renal elimination of Al is dependent on the degree of Al binding. It is proposed that at low Al load in the plasma, the kidney possesses the capability to eliminate Al in an effective manner.

Aluminum and chronic renal failure: sources, absorption, transport, and toxicity

In normal subjects the gastrointestinal tract is a relatively impermeable barrier to aluminum with a low fractional absorption rate for this metal ion. Aluminum absorbed from the gastrointestinal tract is normally excreted by the kidneys; in the presence of impaired renal function aluminum is retained and accumulates in body tissues. Aluminum-containing medications are given, by mouth, to patients with chronic renal failure as phosphate-binding agents for the therapeutic control of hyperphosphatemia. Patients with chronic renal failure are also exposed to aluminum in domestic tap-water supplies used either for drinking or, in those on dialysis treatment, in the preparation of their dialysate. In patients with end-stage chronic renal failure, particularly in those on treatment by hemodialysis, the accumulation of aluminum in bone, brain, and other tissues is associated with toxic sequelae. An increased brain content of aluminum appears to be the major etiological factor in the development of a neurological syndrome called either "dialysis encephalopathy" or "dialysis dementia"; an increased bone content causes a specific form of osteomalacia. An excess of aluminum also appears to be an etiological factor in a microcytic, hypochromic anemia that occurs in some patients with chronic renal failure on long-term treatment with hemodialysis. The various mechanisms involved in the toxic phenomena associated with the accumulation of aluminum in body tissues have not been clearly defined but are the subject of extensive investigations.

Influence of renal impairment, chemical form, and serum protein binding on intravenous and oral aluminum kinetics in the rabbit

The influence of renal impairment on the intravenous kinetics of aluminum (Al) lactate and the oral absorption of eight representative Al forms was determined. The serum protein binding of Al was assessed. Creatinine clearance in renally impaired rabbits was 23% of controls. Systemic clearance of Al was less in renally impaired rabbits (39 vs. 53 ml/hr/kg), as were the steady-state volume of distribution (516 vs. 1175 ml/kg), the half-life of elimination (14 vs. 27 hr), and the mean residence time of Al (14 vs. 25 hr). The shorter Al half-life and mean residence time in renally impaired rabbits were due to a diminished volume of Al distribution. Oral bioavailability of Al in renally intact rabbits ranged from 0.3 to 2.2% (Al borate less than glycinate less than hydroxide less than chloride less than sucralfate less than lactate less than nitrate less than citrate). Renal impairment had little influence on oral bioavailability of most Al forms, although it increased Al citrate absorption to 4.6%. In vitro and in vivo determination of Al ultrafilterability (less than 30,000 D) as an estimate of serum protein binding suggested a greater percentage of ultrafilterable Al species in renally impaired rabbit serum than in control rabbit serum. The increase in ultrafilterable Al species produced the less than expected reduction in Al clearance in renally impaired rabbits. The ultrafilterability of various Al concentrations was greater for citrate greater than lactate greater than nitrate greater than chloride, perhaps partially explaining the similar rank order of oral absorption of these Al forms. The physicochemistry of the eight Al forms was further characterized by determination of their octanol/water partitioning coefficients and their water solubility. There was a significant correlation between the percentage absorbed and the log of the octanol/water partition coefficient. Knowledge of the physicochemistry of Al aids in the understanding of Al pharmacokinetics.

Elimination of absorbed aluminum in patients undergoing continuous ambulatory peritoneal dialysis

Intestinal absorption of aluminum (Al) from the phosphate binder aluminum-hydroxide-chloride (PhosphonormR) and successive renal and peritoneal Al elimination were studied in 11 patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Al was measured by atomic absorption spectrometry in serum, urine, and dialysis fluid. Al levels in serum of all patients increased in average from 28.6 micrograms/l immediately before to a peak level of 41.6 microgramsWl 4 h after intake of 342 mg Al. After 24 h serum Al (34.0 micrograms/l) was still increased. Elimination across the peritoneum increased from 5.6 micrograms Al during the first 4 h to peak levels of 12.9 micrograms between hour 8 and 12 and decreased to 8.1 micrograms during the last 12 h. The Al clearance of the peritoneum was 0.43 ml/min. In the 6 patients with residual diuresis the renal Al excretion was higher than the peritoneal removal (48.1 micrograms/24 h vs. 24.8 micrograms/24 h). The renal Al clearance amounted to 1.6 ml/min. Assuming a gastrointestinal absorption quotient of 0.1% it is concluded that Al removal by CAPD in patients receiving 342 mg Al/day is not sufficient to prevent Al accumulation. In patients with remaining diuresis, the renal Al elimination exceeds the Al removal by the peritoneum.